Inliners International
Posted By: Lennart Forged pistons from LS1 in 292 - 01/18/09 11:58 AM
New to the Inline-6 world, but looking to build a blown 292 to run in a 54-55 Chevy truck.
While looking for forged pistons that could fit the 292 I came across LS1 pistons, which come in a 3.905" diameter (.030 over 292)
The compression height is quite different but with a longer rod (7.25) you should be able to compensate.
Below is a calculation which yields a 7.4 CR, based on a 59cc head.

The piston calculated is from Diamond, Wiseco has similar ones.

//Lennart
Posted By: tlowe #1716 Re: Forged pistons from LS1 in 292 - 01/18/09 01:26 PM
now where to find a reasonable 7.25" rod. it would also be better to get the chamber opened up a bit and maybe bring the piston higher in the cylinder. tom
Posted By: panic Re: Forged pistons from LS1 in 292 - 01/18/09 02:52 PM
Piston down .255" won't work - even a blown motor needs quench (unless you use methanol).
Very few commercial rods in 7.25" × 2.10" journal - most of the long rods are for either 2.20" (BBC) or 2.375" (BBM). What you save in piston cost you spend in rods. I can't find a 2.10" rod at all - everything is either bigger ($$$ crank work), or smaller and shorter (1955-67 SBC), or smaller, longer and weaker (Dodge 230).
I would guess that any cam you would use would have less than .255" lift on overlap, so valve relief position isn't a problem.
What you really need for low-comp is a "D" cup piston (which any can supply) with an open area under the valves and quench under the closed deck, etc.
You can open the chamber to get some volume, the obvious is relieving the wall around both valve OD - but don't move the quench line opposite the plug.
For such a heavy chassis I wouldn't use such low static CR. Even 8:1 is an improvement - regardless of boost, low CR means any big cam will make very poor low speed power.

More details: cam? fuel system? max boost?
Posted By: Lennart Re: Forged pistons from LS1 in 292 - 01/18/09 03:12 PM
I figured rods would be a problem. Actually I just happened to find these size pistons and started playing with the numbers.
Was not aware of the importance of quench >> I am not an engine builder , thanks for clarifying.
If I understand you correctly, you would rather start with a 9:1 CR and add 6psi of boost rather than 7.5:1 and 10psi?
Torque is important, especially in a truck.
Planning to run an EFI, LS1 GM and control a 4l60e tranny.
Posted By: panic Re: Forged pistons from LS1 in 292 - 01/18/09 03:22 PM
9.0 is a bit too high, you may get away with 6 psi without a problem but it's going to be a matter of "how close do you want to get". As the CR drops, more boost = more power, but the trade doesn't favor heavy, tall gears, low stall or low octane. You can try a DCR calculation to see where your cylinder pressure will be with various IVC points vs. static CR. You'll also see "calculations" that purport to show what total press you get from X CR + Y boost - but they don't. They only multiply (boost + ATM / ATM) * static, which is not what happens. More info, see my site: http://victorylibrary.com/mopar/blower-engine5.htm
Boost is roots, centrifugal, turbo? They produce boost and handle compression and cam quite differently.
Posted By: Lennart Re: Forged pistons from LS1 in 292 - 01/18/09 04:04 PM
I was thinking about running a 4-71....which is probably the least effective way of creating boost = high charge temp.
Interesting material in the link you provided!
The more I read the less confident I am in even where to start with the build.
Which combination would you recommend for my needs?
I am confused !
With all the engines out there there has to be a useable rod! The problem I'm having is finding a source of rod specs other than after market Chevy V8s. From all the 4, 6, & 8 inlines including foreign trucks and tractors I can not believe there aren't rods for 292s and 302 GMCs.
Posted By: Coastal Re: Forged pistons from LS1 in 292 - 01/18/09 04:37 PM
Im at the same point, but Im running a turbo, this will be a good thread I hope! So much info its hard to pick what you really need.
Posted By: panic Re: Forged pistons from LS1 in 292 - 01/18/09 04:48 PM
Depends on your budget.
If you want to get away with (almost) no work to the crank (stock rod journal size) you need the exact journal OD and the same or slightly less width. That's a short list for both.
if you can stand and afford to have the crank ground undersize, the choices expand quite a bit, but how fragile the crank is with the lower journal overlap is tough to predict. The 292 is already at a point that would look dangerous in another engine:
Journal overlap = (Main OD + Rod OD - Stroke length) ÷ 2
For the 292: 2.30 + 2.10 - 4.12 = .140".
The slant 6 with a similar stroke:
2.75 + 2.1875 - 4.125 = .406"
If you go down to 2.0625" you can use a Plymouth 218/Dodge 230 flathead rod: 7.9375" long (don't know the width). I wouldn't try to put too much power through it, but they certainly beat them up back in the day.
No offset:
2.30 + 2.0625 - 4.12 = .121"
Dropping to 2.00" journal adds to the last, but how strong is it?
If you can afford to weld the crank, the sky's the limit - just use a BBC rod.
The larger stovebolt and GMC journal allows anything below 2.31" to be used, with the same problems.
The Chrysler/DeSoto rods have 2.125" journals and lengths from 7.75" to 8".
The Buick L8 263 is 2.125" × 7.375".
The Buick L8 320 is 2.25" × 8.25".
The Olds 1957-58 371 rod is 7.00" × 2.25"
Posted By: Lennart Re: Forged pistons from LS1 in 292 - 01/18/09 06:51 PM
Rather than working on the crank, would a bearing spacer solve our problem?
I know they used these spacers to convert a 327 to 350 crank.
http://www.raceeng.com/p-7689-bearing-spacer-327-to-350.aspx
OK Panic, That's what I'm looking for! What is your source for these rod specs? I need to check out those Mopar rods. I need to put this stuff on a chart/spread sheet.
Posted By: panic Re: Forged pistons from LS1 in 292 - 01/18/09 08:55 PM
This has been mentioned before, but evidently it's not quite the same thing. The main bearing inserts are old stuff - they used to just use 2 sets of bearings nested.
Inserting the donor bearing (the one that fits the replacement Buick, Dodge etc. rod) around the actual bearing hasn't been tried that I know of.
Shouldn't been too tough to pin the donor bearing to its rod and cap, assemble and hone the ID to the finished size of a bare 292 or GMC rod big end. This means that the donor bearing ID must be smaller than the 292 etc. rod big end.
Now insert the 292 bearings, and pin them to the donor bearings.
The oil reaches the 292 bearing normally, the only rotating contact is between the journal and the 292 bearing - the right one. Downside: extra weight, larger big end OD for cam clearance.
Now... who's going to be first to try it?
Posted By: panic Re: Forged pistons from LS1 in 292 - 01/18/09 09:25 PM
The 4-71 has the advantage of instant boost at very low speed, which is good for big loads, it can turn slowly and still work. However, mileage will be bad because everything is working at any cruising speed. The 4-71 is also very high on power consumption, high charge temperature, and physically large.
For EFI I'd use a big ex-factory Eaton like a Ford M112. Less weight, lower power consumption, lower charge temp, up to perhaps 12-14 psi max.
Someone looking for "traditional" appearance, without the big expense of a rebuilt GMC ($2,500?) could just make an adapter plate to attach to the existing inlet duct alongside the late Lightning blower. Now rotate the Eaton 90° CW to narrow it and point the discharge to the 292 intake. The adapter is now down-draft, use it to mount your carb.
Posted By: panic Re: Forged pistons from LS1 in 292 - 01/18/09 09:27 PM
Check the older TRW literature for rod data.
Posted By: Nexxussian Re: Forged pistons from LS1 in 292 - 01/18/09 10:37 PM
FWIW our very own Ron Golden built a HOT rod jimmy with some interesting parts, I'll list some quotes from him, but if you're going to boost it I wouldn't reccomend the Hudson rods (beam's kinda thin for that).

 Originally Posted By: Ron Golden
I used 308 Hudson rods (8.115" C-C) vs 7.0" stock GMC rod.
1940-50's Chrysler, Dodge, Plymouth rod bearings
Pontiac pins (.984)
Custom JE pistons with a 50cc dome (11.5:1 CR)(very light)

Ron


 Originally Posted By: Ron Golden
The inline 6 Jaguar rod is 7.7" long, I think, and looks very nice. I don't remember the dimensions but it warrants having a look.

Ron


Those were both edited for relevance and space saving, if you want the whole converstion, search 'Ron Golden' for user, 'rod' for keyword and set the search for posts newer than 1 year (I still have yet to figure out how to set it for further back than that).
Posted By: LGriffin_#4385 Re: Forged pistons from LS1 in 292 - 01/19/09 12:17 AM
There is a catalog of rod spec.s, and it has all the info, length, pin dia., rod width, brg dia.s, etc.. It is put out by the Automotive Engine Rebuilders Association (AERA). I found a 1997 copy and went thru it. The only thing I found close was a 40-50s Jeep. When I mentioned the rods to my machine shop their comment was they were spindly, made for a low HP motor and probably wouldn't last under high HP. Some of the rods in the catalog didn't have all their data. If someone could get a current copy it might be worth looking at.

CNC-Dude found an outfit that would make forged steel rods, but an order of 200-300 was required then the price was about $70 each IIRC. Another that was mention was looking a the possibility that there was enough width on forged BB rods before machining.

If there is one thing a 292 builder could use it's rods.

My two cents.

Larry
Posted By: panic Re: Forged pistons from LS1 in 292 - 01/19/09 02:29 PM
Luckily, most 292 builds do not require a really big rod, because they don't have enough breathing to turn high RPM, and modern gas doesn't allow a big dome for compression.
What breaks rods? It's not power or cylinder pressure except in extreme cases - rods are very strong in compression, it's tensile/inertial loads that kill them. Causes, in order:
#1. fastener failure - easily fixed, use ARP replacements
#2. high piston weight - Venolia, JE, Ross etc. can supply a replica with over 100 grams off, taper-wall pins, etc.
The Dodge flathead 230 rod looks fairly feeble, but those engines were used quite a bit in dirt track back in the day and did fairly well for flatheads, so the metallurgy and quality control must be fairly good.
However, the Dodge is 7.94" is wayyyy too long for a 292, you need a journal about that size (anything at or under 2.100" = 53.34mm, like 2.0625") but only about 1/2" more length.

Langdon's poster child GMC engine: "Powered by a 1957 341 cubic in GMC engine (302 with 1/8" bore and 1/4" stroke using mopar rods and Chevy V8 pistons)"
Does anyone know what this is? To increase the stroke by 1/4" the new journal must be 2.0625" (2.31 - .25) or smaller... unless it was welded?
The 230 rod is too long to use anything like a commercial piston, and any other Chrysler rod is either too big to stroke the engine (not enough journal size difference - like the slant 6 rod), too short to work (shorter than the 302 rod by enough that the piston would be very tall - like the DeSoto 276 rod), or both.

...or the math is wrong (happens far more often than you think).
Posted By: LGriffin_#4385 Re: Forged pistons from LS1 in 292 - 01/19/09 04:01 PM
My thoughts on a 292 rod is one long enough to use forged SBC pistons, and to get the compression up, like on a 250. A custom set of Ross or Arias piston are expensive. If something goes wrong in the motor and it requires reboring, it's another set of custom piston at $500-600. If that money was put into a good set of long rods, they are reusable, and oversize pistons half the cost. How many potential Inliners have walked away from building a performance 292 because of cost. Land speed records and quick 1/4 mile times are great, but not every one wants to do that. We need more hot inlines on the street.

Sorry about being on the soap box.

Larry
Posted By: CNC-Dude #5585 Re: Forged pistons from LS1 in 292 - 01/19/09 08:35 PM
 Originally Posted By: LGriffin_#4385
My thoughts on a 292 rod is one long enough to use forged SBC pistons, and to get the compression up, like on a 250.
Sorry about being on the soap box.

Larry
No need to apologize Larry,you're absolutely correct. Building a pretty hot 292 makes the enthusiast have to step up to the pump twice as opposed to a 250. There is a 6" h-beam rod for the 250 that is fairly inexpensive, and will allow for a more common off the shelf SBC piston for building a 250. The 292 guy will have to buy a high end set of rods just to be able to get a decent set of shelf SBC pistons. The rods costing almost a grand by themself. I think your right, many people have probably walked away from the thought of building a 292 because of that....
Posted By: panic Re: Forged pistons from LS1 in 292 - 01/19/09 09:55 PM
Using as many known quality, commercially available parts is just sound engineering practice. "Thinking outside the box" frequently means "making it more complicated and expensive just to be different".
There's a big hole in the rod journal tables around 2.10", and that's the problem. The crank has to be ground or welded to use something else = $$$
Posted By: CNC-Dude #5585 Re: Forged pistons from LS1 in 292 - 01/19/09 10:01 PM
Yep,thats true!
Posted By: panic Re: Forged pistons from LS1 in 292 - 01/19/09 10:03 PM
Here's some data on rods with big end ID (not journal size, typically deduct .125" Imperial or .118" metric), casting number and application - but no length and no width.
General rule: a V8 rod won't be anywhere near long enough, because the stroke will be much shorter.

http://www.parkville.info/pauls/1_word_docs/rod_catalog.htm
Posted By: LGriffin_#4385 Re: Forged pistons from LS1 in 292 - 01/19/09 10:30 PM
I did come up with an "outside the box" solution. Unfortunately it required cutting the tops of the pistons down to the bottom of the valve reliefs, about 80 thou. I screwed up installation of the rings, I think. I'm waiting for good weather now to pull the motor and put in another set of rings.

Larry
Posted By: tlowe #1716 Re: Forged pistons from LS1 in 292 - 01/19/09 10:50 PM
can you give us details? tom
Posted By: LGriffin_#4385 Re: Forged pistons from LS1 in 292 - 01/19/09 11:53 PM
I used Silv-O-Lite 366 BBC pistons #3481HC std, these pistons have a teflon coated skirt. The compression height is 2.100. My 292 had .072 from top of piston to the deck. IIRC the 292 was bored .0635 over. I don't remember the exact numbers, but the pin bores on the rods had to be enlarged about .043, there was a problem doing this. First the oem rods are not very consistent in centering the pin bores. luckily I had 3 sets of rods and was able to select 1 set that had the same amount of material on both sides (centered). The shop had to send them to be bored. I also had the rods polished. I ended up saving about 1/2 pound per cylinder, compared to oem weight. I had to find the 2 spare piston to get the part number, so I'll try and mic the top of piston to see what the before and after is. I've got some pictures I'll see if I can't get them up on flickr. The shop that did the work is Cal's Machine in Oakdale, CA. I've seen everything in their shop from the usual bent stuff to inlines from f*rd flat head fours to Packard straight eights, so I'm confident about the work they do.

Lennart we've hijacked your thread, but I hope all this helps some. The problem your up against is one we'd like to solve. I wish I had more miles on my 292.

Larry
It appears that getting info from the Automotive Engine Rebuilders Association is more expensive than custom rods! \:o
Posted By: Nexxussian Re: Forged pistons from LS1 in 292 - 01/20/09 06:19 AM
 Originally Posted By: panic

Does anyone know what this is? To increase the stroke by 1/4" the new journal must be 2.0625" (2.31 - .25) or smaller... unless it was welded?


Maybe I missed it being mentioned, but if the stroke increase is 1/4" (.250") then the journal only has to get 1/8" (.125") smaller (not including whatever needed to be ground off for 'cleanup'). Since at that point you are adding 1/8" to the TDC dimmension and the BDC dimmenstion as well (1/8 + 1/8 = 1/4).
Posted By: panic Re: Forged pistons from LS1 in 292 - 01/20/09 12:10 PM
Nope - you need the entire stroke change as reduction in the journal.
This error has resulted in mis-calculating the displacement, deck height, compression distance and static compression ratio many, many times over the last 75 years.
However, unlike certain other errors, it results in conservative but disappointing dimensions (smaller displacement, lower deck height, not enough compression distance, and lower static CR) that are not inherently destructive.
Frequently the motor is run like this, and because it does not fail the owner passes along the mis-understood experience as fact and wisdom.

When you reduce the diameter eccentrically, the centerline of the journal (the point of rotation, and the offset) only moves 50% of the diametric change (less any minor correction).

The only time the movement is 1/2 the stroke change is when the journal diameter is preserved by welding.
Posted By: Nexxussian Re: Forged pistons from LS1 in 292 - 01/20/09 12:50 PM
Huh, makes sense now that you describe it that way. But you're right, it is taught that way (in school too, that's where I learned it).
Posted By: panic Re: Forged pistons from LS1 in 292 - 01/20/09 03:20 PM
In addition to the reduction in bending resistance, using a smaller rod journal also runs a slight risk of unmasking an oil passage in the crank cheek - instant boat anchor.
It may also "bump" the location of an oil hole away from the original point of exposure which is safe unless it's no longer completely under the rod (on a V engine it might also wind up centered between the rods - also bad).
Has anyone had this experience?

I'm really curious about the Langdon motor, because if the math is right (description is correct) it may be assumed that:
1. it's safe to go down the entire 1/4"
2. the Dodge rod has enough beam to handle a big piston if treated with some respect
3. the smaller rod bearing has enough load capacity for 200+ hp
4. the very short CD needed to run this long rod is more or less safe: if the 302 deck is 11.0625" (a guess, probably not smaller than this), the piston CD is 1.000" at zero deck (gasket thickness only for quench + safety).
The piston may have been run with the dome height cut down, but I don't know of any big bore piston with even 1.25" CD.
This suggests that the math is not correct and the stroke is less than 4.25", or that's not the rod used, etc.
If the stroke change was only 1/8" (journal goes from 2.31" down to 2.125", but the full offset wasn't used), the rod might have been the Chrysler L6 265, which is only 7.75" long. That gives a CD of 1.25", still not easy, but easy-er.
Posted By: panic Re: Forged pistons from LS1 in 292 - 01/20/09 03:28 PM
Isn't there a good rod out there for the Ford 240 L6? Even the stock rod is very sturdy. The length is really close at 6.795", the width isn't bad at .982". The nominal journal is 2.123", but that's 2.100" (std. 292) ground -.023", right?
Posted By: Xea I.I. #5390 Re: Forged pistons from LS1 in 292 - 01/20/09 03:44 PM
2.1 ground .023 will leave you at 2.078 The Ford at 2.123 is larger.
Posted By: Lennart Re: Forged pistons from LS1 in 292 - 01/20/09 03:49 PM
That`s fine Larry I am following along your discussion and are glad that this much fruitful information resulted out of my question !
Posted By: panic Re: Forged pistons from LS1 in 292 - 01/20/09 04:31 PM
Ooppss...
I meant the Ford as -.030" undersize can be matched to a different 292 undersize -.007".

Brain fade...
Posted By: Lennart Re: Forged pistons from LS1 in 292 - 01/20/09 05:45 PM
I think I just found a nice combination that would work with 7.25 rods. All these pistons would require is a minor milling of the top (.03 to .05). The good part is that these pistons sell for about $20 ea. !


Pistons for AMC/Jeep 4.0 L

The pin heights and dish volumes of pistons available for the 4.0 engine are:

Stock 4.0 cast aluminium '87-'93 #83500251, '94-'95 #4773157, '96-'06 #4798329----1.601" 13.1cc
Keith-Black Silvolite (UEM) cast aluminium 2228/2228c, 2229/2229c----1.581" 12.2cc
Keith-Black Silvolite (UEM) hypereutectic 3238hc/3243hc, 3241hc/3242hc----1.592" 14.1cc
Sealed Power (Sterling) hypereutectic H802CP/H825CP----1.592" 15.1cc
Sealed Power (Sterling) cast aluminium 677P/677CP----1.585" 17.5cc
Sealed Power (Sterling) cast aluminium 525P/525CP----1.580" 17.5cc
Keith-Black Silvolite (UEM) forged stroker 944----1.353" 21.7cc NEW
Keith-Black Silvolite (UEM) forged stroker 945----1.353" 11.4cc NEW

found here: jeep4.0performance
Posted By: Nexxussian Re: Forged pistons from LS1 in 292 - 01/21/09 01:45 AM
FWIW I've read (I think in Hot Rod) a quote of Hank Cornelieson (sp?) about being able to get a reasonable ring package in 1.25 worth of CD (going with you meaning Compression Distance when you say CD). It had a recommnded minimum thickness for the top ring land, ring spacing and kept the oil ring wrist pin free, but I forget the exact ring size they were quoting, the specific spacings, and the wrist pin diamter (but I think it was SBC for the pin). Was it an accurate quote (IE did Mr. Hank really say that)? I have no way of knowing.

FWIW everything I have read says the trend is towards smaller journals. The NASCAR guys are supposedly (or were) running the 1.888" 'Honda' rod journal (Quad 4 if you're a GM fan). They spin those 9K + w/ crazy compression etc. I read the Pro Stock guys have been trying a 2" rod journal on their humongo big blocks (500 CID?) and they wind the daylights out of those too.

What does that have to do with a low RPM 4 main bearing straight 6 that needs all the rigidity in the crank it can get (w/ more journal overlap = more rigidity)? Hard to say. It would be worth whatever it cost to either have a crank X-rayed, or spend some qulity time with a sonic tester to see how much you had to play with.

Now, if you were thinking of Bonneville, that's a whole 'nother deal entirely.

Yes 2 FWIW's in one post is a bit much, but I'm not claiming personal expertise, just passing on what I've read, and pontificating a bit (it's why they're FWIW's).
Yes,Nascar & other engine builders I know used the smaller journal Honda rods.

Part of the reason they went that route was for a lighter rotating assy & a crank w/huge radius's =(more strength)

Not sure if that will work out w/a 6 cyl crank w/only 4 mains.


MBHD
Posted By: panic Re: Forged pistons from LS1 in 292 - 01/21/09 03:13 PM
1. it's billet
2. it only lasts a few hours, and then scrapped

Yes, 1.25" can be done, just not an on-the-shelf piston.

Not exactly on topic, but: given that an L6 doesn't need percentage balancing?
Does anyone know what the counterweights actually weigh?
Santucci cuts quite a bit off which helps accel, but is the stock weight more or less than the rotating total?

Journal size: (sorry if this is already obvious) pump pressure does not pressurize the crank against the bearing shell for support.
Actual local oil pressure (at the journal) is far, far higher than the 50, 60 psi from the pump.
This is developed by the relative speeds of the journal itself against the bearing in f/s (not the RPM or journal size), bearing width (to the closest leak), oil viscosity and temperature, balanced against clearance (leakage rate).
All pump pressure does is "fill in the hole" and refresh the oil in the annular space at least as fast as the leak expels it (which increases with pressure and load).
This is why low-speed engines have very large journals - so the rotational speed sufficient for the load is high with a modest pump and low leaks.
A very high speed motor can use the same rotational speed, but accomplished with a small journal and high RPM.

(deep breath)

What I don't know (stop laughing!): do these factors (RPM × journal circumference = "skin" speed in f/s) contribute equally? Meaning: if you reduce the journal by 10% and keep the RPM do you lose 10% of the load capacity? If you increase RPM by 10% and reduce journal size by 10% do they self-cancel?
Posted By: CNC-Dude #5585 Re: Forged pistons from LS1 in 292 - 01/21/09 03:15 PM
Just for curiousity sake,I drew several crankshaft cross sections up in CAD, just to see what different engines have for journal overlap. The worst being the 292 crank,with only .138 thickness. On a cast crank, I dont feel it would be a good choice to try and offset grind the journal for more stroke, or even turn it down to a smaller journal size to accomodate a different rod size,further reducing the overlap more. A 235/261 and GMC are very good candidates for this type of mod. Because they both have very large OD mains relative to the fairly large rod journals. Plus there progressively larger main size front to back increases the overlap as the you go toward the rear of the engine. At a minimum, with the smallest main journal, the 235/261 has over .500 of overlap. Lending itself to the possibility of either offset stroking the rod journals or even grinding them down to BBC or SBC size and still having plenty of strength and integrity left in them. The 235/261 and GMC's being steel also is a good foudation for attempting to do this as well. Im going to use some BBC journal size H-beam rods for my project, and even with the most realistic HP levels and RPM you could ever expect to get out of these engines either N/A or blown, you'll never have any problems....even with just 4 mains!
Posted By: panic Re: Forged pistons from LS1 in 292 - 01/21/09 03:19 PM
The big fillet radius prevents load-induced bending from cracking the journal off from the cheek. All cranks (rods, etc.) are subject to fail where the cross-section changes radically - this is one reason why 4340 is used more for rods than cranks - it doesn't tolerate as much change as 4130. Even a change from .020" to .060" radius is huge.
There's even a technique for increasing the radius without reducing the journal. The new radius is undercut in the side of the adjacent cheek, tangential to the journal surface but ending normal to the cheek.

But... the crank isn't stronger overall - it's just less likely to break at that spot.
Posted By: panic Re: Forged pistons from LS1 in 292 - 01/21/09 03:24 PM
The BBC looks like the winner for the 235 and GMC because of the big range of lengths, pin sizes, price etc.
The only downside is no offset to speak of, so you're stuck with near-stock stroke (+.1125" max). IMHO small price to pay for such an important step - it means the engine can turn as fast as the valve gear will stand.
Posted By: CNC-Dude #5585 Re: Forged pistons from LS1 in 292 - 01/22/09 02:33 AM
Yeah, thats what I was thinking about more so than the stroker option. The broader range of lengths available for the BBC(up to +.300 longer than stock 235/261 rod) will also allow for a more common SBC forged piston that could be massaged a little to be made to fit the application without too terrible of an extra expense. Unfortunately for the GMC, the BBC rod choice will only be an extra +.100 longer than the stock GMC rod, so it doesn't really give you the same benefits for that engine group as it does the 235/261 engines! Maybe using the shorter deck 248 engine block bored to 4.000", along with the 270/302 crank and BBC rod im using could get you closer to a more common SBC piston. The 270/302 blocks have such a tall deck height, there just isn't much option for a budget rod and piston swap....
Posted By: Nexxussian Re: Forged pistons from LS1 in 292 - 01/22/09 05:53 AM
Panic, by 'f/s' I take it you mean Feet per Second. Yes / no?

Yes the 'bearing speed' is the important factor there (as I understand it anyway) and lightweight is always a good thing when you're trying to rev the snot out of something.

As for if they would self cancel, probably not, but it would stand to reason it should be close in your + 10% -10% example; the error would likely be exagerated the larger the numerical change (ie +15% -15%, just for numbers).
Posted By: Winter Re: Forged pistons from LS1 in 292 - 01/22/09 06:23 PM
This thread as diverged into two discussions.

Panic, concerning journal bearing oil flow and shaft support:
The shaft is lifted off the bearing surface and support by the oil wedge. This higher pressure film of oil is determined by the physical dimensions of the bearing, the bearing surface speed (affected by engine rpm), and actual oil viscosity (as affected by temperature).

Total journal bearing oil flow, for technical discussion, is divided into hydrodynamic flow (generally 80 to 85%) and pressure flow, sometimes also called side flow(generally 15 to 20%).

For a given journal bearing the hydrodynamic flow is basically caused bt the "pumping" action of the shaft/journal assembly, and is directly proportional to engine rpm.

The pressure flow is basically the additional oil flow to enhance cooling of the bearing, and is directly proportional to supply oil pressure.

A properly design journal bearing will operate with a flooded oil inlet at very low pressure, just several psi. The oil wedge will form a much higher local pressure to support the rotating shaft. Please note that a high pressure may be required at the beginning of an oil header/gallery to provided sufficent flow/pressure at the tail end of the header/gallery.

Unlike most flow/pressure relationships related to the velocity squared, these are directly proportional relationships.

On heavy rotating equiment, in some applications a secondary high pressure lifting oil or jacking oil is supplied to the bottom of the shaft or thrust bearing to phyically lift the shaft at start-up or low rpm's.

One source that discusses and gives calculations for journal bearing oil flow is the "Machinery's Handbook" in the 'journal bearings' section.

Posted By: LGriffin_#4385 Re: Forged pistons from LS1 in 292 - 01/22/09 08:12 PM
Winter is right we have two discussion here.

Lennart, There are a lot of possible piston that would work with longer rods for the 292. That's the problem longer rods for the 292. There are no longer rods available made of forged steel. The only rods that I'm aware of are custom Aluminum and not recommend for the street, because they stretch. The dragsters that use aluminum rods resize them after every season, maybe more.

Larry
Posted By: Coastal Re: Forged pistons from LS1 in 292 - 01/23/09 11:10 AM
So to paraphrase this entire thread, would you agree that it would be just easier and probably cheaper to buy some forged pistons from JE or Ross or wherever that are made for a 292?

Posted By: LGriffin_#4385 Re: Forged pistons from LS1 in 292 - 01/23/09 11:30 AM
That's pretty much what it comes down to for a 292, and what most have done. I hope to measure the thickness of the top of the BBC piston this afternoon and post some pictures. Unless someone can look at the numbers and calculate the strength, I don't know that that will change anything.

Larry
Posted By: CNC-Dude #5585 Re: Forged pistons from LS1 in 292 - 01/23/09 02:48 PM
Just for everyones reference on cost, the current price for the Ross pistons is $459 for a set of 6. The specs are forged Flat top, 2 valve relief, machined for pin locks, forced pin oiling, machined for 1/16 x 1/16 x 3/16 rings, .927 wrist pin bore(pins not included), any bore size(no extra charge),any compression height(pin placement)(no extra charge)+ shipping! Now we have some dollar #'s to have for our wish list....Who's in!
Posted By: panic Re: Forged pistons from LS1 in 292 - 01/23/09 08:26 PM
There are no longer rods available made of forged steel.

There are many, but not in useful sizes unless you want to spend a lot of money. Carrillo will make you a steel rod to your exact dimensions.

The only rods that I'm aware of are custom Aluminum and not recommend for the street, because they stretch.

If the recip. weight and RPM are kept within reasonable limits, the mileage for an aluminum rod can be quite extensive - over 70,000 reported for some stock engines.
Posted By: panic Re: Forged pistons from LS1 in 292 - 01/23/09 08:30 PM
Re Ross: for an extra charge they may have taper-wall pins and a weight reduction program (milling from inside).
You can also make much higher compression by describing the chamber shape for pop-up (they my even have the chamber profiled on CNC already), or lower CR by giving the ratio and they will make a D cup with enough depth to get there.
Blower also needs the ring stack slightly lower down, and more minimum crown thickness.
Posted By: LGriffin_#4385 Re: Forged pistons from LS1 in 292 - 01/24/09 01:11 AM
Panic, If you've got the $$$$ there's lots of goodies to had. The motor in the Junior Fuel Dragster that I teamed on had a Titanium crank. The info on the Alum. rods is interesting. Still $1,200 to $1,800 for a set of rods, that's almost half the cost of a crate motor.

Larry
Posted By: LGriffin_#4385 Re: Forged pistons from LS1 in 292 - 01/24/09 01:24 AM
I was able to measure the top of the BBC 366 ci. pistons that I had the tops cut down to work wih the stock rods today. The thinnest spot I could find on the top of one of the spare pistons was .2418. I then measured from the top of the piston to the bottom of the valve relief and that confirmed the .080 the shop told me that they had taken off. So if my math is correct and there is not to much deviation in the piston casting. The pistons should be about .1618 thick at the thinnest point. Anyone with ideas how weak that might be.

Larry
Posted By: CNC-Dude #5585 Re: Forged pistons from LS1 in 292 - 01/24/09 02:47 AM
The .241 should be safe for a cast piston. Its the .161 that is going to be kinda' on the fence. How big of an area is it that thin. Now that the tops have been cut, how far down is the top ring. Keep in mind the 366 piston and wrist pin are a whole lot heavier than the stock 292 piston and wrist pin. That will potentially put much more stress on a rod that wasn't engineered for that extra mass hanging on the end of it. So be cautious about RPM, as the piston speed of the 292 will be much higher than the 366 at the same RPM. Just curious, did you check the weight difference between them.
Posted By: LGriffin_#4385 Re: Forged pistons from LS1 in 292 - 01/24/09 04:11 AM
CNC-Dude, thanks for the consideration. I'll have to go back and map the top of the piston a bit better. The under side of the top is irregular to say the least. Right now I'd say there is an area about the size of a quarter that is .161. I'll map the measurable area on both spare pistons I have. You can still see part of the valve reliefs and notch here's a picture of the piston installed;

http://www.flickr.com/photos/33950672@N08/3222177846/

you can see the notch on the bottom left and part of the valve relief on top left of center. Here is a picture of the piston showing the Teflon skirt coating before the top was cut and two 292 rods. I think the rod in the center has been lightened and the one on the right is stock.

http://www.flickr.com/photos/33950672@N08/3222177844/

For reference here are the three off the shelf pistons for the 292;

http://www.flickr.com/photos/33950672@N08/3222177836/

The one on the left is the low 7.6 compression piston with full dish, the center is the 8.3 compression with the 'D' shaped dish, and the one on the right is LPG piston with the oval dish that is .180 deep. I'll weigh the stock 366 against the two pistons on the left and let you know how they compare.

I did weigh the stock piston and rod against the 366 and lightened rod. The 366 piston and rod were about a 1/2 pound lighter. Here's a picture of the assembled block just because.

http://www.flickr.com/photos/33950672@N08/3222217572/

Larry
Posted By: panic Re: Forged pistons from LS1 in 292 - 01/24/09 12:19 PM
JM2¢:
The marks left from the valve notches have to be safe, both because they're original and because they're above the skirt.
The "delicate" areas will be the part of the unsupported crown (away from the skirt and especially away from the pin bosses) closest to the exhaust valve, the plug, and the center of this area.
These will fail first on detonation, but shouldn't give up from inertia at .161".
Posted By: panic Re: Forged pistons from LS1 in 292 - 01/24/09 12:38 PM
I found some Jaguar 3.8 rod data:
Length 7.75"
Big end bore 2.233" (292 is 2.225"), would need an undersize and a smaller undersize on the crank.
Piston pin .875"
Width 1.180"
Based on 292 deck height, the piston CD for zero deck (quench distance is gasket only) is 1.065".
Posted By: LGriffin_#4385 Re: Forged pistons from LS1 in 292 - 01/24/09 02:49 PM
I looked at Kieth Black web site for Silvo-O-Lite pistons, they have a listing by bore size. The smallest CD I could find for bore of 3.875 was 1.581. Here's the link.

http://kb-silvolite.com/spistons.php?action=diam

Larry
Posted By: Lennart Re: Forged pistons from LS1 in 292 - 01/24/09 04:09 PM
panic,

there are 3.905 dia pistons for the LS1 that come in a 1.115 CD.
Check Wiseco or Diamond to name a few.
Posted By: LGriffin_#4385 Re: Forged pistons from LS1 in 292 - 01/24/09 07:14 PM
CNC-Dude, I weighed the pistons and the BBC 366 is 28.099, the low compression full dish is 28.423, the 'D' shaped dish is 30.127 ounces. That's piston and pins only.

Larry
Posted By: tlowe #1716 Re: Forged pistons from LS1 in 292 - 01/24/09 08:59 PM
larry,
i have been out in my shop checking out weights. a stock 292 piston with no pin weighs about 740 grams. and using 28 grams per oz, yours is 784 grams. so pretty close.
tell me again how you lost 1/2 lb per cyl, that i believe is 6 oz per cyl.

on a side note, i weighed some performance 292 pistons.
a je flat top weight was 640 with rings and pin
Posted By: CNC-Dude #5585 Re: Forged pistons from LS1 in 292 - 01/25/09 01:42 AM
 Originally Posted By: LGriffin_#4385
CNC-Dude, I weighed the pistons and the BBC 366 is 28.099, the low compression full dish is 28.423, the 'D' shaped dish is 30.127 ounces. That's piston and pins only.

Larry
That looks to be a decent piston swap alternative.
Posted By: Greybeard Re: Forged pistons from LS1 in 292 - 02/17/09 03:57 PM
I talked to someone in the business about the flathead Ford rod today, and he said they'd custom machine their H-beam rod to 2.1 Chev rod bearing, but said their forging would be best @ .787 pin. That would give a 7" rod, but would still require custom pistons rather than off the shelf. They would need to have 10 orders to reset the machines and not have to jack the price real bad. They'd still approach $100 each however.

7" H-beam, 2.1" big end, .787 small end.
Posted By: davesf85 Re: Forged pistons from LS1 in 292 - 03/02/09 03:42 PM
CNC dude, thanks for the info on the Ross pistons earlier! Lurker Dave here; This settles it for me--I'm thinking a 292 bored .060 over, stock rods, ross pistons, water heated intake with a 390 holley (I already have that; tho the megasquirt looks nice) to replace the 250 I've got now. (currently set up with headers, clifford intake and 390 holley)...still have the stock head, so that is the first priority.
Posted By: Z33 Re: Forged pistons from LS1 in 292 - 03/02/09 06:33 PM
292 rods on ebay. The seller might give a few here reason to pause. http://cgi.ebay.com/ebaymotors/Chevy-Inl...A1%7C240%3A1318

Z
Posted By: CNC-Dude #5585 Re: Forged pistons from LS1 in 292 - 03/02/09 06:55 PM
The problem with aluminum rods in a 292,or a 250 for that matter,is you have to use a roller cam. Because you have to grind so much rod clearance in the camshaft to clear the rods,a cast flat tappet camshaft will break in half if you grind them that much....
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