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#46971 - 01/18/09 06:58 AM Forged pistons from LS1 in 292
Lennart Offline
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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

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#46972 - 01/18/09 08:26 AM Re: Forged pistons from LS1 in 292 [Re: Lennart]
tlowe #1716 Offline
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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
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#46977 - 01/18/09 09:52 AM Re: Forged pistons from LS1 in 292 [Re: tlowe #1716]
panic Offline
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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?

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#46980 - 01/18/09 10:12 AM Re: Forged pistons from LS1 in 292 [Re: panic]
Lennart Offline
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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.

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#46981 - 01/18/09 10:22 AM Re: Forged pistons from LS1 in 292 [Re: Lennart]
panic Offline
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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.

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#46983 - 01/18/09 11:04 AM Re: Forged pistons from LS1 in 292 [Re: panic]
Lennart Offline
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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 !

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#46984 - 01/18/09 11:26 AM Re: Forged pistons from LS1 in 292 [Re: Lennart]
Beater of the Pack Offline

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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.
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#46985 - 01/18/09 11:37 AM Re: Forged pistons from LS1 in 292 [Re: Lennart]
Coastal Offline
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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.

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#46987 - 01/18/09 11:48 AM Re: Forged pistons from LS1 in 292 [Re: Beater of the Pack]
panic Offline
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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"

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#46991 - 01/18/09 01:51 PM Re: Forged pistons from LS1 in 292 [Re: panic]
Lennart Offline
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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

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#46992 - 01/18/09 02:37 PM Re: Forged pistons from LS1 in 292 [Re: Lennart]
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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.
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#46996 - 01/18/09 03:55 PM Re: Forged pistons from LS1 in 292 [Re: Beater of the Pack]
panic Offline
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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?

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#46997 - 01/18/09 04:25 PM Re: Forged pistons from LS1 in 292 [Re: panic]
panic Offline
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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.

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#46998 - 01/18/09 04:27 PM Re: Forged pistons from LS1 in 292 [Re: panic]
panic Offline
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Check the older TRW literature for rod data.

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#47001 - 01/18/09 05:37 PM Re: Forged pistons from LS1 in 292 [Re: panic]
Nexxussian Offline
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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).
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#47011 - 01/18/09 07:17 PM Re: Forged pistons from LS1 in 292 [Re: Lennart]
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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
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#47029 - 01/19/09 09:29 AM Re: Forged pistons from LS1 in 292 [Re: LGriffin_#4385]
panic Offline
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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).

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#47030 - 01/19/09 11:01 AM Re: Forged pistons from LS1 in 292 [Re: panic]
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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
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#47039 - 01/19/09 03:35 PM Re: Forged pistons from LS1 in 292 [Re: LGriffin_#4385]
CNC-Dude #5585 Offline
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 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....
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#47045 - 01/19/09 04:55 PM Re: Forged pistons from LS1 in 292 [Re: CNC-Dude #5585]
panic Offline
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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 = $$$

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#47047 - 01/19/09 05:01 PM Re: Forged pistons from LS1 in 292 [Re: panic]
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Yep,thats true!
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#47048 - 01/19/09 05:03 PM Re: Forged pistons from LS1 in 292 [Re: panic]
panic Offline
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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

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#47050 - 01/19/09 05:30 PM Re: Forged pistons from LS1 in 292 [Re: panic]
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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
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#47051 - 01/19/09 05:50 PM Re: Forged pistons from LS1 in 292 [Re: LGriffin_#4385]
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can you give us details? tom
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#47053 - 01/19/09 06:53 PM Re: Forged pistons from LS1 in 292 [Re: tlowe #1716]
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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
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#47056 - 01/19/09 08:04 PM Re: Forged pistons from LS1 in 292 [Re: LGriffin_#4385]
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It appears that getting info from the Automotive Engine Rebuilders Association is more expensive than custom rods! \:o
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#47064 - 01/20/09 01:19 AM Re: Forged pistons from LS1 in 292 [Re: panic]
Nexxussian Offline
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 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).
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#47072 - 01/20/09 07:10 AM Re: Forged pistons from LS1 in 292 [Re: Nexxussian]
panic Offline
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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.

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#47074 - 01/20/09 07:50 AM Re: Forged pistons from LS1 in 292 [Re: panic]
Nexxussian Offline
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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).


Edited by Nexxussian (01/20/09 07:51 AM)
Edit Reason: typ-o-matic
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#47076 - 01/20/09 10:20 AM Re: Forged pistons from LS1 in 292 [Re: Nexxussian]
panic Offline
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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.

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#47077 - 01/20/09 10:28 AM Re: Forged pistons from LS1 in 292 [Re: panic]
panic Offline
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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?

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#47078 - 01/20/09 10:44 AM Re: Forged pistons from LS1 in 292 [Re: panic]
Xea I.I. #5390 Offline
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2.1 ground .023 will leave you at 2.078 The Ford at 2.123 is larger.
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#47079 - 01/20/09 10:49 AM Re: Forged pistons from LS1 in 292 [Re: LGriffin_#4385]
Lennart Offline
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That`s fine Larry I am following along your discussion and are glad that this much fruitful information resulted out of my question !

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#47080 - 01/20/09 11:31 AM Re: Forged pistons from LS1 in 292 [Re: Lennart]
panic Offline
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Ooppss...
I meant the Ford as -.030" undersize can be matched to a different 292 undersize -.007".

Brain fade...

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#47084 - 01/20/09 12:45 PM Re: Forged pistons from LS1 in 292 [Re: panic]
Lennart Offline
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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

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#47109 - 01/20/09 08:45 PM Re: Forged pistons from LS1 in 292 [Re: panic]
Nexxussian Offline
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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).
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#47111 - 01/20/09 11:02 PM Re: Forged pistons from LS1 in 292 [Re: Nexxussian]
Mean buzzen half dozen A.K.A. Hank Offline
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Registered: 09/23/04
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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
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#47127 - 01/21/09 10:13 AM Re: Forged pistons from LS1 in 292 [Re: Mean buzzen half dozen A.K.A. Hank]
panic Offline
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Registered: 01/11/05
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Loc: Hempstead, Long Island, NY
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?

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#47128 - 01/21/09 10:15 AM Re: Forged pistons from LS1 in 292 [Re: Mean buzzen half dozen A.K.A. Hank]
CNC-Dude #5585 Offline
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Registered: 09/27/08
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Loc: N. Georgia
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!
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#47129 - 01/21/09 10:19 AM Re: Forged pistons from LS1 in 292 [Re: panic]
panic Offline
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Registered: 01/11/05
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Loc: Hempstead, Long Island, NY
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.

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