Inliners International Forums General Discussion Bench racing Piston & Rod Specs?

Does anyone know of a web site or other source that lists piston and rod specs? I'm looking for options. Thanks, Beater

I've got a lot of old Sealed Power and Clevite Bearing books that has some info. I have been able to compile a list of some of the more common 6's(235/261,270/302 GMC,194/230/250/292), and have gotten many of the comp.hgts. and rod lengths from it. What I couldn't find, I was able to talk to some manufacturers and they filled in the blanks. Im talking with a connecting rod company right now about some rods for the 235's and GMC's, and am looking at possibilites for being able to offer a rod and piston combo for some high performance use like we have been discussing to go along with the head porting project that im undertaking!

I have a listing from an Eggie catalog but It is confusing. I have some Sealed Power and Clevite books too. I guess you have to actually open them! What kind of power can be made with stock GMC rods? How well would the older GMC heads work with forced induction? Is that a good chamber design? Is there a 4 1/8" domed 302 piston? Thanks, Tom

Lots (just don't expect to wind it up too far).

Great, from what I read (here and on the HAMB).

Which head? The '270' and '302' chambers are different. There is a small-er port head that has a 'closed' chamber too, shouldn't take as much dome to bring the compression in line (lighter piston ) and if you're boosting it, it won't be as critical about the smaller port windows. Then again, if this is for B-Ville that might make a difference, (as I don't know if the exhaust is commensurately smaller too or not).


Nick Aries Jr (and others) will make anything you could want.

Here's a link to Keith Black Silvolite pistons by bore diameter;

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

The only comprehensive listing for rods I found was AERA Rod Manual. I picked up an old copy off ebay. Hope this helps.

Larry

I had seen mentioned that the Ferguson streamliner had gone real high 296 or 7 MPH with a stock but heavily modified GMC head, and only went a couple of MPH's over 300 with the addition of a 12 port head. An OEM head will provide any level of performance you will ever need im sure! The GMC rod is plenty beefy and massive, and could probably take any level of HP you could concieve as well,NA or Forced Induction. Observing several guidelines will help insure longevity and added reliability in them. Naturally, RPM is one of them and getting rid of the 10 lb. piston trying to pull the rod in half is the other. If you choose to stay with the stock GMC rod length, then buying a custom set of race pistons wont hurt your pocketbook too badly. I've seen many NHRA Super Stock 283 pistons weigh just slightly over 300 grams compared to a TRW stlye stock replacement 283 piston of 670ish grams. Those engines will use the same set of rods(OEM small journal) for 3-4 seasons @ 10,500+ RPM with no failures. The 283 piston is going to be real close to the GMC as far as compression hgt. goes for comparison sake. If you are going to get a domed piston, you can always get it blank to maximize your compression and maybe a little cheaper as well. I also have a 302 GMC head I am going to port and develop as well as the 235 head, so far the GMC has much more promising potential for flow, I'll begin to update this week with flow #'s for each to compare against....

Don Ferguson also had 80% nitro and that engine cost cover 20K, plus 30+ years of R&D. CNC is absolutely right you can make a lot of power with the stock GMC head. Don told me that one of the keys was to move the distributor (in his case the magneto)to the front of the engine and increase the cam base circle. The GMC has a big problem with cam twist and if you ever put a timing light at high RPM you will notice the problem.

CNC-dude, glad to hear it.

Is the 283 compression height comparison for the 270/302 deck height, or the 228/248 deck height ( I have no proof, but I expect the taller deck would have a longer compression distance, or am I mis remembering, is it the stroke or bore on the 248 that's common with the 270, hmm? my 'sometimers' is acting up again).

Nexxussian, 228 & 248 have 3 13/16" stroke. 270 & 302 have 4" stroke. Because they all use the same rods it seems the piston compression height should have a difference of 3/32".
$UM FUN, how did he drive the oil pump, or is that the real cam load that needs to be moved?
CNC, I have one 302 head but I'm wondering about the early small port domed combustion chamber. It seems that a lot of the small port draw back could be negated by a little pressure. I've got lots of those heads to play with.
Thanks everyone I this is fun stuff. I don't have 20K or 30 years!

Beater, the smaller ports are going to be better suited for forced induction, as they will keep the air speed and fuel velocity high. Turbos and superchargers are great equalizers for restrictive ports. As for the oil pump drive on Fergusons motor, its probably dry sump, or external wet sump driven from a belt off the end of the crank. Distributor is also driven off the front, or is a crank trigger setup.

Nex, im still trying to crunch numbers with compression hgts. and rod lengths. You can swap the GMC rod into the Chevy and get a more readily available off the shelf piston. But the GMC rod in a GMC, has such a tall compression hgt., unless one of the rod companies i've been speaking to can alter an existing forging they have to create a longer length than the stock GMC 7" center-to-center length. Then that will only make us have to go custom with the piston and rod combos for them. Not many later V-8's had rods that long from the factory. The closest i've found that is a stocking shelf item for an H-beam rod is for a 440 Chrysler(6.760 center-to-center), and uses a Big Block Chevy housing bore. Would work ok in the 235, but is still too short for the GMC. There are still other options im looking at, but nothing absolute yet....

Yeah, I figured that might be an issue.

I haven't seen anyone but Ron beat that, and with those being 'exotic' (harder to come by) parts nowadays.

You would think with all the diesel stuff getting hot rodded these days that there would at least be a forging blank that could be ordered machined to suit (not cheap, but cheaper than billet). Hard part would be finding one that the top of the small end was the same width (maybe not, I don't know enough about forging dies to know if they would strike the rod close to that shape or not).

Larry, Sorry I missed your post earlier. That is a great chart. I know the guy that designed KB pistons. He also rebuilds McCulloch Super chargers. I'm going to enlist him but he doesn't know it yet. I'm trying to get as much lined up here before I stsrt bugging him. He's busy.
CNC, thats just what I was thinking about the head. It seems that I saw a GMC that had a front drive mag but had a cut down distributer in place to drive the oil pump.
I'm running the later small port closed chamber head on my 270 now. It has some port work done and has served me well on the street for over 30 years. It might get pressed into service also.

Thanks guys! Beater

Care to share the 'port work' on that head? I've been told repeatedly it would do anything a sane person could want on the street without port work. Must be great with it (how much do you figure your compression is?).

I recently built a 321 inch GMC (4.125 x 4) and used the #983 head and ported it. We got 264 cfm @ .600 lift. The exhaust sucks @ 144 cfm max. The engine made 347 HP @ 5500 rpm and 346 lb/ft TQ @ 4600. That's with short zoomie headers so I was giving away some TQ and HP. 4x1 header coming this winter.

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)
3 Rochester carbs on a built manifold.
With just 4 runs under our belt the HAMB dragster ran 12.10 @ 120.5 MPH (New records for MPH & ET)
By the way the 270 and 302 have a 3/16" taller block than the other GMC engines.

I saved 1 1/4 POUNDS on each piston/rod/pin. The stock GMC piston and pins are HEAVY. The rod is strong but too short.

Ron

can you give me dimensions of the stock gmc rods.
small end diameter
small end width
big end rod journal size
big end width
bolt size.
thanks tom

Small end diameter: .990(same as BBC)
Small end width: N/A(235 is 1.025/30")
B/E housing bore: 2.4563/2.4458(235/261 is the same)
Standard rod crank journal: 2.3110/2.3120
B/E rod width: 1.238/40(235 is same)
Bolt size: 3/8"
Center-to-Center length: 7.000"(235 is 6.800")
Compression Hgt.of 302 piston: 2.375"

The GMC rod is interchangeable with the 235/261's, provided that the appropriate piston compression hgt. is used!

thanks for those specs. can someone also supply a good pic of one? what material are they made from? in other words, how tough are they? tom

tlowe, thai is the best I could do this morning. Sorry the two sets I could get to have pistons on them.
ROD

beater,
thanks for the pics!

next question.
does anyone think that rod has a chance to have the big end resized to fit the 292 2.1" rod journal. i know the small end can be bushed down.
i want to run a piston that does not have so much compression height. the extra .250 length would help. what i really want is a 7.250 c to c rod. any help there? tom

Tom,what is the width of a stock 292 rod, I got an idea!

CNC ref; gmc rod into chev.more readily available piston of shelf???? Could you give a little imfo. on what piston might be avail to use gmc rod in 261. REALY THANK YOU FOR YOUR TIME AND
SHARING OF KNOWLEDGE 1 OL REDNECK I.I. #113

While I haven't had a stock 261 piston to verify, I have found in a Sealed Power parts book, that the replacement piston for a 261 has a compression hgt. of 2.046". So,doing the math, if we subtract -.200(Difference in rod length from 235/261 to GMC) from that we get 1.846" as our new comp.hgt. Looking through my TRW/sealed power book,I have found several part #'s that can be used with little additional mods(mostly making a bushing for the rod to match piston/wrist pin).I'll list them in order of increasing bore size, not knowing what the overbore limit is for a 261(stock is 3.750"),you'll have to determine how much to go bigger.

L2469F(3.8 Buick): 1.868" C/H, .940 pin, 3.800" Bore!
L2338F(283 Chevy): 1.810" C/H, .927 pin, 3.875" Bore!
L2463F(318 Chrysler): 1.840 C/H, .984 pin, 3.914" Bore!
any overbore or superceded piston # should also work as well!

Additional mods might also include machining lock grooves in pistons pin bores, since GMC rods are floating! Also decking block or flycutting pistons to arrive at your desired actual finish deck hgt. The above piston #'s are for Forged pistons....

cnc-dude,
finally had time to measure up a rod.
292 stock rod specs:
small end width 1.030
pin bore .927
c-c 6.760
big end width 1.030
big end bore 2.225, for a 2.1 rod journal.

ok , what idea do you have?

Several companies I have been speaking to about the 235/261 and GMC rods have a BBC H-beam forging that is 7.100" center-to-center. At least one of them has entertained the idea of making the B/E wider to accomodate the width of the Stovebolt/GMC, and either leaving the housing bore BBC, or trying to go to the 2.312" bore. Since the 292 is closer to the finished dim. on the width as the BBC(.990 vs 1.030), they could easily make the housing bore 2.225" as well.Just make a thicker bushing for the S/E. I dont see how you could make the GMC rod work for the housing bore, you couldn't close it up that much. But as an alternative you could make some bearing spacers similar to the type used when racers install a 350 crank in a 400 block. Either option can be made to work for you without much difficulty....

Did they give any idea what the finished unit price (range) and minmum order was (for them to entertain it more seriously)?

You've probably posted that, but I don't recall where.

Speedway sells a 7" H-beam for Ford Flatheads. I haven't checked any other specs. Pretty small top end I suspect.

I am not well versed in all that you guys are trying to achieve, but I thought I'd point to Tom Langdon's Cadillac 261 article in the Sept./Oct.2003 issue of 12PN. After boring and using an offset crankshaft with Cadillac pistons and 292 rods it's possible to reach 290 cu.in. out of the original 261. The pistons were from Cadillac 368 cu in V8, 1980-84, with a std. bore of 3.80" and then the appropriate overbore to get the final cu.in. one would want. Without head or block milling the piston below deck is .046". All these parts would be easily found at any parts store and cheaper then special made pistons or rods.I don't know if this helps, but I thought I'd point it out. In any case I am enjoying your discussion.

The Flathead H-beam rod is too skimpy! The forging I am talking about is a 7.100" true BBC forging rated at 750+HP. The cost of this forging is $479 a set + shipping and can even be upgraded to a more high end bolt for an additional $65. To use this rod, the crank cheeks will need to be welded up to match the BBC width and them the journal ground to the 2.200" BBC from the 2.312" 235/GMC journal! You could also take this opportunity to offset stroke the journal as well to gain an additional 7-10 cubes. To make a true application specific 235/GMC rod, I will need to send them one so they can evaluate their raw forging to see if it can accomodate the needed dimensions for the 235/GMC. An additional cost per set of some amount is expected for this if it can be made to work. As I was telling tlowe, this forging is a lot closer to working dimensionally for his 292, than it is for the 235/GMC's as a raw forging, but still gives a user a long rod option that will work in the earlier 6's with a little crank work.... I'll keep us updated as I will send them a 235 rod for evaluation!

Sounds good. I'm uploading some pictures I took this morning of rods from a 292, 302, and 8BA. Maybe we could use two flathead rods!
HERE THEY ARE!

RODS

I think the H-beam Flatty rod is the least I would use if building one. I know many people would swear by the stock ones though! I just think of the advances in todays technology for increasing HP with blowers and such in the Flatty, I wouldn't use a stock one....

I just threw it in to show how beefy the other two are, especially the GMC. That other one is from a 327 SBC. It's a little beat up. It removed it's self via the oil pan.
Do you think the big block rods would clear the block sides and cam?

Drew, that"s the kind of information we need to gather and put in one spot. There is so much here on this site but it's very time consuming to find it. Thanks!

beater,
thanks for the pics. thos egmc rods are beefy. esp compared to the 292. i am also afraid of cam clearance with a BB chevy big end. tom

Guys,

I had to grind the cam in 12 places for clearance for the Hudson rods in my 302 GMC. It's definately something one has to consider when a different rod is being used.

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

Dimensionally, the BBC rod will probably be slightly less massive around the B/E than the factory GMC rod is, even in an H-beam design. I think if they could make the housing bore smaller for tlowes application, they would also profile the B/E to be more like the SBC journal it represents, or you would have a rod that would end up weighing 900g.(LOL), and that would be ridiculously heavy,even for a 292 engine. I think if tlowe has a shortblock laying around, he might just look up inside it with a flashlight, and rotate it around and just see how much extra clearance he has for a beefier rod. I know that with all of Cotton's 292 engines, the cams were ground for clearance on all of them. That might work for a steel roller billet, but would weaken a hydraulic or solid flat tappet camshaft too much....

I dont think the caddy pistons are made anymore - what is on the shelves are all there is available - Re: Drew's comments

After much ransacking today, I finally found the most treasured TRW bearing book(definately Holy Grail stuff) that there is! I had it hid from myself forever, and finally found it. There was a time when you could buy reconditioned connecting rods from them, as well as bearings and pistons. The book shows all the rod specs you could ever need such as rod length, rod width on the B/E, wrist pin size, housing bore size and crank journal size and bearing part # for the rod,even forging #'s. True home run! It also reveiled more differences in the 235 vs. GMC than was first thought, other than rod length. The California Bill book just hinted at the swapping of the GMC rod into the 235, and never really said what had to be done. The rod journal is the same size, but the width of the rod is about .200 thicker on the GMC than the Chevy, so flycutting the sides of the B/E is necessary to install it onto the 235 crank journal. So that means making a common 235/GMC rod more remote, but the 7.100" BBC rod with welding the crank cheeks,still a simple swap for either one.

can you use the BBC without welding the crank cheeks?

No, the rods are too narrow.

BBC: .990 wide
235: 1.240 wide
GMC: 1.430 wide

Looking at that GMC rod and handling it this morning along with the 292 and 8BA rods I was very impressed with its mass. I think if they were carefully cleaned up on the edges so that imperfections/flashing were removed, shot penned, and cryoed they would stand anything I would do to them. They already fit and clear block and cam. A lighter piston would lesson the stress. I need a 4.125" piston with a 3/32 greater compression height. Flat or domed depending on which head I use.
CNC, did you find any of my books in your stacks? They must be somewhere!
Ron, That Jag rod sounds interesting. All that grinding on the cam scares me, especially if it is still turning the oil pump and the distributer.
This is a great discussion. Thanks