HEMI Tech- PISTONS! rods and related

looking for some info on using a Pontiac 455 rod in my desoto 330 , I've read that the dimensions are correct but they need to be narrowed by .10 on each side now doing this what bearing would you have to use or do you have to machine the bearing with the rod ? there are really nice h beams for Pontiac motors and would really like the strength for my blown motor

 

330-341-345 rods are the same. Depending on what you find and at what cost, you might also look at one of the aftermarket units like Scat. No, there will not likely be a 'drop-in' piece but the starting price is reasonable.

If the only dimension that is off is the width of the big end, and 0.010 is not much, then your best best is to have your crank grinder 'bump' the stone just enough to make it happen. This is our standard practice when using 440 rods in the 392.


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Is racetec offering forged pistons for 392's?

 

dunno, but Ross does

 

Currently, production is focused on shiverlay stuff so we have to plan ahead a little more than usual for Hemi/Poly stuff. If you need them in a hurry then you need to call around and see if any are 'on the shelf', otherwise, lead time will be 3-5 weeks. On the average order we can beat anyones pricing on forged pistons with the AutoTec line and we can also source other brands. Send some specific details and I'll make a phone call.

Gary

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about the loses of comp with use of 392 pistons in 354

the consuptions chamber are 105 cc on 354 and the 392 have 110 cc

thats the reason that the loses is not so much as 1-2 point

 

Sorry, but I will disagree.

Chamber volumes do vary, and 105-112 range has been observed, but the 392 piston has a smaller dome volume than the 354 so combined with the smaller swept volume of the 354 the compression will drop.

Consider this: Assume both engines are at/near 9:1. The 392 with more swept volume ( approx 804 cc) will use a smaller dome volume to produce the same squeeze in the same combustion chamber. (A 354 is approx 734 cc). YES, this is a generalization but the concept is correct.
Remember, the ratio is the swept volume (cylinder volume minus dome volume) compared to the final combustion chamber volume (everything above the piston when the piston is at TDC).
Remember, the dome volume is present at BTC as well as TDC, however, the effect at TDC is greater due to the chamber shape.

The 5-7 cc difference in combustion chamber volume alone will not produce a 1 point difference in compression. If you play with the numbers you would find that in order to raise the compression approx 1 point you would need to cut 0.060 from the deck. This is approx equal to 12.5 cc.
This also works in reverse; if you add 12 cc to the combustion chamber(dome volume or fat head gasket, or both) then compression drops accordingly.

For those who like to play with spreadsheets it is easy to plug in the various formulaes and then by changing any of the various inputs (gasket thickness, chamber volume, bore, stroke, dome volume) you can see the changes in compression.

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Nice explanation Gary!

 

I'm looking for other forged than ross because in passed expierence they were very noisy.

 

Explain "noisy". What does that mean? This noisy experience you had, what were the specifics of the application?

Only issue I had with Ross was them being picky about me running a specific ring size that I provided them specs on. They kept having to get in touch with me about it and it slowed the order process down TREMENDOUSLY.

JE Pistons are ALSO very good! Just a tad more $$ than Ross, but very good quality.

Ya' know... I walk by Racetec every day when I take a break at work (I work right behind them and have to get some exercise during the day ) and I've never stopped in there. And JE Pistons is also only a block away. Strange... Sorry, rambling.

 

My old Mickey Thompson forged pistons (that I bought/installed in '64) are really noisy until they heat up and stop dancing around in the cylinders. It sounds like an idling diesel for the first few minutes. They're, currently, in the third block and every one has sounded the same.

 

I am planning on building my '56 331 boring to the 354 STD bore size. Can someone expound on the large bore head gasket discussed earlier and it's availability? Thank you.

 

desoto, you are and have been my hero for years(hemi hero) just fact you were hemi before it was fashonable

 

The '56 is already 354. '51-55 engines are 331.

The new line of "Best" gaskets (what Hot Heads & Egge Machine currently offer in their gasket line) are suitably oversized around the cylinder to accomodate a 1/8" overbore.

 

He could be confused, or it's a converted '56 331 Poly.

 

As it turns out, this fellow apparently has a 56 truck engine in 331 displacement. If he takes the time to read through the Tech Index he will find answers to most of his questions including why cutting the block 1/8" is less than ideal even with a truck block.

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Cutting anything 1/8" was a very last resort, as I view it as not the most correct way to raise compression....although it can be executed correctly if you're careful. It was still something i did not want to do, and I have always said that right from the start. As for cubic inches, I don't really care what size it is. I am simply looking for the most cost effective way to raise compression and if it will safely bore to the 354 bore size, that may be it. Yes it is a 331 and yes it is a 1956 truck engine. The HAMB is a very large site to someone new. Rather than spend days looking for some "tech" pages that I am unfamiliar with finding and didn't even know they existed, I did what I thought was normal and asked a question.

 

Size is a problem. If you haven't yet, put Hemi Tech index in search. It'll keep youreading for a while. Unless you're racing, I'd give it a min overbore.

 

Thanks, George. I appreciate that. I will read through it a bit at the time.......now that I know it's there. lol Since all I really want is 300 HP, I kinda figured a 331 would do that very easily to begin with. Especially since there was a 300 HP 331 from Chrysler to start with. I would much rather use the pistons I have as they are still in good shape. Unfortunately, they are 7.5 truck pistons, and it would take way more milling than I really want to do to get compression up. Since no one seems to want to help with some used 331 pistons in my other thread, I can bide my time and buy some new ones. It's no big deal. I just thought that since I had an interest in early hemis and had found one for 400 bucks that I would share the build process because it is destined to be the least expensive hemi build ever since I am doing it. Thanks again George. You're always a big help.

 

A lot of times, when measured, the OEM C/R is found to be optimistic by up to a full point. You're 7.5s could be only 6.5 in reality(& 8.5s might measure @ 7.5). The only way to know is to measure your chamber & go from there.

 

That was the whole premise for asking here and there for some used 331 high comp pistons. 10:1 pistons for a 331 are 1K bucks. That was the whole reason for exploring making it a 354. The 354 is a 9:1 engine and pistons are cheap. My other thought was to mill .140 off the heads and off block in combination and keep the pistons I have. I'm sure there's enough material to do it, but that's just not correct to "me" and I was leaving that as a last resort. I am on disability so this whole thing is a challange to say the least. I see that I can get 8.5 331 cast pistons for around 450. That's a hit, and I will have to save up but I guess I will do that and then mill the heads about .070 because according to my math, .070 on these heads is about equal to 1 compression ratio and that would get me to 9.5 which would be fine. But, .070 is a pretty good cut on the heads. I am also going to have to mill a good bit from the intake side so an intake can fit correctly. As for the intake, I am going to run the Hot Heads single plane with a single 4 barrel top and a Carter Thermoquad. I will plumb in a water crossover and thermostat housing myself. Have not decided yet if I am going to go with the crossover and drill the heads or come off the intake. I will do whichever is less costly. My block is .030 over and is in excellent condition with cross hatch still visible. The heads are in great condition as well and the guides, valves and seats are perfect. All I need to do there is a basic valve job and I can do that myself. All I need to buy there are the right valve springs to match whichever camshaft I pick. It could be a great project, but I am new to hemis. That's why I joined a couple of new sites. If I cannot find help, I will just buy all of the books I need and figure it out myself. I just thought it would be fun to learn and share what I do with others who have the same love for making some new out of something old as I do.

 

You're supposed to mill the intake to fit the heads.

 

Sorry for not responding faster, noisy means that the Ross forged pistons used in two different small blocks built by two different builders for street performance were really loud cold and hot, much more so than w/trw and oem gm forged pistons. I've ordered JE,s.

 

Boring a block an eighth over has absolutely nothing to do with raising the compression ratio.

the compression ratio is raise by removing one piston and repacing it witb one with a higher dome or otherwise raised top. You don't have to bore the engine to do that.

FWIW, I've run one eighth overbores for hundreds of thousands of miles.

 

Although it might be minor, there is a corresponding change in compression due to the change in cylinder volume with no change in chamber volume...

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First, the passenger car intake manifold is NOT the correct one for my engine. It will not fit and work. It does not cover the extended center heat riser ports in the cylinder heads. The truck heads are different in that respect. I would buy one of the "wrong" single four barrel manifolds, but they do not cover the heat riser ports, either. The only ones that I am aware that do would be the 2 barrel that came off, the Hot Heads single plane manifold that I am considering and the Weiand dual quad. That makes the Hot Heads manifold easily more affordable. If there is some reason that it is physically the "wrong" manifold, lay it on me, don't just throw out useless opinions with no data to back them up. That does no one any good and makes it appear that you are either giving out wrong info or have some kinda personal vendetta against Hot Heads products. I already have a thread on my engine at The Hemi.com. I think that's where it will stay. Thanks.

 

Well, yes, actually it does raise the compression a minute amount because there is more surface area on the larger piston that goes in the new larger bore and that larger piston takes up more room in the combustion chamber and raises compression. But you are correct in that it does not raise compression the same as milling the head or block deck. I guess that's what you were trying to say. I suppose in the end, whatever way I decide to build this engine will be "right" for me. This beffudles me. I have never seen a place so ready to tell you your way is wrong yet so stingy to tell you the right way when that's what you asked to begin with. Yall can have it.

 

Hi Rob. These old engines can sometimes take a toll on ones patience for sure! If you ask 10 different people here how to solve a problem, you will find that all of them are right. Just remember these guys are trying to help you.

 

Thanks. I didn't say exhaust heat riser. I just said heat riser....which is what it is. It simply used water heat. You need to call Bob Walker at Hot Heads and tell them that their new single plane will not work with truck heads, because it will. That's what it was designed for. You can even see it on their site. It has a wide section on the manifold rail designed to cover the extended ports. The Weiand also works as well. But as I said, other than the stock one, those two are the only ones I know of that will cover the port.

Here is Hot Head's description. It clearly says tha the intake does indeed cover the ports in the truck heads.

http://hothemiheads.com/intake_manifolds/hot_heads_single_plane.html

I am done on this. You are 100% correct and I am sorry I got this thread off track. I was only trying to get answers. Thanks.

 

That's probably because the Ross pistons (like my old Mickey Thompson forged pistons) are a lot beefier than oem and aftermarket oem replacement pistons. You have to allow for more cold-expansion with a thicker, stronger piston.