HEMI Tech- PISTONS! rods and related

Because the pston is always partially down in the bore at TDC, you have INCREASED the combustion chamber volume by boring the block. The only constant is the head combustion chamber area.

You'll only gain a small fraction of a point by boring a block.

 

I said "minute". Last I checked, you could replace that with "small fraction". A gain is a gain. Boring gains compression all else being equal.

 

Boring the block out an eighth to fit a used higher compression piston from a '56 engine isn't all that sound an idea, either. The used 354 pistons will, most likely, have skirt wear and won't give you the boost you think you might be getting. The early engines used sandwich head gaskets; the '56 engine used a steel shim gasket. There's a substantial difference in compressed thickness and the stamped gasket will result in a higher compression ratio. If you use a sandwich gasket on a '56 354 engine, you lower the compression ratio substantially. OEM compression ratio calculations took into account cylinder head combustion chamber volume, how far down in the hole the piston was at TDC and FACTORY head gasket thickness.

Given the cost of a gasket set, a bearing set and a ring set, (around $450.00 and that DOESN'T include cam bearings or oil pump drive shaft bushings) the machine shop fee to hot tank and bore the block will push you over budget.

 

There's a lot of ways to raise compression a little. Shaving the heads, decking the block, playing with head gasket thickness, and even boring the block. All of these methods are good for a small compression increase. But if you use these methods to get to a BIG compression increase, you're just going to make your life difficult. Shaving the heads or decking the block a significant amount will alter your pushrod geometry, and probably require custom pushrods even for a modest amount. Make it by a large enough amount and you involve rocker geometry and pushrod clearance in the block. Not to mention needing to have the intake cut to fit the engine again. Even just the custom pushrods and machining the heads, block, and intake won't be cheap. Plus, you're also altering the valve to piston clearance, so you could even limit cam choice.

The easiest way to raise compression a lot, ie, from a 7.5:1 to 9 or 10:1, is pistons. The price tag for the pistons will probably be around $800, which looks big. But its all in one place. Machine work like boring it 1/8th, shaving the heads, decking the block will nickel and dime you to death. And as you start adding up extras, like custom pushrods, more expensive head gaskets, paying the machine shop (or using your own time) to check all the clearances etc will rapidly exceed the price of new pistons. Not to mention, when all is said and done, you'll have spent a TON of money to run used pistons. And you'll still need to buy those, and good used pistons for hemi's aren't free.

And of course you'll need the block sonic checked to go .125" over. Most of the hemi blocks will take it, but not ALL of them will.

If you can't afford the price tag for the pistons, you probably won't be able to afford all the work you'll need to do to avoid buying new pistons.

 

The most logical answer by far. As I was saying, the milling was an absolutely LAST resort. I'm new to Hemis, not stupid. Last thing I want to do is ruin a perfectly good engine.......and believe me, it's a good one. Since I'm in no hurry, I will just keep on keepin on tearin stuff down and cleanin stuff up. Maybe a good deal on slugs will come up. Maybe not. But I agree, the pistons are the way to go. Thanks for everyone's input. I appreciate it. Don't worry, I'm not gonna ruin it. lol

 

Watch EBay, a set of 11:1 Jahn's was on there a while back, you never know when a 9 or 10 set might show up.

 

Venolia makes good forged slugs and they're cheaper than Ross. Get a set of Pontiac chromoly H-beam rods and have the bottm ends narrowed to match the Desoto units. You'll have to use Pontiac bearings on these. You can get the Pontiac rods 6.800" long if you want a better rod-stroke ratio. Have Venolia make the pin hole in the piston for Pontiac rods. Go with 2-1/2" long with good E-clips. You can get the rods for about $350.00 and they have 7/16" screws. Stock rods are good but get some ARP bolts and have em magged. Get it bored to 3.800" and use some Buick rings. 10-1 is OK since hemis resist knock better.

 

Desoto?

 

A better rod to stroke ratio than a 331? It's already over 1.8. LOL When you start talkin all that stuff, you're really splittin hairs anyway.

 

The last set of pistons I got from Venolia were only $525. They were set for Pontiac pins. The Pontiac H-beam rods with 7'16" screws were only $319. Absolutely bullet proof. Stock rods are pretty good, but if you're gonna put your foot thru the firewall, some good rods are cheap insurance, especially since broken rods can punch holes thru rare blocks. Bill

 

how much horsepower can the stock rods on a 56' 354 take? i have read the crank can take up to 700.

 

The crank will probably take 1000hp, and we start looking for an aftermarket rod when the power level hits 450hp.

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thanks 73rr. how does one go about picking which rod to use? custom pontiac, bbc, or aftermarket hemi? the scat pontiac ones look like they are around 460$ a set. since my crank will need cleaned up anyways would turning the journal down to bbc size make sense or just use the pontiac and have them machined to size? i see the bbc rods are different lengths whereas the pontiac are the correct length. i don't know how the length affects the build.

 

Are you changing to a forged piston?
If not, then you are pretty much stuck with the 6.625" length.
If custom forgings are part of the rebuild then you can mix'n match. There are plenty of 2.0" and 2.2" rods in the catalogues.

One other option is to weld up your crank for a .28 stroke and use 383-400 con rods. You can 'adjust' the final stroke to put the stock replacement piston just where you want it and perhaps pick-up a little compression.

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yup, will be using forged pistons as i want to run a blower... just dropped the block off this week to get checked out. 354 industrial. good to know about the pistons and rods. thanks. i need at least 600hp to keep up with my current motor. can't go backwards!

 

You might drop a little HP, but upgrading to a blown Hemi is never going backwards!

 

You're good to go. Your engine guy (you?) will just need to find a rod length that can work within the confines of the piston and crank. Pay attention to width of the big end...it needs to be the same or ever-so-slightly-fatter than the 354 piece or else you will be welding up one side of the journal.
The piston people will need to know the rod length and pin size. Look at rods with the 0.990 or 0.927 pin since those pins are very generic and fairly cheap.
Oh yeah, there is plenty of room for a blower piston with the longish 6.625 rod, which is about where you should stay. A bit longer is better than a bit shorter.

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73rr you seem vey knowlegible on the subject. Thank you in advance. Like the previous poster, Im putting a blown 354 together. Pistons will most likely be JE or equivalent. On the subject of rods, do you have a preference? Im hearing the Pontiacs coming up more than any other? Would that be 400 Pontiac? or 455?

 

The Pontiac rod is often cited due to its having the same center to center length and being available, however, as I said in the last post, just look through the various catalogues and find a rod that best fits your exact needs.

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400

 

Just recieved my new ARP rod bolts for my Dodge 315 Hemi and mercy me.........they are the same bolts as for mopar small blocks (273, 318 340 360). Arp # 144-6001.
I even contacted ARP tech before buying these and the techie didn't have any listing for the early Dodge and wanted me to measure the origional bolts and get back with him.
I could have saved some $$ had I known this first....but now you all can at least.

 

...due to the relative high cost of anything labeled as 'Hemi', I always encourage folks to ask questions before ordering anything.
FWIW, the 392 uses the same bolt as the 383-400...

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I've gathered up a 354 marine block and heads - i planed on venolia pistons and like the pontaic rod. I have the marine crank, cam etc can i cut that stuff loose? it is in vgc and the crank is huge. What should i do? I want to get to blown 354 hemi, a serious ground pounder and have an original hemi 4spd, champ qc and this will go in that contraption in my avatar and has chromemoly chassis. I am looking for advice as to block and building the short block and fully expect to make 800hp or more.
Thanks guys, oj

 

You should delete this & start it as a seperate Thread.

 

And put it up on the general board? i'll have more answers than obamas' press secretary - by sheer volume some of it will be right.
Never mind, i'll figure it out, thanks anyway.

 

Now that's funny right there...I don't care who you are.

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This Thread is about rods & pistons, not an 800 HP engine build. How 'bout the Hemi social group?

 

So I get my new wrist pin bushings for the Dodge 315 and they all have a "slit" length-wise, all the way through. I am surprised.....is this standard for hemis?

 

Different styles for different brands... A solid, press fit type is more durable.

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what about this setup for a stock type rebuild for a street car? and if these are used where would be the best spot to put the slit when assembled?