HEMI Tech- PISTONS! rods and related

Bump for the new guys. God thread though complicated.

 

On the side.

..better leave God out of this...there are 'those' who would object...

.

 

i am trying this combo, 6.800 bbc scat rod with jahns 1.75 comp height piston, crank turned to 2.2" journal, putting in my 354 hemi, in fed dragster

 

Hey guys,
Bringin the Hemi piston thread back up. I know dome pistons are the real way to do this but I am curious if there is any worth while gain in compression by milling a Hemi head. My 331 deck and heads were cut just enough to square them up and I ran stock cast pistons and an Isky cam. My static elevation is about 5000 feet and that, I would believe, translates to squat in the compression department! The engine runs great but I know that compression is whats needed to liven it up. Anything is helpful.

Thanks
Hack

 

Pistons. You didn't say what year your 331 is, but the C/R could measure out as much as a full point below the advertised C/R. Measure your chambers & get with a piston co. to get the C/R you want.

 

Not knowing where you are starting from and what you want as a final, the amount of cutting that could be required could also cause huge headaches trying to get a manifold to fit.
If the engine is half-way fresh then step up and get some forged pieces so you actually know what you have.
If the engine is at all 'aged' then a rebuild is in order anyway.

I can almost read into your query that the engine might be a bit lazy and thus the compression issue. Perhaps you have too much cam for the compression that you do have...

.

 

Thanks for the responses guys. The engine is pretty fresh. I would say about 5 thousand miles on it. The cam is a 262 grind and is actually pretty mild. I think the lift is about .410. I know that the optimum thing is to buy forged pistons and do it right but I thought i would ask. Does the piston being above the deck hight at tdc get in the way of the head at some point if you were to remove head material? As head material is removed, it would seem that the dome diameter would also decrease? What do you think?

Hack

 

That is a pretty mild grind so you would need to look at the overlap to see if you are loosing pressure.
It might also be a cam install (position) issue.

Two problems with cutting the heads: as mentioned, intake fitment and then piston-to-valve clearance. You will also need adjustable pushrods to correct lifter pre-load.

If your heads are 54 and newer then you need to cut about 0.070" to get about a 1. raise....at least the first 2 or 3 cuts then the amount of each successive cut decreases slightly as the chamber gets shorter.

Yes, you can do it, but it is still the wrong way to make compression in a Hemi.

.

 

If you were to look at a 354 car engine or a 392 with the pistons above the deck, you will notice that the tops are beveled to fit inside the dome of the head. Putting flat tops above the deck will lead to problems there. Cutting the deck too much with flat tops also puts the top ring pretty far up the cylinder wall.

 

Thanks guys. I will be ordering some pistons asap. I have the adjustables in it already as well. Thanks again for the info.

 

I believe thats a 327 piston. If so, it has a c.h. of about 1.675. A 354 is approximately 1.950. Plus the small block Chevy uses a small diameter pin. They must have valve notches in the tops?
Are they actually on the 354 rods? Sounds to me like you need pistons and rods for a 354. Let me know.

 

How much did you pay for the pile? Are you happy with what you received...minus the shiverlay stuff...? If so, then you got a good deal.

You really should consider using 10:1 forgings anyway so no loss there, and if you are missing the con rods there are plenty to be had, either oem or an aftermarket.

.

 

I thought I would post a couple pictures of what I found the other day. I have no idea if these were factory installed or not, but they are factory pistons. This was a 56 IND 331 hemi.
I could not find any information pertaining to them. You just never know with these early hemis.

 

Nice find if the whole set is usable, definatly not expected to be found in an Ind.

 

They are a nice set. Actually better than the pictures show. They also have new rings on them. This engine was rebuild, but never started, and got some water in the cylinders. All they need is a nice std bore block.

 

Is it possible those pistons where made for a Propane fueled engine?

 

I really have no idea. I can find no reference to that part number.

 

I thought of the idea because of the slightly higher compression domes. Propane has something close to a 110 octane rating.

 

Those are indeed factory pistons most likely out of an early to mid fifties chrysler 331 poly or "spitfire" v-8. If they are standard bore (3.8125) I'd be interested in them or any other parts you may have for that engine as I happen to be restoring one currently.

 

Those valve reliefs don't look like they would be for a poly head.

 

Do a proper Intro in the Intro section before the Forum Police get ya! He said they're out of a Hemi & the valve reliefs are lined up for a hemi, not offset like a Poly.

 

I doubt these pistons would clear the poly chamber.

 

just received my ross pistons, real nice, 4" x 1.75 comp hgt, .990 tool steel straight wall pins, 6.800" rod, using them in my blown 354 hemi on alcohol, s/steel top ring, landed OZ A$1660.00

 

Ok the 315 Dodge Hemi uses ARP rod bolts # 144-6001
and the 392 uses the same rod bolts as a 383 and 440 dodge
any one know which rod bolts a 54 chry 331 uses??

 

Great info here ,thanks guys. Just picked up a set of Venolia forged pistons here, was wondering where to go for piston rings?

 

...which engine?

 

Hi guy's, would like to start with "I am no hemi expert" just want to share something.I've read a lot about the 392 piston in a 354,so here's what I found.I tore apart my industrial 354 the other night.And a while back I bought a set of used 392 pistons(I've read 9.25 and 10:1 compression pistons,by the numbers I believe mine are 1957 9.25 ).
Once I had a piston out, I removed the rod slid the pin over and slid a 392 piston on beside it.From the pin down to the skirt was the same so they sat on the bench even.Now two things stand out.First the dome height difference and the compression height difference.What I would like to say is,besides the obvious pin difference the dome will definitely boost my compression,how much is unknown.
What I would like to know is,anyone here know the compression height difference between the two?
My crank needs to be turned so if I could make up the difference with a longer rod I might do it.
Also I did a crude measurement and found 0.116" in dome height.
So I have a pic but can't load I'll try later.

 

A longer rod is not going to add compression.

 

Because of shorter stroke you'll lose 1 point from the advertised C/R. 9.25 becomes 8.25. Longer rod just increases time the piston is @ TDC. Offset grinding would restore some C/R, but if you want 9.25 you probably need to buy 10:1 & get 9.0 instead.

 

Post the casting numbers of both pistons you want to compare the compression ratio of.