ok im building a 388, using a cola forged crank 3.8" stroke 6" lunati h beam rods.

ok now that leaves 1.126" to deck height. my question is should i use 1.120 compression hieght piston or a 1.125. i cant decide to either go .005 in the hole of zero deck. or should i wait to see what i have when the deck and square the block up. and the other question is, are those to compression hieght a standard hieght. and is there any issues with the shorter piston. i dont want to pay for a custom piston

and i plan on spinning up to 6800 or 6900. that why im going forged.

please give me your opinions please

 

nobody knows....thats what i get for putting my faith in the board.

 

.005 is a trivial difference. What gaskets do you plan to use? If it's the common Felpro #1074 with a .039" compressed height you would be ok either way. I'd opt for 0.005" in the hole to be safe though unless the engine is going to be assembled VERY carefully.

With a 3.8" stroke and a 6" rod if the deck is 9.025" you will need to go with a 1.125" CH if you want to avoid a custom piston. Besides the need for careful assembly (as noted above) you may also have a problem with the deck height. You may need to take something off the deck to get it flat, if so that will not leave enough quench height with a 0.039" gasket and you would need a different gasket.

Rich

 

a 1.125 piston will put me a t zero deck. is a 1.120 a custom piston

 

and what do people say the best quench height is i was thinking .034 to .036

 

See my edited post above re: deck. Yes, AFAIK a 1.120" would be a custom. Keep in mind what I said about careful assembly if you try for a tight quench.

Rich

 

1. Listen to Rich, and understand what he said. I'm not sure you did.

2. Lots of folks know. Maybe they didn't see your post in the 67 minutes you gave them.

3. One catches more flies with honey rather than with vinegar. IOW, if you want knowledgeable advice be patient and listen to it.

My $.02

 

it was more of a joke.



what is considerd a good quench to shoot for on a NA engine.

 

if they have to take .003 off to get it flat and the piston has to come out of the block .003 is that say and long as i get a thicker gasket.

im asking becuase i dont know.

should i wait to buy the pistons, and wait to see what htey have to take off the deck.

 

The "gospel" is 0.035-0.040". For a motor designed to run right on the edge, tighter is probably better but but I am not so sure that a opening up a bit makes much difference in 99.9% of the buildups people do. To go as tight as 0.035" without problems VERY METICULOUS assembly is imperative and the gains are going to be small. I'd aim for 0.040-45" or so unless you are very careful about assembling the motor (have I said that enough times?).

Rich

 

Don't buy pistons until the block is ready.

Rich

 

very careful about assembling the motor (have I said that enough times?).





yes you have


but is it ok for the piston to come out of the head. say .003

 

Yes, if the gasket is thick enough.

Remember to assemble the motor carefully if you are aiming for a tight quench

Rich

 

thank you so much for your help. its greatly appreciated.

you know i might just be careful putting it together.


oh..... where could i get a thicker gasket from???

 

rskrause what do you mean by assembleing the motor carefully if you are aiming for a tight quench as i am doing a 355 in the coming months and i was going to aim for the 0.035 quench

thx