the only .015" shim head gasket that I can find is a 4.1" bore, and no steem holes drilled, does anyone know where you can find one more suited for a 400 with a 4.155 bore and steam holes ? I'm still in the process of buying pistons / rods, but it looks like most combinations are putting my pistons at .025 in the hole, and I would prefer not to have to go back and zero deck my block to get ideal quench.


Any input is appreciated.

 

Not alot of people are bold (foolish? brave? I don't know what the difference would be sometimes....) enough to run a shim gasket on a 400. Especially if it's going to live on the street. That's not a path of wisdom.

You'd be better off to deck the block. We're not talking about alot of money or trouble here, since it's not assembled yet. I don't see why this should be an issue.

Have your racing-specialty machinist deck it to 9.000" from measured crank Lc to deck. Then if you get stock (1.56") pistons, or whatever compression height it takes such that ½ the stroke, + the center-to-center length of whatever rods you're using, + your pistons' compression height, = 9.000".

Don't forget that most - but not all - of the cheaper pistons you will find, including for example virtually ALL cast pistons, MOST hypereutectics but not all, and alot of the TRW forged line, is .020" LOWER THAN STOCK compression height (farther down in the hole). MAKE SURE YOU KNOW ACCURATELY what you're dealing with, or all of your "quench" setup will be in vain.

 

i've been looking at:

3.75/2 + 5.7 + 1.425 = 9, default deck at 9.025, pistons is .025 in the hole.

or

3.75/2 + 6 + 1.125 = 9 , again, .025 in the hole ...... Am i missing something there ?

My machinists wants another $180 to deck it, and I'd really rather not, is running a gasket between .015 and .021 really that bad ?

 

Iunno.....

If a head gasket fails, will it cost you more, or less, than $180?

How much is your time worth?

How much will it cost you to rent a car while yours doesn't work?

Looking beyond the up-front cost, what's the smart choice?

 

You need to measure and stop trying to guess everything because your surely headed for disaster this way. Ive seen deck heights vary alot between cylinders and sometimes the piston rod assembly will throw the numbers off. Ive heard of people juggling around the rotating assembly just to get the piston to deck height accurate.

 

I was planning on measuring tonight, right now the block is bare, so what exactly should I measure , the cylinder wall height or from the center of where the crank would be to the deck ? I'm guessing from center of where crank would be to deck. I dont have pistons yet or rods yet, I'm trying to figure all this out so that I can order the correct stuff.

 

This is a big reason building engines is left for the professionals. I know some engine builders who will buy many sets of pistons and will mock them up trying to find the perfect set. This is why lots of guys will just use a working plan rather that try and piece together a bunch of parts they have laying around. Because its starting to sound like this.

 

"I dont have pistons yet or rods yet"
"does anyone know where you can find one [head gasket]"

Exactly what part of that says that I'm piecing together stuff I have laying around......


It sounds more to me like trying to find the correct parts for the project the first time around ...... But thats just me .... I suppose you can interpret that however you like.

This is still a working plan, with the exception of the block, crank, cam, and heads .... if you can help, please do, if you cant, there are plenty of other threads to post in.

 

The reason Im saying your trying to piece it together is because you have no set plan. Why dont you buy some books or look around for some working setups with part #s rather than trying to piece something that may or may not work. There is alot of trial and error to find the perfect combination of parts to build a performance engine. Unless you have an unlimited budget then you can afford to test a bunch of combinations and see what works. Shoot I would even do a search on here and see if any guys here have put together what your looking for.

 

why dont you try and call fellpro or mr gasket? these people deal with these question everyday. you need to measure and consult with your machinest.this will get you the best results.

 

Well, lets say you have a current deck height of 9.025

What I did was get a 3.8" stroke crank, 6" rods, and use a piston with a 1.125" compression height. That will yeild you with a 0 deck clearance (I.E. would be the same as getting ur deck milled down to 9.000 and using a 3.75" stroke crank) plus youll be getting a few more cubes outa the deal while saving money on decking ur block. Now, this is considering you actually have a deck height of 9.025 and you dont need it milled at all. I needed mine squared and wound up with the slugs about .010 out of the hole. That being said, its still hard to find a 400 head gasket thats .050 in thickness.

Up to you man just something to think about , good luck

 

Theres a couple engines on here that may help.

Dyno Tests of Small Block Chevy Motors in detail

 

how can i measure the deck height for sure .... I checked my cyinder wall height, and got 6.125" Not really sure where to go from there, i tried measuring center of the mains upto the deck, but thats gonna take a little more time than I had right now, is there a constant that can be added to cylinder wall height to get deck height ?

 

Measure the saddle to deck dimension and add half the main bore.

 

I think I decided to just order 5.7 H beams and 15cc dish pistons with 1.425 CH, and check from there. From there, seeing as how I'm going to keep the quench at ~ .04 - .045, I'll measure how far in the pistons are, and deck / select a head gasket from there. I think thats the best idea. (I'm going to measure the deck and make sure it hasnt already been decked first, but there are still casting #s on the deck, so I doubt it has).

 

I wish I would have mocked up my motor first.
my deck was warped, and needed at least .005" milled off to get flat, I figured i'd go for better quench, and get a whopping .010" milled off. Once I put in the 1.54 compression height pistons, normal crank and 5.7" rods, got .015" piston depth.... (instead of the .035" I was expecting... )