Can I use thicker head gasket if piston is too far out of the block?

[ramcharger_440]

I want to build a smallblock that will leave the flat top piston .035 above the deck. Any problems if I just use a Cometic gasket .078 thick for a .043 piston to head clearance?

Thanks!

[robboski]

Depends on the piston. If it is a forged, it will grow more (uder heat) than a cast or better yet hyperutectic.
what's the purpose of protruding and then thicker gasket? your compression will be no higher than a zero deck with .043 gaskets. also be sure to check piston to valve clearance. Another option (if your pistons are thick enough)
would be to have a good machine shop cut down the piston tops. When we do it we only charge like $10 each. but we only do it to forged pistons with enough meat.

[ramcharger_440]

OK, I like to try different things. This is the only justification I need to break from the path of the masses. I know a 360 makes a lot of sense. I WANT to try something different.

Now that I have that out of the way here is my plan:

318 block with deck height of 9.598 - already have
360 crank with mains at 318/340 size - crank in my posession, $70 to turn
cast piston with compression height of 1.720 cost $80

This leaves the piston .035 out of the hole. Add a .078 gasket for a piston to head clearance of .043. Nice quench distance with magnum heads.

This equals to a pretty inexpensive 349 cubic inch engine since I already have most of the stuff. And it looks like a 318 from the outside. Even says so if you look at the casting numbers.

I built a similar engine with the same setup except it has a 3.51" stroke forged crank. These cranks were once inexpensive, now they are not.

My biggest worry with this setup is with the "cheater" gaskets, which would be a .078 Cometic. My other big worry is balancing cost.

Maybe someone here can bring to light other things I have not considered.

[benno318]

as far as balancing goes, the 360 balancer will have to be used, and anyone with an inkling of mopars will instantly know that it aint no 318 anymore. i would weigh the rods and pistons and compare to 360 pieces, if it is much the same then you should get by without doing it for a low rpm application. anything regularly over 4500 i like to balance regardless. thick gaskets are not that hard to pick, especially if the engine is painted all assembled. i have a holden v8 ex speedway, that i put in my tow car and to reduce the compression i have 3 head gaskets per bank - .100" odd thickness, and unless i told someone, they would never know. and in my opinion, 043" is plenty of clearance whether the piston will grow or not. i wouldnt think it could grow more than a couple of thou at worst anyway. i am all for someone using a bit of initiative and old parts, especially for a budget buildup. i say best of luck to you!
ben simpson

[ramcharger_440]

Thanks for the help! I really appreciate all the experience you guys have and the fact that you are willing to help newer (if not younger) engine builders out.

Originally Posted by benno318

as far as balancing goes, the 360 balancer will have to be used, and anyone with an inkling of mopars will instantly know that it aint no 318 anymore.

Can I not just balance internally and then use the 318 balancer?

[Tarrbabe]

use to have a spacer they sold to lower the compression on engines to save having to buy new pistons. You had to use two gaskets on each side. One above and one below. Haven't heard anything about them in years though.

[Billydelrio]

The 318 and 360 piston mass is nearly the same. For example, a Speed-Pro L2329F (318) has a mass of 592 grams while a L2405F (360) has a mass of 584 grams. For this reason, it seems that balancing a factory 360 crank in a 318 block should be easy if going external like a 360.

If I were using a new, never balanced, Mopar Performance crank like the 3.51", then I would absolutely go internal balanced.

I have a few of the 3.51" cranks, one of which has found its way into a 273 block. It is an internal balanced asembly.

[benno318]

on my 308 holden, i used the factory steel shim gasket as a spacer between 2 composite gaskets on each bank. and on an engine design notorious for head gasket sealing problems, i have had no problems. the poor thing has no quench left though!!
ben simpson

[345Dart]

Two more things to keep in mind (1) deck height may be ±.038" higher than stock leading to some carefull attention to the angles for the intake/head mating surfaces and (2) stock pushrod length may be to short due to #1.
make sure you know exactly what the deck height/piston clearance is of the 318 before you buy anything. Deck heights have been known to be off as much as ±.030 from the 9.600. If you are not overboring the block, you need to make sure there is no ridge left at the top from the old piston rings as the new piston/stroke combo will have the top ring coming very close to the top of the deck - plus an allowance of .035 for growth may take you above deck. just some things to check before going too far.

I'd be very interested as you progress along as I've got the same 318/360 crank and have been contemplating the same build for awhile.
:toas

[ramcharger_440]

Deck height is 9.598.

Compression height on piston is 1.720
Rod length is 6.123
1/2 stroke is 1.79"

Piston is .035 above the deck.

Block will be bored .040 cubic inches 350.9 (351)

I will use the Cometic .078 head gasket with magnum heads with polished 64cc chambers compression ratio 10.19:1 piston to head clearance will be .043

Comp Cams XE268H 268/280 degrees duration 224/230 @ .050 lift will be .509/.512 with the 1.6 ratio rocker arms

1 5/8" headers

Air Gap intake with 700CFM Holley

Mild porting on heads (intake flow @ .500 lift is 229)

Looking for approx 350-375 horsepower should be a relatively mild street engine that looks like a 318

Waddya' think?

[diego-ted]

I would like to know what pistons you are useing? I built a 349 using that cam and had PV clearance problems and my pistons were in the hole 30K.
diego

[robboski]

Originally Posted by diego-ted

I would like to know what pistons you are useing? I built a 349 using that cam and had PV clearance problems and my pistons were in the hole 30K.
diego

this will more than likely be a major problem in this set up because the magnum heads have even larger valves.

[robboski]

Originally Posted by Tarrbabe

use to have a spacer they sold to lower the compression on engines to save having to buy new pistons. You had to use two gaskets on each side. One above and one below. Haven't heard anything about them in years though.

"Head saver" shims are still available from victor and felpro. they can come in either .015 or .020 thickness and also come in either stainless steel or copper depending on manufacturer. I think this would be a better way to go with high compression levels as they can be used as a sandwich if needed.
use sealer on the block side then the shim then the gasket then if needed another shim with sealer against the head.

[ramcharger_440]

Originally Posted by diego-ted

I would like to know what pistons you are useing? I built a 349 using that cam and had PV clearance problems and my pistons were in the hole 30K.
diego

The pistons I am looking at using are el cheapo cast pistons made by Speed Pro (or TRW or Federal Mogul) #285.

[diego-ted]

I was using Eddies at the time.
diego

[73scamp318]

You can get 300 to 350 with just the 318 with that combo, not going with the stroker. The cheapest way isn't always the best

steve

[leon441]

Cometic gasket are not cheap. Last ones I ordered for a W8 smallblock were $120 a peice. A stock head design may be a lot cheaper. But all that considered wouldn't it be better to get a good forged piston? I don't have any issues with running a tight psiton to head clearance. I etch the tope of the piston at 12 and 6 O'clock and look for tell tail markings on the head after running. When I get those maks I quit cutting.

[63Fury]

Originally Posted by robboski

"Head saver" shims are still available from victor and felpro. they can come in either .015 or .020 thickness and also come in either stainless steel or copper depending on manufacturer. I think this would be a better way to go with high compression levels as they can be used as a sandwich if needed.
use sealer on the block side then the shim then the gasket then if needed another shim with sealer against the head.

I thought you were to use the shim inbetween two gaskets, not the gasket in between two shims? Which is correct as I'm going to have to do this to lower the compression on my 383. Thanks