surfshark

I want to increase the compression on my small block from approximately 9:1 to 9:5 or more to accomodate a Summit 224/234 .465/.488 cam that I've purchased. I'd like to use FelPro 1094 which is a .015 as opposed to the .041 that I already have. Are there any considerations or compromises to take into account when using a thinner compressed head gasket? It's seems obvious that .015 is much lower than the standard size head gaskets out there so that's why I'm questioning.

My engine is a .030 over 350 with 041 .194/64cc heads. The pistons are flat cast aluminum with 4 valve reliefs. I tried to cc the cylinder volume at 1/2" and made a mess, but I came up with about 9.1 to 9.3 compression. I measured the piston in the hole and they're down there pretty far - about .050. I really want to try to put this top end together myself and learn how to do this in the process. This is a somewhat low-buck project so I'm not installing new pistons for higher compression. Thanks very much for any input.

Simmo

Are you sure the pistons are down that far?

Take your time to accurately measure the depth on all pistons and at various locations and try rocking the pistons. If you have at least .020 (mine were all .022) then the .015 gasket is for you. Ideally it sounds like you need to deck the block some.

The .015 gasket should be coated (I used copper spray) if the machining on the deck and heads are not perfect.

MotorHead

I had good luck with the Felpro 7733 SH-1 steel shim head gasket. I hope you have iron heads ?

Spray the gasket with aluminum paint and you are good to go

surfshark

Thanks for your responses. I ordered a piston stop as well as a deck stand for my dial indicator, but by estimating the best I can at this time, I measured the piston to deck height using a straight edge and a feeler gauge. Last night I tried to using the sliding ruler on my dial caliper and came up with about .050. Not super-accurate measurement techniques I know. Do you have a suggestion for the most accurate way to check p-to-deck height?

The motor was rebuilt in 1994 and has only 15K at the most, but I don't know which pistons (with regard to deck height) the rebuilder put in. Originally that motor was supposed to have 10:1 compression (350/300) and I remember him saying he built it to stock specs, but my burret volume assessment and the seemingly deep deck height leads me to believe it was a rebuild kit with a lower-than-stock compression piston. I have iron heads which have been rebuilt to put back on it.

Thanks again for your help!

cardo0

I wasted a day or more proving that i can't measure piston volume with the block in the car. The plexiglass just wouldn't stay sealed long enough to get the volume filled with oil. Every time i would just 'bout 90
% filled it would **** out. Even tried clay - Not!

Sorry if this sounds sarcastic but unless u can tip the whole car over 45 degrees then u need to remove the block to measure this on an engine stand. I never heard of sb Chevy deck over +.025"??? Again sorry for the bad news but if the eng has been rebuilt u don't know deck height, bore size (well this u can measure) or piston dish. If u measure deck height (maybe u can rent the correct bar type micrometer), do so at at the center of piston over the pin area where rock will be least if any - measure at edges and center to verify any dish to center. Well heck, maybe if u measure every stupid area of piston - no forget that - try and find the eng rebuilder for a piston part# and mfr.

BTW i'm running that FelPro gasket on my stock deck block with stock 13cc dish (4 vlv relief) pistons and have no ping/pre ign. But my c.r. is only 8.8:1. :o Well at least i have good quench now and starting to use regular low oct fuel.

cardo0

tapio

There's no need to spray the 1094 gaskets with paint; they have very thin rubber layer on top of them.

jackson

1094 is coated ... should not need any extra stuff sprayed on them ... do not use 1094 (or other steel shim hg) w/ aluminum heads.

Yes, some 350 sbc have more than 0.025" piston-to-deck clearance ... some have piston with 1.540" compression distance (=0.045" clearance on a stock 9.025" deck) ... actually pretty common. Most of the 1.540" CD pistons I'm aware of have a dish ... but not all dished are 1.540".

Plain cast (NOT hyper) Sealed Power P/N 345NP is flattop w/ 4VR has 1.540" CD ... very common rebuilder piston ... has about -6cc DV. With +30 345NP in a stock deck 350 and a NAPA/Victor Reinz P/N 5746 (0.026") thin composition head gasket & 64cc heads ... that combo will make right at 9.6:1 CR ... but with thin 1094 that combo will be right at 9.8:1 CR. If you have 345NP in a stock deck ... you may as well forget about trying to get an ideal quench ... will not happen without decking block.

Make sure your retainers, springs, guides & valve stem seals are clearanced for .488" lift at valve ... don't guess ... ensure.

Kid Vette

Thanks! Very informative! Is there an advantage to the 5746 gasket compared to the FelPro 1094?

jackson

5746 has the advantage of sealing better than thin steel shim gaskets ... but is not nearly as thick as most other composition gaskets.

cardo0

Sorry Jackson as i know u mean well but your math is in error. For a 350" stroke of 3.48" u divid by 2 for the crank radius. Then add this radius of 1.74" to the rod length of 5.7" for = 7.44". Now add on that piston compression height of 1.54" (BTW which is the same as mine) and the sum is = 8.98". So the piston is only 9.025"-8.98"=.027" down the hole from the stock deck (of a 9.025" deck height that is). Now add the .015" gasket to that .027" in the hole now = 'bout .042" for a great quench hieght.
Now granted there could be a different compression height piston. But this only reinforces the need to measure piston to deck distance with the correct micrometer and piston vol with liquid when possible as the liquid vol method dosen't lie.

Also the FelPro instructions said to use a sealer with my .015" head gaskets so i used the Permitex spray sealer (NAPA or nearly everwhere) just before i installed mine) - very easy to use. Holding up fine.

cardo0

comp

surfshark

I have the engine on a stand and I sealed the plexiglass plate and used a burret and came up with about 107-108 cc's with the piston at 1/2". I didn't cc the cylinder head like a dummy when I had the appartatus, but the 64 cc heads look like they've been milled at some point according to the machinist I took them to today. I'm having him put the aftermarket springs on them next week. The problem I encountered with measuring the cc's was a little bubble that would not fill under the glass. It would float around in spite of keeping the motor level. I'm not so sure about the accuracy with which I measured the piston to deck height either.

My computer calculations (4.030 bore, 3.48 stroke, piston - 107ccs at 1/2", 64cc heads(?), and felpro .041 head gasket) came up with about 9:3 compression, but I figure if I'm in error and the motor is 9:1, then the .015 should bump me up to the 9:5 compression I need for the cam I bought. On the other hand if the motor is 9:3 or even 9:5, then I hope the .015 gasket won't put me too high in the compression department for iron heads.

No way to contact the rebuilder, but we had this motor in an S-10 pickup (10 years ago) that really hauled with a 4.11 gear. It's not a weak motor, but again, he built it to "stock specs" with rebuilder pistons as I presume.

This is quite a learning curve for me. I appreciate your advice. Does it sound like I'm on track with the head gasket formula? It has been kind of fun to try to figure this out and make it work for a low $$ cost.

stingr69

You can measure the deck height with the piston at TDC using a straight edge, degree wheel (cardboard with 3 pencil marks works in a pinch), piston stop, and feelers and get close enough. If you dont want to mess with the piston stop and degree wheel you can use the damper and timing tab. Just a couple of low buck ways to get-r-done.

For the valve reliefs you can stuff them with clay then drop them in the burette to see how much liquid they displace. Then you have what you need to calculate the compression.

As for the .015" gaskets, I spray them with copper coat sealer and bolt them on. Never had a problem with them.

-Mark.

surfshark

Thanks to all for the information. My degree wheel and piston stop should come in the mail from Summit today. I like the clay method of measuring valve reliefs. Thanks again and have a great Saturday!

jackson

cardo0:
I may be a sorry SOB ... but I ain't wrong on this one pardner ... since when did 9.025 - 8.98 = .027 ????? ... it does not ... it's 0.045" ... all day long! Your formula is right but YOUR math is wrong!
-edit- in an earlier post within this thread, cardo0 writes that he has a stock deck block ... here he writes his pistons are also 1.54" & that he has .015" gasket ... if all that's so, his great quench is actually 0.060" ... NOT GREAT, not by any stretch! As for respraying 1094 gasket ... do as you please, but it's not needed. And ... IF ... if cardo0 is running 75-76cc heads on the combo he's described as running ... I'll bet dollars to donuts his static CR is a lot closer to 8:1 than his claimed 8.8:1 ... it oughta run on pump regular ... maybe even turpentine. All the tooling, gaging & specs in world don't mean a dang thing if you don't add & subtract correctly.

cardo0

:o Yep, i don't know how but i managed to goof this one. :o And lately i've been consistant at being 1 decimal place off. Should have checked my own math with a calculator there but had been convinced of my quench height for soo long i must'a jumped at the wrong number. But hey, i know i won't forget this mistake next time i calculate c.r..

Ok my c.r. is lower but my heads are 'bout 69cc (average) - after chamber unshrouding - rather than the advertized 67cc by World Products. That puts me more like 8.6 c.r. which is a safer place to be with only .060" quench. In hindsight i wish i had opted for the Vortec heads with 64cc chambers which would have put me over 9 for c.r. but that's where the quench would have helped more and started to become an issue. Yea, .060" quench is nearly nothing but the only fix would be replace pistons or deck block as i don't know of any thinner hd gaskets than .015".

Regardless this is good disscussion and i still enjoy it though my math has been bad.

But funny thing is my compression is over 180psi cold on every cylinder. So i'm not dissipointed much at all though i realize there was more power to be had while using even cheaper heads (Vortec's). And i find little use for Premium octane fuel now and somewhat of a benifit of the lower c.r..


surfshark while the eng is still on the stand, u may want to take a look a Comp Cams graduated flask - Jeg's may sell it as i know that nonsupporting vendor S..... carries it for $37. Maybe even find a medical supply for a graduated cyl and cover bore/chamber with flat plexi-glass. As i feel measuring the piston volume with the rotating assembly installed at TDC more trustworthy. But please don't ask me to calculate c.r. for u.

Good night folks. cardo0