[wildkatz]

I finally got the heads 12-5(nearly a month later). They had placed the gaskets in the box with the heads and they were mangled. They are supposed to be sending me another set, but that is just another set back. Now I am worried about the compression. Right now it is 10-1 with the 75cc heads and the 492 Fuelies are 64cc. Golens says that it should be about 10 1/4-1 but the dyno guy is saying between 11 or 12-1. That is way too much for me.

Still assessing the whole thing. If those comp. #'s are right ther is no way I am using them.

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69 RS Camaro (383,350t,12-bolt w/3.73s)
79 WS6 Trans Am (406SBC,factory 4-spd,3.23 posi)
87 GTA Pace Car Clone (350TPI,700r4,140k miles)
97 Bonneville SSE 40th Anniv. (3800 V-6, Power Everything, The little woman's car)

 

[TJS69]

I believe that with flat top pistons and these heads you should be at 10:1 compression.

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69 Camaro Z28 "clone" - 327 AT
"461" camel back heads,
edelbrock, hooker, ultradyne,
TRW etc.
700R4 TPI transmission

 

[Eric68]

You'll be at or just over 11:1 with a 383 and flat tops - for sure.

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68 Camaro, 383 small block with TH350 trans. 11.98's at 111mph and never trailered.

 

[DjD]

Do the math, to find cyl vol it's Radius sq x pi x stroke. (radius is 1/2 the bore) A .030 350 with a 3.75" stroke (383ci) is: 2.015 x 3.1416 x 3.75 = 47.83

Chamber vol is: cc divide by 16.387 or 64 div by 16.387 = 3.905

Gasket vol (same math as cyl, replace thickness for stroke) Let's assume gasket bore is 4.166, 2.08 x 3.1416 x .040 = .261

Deck height (same math as cyl, height for stroke) lets assume a 0 (zero) height!!

And you need valve relief or pop-up if any. you say flat top so we'll go with that!

Add each to get your sweep volume 51.996 and divide it by everything but the cyl vol (51.996 - 47.83 = 4.166) is going to give you 51.996 div by 4.166 = 12.48:1 based on zero deck, no valve relief and a .040 thick gasket with a 4.166 bore.

If your deck height is not zero it will greatly change things as will valve relief etc. Do the same math with your 75cc heads and you'll see where you are. I suspect your block isn't zero decked as well...

If I made a mistake in my numbers let me know I went through it kinda fast...

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...Dennis
"The '69, the '96 & the club"

[This message has been edited by DjD (edited 12-09-2001).]

 

[wildkatz]

I have actually been doing a little investigating in Jegs and think that I have come up with the most accurate #'s. First, I found the KB pistons and found the 383piston with the advertised compression nearest to what I was told. I then used desktop dyno and used the compression calculator until I got the numbers that were advertised in Jegs and then the numbers I was told that I had. I am pretty sure, if calculations are right, that my compression to start with was about 9.94-1. To get the compression down a little I have bought a set of Felpro 1044 headgaskets/4.200 bore and .051 thickness. With these gaskets and the 66cc heads, I am coming up with a 10.66-1 rate. I think that I will be ok with that. I will probably have to run a can of octane booster with each tank of gas to be on the safe side, but that won't be to bad.

What do you guys think?

------------------
69 RS Camaro (383,350t,12-bolt w/3.73s)
79 WS6 Trans Am (406SBC,factory 4-spd,3.23 posi)
87 GTA Pace Car Clone (350TPI,700r4,140k miles)
97 Bonneville SSE 40th Anniv. (3800 V-6, Power Everything, The little woman's car)

 

[DjD]

Without knowing the deck height you are still guessing... Here is how KB figures the compression ratios they publish... www.kb-silvolite.com/1toc.htm#sect4 (it's just below middle of the page) Is that 9.94 ratio what KB published?

I'm interested to know what the shop's view on compression is. Have they provided you any numbers? Glad they continue to work with you, I know this has been one big headach!! With 400hp at your disposal you may be able to avoid detonation by running the timing with a little less advance when on the street and for the track use an additive and more advance if the compression is a bit high..

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...Dennis
"The '69, the '96 & the club"

 

[wildkatz]

The 9.94 is what I figure for the compression I have right now. KB only advertises for 76cc heads and mine are 75. KB's figures with 76cc heads is 9.6-1. Golen's advertised 10-1 but they told me changing to these heads would only up the compression to about 10.25-1. I have talked to them about 3 times about this and they are stead fast with #'s close to that. They are using .041 gaskets and I found the bore for that gasket and using the #'s with the KB#'s. I came up with that 9.94-1 for the compr. rite now. I come up with 10.9-1 with the .041 head gaskets. I have asked about the deck height and he said that it was the standard deck height.

Thanks

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69 RS Camaro (383,350t,12-bolt w/3.73s)
79 WS6 Trans Am (406SBC,factory 4-spd,3.23 posi)
87 GTA Pace Car Clone (350TPI,700r4,140k miles)
97 Bonneville SSE 40th Anniv. (3800 V-6, Power Everything, The little woman's car)

 

[DjD]

Std deck height could be .020 - .030 or so in the hole. That would explain the lower compression numbers the builder gave you with the flattops! Are you going to dyno it again?

 

[davidpozzi]

It is really bad to increase head gasket thickness to lower compression. When the quench area get's too large, detonation will be a big problem.
David Vizard and others talk about this in their books. I believe I've read that the gap between the head and piston top at TDC to be around .045" is nearly ideal, if you get to .060" gap, detonation will be happening very easily.
(Smokey Yunik book P44)

A good head porter could probably open up the chambers a little to drop compression and probably improve breathing too.
David

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Check my web page for First Gen Camaro suspension info:
David's Motorsports page
First Gen Suspension Page
67 RS 327
69 Camaro Vintage Racer
65 Lola T-70 Chev 350 Can-Am Vintage Racer

[This message has been edited by davidpozzi (edited 12-09-2001).]

 

[DjD]

Good point David... KB recomends .040" max using their pistons in a 383 build. The builder doing mine went .016 down and is using a .020 gasket for a .036 squish (quench) area. I guess they have had good results with 9.7 - 10.25:1 compression on pump gas. Should be plenty of room for valve clearence this way...

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...Dennis
"The '69, the '96 & the club"

 

[wildkatz]

I'm going to call them tomorrow and try to get it straight. Thanks guys

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69 RS Camaro (383,350t,12-bolt w/3.73s)
79 WS6 Trans Am (406SBC,factory 4-spd,3.23 posi)
87 GTA Pace Car Clone (350TPI,700r4,140k miles)
97 Bonneville SSE 40th Anniv. (3800 V-6, Power Everything, The little woman's car)
Check out my site http://rodsrides.freeservers.com