how much compression did I lose with a flat piston ? - Team Camaro Tech
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post #1 of 19 (permalink) Old Mar 21st, 08, 06:01 PM Thread Starter
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how much compression did I lose with a flat piston ?

I went from dome pistons in my 327 to flat top pistons.
About how much compression do you guys think I lost by doing so ?
. . . . and I probably lost a few horses too.

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post #2 of 19 (permalink) Old Mar 21st, 08, 06:10 PM
 
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Re: how much compression did I lose with a flat piston ?

If it's an old engine, you went from 11 to about 10.25 STOCK 1967 327's here.

I figure probably more like 10.

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post #3 of 19 (permalink) Old Mar 21st, 08, 06:21 PM Thread Starter
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Re: how much compression did I lose with a flat piston ?

its a 1969 327 from a Chevelle.

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post #4 of 19 (permalink) Old Mar 21st, 08, 06:27 PM
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Re: how much compression did I lose with a flat piston ?

then as paul said, you lost a full point.





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post #5 of 19 (permalink) Old Mar 22nd, 08, 04:55 PM
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Re: how much compression did I lose with a flat piston ?

What is your total combination like; heads' cc, cam, intake??? They all gotta work in unison or you might be disappointed. RPM range you are after??? Tranny you are running??? Rear gears??? Standard or Auto??? At what rpm point do your heads quit???
Did you flow a couple of ports to know the REAL rpm range??? On and on and on!!!
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post #6 of 19 (permalink) Old Mar 22nd, 08, 06:02 PM Thread Starter
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Re: how much compression did I lose with a flat piston ?

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Originally Posted by opelitis View Post
What is your total combination like; heads' cc, cam, intake??? They all gotta work in unison or you might be disappointed. RPM range you are after??? Tranny you are running??? Rear gears??? Standard or Auto??? At what rpm point do your heads quit???
Did you flow a couple of ports to know the REAL rpm range??? On and on and on!!!
Heads = Chevy double hump iron heads 2.02 & 1.60 ported and polished stock rockers stainless valves

Cam = Crane H-284* - intake max lift 109 @ 222 exhaust max lift 119 @ 222 rpm range 2200 to 5200

Intake = Weiand aluminum dual plane with Holley 600 single pumper 4bbl mechanical secondary

Tranny = Muncie M22 4sp

Rear gears = 4:11 Eaton posi

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post #7 of 19 (permalink) Old Mar 22nd, 08, 08:28 PM
 
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Re: how much compression did I lose with a flat piston ?

I bet it will be closer to 9.5 to 1 than it will be to 10 to 1 CR. b/c my -461 big valve double-humps cc'd at 66 cc's virgin!

It will run, but imho, it will run better at 10.5! At 9.5 to 10 to 1, I'd pick a 268/270/272/274 hy-cam! And it would be a solid lifter equivalent jobber only b/c a 327 like's to rpm!

And I would run either Fel-pro's #1094 .015" rubber coated shims or Stock GM/Mr. Gasket .020" thick steel shims just like GM used back then to hold a decent quench!

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post #8 of 19 (permalink) Old Mar 22nd, 08, 08:36 PM
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Re: how much compression did I lose with a flat piston ?

Nice work on your car!!! Looks like a decent combo and the CR ratio at 10:1 would still work... Things I might change would be to go to a 1:5 ratio rocker instead of the most likely 1.42 stocker and maybeeeee a bit more cfm 650. Congrats on the fien effort!!!
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post #9 of 19 (permalink) Old Mar 22nd, 08, 09:06 PM Thread Starter
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Re: how much compression did I lose with a flat piston ?

Thanks Ted , I don't race it just cruise city streets and with that low rear end it seems to give me plenty of snap. I was just wondering what compression I lost by replacing my dome pistons with flats and the reason I did that is so I could run pump gas.

Hey PDQ , how many horses do you think I lost just by reducing the compression ratio like I did ?

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post #10 of 19 (permalink) Old Mar 22nd, 08, 10:19 PM
 
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Smile Re: how much compression did I lose with a flat piston ?

Maybe 30/50hp(??) off the top of my head.

Remember the 300hp/327 ran medium valve heads, close to 10 to 1 CR. flat-tops and the old -929 cam whereas the 350hp and 325hp/327 engine ran 11 to 1 domed pistons, big valve heads and the -151 cam.

Ain't NO diff between a 325 and a 350hp/327 except for the carb and intake! the 350hp ran a stock aluminum high-rise like the old Holley 300-36 and a 585 cfm Holley carb and the 325hp ran a 750 Q-Jet on a Q-Jet cast-iron intake is all!

IF I have my carb's right?..................

Way back then, I didn't know this b/c I REALLY wanted a '66 Duece Coupe w/ the 350hp/327, 4-speed, 3.73 posi- but I was too late in ordering it due to gathering up the down payment money!

So I bought my '67 350SS/RS Camaro in Oct. '66 instead not knowing that the '67, 325hp/327 Duece was still the old L-79 engine w/ a Q-Jet on it!

Or I would have bought '67 Duece instead!

pdq67

PS., oh, and btw, the 300hp/327 ran an AFB on a cast-iron intake that is I figure is the best cast-iron intake made back then up until the GM made the cast-iron marine engine copy of the Z-28/300-36 Holley dual plane!

I have one up on the shelf out in my garage!




Last edited by pdq67; Mar 22nd, 08 at 10:30 PM.
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post #11 of 19 (permalink) Old Mar 22nd, 08, 10:55 PM Thread Starter
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Re: how much compression did I lose with a flat piston ?

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Originally Posted by pdq67 View Post
Maybe 30/50hp(??) off the top of my head.
So before I stick my head in the oven.
there was no way I could have run an 11 to 1 motor on 93 octane , right ?

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post #12 of 19 (permalink) Old Mar 22nd, 08, 11:08 PM
 
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Re: how much compression did I lose with a flat piston ?

I will say this.

The old -151 and 30-30 cammed 11 to 1 engines WILL run today on GOOD octane PUMP gas! You might have to dial back just a schosh on timing, but it will run fine!

I ran my -151 cammed 350SS engine on regular leaded back then ALL the time!

If I wanted to play, I pumped in some good leaded regular like Shell or Mobil instead of the cheap stuff I generally bought to save beer money and it ALWAYS ran better under full throttle.

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post #13 of 19 (permalink) Old Mar 23rd, 08, 05:24 AM
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Re: how much compression did I lose with a flat piston ?

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Originally Posted by jr68 View Post
Thanks Ted , I don't race it just cruise city streets and with that low rear end it seems to give me plenty of snap. I was just wondering what compression I lost by replacing my dome pistons with flats and the reason I did that is so I could run pump gas.

Hey PDQ , how many horses do you think I lost just by reducing the compression ratio like I did ?
No way you've lost 30-50 hp by reducing the compression by a point, maybe 2-4% of your hp. This would be 6-12 hp in a 300 hp engine.
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post #14 of 19 (permalink) Old Mar 23rd, 08, 09:23 AM
 
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Smile Re: how much compression did I lose with a flat piston ?

I'm going by GM's advertised hp numbers here is all. 300hp/327 vs a 350hp/327. That's why I'm trying to explain about the differences between the two engines.

Right, about 4 percent if EVERYTHING is equal.

pdq67

PS., probably down 25 to 30 hp.......... As alway's, imho..



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post #15 of 19 (permalink) Old Mar 24th, 08, 08:24 AM
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Re: how much compression did I lose with a flat piston ?

Jerry

I'd say you'd have been on the edge with 93 octane. Mine ran fine with 91-93 octane, but my cam is a bit bigger.

You can alter your comp. ratio a bit with headgaskets depending on your deck height.

I don't think you lost much, maybe 10 hp. Cheap price to pay for peace of mind.

Mark

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best so far... 13.25 at 106mph

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65 Mustang convert. 6 cyl. 3-speed
66 Mustang coupe 6 cyl. auto
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