compression ratio and HP
Thread Starter
Intermediate
Joined: Aug 2001
Posts: 47
Likes: 0
From: Royse City Texas
compression ratio and HP
I am new to the forum and recently bought a 79 driver. I am trying to learn all I can about my purchase and in viewing the comments on the post in the forum it looks like I found a place with a lot of Knowledge on Vette's and engines.
Here are the specs on the installed engine: 350 bored .060" over,Keith Black flat top pistons, 70 model chevy "041" heads with 64cc combustion chamber and 202/160 valves, Summit cam with 218 deg duration and 454/454" lift, Dynomax coated headers, Stealth intake with 625cfm Carter Carb.
My questions are is there a way to determine what the approximate compression ratio is with a compression gauge and what Approximate HP should be expected from this engine.
Thanks for any replies and am looking forward to a long relationship with the forum.
David
Royse City, TX
Here are the specs on the installed engine: 350 bored .060" over,Keith Black flat top pistons, 70 model chevy "041" heads with 64cc combustion chamber and 202/160 valves, Summit cam with 218 deg duration and 454/454" lift, Dynomax coated headers, Stealth intake with 625cfm Carter Carb.
My questions are is there a way to determine what the approximate compression ratio is with a compression gauge and what Approximate HP should be expected from this engine.
Thanks for any replies and am looking forward to a long relationship with the forum.
David
Royse City, TX
Thread Starter
Intermediate
Joined: Aug 2001
Posts: 47
Likes: 0
From: Royse City Texas
Re: compression ratio and HP (countryvette)
Thanks Ganey for the reply!
I see from earlier post that the CompCam XE268H cam is a good fit for a daily driver but when I went to the Summit web site it says it is no longer available at Summit. Does anyone know if this cam is being discontinued.
Thanks
David
I see from earlier post that the CompCam XE268H cam is a good fit for a daily driver but when I went to the Summit web site it says it is no longer available at Summit. Does anyone know if this cam is being discontinued.
Thanks
David
Racer
Joined: Jun 2001
Posts: 275
Likes: 0
From: Denville NJ
Re: compression ratio and HP (countryvette)
Try calling summit, I was buying guages and they said it was unavailable on the web site, when I called, the guy told me the product number changed and they have plenty in stock.
Race Director
Joined: Apr 1999
Posts: 11,520
Likes: 13
From: CORVETTE 77 385 C.I. TEXAS
Re: compression ratio and HP (countryvette)
David
W/ your current setup you are in good shape to determine for yourself if the XE268H is what you want. It will rock the power curve up so that you will lose some low end & gain about 20 HP at the upper end. Fine if you have a manual & drive hard. If you have a stock auto., you might want to reconsider.
W/ your current setup you are in good shape to determine for yourself if the XE268H is what you want. It will rock the power curve up so that you will lose some low end & gain about 20 HP at the upper end. Fine if you have a manual & drive hard. If you have a stock auto., you might want to reconsider.
Thread Starter
Intermediate
Joined: Aug 2001
Posts: 47
Likes: 0
From: Royse City Texas
Re: compression ratio and HP (countryvette)
Thanks for all the info!
Ganey,
I do have an Auto with a shift kit. question: If I did install the XE268H and I advance the cam 4 degrees on the crank sprocket to regain some low end torque would the difference between this setup and my present setup be noticeable or a lot of work for very little gain?
Thanks again,
David
Ganey,
I do have an Auto with a shift kit. question: If I did install the XE268H and I advance the cam 4 degrees on the crank sprocket to regain some low end torque would the difference between this setup and my present setup be noticeable or a lot of work for very little gain?
Thanks again,
David
Le Mans Master
Joined: Jul 2001
Posts: 9,622
Likes: 16
From: absecon nj
Re: compression ratio and HP (Ganey)
i think you got a really good setup ther with what you got ...depending what gears are in the rear it probably runs real good.Ive used that summit cam ina truck and it had plenty of low end .
Burning Brakes
Joined: Nov 2000
Posts: 813
Likes: 2
From: da up
Re: compression ratio and HP (countryvette)
I have the ex268 in a 327 in my '64 w/ a m20 (2.52 1st gear) and 3.55 gears.
It has to have throttle to take off, pulls ok at 1200rpm -up, wakes up nicely at 2500-3000 to 6000pm.
Depending on gearing you're probably better off with what you have, or maybe a ex262
I believe the EX cams are already advanced when installed straight up.
rod
It has to have throttle to take off, pulls ok at 1200rpm -up, wakes up nicely at 2500-3000 to 6000pm.
Depending on gearing you're probably better off with what you have, or maybe a ex262
I believe the EX cams are already advanced when installed straight up.
rod
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Thread Starter
Intermediate
Joined: Aug 2001
Posts: 47
Likes: 0
From: Royse City Texas
Re: compression ratio and HP (yooperod)
Thanks for all the input.
Rod- I also have 3.55 gears in the rearend.
From the sounds of it I will probably stay with what I have for a while.
It seems no matter what HP you have you always want a little more.
Thanks again for all the comments!
David
Rod- I also have 3.55 gears in the rearend.
From the sounds of it I will probably stay with what I have for a while.
It seems no matter what HP you have you always want a little more.
Thanks again for all the comments!
David
Drifting
Joined: Nov 2000
Posts: 1,361
Likes: 0
From: Honolulu Hawaii
Re: compression ratio and HP (countryvette)
That sounds like a very strong setup. A cranking compression test is a good way to measure how "strong" your setup is. The cranking compression gives you the NET result of your static compression ratio, cam timing, and general cylinder sealing condition. David Vizard says, 180 psi is okay, 200 is good hi-perf, 220 is street/strip, 240 is race. If you got a compression gauge, try it out. You might be pleasantly surprised!
Melting Slicks
Joined: Jun 2001
Posts: 2,429
Likes: 14
From: CA
Re: compression ratio and HP (countryvette)
I wouldn't advance that cam any. You might run into a detonation problem, especially with already having 10:1. If anything, I would run the next size larger -274 to bleed down some of that pressure.
Burning Brakes
Joined: Jul 2001
Posts: 1,160
Likes: 0
From: Ajax Ontario
Re: compression ratio and HP (71coupe)
From gaining knowledge on this from people that know (like Ganey), I'd pass on the XE268 cam with the auto, if using stock converter and move down one notch to the XE262. I have this cam in my 327 with 4 speed and it works nice. Would be too "much" with an auto with my displacement, but should be fine for the 350 auto combo.
Thread Starter
Intermediate
Joined: Aug 2001
Posts: 47
Likes: 0
From: Royse City Texas
Re: compression ratio and HP (68shark)
In looking at the XE262 Compcam spec's the duration is the same as what I have but the lift is slightly higher than my cam and the LCA is 110deg versus my 114 deg.
Will the change in LCA and slightly more lift give me noticely more power or another possibility is the way the cam has been grind (ground, EH! whatever) at Comp Cams superior to the Summit cam grind.
Maybe 1.6 ratio rocker arms are all I need?
This mind bending is Fun!!!!
David
Will the change in LCA and slightly more lift give me noticely more power or another possibility is the way the cam has been grind (ground, EH! whatever) at Comp Cams superior to the Summit cam grind.
Maybe 1.6 ratio rocker arms are all I need?
This mind bending is Fun!!!!
David
Burning Brakes
Joined: Jul 2001
Posts: 1,160
Likes: 0
From: Ajax Ontario
Re: compression ratio and HP (countryvette)
One thing I know is the tighter the lobe separation (110 vs 114), the "lumpier" the idle will sound. 114 is typical of the stock 300hp and 350 hp cams, which have a smoother idle. I like the slightly lumpy (but still smooth) idle the 262 gives. One thought....make sure you have valve springs good up to .500 lift with either of these cams, the XE series mandates this. Watch this especially if you increase lift further with the 1.6's.
