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Old 04-13-2008, 04:13 PM
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Compression questions

I was running 12.7:1 compression with 58cc chambers ,180cc runners, 202/160 valves. I just purchased some nice aluminum heads 210cc runners, 205/165 valves, but they are 64cc chambers. This brings me down to like 11.5:1 compression if I did my math right. The cam I am running is - RPM Range: 3000-7300 Advertised Duration: 287/298Duration @ .050: 254/263Lift: .534/.555 Lash-Lobe Center: .026-105c. The question is how much would I be losing power and torque wise. should I buy new pistons to bring the compression back or save the heads? Is either worth it?

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Old 04-13-2008, 04:15 PM
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Quote:
Originally Posted by Jamie Thomas
I was running 12.7:1 compression with 58cc chambers ,180cc runners, 202/160 valves. I just purchased some nice aluminum heads 210cc runners, 205/165 valves, but they are 64cc chambers. This brings me down to like 11.5:1 compression if I did my math right. The cam I am running is - RPM Range: 3000-7300 Advertised Duration: 287/298Duration @ .050: 254/263Lift: .534/.555 Lash-Lobe Center: .026-105c. The question is how much would I be losing power and torque wise. should I buy new pistons to bring the compression back or save the heads? Is either worth it?
IT SHOULD SAY SHAVE THE HEADS, NOT SAVE THE HEADS.-SORRY-JT
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Old 04-13-2008, 04:38 PM
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cam question

This engine is going in a street 1968 camaro, I do not know what gear yet. It does have a power glide tranny. We are going for a sleeper. I want a nice cam but not alot of noise for everyone to know. The engine is a 383 stroker,aluminum heads,205/165 valves, 210 runners,12.5:1 compression. Need suggestion on a intake/carb combo also. What do you think?
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Old 04-13-2008, 04:42 PM
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compression questions

How bout thinner head gaskets. Or if you can find a good shop, you could tig weld the chamber,then polish to match.
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Old 04-13-2008, 04:42 PM
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Can't comment on the cam selection but I hope you live close to an airport so you can buy gas! LOL 12.5:1 compression???? Ouch!
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Old 04-13-2008, 04:47 PM
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hmmmmm....

Really, Tig to make the chambers smaller? I did not think of that. What does that cost?
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Old 04-13-2008, 04:52 PM
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gas

Quote:
Originally Posted by Jmark
Can't comment on the cam selection but I hope you live close to an airport so you can buy gas! LOL 12.5:1 compression???? Ouch!
ITS NOT A DAILY DRIVER, JUST A WEEKEND CAR. YOU KNOW A TRIP TO THE DAIRY QUEEN AND MAYBE A RACE BACK HOME
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Old 04-13-2008, 04:53 PM
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Oh Yea

Quote:
Originally Posted by Jamie Thomas
This engine is going in a street 1968 camaro, I do not know what gear yet. It does have a power glide tranny. We are going for a sleeper. I want a nice cam but not alot of noise for everyone to know. The engine is a 383 stroker,aluminum heads,205/165 valves, 210 runners,12.5:1 compression. Need suggestion on a intake/carb combo also. What do you think?
tHOUGHT ABOUT 125 SHOT OF NOS. i have it here just sitting aroung.
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Old 04-13-2008, 05:06 PM
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The power gain from the better heads will far overshadow the compression loss, I would leave what you have alone, as 11.5:1 is plenty of compression for your combo.
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Old 04-13-2008, 05:19 PM
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Just incase you are curious, I merged the two similar threads.

Mark
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Old 04-13-2008, 05:20 PM
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compression questions

a good tig welder is gonna be 70-80 bucks an hour. Not a cheap alternative. But if you know how thick your compressed head gaskets are, you could use a thinner one and gain 2-5 tenths of a point which would put you back closer to what you had. What are ya doin with 12.7 compression anyway??
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Old 04-13-2008, 05:32 PM
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based on your info; if the cr was 12.7 before then the cr would now be 11.74:1
assuming the same head gasket volume.

So its less than 1 cr difference. Theory says for every 1cr increase you get approx a 4% increase in power. Actualy the % increase is not quite linear.
You actually see less than a 4% gain at higher cr's per unit increase.

If you're running pump gas You don't want 12:1 anyways.
If you can actually tell the difference in power and feel a lose of low end torque and say the cam is now "straight up" on 105 in C/L, you could advance it say 5deg to enhance the torque. You can also make the ignition advance curve more aggressive if not already so.
Does this motor have a flat top piston or a dome piston?
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Old 04-13-2008, 05:42 PM
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383

Quote:
Originally Posted by Jamie Thomas
This engine is going in a street 1968 camaro, I do not know what gear yet. It does have a power glide tranny. We are going for a sleeper. I want a nice cam but not alot of noise for everyone to know. The engine is a 383 stroker,aluminum heads,205/165 valves, 210 runners,12.5:1 compression. Need suggestion on a intake/carb combo also. What do you think?
THIS IS A TOTALLT DIFF MOTOR THEN THE COMPRESSION QUESTION! I ASKED TWO DIFF QUESTIONS AT THE SAME TIME AND THEY ENDED UP IN ONE THREAD.
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Old 04-13-2008, 05:44 PM
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...

Quote:
Originally Posted by cqboss
a good tig welder is gonna be 70-80 bucks an hour. Not a cheap alternative. But if you know how thick your compressed head gaskets are, you could use a thinner one and gain 2-5 tenths of a point which would put you back closer to what you had. What are ya doin with 12.7 compression anyway??
8TH MILE DRAG STRIP,2600 LBS CAR
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Old 04-13-2008, 05:48 PM
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...

Quote:
Originally Posted by F-BIRD'88
based on your info; if the cr was 12.7 before then the cr would now be 11.74:1
assuming the same head gasket volume.

So its less than 1 cr difference. Theory says for every 1cr increase you get approx a 4% increase in power. Actualy the % increase is not quite linear.
You actually see less than a 4% gain at higher cr's per unit increase.

If you're running pump gas You don't want 12:1 anyways.
If you can actually tell the difference in power and feel a lose of low end torque and say the cam is now "straight up" on 105 in C/L, you could advance it say 5deg to enhance the torque. You can also make the ignition advance curve more aggressive if not already so.
Does this motor have a flat top piston or a dome piston?
THIS MOTOR HAS POP UPS AND RUNS ON 116 OCTANE
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