383 Compression Ratio Question
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From: Cheyenne, Wy
383 Compression Ratio Question So I was originally looking at running 11.45:1 Static Compression on my 383 Stroker build with a set of A.I. TrickFlow 215cc Heads. I have been talking to some people and hearing that I would build more power if I were closer to 12.5:1 Static Compression. Thoughts?
I want the car to be capable of being a daily driver, capable of driving cross country if needed, and I want to be able to take it down to sea-level safely both to race and cruise. With that said, if I can gain some power by upping the CR some and still meet the requirements above, then I will. I am not too savvy yet on CR's, so please enlighten me! Thanks in advance!
Current CR related specs:
4.030 Bore
9.012 Deck Height
-5cc Pistons
.026 Thickness Head Gasket
62cc Chamber (if I want 11.45:1)
or
54cc Chamber (if I want 12.5:1)
Rod Length 6.000"
I want the car to be capable of being a daily driver, capable of driving cross country if needed, and I want to be able to take it down to sea-level safely both to race and cruise. With that said, if I can gain some power by upping the CR some and still meet the requirements above, then I will. I am not too savvy yet on CR's, so please enlighten me! Thanks in advance!
Current CR related specs:
4.030 Bore
9.012 Deck Height
-5cc Pistons
.026 Thickness Head Gasket
62cc Chamber (if I want 11.45:1)
or
54cc Chamber (if I want 12.5:1)
Rod Length 6.000"
You stated deck height, but what's your deck clearance? ie. how far in the hole are the pistons? Ideally it's down around .010" to give you a nice tight quench with that .026 gasket.
What cam do you intend to run?
With your stated goals of driving the car anywhere, and possibly not the best pump gas always available, I'd be inclined to stay closer to the 11.5 number than 12.5. But.....depending on your answers to the questions above, that recommendation could change.
What cam do you intend to run?
With your stated goals of driving the car anywhere, and possibly not the best pump gas always available, I'd be inclined to stay closer to the 11.5 number than 12.5. But.....depending on your answers to the questions above, that recommendation could change.
So I was originally looking at running 11.45:1 Static Compression on my 383 Stroker build with a set of A.I. TrickFlow 215cc Heads. I have been talking to some people and hearing that I would build more power if I were closer to 12.5:1 Static Compression. Thoughts?
I want the car to be capable of being a daily driver, capable of driving cross country if needed, and I want to be able to take it down to sea-level safely both to race and cruise. With that said, if I can gain some power by upping the CR some and still meet the requirements above, then I will. I am not too savvy yet on CR's, so please enlighten me! Thanks in advance!
Current CR related specs:
4.030 Bore
9.012 Deck Height
-5cc Pistons
.026 Thickness Head Gasket
62cc Chamber (if I want 11.45:1)
or
54cc Chamber (if I want 12.5:1)
Rod Length 6.000"
I want the car to be capable of being a daily driver, capable of driving cross country if needed, and I want to be able to take it down to sea-level safely both to race and cruise. With that said, if I can gain some power by upping the CR some and still meet the requirements above, then I will. I am not too savvy yet on CR's, so please enlighten me! Thanks in advance!
Current CR related specs:
4.030 Bore
9.012 Deck Height
-5cc Pistons
.026 Thickness Head Gasket
62cc Chamber (if I want 11.45:1)
or
54cc Chamber (if I want 12.5:1)
Rod Length 6.000"
Now he hasn't taken it to sea-level, but a lot of people here run over 12 to 1 at sea-level and I haven't seen issues posted on it. Maybe more of them can chime in and share their experiences and tuning hints.
My own 383 I'm putting together will be 12.43 to 1. Should have running this spring, the short-block is already together.
Good luck on your build.
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From: Cheyenne, Wy
I don't know the cam yet, I am going back and forth on heads and I am gonna spec a cam to the heads so I haven't decided on it. It will be a custom grind whatever it is...probably an XFI lobe from Comp Cams but not sure.
I had my quench calculated a while back but I forgot it...it is between .032 and .035.
I run nothing less than 91 octane in it...period. I might stick with about a 12:1 then. What do yall think?
I had my quench calculated a while back but I forgot it...it is between .032 and .035.
I run nothing less than 91 octane in it...period. I might stick with about a 12:1 then. What do yall think?
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Sure why not? I DD'd mine for several months before I got a second vehicle to drive around. Everyone is so scared of higher compression but the common misconceptions about high comp. doesn't necessarily apply to the LT1.
Good tuning and a good cooling system and you can run around 12:1 all day without a problem.
Good tuning and a good cooling system and you can run around 12:1 all day without a problem.
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From: Cheyenne, Wy
I will have a 160 Thermostat, electric water pump, and he tune has my fans kicking on at 180 and 190. I also deleted my ac so more air crosses the radiator now...cooling should be all set. I am just trying to learn what the actual limits are of the LT1 as far as compression ratio goes.
What IS safe...What is NOT safe...Why? I want to learn. I want to know but I would rather not learn this the HARD way...what bad comes from running high compression exactly? What power gains are we talking about between 11.5 and 12.5?
I am requesting information right now, not opinions. I know what most people think and what their opinions are, but I want to know what the legitimate and real risks are and that the gains/losses are so that I don't have to ask these questions NEXT time...no sarcasm or malice or hate here lol, I just wanna get info so I can make an educated decision of my own instead of listening o opinions and hearsay and making a guestimate
What IS safe...What is NOT safe...Why? I want to learn. I want to know but I would rather not learn this the HARD way...what bad comes from running high compression exactly? What power gains are we talking about between 11.5 and 12.5?
I am requesting information right now, not opinions. I know what most people think and what their opinions are, but I want to know what the legitimate and real risks are and that the gains/losses are so that I don't have to ask these questions NEXT time...no sarcasm or malice or hate here lol, I just wanna get info so I can make an educated decision of my own instead of listening o opinions and hearsay and making a guestimate
12:1 is no problem for a daily driver LT1. If you have a real tuner and not just a mail order, go 12.5:1.
Our engines are reverse cooled, which means cooler cylinder head temps and reduced chance of detonation. Just make sure your cooling system is functioning properly and you run your steam vent lines and you'll be fine.
Our engines are reverse cooled, which means cooler cylinder head temps and reduced chance of detonation. Just make sure your cooling system is functioning properly and you run your steam vent lines and you'll be fine.
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From: Cheyenne, Wy
I know I might be losing out on a little hp. But I was a puss....I'm running 11.3:1. You will make good power even with a mid 11 CR
12:1 is no problem for a daily driver LT1. If you have a real tuner and not just a mail order, go 12.5:1.
Our engines are reverse cooled, which means cooler cylinder head temps and reduced chance of detonation. Just make sure your cooling system is functioning properly and you run your steam vent lines and you'll be fine.
Our engines are reverse cooled, which means cooler cylinder head temps and reduced chance of detonation. Just make sure your cooling system is functioning properly and you run your steam vent lines and you'll be fine.
So to expand my knowledge, why exactly does higher compression increase the chance of detonation? I know why detonation is bad and I know what it is, but how does compression effect it?
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I think on good quality fuel 12.5:1 compression would work fine at your altitude. I personally don't trust pump gas enough to push the compression for a couple ft lbs. Then again I'm from CA where the oxygenated 91 octane stuff would knock occasionally in my 4 cyl ford ranger 
I'm running 50/50 110 octane and 91 pump in mine, 13.6:1
So far at 32.5 degrees at peak torque and no knock.
I'm sure your NEW TUNER can handle it, crank that bitch up to at least 12:1.
Your cam specs play a big role in it too. Everyone likes to bash someone who even mentions DCR, but it is worth looking at in this situation...
What it all boils down to is cylinder pressure, and whatever semantics people want to argue, at the end of the day cylinder pressure is mostly what determines octane requirements. More SCR and DCR, more cylinder pressure. Higher altitude, less cylinder pressure, and so on.
So far at 32.5 degrees at peak torque and no knock.
I'm sure your NEW TUNER can handle it, crank that bitch up to at least 12:1.
Your cam specs play a big role in it too. Everyone likes to bash someone who even mentions DCR, but it is worth looking at in this situation...
What it all boils down to is cylinder pressure, and whatever semantics people want to argue, at the end of the day cylinder pressure is mostly what determines octane requirements. More SCR and DCR, more cylinder pressure. Higher altitude, less cylinder pressure, and so on.
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From: Cheyenne, Wy
Wow Calvin, why the hostility at the "NEW TUNER"? That was nothing against you AT ALL. I loved your tune on my car and I would not have a problem having you tune my car again...the reason I did not choose to have you tune it THIS time is because Trent is going to let me use his shop to finish my build, install my rear end and get it going. I will want to drive it right away, and since I am already there Trent is going to put the street tune on it...since he is doing the street tune I am just gonna stick with him for the dyno and track tunes. No drama, no trash talking and I squash the rumors every time someone asks me why I didn't like your tune. Just saying lol. Besides....I never used the word "new" lmao.
I will definitely be looking at DCR for my new cam. I am getting some ideas from several different people... AI, LE, Calvin, Trent, and possibly a few other sources just to compare and I will figure out what to go with from there. Calvin spec'd my last cam and for the build it was rather small but it was perfect for what I wanted. It hit hard, had great lope, great bottom AND top end, made good power and screamed at the track. No complaints...I am just trying to learn the art myself a little more this time instead of relying solely on other people to pick my parts.
It looks like it would take a 55cc Chamber to achieve a 12.5:1 SCR, and A.I. will only go down to a 58cc Chamber which nets me a 12.04:1 SCR, so looks like 12:1 it is.
I will definitely be looking at DCR for my new cam. I am getting some ideas from several different people... AI, LE, Calvin, Trent, and possibly a few other sources just to compare and I will figure out what to go with from there. Calvin spec'd my last cam and for the build it was rather small but it was perfect for what I wanted. It hit hard, had great lope, great bottom AND top end, made good power and screamed at the track. No complaints...I am just trying to learn the art myself a little more this time instead of relying solely on other people to pick my parts.
It looks like it would take a 55cc Chamber to achieve a 12.5:1 SCR, and A.I. will only go down to a 58cc Chamber which nets me a 12.04:1 SCR, so looks like 12:1 it is.
It appears to me that's a very good compromise for your intended use of the car. Unless you're out to set records, you'll never notice the difference in that 10-15 hp window you're agonizing over.
I hope you get input from Phil at AI on cam selection to go with those heads and your CR. Better advice there than you'll get from the average "helper" on here.
I hope you get input from Phil at AI on cam selection to go with those heads and your CR. Better advice there than you'll get from the average "helper" on here.