Compression Ratio Normally Aspirated

first/thridgen · 12-14-2006

I am in the process of assembling the following engine for my 68 camaro and would like to know my compression limit with alcohol.

I want to run About 50 GPH of straight meth at the peak. I have a chip burner and a wide band O2 and will zero out the power enrichment on the chip and be putting a 10% rich (lamba) curve of extra fuel using methanol under load (0 - 15" vacum). At cruise speeds there will be no alcohol injection (high vacum).

I will only be running regular unleaded (87 octane) fuel.

This is a every day street driven car. I am trying to build a high efecency motor.

The combo is,,,,

1987 5.7 Tuned Port Injection

Flat top pistons

50 cc Rhs IRON heads

Stock Roller Cam 204 /208 @.05" .430" / .460" (including the 1.6 rockers)

.035 Quench distance

I am getting down to putting the heads on.

With all my chamber and piston polishing done, I will have a measured 12 to 1 static compresion ratio.

If I take my heads into work and surface grind the heads .060"
I can have up to 14 to 1, or anything between.

Do you think 12 to 1 should be my limit, or for a little work and no extra money should I go up in compression?

dvldoc · 12-14-2006

You want to stay in a safe enough compression ratio so if you had a methanol system failure your motor does not blow. We have 9 second big block cars running the kits with high compression motors on pump gas. What ever compression ratio you can run with 104 octane you can run with alcohol injection. You can actually run more with the methanol because of the lower intake temps and EGT's.

50gph seems way to much for any 5.7 TPI motor maybe that's a type O. But unless your making 1000hp your not going to need that much.

Play with our nozzle size calculator to get close you your required nozzle size. Since your N/A a M14 would be about the MAX you would need. Our Progressive Controller is also a good option for a N/A motor.

first/thridgen · 12-14-2006

Thanks for the info,

The 50 gal a hour was for 6000 rpm and the total from all 8 injectors.

I should of said 50lbs per hour or roughly 7GPH. My mistake.

first/thridgen · 12-14-2006

From your information and from the following link I believe I will cut the chambers down to 13 to 1.

MotorSports Racing Fuels - Racing Gas - Nitromethane - Methanol - Racing Lubricants - Additives

Rhinoman · 03-22-2007

I have a 5.7 with TPI from an 87 IROC in my Wagoneer. My compression is 11:1, and the rest of the moter matches. Goes like stink, but without the Alcohol (75% alcohol, 25% water), detonation is a bitch. I think a lot of it is the intake runners heating up the air on the way in. My plugs (NGK) are 2 ranges colder than stock. Anyway, I feed it from a 175 ml/min nozzle, (I'm surprised I use such a small nozzle) and use a 140 PSI pump starting at a very low ported vacuum...starts early and stays on. I fill a 4 litre reservoir about every 3 or 4 gas fillups, and am running 87 octane.
You should put in a knock sensor (with a switch) for everyday.

first/thridgen · 03-23-2007

Thanks for the reply. It is hard to get info on NA aplications.

My engine is assembled with a measured 12.98 to 13.25 static compresion ratio. In a few weeks it is going in.

I don't understand the switch on the knock sensor?

Rhinoman · 03-27-2007

The switch on the knock sensor? I leave the knock sensor on day to day, but if I'm running it hard (or going to) I turn the sensor off. I find that it retards the timing excessively, and starts to do it at the incipient knock point. (TPI cars were notorious for detonation, and I think they went a little too conservative with the sensor). It drives me nuts when it backs the timing off to the point that I don't have the power I need (or want).

12-14-2006	#1 (permalink)
first/thridgen Alcohol Injection Year: 1968 Make: Chevy Model: Camaro Join Date: Dec 2006 Posts: 32	Compression Ratio Normally Aspirated I am in the process of assembling the following engine for my 68 camaro and would like to know my compression limit with alcohol. I want to run About 50 GPH of straight meth at the peak. I have a chip burner and a wide band O2 and will zero out the power enrichment on the chip and be putting a 10% rich (lamba) curve of extra fuel using methanol under load (0 - 15" vacum). At cruise speeds there will be no alcohol injection (high vacum). I will only be running regular unleaded (87 octane) fuel. This is a every day street driven car. I am trying to build a high efecency motor. The combo is,,,, 1987 5.7 Tuned Port Injection Flat top pistons 50 cc Rhs IRON heads Stock Roller Cam 204 /208 @.05" .430" / .460" (including the 1.6 rockers) .035 Quench distance I am getting down to putting the heads on. With all my chamber and piston polishing done, I will have a measured 12 to 1 static compresion ratio. If I take my heads into work and surface grind the heads .060" I can have up to 14 to 1, or anything between. Do you think 12 to 1 should be my limit, or for a little work and no extra money should I go up in compression?

12-14-2006	#2 (permalink)
dvldoc DevilsOwn Staff Join Date: Apr 2005 Posts: 1,931	Re: Compression Ratio Normally Aspirated You want to stay in a safe enough compression ratio so if you had a methanol system failure your motor does not blow. We have 9 second big block cars running the kits with high compression motors on pump gas. What ever compression ratio you can run with 104 octane you can run with alcohol injection. You can actually run more with the methanol because of the lower intake temps and EGT's. 50gph seems way to much for any 5.7 TPI motor maybe that's a type O. But unless your making 1000hp your not going to need that much. Play with our nozzle size calculator to get close you your required nozzle size. Since your N/A a M14 would be about the MAX you would need. Our Progressive Controller is also a good option for a N/A motor.

12-14-2006	#3 (permalink)
first/thridgen Alcohol Injection Year: 1968 Make: Chevy Model: Camaro Join Date: Dec 2006 Posts: 32	Re: Compression Ratio Normally Aspirated Thanks for the info, The 50 gal a hour was for 6000 rpm and the total from all 8 injectors. I should of said 50lbs per hour or roughly 7GPH. My mistake.

12-14-2006	#4 (permalink)
first/thridgen Alcohol Injection Year: 1968 Make: Chevy Model: Camaro Join Date: Dec 2006 Posts: 32	Re: Compression Ratio Normally Aspirated From your information and from the following link I believe I will cut the chambers down to 13 to 1. MotorSports Racing Fuels - Racing Gas - Nitromethane - Methanol - Racing Lubricants - Additives

03-22-2007	#5 (permalink)
Rhinoman Water Injection Newb Year: 1986 Make: Jeep Model: Grand Wagoneer Join Date: Mar 2007 Posts: 2	Re: Compression Ratio Normally Aspirated I have a 5.7 with TPI from an 87 IROC in my Wagoneer. My compression is 11:1, and the rest of the moter matches. Goes like stink, but without the Alcohol (75% alcohol, 25% water), detonation is a bitch. I think a lot of it is the intake runners heating up the air on the way in. My plugs (NGK) are 2 ranges colder than stock. Anyway, I feed it from a 175 ml/min nozzle, (I'm surprised I use such a small nozzle) and use a 140 PSI pump starting at a very low ported vacuum...starts early and stays on. I fill a 4 litre reservoir about every 3 or 4 gas fillups, and am running 87 octane. You should put in a knock sensor (with a switch) for everyday.

03-23-2007	#6 (permalink)
first/thridgen Alcohol Injection Year: 1968 Make: Chevy Model: Camaro Join Date: Dec 2006 Posts: 32	Re: Compression Ratio Normally Aspirated Thanks for the reply. It is hard to get info on NA aplications. My engine is assembled with a measured 12.98 to 13.25 static compresion ratio. In a few weeks it is going in. I don't understand the switch on the knock sensor?

03-27-2007	#7 (permalink)
Rhinoman Water Injection Newb Year: 1986 Make: Jeep Model: Grand Wagoneer Join Date: Mar 2007 Posts: 2	Re: Compression Ratio Normally Aspirated The switch on the knock sensor? I leave the knock sensor on day to day, but if I'm running it hard (or going to) I turn the sensor off. I find that it retards the timing excessively, and starts to do it at the incipient knock point. (TPI cars were notorious for detonation, and I think they went a little too conservative with the sensor). It drives me nuts when it backs the timing off to the point that I don't have the power I need (or want).