View Full Version : Compression Ratio with pump gas??
whitey70ss
04-26-2009, 07:07 PM
What is the max comp. ratio if I still wanna run pump gas??
Tod74
04-26-2009, 08:48 PM
I have ran 11 to 1 with premium gas with no issues. Most will tell you that's too much and maybe it is...but I got away with it.
ARUSSELL
04-27-2009, 10:24 AM
I am the same as TOD running 11.0 to 1, but 10.5 is a safe number to shoot for.
I have a 355 sbc with 10.5 flat tops. It previously detonated when I ran some old steel 64cc turbo Chevy heads, #340292. We replaced them with a set of 68cc AFR alum heads with 180 runners and the detonation went away. I don't know if it was more from the larger chambers or the alum head material, but I suspect it was more from the aluminum since it dissipates heat better. It's may be easier and cheaper to swap heads than pistons. JMO Mep
Tod74
04-27-2009, 01:28 PM
let me rephrase...mine was 11 to 1 on paper, I never measured anything and did the math. It was a flat top piston 406 with 5.7 rods and it had a small hyd cam .507 lift dur @ .050 was about 244 I think. It had a set of the original sportsman cast iron heads with 64 cc chambers( advertised I didn't measure them)
whitey70ss
04-27-2009, 02:46 PM
is there any way to measure comp. ratio with the engine in the car???
Tod74
04-27-2009, 03:27 PM
is there any way to measure comp. ratio with the engine in the car???
NO
suicidebomb
04-27-2009, 06:00 PM
Oh, Boy :!: :lol:
MEMRACING62
04-27-2009, 07:36 PM
are we going to use that magical compression guage again!! :lol: :lol:
Tod74
04-27-2009, 08:28 PM
are we going to use that magical compression guage again!! :lol: :lol:
I almost went there but decided against it...lol
russ67chevelle
04-27-2009, 09:32 PM
how efficient the heads also play role,so does cam specs.rod to stroke has a bit in it too.inlet temperature,boy ya know there are other things too....good luck,
the bigger the cubic inches the more cylinder pressure more cylinder pressure means more possible detonation.example a 350 chev vs a 632 big chev......11:1 could be more tunable to run without detonation vs a big motor with comparable builds
oldandtired
05-01-2009, 07:29 AM
is there any way to measure comp. ratio with the engine in the car???
NO
Tod, Hate to correct you, but it can be done. Remove the carb, put one ounce of chicken feathers in the intake manifold and the rotate the engine exactly one revolution with your wifes vacuum cleaner drawing on the header collector. Count the feathers and thats your compression ratio.
Very accurate... Dave
kbartley
05-01-2009, 07:50 AM
Old and Tired, feathers, be my luck that if I told him to do that he would and watch him pull a golden egg out of the collector, but thats how my luck goes. Kris
CamBirdRacing
05-01-2009, 10:15 AM
I have a 355 sbc with 10.5 flat tops. It previously detonated when I ran some old steel 64cc turbo Chevy heads, #340292. We replaced them with a set of 68cc AFR alum heads with 180 runners and the detonation went away. I don't know if it was more from the larger chambers or the alum head material, but I suspect it was more from the aluminum since it dissipates heat better. It's may be easier and cheaper to swap heads than pistons. JMO Mep
Alum heads can run a little more comp than cast iron.
Scooterz
05-01-2009, 11:05 AM
Well, I have seen many talks about this subject in the past...
I have a BBC w/ 12.5 pistons. Cast heads that have alot of port & polish, which I was told by the builder it comes out to 10.2 in the end. I run pump gas occasionally w/ zero problems as long as timing is accomidated too. Sometimes I do 50/50 mix also.
One day, I wanted REALLY find out if my builder was right/accurate. So I did the "Balloon Compression test" using a basic auotomotive balloon that fits over the intake w/ carb removed. Using a remote starter, I turned the motor 1.76 revolutions & the balloon inflated to the erect position... something did not look right.... where it should have had the compression mark for 10.2, it said "Trojan"?? I am still confused...
heshtesh
05-17-2009, 11:42 AM
I'll be running 12.1 to 1 in my street engine on 93 this summer, think we can pull this off with cam profile and tuning ability with fuel injection let you know how it turns out.
Tod74
05-17-2009, 11:57 AM
I'll be running 12.1 to 1 in my street engine on 93 this summer, think we can pull this off with cam profile and tuning ability with fuel injection let you know how it turns out.
You're brave.
heshtesh
05-17-2009, 01:01 PM
This post has made me realize a point i overlooked when deciding to go with the Mass- Flow system. With the Edel Pro- flow system i currently own i have the ability to set parameters such as fuel and timing how i like at any RPM with the hand held programer an important aspect for what i'm trying to do. I'm getting rid of the Pro Flow because the electronics do not allow it to run properly at under 10" of vacum, i won't be able to make it idle. In order to update my Pro- Flow it would require new electronics $ 1800.00,new intake Vortec to standard 23 degree $350.00 and larger injectors $440.00. Fortunately i won't get hurt by this as i still have the ability to choose between the new Edel Pro-Flow & Mass-Flow if the Mass-Flow does'nt have the tuning options of the Pro-Flow.