A/F Ratio Question

BlackSS/SC · 07-10-2008

I've got a turbo on my Cobalt SS 2.0l and I run 18psi on the street with an A/F ratio of 11.5 roughly.

I want to run 80/20 or straight meth in my progressive system. I have tuning capability, a/f gauge and a way to monitor knock.

So what would a good A/F ratio be once I add in the meth injection? I've been told to try and lean the car's computer out when on meth to run high 11s or low 12s.

I mostly am wanting to make the most power possible and not looking for the cooling effect so much. Car have pretty low IATs as it is now.

I have the M5 nozzle install btw.

dvldoc · 07-11-2008

11.5 is already a good safe A/F ration and is what most people shoot for.

califcarm · 07-17-2008

I have read conflicting information on this. But, the best sources (reputable tuners, information coming from their customers) seem to say that they make more power by running a bit richer when on meth compared to when on pump gas alone. the richer they go, the more power they make.

If you make good safe power at 11.5 on pump gas, then run that or maybe a bit lower towards 11:1 on meth. I think the tuners can make more power slightly richer by the tune accepting more timing at this state, compared to when it is run at 12:1 or a little leaner as I have seen some others do.

pacemkr86 · 07-22-2008

i shoot for 11.5 a/f ratio on pump gas.. and somewhere between 11.0 -10.5 with the alcohol.. some cars will take more alcohol then others..

Racer704 · 07-25-2008

When shooting for more timing always read your plugs for detination, if your tunning for AFR only and not looking at your plugs you can hurt a ring or piston.Plugs should be read with a clean shut off at the end of the track and check them there is the only way you can read them correctley.

The reason for more power with a richer setting on methanol over gas is because there is oxgen in methanol and zero in gas and you can usally run methanol 10% richer then optimal with no power loss.

pacemkr86 · 07-25-2008

most late model EFI cars have knock sensors and with scan tools / data loggers we can see knock retard " aka detonation"

but still good info from Racer704

Racer704 · 07-26-2008

Thanks Phil

07-10-2008	#1 (permalink)
BlackSS/SC Water Injection Year: 2005 Make: Chev Model: Cobalt SS Supercharged Join Date: Apr 2007 Posts: 17	A/F Ratio Question I've got a turbo on my Cobalt SS 2.0l and I run 18psi on the street with an A/F ratio of 11.5 roughly. I want to run 80/20 or straight meth in my progressive system. I have tuning capability, a/f gauge and a way to monitor knock. So what would a good A/F ratio be once I add in the meth injection? I've been told to try and lean the car's computer out when on meth to run high 11s or low 12s. I mostly am wanting to make the most power possible and not looking for the cooling effect so much. Car have pretty low IATs as it is now. I have the M5 nozzle install btw. __________________ 2005 Cobalt SS Turbocharged T3/T04E 50 trim

07-11-2008	#2 (permalink)
dvldoc DevilsOwn Staff Join Date: Apr 2005 Posts: 2,043	Re: A/F Ratio Question 11.5 is already a good safe A/F ration and is what most people shoot for. __________________ Currently deployed to Ramadi 1 battalion 12th Marines Task Force MP

07-17-2008	#3 (permalink)
califcarm Water Injection Newb Year: 1988 Make: toyota Model: mr2 Join Date: Feb 2008 Posts: 1	Re: A/F Ratio Question I have read conflicting information on this. But, the best sources (reputable tuners, information coming from their customers) seem to say that they make more power by running a bit richer when on meth compared to when on pump gas alone. the richer they go, the more power they make. If you make good safe power at 11.5 on pump gas, then run that or maybe a bit lower towards 11:1 on meth. I think the tuners can make more power slightly richer by the tune accepting more timing at this state, compared to when it is run at 12:1 or a little leaner as I have seen some others do.

07-22-2008	#4 (permalink)
pacemkr86 DevilsOwn Tech Year: 86 Make: Buick Model: T Type Join Date: Oct 2005 Posts: 644	Re: A/F Ratio Question i shoot for 11.5 a/f ratio on pump gas.. and somewhere between 11.0 -10.5 with the alcohol.. some cars will take more alcohol then others.. __________________ Phil Underwood My Turbo Buick

07-25-2008	#5 (permalink)
Racer704 Water Injection Year: 1963 Make: Chevrolet Model: Vette Join Date: Jul 2008 Posts: 24	Re: A/F Ratio Question When shooting for more timing always read your plugs for detination, if your tunning for AFR only and not looking at your plugs you can hurt a ring or piston.Plugs should be read with a clean shut off at the end of the track and check them there is the only way you can read them correctley. The reason for more power with a richer setting on methanol over gas is because there is oxgen in methanol and zero in gas and you can usally run methanol 10% richer then optimal with no power loss.

07-25-2008	#6 (permalink)
pacemkr86 DevilsOwn Tech Year: 86 Make: Buick Model: T Type Join Date: Oct 2005 Posts: 644	Re: A/F Ratio Question most late model EFI cars have knock sensors and with scan tools / data loggers we can see knock retard " aka detonation" but still good info from Racer704 __________________ Phil Underwood My Turbo Buick

07-26-2008	#7 (permalink)
Racer704 Water Injection Year: 1963 Make: Chevrolet Model: Vette Join Date: Jul 2008 Posts: 24	Re: A/F Ratio Question Thanks Phil