Gas/Alky Ratio-Razor System

Garycar

Member
Joined
Oct 16, 2003
Is there a gas/alky ratio (percentage) that is recommended? I backed out approximately 13% gas in preparation for the alky. At the present time I am using alky on the street with relatively low boost (10-15#'s) I have the gain knob on 7 (1-8 scale). I notice that the plugs are very clean to the point of being white. I'm concerned that it may be running lean but it is not detonating according to my very sensitive "Larry Fisher" knock detector. Any thoughts?
 
That is probably a good place to start. Some get as much as 20% fuel replacement.
You likely have a pretty fat tune on 15 lbs, crank it up some...:cool:
 
Is there a gas/alky ratio (percentage) that is recommended? I backed out approximately 13% gas in preparation for the alky. At the present time I am using alky on the street with relatively low boost (10-15#'s) I have the gain knob on 7 (1-8 scale). I notice that the plugs are very clean to the point of being white. I'm concerned that it may be running lean but it is not detonating according to my very sensitive "Larry Fisher" knock detector. Any thoughts?

i would start at the 5 to 6 preset number i have mine on 7 and i am running 27 psi and 24/21 on timing. 15 psi you would not need any alky
 
i would start at the 5 to 6 preset number i have mine on 7 and i am running 27 psi and 24/21 on timing. 15 psi you would not need any alky

By his sig he has a stage motor and likely a large turbo, he may very well need some alky at 15lbs...
 
Around 1999-2000 we were doing these kinds of calculations, and 13% seems a little low.

Back then, I'm pretty sure that around 20% to 25% of all the btu's going into the cylinder were from alcohol. This was based on 6 blue top injectors at 100% DC and 45 psi FP, stock motor, and we flow-tested our alky nozzles into a graduated cylinder. At the time we were running anywhere between 25and 28-29 psi boost on a stock block/head/cam motor.

I'm not sure what the number works out to today - I've since changed injectors, turbo, heads, intercooler, added more alky nozzles.

One simple way to ensure you are not too lean would be to gather a baseline of max EGTs on gasoline. Then turn on the alky, and watch the EGTs. In my world, 1500 deg F is lazy, 1600 deg F is good and reliable, and if you can control the knock, 1700 deg F egt is hell on wheels. Measured at inlet to turbine.

Hope this helps.

ps - Nice old-school Larry Fisher knock detector reference! He used to live not far from here. Had a sweet 87 GN with GNX dash, and his electronics lab in the basement. Now he drives a C4 or C5 I think..
 
Thanks for the responses guys. Appreciate it. John, you are correct. Car has a GTQ 76 turbo. Its a 9 to 1 motor and unlike my original motor sitting on my work bench in running order the stage motor will detonate on 93 octane under 15 #'s. As I previously indicated the aftermarket computer does not pull timing so its easy to hurt this motor on 93. The program was set-up by Duttweiller on his dyno some years ago to run on race fuel. I like the way it performs so I have left it unaltered with the exception of some adjustment to the fuel map. There's no detonation when the alky is on or when running race gas. Dennis, yes I still rely on Larry Fisher's knock detector for knock. He built the unit for me way back in 1990. Unfortunately, he sold his GN and now owns a C5. He just ordered an 08 C6. In my opinion the turbo Buicks are like the original 427 Cobra, endless beauty that never age.
 
I think your doing the correct thing. I would always go with more alcohol than needed on applications that are sensitive like yours. So the knob on 7 is fine.. that motor will love the meth.
 
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