Inliners International Forums General Discussion Blown and Injected forced induction

My last car was a blown ( 12-71) big block on methanol. I ran locked out on the mag with no retard. Why do I need to set up a Rpm related retard if I put some sort of forced induction on my inline and run methanol. The v-8 was 11-1 static and my inline is 10-1 which would work with methanol.I don`t plan on putting to much boost on it. I ran 19lbs on the v-8 and never hurt it.

You had two things going in your favor. One you used a blower instead of a turbo, which has a much cooler air charge than most turbos do and you were using alcohol, which again greatly cools the intake charge even more. Heat is the enemy on forced induction setups using turbos making them more susceptible to detonation compared to a blower which only uses the outside air to force into the engine instead of heated exhaust air.

Granted, it you add an intercooler and a methanol spray mist cooler, then you can help this to some degree with a turbo, but if you use gas instead of alcohol as a fuel, you will always be at the mercy of the detonation gremlins, and a boost retard will just be a part of life. And even with alcohol as a fuel in some engines, it still may not completely eliminate this issue.

Sparks, you are correct if every thing is the same, but exactly the same, cam, chamber shape, etc. the saving factor is the alcohol fuel.

I don't think CNC meant the hot exhaust temp on a turbo is any different than temps on any engine with every thing the same.
The intake temps are the same and the exhaust temps are equal on both setups. EGT temps have no effect on the combustion temps only ignition timing, A/F ratio, pressure and design effects the combustion process.

Ignition timing is the easy way to control peak pressure.

Actually a turbo compressed air is cooler than a roots blower because they are more efficient in compressing air.

Is there any general rule of thumb for amount of retard? Is the rate of retard controlled by rpm or boost? May be there are instruction with the msd unit But I doubt that for obvious reasons. I have a turbo from a cummins and have an m-90 sitting on the shelf just begging to be used.The problem I see is my compression is to hi to run gas( I think ). I`d have to change cams because I`m only running 109 lobe separation and I think to much boost will be wasted. Last is I`d have to figure how to extend the blower snout.

No, its completely trial and error for your specific engine build and needs. So there is not a baseline to start with. Usually you remove the most timing you can at first to be safe and then gradually add some back to it.

Sparks, the amount of retard is based upon boost, you retard the ignition point to control cylinder pressure.

A 109 c/l cam may work but if you use a turbo it can not have more pressure in the turbine than boost pressure other wise the exhaust will back up into the chamber and end gasses will make it more sensitive to detonation