[ALO]

What is the method for building boost on the rev limiter with a draw thru carburated system? This is a drag racing application.

[Robert]

Originally Posted by ALO

What is the method for building boost on the rev limiter with a draw thru carburated system? This is a drag racing application.

Just to clarify are you referring to building boost at the stagning line?

[ALO]

Originally Posted by Robert

Just to clarify are you referring to building boost at the stagning line?

Yes that's correct.

[Robert]

Originally Posted by ALO

Yes that's correct.

A lot of tuning systems these days can make that happen using an "anti-lag" type system. Essentially these systems would drop timing while bumping up fuel flow causing essentially post detonation in the exhaust manifold to spool up the turbo even with limited or no airflow through the motor. The main issue here is trying to make that work in a carb environment. Assuming you are running no electronic management system its not going to be as easy as it is for everyone else. Quite honestly I don't know how you could set it up without an ECU. In this case the carb alone wouldn't be the limiting factor as long as you could throw enough fuel in but you would need to seriously retard timing with the brake applied (trans or other) and then allow timing to return to normal when it was time to get moving. Something like this:
Two Step Module Selector - 8739
should work in conustion with electronic timing control.

[ALO]

I have a 2 stage retard control and a 2-step rev limter. This is on a standard tranny so I can only put it on the limiter at the line.

[ash]

Originally Posted by ALO

What is the method for building boost on the rev limiter with a draw thru carburated system? This is a drag racing application.

with your type of fuel system,combined i gather you are using a torque convertter ??
90% of the converter cars ADD timing , to help the engine 'climb' up on the stall.
once the pre set laurnch rpm is reached, the 2 step hold the engine rpm at this level, till the trans brake is released,
then the timiing is put back to its orginal setting.
you require a digital timing unit to do this. this unit also allows you to retard timing during a run...

if you cannot get the engine rpm up to reach the required boost , or rpm , so you can accerlate down the strip , the converter is either too tight, or not enough engine rpm.

the balance of turbine wheel and housing size verse power required from the engine also plays a part in this tuning.There is no set rule, but rather the information is gained from turbo tuners.

small housings help spool up , but kill top end power


i use mechanical fuel injection, and msd ignition.
i cannot change fuel injection rates, or timing , while the engine is running, much like you cannot.
But i can change ignition timing, to suit the required purpose. I increase timing, for sppol up , BUT then put timing once the trans brake has been released.
this is a youtube video , of how quick the engine sppols up....

YouTube - willowbank winternationals 2009, twin turbo altered
YouTube - twin turbo sbc altered , willowbank 2009
YouTube - Ash Hamblin 6.819 @ 200.29mph Fuchs Nats 09

7000 rpm converter, 29 psi boost , twin hp66 turbos , methanol fuel

[ALO]

I've had a smaller turbine housing on this combo but the top end was lacking for power. An automatic trans is not possible for my combination. So I must find ways to build boost with the setup I have now. So you say to retard timing for the spool up and then put it back on the launch? How much do you use?

[ash]

Originally Posted by ALO

I've had a smaller turbine housing on this combo but the top end was lacking for power. An automatic trans is not possible for my combination. So I must find ways to build boost with the setup I have now. So you say to retard timing for the spool up and then put it back on the launch? How much do you use?

ok,
i use the MSD 8973, and just plug it into any msd ignition
the digital ignitons does not require this, as it already has the same software...
for my sbc, i put the timing at what ever the engine wants , if it was naturaly aspirated, eg sbc 36-38 , sbf 26-29 deg...
then pull timing once you leave the start line, can pull up to 8-9 degress, depending on the fuel type and octain.

since you have a manual , with a clutch ?????
maybe you will require a limit switch / micro switch that is activated by the clutch , when it is engaged... and then RETARD the timing to "transfer" the heat or combustion outside the chamber, to burn / bang in the pipes, this will spool the turbos very quickly.

did i answer your question ?