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1/2 mile race

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Hello,

i need boost recommendation for a 1/2 mile race without breaking the engine for a full build race engine that should be able to handle up to 1700whp on race fuel.

There's really not enough information here to be able to advise you. The specific engine and capacity, along with fuel and turbo size would be helpful to know. Boost is only a factor of the power you want to make, the turbo size, and the engine's ability to support airflow so in and of itself, boost pressure when considered in isolation is almost meaningless.

Here's some considerations that are probably more important though:

1. Thermal management is very important over the course of a 1/2 mile race. You're going to want to closely monitor your lambda but also I'd strongly advise EGT. Often you may need to purposely richen the AFR in the higher gears to control EGT, even potentially at the expense of a little power.

2. Turbo sizing is very important and in this sort of application I'd normally try running a turbo that is relatively loose on the hot side to help keep EMAP low. I'd be trying to get the IMAP/EMAP ratio close to 1:1 where EMAP is at or below IMAP. This isn't always possible but it's a good aim.

3. Your engine needs to be designed and built to handle the sustained high power and high thermal loads that you'll see in this sort of application.

Let me know if you have any more questions.

I am running a 104mm turbo with pure methanol m5 fuel. Im targeting .75 lambda on 4 and 5 gears on 3 bar of boost

0.75 lambda is actually quite lean for methanol fuel. The correct fuelling will be engine dependent but it's not uncommon for target lambda values to be in the 0.55-0.65 region. Particularly for a 1/2 mile race you want the additional fuelling to help cool the combustion charge.