Running Variable Boost Through Out The Rev Range For More Midrange.

[Rolls]

Lets say the limiting factor for your engine producing more power is the turbo, and not the fuelling system/strength of internals.

An example is the stock turbo on say an rb25det, being as to run say 12psi the turbo has to spin harder and harder as the revs rise to continue to keep producing the same boost level (as more air is required) it is obvious it is going to be spinning almost twice as fast at say 7500rpm opposed to 3500rpm even though the boost level remains the same.

Now I was wondering if this means you could run say 15-18psi at low rpms when the turbo first comes on, say around 3-4500rpm and then have it drop back down to 10psi towards redline. This way you would be maintaining fairly constant rpms in the turbo and you would be getting far more power in the midrange without overspeeding it at redline.

Now this is assuming that reason the air heats up in the turbo is due to the speed it is operating at, and not the pressure it is running. Could someone confirm if my thinking is correct or not? Because if it is and the air temps are ok at low rpm even at higher boost levels, then I cannot think of any reason why this would be detrimental to the engine or the turbo, providing of course the motor/fuel system could sustain 18psi.

[89CAL]

think youll find that running higher boost will be a problem rather then the rpm

I dont think the RPM of the turbo vs the RPM of the engine is as relative as twice the engine rpm is equal to twice the turbo rpm exactly. Boost creates heat through friction im pretty sure, there will be heat from high rpm as well but yeah im not sure your plan will work, though it is a good idea

[Rolls]

I'm not sure it will work either otherwise other people would have done it by now, but I'm curious as to where I am going wrong. I suspect that intake heat is a function of boost pressure, not how much air it is supplying as if this is the case, then what I proposed doesn't work.

[Adriano]

Evos do this from the factory, and if you look at a compressor map, you can see why. The factory boost control runs directly along one of the efficiency line.

[Munkyb0y]

when my ebc was still working, my car was tuned at 15psi on the stock turbo up to about 4krpm, and then down to 12 psi till redline.

i asked the tuner about it, and he said at the lower rpm the turbo can handle it fine, as long as it's not still running 15psi at the top.

i was a bit suss, but he was confident.

his reasons were the same as yours. to give it a nice kick coming onto the power. makes it feel much quicker.

it was absolutely fine till the ebc stopped working. now i'm just running 13ish psi with a MBC.

Edited July 10, 2010 by Munkyb0y

[lachlanw]

wrx does it too and so do m35 stageas

[R31Nismoid]

Evos do this from the factory, and if you look at a compressor map, you can see why. The factory boost control runs directly along one of the efficiency line.

In factory spec they spike to what, 20psi and drop back to around 1bar

However - interestingly - you can actually hold 18-20psi right until redline once you give some boost control & a tune on the factory turbo.

Suddenly you've then gone from 140-150awkw (EVO9) to a tad over 200 on the factory turbo without a drama in the world. Clearly arguing the point about efficiency.

It could just being setup like that most likely to conserve motor/parts and so on.

I'm a bit dubious of such a compressor map for the EVO turbos based upon this (the above im talking EVO 7/8/9)