How Much Boost Without Tune?


The White Blur
How much boost were you old timers willing to go without a tune? I know this is a weird question to be asked of today, but I always wondered how much the Stock MAF window could take before Fuel was needed.

Over the years, I always thought 1-2psi and then you needed to squish the FPR to squeeze more fuel?

1986 Buick GX1

GX1 #001 [The One and Only]
The Buick GSX-tra newsletter mentioned if you spent any time at 23 psi boost you would blow head gaskets.
I think that was with the stock chip, injectors and fuel pressure regulator.

I think it boils down to what fuel you're running and what chip.
You would either run out of fuel and get knock or run out of octane.

In '88 I had the ATR Pitbull street chip (92 octane) running 20 psi boost on 100 octane with a slight knock at the 2- 3 shift.
I had a knock detector so I knew how much was too much.

Hopefully you get more answers based on experience than theory.


Well-Known Member
I was at 19-20 psi on 100 octane in 87 . An engineer at the GM plant I work at now , cloned the HyperTech chip and sold them cheap . He also had a set-up with a T fitting that went to the waste gate . The T had a plug in it with a very small hole in it to bleed off waste gate pressure . You would select the plug with a larger hole for more boost . If I remember right I think the bleed hole size I used was around .015" . Never blew a headgasket with this set-up , but you could get the high octane fuel at the pump .


Staff member
What do you mean without a tune? In the 90’s I ran the Bosch Pintle 36/lb/hr injector on a KB hi/lo chip with 110 octane and it would take whatever I threw at it on a stock turbo. Probably mid 20’s. The car ran hard and I crushed hundreds of Mustangs with it. Then I started watching 02 millivolts on a multimeter at WOT and added methanol injection and continued to pound on a lot of cars. The car dead hooked on the street with the original BFG drag radials. 4-5psi foot brakes and flat foot as soon as I let off the brake.

Sent from my iPhone using Tapatalk