Part throttle boost aka part throttle super boost

[Stkid93]

Hey fellas,

I don’t know much about this as I’m not much of a tuner. From what I’ve read it seemed to be a bigger problem with older cars that used manual boost controllers. You would give it 50-75% throttle but would get full boost. But because you were only at 50% throttle would wouldn’t get enough fuel and the afrs would go super lean and you would get a ton of power. But it was horrible for the engines.

is this a problem with fists/modern cars? I have noticed that the car feels a lot stronger at part throttle in certain situations. i dont stare at the accessport while doing part throttle pulls but I don’t think I ever noticed the afrs go super lean when doing part throttle. But I could have missed it.

anyone know anything about this and whether it affects our cars? And if this doesn’t happen on our cars, why does the car feel way stronger at part throttle?

I have read explanations ranging from

- air velocity is really good for torque, while overall air mass and amount of air is better for high rpm’s. and by only giving it part throttle the throttle body doesn’t open as much, forcing the air to go thru a smaller opening increasing the velocity and efficiency of the engine at Lower rpms

(this explanation makes the most sense to me, there has been a lot of testing on intake manifolds and their design, and how longer and thinner runners are better for torque. And actually a lot of company’s use butterfly valves in their runners to help aid Low end torque. Further giving validity to this explanation, however if this explanation is true, why did part throttle super boost happen and why is it so dangerous to the engine? Manufacturers wouldn’t put butterfly flaps in knowing it would make the engine dangerously lean)

-it’s all in your head because you aren’t expecting the power as much during part throttle therefore you don’t tense your body in preparation (I don’t believe this because if you look it up there are posts on literally every forum about this, and part throttle super boost was at least at one point a real thing)

 

[Intuit]

is this a problem with fists/modern cars?

If your programming or hardware has been altered, LSPI can be an issue. Otherwise don't worry about it.

 

[gtx3076]

Bro.

Chill.

 

[Dialcaliper]

This is not a problem in modern cars with electronic throttle bodies because the throttle plate is no longer even connected to the foot pedal - the computer does all the work and can always put the throttle plate at the correct position for the operating point.

What you’re describing sounds more like “tip-in” fuel enrichment - old EFI systems would compensate for the throttle plate snapping open by dumping more fuel in than the tune table requires to safeguard against going lean. However with modified cars, upgraded turbochargers and manual boost control, you can sometimes get enough exhaust manifold flow/pressure to spin the compressor up to full boost at part throttle.

This was more a problem with some old (late 80’s early 90’s) systems that didn’t use a variable throttle position sensor and only had limit switches for WOT and Idle. Usually tuning on a budget was still done with primitive airflow controllers (like the old SAFC) or even worse (AFPR’s!).

In that case if you didn’t fully floor the pedal, you wouldn’t get enough extra fuel on tip-in, as you still relied on fooling the factory ECU.

Basically, this problem was largely solved on cars produced by the late 90’s