Hitting rev limiter with supercharger

[xsnapshot]

I have a BRZ automatic with the JRSC and high boost pulley on E85.

When I floor it in D, I bounce off the rev limiter in 1st and 2nd before it has time to shift. I think it's just simply revving too fast. 3rd and onward seem ok.

Is there a way to program the transmission to shift sooner or am I SOL and have to use manual mode?

[cdq85]

in before "should have bought manual".










to offer some help though, would keeping it in snow mode help? maybe keep you in 2nd gear when stopped and help alleviate some of the torque. idk other than that.

[Toyarzee]

Are you just possibly breaking traction in the shorter gears before the load and speed warrants an AT upshift?

[xsnapshot]

Originally Posted by new2subaru

Have you tried sport mode or shifting manually?

I don't think I've ever had my automatic in automatic.

Shifting manually is great. I can control it to shift whenever I want, and it's how I usually drive. I just thought it was strange that it didn't shift soon enough in D.

[Freeman]

I don't think anyone has cracked or maybe even bothered to crack the computer for the A/T yet. You might look into SSP and their offerings for the A/T.

[xsnapshot]

Originally Posted by Toyarzee

Are you just possibly breaking traction in the shorter gears before the load and speed warrants an AT upshift?

I suppose that could be happening.

So you are saying that when it breaks traction it's essentially revving so fast it has an opportunity to hit the rev limiter before it has a chance to shift?

[go_a_way1]

Originally Posted by new2subaru

Have you tried sport mode or shifting manually?

I don't think I've ever had my automatic in automatic.

^this lol. Some people forget I drive a auto I uses the "manual" mode so much.

[go_a_way1]

Originally Posted by xsnapshot

I suppose that could be happening.

So you are saying that when it breaks traction it's essentially revving so fast it has an opportunity to hit the rev limiter before it has a chance to shift?

This could be happening?

[Toyarzee]

Originally Posted by xsnapshot

I suppose that could be happening.

So you are saying that when it breaks traction it's essentially revving so fast it has an opportunity to hit the rev limiter before it has a chance to shift?

I've had it happen, though on a much much more powerful and squirrely muscle car.... but based on your mods and since you say you're flooring it, if on oem or equivalent tires, and possibly turning while applying the load, I suppose it's possible. Never owned an auto so I could be mistaken due to my lack of familiarity with this issue. Normally if I hit rev limiter, it's cause I'm too slow!

Originally Posted by go_a_way1

This could be happening?

Is that a question or confirmation? Lol

[go_a_way1]

Originally Posted by Toyarzee

Is that a question or confirmation? Lol

Well I have had mine fail to shift NA and bounce off the limiter before (in the rain) so I can see that happening but I have not tested it further to my anwser is both ?

[justatroll]

I would argue that adding the extra rotational inertia of the SC and then hitting the rev limiter frequently is bad.

You are almost certainly exceeding the max revs each time you do this due to the exrtra inertia of the SC.

[xsnapshot]

Originally Posted by justatroll

I would argue that adding the extra rotational inertia of the SC and then hitting the rev limiter frequently is bad.

You are almost certainly exceeding the max revs each time you do this due to the exrtra inertia of the SC.

I know hitting the rev limiter is bad. That's why I'm asking the question.

But that's also not how engine's work. If you have a rev limit set to 7400 RPM, and you cut ignition right at 7400 RPM, then there will be no energy in the engine to INCREASE the RPM. The rotational inertia of the system may keep the engine AT ~7400 RPM for slightly longer than without, but that's it.

Additionally the extra rotational inertia from the supercharger would actually impede the ability for a non-powered system to accelerate. Think of how long/extra energy it would take a 1,000 lb two foot diameter wheel to slow down compared to a 100 lb two foot diameter wheel.

[justatroll]

Originally Posted by xsnapshot

I know hitting the rev limiter is bad. That's why I'm asking the question.

But that's also not how engine's work. If you have a rev limit set to 7400 RPM, and you cut ignition right at 7400 RPM, then there will be no energy in the engine to INCREASE the RPM. The rotational inertia of the system may keep the engine AT ~7400 RPM for slightly longer than without, but that's it.

Additionally the extra rotational inertia from the supercharger would actually impede the ability for a non-powered system to accelerate. Think of how long/extra energy it would take a 1,000 lb two foot diameter wheel to slow down compared to a 100 lb two foot diameter wheel.

I think you need to rethink your "physics".
If the ignition "Cuts" at 7400, the engine RPMs will continue to climb for a fraction of a second and exceed 7400. that is called inertia.

And the additional rotational inertia of the SC will help the engine to KEEP GOING and overshoot 7400. And since the SC has a belt and possibly internal gearing, the increase in inertia is magnified by the transfer ratio.

That is why it is harder to stop a dump truck on ice than it is to stop a VW beetle. - "Inertia".

Normally hitting the rev limiter is not bad.

[Alltezza]

Originally Posted by xsnapshot

I have a BRZ automatic with the JRSC and high boost pulley on E85.

When I floor it in D, I bounce off the rev limiter in 1st and 2nd before it has time to shift. I think it's just simply revving too fast. 3rd and onward seem ok.

Is there a way to program the transmission to shift sooner or am I SOL and have to use manual mode?

You know it's raining in our area

You might have wheel slip and your RPMs just jumped while you was drifting(;