Downshifting

[ViperJ]

Quick question, when you are racing and you floor it (in an automatic) once there is more than about 3500rpms the car jerks and accelerates much faster. What is the car doing when you do this?

Thanks in advance

[burly]

Note that this vehicle has the GM 4T40-E transmission. I also have a malibu - 2003 - that has the same tranmission. My vehicle also exhibits a jump in acceleration ~3200-3500 RPMs and above. It *feels* like my engine is reaching is torque curve and pulls hard until it reaches its HP peak and starts to run out of breath. My vehicle has the 170HP/190ft-lb 3.1L SFI V6 versus ViperJ's 150HP/??ft-lb DOHC I4. This is why I noted that our transmissions are the same and that the RPM at which the increase occurs is very similar. It's very possible that both engines are reaching their power curves within a few hundred RPMs of each other, but the transmission/gearing could have something to do with it.

[quaddriver]

my 98 olds gls (same car) does the same damn thing....Im not 100% sure but I think the pulse modulated lockup lets go

[ViperJ]

Im just wondering because most automatic cars do this. I want to know what is actually happening inside the tranny or engine. To answer Burly's question its 167ft-lbs for the 2.4L.

[Evil Result]

If your racing and you floor it the engine is WOT where the computer uses preprogramed fuel curves, this also causes the Transmission to shiftdown into the engines powerband.

basicaly all automatic transmissions shiftdown if you floor it unless your already in high rpms.

[Reed]

this is just a guess but maybe it has something to do with the torque converter. i am not that familiar with autos but thats what i would say is doing it unless the tranny is actually downshifting. i used to drive a corrolla and it downshifted whenever i floored it in like 3rd.

[burly]

I'm not if ViperJ is saying that if he floors it above 3500 RPM it downshifts and accelerates harder. I think what hes saying is that when he is already at WOT, once the engine reaches 3500 RPM it accelerates a lot harder before the next shift. That is the case with my vehicle at least.

[Reed]

well then i would say that it is either a really pronounced powerband or it is the torque converter catching up with the engine rpm

[rubix777]

maybe downshifting is your answer.

You say when you floor it, the rpms go up and you feel that it accelerates harder?

or

When you floor it, the car downshifts, but you don't feel it accelerate harder until past 3500rpm?

[Reed]

if in the original question you are saying that you are flooring it from a stop then it is not downshifting cause if it was floored from the beginning it would not shift up and then back down if you never take your foot off the gas. the answer has got to be either a super defined power band or maybe v-tec/vvt-i etc. Or else it is jsut the torque converter catching up with engine rpm.

[ViperJ]

I found out i was the torque converter. Thanks for all the help.