Engine dies at full throttle

[fukaynaedfu]

.

[Owen Thomas]

This sounds like a tuning issue to me. Particularily, it sounds like you may be running a little too lean (>14.7 AFR for gasoline).

I have little practical tuning experience, but here's my reasoning:
- A 2L plenum is not all that large and should not cause throttle lag by itself (we have ~2.5L plenum on a 4-cyl with decent response).
- Lag from opening the throttle is a symptom of under fuelling.
- Engine racing when throttle closed or part-closed is a symptom of under fuelling.
- Engine unable to rev at WOT is another symptom that there is too little fuel for all the available air.

These problems could also be caused by an intake leak, so I would check that as well.

[Racer-X]

Check your lambda trace (or plugs if you want to be a badass) and see if you were/are running lean. It sounds like you aren't getting enough fuel for the air you're putting in.

I'd be surprised if a leak in the intake was causing it to quit. Generally vacuum leaks are less pronounced at higher RPM and load due to the higher flow and lower vacuum*.If you had crappy idle I'd suspect a vacuum leak.

*The restrictor is going cause intake vacuum to climb as RPM rises but that isn't much of a concern until you get near choked flow.

[Racer-X]

Our torque curve is something I don't have the authority to share. I can compare yours to others I have seen.

Are those non adjusted numbers at the wheels? If so that's about 5ftlbs (7nm)over what I have seen from some good teams. If its adjusted for the crank or some dynojet hocus pocus I'd say you're a bit low on the peak. Your torque really starts to drop off at 8K though. Was that intentional?

If you want to compare you can poke around online and find some charts. I haven't looked recently but there is a website that has some numbers from a few different teams.

EDIT: here is the site http://www.formulastudent.de/f...ults-fsg-2007-event/

[Warpspeed]

Originally posted by fukaynaedfu:
At semi or partial open throttle the engine revs like a mad bull but open the throttle wide open and it dies down.

How large is the throttle body ?

A grossly over sized throttle body might control airflow well up to some point of opening, then further opening can have almost no further effect.

[Boffin]

http://fsae.com/eve/forums/a/t...20052151#68020052151

Couple of graphs in there from the Australian teams

[MarkSchaumburg]

Are you running TPS or MAP load control? If you're running TPS you might double check the voltages for 100% throttle. Back when we ran the old PE1 ECU, we had a problem where we set the TPS=100% voltage to some level, and then something moved on the throttle body, making the ECU think it was over 100% at WOT. This would cause the fuel to cut off whenever we hit full throttle.

[Racer-X]

Originally posted by fukaynaedfu:
@RacerX : that torque curve is wrt to crankshaft speed. Its been a brainstorming session and i still cannot figure out as to why does it drop so early. I even have tried with large plenum volumes(6 liters) and the software shows smoother pulsations as expected. What concerns me is even with such a large tank, the peak power is only till 8k rpm.
http://i48.tinypic.com/m9xgg4.png

@ warpspeed, our throttle body size is 25mm. And i have read many of your posts. You have contributed to the forum immensely.

By wrt do you mean rear wheel torque? If so good for you with those peak numbers.

Stock these motors are all top end and even heavily modified ones don't have that that much of a torque drop off at high RPM. So this makes me think it has more to do with the engine being starved of air or fuel, not an intake or exhaust tuning thing. I would make sure the engine was getting enough air and fuel before I messed with plenum volumes.