When does the rev limiter cut in on a 99 XJR? Is it at 6150 rpm or a little later?

 

I thought it was 5900 on S/C engines?

 

Definitely not 5900. The factory numbers were 370 hp @ 6150 rpm so I'm assuming that it revs to at least 6150.
When I did my dyno runs, they ran it to 6050 with no problem. I want to know how high I can run the rpm on the dyno before the rev limiter kicks in.

 

My XJ8 coughed a bit as the rev limiter kicked in when I left in 2nd to about 7200.

 

If peak power is at 6150, one can assume that it's somewhat above that. This makes Kansas's 7200 sound reasonable. The shifts want to happen such that peak power is somewhere near halfway between just shifted and about to shift again. This maximizes average power.

 

The engine revs until about 6200 but the torque converter doesn't lockup at wot. So when the dyno man calibrates the rpm by having the engine rev at a constant speed/constant power, they record the rpm in locked condition. At full power the RPM shown on the dyno will be lower than the actual engine speed.

 

Are you suggesting that the dyno calculates RPM from rear wheel speed?

Otherwise, if they're looking at spark via an inductive pickup, or plugged into the OBD and reading RPM digitally, engine RPM is RPM, regardless of what the tranny is doing.

Certainly if the TC is not locked, the tranny INPUT SHAFT rotation rate will be lower than engine RPM... but does that have anything to do with torque/power at the rear wheels relative to engine RPM measurement, other than a loss component?

 

Seldom seen a dyno operator use the ODBII signals, and I guess getting a spark signal on our cars would be somewhat cumbersome, as for most cars (the older 4.0 ones) you would need to take of covers which takes time.

The dyno measures the power, that has nothing to do with the RPM indication, but when the dyno software then also wants to calculate engine power, then these numbers will be even more off if they use the wrong rpm.

 

The dyno operator actually took off the spark plug covers and measured the spark signal.

That's after he looked under the hood and asked, "Where the hell are the spark plugs?"

 

Actually, the dynomometer measures only torque. The subsequent power is calculated from this torque times RPM times a conversion constant... so if engine RPM is not known accurately, power at the rear wheels can still be calculated, but not related to any engine RPM, only to effective vehicle speed instead (or transmission input shaft RPM using drivetrain ratios).

 

And the answer is ?

 

I have hit the limiter a few times when rev with 2nd gear. I think it's 6200-6300rpm. If using D, it changes at 6K.

 

.
Thats kinda what i was hoping, i was a bit worried it might be dipping into the low 7's and i wouldnt be very comfortable with that...

I'm very confident in the strength of this engine, but on the other hand i kinda need to know there is a safe guard so it dosent implode...

and that the limiter is well within the safety level on the R's...

Thanks for the info

 

From Jaguar's Technical Guides, the supercharged engine is rev-limited to 6200rpm and the normally-aspirated engines are rev-limited to 6950rpm.

The supercharged engines have a noticeably lower rev limit in order to prevent the supercharger from overspeeding beyond it's safe design limits with the stock pulley sizes-the Eaton unit also becomes noticeably more inefficient if the rotational speed rises too high.