From another Forum, but the print out from the rolling road makes for interesting reading.

F-type V6 S BHP - PistonHeads

 

So many things could contribute to this...

I've had my car on 3 different dyno's and had variations of 40rwhp... which could be 50hp at the crank if you take a rule of thumb for drivetrain losses.

The guy himself is saying he doesn't understand much about dyno's, so good luck to the PH guys getting answers.

 

Interesting stuff - thanks for the link.

 

Dynos read inaccurate in comparison to one another. Mustang dyno's vs. dynojet dynos can easily read 10% different. Conditions also play a big factor. On top of that rumor has it Jaguar rated these cars high anyways.

 

One thing that does ring true is that the power does seem to "fall off a cliff" once you hit 6K rpms. My "butt dyno" feels that routinely.

 

According to the posts, Jaguar are involved in checking this out. I will be interesting to know what the outcome will end up at.
Wonder what the 'R' actually puts out on a dyno.
Lawrence.

 

Just take it to a drag strip. More reliable than dynos. If the car is down on power, it'll be reflective in the time and trap speed.

 

Only way to know for certain if there is an issue is to sequentially run a base V6.

 

if it were a normally aspirated engine, I would conclude a different cam profile should resolve this. However, forced induction should not suffer from that problem unless the super charger is undersized or the mapping is just plain crappy. If anyone knows which model Eaton is being used, I could check the performance curve of the SC to confirm whether it is to blame. If the SC is undersized, a reduction pulley will just bring on the power drop-off at a lower engine speed.

 

I've never owned a supercharged vehicle, but have some experience with turbocharged ones. For that type of forced induction, the power dropoff could be caused by the ECU detecting detonation and adjusting timing and boost pressure accordingly.


Where I am, premium fuel is rated at 91 and we have seasonal blends. My current car (Volvo C30 T5 with Polestar optimized tune) expects premium, although their notion of premium is probably 93, perhaps even more. The engine management system adjusts for lower ratings, leading to reduced performance.

 

I've noticed the same, and short shift at about 6K RPM because of this. Interesting to see this reflected on paper (and validate our butt dynos).

 

That's exactly what I do, and I'm fairly certain, it's quicker using that technique.

 

Unless I missed some clarification, the dyno sheet and numbers seems to indicate rear wheel horsepower only and not net HP at the flywheel, the latter being what all OEMs use as advertised numbers.

If so, the 340 RWHP is pretty much on target if an approx 10% loss is allowed from the flywheel.

 

Mikey,

The discussion in the link wasn't very clear, but the implication was it's 340 at the flywheel, and considerably less at the rear wheels. Some sort of correction factor is applied on the dyno they used, which has always been a controversial topic.

 

it is a dual drum dyno, which usually shows a lower rwhp output (also pending on how the car is strapped down).

The dyno slip shows the rwhp in green (so 293 ish rwhp), the red line is an estimated engine hp figure (ie the 335 and 340 bhp).

I have seen some 300 rwhp figures on these type of dynos for stock 4.2 XKRs with advertised 400 bhp.

 

Given the suspect nature and variability of RWHP dyno numbers, I'd trust reverse-engineered flywheel numbers even less.

 

Since Foosh is experiencing drop-off at 6k with 93 octane, that's probably not the issue.

 

If the results of two different cars look similar, wouldn't that possibly hint that there may be a consistent error with the dyno itself perhaps?

 

Perhaps the discrepancy is due to the U.K.'s higher octane fuels? Jaguar's performance claims for this engine could be based on the 98 RON fuel available in the U.K., and the crap 91 octane (93 if you're lucky) we have here in the States accounts for the drop in power.

Although a 40hp decrease due to octane seems unlikely, it is an FI engine and would have to dial back boost to avoid detonation.

 

If Jag recommends 95 RON fuel and says the engine makes 380 HP SAE NET, the tests would have been done on 95 RON. It's part of the SAE requirements.

How would an engine 'dial back boost'?