Well my car must of been performing under stock to begin with and is now performing as stock. Who knows? Too many variables at play. Either way it's better than before so that cannot be argued with. So really the starting power is irrelevant it's the ending power after mods and if it actually is different from my point of view which I know it is because it's my car and I am used to driving it.

 

Not really possible when the crankshaft is in a sealed unit.
When bhp and torque are being measured on a dyno aka rolling road it measures at the rear wheel contact surface.
Thats the whole point of using a dyno.

 

@Busa


I think Mikey is talking about when the engines are in the manufacturers testing facility where the engine is on a dyno rig on its own, that's what I am thinking he is on about

 

The clue is in the words, as posted!

 

Hey, I'm a little puzzled, isn't an STR supposed to be 400hp at the crank?
Loosing 90 hp seems pretty steep.

My 4.2 is supposed to be 300hp, and my clean box-stock car made: 250.06 whp / 259.67 torque.

Also, what's responsible for the big hp dip around ~2500 rmp? Is that the drag of the blower as it begins to spin up?
================================================== =
You dreamed of a big star -
He played a mean guitar -
He loved to drive his Jaguar...

So welcome to the machine

 

Various dynos under or over estimate. Other things like air temp, humidity etc all matter.

Yes, 400HP but kinda meaningless unless the car is typical and new.

 

Probably.
The claimed power outputs from manufacturers are often wide of the mark. Whether measured at the crank or orientated for sales. Kawasaki had a reputation for rather too enthusiastic figures.
The power at the wheels is the only true measure for road or track cars.
A test bed is a test bed.

Good luck with achieving the power increase your desire.

 

You're referring to the distant past when Gross HP was the measure used by the OEMs. Starting in 1972ish, at least in North America, Net HP became mandatory, in accordance with strict SAE procedure which does not allow for embellishment. If Jag certified the -R engine at 400 net HP, that's what it produced.

If there's numbers that are not of much use, it's chassis dynos which are known to be inconsistent from one example to another and subject to operator error. The Mustang dyno has a poor reputation in this respect.

Not having the 'before' numbers makes the 'after' numbers of questionable value, especially in this case where it appears that the car has lost power.

 

I've always been a bit dubious of manufacturers claimed power outputs and the bhp can vary quite a bit between same models.

What's a piece of paper worth if you're not going to use the power or race?

Has anyone tried fitting a bigger blower on their STR ? I'd imagine so
Rotrex have quite a few car kits.

I fitted a c15 Rotrex blower to my 1300cc bike and kept the power output real @ 240 RWHP for the sake of better reliability. But with different fuelling it could have achieved 300 bhp. I know the cost of large increases in power is fairly steep.

 

https://www.jaguarforums.com/forum/p...7/#post1353706

 

 

I can see graph just up to 5,000rpm - where is the rest 1K?

 

That's all I have received

 

4.2 with Gen V Eaton should rev well up to near 6K even with smaller upper pulley. If they really have missed last 1K, you can expect 25-35whp more than @ 5K. I would ask this from Viezu if they have any reason for the odd rpm range.

 

That is the business !
I'll have a proper read of the thread later.
Thanks for the link.

 

All Dynos read different, yes transmission losses can be any wherte from 15 to 25%.
I prefer actual on the road comparisons.
Check out the before and after graph for my standard STR after it was remapped, yes you can certainly feel the differance.
I also added a 10% top pulley on a customers car and again there was quite a differance.

 

Talked to the engineer who dyno'd my car, here is his description of the graphs


Hi

We have had many of these on the dyno that have done similar on the RPM as the gearbox is always trying to upshift above 5000rpm which screws up the readings if the dyno reads the data through the shift.
The graph is showing an increase of 40ft lbs of torque and 60hp
The 60hp is a little higher than expected as the stock car was running warm on the original runs at the top end so the Original power tapered off a little earlier than normal.
The gains corrected for temps etc would be approximately 45-48hp which is what is seen in the midrange.