Discussion
I know I have posted a question about exhaust options for my XKR. I thought this topic, while related, deserves to stand alone.
In my hunt for a new exhaust, I have been given a choice...Tune for more torque, or more hp.
Apparently from a particular system, I can get 12-22hp but lose a bit of torque, or gain 8hp and 14-26lbs torque.
Which one is more important?
In my hunt for a new exhaust, I have been given a choice...Tune for more torque, or more hp.
Apparently from a particular system, I can get 12-22hp but lose a bit of torque, or gain 8hp and 14-26lbs torque.
Which one is more important?
Torque at the flywheel is a completely useless figure.
Torque at the wheels is all that matters, and that depends on gearing, and the gearing you can use depends on how much the engine revs.
So all that matters is a good combination of raw torque and a good range of revs.
Otherwise known as, power....
You can be producing loads more raw torque in say a Focus turbodiesel than say a VTEC, but by the time it has gone through the gearing there will be less torque at the wheels.
Mark
Torque at the wheels is all that matters, and that depends on gearing, and the gearing you can use depends on how much the engine revs.
So all that matters is a good combination of raw torque and a good range of revs.
Otherwise known as, power....
You can be producing loads more raw torque in say a Focus turbodiesel than say a VTEC, but by the time it has gone through the gearing there will be less torque at the wheels.
Mark
BT52 said:
Torque at the flywheel is a completely useless figure.
True, but ...
He's being asked whether he want to improve top end power by compromising mid-range torque. Unless you routinely red-line the engine, that's a probably the wrong way to go. Mid-range torque is what you use in day-to-day driving. Top-end power is what you quote people down the pub but pretty meaningless in the real world.
Actually it's the whole spread of torque that matters I suppose.
Unless the whole of the new torque curve is above or on the old one rather than dipping above and below then I'd probably avoid. I'd be surprised if an exhaust would give more torque at X revs and less at Y. Isn't it normally more throughout?
Mark
Unless the whole of the new torque curve is above or on the old one rather than dipping above and below then I'd probably avoid. I'd be surprised if an exhaust would give more torque at X revs and less at Y. Isn't it normally more throughout?
Mark
jcumpsty said:
I know I have posted a question about exhaust options for my XKR. I thought this topic, while related, deserves to stand alone.
In my hunt for a new exhaust, I have been given a choice...Tune for more torque, or more hp.
Apparently from a particular system, I can get 12-22hp but lose a bit of torque, or gain 8hp and 14-26lbs torque.
Which one is more important?
Assuming this is for your XKR - how will it "tune" for more torque?
Is it a replacement exhaust SYSTEM or the tubular exhaust manifolds PRE-Cat?
The system in question is a cat back system.
I dont know how they would "tune" for torque. That is what the company said where my options.
In the end I have elected for the borla system anyway. I have read good reviews about them, and got a good deal on a package from Jaguar XP in the US.
I dont know how they would "tune" for torque. That is what the company said where my options.
In the end I have elected for the borla system anyway. I have read good reviews about them, and got a good deal on a package from Jaguar XP in the US.
You can't tune much for torque on a Supercharged Jag via the exhaust system.
There would potentially a LITTLE bit to be gained by having tuned equal length "headers"/tubular exhaust manifolding but hardly worth talking about.
The jag SC runs next to no overlap (to stop "push through)- and overlap is the mechanism which helps exhaust tuning for torque.
If the pipes behind the cats are constricted- you might gain a smidgen of torque at very low rpm (1000 rpm) however alot of this wouldn't be realised because you're so knock limited there anyway. However the backpressure increase in doing this would knock ALOT of power off your engine.
A good compromise may be to run a lower backpressure system as the engine responds nicely to lower backpressure, and you don't have the same noise contraints to meet as the manufacturer did.
Beware of SC pulley ratio changes also- the pulley on your Jag currently was set after alot of painstaking work ( I think the current ratio is about 2.05) if you make the Super charger workharder,the supercharger will drive less efficienctly and Eaton have set limits as to how fast to turn the M112 Supercharger unit.
If you want to change the system for noise, fine, but don't go believing claims by the aftermarket indiscriminantly. Most of them, even supposedly reputable ones, don't know what they're on about.....
>> Edited by Marquis_Rex on Wednesday 7th September 09:49
There would potentially a LITTLE bit to be gained by having tuned equal length "headers"/tubular exhaust manifolding but hardly worth talking about.
The jag SC runs next to no overlap (to stop "push through)- and overlap is the mechanism which helps exhaust tuning for torque.
If the pipes behind the cats are constricted- you might gain a smidgen of torque at very low rpm (1000 rpm) however alot of this wouldn't be realised because you're so knock limited there anyway. However the backpressure increase in doing this would knock ALOT of power off your engine.
A good compromise may be to run a lower backpressure system as the engine responds nicely to lower backpressure, and you don't have the same noise contraints to meet as the manufacturer did.
Beware of SC pulley ratio changes also- the pulley on your Jag currently was set after alot of painstaking work ( I think the current ratio is about 2.05) if you make the Super charger workharder,the supercharger will drive less efficienctly and Eaton have set limits as to how fast to turn the M112 Supercharger unit.
If you want to change the system for noise, fine, but don't go believing claims by the aftermarket indiscriminantly. Most of them, even supposedly reputable ones, don't know what they're on about.....
>> Edited by Marquis_Rex on Wednesday 7th September 09:49
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