13-04-2012, 04:25 PM
I won't say big turbos are more laggy, but it's often not exactly desirable to have a massive wodge of torque low down anyway.
I actually prefer the rainbow output of a 'proper' turbo diesel.
VNT flattens things out and lets you get massive peaks low down, but the result is a curve which isn't so sweet to drive. It's harder to anticipate when you are 'driving' the car (ie, enjoying a back-road blast)...
My FMIC HDi with GT15 spooled up really low down and went like a rocket, but I'd have given some of that up for just being a bit smoother and easier on the clutch/drivetrain/less likely to spin up, and gone for a bit more at the top end.
The shape of the curve is just as important in my view, balancing torque with power to give a rewarding run through the revs. Just going for the most you can everywhere looks good on a before/after dyno, but the result when driving is often just unrewarding.
Add too much torque down low and it makes the top end even less inspiring than it already is in a diesel.
Yes the specs of VNT appeal on paper and on a dyno, but I think I'd find myself tuning out half of the 'benefits' it offers just to make the delivery feel a bit smoother and peakier!
Getting the biggest numbers in my view is missing the best point of making cars faster, which should be all about appealing to what drivers really want. And that is a bigger grin on their face after going WOT from the lights, or when guiding their car around a long sweeper. Neither requires more power, but both require a characterful interesting delivery and good response
And that is where you are right Ruan, the Td when tuned has so much character. The way it makes it's torque is just as important as how much it makes.
I'd happily give up VNT for the cost/hassle/benefits I don't want, to retain benefits I do want in a good old naturally wastegated turbo delivery... I'm sure on the road, track or drag strip, a 180bhp VNT and a 180bhp hybrid would be inseparable anyway... only on the dyno would you notice... and on your wallet
Dave
I actually prefer the rainbow output of a 'proper' turbo diesel.
VNT flattens things out and lets you get massive peaks low down, but the result is a curve which isn't so sweet to drive. It's harder to anticipate when you are 'driving' the car (ie, enjoying a back-road blast)...
My FMIC HDi with GT15 spooled up really low down and went like a rocket, but I'd have given some of that up for just being a bit smoother and easier on the clutch/drivetrain/less likely to spin up, and gone for a bit more at the top end.
The shape of the curve is just as important in my view, balancing torque with power to give a rewarding run through the revs. Just going for the most you can everywhere looks good on a before/after dyno, but the result when driving is often just unrewarding.
Add too much torque down low and it makes the top end even less inspiring than it already is in a diesel.
Yes the specs of VNT appeal on paper and on a dyno, but I think I'd find myself tuning out half of the 'benefits' it offers just to make the delivery feel a bit smoother and peakier!
Getting the biggest numbers in my view is missing the best point of making cars faster, which should be all about appealing to what drivers really want. And that is a bigger grin on their face after going WOT from the lights, or when guiding their car around a long sweeper. Neither requires more power, but both require a characterful interesting delivery and good response
And that is where you are right Ruan, the Td when tuned has so much character. The way it makes it's torque is just as important as how much it makes.
I'd happily give up VNT for the cost/hassle/benefits I don't want, to retain benefits I do want in a good old naturally wastegated turbo delivery... I'm sure on the road, track or drag strip, a 180bhp VNT and a 180bhp hybrid would be inseparable anyway... only on the dyno would you notice... and on your wallet
Dave