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tj930 tj930 is offline
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Join Date: Jun 2008
Location: England
Posts: 301
Woah! Woah! Guys!... I have a certain amount of agreement with both of what you guys say.

For starters, I've taken my car to x3 different 'rolling roads' in my time and seen x3 very different sets of data. Now the runs weren't done with the car in exactly the same condition and on the same day - but the old 'seat of the pants' Dyno is fairly accurate at telling whether the car is running well or the car feels sick.

i) kkk-3LDZ, SC Cams but cracked exhaust header - 220RWHP (Lambs Garage, Chesterfield)
ii) kkk-K27-7200-S, SC Cams, engine rebuild, new exhaust - 276RWHP and 293RWTQ (AET Turbos, Sheffield)
and
iii) Same spec as ii and taken 1 week afterwards - 316RWHP - est. 376FWHP and 404FTLbs (DSA, Oxfordshire)

Since (i) couldn't log AFR readings if they went below 10.5 (it just flat-lined at 20.0 after that point) ; on Dyno (iii) I saw a stock, 7-year-old 996tt register 433FWHP the next run after me; and (ii) doesn't employ a roller but bolts directly to the rear wheels - I'm inclined to think that the guys in Yorkshire have the most accurate Dynomometer.

But let's be realistic here guys - we might as well be talking about 'speak your weight machines'

When you're talking about big numbers, a 1% difference is itself a big number! Tuning on the Dyno is a great idea for getting a base map sorted out, but what REALLY matters is the tuning on the road because that's where the car spends its life. (It's just too easy for Dynos pulls not to be conducted in repeatable, Scientific, controlled conditions.)

And, Brian, early in the thread you made a fair point about air intake temperature into the turbocharger... Well I've got a graph (which I'll post up as soon as my FlickR account reactivates itself) taken on the 2nd Dyno, which shows the repeatable results of adding a blue 'air scoop' to pull colder air from rear wing instead of from above the warm engine. (My car has had the broken air conditioning unit removed, so there is an open hole to the outside world.)

The graph shows a difference of 19.2 RWTQ and 14.4 RWHP. But do I feel any difference when driving the car (with an additional 17FWHP)? Not a jot of it - I want to do 2 controlled 60-130 runs (with and without) and see if there is any positive effect.. I'm doubtful - I reckon the scoop's extra few grams of weight may actually slow the car
Old 05-28-2010, 08:41 AM
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