KPG

[QUOTE=NineMeister.
To make the power estimate more accurate we have to measure air resistance and rolling resistance, therefore given that we all have an AX22 or Driftbox to play with anyway, the simple solution would be to log the coast down time from say 100 to 60mph and then from 40 to zero. [/QUOTE]

The new Racelogic Performance Box has a coast down feature to measure air resistance. http://www.vboxusa.com/datasheets/Pe..._datasheet.pdf

Oh, I have a group buy for the performance box up a 6speed if anyone is interested. We already have enough orders for a 10% discount. Kevin


http://www.6speedonline.com/forums/s...ad.php?t=66304

NineMeister

Careful Geoff or you will be branded a heretic, but I'm glad that you mentioned this, especially given your vast experience of chassis dyno tuning.

One of the common misconceptions is that an engine dyno is the best way to tune an engine simply because it is capable of holding the engine at constant speed for extended periods. Whilst this may be the best way of measuring the "true" hp of the engine under the most extreme conditions, I do not believe this to be the best way of tuning the engine for the real world. There is no doubt that an engine tuned this way will withstand anything the road or track could throw at it, but what is the point of building a bombproof engine that does not reach its potential unless it runs at 180mph in top gear? (Before anyone jumps on me for saying this, I'm not writing this with anyone in mind - this is just an observation of how we can potentially make all our cars faster)

It has always been my view that since engine power is required for the sole reason of accelerating the car it is fitted into, the fact is that the engine is loaded under a constantly changing rpm condition, therefore the best way to tune the engine is to maximise power for transient loads. There are a few transient engine dynos available but these are not common and fairly expensive.

As you say a typical inertia chassis dyno run lasts around 3-5 seconds in top gear, however in ideal circumstances any dyno should replicate the identical acceleration rates to that which the engine would experience in the car in all gears. This is one aspect of tuning that I am keen to investigate in more detail, hence why I opted for a software/hardware upgrade for our Bosch dyno that has provision for adding both a fixed % of eddy current brake load (to simulate different gears) and also a variable "air resistance" brake load to simulate increasing load from drag.

Now, with respect to turbos that don't spool up fully in 2nd or 3rd gears, surely if you want to accelerate the car as fast as you can, the solution is to either fit turbos with a faster response or simply tune the engine differently for each gear.....

Geoffrey

Colin, I will agree with you on your observations, in fact, if you have engine data logging, and you run the engine through the gears you will see different AFRs at the same boost pressure and RPM depending on gear, particularly with a MAP based load strategy. This is indicitive of the pressure ratio across the engine changing based on gear or said another way, load. I believe this is primarly a back pressure statemet. I have begun to tune my MoTeC cars using exhaust back pressure as a compensation and it allows for more consistent AFRs in different gears.

I think that if you are going to use a dyno, engine or chassis, you need to be able to properly simulate the load the engine will see. I generally do my swept runs at 300rpm/sec which allows for loading the engine similar to 3rd or 4th gear in a road car.

AVoyvoda

"Now, with respect to turbos that don't spool up fully in 2nd or 3rd gears, surely if you want to accelerate the car as fast as you can, the solution is to either fit turbos with a faster response or simply tune the engine differently for each gear....."

Hi Colin. Can you explain how the above statement is different from: "If your car isn't fast enough, you need to get a different box or re-gear". Isn't it exactly the same concept, approached from another angle? Not as optimal perhaps, but the same concept nonetheless.

In essense, you are saying: "Change the engine to fit your gears". I am saying "You may also consider changing the gears to fit your engine"

And, if you accept the logic of the above, wouldn't you then have to agree that gear changes should be counted?

Jean

Sorry to cut through the little advertising break , to try to answer this interesting question posted by Colin,
I have posted a thread here: https://rennlist.com/forums/993-turbo-forum/317062-acceleration-drag-engine-power-applied-formulas-to-993tt.html

If someone is interested to continue this conversation, you are invited to join the thread above...

TB993tt

Here's one for you:
Engine spec was 3.3 with special GroupB+ cams (similar to 964) Holset twin inlet turbo (from Todd Z) B&B headers, High flow metering head, gutted cat, K&N canister filter.
The car ran on Ruf Nurburgring suspension kit, had RS style rear PU and Ruf front spoiler lip with brake cooling air intakes:



-A magazine called Performance style used my car in a group test in 1995. They ran some performance numbers with proper testing kit. The acceleration runs from a standing start were difficult since it either bogged down or lit up the tyres. The numbers used were from a bog down start - mine is the "Mod Turbo"


Also half the pic of the 4 cars at the drag strip - check out the B&B undercarriage


so 60-130 in 11.8s with ~428hp (chassis dyno proven ) from memory weight was around 1420kg and the drags were 2 up so test weight ~1600kg

JamesE

The undercarriage is a result of not routing the exaust towards the front of the car and back round to the back (like porsche did). Saves a reasonable amount of weight and gives much better energy transfer per unit exhaust gas.

What does 11.8 really translate to?

TB993tt

I seem to recall bolting the headers on gave an instant 30hp on the chassis dyno -an impressive VFM mod
Good question on the 11.8s -
The car had a boost spring which gave 1.2bar and no doubt heat soaked away from the chassis dyno #s quickly -I remember in those days reading the quote from RS Tuning and being incredulous to the cost of their 420hp package compared to mine and them warning me not to run mine flat out on the autobahn -its the same old chestnut, it probably had the ~400hp for the acceleration run to 140mph but if I'd carried doing acceleration runs like at vmax it would have had zero hp as it melted itself - no knock sensing boost protecting computers in those days

JamesE

I see. The thing that most (930/965) people don't realise is that a lot of headers have a "poor" wastegate circuit (old GHL's for example). This, to bring up another thread, means that you get boost creep i.e. your 0.8bar spring will produce 1bar boost. So, if I was a betting man (which I am), I suspect that most of the performance gain from some headers, in terms of BHP, is from nominal increase in boost. However, headers are still the best value for money increase in BHP/TRQ (assuming good WGC design) when you think of the weight loss and energy transfer.

TB993tt

I think you are spot on there - I do remember the 1 bar boost spring suddenly (after various component changes, can't remember specifically which but quite possible was after fitting the headers) giving 1.2bar and never quite understood how that happened -interesting

JamesE

I suspect that was kept in the "industry" for quite some time...

Woodster

11.8 relates to about a stock 996 Twin Turbo.

MK

CP

Hi,

My buddy Jason (Atomic80) just posted this thread, 60-130 MPH in 7.42 seconds. There is a video too.

http://www.m5board.com/vbulletin/showthread.php?t=87467

CP

Bill S.

I just got a chance to try the PerformanceBox by Racelogic. I did about thirty 60 to 130 runs on my Ruf and CS. The data is extremely consistant. No errors like several of us in CA have been seeing with the AX-22. Here's my best times:

TB993tt

Bill
That is very consistant isn't it - exactly the same time as your previous runs !

Did you try a crack at the "world's fastest 4th gear only 100-200kph run" your car I'm sure would hit the 200kph (124.4mph) with your ~7200rpm limiter - at the very least you could claim "World's second fastest"

BTW you can change the mph scale to start at zero by editing the axis.