Amazing car , enjoy in good health

 

Senna. PJS, Savy,Tripleblack,tkrtape,Bradford,Lars,Sharpman,bbywu,Tacet,F1crazy,TTtu rbine – many thanks guys for your comments....

GT2urbo, mine took too long but they are doing another one for a guy from Munich and the build “should” take 6 weeks.

Rickard, Look forward to your details although I suspect yours will be track orientated, mine is daily driver ?

I mentioned above that the engine was finally signed off the dyno again with the bigger VTGs and I was given a set of the customary RS engine dyno sheets





You notice that they hadn't sorted the scaling out since 900NM was way above what their old dyno could measure and I guess their graphing software needed some adjustment.
I extrapolated the torque from the power curve using
NM (Torque in ftlb * 1.36) = (hpSAE (PS*0.9863) * 5232) / rpm

and stuck it in excel to give the real engine dyno curve



Because this was the first 3.9 VTG engine they had done using the 997 turbo intake system it needed quite a lot of fine tuning on the road in terms of setting up how the boost came in at low revs and how the aforementioned traction control worked.

When I first tested and data logged the engine at the airfield I noticed that consistently it was producing its maximum MAF reading at right around 6600rpm. Now it was my guess that maximum MAF reading = peak power so the peak power was different on the road to what was recorded on the engine dyno and certainly the pick up at low revs does not seem to mirror the engine dyno numbers in terms of what rpm the boost comes in, it comes in sooner on the road. The latter will be parttly due to the fine on road tuning and the former is just the way it turns out....



Sharp eyed amongst you may notice on the numbers above that I am doing 291kph (thats 181mph) at 6666rpm, that is gearing of 27.1mph/1000rpm in sixth gear so at factory limit of 6750rpm my car is only going to manage 183mph – something is different ?

Changing gear

I met a pal the other day in a sports club car park, he had just arrived in his new Mclaren (in orange – yuk, looked just like a Lotus on first sight) and we started chatting cars. He has done a lot of Porsche GT3 Cup type racing and owned all sorts of exotica. He absolutely loves the double clutch type gearboxes (says he prefers sequential) but even on his road cars he says he would not go back to manual......

Well I am different, I spent hours as a young kid sitting in my parents friends cars on our drive way, (keys out) pretending I was driving said cars and changing the gears using the clutch, imagining the revs soaring and timing my changes as the red line was hit...... nothing has changed all through my driving life, I love the physical pleasure of operating clutch, gearbox and engine and I know I am not alone in these forums....

So the 997GT2 ?

At 7000rpm it does about
2nd gear 84mph
3rd gear 114mph
4th gear 145mph

Now the question begs, just how much revving out gear change action is one going to get with this gearing ? Second gear is ticket time and third gear is ban time, fourth is tabloid newspaper and probably jail time !!

I had a plan, I got RS to get hold of a new ring and pinion which I think I first read about on here, it is a 9:35 set, with a view to more gear change action.

I was a bit worried about it being a bit too lively in first and second but pressed the button anyway.


On the road the gearing ended up with a 7000 gear change (7100 limit) at the following
2nd 74mph
3rd 100mph
4th 128mph
5th 157mph
6th 192mph



Pleasingly the GT2 is able to give some semblance of traction in first and second gears and the objective was achieved apart from that pesky 6th gear which now only managed a paltry 192mph !

I decided I wanted a sixth gear which would do this engine justice, my UK shop said I should change fifth as well otherwise I would lose acceleration as the
drop from fifth to sixth would be too great.

I played endlessly with the gear calculator and what is worth noting is that for my car the rolling circumference (ie tyre diameter) is not what the book said or even what a theoretical calculation should be and in the end it was RS Tuning who gave me the correct size by measuring a 997GT2 rear which they had in the shop. When I say “correct” I mean this number (663.6mm) gave the exact correct GPS speeds which I was observing with the current set up and they were quite different to the speeds one gets if one feeds in Tirerack's 26.7” or 678mm the numbers from the gear calculator below are not what I am observing for GPS speeds however with RS Tuning's 663.6mm the speeds are spot on (I still don't quite understand this but am happy with the result)

So I decided on a set of gears which GT in the US had in stock 30:20 to give the ratio 0.67 to hopefully achieve the result below.



You may be thinking “how come he has put in a 7300rpm change when he just said before it had a 7000rpm limit” ?

Well one of the benefits of its last trip to Germany was that I presented RS with the data about my on road peak power being at 6600rpm not the 6250rpm (which the dyno showed) and also showed them the data below which to my simpleton thinking (see my comments in red) shows that I still have 96% of peak power MAF at 7048rpm so maybe the whole power curve has shifted up somewhat and the motor is still making good power into the 7000rpms.



Now rpm limits on turbo motors and in particular on road tuned turbo motors are a bit of a “red line” (no pun intended) area for RS, he makes the power lower down so the engines last a long time and he refuses to let them rev.....but a few times I barracked him about various US Tuners allowing 7500+ on stock motors and mine was supposed to be his fuilly built masterpiece..... I also showed him a video of my pal's (who posts on here as GT) Sportec engine with the rev counter swinging round to 7800rpm and I told him they had guaranteed it !

Anyway whatever elements of the above worked because on the new ECU they fitted they announced to me that the rev limit had been raised to 7400rpm – this is quite a thing for them since customers are certainly not supposed to know best !!

So equipped with new taller sixth gear and 7400rpm limit I ran the engine again at the vmax event last Saturday (I was actually changing at arount 7000/7100rpm).


You can see the top gear doing its thing. I am running different tyres (Conti vmaxes) so I think maybe the diameter has changed and also some tyre growth at 205mph since the mph/1000rpm thing wasn't matching up perfectly.

Now here is the awesome bit of info I gleaned when analyzing the data......

A longer sixth gear, one which will allow 220mph at 7300rpm instead of 201mph at 7300rpm will accelerate slower in the gear particularly (as my UK shop pointed out) as on the fifth to sixth change the rpm drop to near 5000rpm (I only revved to about 7000rpm in the fifth to sixth gear change in the chart above) ?

Well the data says otherwise and exactly as my good friend Jean cacluated in theory the acceleration in my new sixth is just as strong if not slightly stronger as it was with the older shorter ratio – I measured the acceleration from 252kph to 310kph on same track with both gears, comparing about 4 runs each and they are nearly identical with the longer gear being slightly faster on average..... that is VTG torque magic

 

Respect for what you are doing Toby.
Hat off.
Best, wurlie

 

Toby you always wanted a 7000+ Rpm since day 1

 

+1 wow...

 

Fantastic project! subscribed!

MGR

 

Ye smy car is more race oriented but still intressting with my timing figures and my intake temps and etc.. my car does 100-200 in 4,7

 

Nice write-up indeed! It sure gets scary above 200mph....

 

Great work Toby!

Now buy a camera mounting kit, so your VBox videos are watchable.

rgds

Guy

 

You are one crazy petrolhead, a speed junkie and a lost cause. Bravo.

btw Don't worry, he did the same thing to me and I had to use "diplomacy" to make them raise the rev limiter in the GT3. Asked for 9K.. settled where I wanted.

 

makes me want to ship my car to UK and do a run next to Toby up to 205 miles per hour! Want to see my 7800 rpm limit hit at 6th gear and see if the engine holds! lol!

 

Toby, you mentioned you swapped intake manifolds to a modified 997TT - so you have abandoned the "expansion" manifold concept to increase flow at a lower boost level?

 

Wurlie,Basal,MGR, thanks for reading

TT Turbine, what petrolhead doesn't like revving out

911Slow, It is a feat getting these stubborn engineers to change their views - well done !

Sharkster, the 200mph club is growing

Guy, Exactly where do you want me to attach this camera, to my 3 year olds car seat in the back

Rickard, yes I am looking forward to sharing data with you, particularly further up the speed range, but you are using conventional turbos I think so you will not be pegged at 700hp ?

GT, When you stop terrorizing mainland Europe in your beast we need to do that back to back, there's a lot to learn from that comparison. same day, same conditions....

bbywu,
Bob, following on from my comment to GT above, he runs expansion manifolds and his acceleration indicates he can run 740hp, this is contradictory to what RS told me, he tested the expansion manifold on the engine dyno and says 680hp is the limit. He says it cannot flow enough air, not big enough......

So the turbo manifolds are to flow the air needed to go above 680hp and theoretically at lower boost although my maximum power only available sub 50c IAT is at 1.55bar so not exactly lower boost ?

Using turbo intake manifolds was the biggest challenge because the GT2 ECU could no longer be used, the 997 turbo program had to be completely re-written to work with the two wheel driven GT2 with all the interaction between the 4WD system being redundant and a new traction control had to be written in..... this is what took them 3 weeks with the Porsche/Bosch engineer !

What I find baffling is that other tuners say they "use" the 997 turbo intake on GT2s without problem, notably Todd K...... I suspect a little band aid/hot wiring is going on ?

 

Aye it is! I was seriously impressed with the GT2RS although _not_ on 91. Shove some 93 in there and it runs like it should. You've got a LWF and 764 PP in yours, right?

Hmm I wonder if there's a xena diode or resistor here and there

 

Wow! This is some crazy build. I probably would have given up on the car She looks beautiful!

Kudos to you for being so determined and seeing it to the end