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So over the last couple of years, i have been gradually modifying and tuning my 997.1. There has been no specific power or performance goal, rather to gain data and experiment with various setups, The car is tested on my own 4wd braked dyno, which is more or less identical to a Dyno Dynamics. A totally stock 997.1 turbo makes 477bhp on this Dyno, run in 4wd. All numbers are crank.
First off i developed high speed datalogging software which can read any variable in the ECU so that I could get a clear picture of what was happening. Any tune I did was designed to be used at very high speed as I run events such as VMax on the runway, exceeding 300kph many times in a day. The first hardware mods were to remove the cats from the standard exhaust and fit .2 intercoolers. The car made 540bhp on 98octane pump fuel, and around 570 with water injection (no meth). At this point, the standard turbos were at their limit, boost up at around 1,3 bar. They could run a little higher for short periods, but ignition efficiency would drop on anything over 130mph or so.
The next move was to uprate the turbos. The initial plan was to use a GT2 based hybrid due to it's better flowing exhaust housing. Sadly Borg Warner has not been supplying new units to the aftermarket for around a year now, and so they are impossible to get hold of unless you pay Porsche dealer prices which are more than double what I would pay direct. I did manage to get one brand new GT2 turbo which is currently sat in a dark room I therefore had to use my existing cores and have larger compressor wheels fitted as well as clipping of the turbine wheel to increase it's speed resistance and allow more flow.
For some reason, Porsche hybrid turbo suppliers like to quote their wheel sizes by quoting exducer sizes. This is strange, as the exducer has little effect on flow capacity, and is there to allow certain pressure ratio and surge characteristics to be met. The exducers being used are also huge for a gasoline application - 63.5 mm is massive, never mind 68mm. Our VNT turbo's originally started out life as diesel turbos, which typically use much higher pressure ratios but lower flow rates than gasoline. There were a few billet wheels knocking about for use on Diesel turbos and it's these that found themselves into many of the Porsche VNT hybrids. They are generally ill suited, with the exducer being unnecessarily large. It's the inducer that does the flow work. For reference, the standard inducer on a .1 turbo is 43.5 approx and the GT2 is 45mm. They both use the same size exducer. The wheel I'm currently using has a 49mm inducer with a 62mm exducer. A typical "65mm VTG" usually has an inducer at a little under 47mm,
I was expecting to hit back pressure issues and this proved to be the case although I can't quantify them yet The car is on a stock block so the boost and torque is modest in the low range, Power is a little more than I expected, but no matter what combination of boost pressure and ignition timing is used, power drops off after 6300rpm. Two different boost profiles are shown as comparison. Unfortunately, the Dyno pressure sensor is out of calibration, and is currently reading 0.12 bar higher than the true pressure. Peak boost is really 1.52 bar.
Looking at the boost curve, at 6300 the boost tapers down to 7000rpm. This took many many hours of tuning - the goal being to try and hold the power for as long as possible, If the boost was held flat from 6300, power was down at 7000rpm by 20bhp, even though ignition timing was largely the same at 24 degrees. (98 octane pump fuel plus 50/50 water meth). To confuse matters slightly, with the boost tapering down I saw a 20bhp gain, but the MAF reading dropped approx 20g/s, If there was no Dyno and you were road tuning, the logs would be pushing you to keep the boost in, rather than pull it out which is what works best.
Clearly there is a back pressure issue which is not going to be helped with standard .1 housings rather than the preferred GT2. But.... we are still on a standard, albeit catless exhaust. When time allows, i plan to measure the backpressure the exhaust is generating and then move onto a number of custom exhausts I have in the pipe line. The problem is I don't like noise so there maybe a lot of swapping going on It will certainly be interesting to find out just how much I can gain from changing the exhaust!
yes you are holding power better at the top end. I am keen to see what happens with an exhaust change here. Your race fuel map runs more boost at the top end than your pump fuel map. I don't think I can run anymore than I already do with this current hardware spec even with race fuel. Of course race fuel would produce bigger numbers on the same boost. This may change with an exhaust swap but will need to be tested. When you are in the UK give me a shout and we will do some back to back dyno pulls
Nice work, Rick. When you measure backpressure,measure the boost pressure at the same time as well and calculate backpressure/boost. This will show you the efficiency of your system quite nicely and shows you the point of diminishing returns where adding more boost just creates heat.
What I don't like is running catless. For environmental reasons you shouldn't do that. HP loss is not that much of an issue if you use good cats. Just a personal opinion.
Nice work, Rick. When you measure backpressure,measure the boost pressure at the same time as well and calculate backpressure/boost. This will show you the efficiency of your system quite nicely and shows you the point of diminishing returns where adding more boost just creates heat.
What I don't like is running catless. For environmental reasons you shouldn't do that. HP loss is not that much of an issue if you use good cats. Just a personal opinion.
That's the plan, and i need to get on with it! Re the cats, it was a last minute thing in lieu of a new system. We will see what the future brings!
Did modify your tune after water inject, or were the gains purely from the water inject?
I tuned for it, without any tuning there was around a 20bhp difference in peak power. However, without the water you would see some drop off at high speeds, where as there is none with the water. This is with .2 coolers which are very good for their size. With larger coolers i imagine the gains without tuning would not be as significant.
Add some cut outs and keep stock exhaust! Best of both worlds!
Ecu is OEM, my own software.
I am seriously considering doing some cutouts, perhaps putting a hole in the cat towards the tailpipe end and putting in a valve. It would be loud with it open though....
