D-day arrives and it's an earlyish start to get over to emerald. It had been snowing every night for the past week so I was well prepared for a horrid drive over. In reality though we had a stonking drive over in terms of scenery, covered in snow and frost with bright sunshine and blue skies. The cold really wasn't a problem as I'd prepared for it with thermals and sallopettes. The new sidescreen worked brilliantly and the extra elbow-room was much appreciated.
Dave Walker took a look at the setup and expressed doubts that we'd see much, if any improvement from the new plenum - this agrees with the various "experts" on the boards that say that there's no point changing plenums till you're aiming for 450BHP+. I was hoping for a little improvement but given the design compromises would have been happy if it had worked no worse than the old one given that the change is primarily intended to ease packaging.
I went first to get the baseline run and all looked ok till we put the power down, which was when terrible wheelspin hit, despite both Adam and I sitting on the bootbox. We tried warming the tyres up some more and using a whole load of gloop on the tyres to help them stick. The gloop in question is "adhesive grease" - yeah, adhesive grease, go figure! Finally we went back to first principles and bled out 11 of the 35 psi that the tyre place had put in the wheels when I had the tyres changed a couple of weeks ago. I had been meaning to drop them down myself but had been waiting for an oportunity when they were hot, D'Oh.
Anyhow we did a run with traction this time and things looked great until the wastegate opened, the boost dropped down from 20psi to 15psi, from this point on the torque dipped and whilst the power climbed it just didn't do what it was supposed to. Rather than the hoped for 300-330BHP we instead were getting just 240. We talked things through and couldn't really come up with any good reasons, other than the boost levels being lower than expected. Comparing the plot to one done back in November 2000 when the engine was sickly things looked *very* similar. Lambda reading was perfect and flat so it wasn't fuelling and we were a bit confused.
A couple of frantic phonecalls to the most wonderful Steve Wiseman reassured me that the engine was probably behaving as it should and all that was required was more preload on actuator, which I'd previously set very conservatively. With that in mind I planned to up the boost and change the plenum and see what happened, commiting the cardinal sin of changing two things at once. Time was running out though and I wanted some nice big numbers to cheer me up.
So I fitted the new plenum which turned out to be a much more involved job than I'd planned and I'd only just finished by the time Dave had finished mapping Adams car. Whilst the fuel rail was off I got Dave to test the injectors, just to rule out anything in that area. The injectors were within 1% of each other and the spray pattern was good so back on they went with a set of new O-rings for good measure.
On the rollers Dave picked up a hesitation which we initially thought to be fueling reted as it was quite a soft misfire so we aborted and after some faffing we decided that the TPS on my spare TB was probably the culprit. So off came the TB, I swapped the linkage over and with Adams help we fitted the original TB back on. Dave convinced me to back the wastegate preload back to the original setup so we could compare like for like and we could after all always do another run and there was no point risking anything going wrong by pushing it too early.
We spun up the rollers again and once more we were getting wheelspin again so more grease, a bit of tyre warming and off we went. Lots of whooshing and noise later Dave backed off and coasted down to see what had happened. We'd definately got traction so he pulled up the baseline that we'd done. The solid line was somewhat lower than the dotted one and I started swearing at myself, wondering what I'd done wrong - I'd done my research, the design *should* work. So I started working out where I was leaking boost, was the pipework leaking perhaps?
It was about this point that Dave hopped out of the car, shut down the blowers and said something like "Well that's alright innit." The I twigged, the dotted line was the new plot! At first Dave didn't believe that I'd returned the preload to it's original setting. I had though, absolutely spot on what it was before as I'd very carefully noted the number of turns it had gone and it's only possible to set it in half turns. The reason for his disbelief was an extra 1-1.5psi of boost throughout the plot.
Because we stopped the run at only 5500rpm versus the supposed peak rpm at 6500 we can only speculate what it does beyond but it looks reasonable to assume that the 15-18bhp difference that we saw continues to increase. Peak power that we saw was 255bhp.
As far as torque goes it was up 20lbft in places and it pulls like a train with 150lbft at 2750rpm increasing to 254lbft at 3600, with 240lbft all the way from 3500 until we stopped the run. In that respect it's utterly amazing, as soon as it's got boost you've got a more or less horizontal straigt line of torque.
Everything does seem to indicate that if the boost is wound up to the prescribed 22psi we'd be right in the 300-330bhp ballpark that we were expecting to be in. Having thought it through though I don't think I want to go that route at present, I already have a car that'll do 140mph+ and has more power than I can make the most of and on wintery roads I'm plenty likely enough to end up in a hedge as it is.
OK, so I'm a little disapointed that I didn't get a big number to shout about but who cares, I'm happy with it as is, I've proved that my plenum design is good, yields useful amounts of free power and disproved the myth that a replacement plenum is a waste of time. Dave Walker though is something else, I still can't believe that I spent 2-3 hours on the rollers for very little money. I was actually complaining that it was too cheap when I thought he was charging me twice what he was quoting! I really can't recommend him highly enough, it really is no wonder that he's booked up 6 days a week well into next month, top day out and one I hope I'll be repeating soon.
If you're looking at the graph the green line is lambda and is saisfyingly flat where we care about it. The solid lines are before, the dotted are the after plots. Boost shoots up as we go into overboost then drops back to the held levels. Torque is blue and power red. The relative lumpiness of the graphs is because the wastegate is fluttering open as it tries to hold the boost steady, of course this has a knock on affects the other plots as well. Winding up the boost won't affect things below 3500rpm, but from then on it'll just shift everything upwards.
Sidescreens are both in place now and look great and work pretty well. I've also had the tonneau cover modified by D S Thompsett in Cambridge, the result looks excellent and the flap over the seam should keep the rain out.
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