Dave gets sent to Coventry...
It’s not often that I manage to escape my rolling road cell but this month I had a day out at TVR power near Coventry. The purpose of the visit was to try to get a better map for Craig Taylor’s twin turbo V8 RX7. TVR Power has a Dynojet rolling road that basically consists of a one ton single roller set in the floor with a dyno on the end of the shaft. This means you can hold load or do accurate acceleration runs - almost without any power limit.
I arrived late (living in Norfolk you forget what a traffic jam is) and the car was already strapped down and waiting to go. After a bit of a delay finding a suitable lap top I began doing a bit of mapping on part throttle. Initially the wheel spin was insane but that was because someone had put some big numbers in the boost control map and we were seeing 20 psi of boost!
I cleared the boost map and tried again. The original springs in the waste gates had been replaced with very light 4 psi springs so the boost was quite controllable. I managed to get a few power runs and once I was happy with the timing and fuelling I started to try to wind up the boost a bit. The level of grip available from the big single roller was impressive but the completely alien set up took some getting used to. I am indebted to Jason Oakley for operating the rollers so that I could concentrate on the map. Jason gave me a head-set with microphone so that we could talk to each other above the noise of the cell. I told him that I felt like Madonna with this microphone kit on and he replied that I didn’t look like her!
All was going swimmingly until we got to one bar of boost when the engine started to misfire. The problem was that the boost was putting the spark out. Craig was still on the running-in plugs, standard with really big gaps intended to fire up weak mixtures – not exactly what we needed. Even though the engine was misfiring we still recorded an impressive 804 bhp at the driving wheels.
Craig reports that the car has better fuel consumption now than when it was a 7.0 litre aspirated engine and it’s pretty fast. Apparently you can cruise on the motorway and just by squeezing the throttle you can leave two black lines down the middle lane! We are now inspired to get our own twin turbo V8 going but we will have to do something about the current diff if we want to run the planned 1200 bhp.
A while back I wrote about Harry Dent’s TR5 conversion. This was basically junking the old Lucas mechanical injection and going electronic. After 400 trouble-free miles it all started to go wrong. There was blue smoke from the exhaust and performance was down.
When the car got back here a compression test showed very little compression on cylinder number six and some pretty nasty noises from the cam gear. The engine was stripped and the cam had something like 4mm of metal missing from the lobes. Basically it was worn down and the particles had been going around the engine. Harry opted for a total rebuild and a replacement David Newman cam. This cam is less stressed that the original and should give a smoother idle and better mid-range torque.
At the same time Harry had a new cylinder head ported by Peter Burgess. Peter has been doing Triumph/MGB/Crossflow heads for almost longer than I can remember and his work is as good as it gets. So with a fully rebuilt brand-spanking-new engine Harry was back on the road – but with lots of pinking noises and misfires. After some initial investigation Harry came back to Emerald for a running-in map.
The pinking was caused by a higher compression ratio and better cylinder filling from the Newman cam. The misfire was another story. The problem was that the rpm signal was dropping out. One look at the trigger wheel showed up a problem. The toothed wheel was slightly smaller than the pulley that it was bolted to. You might be able to see in the pic that the sensor is off-set. If you lined it up correctly the sensor was seeing the balance holes in the pulley and refusing to lock on. It was such a fine balance to get it to see the teeth (and not the pulley wheel) that we could not leave it like that. Half the car came apart and I turned down the Pulley to leave the teeth proud. Then the bracket was re-machined/re-angled to line up correctly.
The engine was fired up and...it was still misfiring and playing up. All that work and no real improvement! To cut a long story short I tried everything to stop the misfire without finding it. In desperation I decided to try a new coil. The coil was new anyway and they never give trouble but I had to try something. The mystery misfire disappeared! Harry has since reported back that the engine “runs like a dream”. Phew, some days are harder than others.
Cosworth V6 Turbo
We see a lot of V6 Cosworth engines here in various cars and some have twin turbos and some have a big single one. Apart from packaging I can’t honestly say which set-up works best. This one had a boost problem though. The waste gate spring was supposed to give 10 psi but this rarely works out to be the case. In this instance we were getting 20 psi of boost where we only wanted a maximum of 12 psi. The compression ratio was stock so we needed to keep the boost down.
Taking the gate apart, one coil was cut from the spring which resulted in a boost reduction but still not enough. Another coil off gave us 12 psi but then the waste gate stuck open. The spring, we believe, was canting over. It wasn’t a question of being too tight to buy a new spring; we just needed to get the mapping done. 310 bhp and 380 ft lbs of torque was the end result.
Yet another RX 7 that has been “destroyed” by fitting a V8 engine. When I say destroyed I am quoting the rotary engine fans here. This one is used in sprints and hill climbs and the 480 bhp LS1 is said to give more than enough power for the weight of the car. It was mapped previously by someone else but it melted a piston. I never get involved in post mortem examinations or recriminations about other people’s mapping work. I just got on and sorted it out. Even more fired up about our twin turbo V8 RX7 now!
This is a very popular conversion but not one I have seen here before. The car was not really ready for mapping so it was left with us. I fitted a crank trigger wheel and made up a bracket for the sensor. The biggest problem was the lack of any seat. Young Jono here brought in a Mini seat from home and we bodged it up so that the car could be driven on the rollers. My first attempt, sitting on an upturned plastic bucket (bucket seat – geddit?) resulted in a near miss when the car shot forward and the steering wheel came off in my hands! Luckily I am a crap driver and I stalled it.
Just over 170 bhp in a Mini should be exciting enough. My first car was a Mini with a 34 bhp 850cc engine. I “tuned” the engine by removing the air filter. Well it sounded faster to my 17-year-old ears.
Don’t you just love ‘em? I do but this one had an idle problem. Easy fix: throttle body balance. This is really important with a throttle angle system because all the injectors get the same squirt regardless of how much air they are flowing. You really do need to balance the flow before you try to get the mixture right. That’s it, lecture over, go and enjoy the rest of the mag.