|View single post by Jensenman|
|Posted: 11-20-2010 12:25 pm||
|A lot has happened in my life since my last post, but even with all that the car has had some shakedown events with a few breakages, updates and repairs along the way. Everything has been autocross so far, if all goes well I will be running the first hillclimb with it in spring 2011.
The first event was a small low speed course, I was still learning the car so did not place very well. The motor ran strong and even with the 13x10's I could easily step the back end out on acceleration. I didn't learn much about what the car needed except for one thing: the 13" steering wheel was way too small. There just wasn't enough leverage for the fat tires. I installed a 15" wheel and things were MUCH better.
The accelerator pedal broke off at the second event I ran. Not easily fixed in the field, but it's now been welded and reinforced to prevent a reoccurence. I couldn't get full throttle throw at that event so again I wasn't able to truly evaluate the car's performance. But I was still in the top 10 so that was encouraging! I did discover a disconcerting tendency for the engine to go into 'limp mode'. S5's use an electronic oil metering pump, if the ECU thinks it failed it kills the trailing ignition and drops the fuel pressure so you can limp to the side of the road. Obviously that's not a good thing when trying to race, so I got an S4 ECU and converted the engine to a mechanical OMP. So now that problem is solved. But even with that going on the car was still stinkin' fast.
At the next event, the car ran strong but understeered like mad. This was due to the extremely aggressive Mazda Motorsports limited slip, it's essentially a spool. I swapped a normal spring loaded clutch type limited slip in, much better. The 4:86-1 gear was also noisy as hell, even though properly set up. So it had to come out as well.
The next event was much higher speed, some cars were clocked at 80 MPH. I had a co driver whose input was invaluable. He and I discovered that the brakes were, to put it mildly, inefficient at these higher speeds. I'm glad I didn't discover the brake problem at a hillclimb! This was due to the pedal ratio, the stock J-H is 4:5-1 ratio and I had to redrill the pedal pushrod hole for 6:1. This involved fabricating a new master cylinder mounting plate to raise it 3/4" so the pushrod would enter the cylinder straight. I also was able to finally get some proper heat in the tires to dial in tire pressures. The downside to that event was the motor smoked heavily on deceleration. In 40 runs over two days, the engine used nearly 2 quarts of oil. Not good, obviously a swap and/or an overhaul was in its future.
I didn't want the car sitting around undriveable while waiting for parts etc so I bought another used running S5 13B and installed it. It smokes much less than the first one but still more than I would like. It makes good power, though, and is sitting in the car now. I have the original motor apart and as I suspected the O rings for the oil control rings were brittle. The apex seals were pretty well worn out as well. The big parts (rotor housings, rotors, eccentric shaft, stationary gears and the 'irons') are all good. I'm waiting on the overhaul parts from Atkins Rotary.
The car has been to one other event with motor #2 and it did well, as in top 5 and winning my class. I discovered that the inside front tire was lifting off the ground in very hard turns, telling me my roll stiffness was way too soft in the rear. I have now gone from 150 pound rear springs to 250 pounders. Haven't had a chance to run it with those yet, but the math tells me the roll couple should be pretty close to right.
Something I figured would come up during tuning: first gear in an RX7 transmission is a very low stump puller, then there's a big jump to second. That makes downshifts for very slow corners nearly impossible; second is too tall and first way too low. I can fix that with more 'gear' in the rear so am planning a 4:77-1 ratio swap soon. It's currently 3:89-1.
So it's been an uphill battle but the sun's starting to show through the clouds.
No new pics at the moment, the car looks pretty much the same. Oh, I took both it and my JH5 to a local British car show, there was much head scratching and furrowed brows. :-D
Last edited on 11-20-2010 12:35 pm by Jensenman