GT750 Powered Race Car (D-Sports Racer)

[sav0r]

We had a fairly successful outing yesterday. Despite on and off drizzle there were enough cars to keep the track dry for our three sessions. We probably ran around 20 laps total despite having to go through basic checks with several stops through the pits.

Cooling seems to be working very well. That huge impeller kept water temps against the thermostat during all runs. I think we are good there. Ambient temps were in the low 50's, but if we had a major cooling issue it would have shown up despite that. The new water pump cover did exactly what it should do, which is hold the water in and get it from point A to B. The major clutch slippage issues we had are completely gone. The brakes work and work well, which is confidence inspiring. This all added up to a huge jump in performance from our last outing. We also went significantly longer in final drive ratio from our last time out, that made a huge difference in drivability. The engine seems to have relished in it too.

Jetting seemed very good and the engine changes we made over the winter kept the RPM range in a much safer range. It was still pulling hard at 8500 and definitely would keep going but grabbing the next gear put it back in the meat of the power. We ran a mix of the oil pump and 40:1 premix, it produced a nice blue smoke once cleaned out and fully warmed up. The car really hauls and despite us not really evening coming close to the full potential of the car we were able to outpace a lot of serious hardware. We managed 120mph on both the front and back straight and it has a lot more in it. We were geared a bit short for Pitt Race, and I wasn't particularly taking the car deep into the brake zones, nor was I working it particularly hard or well in the corners leading onto the straights. Given better mid corner speeds and later braking it stands to reason that we could probably get another 5 to 10 mph out of the car, and that's a conservative estimate. Plenty of speed left.

The bad news, the charging system wasn't working. We ran out of voltage and gained a high RPM misfire in the second session and eventually it pooped out before I made it back to the pits. It should be an easy fix, except we couldn't identify any issue with the alternator or wiring. The seat and seating position is perhaps one of the worst I have ever encountered. In right hand turns I was falling out of the seat, literally. The track is clockwise, so it was like most of the turns that I was hanging on for dear life and thanking my 6 point harness for not letting me go. A big redesign of the seat is going to have to happen before the next test. Then our data acquisition simply would not work. We couldn't even connect to the logger to diagnose it. Finally, the clutch (as in disengagement) only worked like twice then gave up. Not a big deal at a track with a huge pits where you can get it rolling and then pop it into gear, but it will be a significant issue when we get to the Pittsburgh Vintage Grand Prix were pit space is minimal. Of course the clutch is never used outside of the pits, so the other issues will get focused on first.

All in all, the car is ridiculously fast and I am way too out of shape to drive something this fast. The bad seat certainly didn't help, but I will spend the next few months going to the gym and eating like a bird.

We are hoping for another test in about a month. Plenty of time to get the issues sorted, we hope. The Pittsburgh Vintage Grand Prix is the third weekend in July. So we are feeling a bit ahead of the game, but anything could happen between now and then.

Here's the only picture I took. We built the trailer too.

[Czakky]

  Love these updates. Thanks for letting us live vicariously.

[sav0r]

Hopefully I'll have some in car video after the next test. That way you guys can hear the sweet song she sings.

I spoke with Dave (my father) today. We are doing a seat fitting tomorrow with the hope to make a test Thursday. I hope we will schedule at least one more test before we race in July. Of course we have to be a bit cautious to avoid using the thing up. It's a born sprint racer and the design has little consideration for longevity as far as rebuild cycles are concerned.

In there, we might have time to build out a few prototype parts as well. Most likely suspension parts as the unsprung weight for the car is pretty terrible.

[sav0r]

We decided to postpone. I have to run to Eastern PA for work Monday Tuesday, and forgot I am coaching drivers at Mid Ohio from Friday to Sunday. As to hopefully preserve my marriage I decided two more days away out of the next 7 was probably best avoided.

[sav0r]

We are heading to the track on the 11th.

The clutch seems to be fixed, it was a geometry issue on the slave cylinder. We are doing a seat fitting on Saturday. Nelson Ledges here we come. Probably the best road course nobody has ever heard of.

[sav0r]

The car is together. The seat has been vastly adjusted, I think it will work this time.

We have some updated aero, the front of the car was feeling a spot wandery at top speed while it was perfectly stable up until about 105/110. So we added a front spoiler and two new fender vents on the front. Hopefully helps seal the car to the track a bit better and relieve any high pressure buildup on the underbody. I'm not digging the all black spoiler, it detracts from the look of the gar big time, but it is what it is.

Automobile aero even at high levels was more or less purely an art form when my father built this car, and the car has already gone faster than it ever did in the 70's. As a result I expect us to have to do more tweaks like these along the way.

Nelson Ledges is quite a fast track, in fact it is said to be the fastest road course in North America. I am not sure if that is true, but I do know that it is incredibly quick. We will certainly be geared too short, but we aren't really testing for Nelson Ledge's, we are testing for a street course. So it's important we stick to slightly high ride heights, a little too softly sprung, and a few other small adjustments that make manhole covers, cambered roads, and curbs easier to navigate.

[sav0r]

Well, we got out yesterday. Weather was damned cold and windy, not even getting into the 50's.

Overall it was a good test. Easily the hardest we have pushed the car. We were jetted a bit lean and never quite caught up with it, it didn't want to rev much past 8,200 which we achieved after bumping the mains up.

The good, we are feeling confident with the cooling. The car sat on the thermostat all day. The seat works now, I managed to run 10 laps without feeling like I was going to die. In fact, I was almost comfortable. A bit more tweaking and the seat will be perfect. Nothing broke, and the car ran pretty much without issue, though it did load up on the grid once. Our tires are old as dirt, that may seem like a negative, but given the performance we achieved on old tires we stand to make serious gains on better ones. We have to run a grooved vintage approved tire on the car, not a proper slick, but new ones make a huge difference. I calculated about 6mpg, which puts us right in the window to finish a standard race with our 5 gallon tank. We got actual data, RPM, voltage, EGT temps, wheel speed, lap time, but no accelerometer so no track map

The bad, we still aren't braking quite as well as we should. The brakes work well, but it just isn't stopping as fast as it should. I might not be achieving enough brake pressure, that's a me issue, but at the same time I never felt like adding pressure would make it stop faster. I don't know? Battery management is still a bit precarious, the car is charging now, but system draw is high enough that if we don't keep the car on the jumper things get a bit touch and go when navigating the paddock and grid. The car only charges over like 35mph as the alternator is axle driven. The car is a bit twitchy loose near apex and on power loose after apex. It wasn't exactly confidence inspiring on a track where we averaged 95mph and topped out at 125mph. I wasn't super pleased with our ultimate pace, we should be a good 5 seconds a lap faster. If spares existed for the car I probably would have pushed a bit harder, but there are none, so I had to run up to a comfortable limit and just stay there. I didn't get any video, I forgot the Micro SD card at Mid Ohio last weekend. Jetting, we aren't there for 90 degrees in July as we've done zero warm weather testing.

We may push for one more test, or we may just adjust some things and hope for the best at the PVGP. I don't know yet. The PVGP is late July, so plenty of time to plan and scheme.

[sav0r]

Double posted accidentally.

[sav0r]

I'm going to make a really long story as short as I can.

Front brakes, the balance bar wasn't right, we've fixed that. New rotors and pads too.

The Koni dampers were all junk, they are still junk, just better. This may be good or bad, we don't know yet. Obvious issues have been repaired, but we don't know how that will change the car. We've gone to a droop limited setup, fundamentally better than the old arrangement. Wish me luck.

My father made a new steering wheel, it's awesome (I really wish I had taken a photo, it's classic Dave, super functional and beautiful in that sense), we just need the steering to be a bit less sensitive. The new wheel is larger in OD by a lot, well as much as it can be and still get my legs under it. An 800lbs car is not hard to steer.

We are on track this Saturday. I have two video cameras ready and will take photos too. I assume the thing will melt down before I get actual proof of it turning laps.

[sav0r]

Oh, and I've lost 13lbs and am trying to be less of a garage rat. When I drove professionally, I was fit as all get out. Life has changed a lot in the last decade... I'm only like 15lbs over where I'd like to be now. So hopefully by race time I will get there. 7 weeks to go.

[85RZwade]

This is a great read, Chris. Thank you for the updates!

[sav0r]

Thanks, man! We are pushing pretty hard on this, which is a kind of silly, but I guess we are having fun.

We went back to baseline on the jetting with exception of the mains. We monkeyed around a bunch with the carbs and all of it was bad tuning except that mains. I ordered a new data acquisition system, we will get lap times and real data this time. Though my father is confident he has fixed our Pi system (fourth time is a charm I suppose). We may get double data, which is perfectly okay. The new steering wheel also moves the Pi mini dash up to the top of the steering wheel where I can see it. The seating position is so reclined I cannot view the center of the steering wheel where the mini dash was mounted before.

Assuming we aren't totally lost handling wise after the damper rebuild, we will go faster this time. The brakes alone are worth a good four or five seconds assuming they work as we need them to. We will also dig into tire temps and actually start to work on handling. Testing has almost all been reliability and function based until now. That said, this will be our last test before the Pittsburgh Vintage Grand Prix. So any developments after this test will go straight to the race without confirmation. Classic racing scenario.

[sav0r]

Finally some video.

https://www.youtube.com/watch?v=jyTmjOpD-Cw

We didn't melt down, we didn't break, in fact we ran the most laps with the best reliability in the hardest conditions we have faced thus far. That said, we were left a bit perplexed on a number of issues. There's a lot to unpack here, and honestly I am not sure where to start.

Hopefully video is good for something. Once we have more answers I will talk more on the technical aspects of our test.

[50gary]

I've raced Nelson Ledges,  Have fun and yes, the cheapest way to go faster is losing weight.
  Cheers, 50gary

[sav0r]

In our case the cheapest way to go faster is to fix the brakes and get the handling sorted. I'm sure we can go many seconds a lap faster doing those two things.

Of course it's easier said than done. We are picking through data and performing set down and simply don't have any decent answers at the moment.