Archive for the ‘Uncategorized’ Category

Accelerator Pump Jets

June 14th, 2012 No comments

So, last October I went to Thunderhill and had some carb tuning done at MCE. They did a nice job – leaning it way out and boosting the HP and torque about 15 points each. However, once they were done, there was a big hesitation right at the beginning of accel that was really disturbing on track. I asked Scott about it, and he suggested that with it leaned out, it wasn’t getting enough gas right at the first push of the throttle, so the accelerator pump probably needed bigger jets. It’s taken me 9 or 10 months to finally get around to replacing these things! I had some in the garage already. The existing jets were 28 (primary) and 31 (secondary). I watched this video here, which gave me a great instruction on how to pick and install new ones.


I tried out 31 in front and 37 in back and took a test drive. Better! but still some hesitation. So I put a 37 in front. Great! the car is off the line like a mountain goat. I may try out 37/40 at some point, but the 40s I have are a different shape, and I don’t have the necessary drilled screw, per the video.


I’m looking forward to getting this on track again to try it out. There’s some chance of me going next weekend to Laguna. However, it’s a 90dB sound limit! I’ve been metered at 94.5 at Laguna before but then passed the 92 limit by just lifting a bit when I passed the booth. Not sure about 90. We’ll see how it shakes out!



There was still some initial lag. I took a look at the throttle action and pump actuation. I saw that not much was happening at the beginning of the throttle action, so I have moved the cam to position 2. I reset the clearance at WOT to .015. The jet seems to start much earlier now and that may be what I need. I also learned from the video that I should have the 50cc pump diaphragms in there for these .037 nozzles. Not sure if that’s what I have! I’m on the borderline though if not, so I think I’ll run this and see what happens.

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Laguna Event

September 7th, 2011 No comments

Took the car to Laguna in March. Craig drove his BMW and had a great time. The track was rainy in the beginning of the day, which made for some excitement! I ended up wrong-way around after Turn 2 entrance. Thereafter, I learned to be subtle with the throttle. Rain teaches you a lot.

The car was fantastic!

More and more confident through the day, and started really getting on it after Turn 5 where the sound station is. Black flag… Came in at 94.5 dB so very close. Just backed off a little after that in that spot and the rest of the runs were fine.

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June 20th, 2009 No comments

I have to give a shout out here to my mentors for this project – Scott and Ray. These guys are in Nor Cal Shelby Club with me and they’ve been incredibly patient with my incessant questions, and giving with their time and advice. These guys are both intensely smart, meticulous engineers who are passionate about open tracking their vintage Mustangs and have spent many years building and rebuilding them.

I’m feeling really confident about my project at this point. I think it’s going to be a fast, fun, and safe car. A lot of times when you do a project like this, you’ll buy parts, put things together, realize you got the wrong stuff, and lose money as you buy all new stuff and try to move the old stuff on the used market. Sure that’s happened a bit to me, but remarkably little, and that’s largely because I have some incredible guides in the process. I’m getting the benefit from their long trial and error processes, and their experience and ability as engineers. I wouldn’t be able to take on these kinds of projects without them.

Thanks guys!

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Moving the Battery to the Back

June 4th, 2009 No comments

A lot of folks move the battery to the back of the car to help out the weight balance. This was done in the early GT-350s, until some time in ’66, when people started complaining about fumes in the passenger compartment, and then they moved it back. I thought about it, but while reading Race Car Engineering and Mechanics by Paul van Valkenburgh, I found the formula for calculating the difference it would make.

The formula is:

((component move distance in inches)(component weight))/(vehicle weight) = (CG distance moved in inches)

This comes out to (144×20)/2500 or so (could be up to 3000 lbs). So I’d only be moving the center of gravity back about 1″. Not worth it! Not to me anyway. That’s the sort of thing that would be a great part of a bigger plan. If you’re moving a lot of stuff and lightening the car a lot, it would be a part of a larger difference. For me, my car is not the sort where I’m getting every last HP and every last bit of handling. I’m not stripping out the interior or putting on fiberglass panels (except for the hood). I doubt I’d notice it at all, though I don’t doubt it makes a difference for someone.


May 24th, 2009 No comments

So I’ve read some great books along the way that have helped me out with my journey. I mentioned Carroll Smith already. Here are some, titles:

Carroll Smith:

  • Drive to Win
  • Engineer to Win
  • Prepare to Win
  • Tune to Win
  • Nuts, Bolts, Fasteners and Plumbing

These all work together as a great set. They’re old, but so is my car! And the basics are all still good. I learned a lot by reading this set (a couple times).

Paul Van Valkenburgh: Race Car Engineering and Mechanics – great, in-depth discussion of race car engineering. A dose of physics and math but nothing too out of control.

Paul Van Valkenburgh and Mark Donohugh: The Unfair Advantage – this is Mark Donohugh’s story of his racing career, mostly with Penske Racing. He was intensely involved in the development of their cars, and Penske Racing made a lot of breakthroughs during his time there. Reading it makes you feel like you’re there. Great stuff.

I just ordered Race Car Vehicle Dynamics by William F. Milliken. I think this one will be on the more hard-core side. I expect there will be a lot I don’t get, and I’ll have to go back and study my math. I can’t avoid it!

I’ve also learned a lot from the magazine “Race Car Engineering”. This is a great magazine that has some stuff I understand, and some stuff I don’t. In a lot of cases, the stuff they work on is about 35 levels above what I’ll be working on, (and 40 levels more expensive), but it’s still very interesting and very useful. I find that most magazines have very little substance and can be consumed in 20 minutes. Not so with RE. It keeps you thinking. Right now it’s one of my 2 favorite magazines (the other, for different reasons, is MotorSport).

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