Doing more work on the Sprint-T

I’m still thinking about that car. I ran the numbers again for the PG transmission and it turns out I would only have to buy one extra set of QC gears for the SCCA Solo Racing. For the Goodguys Autocross series I could just swap the gearset over, that is reinstall the gears for underdrive instead of overdrive. Turns out there are no gears I could use that would get the final drive low enough (high numerically) to get to redline at 35 MPH in low gear with a PG transmission, and swapping places so the overdrive for highway cruising is an underdrive for racing gets me a 37 MPH redline in first gear, and with the gears in highway configuration 1800 (+/-) RPM in high. Thirty seven MPH is close enough in my book. If you want numbers the spur gears (set 30A, 26/15 teeth) and a 4.11 ring and pinion would get a 2.37 final drive in highway mode, and a 7.12 final drive in Goodguys mode.

So I would be swapping convenience at the track with better in-town performance for an extra 50 pounds weight. Installed costs would be similar, so that’s a wash. Basically with the 700r4 or the electronic equivalent 4l70e I could drive up and swap tires and adjust the suspension and be ready to go racing. That’s because of the 3.06 first gear and the 0.70 4th which gives me the RPM I want on the highway with the gearing I need to race in low gear. Running the PG I have to open up the QC and change the gears, in addition to all the other things.

The good thing about this is I have the ability to make models of both configurations. I have the SBC backed by a 700r4, and I have the LS7 and know where to get the 1/25th scale PG transmission for $2 plus shipping. I think while I’m at it I will order the Wide 5 wheels from the same vendor to spread the shipping costs over a larger order.

Speaking of Wide 5 wheels I have been thinking about how to better make those in scale, to any width desired. What I was thinking about was using a photoetched center like the Dirt Modeler 1/24th scale wheel that fits into a machined recess on an aluminum wheel half which gets superglued to the center and an outer half so that the center looks like it was welded to the wheel (or bolted depending on the particular center). The outside diameter of the wheel half inside the flanges is 0.6″ while the ID is 0.505 leaving .04 for holding the center and 0.0075 for a flange to center the wheel center while also giving something for the superglue to glue together. The wheel halves could be made whatever width desired to give correct backspacing and width for the model being built. Meaning there would be a way to build an accurate pavement sprint car or Supermodified complete with the 18″ wide wheel covered in 20″ wide tires. (Tires made separately.) Of course the drawback to this is a separate Wide 5 hub has to be built to mount the wheel on.

OK time to stop typing.

Billed @€0.02, Opus


Leave a Reply

Fill in your details below or click an icon to log in: Logo

You are commenting using your account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s