And just to follow up. The reason the late cars can remove this while the early cars can't is the smller steel tank causes underbody airflow to impact the tire well. In the plastic tank cars this are is shielded by the tank so there is no aero benefit from removing the tire well in late plastic tank car.

The other side benefit is that that late tubs tend to be heavier so this extra weight be nice remove. Even so I wonder how much of that 18lbs was undercoating?

Here's what I've done so far:

WOW! Now that's body prep - should make for a great paint job!

Lookin' good, and on budget , in true Spec spirit!

so for the late cars, there is no benefit to removing the spare tire wheel well except weight savings. the early cars are the ones with the bad aero effect? what modification can be done then to the early, steel tank cars? a flat piece of aluminum to shut off the bad zone?

Nothing!

The bad aero on the early cars is not that bad. Really comparing underbody aero is hard due to all stuff hanging down there in the first place. The idea was to see if cutting the tire well away could make the car faster.

Answer... early car possibly.... Late car... NO!. So we allow it on late cars to make access to the tranny easier and to help balance out the percieved weight disadvantage of the later tubs.

The biggest underbody airflow advanatage is to run the stock front undertray or to fab one like it if stock is missing. That is supposed to have a 2 mph difference in top speed at long tracks. Plus better airflow through the radiator.

Been a while since I updated - been working more than posting, so it's overdue - here goes:

Got the head done, with Nick Miller's Steam vent (legal in the '09 rules). This bleeds the head quickly & completely - no air bubbles/hot spots.




Dash is about done. Fuel gauge is home made - removed the OEM gauge from an early cluster (thanks Andy/Co-op racing for gauge!), and put it in another gauge body that I gutted (ATL fuel cell gauge that I had no sender for). Color doesn't match, but it's free, and properly calibrated!



All new, color-coded wiring!


After some encouragement from multiple sources, I redid the spring plate bushings, so that the inner surface is the bearing surface. The Racer's Edge bearing are designed to do the opposite, but those surfaces are rougher, and tapered. I found a torsion tube mount casting that was a bit tighter ( I found them to vary by as much as 1mm in depth and diameter), to tightly grip the outer side of the bushing. I put the Delrin bushing in the freezer, and heated up the aluminum mount with a torch:

What was easy fit into the other casting, was a nice tight press fit in this one, possible only through the frozen bushing and heated aluminum mount. Here the bushing in place, and how much sticks out:

Once that was in nice and tight, I used a sand paper flapper wheel to open up the ID on the bushing. This works nicely, but you have to be careful. The flapper wheel should be just slightly larger than the I.D. of the bushing, so it sands the I.D. evenly - this need to stay round, and straight! Don't go too fast - you can melt & scallop the bushing. I did this lightly, but fortunately, had enough material left to remove that it was gone when I was done. Go slow, use water to cool, etc. I did a lot of test fittings along the way to get the fit just right:


I used Syl-glide to lubricate it - a thick high-temp grease that's made for lubing brake calipers - it stays put. There are some more exotic lubes out there, but elected to keep it simple with what I had.
Here's the spring plate & mount together - you can see a bit of the busing remains between the two.

I had to do a few test fits bolting this all on the torsion tube to get this depth right. A little too deep, and it binds the spring plate when you tighten down the mount to the torsion tube with the spring plate sandwiched in between. Any too shallow, though, and you'll get end play - might as well have rubber in there then!

Here's a pic of the torsion tube. You can see the welding flash inside, and there was quite a bit on the surface the bushing sits on (I had sanded that out, but that surface was still not great). Using this as the bearing surface would chew up the Delrin pretty quickly! I used Silicone to help lock the bushing in place on it's outer surface, and use the inner surface as the bearing surface (much smoother)


It feels good to make progress - things are moving along better, but less than 2 months left!