BUILD THREAD 86 GP 2+2~Blown 6.0

81cutlass

Comic Book Super Hero
Thread starter
Feb 16, 2009
3,098
113
Western MN
Ok so I did remeasure the rear suspension angles last night to get a formally correct instant center calculation.

I have spent the last few days reading and drawing free body diagrams in my brain to solve my my lousy launch. Yellowbullet, although a colorful place and dead these days, still has the best archive for drag racing.

This is where my car sits today. Honestly the AntiSquat value in % makes no sense to my engineering brain (what is it in relation to? Not sure, seems like a made up number unless they show the equation) but essentially the consensus on YB is that the antisquat needs to be between 100% and 130%. Anymore than 130 and you need a REALLY good shock.

I have 33%. That means the rear suspension is pulling the body down and essentially unloading the rear tire from the track.

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My best bet is to lower the hole on the rear housing 2.5". It has a reasonable 110% antisquat value if I do.

I could raise the diff side UCA pickup point or lower the chassis side UCA mount but that is a lot more invasive and more for a 1000hp grudge car where you want 130% antisquat and have good shocks to control.
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81cutlass

Comic Book Super Hero
Thread starter
Feb 16, 2009
3,098
113
Western MN
Got time to get the lca drop brackets in.

I started drawing them up last weekend and cut one of them out early this week but my bandsaw blade snapped and I need to get a replacement.

These lower the lca 2.5" which should get my instant center set up so the car doesn't squat.

I also had a bit of driveline vibration and checked my pinion angle and it was a bit funky. Up 2.5 degrees. With my uca bushing slop problem solved the rear doesn't move as much (good) and I had it set to be ok when it had slop to one direction but it went really bad when it took the slack out on the other side.

The trans is angled down 6 and the driveshaft is down 1.5, and the rear is now at zero, when it was up 2.5. The set your pinion angle guides says this is wrong but it doesn't shake anymore so I'm claiming a win.

Took the thing on a 40 mile round trip to the night cruise for the first time this year and it stayed cool so my fan fuse up size worked.

I've gotta convince myself to buy expensive adjustable rear shocks now...

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