Joined the wheels-up club

[texis30O]

I heard that William.

[RebekahsZ]

That was my plan, good friend! I was next in line to go with the 2-step pushed up to 4500 (the level that has cost me the two driveshaft yokes and an inner CV at this sticky track) when the car ahead of me deposited his transmission case and all of its oil at the staging lights. The plan was to turn it up 500 rpm per run till it either didn't bog or broke. Unfortunately the day got cut short, but I was game to leave it all at the track. Hell, I'd have all winter to get it back together! But at least I can daily it now till my truck is out of Purgatory. I was at Subway today and coming back out and strapping into the Z, I got the biggest grin knowing that I was eating a sub while driving back to work in a car that can hoist the front wheels. All thanks to hybridz!

[weedburner]

Weedburner-you are totally right.  I've read your stuff and it is super cool, but I don't want a slippy clutch, but I did pay attention to your advice on tires and shocks.  A couple questions:  If I raise my air pressure, will the bias ply slicks be less shock-absorbant (less sidewall wrap?)?  I was thinking that maybe by dropping tire pressure I was reducing the tire diameter at launch so that it would behave more like a shorter slick.  When you say "less rear shock", do you mean less compression resistance or less rebound resistance?  I had the rear shock on full stiff for rebound and the front shock on full soft for rebound.  Compression is non-adjustable.  I run 250# rear springs and 225# fronts.

 

To prevent your current bog, either your clutch has to slip or your tires have to spin. My suggestions regarding air pressure and shocks are aimed at going away from clutch slip and reducing traction to gain some spin and pick up some rpm. The less rear shock suggestion was assuming your car squats when power is applied, as less compression would allow it to squat faster, momentarily reducing traction possibly enough to get the tires spinning. Dropping air pressure isn't going to make much difference, at least as far as gaining enough rpm to prevent your bog. More air pressure will make a difference only if traction is reduced enough to let the tires spin, which will gain you some rpm. 

 

Here's what your rpm is at different lockup time intervals down the track, assuming 2.97 T56 1st gear, 3.54 diff ratio, and your car accelerating at a 1.76g rate (1.45 60')...

.3 seconds in, 11.7mph 1590 rpm w/ 26" tire, 1476 w/ 28"

.4 seconds in, 15.6mph 2120 rpm w/ 26" tire, 1968 w/ 28"

.5 seconds in, 19.5mph 2649 rpm w/ 26" tire, 2460 w/ 28"

.6 seconds in, 23.4mph 3182 rpm w/ 26" tire, 2955 w/ 28"

.7 seconds in, 27.3mph 3713 rpm w/ 26" tire, 3448 w/ 28"

.8 seconds in, 31.2mph 4239 rpm w/ 26" tire, 3986 w/ 28"

As you can see, if your clutch locks up at .3 seconds in and the slick is stuck to the track, that bog to 1476 rpm with a 28" tire is only going to improve to 1590 rpm if you swap to a 26" tire. Even if you were to spray some nitrous to help off the line, without wheelspin the rpm would be pulled below the minimum recommended 3000 unless clutch lockup is extended out to .6 seconds. If you want to carry the wheels down track, the engine needs to be spinning fast enough at lockup to make some power.

 

 Just to be clear, my clutch slipper doesn't make it a slippy clutch, as the intent is only to delay lockup just until your car is going fast enough that lockup won't cause a bog. You still have all the original clamping pressure, just slightly delaying it's application. RPM does not have to flare up above the staging rpm if you don't want it to. If you are afraid of hurting your clutch, you can easily adjust so that you still have most of your bog, just not as much. Much more predictable than relying on wheelspin to overcome the bog.

 

I know what you mean about driving around town knowing your car can pull the front tires. My favorite part about going to the track is driving back home late at nite with a big smile on my face.

Edited November 13, 2014 by weedburner

[mistafosta]

My ultimate plan is to build a drag-only Z, 275 drag radial car and put a solid axle and a powerglide in it (funny car style cage, wheelie bars, a trailer hitch and a parachute will be part of the initial build).

 

To warn you, radials on a car with 90" wheelbase is an awful way to go. Even with wheelie bars, you are going to be skating a thin line between dangerous monster wheelies, and blowing the tires off. (Ask me how I know this one....)

[RebekahsZ]

I'm so far from making this a reality that tire technology may be totally different by the time I get to it!  I'm not set on radials, but I am set on a solid axle.  Not sure if I want to do stock Mustang style or a true 4-link.  Wow, that's one heck of a wheelie!  Did you break anything (rear valance, bumper or oil pan)?

[mistafosta]

Nothing got broken externally, I used throttle to set the front down again nicely. But this is why I added an accusump and rerouted the location of the pickup. This wheelie killed a few bearings and one piston. (found out after driving 100 miles home...)

[thezguy]

To warn you, radials on a car with 90" wheelbase is an awful way to go. Even with wheelie bars, you are going to be skating a thin line between dangerous monster wheelies, and blowing the tires off. (Ask me how I know this one....)

That's awesome.