I plan to buy a new Moser 12 bolt rear-end for my 1997 Z28 (396 LT stroker, 4L60E Auto w/ Vigilante 3200) before the 2007 bracket season begins and want some opinions on the correct (best) gears for my specific setup. Also, the car is primarily used for bracket racing and seldom driven on the street, so strip performance is the bottom-line.

The car currently has a 10 bolt w/ 3.73s and 26” tall ET Streets. It is showing about 6100 RPM at the stripe on the factory tach (I think the factory tachs read high). The rev-limiter is set to 6600, so I’m currently leaving some performance on the table with only 6100 trap RPM. The low profile 26” slicks helps to keep me geared low in the ¼ and improves the trap RPM some, but not perfect. The current best run is 11.22 @ 119 w/ a 1.61 60ft.

When I go the 12 bolt I also plan to go to 28” tall slicks for better and more consistent launches, therefore I’ll need 4.10s, or possibly 4.30s to get my trap RPM up to around 6500.

I’ve used the online drive-train calculators and most of them pick 4.30s, although, I wanted to get some opinions here on the forum what everyone thinks, and/or what gears and tire height they are running and what combination has worked well for them.

WD

 

A 28" tired car may lose between 1-2mph due to the added hp required to pull them on the top end.

A 28" slick will grow approx. another 1/2-1" at your speed depending on wheel width & air pressure. Radials generally do not grow much. Figure this into your calculation.

You should cross the finish line at roughly 0-10% rpm over peak power assuming it does not drop off steeply due to valve float etc.

Your factory tach is likely reading 200rpm high. Most of them that I checked were very close to 200rpm off at 6000.

If you use the same tire brand in a 28" & assume the same growth as you currently have with the same converter etc., a 4.0:1 will be nearly the same overall mph. A 4.3 will get you closer to the 6500 (tach reading....not actual) & assuming no mph loss due to the added tire.

Ideally, you need to determine where it makes the most power, work backward & remember to calculate in the converter slippage.

You are currently 400 rpm off from calculated mph vs. actual track mph.
Not sure how much is tach and/or converter slippage which may also be offset by tire growth as 5750rpm should give you 119mph.

I'll let the determination up to you as everyones combination is different.

Hope this helps.

 

Wow! Im lost.

 

Agree with Lonnie's post. But since you are emphasizing brackets, consistency is the key. More gear may make it harder to hook and hurt your consistency. On that basis, I'd say 4.11's.

Rich

 

It is never easy. The reason racers have so many used parts for sale is that even the best thought out combinations end up with trial & error testing.... especially if you are trying to get the most out of it.

 

I have 3.73s in a Moser 12 bolt, with a 700R4 tranny. I run 28" Et Streets. I was previously using the same setup with 26" ET Streets. My ET went from 11.8s at 110 with 1.5 sixty foot times to 12.0s at 112 with 1.6 sixty foot times.

I switched for exactlt that reason. The lowest I can dial in Street is 12.00. The 28" tires made my launched far more consistent. My reaction times became far more consistent. A steeper gear and a taller tire is the way to go if you want consistency and reliability in my opinion.

I am not a believer in pushing the car to the max every run. In my opinion it is better to have less stress on the motor and run the same number every time if you are serious about bracket racing. If you need to run quicker than your dial, you can do it by changing your shift point as opposed to dialing a different number. It is always better to provide your competitor less information.