I currently have a 6 speed, but I am getting a full TH400 setup. It has a 2.75:1 first gear for what it's worth, and I am running 28x12.5x15 ET Streets. I currently have a Strange 12 bolt with 3.73:1 gears. My current setup revs to about 6600rpm with my peak hp at 6200. I am wondering if I should stick with my 3:73's, or try something different. I expect to trap in the low-mid 120's, but that may be optimistic. I do plan on adding additional power possibly over the winter. Any suggestions would be much appreciated.

 

Anyone?

 

Well, I would try them before changing them, if that's what you are asking? But 6,000rpm with a 28" tire is 133mph not allowing for either slip in the converter or tire growth (which will cancel each other to some extent). So, if you are going to trap in the mid 120's you might be able to use 4.11's. But you really should try what you have because of the variables involved.

Rich Krause

 

Thanks Rich. That's what I had planned on doing, I was just looking for a little insight into the situation. Thank you very much.

 

Why not a TH350?

Daren

 

Turbo 400 > 350

Too many reasons why...and especially if he's using a transbrake. The few extra pounds and little HP loss differential isn't worth the risk of a much weaker transmission in the 350 IMO.

 

And sorry Birdie....I was going to get to your question last night when my internet took a major dump on me.

Here's a good site for gear ratio's, transmission ratio's and trap speed http://www.f-body.org/gears/

While it isn't as much of a help to a 3 speed as it is to an M6, you can still take a good look at what top speed you're looking at depending on gears, tire height and at what RPM.

I would also agree with Rich. See how well you're doing with the 3.73's and at what RPM you're hitting the traps.

Not sure if this is your daily driver or if you have a GV OD in it or not....but that would play some part on whether or not you'd want a taller gear.

 

Thanks guys!

I am going with a TH400 because I got a really good deal on it, and it came complete with a chromemoly driveshaft, shifter, crossmember, cooler, lokar dipstic, and a transbrake, plus all the braided stainless lines. It is supposedly built to the hilt and has a custom 1st gear, and it came lightly used out of a car that was running 9.8's with it. Basically, it came with every last nut and bolt to make it work.

This car is far from my daily driver, although I do plan to drive it on the street as often as I can. No GearVendors is planned as that is too rich for my blood. I have already looked on those websites, and I realize that the gear may or may not be appropriate. I am certainly going to try it before anything, I was just looking for the input of the more experienced racers out there.

 

You really need to look at it with the variables, like convertor slip, and tire growth. My TH400 setup is running more than 10% slip, and as best I can tell, I'm getting about 3.5% growth. That estimate is based on 128mph trap speeds with a 125-shot. Hopefully, I'll be getting some new data with the 300-shot.

If we look at 6,500rpm at the traps, 10% slip, 3.73 gears, 28.1" tires w/ 3.5% growth, I get 135.7mph. Substitute the 4.10's and that's 123.4mph. Looks like the 4.10's are cutting it a little too close, and the 3.73's are leaving too much on the table. A set of 3.90's would give you 129.7mph.... seems like the best solution. My 4.10's are going to force me to use O/D at the end of the track, even with a 7,000rpm target.

I would consider the impact of street driving, and how important it is to you. 4.10's on my setup have me close to 4,000rpm at 70MPH with 25.66" street tires. The GV dropped me a lot closer to 3,000rpm.