Any one running a TH400 here?

I'm looking to do a TH400 and am wondering what everyones expirences are with 26" over 28" tires. Also what rear gear are you running? Is any one running Higher the a 3:73?

~Jim~

 

Not sure what kind of "experiences" you are looking for. I run a TH400 with a non-locking convertor, 4.11 gears and 28" tires, either QTP 28x11.5-15 or ET Drag 28x10.5-15W's. What do you mean by 26" over 28" tires..... are you looking for the advantages and disadvantages of both sizes?

 

What time of RPm's are you running at the top end with the 28" and 4:11.

Reason I ask is I'm going to do a TH400 with a 3:73 gear out back and am looking for an appropriate tire size. I'm guessing the 26" will be adequate for the track use but the cars is going to be a double duty street and strip.

Which combo is going to be better for mild street driving ( weekends, not over 60 mph)

Thanks for the reply

~Jim~

 

Tire/gear selection is a little tricky, because you have to take into consideration the tire growth at the top end (mainly with bias ply slicks, not so much on radials) and torque converter slip (if non-locking). I've got a spreadsheet set up for the TH400 that accounts for all of this. I was able to figure the tire growth based on the MPH point that the tires grew enough to start hitting the front edge of the wheel opening. We figured the converter slip off the chassis dyno data.

With a 7,000rpm nitrous cutoff, I will max out at 129 MPH in 3rd gear. Its trapped 128mph with a 125-shot, but I had 3.73's at the time. Have never sprayed the 300-shot on the track.

The rev's on the street, with 25.7" tires were driving me nuts, so I added a Gear Vendors O/D and then switched to 4.11's. In 3rd gear, it was running 3,950 RPM at 70 MPH. The GV O/D drops that down to 3,080 RPM.

If I ever get back to the track, and spray the 300-shot, it should be trapping close to 140 MPH, which means I'm going to have to engage the GV to reach the traps without hitting the nitrous cut off.

All things considered, for the track I could have just left the 3.73's in it, and I would have been able to cross the traps on the 300-shot without engaging the O/D. And then the street rev's with 25.7" tires would only have been 2,800 RPM at 70 MPH in O/D.

You also have to consider the weight of the 28" tires. The more the tires weigh, and the larger the diameter, the more you are going to lose at the rear wheels. If you are under 500HP, you should be OK with 26" tires, and not lose any unnecessary HP. If you are looking at a power adder setup, and hitting the tires really hard off the line, you may need to go to 28's.

For a 26" tire, with 3.73 gears, depending on your redline RPM, you would be at:

RPM - - - - - MPH
6,000 - - - - 113
6,200 - - - - 117
6,400 - - - - 121
6,600 - - - - 124
6,800 - - - - 128
7,000 - - - - 132

That assumes an 11% converter slip and 2% tire growth at 125 MPH.

What are you doing with the engine? Apparently a lot more than shown in the signature, because what you have shown does not justify the higher weight and drivetrain losses of the TH400, or 28" tires.

 

Injuneer:

First thank you for the time and information it has been very helpful.

Here is my situation. I'm building the rear half of the car this year to make way for new engine next year while still keeping it drivable. I just personally don't want to take that car apart and have it sit for a year.

The engine will be a 540 big block chevy. I'm planning on 750+ out of the motor N/A. Nitrous may or may not be installed in the future. At this point in time I'm leaning towards not using it but things change every day.

I have not decided on my builder for the trans but there are two local to me that do terrific work. I'm set on using a th400 purley because I don't think a M-22 will handle that power for long or at all.

Do you think it's a bad idea to setup the back half of the car before I have the engine/trans in or is it not a big deal?

Thanks again

~Jim~

 

My experience with 28's and 3.73. At 6400 rpm crossing the traps I'm at 122mph. On the hose at 133+ I'm closer to 6800'ish rpm. I really need to take my GPS with me but cruising at 3000rpms is in the 60-70mph range.

I'm doing an OD trans soon to make it streetable again. I'd like to do 75mph at 2400-2600rpm.

 

AutoRoc:

Thats not to bad then on the 28's. I think should be fine with that setup.

I don't think I'll be doing much 60+ cruising in the car but an overdrive maybe be something to consider.

sounds like a pretty sweet car.

~Jim~