Steve Lancaster at California Performance Transmission advocates automatics. He told us, "The advantages of a properly built automatic transmission in a kit car application are numerous. Dragstrip results speak for themselves; unless it's a clutchless manual transmission, nothing will be as consistent or as strong as a properly built automatic and complementing torque converter.

While the open road course is a different environment than that of the dragstrip, a properly built automatic will boast better times than those of an identically outfitted manual vehicle in all but the most competitive vehicle.

On the street, auto gearboxes greatly increase the driveability and "fun-factor" for the kit car enthusiast. No more traffic jams spent with the clutch halfway engaged (and the accompanying spaghetti-noodle leg).

Jon McKean, director of operations for TPI Performance, builders of automatic transmissions, likes automatics for rear-wheel-drive cars and for cars that take on the dragstrip for "quarter-mile consistency." He said, "For street use, it is an issue of labor for the driver--the way traffic has increased. Heat is also a factor that is improved with an automatic, and wear and tear on the engine and clutch is lessened. An automatic allows you to do what you want to do EVERY TIME. You rev the engine to 2,500 rpm to move gears without missing a shift."

McKean is sympathetic to shift-heads, too. He said, "If shifting is your thing, you can still shift with an auto tranny. We can build one for you that shifts; you just don't have to activate the clutch pedal. That will put you in full control, and you can shift when and where you want to shift--it is called 'a full, manual valve body.'"

McKean told us that high-performance only for manual shifts is a thing of the past. He said, "Higher horsepower works with an automatic. If you have 600-700 hp, you can still run an automatic with overdrive. We package a Turbo 400 for Chevy trannies, a Ford C6, and a 727 Chrysler, mated with bolt-on overdrives that will take 1,000-plus hp."

 

how's your build going?

 

Hey JP,
The Th400 is overkill for the power we are running. Here are a couple of issues: Drivetrain loss, if you are planning to run anything smaller than a Pt74 turbo , then your hp power range will be in the 650whp. High rpm at cruising(how about 4000rpm at 60mph ), unless you have the 0.D which will run about $3k. There are 3 gears in the Th400, but you have to shift them manually. Modify an adapter plate to mate between lexus engine and Th400, modify cable shift linkage cable, driveshaft, driveshaft loop, transmission mount, shifter unit(might have to go with the B&M kit). Modify the transmission tail shaft speed input so your speedo will work. Not to mention you have to do some cutting around transmission tunel. This whole set up will run you at least $15k for labor and fabrication.
We have a Th400 is our race car, it does the job for what it is. But not for everday driving. We are testing a built lexus tranny and valve body upgrade. So far it does more than what we expected. PCS make a transmission controller for our application. Hopefully we can get a hand on those and test them soon.
JPI

 

Looks like a sales pitch rather than any useful info.

 

I just copied and pasted from a web site. I just like to hear others opinion on automatic vs. stick shift. I would like to rebuild my transmission to shift faster, and be able to handle more power. JPI, I do like how you walked us through the whole process of putting a th400 in our cars. It would be better I think, just to build the stock tranny.

 

The stock tranny can be built, but it will never be as strong as a race/drag tranny such as the TH400. Those monsters are built to take 1000hp+, while the GS tranny will probably hold 600-700hp fully built. I'm not even sure if it will do that much even.

 

I hope you know what 600-700hp will do to the GS300. Our race car made 646whp @27 psi with PTE74 GTS through AEM EMS with C16 race gas. We could push a little more but I decided not risk the not TT internals. All of this through the Th400, if you aren't familiar with the Th400. The drivetrain loss is close to 20% ouch . With the lexus built tranny you are looking at a PT74gts .96 on pump gas for the 600-700hp range. Can't do more than 18psi on pump gas and C16 is like $11 a gallon . So 500whp is plenty for the street.......Plenty to smoke 90% cars on the street.
The Lexus built tranny will hold if you know what you are doing and what part do fail at the hp level. Btw, Jeff if you have time come by our place. I will be happy to show you what the GS300 T do at 10 psi.
JPI

 

As far as consistant times at the drag strip, durability, and strength... i think i would still go with a manual transmission anyday. With an auto, you have a hell of a lot more moving parts to deal with, and heat is its worst enemy. I used to drag race pretty often when i had my camaro, and it was a 6 speed manual. When it comes to consistancy... i think that has to do more with the driver. As long as the clutch, hydralics, and related linkages are in good working order, there isnt any factors other than the drive to reduce the efficiency of consistant 60 foot and 1/4 mile times. One of my very close friends runs in the mid 9's with a bone stock 6 speed transmission in his camaro.. Once he got used to the car, with a huge shot of nitrous, the consistancy of the car was very predictable. To me, it all comes down to the driver. Assuming the clutch is in good shape, a manual transmission will always be more durable and reliable than an automatic. Many may argue that no human can shift faster than a machine... while that may be true... the few hundreths of a second you lose in shifting manually, you'll gain back with a full solid connection of the engine to the rear wheels, while with an automatic, unless the converter is locked.. you have more parasitic loss through the auto. just my 2 cents...

 

Most of the pro class run the auto. 99.99% of us run th400 for 1/4 mile. Manual won't give you consistant times, We used to have a 6spd on our race car. It's now replaced with a Th400. How do we launch? Nitrous will do the trick. 400 shot of nitrous will spool the big Gt47-88 turbo, we set them up through different stages and rpm. Our Neal Chance torque converter is made by billet aluminum. Lighter material will help the turbo spool quicker etc.... Ok i need to get some sleep now.....
JPI

 

Werd. For drag auto is king.

The fastest supra out there uses an auto tranni btw.

 

kinda interested in what dyno you made that power on??? my supra made 642whp with a pt67 at 28.5 psi on 110octane gas on a dynojet and 575whp on a mustang. seems kinda low to me even if it is going through the th400.

 

It was a dyno jet. We had some fueling problem, fuel pressure would drop at high rpm due the third fuel pump in line. Also the D/R tires was rubbing so bad, I though we would blow it up on the dyno. Our converter was lose, It could make more hp if we decided to teak it a little more.
JPI