Xanath

Hi all,

I am trying to work up a build for my '82 Trans Am with an overall goal of having the car being able to surpass 200mph easily, (meaning I don't have to climb up to 6,000+ RPM to do it). I still have my stock TH200c installed on the car, but this is long overdue for retirement. My question is, I'm *heavily* considering buying one of Art Carr's, (the man, not the business) 200 4R transmissions from his http://www.cpttransmission.com/ shop, but even though he makes trannys that can handle up to 1,000HP, (far more than I'm looking for), will four gears be enough for me to crack into 200mph, quickly and easily, if at all?

My other option that I was considering was going with a 700 R4 transmission from someone like TCI and throwing a GearVendors Under/Overdrive on it that would effectively give me 8 gears. More gears = more speed @ lower RPMs was the thought there.

Although I'm not really opposed to this option, my big problem with it is that in contrast to the 200 4R which is plug 'n play, (all I need to do is slide down my crossmember to holes that are already drilled in the frame from the factory and throw the unit under the car), with the 700 R4, I have to make provisions for a new crossmember, as well as have a new driveshaft made up due to the tail housing extending out further than my existing TH200c or a 200 4R would extend.

And, as due to cost, I wouldn't be able to get the 700 R4 and the GV units at the same time, I'm afraid that I'll have to replace or customize my drive shaft twice (first for the 700 R4 and again after I get and install the GV Under/Overdrive). I am planning on replacing my drive shaft, but I'm swapping out the rear-end this winter, and wanted to wait to do it then. My existing transmission is on it's way out now though, so it can't wait for the snow season.

The car is a street/strip-mobile, so that's why I'm bouncing between those two transmissions. Any opinions, recommendations, theorys, etc. are much apprecaited. Thanks guys!

Apeiron

The engine will have more to do with making 200 mph than the transmission will.

Xanath

Oh, I know that, the thing is that I know a few folks that have plenty strong engines that have the possibilty to make 200+ mph, but they're limited by their transmissions, mostly because they just peak out in 4th and can't climb to that high of a speed.

In their instance, it seems that if they had an extra gear of two, then they'd be able to climb up and above 200mph, but as they've built their vehicles for 1/4 miles, they don't seem to mind topping out at around 150-170 mph.

My ultimate goal is for top speed, so I'm trying to figure out what the better investment for my vehicle is. I know a 200 4R can be made to handle the power that the engine can throw at it in the hopes of meeting and passing 200 mph, but can it do it in 4 gears? Or do I need to go the route of a 700 R4 and a GearVendors Under/Overdrive?

Dale

iTrader: (12)

In my mind, if they have the car built for 1/4 mile times. They likely have steeper rear axle gears then you would want for a long out mph that will take a mile or more to obtain your goal.

vette9190

iTrader: (2)

For that speed I'd go with a manual T56 outa a ls1 f-body or maybe a richmond 6 speed. The 4th gear is an overdrive gear its in both the 2004r and the700r4 so they aren't really made for that kinda use. I'm not sayin you can't do it but I think a 6 speed manual would be the better bet for you. Either way you will need like a 2.73 or higher rear gear. Just my

RebornFromAshes

The driveshaft critical speed will be an issue. You can't spin the engine at 6,000 RPM and run enough overdrive to spin the driveshaft at 14,000 RPM. You will have to run a large diameter, very strong and well balanced driveshaft with a high rear gear. You are better off going with something like a 2.50 rear end and gearing down at the transmission than running a 3.42 and spinning the driveshaft fast enough to make up the difference.

Timothayyy

iTrader: (2)

Maybe one of those carbon fiber driveshafts?

91 RS Drop Top

I am no transmission expert but I think the following may help.

https://www.thirdgen.org/calculations

It has calculators where you enter rear end gear ratios, mph, transmission gear ratios, rpm, tire size, etc and solve for whichever of those variables you don't have. (you just hit enter, it solves). Play around in there and you should be able to figure out what final gear ratio you need. Then base your trans and rear end choices on that. After just a little playing around with it, I think you would have no problem (assuming a powerful enough motor) getting their with a T56. I think there 6th gear is in the neighborhood of .50-.60, and from experience driving one a few times in a vette, you can barely even shift into sixth below 65mph. Drop down to a 2.73 or higher rear end and your talking about a gear you can't even shift into until 75+

This might also help: https://www.thirdgen.org/gears just don't pay any attention when he talks about target mph in the 1/4. use 200 for your target.

I don't know anything about the driveshaft rotation speed issues, but you might not want to go too low in your axle ratio because you are going to need torque to overcome drag at these speeds. I'll let somebody else address driveshaft issues.

Which brings me to one more thing. I was an aerospace major, a certified commercial pilot, and I work on military aircraft. Aerodynamics applies to cars just like airplanes. Drag increases exponentially with velocity. When you get above about 120 aerodynamics rapidly start to become almost as important as power. I don't know how serious you are willing to get in your pursuit of 200, but making even small modifications to reduce drag will likely make a big difference. Waxing an F-4 phantom resulted in a gain of about 46 mph. adding wheel fairings or flush riveting all the joints on a typical cessna aircraft that cruises around 125 can add about 8 mph.

Luckily our cars already have excellent shapes overall. its hard to think of things to reduce drag, but a few come to mind. Removing the side mirrors would probably make a big difference, as would lowering the car. If you have flip up headlights definitely keep them down. If not try to fab up some kind of cover that blends with the hood profile. A hard top would be better than a T top. make sure your wheels aren't sticking out to the sides from Axle mods or wider rims. Removing the spoiler might get you a couple of mph. I would need to see the profile of the car to be sure, but I would reccommend ditching any ground effects, even on the sides. Bottom line, if you hit a brick wall where you have RPM left and are getting no where, consider drag reduction. It might save you a few radical engine teardowns. And if you find yourself oh-so-close, but not there, try hand waxing the hell out of it. Good luck and keep us posted.

Chris

ScottieB

16" tires, 5k rpm, 200 mph = 2.380952380952381 gear ratio for instance. nice calculator!

20" tires @ 4600 rpm, 200 mph = 2.73 gears btw

Zepher

iTrader: (1)

You are gonna need almost 1000hp to get there with the numerically low gearing that you will need.

You will want to have the 87-90 wrap around spoiler on the car. It does increase drag, but will keep the car on the road.

3rdgenmaro

iTrader: (9)

so you are thinking that a 2.38 gear with a motor that maxs out rpms at 5k will put you at 200mph? How far do you have to run this thing? Where are you going? Salt flats? Abandoned airport? Or are you planning on killing yourself and someone else on the highway?

what kind of safety do you have in the car?

Im sorry, but I have to think you are completely out of your mind. If you had any sense to you about what going 200mph consisted of, then you wouldnt come on here asking about what transmission would get you there. If you hadnt realized that rear gear and motor has more to do with it, then how have you realized what the car is going to want to do when it hits that speed? What tires are you running? What room would you need to decelerate?

sorry, I 1) hope your smarter and have thought things through alittle bit more.
2) hope I dont have all the details on your plans.
3) hope you are not serious

Aaron91RS

iTrader: (2)

If you can't use a simple gear/tire/speed calculator and have to ask us if it will hit 200mph I'm going to guess you really don't have the other skills needed to accomplish such a feat. Or the money

Why people on here continue to feed the absurd, never going to happen posts I don't know.

</reality check>

Dale

iTrader: (12)

http://www.popularmechanics.com/auto...s/1268801.html


As for the spoiler. That car shows it has one. However, the Koenigsegg CCR actually removed his because it created more wind drag and the car had enough downforce already.

91 RS Drop Top

Hey lets give the guy some respect for coming on here looking to learn. This is the kind of thing people get into, realize they are clueless, educate themselves, and 5 years down the road make it happen, or try and learn something along the way.

That sadi I would also have serious safety concerns about attempting this, and attempting it on the interstate would be absolutely criminal.

As I stated before, the only way to even get close without needing 1000 hp is going to be drag reduction. Look at the kind of cars that go those speeds and how aerodynamic they are. I think C-5,C-6 vettes are can approach 180+ with less than 400hp, but they have significantly better aerodynamics than we do.

In the military we refer to "SWAGs." That stands for Scientific Wild *** Guess, which is slightly better than a Wild *** Guess. I would make a SWAG that you are definitely looking at needing at least 650 HP, and you may well need 1000. If you end up going to a cowl hood you are going to wreck your aerodynamics, so I would suggest considering some kind of high-compression high boost intercooled twin turbo set up to boost your power without putting in a big block, and some massive cold air intakes tofeed it without a cowl or shaker hood.

And listen to the folks on here about things like tires rated for that speed, and don't forget brakes, suspension, etc.