Rear Gear Selection for a 200 MPH GT? Who's done one?

[marcspaz]

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I am getting ready to start putting parts aside to do a 200 MPH GT build. Not a car that will do 200 in a standing mile, but capable of top speeds of high 190's - low 200's. I am shooting for around 600-650 RWHP to do it. I am looking for some input from folks who may have built some road track cars or standing mile drag cars who have GT's capable of doing 200 MPH.

So, I really like my GT500... and it can do 200, but I don't want to fuck it up while doing high speed racing. GT's are everywhere and if I pop the engine or trans, I am not going to be so heart broken over having to replace parts since a GT is not a numbered car. However, I love the gearing of the TR6060, as I can do 70 MPH in first and 110 MPH in second. I want to get that kind of gearing without spending $5k-$7k on a built TR6060.

Something I noticed in the TR6060 has gear that are on average about 25% more shallow than the stock MT82. Both cars have 3.31 gears. The big gear difference appears to all be in the trans.

So, what I was thinking is getting a rear gear that is about 25% more shallow instead. It's a lot cheaper, and I am assuming it will have the same result. What is troubling me is, that is a 2.48:1 rear gear ratio, which seems way too low for a practical application for a 650 RWHP car.

So, my questions are; for those who have built them...

1.) with a clutch assembly upgrade, is the stock Mt82 stout enough for 650 RWHP? (Roush and Whipple say yes, but what have you found)

2.) is a 2.48 gear a bad choice for what I want to do? Is something like a 3.08 or 2.7x better for acceleration while still getting to that 200 MPH benchmark?

3.) I am not seeing anything lower than a 3.08 for the 8.8. Are gears available numerically lower than a 3.08 for the 8.8 rear?

Thanks in advance...

Spaz

 

[stkjock]

How are you getting to 600-650?

Gonna need a lot of cooling mods for the trans and coolers

 

[BadPiggy]

Gonna need a lot of cooling mods for the trans and coolers

That was my first thought on the rear end. That thing will be blistering hot by time it reached 120mph.

 

[NotaHybrid]

Pm gmitch on here. He is hoping to hit 200+ mph in his car in the mile in his gt. He has done a lot of work to get that high of a speed and I'm sure has a lot of info.

Sent from my helicopter

 

[marcspaz]

How are you getting to 600-650?

Gonna need a lot of cooling mods for the trans and coolers

I am looking at a couple twin screw blowers at or over 2.8L to get most of it. May get a turbo setup, but I am not a fan of all the plumbing. Exhaust such as LT's and some other common mods to make up the rest.

I kinda figured a lot of cooling (not ice dependent) would be needed for racing and sustaining high speeds and boost levels without the motor falling apart on me.

That was my first thought on the rear end. That thing will be blistering hot by time it reached 120mph.

Not sure I follow... 120 on a stock rear is not a big deal. I have sustained 170+ on a stock 8.8 for more than 5 miles with no heat issues.

Pm gmitch on here. He is hoping to hit 200+ mph in his car in the mile in his gt. He has done a lot of work to get that high of a speed and I'm sure has a lot of info.

Sent from my helicopter

Cool. Thanks for the heads-up.

 

[05yellowgt]

For longevity if you are going with a twin screw, go as big as you can afford on the blower. If I were to put together a power adder road race car I would go turbos or centri with as big an a2a inter cooler as I could stuff into the car. The problem with a2w is that no matter how much water is in the system, you have a fixed medium which will get heat soaked, where as an a2a is constantly refreshed by the air you are driving through.

A drag car, is a different story when you can use ice.

The cooling mods that were mentioned are for the transmission and rear gear. You are going to be cooking the trans and diff fluid without them.

 

[s8v4o]

.

So, what I was thinking is getting a rear gear that is about 25% more shallow instead. It's a lot cheaper, and I am assuming it will have the same result. What is troubling me is, that is a 2.48:1 rear gear ratio, which seems way too low for a practical application for a 650 RWHP car.

So, my questions are; for those who have built them...

1.) with a clutch assembly upgrade, is the stock Mt82 stout enough for 650 RWHP? (Roush and Whipple say yes, but what have you found)

2.) is a 2.48 gear a bad choice for what I want to do? Is something like a 3.08 or 2.7x better for acceleration while still getting to that 200 MPH benchmark?

3.) I am not seeing anything lower than a 3.08 for the 8.8. Are gears available numerically lower than a 3.08 for the 8.8 rear?

Thanks in advance...

Spaz

What about the 2.73 gear? IIRC this is the gear ratio lots of the late 80's and early 90's mustang came with.

 

[lito]

If the mt-82s hold is nicely geared for that, depending on tire size, 3.08 will do, if not 2.73. If they don't hold, get a short radio Magnum. You need the ratios close in the high gears. Use a centri better, A/A.

Sent from my Nexus 7 using Tapatalk

 

[Marc s]

I did it with my car when I had the Procharged 4.6, 734whp, 3.31 gears, and a Liberty built 3650. Once I hit 200 mph, the coolant temps were 240 degrees. Shifting from 4th to 5th is a big drop in RPM so I ran the car to 7500 RPMs in 4th which dropped the RPMs to 5100 in 5th. I lifted at 6200 rpms which was 218 mph. This high speed run overheated the diff and damaged parts.

With my car in it's current configuration, my 4 speed transmission has a pump and a cooler. The trans temps stay at 160 degrees during road racing. I also have a belt driven diff pump and cooler but have not installed it yet. Just on the road course, my diff temps exceed 280 degrees which is too much even for synthetic gear oil.

To be safe, any car needs much more than just hp to reach speeds of 200 mph.

 

[marcspaz]

Lots of good info... I am coming from NA drag to FI road race and I have very little FI experience. Glad I started asking questions before spending money. I appreciate it guys.

If the mt-82s hold is nicely geared for that, depending on tire size, 3.08 will do, if not 2.73. If they don't hold, get a short radio Magnum. You need the ratios close in the high gears. Use a centri better, A/A.

Sent from my Nexus 7 using Tapatalk

Any opinion on brand or type? I have seen some Prochargers that look like they would make the boost levels needed.

For racing, should I stay away from self contained oiling systems; would it be a benefit or does it not matter, just personal preference?

I did it with my car when I had the Procharged 4.6, 734whp, 3.31 gears, and a Liberty built 3650.

Man, that is a lot of power. I am hoping that I can do it with less so I can keep the stock internals, at least for a season. I want to make sure I enjoy it before spending money on an engine.

Once I hit 200 mph, the coolant temps were 240 degrees. Shifting from 4th to 5th is a big drop in RPM so I ran the car to 7500 RPMs in 4th which dropped the RPMs to 5100 in 5th. I lifted at 6200 rpms which was 218 mph. This high speed run overheated the diff and damaged parts.

Nice. what trans gear ratio's did you have? Stock? I have 3.31's right now. I have my doubts about having enough RMP... but maybe it will work. My assumptions about needing to gear down are based on the Shelby rather than experiences with my GT's. I may be over-thinking it.

I wonder if I damaged my diff housing on the 174 MPH run I did on my 2007 GT? I noticed a few weeks later, the next time I raced, I starting getting a really bad vibration on deceleration (in gear) from over 120. I completely rebuilt the rear thinking it was the gears, carrier, bearings, but it never went away. Seemed in spec... but now you guys are making me rethink it.

With my car in it's current configuration, my 4 speed transmission has a pump and a cooler. The trans temps stay at 160 degrees during road racing. I also have a belt driven diff pump and cooler but have not installed it yet. Just on the road course, my diff temps exceed 280 degrees which is too much even for synthetic gear oil.

To be safe, any car needs much more than just hp to reach speeds of 200 mph.

That's my biggest concern. I want to make sure both the car and I live through it. Honestly, most of the tracks around here won't be big enough to get over about 160 on a "truly street driven" car that is raced. I Think the longest straight anywhere near me is about 1,000 feet. But I am hoping that once I have some experience, I can get out to a privately owned test track that has a 5 mile straight. Plus there is always the possibility of the salt flats or the standing mile too.

 

[rcm90]

I went 160+ on the autobahn on a regular basis for almost two years and have never had any issues with the rear end.

 

[Department Of Boost]

IMHO building a roadrace/standing mile car is an oxymoron. Two totally different things. You need BIG power to go 200mph, and that means a blower (or a big, big big block). And going FI on a track car is a very steep uphill battle. I’ve gotten to the top of that hill with my 2007, but it took the most complicated/big/custom/$$$$$ intercooler system that has ever been attempted on a S197. And a really big blower so it doesn’t make as much heat as a smaller/overspun one. And you really need to be running e85 to keep temps anywhere near “warm” (never pulling timing). Like I said, it can be done. But for what. 700+hp at the road race (RR) track is near useless. Fun, but useless. Plus you will never be able to do anything about the extra weight of the blower/cooling system (150+lb, maybe more) which counts on the RR quite a bit.

My next car will be a road course car that will have a NA Coyote in it and be as light as possible.

But, if you want one that does both here are some highlights/thoughts:

-Cooling, lots and lots of cooling. You are going to spend a ton of money on coolers, lines, fans and pumps. And at some point you will need a big amp alternator to run those pumps. This will be your #1 concern. If you run e85 and the right coolers you can go without an ice chest for the mile. Which is something to consider because an ice chest would be a PITA and useless at the RR track.

-Aero, aero, aero. The S197 is a brick wall. They go a lot faster with some aero help. Big vented hood (Tiger Racing), fully functional splitter, smooth belly pan, functional diffuser or belly pan from axle to rear bumper.

-“Fence” in all of the coolers. This will help with cooling and aero.

-A lot of people will say go A2A with a centri or turbos’, and I don’t dispute that has it’s advantages. But with a big/good enough cooling system you can get a twin screw with a A2W setup working very, very well. And there is one huge advantage to running a A2W setup. You can run the pumps/fans between sessions (you will need a 110v power source and a converter though) and cool that sucker right down. That is something you can not do with a A2A setup. Additionally a A2W will cool while sitting still or driving under 50mph much better than a A2A will (normal driving, if you will still be doing that sort of thing).

-If I were building a dual purpose 200mph/RR car from scratch I would be real tempted to go with twins. I would still run e85 and I would go with a A2W setup still. Twins have a lot of pluses. But for me they have one huge minus, and that is packaging (on the S197 at least). Even if you gut the engine compartment, move the electronics, etc you are talking about 10lb of shit in a 5lb bucket. Not so fun to work on. Additionally from what I have seen most twins have the air filters under the hood…..which sucks in underhood air…..which is already really hot because of the turbo’s. It’s hard to keep IAT’s down when you are sucking in 150-175deg air BEFORE you compress it. And at the end of the mile or on the RR course you will see underhood temps as high as 200deg without much trouble (I log underhood temps, they get HOT with a screw blower, let alone two turbo’s). You would want to run the air filters “outside” of the engine compartment……which is even more tubing in an already busy engine compartment.

And then there is the money. Setting a 5.0 up to make 700+hp as a RR/mile car will cost CUBIC dollars. Done even remotely right you are looking at big bucks, even if you are a fabricator. If you need stuff made and have to pay for it things will get silly real fast. And when you are done the car will be effectively useless.

Or you could call up John Kaase, fork over the $20-22K for an all aluminum 1000+hp big block and save yourself a lot of time and aggravation.

 

[lito]

Any opinion on brand or type? I have seen some Prochargers that look like they would make the boost levels needed.

If you get to route the shitty designed intake they use, maybe. In stock form, forget it.

For racing, should I stay away from self contained oiling systems; would it be a benefit or does it not matter, just personal preference?

Without data it can swing both ways. Engine oil during runs gets really hot, need to do a temp comparison and study the different oils they use.

I wonder if I damaged my diff housing on the 174 MPH run I did on my 2007 GT? I noticed a few weeks later, the next time I raced, I starting getting a really bad vibration on deceleration (in gear) from over 120. I completely rebuilt the rear thinking it was the gears, carrier, bearings, but it never went away. Seemed in spec... but now you guys are making me rethink it.

It didn't, I have done quite some 170+ runs in my car before installing the truetrac and everything was like new in there.

-A lot of people will say go A2A with a centri or turbos’, and I don’t dispute that has it’s advantages. But with a big/good enough cooling system you can get a twin screw with a A2W setup working very, very well. And there is one huge advantage to running a A2W setup. You can run the pumps/fans between sessions (you will need a 110v power source and a converter though) and cool that sucker right down. That is something you can not do with a A2A setup. Additionally a A2W will cool while sitting still or driving under 50mph much better than a A2A will (normal driving, if you will still be doing that sort of thing).

-If I were building a dual purpose 200mph/RR car from scratch I would be real tempted to go with twins. I would still run e85 and I would go with a A2W setup still. Twins have a lot of pluses. But for me they have one huge minus, and that is packaging (on the S197 at least). Even if you gut the engine compartment, move the electronics, etc you are talking about 10lb of shit in a 5lb bucket. Not so fun to work on. Additionally from what I have seen most twins have the air filters under the hood…..which sucks in underhood air…..which is already really hot because of the turbo’s. It’s hard to keep IAT’s down when you are sucking in 150-175deg air BEFORE you compress it. And at the end of the mile or on the RR course you will see underhood temps as high as 200deg without much trouble (I log underhood temps, they get HOT with a screw blower, let alone two turbo’s). You would want to run the air filters “outside” of the engine compartment……which is even more tubing in an already busy engine compartment.

There is nothing too cool between runs aircharge wise, as soon as you start moving air, your ACTs will go back to normal.

BTDT, stay away from aftermarket turbos on RR cars, there is way too much heat in there.

Forgot to add, I would do a centri with E85, make sure it sucks outside air, invest on every cooling solution you can implement (hood, vents, radiators), catch can everything that has oil in it (trans, rear, etc.) and start your own R&D project on the way, you'll see what you need to change, we can chart a somehow good start but only time and testing will tell.

 

[skwerl]

Aerodynamics play a big part as well. Don't know if you saw that video last month of the Toyota Prius out on the salt flats. Totally race prepped and it ended up getting sideways at about 185. I stopped counting the rollovers at about 14. Wind got under it and flipped it over.

 

[stkjock]

I think that was a Honda Insight that did the roll over wreck. It was also on a lake bed not asphalt.
However I agree, Aero is a big part of stability at those speeds.

 

[Department Of Boost]

There is nothing too cool between runs aircharge wise, as soon as you start moving air, your ACTs will go back to normal.

I agree there is more to cool when running a PD blower.......all that water for example.

But a centri still has a lot of stuff that sure wouldn't hurt to cool down, which you can't do aside from blowing a fan on it. The head unit, all the piping, IC, intake manifold, etc do not immediately drop to ambient the second you shut the car off. After a hard run/shut off it could probably be argued that the above parts heat up for a period of time before they even start to cool.

I would be curious how long the above centri parts take to get to ambient vs a PD blower that has water running through it (not running). IDK the answer, not even enough to speculate.

 

[Department Of Boost]

However I agree, Aero is a big part of stability at those speeds.

This Mustang went 252mph. Lots of aero. Check out the "mohawks" (or would they be bi-hawks?) along the roof. Most of the aero was done to keep air from under the car, not to manage the air going under the car. I got to check this car out quite a bit when it was being built/tuned.

Amazingly is made "only" 1011hp.

It was running a GT Supercar motor spinning to something like 8800rpm with (at the time) a prototype 3.3L Whipple on I think e85. They ran a 25gal ice chest.

 

[TurboX]

Tire size will play a huge roll in gearing. With 275/40 18s and a 2.73 rear gear, I could do 211 on paper at 7500 in 1:1(4th). (Y) rated tires really limit your selection of tires, I noticed saw a few cars with 315/40 18 Hoosiers at the Mile and that is prob what I will run, while they aren't speed rated I imagine they pass tech cause I saw a few 200mph cars running them. I do not know if I will stick with 2.73s or go back to the 3.31s.


I agree with GMitch that Road race/Mile car is hard to do, car isn't going to pull out of corners with a high(numerically lower) rear gear.

 

[TurboX]

This Mustang went 252mph. Lots of aero. Check out the "mohawks" (or would they be bi-hawks?) along the roof. Most of the aero was done to keep air from under the car, not to manage the air going under the car. I got to check this car out quite a bit when it was being built/tuned.

Amazingly is made "only" 1011hp.

Is that a custom rear spoiler ?

But a centri still has a lot of stuff that sure wouldn't hurt to cool down, which you can't do aside from blowing a fan on it. The head unit, all the piping, IC, intake manifold, etc do not immediately drop to ambient the second you shut the car off. After a hard run/shut off it could probably be argued that the above parts heat up for a period of time before they even start to cool.

I would be curious how long the above centri parts take to get to ambient vs a PD blower that has water running through it (not running). IDK the answer, not even enough to speculate.

Are you speaking about road racing ?

On my car on a 70/80 degree day, intake temps were less than 115 degrees at the end of the mile. I believe temps actually fell thru out the entire run(Don't recall for sure and haven't downloaded logs to my PC) My stock cooling system with a reicherd(sp) thermostat also had coolant temps of roughly 200 degrees. After I came back into the pits and popped hood all charge pipes were cool enough that I was able to hold or touch with no discomfort or burn. I did use meth injection but piping temps are pre meth injection and IAT temps are post meth injection.

 

[lito]

I agree there is more to cool when running a PD blower.......all that water for example.

But a centri still has a lot of stuff that sure wouldn't hurt to cool down, which you can't do aside from blowing a fan on it. The head unit, all the piping, IC, intake manifold, etc do not immediately drop to ambient the second you shut the car off. After a hard run/shut off it could probably be argued that the above parts heat up for a period of time before they even start to cool.

I would be curious how long the above centri parts take to get to ambient vs a PD blower that has water running through it (not running). IDK the answer, not even enough to speculate.

Heat transfer from the piping is usually overestimated, that amount of air is barely heated by it, I/C would be the bigger factor and once you roll it comes down quick. In essence is the simplest and more effective option for a RR FI car (as long as you keep the boost levels somehow low).