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The capabilities are whatever you make them. I have no doubt that there are GTMs out there that have enough HP to go well past the 250 mark. I just two weeks ago took a GTM to over 2 Gs in a corner with DOT tires. There is no question that the GTM has certain advantages over the Enzo...like weight and potential horsepower...that will allow it to out perform an Enzo in many respects. Will your girl want to get naked on the buttery leather of the GTM...only if you put that buttery leather in YOURS! :)
 

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IIR I've seen someone report ~180mph.

The "faster" comes from the Car & Driver Magazine data collected with the LS7 GTM and is refering to the 0-60mph, 0-100mph and 1/4 mile times.

Here's a link. Design | | Factory Five RacingFactory Five Racing

Just click on "Performance" near the bottom of the page.
 

· North Florida
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For all intent and purposes, the limiting factor on a "stock" GTM is going to be the vavle springs in the heads !! PERIOD... end of sentence.



How is this you ask ?? Well, let me elaborate. Since your STOCK porsche transaxle ( even the G5050/52) only has gearing to accomodate 165 mph based on the top rev limited stock valve train of aproximatley 6200 rpm of the stock LS based motor... thats all your gonna get, even if you have 2000 hp and mclaren based road stability.

correction: Looks like the G5052/50 could make it to 190 mph at redline.... but you would quite literally have the engine on the edge of grenading itself which could prove fatal if something happened that locks up the driveline on you if even just for a second before you could mash the clutch in you would be history !
 

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It's kind of academic here in the US anyway. I've owned several cars, including a Maserati, vette, as well as several cars I've built myself. Most "displays" of speed are over well before you'd reach terminal velocity. 99% of street encounters are over by about 100-120 mph when the loser realizes there's no way he can win.

If you want bragging rights for something like that, you gotta go do the Texas Mile or enter a race like the Silver State Classic Challenge. Now that looks like fun!!
 

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I'd worry more about the tires exploding than high speed stability. Yes there is an issue, but it can be dealt with through a couple canards, a splitter, and good vehicle setup.
I also remember a thread about steering at high speeds being an issue, can't remember the specifics, basically someone thought it darted too much over 160mph? But one guy posted a reply saying "if I can't get my GTM to go 200 I'll burn it!" HAHAHA.....pretty funny.

At any rate I think it's worth bringing up...I don't have a GTM yet but I'm curious to know if it's that big of deal or not?
 

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I've seen 162 on the heads up display.

That was nowhere near the limits of the gtm, but it was beyond the limits of this driver and the road I was on. I wish I could say it was smooth and stable ride. I'm sure the body modifications we made are contrary to good aerodynamic principles and our car was not built for that type of activity. But I had to do it once right?
 

· Snake Farmer
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I imagine that Ferrari does wind tunnel tests on their body designs, to look for issues at higher speeds.
Not sure if anyone has been able to do that with their GTM, but I question if FFR has ever done them?
 

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From 'Competition Car Aerodynamics' by Simon McBeath:

Vmax (mph) = cubed root of [(whp x 146,600)/(Cd x Frontal area in ft squared)]

425 Wheel hp, 18 square feet, and drag coefficient of .50 = 190.5 MPH

Seems kind of high even with a dirty Cd.

Cd of 0.55 = 184.6 MPH.


By the way, if you want to go this fast in a GTM, evidence seems to suggest that a rearward aerodynamic ballance is reqired for high speed stability. This is detailed in 'Competition Car Aerodynamics' as well as 'Race Car Aerodynamics: Designing for Speed' by Joseph Katz. At speeds this fast, understeer is a good thing, oversteer= bad.

In other words, put a good rear wing on it and the aero should be fine. Work the bump steer out and get your toe settings right and the suspension geometry should be fine. Get some good dampers and the suspension dynamics should be fine. Then go fast!

Mark
 

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Therefore, 22.5 Ft, 0.8, and 400 Hp, Typical roadster = 148.24287?
 

· Too much is just enough.
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Therefore, 22.5 Ft, 0.8, and 400 Hp, Typical roadster = 148.24287?
For the roadster, the data has already been done. All theoretical however I'd guess spot on to about the 200 MPH mark. I don't think a Cobra could do 250 MPH with 1,000 HP, regardless of how long the straight was. It would end up in an ugly accident north of 200 MPH. Terminal velocity for the Cobra is how big are your balls?

The Mayfield Company Homepage - Automotive Analyses

As said before, most vehicles have a terminal velocity beyond that of their performance abilities. With enough power and correct engineering, the super cars and hyper cars of today could hit 300 MPH. The problem you end up facing is tire life. The Bugatti Veyron's tires only last a short time at high speeds. There are Ford GT owners who have taken their rides in excess of 260 MPH in a standing mile and I believe they ran slicks.

If you have enough power, engine layout is not a problem. If you twin turbo a well built LS engine, you'll probably let off the gas with plenty of untapped ability. This is assuming that your suspension and steering is set up correctly for high speed runs. FFR did some wind tunnel testing for the GTM but I don't think they looked at speeds north of 200 MPH. If stupid fast speeds is your desire, I would look at a different vehicle that has already been tested for such speeds.
 

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For all intent and purposes, the limiting factor on a "stock" GTM is going to be the vavle springs in the heads !! PERIOD... end of sentence.



How is this you ask ?? Well, let me elaborate. Since your STOCK porsche transaxle ( even the G5050/52) only has gearing to accomodate 165 mph based on the top rev limited stock valve train of aproximatley 6200 rpm of the stock LS based motor... thats all your gonna get, even if you have 2000 hp and mclaren based road stability.

correction: Looks like the G5052/50 could make it to 190 mph at redline.... but you would quite literally have the engine on the edge of grenading itself which could prove fatal if something happened that locks up the driveline on you if even just for a second before you could mash the clutch in you would be history !

Presumably, if you are going to be utilizing an engine that has the kind of power to get the GTM up to,and perhaps beyond 200 MPH, then I would not expect you to be using a G50 gearbox of any type, and if you were then you would certainly have had it re-geared, and strengthened, and a limited slip differential installed into it.

If you were to use the more robust GT2 or Twin Turbo gearbox, and assuming that you have a rolling tire diameter of 27 inches, then I think you will find that you can break the 200 MPH mark with room to spare on the tach, using just the stock gearing. With a simple gear change you can further your protection of the engine even more.

As with any project you have to have the correct tools to do the job safely, otherwise bad things can, and often do happen.

Erik Johnson
 

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I finally dynoed my new LS3 I built last weekend. @ 6500 RPM in forth gear I was at 157 MPH.

I built my motor to handle 7000 RPM, that said max power was made at 6154 RPM and I was making 425.1 HP and torque was at 362.8 at the rear wheels. With about 19% power loss because of the tranny I should be at 505 at the motor.

It blows my mind that some guys are putting 1000 HP in the GTM.

Happy Building, Ron
 

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is there not a very long straight at Neubring? Shirley the pro driver in that youtube video topped out. I don't have youtube at work, but that's where I'd look first.
 

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Ron my LS1 dynoed at 408 HP 362 Ft Lbs of torque at the rear wheels. Funny our torque numbers are identical. So according to my gear chart my G50-20 with taller 5th & 6th gears woulld give me 165 mph in 5th and 212 in 6th at 6500 rpm.

Math was never my stongest subject but if you have a 19% power loss and the result 425.1 wouldn't the motor HP actually be around 525? 525 X 81% = 425.25
 

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Unless you engine dyno, then put right in and chassis dyno again, you really have no way of knowing what the % drop is. I have heard dyno guys say anything from 10% all the way up to 20% in driveline losses. Seems to me this number is more determined by the desires of the customer hitting a particular HP number than actual science, so be aware. The only numbers I would actually trust will be expensive to get, and even then, there can be variances between the engine and chassis dynos.
 
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