Robby

Lutgens- Yes, that'd be the tallest combo for our cars, short of something custom... you'd have a hole b/t 4th & 5th, but it might work. Let's see, you'd shift into 5th at ~126mph at ~ 4150rpms, so assuming you have decent HP & TQ at that point, you should still be able to accelerate through that tall 5th gearto ~194 @ 6400 & even 200mph, if you have 265/35/18's. But, 7k rpms would give you a potential ~219mph. Of course, if HP peaks at 7k, you could conceivably do it w/an S2 5th gear (.778) & taller tires in the 275/35/18 range. This would be better, overall, since youwouldn't have as big a hole b/t 4th & 5th, although, if you want the ultimate top speed potential, a 3.38 w/.72 5th & 285/35/18's @ 7k rpms would give you right at 220mph!

special tool

Yes, forgot to mention rear tire size. They are 275/40/17.
Torque peak is around 5000, with about 480 at wheels.

Rich Sandor

You can definately do it with an N/A 5th gear, over 380hp, and a long enough stretch of highway.

I still recommend removing the mirrors, rear wiper, dropping the car as low as possible, and putting narrow tyres on. I would even get some racers tape and tape up the lower two vents for the oil cooler, brake ducts & a/c. Maybe even tape up the body panel gaps. It make it a lot easier for the car to cut through the air above 120mph, and you'll reach speed faster.

hosrom_951

Guessing that would be a very bad idea, with that high load and rpms, you definately don't want anything blocking cooling.

Rich Sandor

^ Nope - you forget at that speed, you are going so fast that you barely need a penny size of a hole at 200mph to flow the same amount of air as stock size at 100mph.

If you look at Gemballa's 200mph 996, they did the same thing. So didi Al Holbert's record setting 928.

Rock

How can the N/a 5th gear go that high. I would blast that N/a motor and I was never able to redline 5th, but I would get it up to like 4-5000ish and it was only going like ~130.

Theoretically if the N/a had enough power, wouldnt it only take the car to like 164mph?

reactor2

According to the owner's manual ('87 model), the N/A 5-speed transmission with 215/60 VR 15 tires hits 7000 at about 180 mph. The 944 Turbo transmission with 225/50 16 tires hits 7000 at about 185 mph. I don't know the actual tire diameter size difference between the two, but there doesn't seem to to be a whole lot of difference between the 5th gears.

special tool

Gentlemen - you are forgetting to factor in the huge difference in ring/pinion ratio between NA and turbo.

We are talking about using the turbo R/P with the NA 5th.


rock - that is 3 demerits for you.

reactor2

Thanks SP I wasn't taking that into consideration. The N/A axel ratio is 3.889:1 and the Turbo is 3.375:1. So the N/A 5th is most definitely a taller gear.

DFASTEST951

So at 80mph, I'm at 3,000 rpms.

Does anyone know what rpm I'd be at with an N/A fifth at 80mph?

RKD in OKC

Marc Thomas and Susan Kirby of Devek made the street legal top speed record for both male and female drivers with a 549 hp 928 If I remember correctly. He had some sort of cover that sealed all the intakes, holes, hoodlines, everything on the front end. He tipped up the hood a little in the back at the windshield and fabricated the intake to suck air from the opening made by lifting the rear of the hood. The runs were made at the Silver State Classic, postal runs. I think his top speed was 212 mph and his wifes was 205. The drove the car to and from the event. He stated the car would have been faster with narrower tires and that each mph above 200 takes a lot more power and feels like 10 mph.

I looked for the web site with all the information on his car called "The White Car" but Devek's web site devek.net is under construction. I did find a listing where their average MPH was 167 for the 90 mile public highway cours.

I also remember the wedge shaped smaller Firebird taking 400 rwhp to make 200 mph.

RUF also is pretty good at making high speed run cars. He puts on much smaller mirrors and removes all the seams in the bodywork. When his YellowBird was the fastest around he stated he couldn't make an over 200 mph car with a sunroof because they couldn't keep it from being sucked out of the car.

Robby

There are SOOOOO many variables at work in these sort of debates- yes, removing mirrors, wipers (front & rear), etc, would definately help, but the car still has a .33 Cx & 20.4sq/ft of frontal area w/all of this on it, as a street car- lowering will reduce FA a tiny bit. IIRC, Scott Gomes said that removing the big flag mirrors was worth ~5mph for a stock Turbo S- I got this 2nd hand, so didn't hear it from Scott himself.

Yes, I agree w/Rich's point on cooling, although I I think the penny example is a little extreme- the car still needs some airflow, but holding back the drag is important. Also, remember downforce- I think it was Konstantin(?) who said he had a lot of downforce & would rather have that & lose a few mph than not have it & be unstable at those speeds- I agree 100%...

Special Tool- are you REALLY running 275/45/17's...? I don't see how that's possible, but the biggest I'd ever heard of until yesterday (& I had looked around a LOT) was a 275/40/17- a 275/45/16 is bigger than that, but a 275/45/17...!? That would be 26.74" RD, which is almost 2 full inches taller than stock RD- IF you could fit these under the fenders, at 7k w/a .72 5th, IF you had the 700RWHP or so to do it & the car didn't lift off the ground, or the SR didn't suck out, or Mars didn't explode at the wrong time sending a bunch of 3ft tall gnomes & leprechauns into your way causing you to wipe out, you'd be able to hit 227.6mph!!! Good luck!

Defastest- w/your taller tires, that sounds pretty close- remember, it's consistent, so if you double the speed, you'll have the answer for 6k, 80 X 2 = 160mph... You can divide 80 by 3 & then you'll have the mph / 1000rpm which comes out to ~26.67 & then you can multiply that by 6.4 (for 6400) & get 170.67mph. There's still a TON of speculation on these tachs/speedos. I tried the mile-marker method the other day, as someone suggested- HORRIBLE idea! I tried it at 60mph, then 75mph, 80mph, 90mph, & 120mph for runs of 5 to 10miles (the 120mph run was 2 miles). Mile markers are NOT perfect & I'll leave it at that. With a stock 24.86 tire diamter, you'll get ~26.1mph / 1000rpm in 5th. MO30 size 25.03 is ~26.4mph / 1000rpm & your 25.30" is ~26.7mph / 1000rpm. But, I rounded to 3.38 on the FD (w/.83 5th) & my formulas do NOT take into account static load, etc, so assume that by the time you're running some 190mph or so, they could be off a tiny bit. Plus, the variance b/t tach & speedo & tire size b/t manufacturer to manufacturer, not to mention specific air pressure, etc... I mean, it's possible to have two dif brand tires in 265/35/18 be off by .2" or more... That's why I hate being so adamant & technical in threads like these... There is SOME range for error here & I'd be willing to believe that by 190mph, if everything were off by the maximum amount possible, that 3-5mph could easily be in question...

Anyway, the forumla I use is:
(rpm X RD X 2.96) divided by[( FD X gear) X 1000] = mph
[rpm X (rolling diamter) X 2.96] divided by [(final drive X gear) X 1000]= mph

So, for my RD of 255/40/17 at stock redline, etc, I'd have:
6400 X 25.03 X 2.96 = 474168.32
474168.32 divided by [(3.38 X .83) X 1000] = mph
474168.32 divided by [2.8054 X 1000] = mph
474168.32 divided by 2805.4 = 169.0198617

What I want is a .778 S2 5th w/a 275/35/18 (since I KNOW it will fit- would rather have a 285/35/18)
This would give me:
6400 X 25.58 X 2.96 divided by [(.778 X 3.38) X 1000) = mph
484587.52 / 2629.64 = 184.3mph

This would still be taller than stock & not leave as big a hole b/t 4th & 5th- redlines in stock gears w/stock RD are 40, 67, 99, 134, & 167. W/this taller RD & 5th gear, they would be:
41, 70, 102, 139, 184....

RKD- was the SR thing in the yellow bird in that old issue of R&T in 1987 when Ruf first started the 200mph club by hitting 211 or 213mph in that thing...? I don't remember that, but have the issue- would like to see it- having a SR panel blow out seems pretty tough to do, but I guess it just goes to show... Hell, terminal velocity isn't even 200mph & that's w/the most air resistant clothing & a perfect needle nose dive, etc... If you can't even drop perfectly from 10 miles high & FALL to the earth at 200mph, then you know it takes some power to push a car that fast...

reactor 2- here's a few #'s for you...
.72 5th X 3.889 = 2.80008
.83 5th X 3.375 = 2.80333
.72 5th X 3.375 = 2.43

205/55/16 = 24.88
225/50/16 = 24.86
245/45/16 = 24.68
225/45/17 = 24.97
255/40/17 = 25.03
265/35/18 = 25.30
275/35/18 = 25.58
295/30/18 = 24.97

To get the rolling diamter of a specific tire like a 245/45/16, you have to know that 245 is width, in mm, then 45 is aspect ratio or sidewall height & this is a percentage of the width, & the last #, I'm sure you know, is diamter of wheel in inches. So,
245 X .45 = 110.25mm & this is sidewall hieght. But, you have to remember to multiply this by 2, since the sidewall is all the way around the wheel- look at it as if it's on top & bottom. So, if you had a 225/50/16, you'd have half of 225 & then multiply by 2, which brings you right back to 225mm. anyway, back to the 245/45/16 example.
245/45/16 = 110/25
110.25 X 2 = 220.5
you need to convert to inches- an inch is 25.4mm, so-
220.5 / 25.4 = 8.68
16 + 8.68 = 24.68"

Another example would be 255/40/17
255 X .4 = 102
102 X 2 = 204
204 / 25.4 = 8.03
17 + 8.03 = 25.03

Hope this helps...

sweanders

When doing the number crunching it is important to take the tire growth into account. At 200 mph it will most likely be around 4%. Better make sure that it won't rub at those speeds or you'll get a blowout due to the heat...

Robby

This is a good point & is sort of what I meant when I said that tire pressure & even manufacturer differences b/t tires of same sizes, etc, will affect things. BTW- not sure, but would static load not take some of this tire growth OUT of the equation?

sweanders

Static load would give a lot of heat. I haven't done a lot of testing myself but I have seen indications of it on my own cars. I got the 4% number from talking to open road racers.