Candleman

Hi, I'm wondering if those of you with modified Uber-928's, where top speed is limited by the top gear and not by hp/tq if you can list the theoretical top speeds of the following gear sets at 6200 RPM:

1987 S4 2.20 5-speed vs auto (are they the same?)

1989 S4 2.54 5vA

1993 GTS 2.75 5vA

Will larger diameter wheels/tires have a significant effect on icreasing maximum velocity as well?

What is done to the tranny's of these 928's that can break 200mph?

Anyone???

Lizard928

I just asked the other day for the gear ratios of the G28/10 do a search for it, in there is a link to an excell spreadsheet that will answer your questions,

I found that with the 25.66" diameter tire and the gear ratios of a G28/11 with the 2.20 you would redline 5th gear at 214.4 MPH at 6500rpm.

IcemanG17

With the 2.20 rear end the top gear in the auto or 5 speed is 1-1 so your final drive is 2.20.... With tall tires (think 275/40-18's which are 26.7" tall vs the 24.7" stock S4 tires) @ 6200 rpms you would be at 221mph...... The lower rear end cars in theory would be gearing limited to about 195mph at the fuel cutoff of 6800rpms.....

With that said there is not a 928 around right now that has the power & aerodynamics to push 221mph.... 210mph....I think there is......maybe a touch more under the right conditions....but 221 takes ALOT more power than 210!!

The formula works like this.....

RPM of the motor divided by the final drive of the gear (2.20) So at 6200 rpms & 2.20 would be a wheel rpms of 2818rpm divide this number by the number of rpms it takes that wheel to go 60mph (taller tires turn less for same distance) in this case use 765 (for the 275/40-18 tire)which gives you 3.68 then multiply this # by 60 (for # of times 60 is mulitplied) which give you 221.02mph......

2.54 is 190.70mph @ 6200rpms
2.73 is 178.12mph @ 6200rpms

You should be good and confused now!

jorj7

Here are a few numbers I came up with. These are based on experience with my
car and extended to the other Final Drive Ratios. I'm sure other's have their own
experiences/methods of figuring this out, so they could get other numbers.

With a 2.73 Final Drive Ratio (FDR) and 24.7" diameter tires and stock aerodynamics:
6200 RPM = 167 mph (would need about 280 rwph)
6400 RPM = 172 mph (needs ~305 rwhp)

With a 2.73 FDR and 26.6" tires with some aerodynamic changes:
6200 RPM = 180 mph (~323 rwhp)
6400 RPM = 186 mph (~358 rwhp)

With a 2.54 FDR and 24.7" tires and stock aerodynamics:
6200 RPM = 179 mph (~342 rwhp)
6400 RPM = 185 mph (~374 rwhp)

With a 2.54 FDR and 26.6" tires and aero mode [This is what I was running last year when the engine died]:
6200 RPM = 193 mph (~393 rwhp)
6400 RPM = 199 mph (~429 rwhp)

With a 2.2 FDR and 24.7" tires and stock aero:
6200 RPM = 207 mph (~512 rwph)
6400 RPM = 214 mph (~560 rwph)

With a 2.2 and 26.6" tires and aero mods:
6200 RPM = 223 mph (~588 rwph)
6400 RPM = 230 mph (~690 rwph)

This year I'm hoping to run 5700+ rpm with a 2.2 and 26.6" tires, this would be 205+ mph.

Ed MD

I had 200+mph at 5900rpm at the first NC dyno day that Chris Lockhard set up a couple of years ago. We did this twice, the dyno set up shut done after 200 mph. This was with my 85 5 spd w/2.2 rear end, 17" Z-rated tires. Ed M

mark kibort

If the holbert car got to 180mph and had the same dyno hp as i found it to have 15 years later, it would be 292rwhp. Say you wanted to go 22mph. So, 220mph / 180mph cubed and then take that number times the 292 rwhp number. (to get to 220mph for example)
the hp required adds up pretty quick!
mk

mark kibort

221/210 = 1.05 cubed = 1.16.

if the hp was 600hp for 210mph , it would take700hp to get to the 220mph mark

isnt the redline of the S4 6600?

mk

Candleman

Ahh well I just looked and actually my 89 S4 is colored red. starting at 6400. And Al Holbert's aka Your car hit 172 on the salt flats. I've never heard of it hitting 180 but maybe it did after being modified or something.
Thanks for all the knowledgeable answers! You guys are great.

mark kibort

The Holbert machine actually did 180mph at a track in italy, called Nardo.

However, it was an unofficial run as the story goes. that was in March of 1986, then the attacked Bonneville in August for the world record. They say wheel spin on the salt was a limiting factor.

Mark

AO

I beleive you are correct. 6800 on the GT's, which I'm thinking about bumping up to 7,000.... on second thought... probably not.

Vilhuer

Fuel cut off is at 6600. Dial has less in early MY's. '87-88 6200 and '89-91 6400 IRR.

AO

GT is definitely at 6800

Brett928S2

Hi

My auto ratio is 2.357 and for my 200 mph plus runs I will fit 275/40 18s (spot on Brian)

That will overdrive my ratios by 7.25%...

Then my rev limiter will be set to 9800 (not that I will ever get those revs, but its to move it away from the normal 6375)

Then add Nitrous for almost unlimited hp

I am aiming for 208 mph but may do better or worse...we will see

All the best Brett

PORSCHE 928 S2 AUTO V8 4.7 LTR 1986 IRIS METALLIC BLUE WITH X-PIPES ,RMB ,PROMAX CHIPS, KICKDOWN SWITCH, K&N, WIZARDS OF NOS - NITROUS KIT 150 HP JETTING - 505 BHP / 500 FT LBS TORQUE
PCGB UK 928 FORUM MODERATOR - Email managingdirector@pchealthcare.co.uk

Larry928GTS

www.f-body.org/gears

AO

Very cool Larry! Thanks!