Top speeds???

[porski]

I have a 79 911sc,targa,wide body,3.0L. My question is when i`m
on the highway in 5th gear at about 5000RPM i`m going about
170 km/h,and at 6000RPM i`m going 190 km/h. When i picked up
the car about 3 years ago it just had a new rebuild tranny installed. Does this seam like a slow speed for the gear and
RPM its at. A good friend has a 1980 911sc and his car does
about 260 km/h at about 6000 RPM. Thanxs a head of time
for any help with my question. Thanxs

1992 chevy blazer (work truck)
1979 Porsche 911sc (my toy)

[k9handler]

damn the metric system!!!

Ok, my car will do 130 mph at 5000 rpm in 5th. Above that is yet to be seen...but soon I will be in Germany with her and maybe we will find a place to open it up a liitle more. So from the sounds of it, yes that is a bit low for the gear/rpm.

[Dana_Drury]

Thats definately not right. Are you sure you don't have a short gearing ratio? You should be seeing around the 250 km/h mark at those gears and revs.

[ZAMIRZ]

I think for U.S. spec cars redline in 5th gear is just a hair under 140mph.........I haven't been able to find info for the euros, can anyone shed some light on this?

later,

amir ('83 euro SC here by the way)

[Zendalar]

Hmm, my german manual for my -72T states that my car has top speed of 225km/h. What do I need SC for =)

[Milu]

Over 120 mph the wide body could be costing you some speed.

But why assume your speedo and rev counter are accurate?

[CamB]

This is just maths based on tyre size. Working on std sized tyres (check your size at Tire Rack) and (eg) 6000rpm...

Eg, Bridgstone S03s have 837 wheel revs per mile (this is the critical number) or 520 per km.

5th gear in a 915 could be 28:23 (SC), 38:30 (US Carrera) or 29:21 (early gearbox????).

Actually, the only number I am confident of is the first - the 28:23 because that is the one of concern to me so the only one I have checked up on. 28:23 is a ratio of 0.821 (overdrive, in other words). Ignore the other two gear ratio guesses.

You also need to know your ring and pinion - on an SC should be 8:31, or 3.875.

So, 6000rpm x 60 mins / (837 x 0.821 x 3.875) = 135mph, or 217kph.

6500rpm will give 6500/6000 x 135 = 146mph.

It looks like you speedo doesn't work properly though - an increase from 5000 to 6000rpm in 5th should increase speed from 170kph to 170 x 1.2 = 204kph. This is a problem regardless of whether you have standard gears and tyres or not.

My 2002tii has a shorter diff for racing. Now the speedo reads much higher than it should... The same goes for smaller diameter tyres than standard.

[cary]

With USA gears. 915 gear box.

2.7 Redline 5th. 137 mph 75s
3.0 Redine 5th. 143 mph 75s ( new engine, chain failure on 2.7 )
3.2 Redline 5th 152 mph 77 Carrera

Not real scientific. This is where I was at when I ran out of pedal and the rev-limiter kicked in.

[RarlyL8]

My car has a nearly identical setup.

'78SC 3.0L
Widebody (coupe)
Rear tires 24.5" tall (345/35-15)
Stock 915 gearing

My speedometer and tach have been checked against a mechanics tach and a stopwatch. Both are spot on.

Top speed @ 6250rpm in 5th gear is 140mph. Pulls hard all the way.

[phe]

I have a SC 3.0L widebody,

1. with 195/65-15 & 215/60-15 top speed on the speedo about 235 Km/h
2. with 205/55-15 & 225/50-15 about 255 Km/h
3. with 225/50-15 & 285/40-15 about 245 Km/h

real speed for case 1 & 2 are about the same, case 3 should be a little slower.

I do like crossing germany

phe