3:55 gears...Top Speed?

tbirdsc357

Registered User
Just wondering what top speed can you guys reach with 3:55 gears before it starts to get rough. I have a 95 SC and at around 165km/h (a little over 100m/h) it starts to get rough, the rear end that is. Do I need to get this looked at or is this normal.

Thanks.
 
I think you are feeling the effects of the drive shaft out of balance. An aluminum one will solve that. You will also encounter the top speed limiter in the same speed range. A new chip for your EEC will take care of that, and MANY other things such as improved shifting on the 95 and up cars, better fan operating ranges, more HP, etc.
 
Multiple items can lead to that type of vibration.

Low frequency vibration:
Tires Almost exclusively.

High frequency vibration:
Depends on where you feel it.
Could be driveshaft or axle shaft, or wheel bearing.
Failing CV joints could show up as a vibration at high speed.
Failing U-joints could show up as a vibration at high speed.

And probably the most likely if all the others look good is what 392Bird mentioned, a driveshaft slightly out of balance.

An aluminum one isn't necessary. But a driveline repair shop that can balance the shaft to close tolerance would be necessary.

Factory balance may not have been all that great, and with rust buildup and possibly weights falling off, it's easy for the balance to change.

If you plan on sustained high speed runs it's important you check all of the above though. It won't take long for something to come apart at 110mph if it's "questionable" at 70mph.
 
Steve, mine was smooth going down 427 about 2 a.m. Sunday morning at 4600 rpm in 5th ... with my 27.0" tall tires, that works out to ... hmmm ... 150.72 mph !!! :D


cheers
Ed N.
 
C'mon Mike, it's only 150 mph, not a 300 mph Top Fuel car ! :D

Anyway, I would not do crazy-ass things like that without the appropriate equipment ... good suspension, big brakes, Z-rated tires, and some previous racing experience.

cheers
Ed N.
 
I know.. I know.. just play'n with ya.

Z rated tires should hold pretty true to shape up to their rated speed. But certainly the heat that is generated plus the rotational forces likely do, slighly increase the circumfrence.

Maybe then you were doing 150.72023 mph?


;)
 
Hey Mike, just redid the calculations after looking in the Goodyear catalogue for the exact specs on my tires. They are 27.05" tall, so when I figure it out again, it comes to 150.99995 mph !! So now I have a 151 mph car ...... WOOHOO !! :p

cheers
Ed N.
 
Tire growth from spin

Hey, have you guys heard of the BAZ technology in the BFG and Michelin "Z" rated tires and now in the Concord tires?

As you know, rubber cuts better if you stretch it. So when the Concord's tires hit a sharp piece of metal on the runway at over 100mph they sliced wide open. High speed cars have the same problem. Michelin has been using BAZ (a french acronym for "Near Zero Growth") technology for several years now, the prime "trick" being to wind the reinforcing belt on as a continious fiber instead of as a compounded biased belt. The tire grows about 3% compared to 15% for conventional radial (bias ply are worse).

Hey Ed, I've had the SVO up to 7200 in high with 3.73 and the T5 with the stock 225/50R16 tires ("Z" rated of course!). How fast is that? The speedo stops at 230kph and I was well beyond that. I was fending off a pass attempt by a buddy's LS6 powered GM. Any attempts he trys to make at the Ford vs GM thing are quickly shut down with a:
"I hear you couldn't pass a stock (wink) Ford 4 cylinder?"!

Steve Best
 
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