What rear diff ratio?

Adrian Worman · Post by **Adrian Worman** » Wed Mar 11, 15 7:49 pm

All gear/cam/carb etc combos are a compromise, they either work for just street, just race, etc but they can't ever do both perfectly, they're outdated components & concepts compared to modern transport, the whole concept of a classic is a compromise really innit?

End of the day Jon you build it just how you want it, as long as you enjoy it that's all that matters mate

I must admit I couldn't live with 4000 at 55.
By contrast tho my RPM's are about 3500 at 75 or so.

GJUK · Post by **GJUK** » Wed Mar 11, 15 8:00 pm

We had a small convoy to the mopar nats going on... Until my friend got bored of driving at 52mph

... And left. lol

60mph at 3500 rpm I could deal with.

Thanks again, will keep playing with the calculators and playing about with ideas.

autofetish · Post by **autofetish** » Wed Mar 11, 15 8:07 pm

Have you though about an over drive unit

Get the best of both world

GJUK · Post by **GJUK** » Wed Mar 11, 15 8:13 pm

autofetish wrote:Have you though about an over drive unit

Get the best of both world

$$$$$$ are they not.

Mick · Post by **Mick** » Wed Mar 11, 15 9:05 pm

If you're going to drive it on the street and to shows, you may as well put at least a 3.23 gear in it maybe even a 2.87. Nothing worse than an engine droning away on a motorway at 50-60 mph, unless you're being rewarded with some strip action at the other end.

mopar_mark · Post by **mopar_mark** » Wed Mar 11, 15 9:07 pm

Mick wrote:If you're going to drive it on the street and to shows, you may as well put at least a 3.23 gear in it maybe even a 2.87. Nothing worse than an engine droning away on a motorway at 50-60 mph, unless you're being rewarded with some strip action at the other end.

I agree wit Mick...

Dave-R · Post by **Dave-R** » Wed Mar 11, 15 9:11 pm

A GV overdrive is not cheap but with 295/50/15 tyres I was running 4.30:1 gears and with the overdrive 4000rpm was about 90mph if I remember right.

I think 70mph was a little over 3000rpm. I had a top speed of 140mph, 0-60 in about 3.5 seconds, ran 12.2 on the quarter, high 11s on a track not covered in glue, and returned 13mpg from a 530hp 440 six pack.

The GV overdrive was one of the best ideas I ever had. Made the car drive great around town.

Dave-R · Post by **Dave-R** » Wed Mar 11, 15 9:15 pm

My peak torque was around 3500 rpm I think. From 3000rpm to 4000rpm you could feel and hear the engine was "on song" and running happy and sweet as a nut. Peak torque is where the engine is at peak efficiency.

I don't know about you but I loved driving at 4000rpm the length of the A1 to get home after a weekend at SPR. I never felt so alive.

Mick70RR · Post by **Mick70RR** » Wed Mar 11, 15 9:38 pm

I've got a Gear Vendors overdrive in the RR. I went from 3.23 to 3.91 gears a week before the overdrive turned up and decided during that week that I'd never live with 3.91 gears without an overdrive. Once the overdrive is in it's like 3.08 gears, great for cruising. I still don't like the low first gear, feels like I'm changing into second the moment the clutch is out.

latil · Post by **latil** » Wed Mar 11, 15 10:02 pm

My old Fury had 3.23 gears/255 70 15 rears and turned around 2800rpm @ 70 mph 318/904.

MilesnMiles · Post by **MilesnMiles** » Wed Mar 11, 15 10:29 pm

3.55 best compromise.

MilesnMiles · Post by **MilesnMiles** » Wed Mar 11, 15 10:42 pm

Hers a nice polemic in favour of 3.23 from Mopar Action

I took this from Mopar Action a couple months ago...

3.23 Rant:

"Have we ever gone on a good rant about 3.23s? No? Well, why don’t you just cinch down that lap belt while we tell you like it is. 3.23s are sheer genius. Brilliant. The perfect gear. Ever try actually living with 4.11s or 3.91s or even 3.55s? Your crankshaft ends up spinning like a turbo impeller, you go insane from the noise, your top end is like 48 mph, and you get the same mileage as the Exxon Valdez. Don’t tell us about some TKO II overdrive tranny and carbon fiber driveshafts and how your cousin’s buddy ran one for four minutes in San Luis Obispo before that karaoke chick got involved, okay? First of all, there’s like eleven people who can afford that stuff. Plus the paternity suit. But you get the idea. And don’t tell me “Gear Vendors.” Same problem. Yes, they are stunning, yes the U-joint angles are nuts, and yes they cost more than the entire staffs’ monthly trailer rental and federal restitution payments together. So what do real people with real lives and real probation officers do? We yank a full 8.75 setup out of a 68 truck, reweld the spring perches, throw in some hypoid gear lube, hope it’s not frozen solid, and proceed to go collect a bunch of moving violations because it will both accelerate magnificently and still allow us to hit enough velocity to lift the windshield wipers off the glass (that starts about 115), just as the Excellence in Engineering guys intended. Perfect."

Mick · Post by **Mick** » Wed Mar 11, 15 11:10 pm

Very good Miles

My little 302 Mustang ran 14.87 with a 3.25 rear geared one legger and that got on my nerves on the motorway.

Dave-R · Post by **Dave-R** » Thu Mar 12, 15 9:00 am

How can the sound of a high revving V8 get on your nerves? Bloody million times better than radio two that's for sure.

MilesnMiles · Post by **MilesnMiles** » Thu Mar 12, 15 10:40 am

Dave 3.91 gears -Cornwall to Santa Pod =290 miles@ 3,700+
Chris Evans pleeze