Gears.

Anonymous · Post by **Anonymous** » Sat Feb 10, 07 8:46 pm

Anyone tell me if there is a vast difference on street/motorway,between 3.23 gays & 3.9s.

Anonymous · Post by **Anonymous** » Sat Feb 10, 07 8:53 pm

Don't wanna go for the 3.9s,but I think it's time.

Pete · Post by **Pete** » Sat Feb 10, 07 9:49 pm

Use Dave Robson's Auto maths calculator off his Challenger site.
I would guess it would be worth about another 500rpm....

Anonymous · Post by **Anonymous** » Sun Feb 11, 07 1:33 am

Thanks Pete,I had a feeling you would pop up,you knew I would change them gears in the end.

RobTwin · Post by **RobTwin** » Sun Feb 11, 07 1:51 am

3.23's are great for road use but I wouldnt want to go any more 'radical' than 3.91's if you're planning to do as many miles as you currently do.

Our mph/rpm works out about 70mph at 3500rpm with 3.91's. So motorway cruising gets a bit frantic any faster than that

I remember doing 100 at 4000 in the Satellite when we had 3.23's (ssshh

dont tell Matt)..... took up both lanes of the A1 tho

Better start saving for a bit of Gear Vendors kit......

Anonymous · Post by **Anonymous** » Sun Feb 11, 07 2:22 am

Rob'I take it Stu was driving @ 100 MPH

RobTwin · Post by **RobTwin** » Sun Feb 11, 07 2:27 am

Come to think of it, I dont think I was even there that day

Pete · Post by **Pete** » Sun Feb 11, 07 9:33 am

Remember tyre height is a major factor here.

When I had the Daytona with the factory Dana & 4.10's and 14" original tyres, the car would only do 85mph taking into account a standard 5200 rev limit.
Whack on the 275 x 60 x 15" tyres and that was up to a (theorhetical) 109mph

.

You have very tall tyres so that will mitigate the effect a lot whilst having tall gears for a good launch and 60 foot time.

Anonymous · Post by **Anonymous** » Sun Feb 11, 07 2:13 pm

Thanks Mr Wiseman

Blue · Post by **Blue** » Sun Feb 11, 07 4:40 pm

And if you ran a 28" tall slick at the track, it would be even better! There's nothing like a set of 3.91's or 4.10's to really wake a car up. I have 4.10's and 29" tall street tyres, and I'm happy to cruise at 70 on the motorway.

Anonymous · Post by **Anonymous** » Sun Feb 11, 07 7:56 pm

Blue'I'm using 28" tall Hoosiers,so should be good then?

Blue · Post by **Blue** » Sun Feb 11, 07 8:03 pm

I reckon.

Matt · Post by **Matt** » Mon Feb 12, 07 10:41 am

to calculate the difference in rpm at a particular speed ,

3.9 divided by 3.23 is 1.21

hence, for the same road speed, your engine will be spinning 1.21 times faster with the 3.9's than with the 3.23's

if you're currently turning 3000 rpm at cruise , new rpm is 3000x1.21 = 3630
630 higher

if you're at 2500 currently, new rpm is 2500 x 1.21 = 3025
525 higher .

Absolute road speed per engine rpm (as previously stated in this thread) is dependent on tyre rolling diameter as well as axle ratio (well mainly these two, anyway) , and is a different calculation.

Anonymous · Post by **Anonymous** » Tue Feb 13, 07 12:09 am

Thanks Matt,useful bit of calculating