Reducing Revs at Higher Speeds

[BoyRacer]

I take back what I said about keeping the 3.90 for city driving. The 3.54 makes first gear so much more usable.

 

[Bob_Spidell]

Nowhere yet in this discussion has anyone mentioned tire size. ...

See above:

"There are gearing calculators online that will give pretty accurate RPM/speed numbers; some even include actual wheel/tire diameters."

Begs the question: Measure tires standing still or use manufacturers' numbers? I think the latter are probably most accurate, as diameter will increase at speed due to centrifugal force; anyone seen the slo-mos of the top fuel dragsters--we used to call them 'rails'--getting off the line? The sidewalls twist something crazy and the wheels squat, then the tires grow vertically big time--like 15-20% or more--as the centrifugal force slings them outward.

 

[Martin AH 3000 MK III Phase 1]

I am now looking for a reliable supplier of the ‚pumpkin‘ with ratio 3,54. I want to change the whole unit and not only crown pinion and crown wheel as I want to shelf the original differential and keep it as is.

Can anyone recommend a good supplier for a remanufactured rear differential In the UK? Any hint is welcome.

best regards, Martin

 

[Michael Oritt]

And a larger-in-diameter tire, such as the XAS 180R, will effectively reduce revs by producing slightly higher speeds, etc.

 

[Hamish Racing]

Not too many places allow outright purchase and they are not cheap.
But these will be good

Recon Diff with new 3.54 CW & P- Reconditioned Diff with new Crown Wheel & Pinion size 3.

Recon Diff with new 3.54 CW & P, Reconditioned Diff with new Crown Wheel & Pinion size 3.54.

www.bighealey.co.uk

 

[Bob_Spidell]

Kinda surprising they don't require a core; they must have a stack of them. LSD installed labor-free is tempting (though arguably not necessary on a street Healey).

 

[Bob McElwee]

Might be cheaper to buy a used pumpkin and put the 3.54 gear in it.
jus a thought.

 

[Jack T]

I put 3.54 gears in a 67 BJ8 with a 4 speed w/OD and a 62 BT7 with a Toyota 5 speed (synchro 1st gear is heaven).
Initially on the BJ8 I ran 195/70 X 15 until I could no longer get them. They look much, much better IMHO. I went to 185/70 X 15 on both cars eventually.
we did a lot of long distance trips to regional meets and Conclaves. Needless to say my speedo was just for approximate MPH. GPS have me close to 75 MPH at 2500 RPM.
the 3.54 also made both cars so much more bearable around town.

While wider, 185/70 -15 tires have less sidewall height than 165 - 15. 185 x .7 = 129.5; 165 x .8 = 132. With new springs and rebuilt shocks at all four corners I found that I can run 185 -15 with no rubbing issues. 185 x .8 =148. They fill the wheel arches very nicely. Also gives me an extra measure of clearance, which is always a good thing.

 

[Bob_Spidell]

"Needless to say my speedo was just for approximate MPH"

Aren't they all?

 

[BoyRacer]

While wider, 185/70 -15 tires have less sidewall height than 165 - 15. 185 x .7 = 129.5; 165 x .8 = 132. With new springs and rebuilt shocks at all four corners I found that I can run 185 -15 with no rubbing issues. 185 x .8 =148. They fill the wheel arches very nicely. Also gives me an extra measure of clearance, which is always a good thing.

I don't know what any of that means. My Michelin XAS 180 HR 15s have an overall diameter of 26.8". That 's how I compare the height of tires.

 

[Hamish Racing]

This is a useful site
you can compare tyre sizes and speedo function. Set to imperial or metric.

Tire Size Comparison

Tire size comparison the easy way. Use our tire size comparison calculator to compare diameter, width, sidewall, circumference and revolutions per mile.

tiresize.com

 

[Jack T]

I don't know what any of that means. My Michelin XAS 180 HR 15s have an overall diameter of 26.8". That 's how I compare the height of tires.

Your sidewall height is approximately 180 x .8 = 144mm. Much taller than 165-15s or 185/70-15s.