Final Drive gearing change?

All of the gear ratios are shown in the OM (page 17 for the US 308i OM and page 13 for the standard 308i OM). Surprisingly, the standard version has a lower pinion & crown set-up 16/65 vs the US 17/63 (I thought on some F models they did it the other way around to give the standard version more top end), but it won't be cheap (neither parts nor labor ).

I also recall a custom drop gear set-up was/is also available out of a source from Australia, but I'd bet the costs are in the same league.

 

I imagine you could have the differential remade in a higher ratio with a better LS unit, like a Quaife. http://www.koalamotorsport.com/ are well known for doing this on BMWs. I am sure they can work with you on something for your car, and offer it to all 3x8ers then as well.

 

Ferrari 3x8s already have a rather high final drive factory. No other car I have owned crusies on the highway at over 3000 RPMS.

 

It wouldn't be $20K, but I'd bet somewhere in the $5K-$10K range depending on the cost of the parts (like if you could find a complete used gearbox/diff for a good price).

I checked the FerrariUK website, and it's a little confused (for the standard version 308i they list a US version gearset, and for the US version 308i they list a CH version gearset -- they can easily count the teeth so you should know what you're getting) but the price is 3K~3.5K Pounds either way. Add in the cost for R&Ring the engine and doing the gear work, and it's the same old story -- you'd be better off $-wise selling your 308i and buying a 308QV or 328

 

Agree with Steve cost would more than likely be prohibitive (however would give a substantial discount on these parts), but for the record I have checked our stock and counted the teeth and the US spec shows 16/65 and the CH spec shows 17/63, which is opposite to what the handbooks state !

 

At least that makes sense for the taller gear ratio being non-US, but your on-line SPC actually matches the handbook since the 17/63 CH gear set is associated with the US 308i (and vice versa)? Or would you send the set based on the gear version rather than the car version?

Anyone have a known 308i car version gearbox/diff apart that they can count to double-check?

 

Steve,

I would always send (and clarify in advance what ratio was wanted) the gear version rather than the car version. I would also check and count the teeth on any crownwheel & pinion / gear set just to make sure want is sent is exactly what is wanted.

 

They used to have Michelotti (sp?) kits for the 308 series with changeable drop gears many years ago which would probably be the easiest and most economical way to go if you could find one.

 

I once changed the final drive gear in a USA 2V 308 with one for a USA '83 308. Great low end power but lost a lot of top end speed.

 

Drop gear components still available. Trust me, you don't want the old Michelotto design from their rally program.

I don't have current cost. Over $5000, but should be less than $10,000 for parts. Gives you seven different ratios, so you can vary top speed from 160+ mph (if you had the HP) to only 100 mph. Comes with a beautiful magnesium casting for the case and your choise of straight cut (for that full-race sound) or helical gears.

Complete dog synchro convertions too so you can do no-lift shifts!

Send me an email if you require additional information.

Best regards,

Rob

 

I've wondered about changing the gearing too at times. The stock US is painfully short, which works very well here in NJ where over 70mph is no man's land, but should you try and take a trip to say the US Grand Prix, cruising 8 hours at 90mph+, you'd go insane.

Looking at the manuals on the owners site, the drop down gears are always 27/30 (1.11). The diffs are 17/63 (3.71) for carbed, 17/65 (3.82) for QV euro, and 16/65 (4.06) for QV USA. (calculated trans gear ratios - ie 1,2,3,4,5 and rev - in the manual account for the drop down gears, so use the tooth count to calculate the actual gear ratio for that particular set). WIth stock height tires on a US 308QV you should be able to pull 158.5mph@8000rpm (not accounting for different manufacturers sizing differences or centrifugal force, just using 225/50 on a 16"). 80mph@4038rpm, which is great for a track car with the 308s power to weight, but sucks in general, especially if you are making noticeably more than stock power.

My objective is to gain ~175mph top speed. To do this I can either swap in a carbed diff and get 173.4mph and 3691rpms @80mph. Taking a trans apart takes time though to do right. And, you still need to find a stock carbed diff gearset. And then if you ever want to swap back you need to pull the trans back apart.

My thought is to work with the drop down gears. If you were to change them to a 1:1 ratio you would be have a top speed of 175.9mph@8000rpms and 80mph @3638rpm. The cover should be able to clear a 30 tooth gear (that diameter). So, 29-29-29 would be ideal, but then you deal with having one tooth to one tooth all the time. Something like a 28/29 would give you 182.2mph top speed and 3513rpm @80mph and avoid that direct correspondence. Might be a bit too much for a stock engine. And by using the drop down gears you can swap them in like an hour, and don't have to drain the engine or trans (top off after). It seems that 3 gears can't be insanely expensive, every serious race shop in U.S. seems to be able to make them nowadays with how far CNC has come. Some place like Carobu, Norwoods, or Modena Engineering should be familiar with the application.

For like $700-800 it is a great mod. Just my $.02

 

Just be warned you will be increasing engine wear and decreasing gasmilage (in general, more so on the highway)

 

Anyone got a carb'd diff cheap? Wouldn't mind the option of increasing my highway MPG & reducing engine wear.

Guess what I'd really like would be just a taller 5th gear so cruise RPM would be down.

 

Yes, I want one too !

Wouldn't doing 65 mph with the engine slowly purring @ 2250K ( or lower)
be nice and quiet, saving $$ on gas, and lowering the engine wear be a good thing for our old 308s.

That would save about 2,000,000 piston strokes (per cylinder)
4 million valve operations (per cylinder) on my drive from the Twin Cities to Chicago and back, and cost the difference of gas for the trip will drop from
$128 to $96 (approx) not huge, but thats just a one weekend drive for me.

Can a group of people get together with some guy with a CNC and get a good deal on a gear design\cut. ?

 

AMEN MRFOTOS,
We're on exactly the same wavelength!

 

Hi, Sam. I just wanted to point out that many Ferraris have a transaxle, in which the rear end and the transmission are combined. This makes changining the final drive ratio more difficult than it would be on most cars that simply have a rear differential.

--Matt

 

Ditto! Most of my driving is on the highways, and after a while that 3500/4000 RPMs just kinda drones into your head. I always feel like reaching for 6th, and then I remember it's not there

 

The Michelotto cars (Group 4) used interchangeable drop gear that allow changing gearing in a snap (less than 20 min).
This setup for 308 and 328 cars involves using a different (bigger) drop gear cover in order to clear the center double gear cluster (instead of single gear in normal cars) and changing the clutch shaft as well as the gearbox shaft in order to allow securing the drop gears by circlips.
Serveral ratios were available that allow top speeds anywhere from 100mph to 200mph but these are now extremely hard to find and very costly.

The drop gears of the Michelotto cars would look like this:

I ->top gear to clutch shaft (longer than OEM)
II ->center double gear cluster
I ->bottom gear to gearbox long shaft (longer than OEM)

The top gear drives the center inner gear. The center outer gear drives the bottom gear.

whereas in the normal cars its like:

I ->top gear to clutch shaft
I ->center gear
I ->bottom gear to gearbox to gearbox long shaft (longer than OEM)

 

Count me in too. I'd love to get the revs down, I hate the highway drone...now that it's kicking out oner 400 ft-lb torque, 1st gear is about useless anyway

 

You can drop your revs by increasing your rear wheel and tire size. This has the same effect of changing your final drive gear. You'll also be getting better mileage with the drop in RPMs on the highway. But, don't forget you'll be trading this for slower acceleration.

Go here to the Speed/RPM Calculator.

Plug in the numbers you have, print out the info. Plug in your options and you can then see what the differences are.


Just a thought.

 

Yes Charles, that will help, but I think the speedometer will also have to be recalibrated, and Ive moved up from 14" stock to 18" wheels and now no more room in the wheel wells for bigger tires.
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For those who have requested further information on drop gear kits and transmission conversions, I'll have information regarding price and availability toward the end of next week. The manufacturer I distribute for is on holiday for two weeks.

Thanks for your interest and patience.


Best regards,

Rob