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 Post subject: Ferrari Drop Gears
PostPosted: Sun May 01, 2016 3:15 pm 
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Joined: Sun May 01, 2016 10:48 am
Posts: 6
Location: NYC
1st off,,, hello Gemellocattivo!!!!

I found this site looking for information pertaining to Ferrari.....

To introduce myself, my name is Chris and some of you may remember my car from other forums,
a turbocharged 87 Ferrari 328GTS

The question that brought me here is about drop gears.
I remember on other forums Mk e spoke of changing his drop gears on his supercharged 308
My car is currently in for service, so I figure this is a good time to inquire if this is a modification right for my application.

Are these gears available?
Cost?? direct replacement??
speedometer recalibration??
and did they effect the cars manners when not driven wide open?

Mark, I woulda sent this as a PM,, but don't know how to do it on this forum.
I hope this topic is in the right section.

Thx,
C.

here's a couple recent pics of the car


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 Post subject: Re: Ferrari Drop Gears
PostPosted: Sun May 01, 2016 7:55 pm 
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Joined: Thu Jan 01, 2015 6:47 pm
Posts: 4251
Welcome Chis...and nice job on reviving the bikini thread :)

Drop changes are not so simple or cheap. Nick Forza was importing a race set I think but they were straight cut so loud and I think I heard around $10k for the set. there was some talk about making a helical set if i10 sets were ordered...again 5k-10k per set is coming to mind. But these were 308 not 328 setups...don't know what's out there for the 328 gear box.

What I did was swap the top and bottom gears which was not so easy and I still haven't actually tested it yet.

For you I guess besides the money I think it depends on how you drive. I turbo is not going to help you off the line much so changing the gearing will likely slow you down for the fist 100-200 feet....I'd guess. On my supercharged car keeping the wheels from spinning off the line was an issue and I expect the same issue with the 5.4 line V12 so I thinkg the change would help acceleration a bit in my case. After that it shouldn't matter acceleration wise but get you the reduced cruising ropm or higher top speed I'm guessing you're after?


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 Post subject: Re: Ferrari Drop Gears
PostPosted: Thu Sep 15, 2016 8:30 pm 
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Joined: Sun May 01, 2016 10:48 am
Posts: 6
Location: NYC
Yes, I'm thinking better overall performance.
The car lights up the tires pretty good but not as hard as a big inch American V8 would w the same tires.
It's pretty controllable, but it seems to rev very fast & 1st gear feels pretty useless.
So I'm really just thinking about longer gears to make the most of the turbo's power.
Lower cruise rpm and a higher ceiling for top end would be added perks.
But this vehicle can probably already hit a top speed that a car this small and light probably shouldn't ever see.


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 Post subject: Re: Ferrari Drop Gears
PostPosted: Fri Sep 16, 2016 9:06 am 
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Joined: Thu Jan 01, 2015 6:47 pm
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328turbo wrote:
..... 1st gear feels pretty useless.
.


That is certainly what I found on the supercharged engine. 1st gear was good for idling around the parking lot, but even look at the throttle and the tires were spinning or you were at redline. I stopped using it for rapid acceleration runs and stuck to 2-5, which also solved the 1-2 dog leg issue.

If only new gears weren't so stupid expensive :( I spoke to someone about making a single new ratio helixal cut set, but even then was quoted $5k each IIRC for 10 sets which I didn't have buyers for so I moved on.


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 Post subject: Re: Ferrari Drop Gears
PostPosted: Wed Jan 04, 2017 2:52 pm 
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Joined: Sat Jan 03, 2015 10:13 pm
Posts: 794
And actually... since the drop gears are a THREE gear set with an idler in the middle... the ratio can't be changed without moving the idler.

So it's literally impossible with just a parts swap.

Edit: The overall ratio will always be the ratio of input-to-idler shaft center to idler-to-output shaft center.


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 Post subject: Re: Ferrari Drop Gears
PostPosted: Wed Jan 04, 2017 3:02 pm 
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They do it by splitting using a new outer cover with more room and outer bearings like the 328, then and inner/outer gear sets with the idler having 2 gear. You get a set with 8 or 12 ratio choices in the $15k kit I saw.

or you could simply relocate the idles :)


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 Post subject: Re: Ferrari Drop Gears
PostPosted: Wed Jan 04, 2017 3:10 pm 
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Actually, I was wrong about not being able to change the overall ratio... I just wasn't playing with enough variables in my model.

If the two shaft separations are the same, the overall ratio will always be 1:1.

But if the shaft centers are different, then multiple overall ratios are possible.

I'd attach a file, but the form won't let me upload a .xlsx


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 Post subject: Re: Ferrari Drop Gears
PostPosted: Wed Jan 04, 2017 8:03 pm 
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you can upload anything as a .zip

The idler does nothing in the gear ratio as you say but the centerline location matters. You can't changed the pitch diameter without changing the centerline location.

The kit uses an idler with 2 gears is part of the ratio and gives you a lot of options without moving the centerline


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 Post subject: Re: Ferrari Drop Gears
PostPosted: Sun Jan 08, 2017 1:27 am 
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mk e wrote:
you can upload anything as a .zip

The idler does nothing in the gear ratio as you say but the centerline location matters. You can't changed the pitch diameter without changing the centerline location.

The kit uses an idler with 2 gears is part of the ratio and gives you a lot of options without moving the centerline


Doesn't it need a deeper side cover, then?

The ratios can be changed without changing the shaft separations, but the "input" side and "output" side have to change together to make the numbers work out. The range of adjustment ends up being limited for practical reasons.

I don't know the original shaft center dimensions from the 308 transmission, so my model is only good as a demonstrator of the math, rather than telling what's workable with the existing metal.


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File comment: Very simple math model for drop gear ratios in a Ferrari transmission
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 Post subject: Re: Ferrari Drop Gears
PostPosted: Sun Jan 08, 2017 8:45 am 
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Your math looks right...but the caution is you end up with unworkable gear sizes pretty quickly so only small changes can be done that way.

Yes a deeper cover...found a pic. It looks like they add an outer bearing on the top only but the whole cover looks an inch deeper plus the bearing on top.


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