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Graziano Gearing and Drop Gears
I put this post together on the SLC board (http://www.gt40s.com/forum/rcr-forum...rop-gears.html) to help others avoid the pitfalls I've encountered with my Graziano L140 - transaxle from the Ausdi R8, Lamborghini Gallardo and some others. There's a huge amount of misinformation out there about gear ratios (including Audi's own product guides) and all aspects of a drop gear solution - in particular their impact on ratios/engine rpm and ease of install.
This post has been over a year in the making - starting with when I ordered my 2014 R8 Gearbox (Audi code: KBA). Shortly after it arrived I realized the gearing in it didn't match Audi's published materials. What was supposed to be just a nuance of my Superlite Coupe project took on a life of its own. Getting to the answer wound up involving more effort than I'd like to admit - hours and hours of research, conversations with the Audi Executive responsible for the R8's launch, more conversations with the lead engineer in Germany and ultimately installing a set of drop gears on my transaxle and driving the car.
In short - there's a transfer gear in the transaxle. It's the gear set the drop gears replace and it has a ratio of 1.32.
Audi materials don't disclose this gear, and Audi represents different ratios in its early product guides than it does in its later product guides. This was news to the folks at Audi when I brought it to their attention.
In short - the ratios represented in the early materials are effective gear ratios; they incorporate the transfer gear ratio into the number shown. The later materials represent the ratios of the actual gears themselves and make no mention of the transfer gear. For the purpose of swapping gears, it makes sense to work from the actual ratios. For simplicity, for the V-8 version of the R8 Graziano, they are:
1st - 3.31
2nd - 2.05
3rd - 1.42
4th - 1.07
5th - 0.85
6th - 0.7
Transfer - 1.32
What this produces is great for the low torque, high revving Audi motor - not so much for the LS motors, particularly for street use where 1st gear is far too short (37mph) and 6th gear has you sitting at about 3400rpms on the highway at 80mph. I've attached a gearing model to this post for my car showing rpm and speed for each gear.
The solution available thus far has been to swap for a .76 ratio transfer gear. It's been advertised this drop gear:
1. will produce about a 240mph top speed,
2. highway cruise at 2500rpms
3. is an easy, 30 minute install once the gearbox is apart
I bought one of these gear sets, had them installed by a well-respected Ferrari shop familiar with Grazianos and learned the hard way this is all wrong. During install, I learned changing the transfer gears require the entire gearbox to come apart, every gear to come off the shafts and a portion of the case to be machined - hardly a 30 minute job. After driving the car (I believe mine is the first set actually installed and in a car that's been driven) I realized the impact of the .76 drop gear is much greater than advertised. Try a 302mph top end and highway cruise at 1800rpms. Gearing model attached.
Now these gears aren't all bad; they're actually just slightly taller than the factory Ricardo gearing. For someone building a high horsepower car, or one they want to have similar gearing to that of a production Corvette, they are great - but they're not what's being advertised on any level. I've learned subsequently this 0.76 ratio set was developed for the 1,000hp+ Twin Turbo Gallardo guys who wanted to run the Texas Mile. With a higher horsepower car or that type of application, this set is a good fit.
For me, though, with the 525hp LS376 motor in a car I plan to drive on road courses and on the street, it's not such a great fit. When I drove the car with the .76 gears the gearing felt too tall - acceleration didn't impress with my horsepower level and 6th gear became unusable. To match what I was looking for I needed something closer to a 1.038 ratio... so I commissioned having them made. They produce what the other gear was originally advertised to do - the 2500rpm highway cruise, a reasonable 1st gear (47mph) and a 221mph top speed. Gearing model attached.
MOD EDIT: Removed non-vendor group buy before approving post
PS Gear calc files - https://drive.google.com/open?id=0B9...G5odGpNNFVEbzg
It sucks to be 'the guy' who figures out stuff like this. Thanks for sharing
MK3.1 2004 Mach 1 donor.
Yes - this little quest was quite expensive!
Originally Posted by beeman
Good news is there is a solution available for those not wanting to buzz an LS engine at 3400rpms on the highway.
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