Yes I'm very tempted too although inclined to wait until my box needs some attention. I admit I'm finding it hard to try and imagine what this will be like in comparison to stock and whether time will be lost from more gear changes rather than gained.

Thanks for the charts Matt. I guess I need to sit down with some datalogs and see how it would change a lap for me.

 

Hello Dan,
Just let me know if I can help you in any way with your analysis. As mentioned above, we've got a bunch of alternative gear ratios as well. Depending on what you are trying to achieve, changing a few gears may be more effective for your particular application.

Though I will tell you that you aren't going to lose time from more gear changes. If that was the case, they wouldn't be putting a very similar ratio in the Cup Cars from the factory.

 

I'll be the resident race engineer chiming in. Shorter gears mean you are putting more torque to your wheels given the same engine torque. To accurately predict the resulting performance increase, you need to know a lot of information about the car: dyno curve, shift schedule (essentially a more detailed analysis of your shift times), rolling friction, gearbox inertia, etc). I do this kind of stuff at work (albeit in more detail), but I can't do it for you (for free).

That being said, Bosch makes a nice little sim tool that many pros use to get their ratios right for different tracks (even the top ALMS and IndyCar teams use the free version). With some educated guesses on the parameters of a GT3, you should be able to get a good indication of a lap time change.

The tool takes only a few hours to learn. The download link is at the bottom of the page:

http://www.bosch-motorsport.com/cont.../html/3589.htm

 

I downloaded lapsim a while back and got a bit disheartened with all the static data it needed to even start trying to use it Be a lot simpler if we could say this mod was equiv to another x bhp. I guess it is in some ways but have to factor in impact of the changed shift points which is what I was going to look at from a datalog and work out where I would be shifting instead. Sure would be strange to make use of 6th!

 

Send me a list of what you don't know, and I'll fill it in with numbers close enough to give you a good idea. lap time simulation is extremely complex, but even the simplest models can be very powerful if they predict trends correctly.

 

Thank you - that's a very kind offer, but I don't think its really worth it for me to pursue lapsim type stuff. I'm still several seconds of the pace in my car so this kind of high level work is pretty much an irrelevance

 

Flavorpacket,
What if you ran it for a bone stock GT3 with nothing changed except this single part? Would you be willing to do that for us and put up your findings?

 

curious... going from a 3.44 -> 4.0 is a 14% reduction in gearing... how does that equate to horsepower... does that mean you have 14% more HP and Torque... is it even linear?

 

It's not linear because it has to go through the multiplier effect of the various ratios. Only 5th gear is a 1:1 ratio and could be directly comparible to the change in FD ratio. Every other gear would go up or down relative to the specific ratio for that specific gear position.

 

so your saying that gears 1-4 would have more of an effect than 5 and 6.... also how could gears go "down" if the FD is now 4.0 as you say above... I understand they will be shorter and the multiplier higher for the lower gears but where does the down part come in... maybe I'm understanding fully...

 

Sorry Pete. I didn't word that very well. The relative effect will go down, as in be less than 14%, which is the difference between the two R/P ratios.

 

I must go slow on the track to avoid tempting another ring and pinion buster DIY lol

Matt, some people do the poor man short ring and pinion conversion by going with shorter profile tires - such as 35 front and 30 rear on 18" wheel compare with stock 40 front and 35 rear. How much benefit (or lack of) do you get by doing the low profile tires compare with stock and your kit?

Do we need to remove the transmission for this mod?

 

Hello Mike,

I already assumed 30's in my initial numbers because that's what so many people run on the track to start with. However, compared to 35's, the change isn't terribly dramatic. It's a couple of miles an hour in 1st gear and still less than ten in 6th.

This is definitely not a DIY mod. Most shops will charge you upwards of 8 hours for just the work inside of the box. The whole thing has to come apart for the work and most people will wait until it's time to refresh the box so that there's some efficiency there. The box does have to come out of the car for this.

If you get serious about this at some point, just let me know. There are several excellent shops in the bay area as well as up towards Sacramento that could be capable of this kind of gearbox work locally. There's no reason to ship your gearbox off somewhere to get it serviced.

 

Does your shop make this for a standard non-gt3 996 gearbox?

 

Hello Pete,

We do not make it for 996 C2 gearbox. At this point we haven't seen enough interest in racing those cars to warrant making any parts for them beyond the LSD and TBD.

California Motorsports has a couple of products for that gearbox. There's a 4.00 R/P set, as well as a short 3-6 ratio gearkit for it. You should be able to find pricing and the exact ratios for the short ratio kit on their website.