http://www.rsctuning.com/product_inf...roducts_id/826

Been available for some time. You can order through us, or it's probably in stock at your local Pep Boys.

 

Does going to 20" wheels have an affect?

 

Probably not a significant impact b/c it's only one inch but, generally speaking, the larger the wheel/tire, the slower the acceleration and the higher the top speed. You could go to 15" wheels to improve acceleration, but I wouldn't recommend it.

 

"Does going to 20" wheels have an affect?"

Only if the overall diameter of the wheel and tire combination change significantly... like 2.5%+

 

Plus the added weight (if any) from the wheel/tire package, and the fact that it is further from the center of rotation.

Mike, are the engines SAE certified? I remember a number of engines going through this process...some gained and some lost hp rating.

I imagine the problem is more "area under the curve" for the engine with less usable torque down low. I like the idea of shorter gearing but couldn't really use it in my situation since traction off the line is already a problem. If I didn't have he supercharger a shortened final drive set would be at the top of my list. The multiplication of engine power it provides to the wheels makes a huge (proportional) difference.

 

Yes, If you look through literature original Vanquish and DB7GT were last to be homologated DIN before switching to SAE. Same engine going from DIN to SAE will loose performance whereas SAE standards allow for the engine on the engine dyno to be controlled (temperatures / pressures) in more of a way that replicates actual in-vehicle conditions.

My feeling is that there should have been a 'win' going to each level of SAE if people 'used their allowances', lets say.

For example, previously the engine had to make its power with a full vehicle exhaust system in the engine dyno, delivering the correct back pressure. Whereas SAE allows the manufacturer to control exhaust back pressure to normal vehicle conditions. This means that normal vehicle conditions is exhaust back pressure during transient, not during prolonged heat sink, which means the exhaust back pressure on the engine dyno during SAE test could be set lower to replicate car and not set artificially high as it previously was.

This is just one example of one variable meaning that generally SAE was more in-tune with how the engine behaved in the actual vehicle - hence everyone should have had a win..??

Mike.

 

Ok great explanation, thanks! I remember the ones that were negatively affected were mostly the Japanese manufacturers, particularly Toyota/Lexus. I think their "300hp" V8 got readjusted to around 273, along with some others. Ouch!

 

Anyone down the crown and pinion yet?

What would the top speed reduction be with that mod?

I would think there would be a noticeable difference in acceleration.

 

I do have a couple of 'road' customers who have purchased this from us, but they are also being used in a variety of race applications.

OE Diff: 3.909:1
6th Gear @ 60 MPH = 2305RPM
6th Gear @ 100 MPH = 3841RPM
Top Speed 178MPH

RSC 4.55:1 CWP
6th Gear @ 60 MPH = 2683RPM
6th Gear @ 100 MPH = 4471RPM
Top Speed 163MPH @ 7288RPM

 

Stuart, do you have any performance data for the 4.55:1? I'm really curious what effect this mod has on acceleration numbers.

 

When I was running my Supercharged M3, that was going to be my next mod. I heard great things about acceleration. That it was like adding another supercharger.

 

You can basically think of a gear as a multiplier for engine power. If you take crank hp and multiply by the ratio of the gear you're in and by the final drive ratio, you get the horsepower/torque that the wheel is seeing.

So if you go from 3.909 to 4.55, you're getting 4.55/3.909 or roughly 15% more power/torque to the wheel. At the same time, the gears are shortened 15%, so for every speed you'll be running 15% higher rpms in a given gear, and you'll high redline in each gear at 15% lower speed. In the V8, redline in first, second, and third will be roughly 40, 63, and 85, instead of 47, 74, and 100 in the stock car. Even for an otherwise stock V8 you'll probably run into traction issues with this in at least first gear, so you'd probably want to combine the final drive with bigger rear tires to get it to hook up.

Stock gearing for the V8 is pretty tall for a naturally-aspirated sports car, so this has a lot of potential. The downside will be worsened MPG.

 

Does anyone know what was the train of thought behind AM's decision to go with such tall gearing? Anyone? Mike?

 

Higher top speed they can tout.

 

They could have gotten the same top speed by going with a short final drive and using a taller 6th gear...Mike would know this but if I remember correctly, even with 15% shorter gearing the top speed wouldn't be affected much if any because the car isn't able to hit redline in 6th with the stock power.

Part of the gearing choice probably goes to mileage targets and part to this being a gentleman's GT as much as a sportscar. Probably a compromise as with everything.