Pinecone - question for you

Pinecone - Question
Could you compute 0-60 improvement for my Z3 3.0 with steptronic. I think I have a 3.46 in it already, but considering going to a 3.73 or (I'm not sure what the next gear is, do you know?)
Thanks.

Hard to say with a Step. The torque converter changes things. With a manual, as long as the clutch doesn't slip (which is what a TC does) and the tires don't spin, the power hits the pavement.

But in general you figure the % increase in gear ratio.

% increase in ratio = (new ratio - old ratio)/old ratio

The subtract the % increase from 100% and multiply by the current 0 - 60 time. That will give you an IDEA only.

And it doesn't work for 1/4 mile since you start getting into aerodynamic drag, which is a HP thing, and gearing doesn't change HP.

Oh, and check Bimmerworld for available gear ratios.

Originally posted by Pinecone
Hard to say with a Step. The torque converter changes things. With a manual, as long as the clutch doesn't slip (which is what a TC does) and the tires don't spin, the power hits the pavement.

But in general you figure the % increase in gear ratio.

% increase in ratio = (new ratio - old ratio)/old ratio

The subtract the % increase from 100% and multiply by the current 0 - 60 time. That will give you an IDEA only.

And it doesn't work for 1/4 mile since you start getting into aerodynamic drag, which is a HP thing, and gearing doesn't change HP.

I'm not trying to bust gonads or anything, but that computation is a pipe dream, particularly since you'll now have to shift into 3rd to hit 60 mph, not to mention all the other variables not taken into account

Originally posted by TeamZ4
I'm not trying to bust gonads or anything, but that computation is a pipe dream, particularly since you'll now have to shift into 3rd to hit 60 mph, not to mention all the other variables not taken into account

So how long to shift? And add to the fact that it may be better to shift earlier than redline anyway for maximum delievered torque. SMG shifts in 80 milliseconds (0.08 seconds) and most people seem to agree that the big plus from SMGis consistancy, not speed of shifting, lets be nasty and say you shift in .2 seconds. So if you can get a theoretical decrease of more than 0.2 seconds, the higher numerical rear may still be faster.

And you seem to believe the world does not revolve around 0 - 60 (which I agree, but we have to use something). Something like 0 -100 (where both cars have to shift the same number of times) would be much better for the higher numerical gearing. Same for 0 - 50, or 30 - 50 (a popular C&D number) or 50 - 70, etc.

Oh, and what are the effective transmission gear ratios in a Step? It may be a better setup for a step.

No, it is not a cure all, but other than highway RPM and gas mileage, it is a mod with little downside.

Originally posted by Pinecone
No, it is not a cure all, but other than highway RPM and gas mileage, it is a mod with little downside.

well maybe in your opinion based on limited experience, but there's really no justification for making that mod in a stock 3.0 Steptronic. Personally I would consider the mileage and highway rpm to be serious downsides for anything short of an occasional driver or track car. The 6 speed on the newer models is a god send for anyone making a long trip on the interstate, and that's with the OE diff ratio.

Understand that a number of companies would be more than pleased to promote and sell you one, but that doesn't make it the smart thing to do. IMO a custom torque converter with a few engine mods would be a much wiser action plan.

Originally posted by TeamZ4
well maybe in your opinion based on limited experience, but there's really no justification for making that mod in a stock 3.0 Steptronic. Personally I would consider the mileage and highway rpm to be serious downsides for anything short of an occasional driver or track car. The 6 speed on the newer models is a god send for anyone making a long trip on the interstate, and that's with the OE diff ratio.

Understand that a number of companies would be more than pleased to promote and sell you one, but that doesn't make it the smart thing to do. IMO a custom torque converter with a few engine mods would be a much wiser action plan.

Actually, we don't disagree.

For a Step, I would not bother with much of anything.

But high stall torque convertors have their problems also. Like reduced mileage in around the town driving because of the more slippage.

Also realize that the RPM goes up and the mileage goes down by the percentage change in rear ratio. The change from a 3.46 to a 3.73 is 7.8%. So your RPM at cruise will go up by 78 RPM for every 1000 RPM you currently run. So a car that runs at 3,500 RPM curising now will only be at a whopping 3,773 RPM. Not a big change.

The gas mileage, on the highway cruising, would go down about 7.8%, so say a car that now gets 25 MPG, would get about 23 MPG after the rear ratio change. Again, not a big deal for some extra performance.

Around town, the gas mileage wil not be that much different, because at times you will be running in a higher gear, and at times in teh same gear, but it will somewhat balance to not significantly change the mileage.

All this is why Ron went from a 3.15 to a 3.46 in his M Coupe and not a 3.73. This means a 9.8% change instead of a 18.$% change. ANd he finds the 9.8% change to be very liveable with a nice perofrmance enhancement.

And this change is MORE than the 3.46 to 3.73 change.

Thanks Pinecone for your info. Other responses dwell too much on mileage and RPM at high speeds. I don't care if my city mileage goes down to 19 or 18 or 17 mpg. I don't drive the highways at 80mph, 90mph, +, so i don't care. So these other posters are too worried about things that don't matter to me. I wanted some extra takeoff speed where I do most of my driving, under 55mph. You have provided me with good info. Thank you.