Forged Performance: Project 370Z Race Car Build!!

t-ray · 08-12-2009, 10:50 AM

Quote:

Originally Posted by Sharif@Forged

3.9 would be too short a gear for the power levels, and intended use for this car.

For an NA car, and more moderate power/weight setup, there may be some benifit to the 3.9 rear end.

God I can be such a dumb **** sometimes. I meant "your" power levels, and I totally forgot that you were going to be adding boost at some point in the future. I was framing the gears question in terms of the car staying NA.

Sorry for the confusion.

So - going back to one of my earlier questions, NA, where does the car stop accelerating?

wstar · 08-12-2009, 11:05 AM

Quote:

Originally Posted by t-ray

God I can be such a dumb **** sometimes. I meant "your" power levels, and I totally forgot that you were going to be adding boost at some point in the future. I was framing the gears question in terms of the car staying NA.

Sorry for the confusion.

So - going back to one of my earlier questions, NA, where does the car stop accelerating?

Well the answer to that is "at the drag limit", and I don't think many people know that since the ECU speed limiter is below the drag limit. If I had to guess, I'd say with no wind it's probably around 170-180 mph with good bolt-ons in top gear, although it probably varies by transmission type. You'd probably loose all steering control and wreck the car before then though, at least without some aero upgrades and/or lowering to keep the nose planted harder.

wstar · 08-12-2009, 11:09 AM

A more useful answer: I don't think I would see myself using my 7AT's 6th or 7th gear to accelerate on any reasonable track. If the track had a long slow curve or straight where for whatever unrelated reasons I desired to maintain constant speed for a stretch, I might drop into 6 or 7 just to give the engine a rest, but useful acceleration at speeds the stock aerodynamics can handle all occur in gears 1-5 on the 7AT w/ stock diff ratio. 6MT may have a different answer, as the transmission and diff ratios are all different.

t-ray · 08-12-2009, 01:33 PM

Quote:

Originally Posted by wstar

A more useful answer: I don't think I would see myself using my 7AT's 6th or 7th gear to accelerate on any reasonable track. If the track had a long slow curve or straight where for whatever unrelated reasons I desired to maintain constant speed for a stretch, I might drop into 6 or 7 just to give the engine a rest, but useful acceleration at speeds the stock aerodynamics can handle all occur in gears 1-5 on the 7AT w/ stock diff ratio. 6MT may have a different answer, as the transmission and diff ratios are all different.

That is ultimately where I was going with the gears question - based on the assumption that the car remained NA. I was wondering a gearing-reduced top speed had any practical impacts on real-world tracks.

wstar · 08-12-2009, 04:35 PM

Quote:

Originally Posted by t-ray

That is ultimately where I was going with the gears question - based on the assumption that the car remained NA. I was wondering a gearing-reduced top speed had any practical impacts on real-world tracks.

From the service manual, the 6MT's ratios are:

1st 3.794
2nd 2.324
3rd 1.624
4th 1.271
5th 1.000
6th 0.794

.. and the rear end is 3.692. From that you can derive that 5th (on stock Sports Package wheels and rubber) tops out at about 160mph @ 7500rpm. So technically you don't *need* 6th unless you're on a track where your car could exceed 160, which doesn't sound like the kind of track people run these cars at

. But still, it's not like you always have to be in the lowest possible gear all the time. 6th will still pull decently and be useful. If you went to a 3.9 rear end, it just makes 5th top out sooner, at about 152. If you also combined that with moving to say, 305/30/18 tires in the rear, the number drops to about 144.

08-12-2009, 11:09 AM	#3 (permalink)
wstar A True Z Fanatic Join Date: Mar 2009 Location: Houston, TX Posts: 4,024 Drives: too slow Rep Power: 3596	A more useful answer: I don't think I would see myself using my 7AT's 6th or 7th gear to accelerate on any reasonable track. If the track had a long slow curve or straight where for whatever unrelated reasons I desired to maintain constant speed for a stretch, I might drop into 6 or 7 just to give the engine a rest, but useful acceleration at speeds the stock aerodynamics can handle all occur in gears 1-5 on the 7AT w/ stock diff ratio. 6MT may have a different answer, as the transmission and diff ratios are all different. __________________ 7AT Track Car! Journal thread / Car setup details

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