Forged Performance: Project 370Z Race Car Build!!

t-ray · 08-10-2009, 10:17 AM

Quote:

Originally Posted by Sharif@Forged

Yes, stock gears, gearbox, and ring/pinion. The OEM Nissan stuff has proven race worth, so no plans to upgrade.

Sorry, my question was not one of reliability, rather it was in regards to the final drive ratio. How often do you top out 5th gear? And if you ever do, can you actually accelerate in 6th gear at those speeds?

Sharif@Forged · 08-10-2009, 02:15 PM

Quote:

Originally Posted by t-ray

Sorry, my question was not one of reliability, rather it was in regards to the final drive ratio. How often do you top out 5th gear? And if you ever do, can you actually accelerate in 6th gear at those speeds?

You will definately use 6th gear at many tracks, and there is acceleration capability in 6th in problem at all.

Really depends on the track, as to how often you will use 6th gear.

Does that answer your question?

t-ray · 08-10-2009, 04:37 PM

Yes, thanks. I know it's probably a newb question, but I've never taken anything over ~120mph.

At your target hp levels, at that weight, that car is going to be major fun. But I bet if would be even moreso with 3.9's or 4.0's in there.

Sharif@Forged · 08-11-2009, 06:48 PM

Quote:

Originally Posted by t-ray

Yes, thanks. I know it's probably a newb question, but I've never taken anything over ~120mph.

At our levels, at that weight, that car is going to be major fun. But I bet if would be even moreso with 3.9's or 4.0's in there.

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.

RCZ · 08-11-2009, 09:11 PM

Man, coming from an STI, I can tell you that short gears are fun for like 10 minutes, it gets very old to shift from 1st at 15mph and cruising on the highway 80mph @ 3800 rpm.

Not to mention a car with 400+ and 2750lbs can most certainly make use of long gears

Sharif@Forged · 08-11-2009, 09:18 PM

Quote:

Originally Posted by RCZ

Man, coming from an STI, I can tell you that short gears are fun for like 10 minutes, it gets very old to shift from 1st at 15mph and cruising on the highway 80mph @ 3800 rpm.

Not to mention a car with 400+ and 2750lbs can most certainly make use of long gears

Well put.

I really like that smiley^^^

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?

KingDavid · 08-12-2009, 10:54 AM

Updates??!?!?!?!?!??

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.

Phimosis · 08-12-2009, 10:51 PM

It's all about the ratios of the gears in the trasmission, not in the rear end.

The 370z is geared for good acelleration off the line to get good 0-60 and quarter mile times and it is geared for progressive shift points to get you to its terminal velocity of ~185 mph. Those gears are meant for the street.

Most track cars and motorcycles are geared for shift points that roughly go 60, 80, 100, 120, 140, 160 mph, because until you get to the elite classes, 160 mph or so is all you will see on most tracks. For example, at Portland International Raceway, I could get my Aprilia RSV to trap 165mph at the end of the front straight.... and they run indy cars at that track.

The 370z is geared for 42, 69, 99, 126, 160, 188 mph. (I calculated 6th gear at 7,000 rpm, the rest at 7,500). If you give it, say 4.0 rear end gears, you'll get shifts points of 39, 64, 91, 116, 148 and 185 mph. in that scenario, you've made 1st gear useless and 6th gear still gives you the same top speed, just at 7,500 rpm instead of 7,000.

The real solution would be to rear gear the entire tranny.

Sharif@Forged · 08-13-2009, 11:24 AM

Cage is in progress right now.

tbonesteak · 08-14-2009, 01:41 AM

08-12-2009, 11:09 AM	#205 (permalink)
wstar A True Z Fanatic Join Date: Mar 2009 Location: Houston, TX Posts: 4,024 Drives: too slow Rep Power: 3594	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

08-13-2009, 11:24 AM	#209 (permalink)
Sharif@Forged The370Z.com Sponsor Join Date: Dec 2008 Location: Marietta, GA Posts: 840 Drives: 2009 GT-R, 2010 370Z Rep Power: 17	Cage is in progress right now. __________________ Sharif@Forgedperformance.com General Manager/Certified Tuner/NASA-PCA-BMWCAA Instructor JRZ RS1's Available NOW...PM me Cobb ProTuner, Uprev ECU Flash, FCON Vpro, Haltech, Motec Certified

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08-10-2009, 04:37 PM	#198 (permalink)
t-ray Base Member Join Date: Apr 2009 Location: bham al Posts: 91 Drives: 05 g sedan 6mt Rep Power: 16	Yes, thanks. I know it's probably a newb question, but I've never taken anything over ~120mph. At your target hp levels, at that weight, that car is going to be major fun. But I bet if would be even moreso with 3.9's or 4.0's in there.

08-11-2009, 09:11 PM	#200 (permalink)
RCZ A True Z Fanatic Join Date: Nov 2008 Location: Miami Posts: 6,403 Drives: '09 370Z Rep Power: 1118	Man, coming from an STI, I can tell you that short gears are fun for like 10 minutes, it gets very old to shift from 1st at 15mph and cruising on the highway 80mph @ 3800 rpm. Not to mention a car with 400+ and 2750lbs can most certainly make use of long gears

08-12-2009, 10:54 AM	#203 (permalink)
KingDavid Base Member Join Date: Mar 2009 Location: Miami Posts: 176 Drives: A car Rep Power: 16	Updates??!?!?!?!?!??

08-12-2009, 10:51 PM	#208 (permalink)
Phimosis Enthusiast Member Join Date: May 2009 Location: Oildale, CA Posts: 412 Drives: 2013 911 4S Rep Power: 416	It's all about the ratios of the gears in the trasmission, not in the rear end. The 370z is geared for good acelleration off the line to get good 0-60 and quarter mile times and it is geared for progressive shift points to get you to its terminal velocity of ~185 mph. Those gears are meant for the street. Most track cars and motorcycles are geared for shift points that roughly go 60, 80, 100, 120, 140, 160 mph, because until you get to the elite classes, 160 mph or so is all you will see on most tracks. For example, at Portland International Raceway, I could get my Aprilia RSV to trap 165mph at the end of the front straight.... and they run indy cars at that track. The 370z is geared for 42, 69, 99, 126, 160, 188 mph. (I calculated 6th gear at 7,000 rpm, the rest at 7,500). If you give it, say 4.0 rear end gears, you'll get shifts points of 39, 64, 91, 116, 148 and 185 mph. in that scenario, you've made 1st gear useless and 6th gear still gives you the same top speed, just at 7,500 rpm instead of 7,000. The real solution would be to rear gear the entire tranny.

08-14-2009, 01:41 AM	#210 (permalink)
tbonesteak Track Member Join Date: Mar 2009 Location: Socal Posts: 914 Drives: MY09 MB 6MT Rep Power: 375