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3.8 vs 3.6

 
Old 11-27-2018, 12:22 PM
  #46  
Bill Verburg
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Originally Posted by Spyerx View Post
No, just pate :-) Thanks for all the posts. Gear ratios, while not permanent, are expensive changes :-) Hence my over analyzing. I literally have a dozen charts printed out. What I need to do is go drive a car that has the gears I think I want in it. I think I'm most concerned on 3-4 on the street, are they still in the 'fun zone' - not luggy, not too revvy.

These are the ratios I'm considering:
Tire diameter 25.8"
Final: 3.444
1st - 3.154
2nd - 2.176
3rd - 1.526
4th - 1.174
5th - .868 (stock)
Here are some comparisons
various 993 for a stock 964 the g50/21 would probably be best, for a modified 964 w/ better torque curve and extended rpm one of the g50/3x would probably be best, the 31 or 32 better for street the 30 for track, but all certainly nice for either



various 964 variants, for the tires I use the loaded rolling diameter, for a 275/35 x18 that is 24.8" I didn't change some of the irre heights to match so there will be a small discrepancy between the cars w/ different tires.


a comparison of a stock 964 w/ a 964 w/ /31


for street use a top of ~165+/- is desirable to get a reasonable cruise rpm, the 5 speeds either need more of a spread or a bigger step up to the top gear to do this

a taller first is really nice unless you have a lot of hill starts, can also be a bit tough to get on a trailer if the bed height is a bit high, enclosed will be less of a problem because of generally lower bed heights

for track use the money gears are 3, 4 & 5, It does depend on the track though, There are some places like Monticello that have multiple 2nd gear turns,

Generally the factory special cars have outstanding gear stacks, but again for general street use look for ~165 top
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Old 11-28-2018, 09:43 AM
  #47  
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Gus-

Pluging bigger midrange numbers seems to be a good way to do in terms of getting more acceleration thru the gears with your current ratios. Not sure how or if that’s possible with a change in cams



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Old 11-30-2018, 02:03 AM
  #48  
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How about a slightly less scientific question -

best gearset/transmission for 3.8, itb, cams, exhaust... G50/03 or RSA G50/05? Mostly enthusiastic street driving.
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Old 11-30-2018, 11:30 AM
  #49  
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Originally Posted by jeff33702 View Post
How about a slightly less scientific question -

best gearset/transmission for 3.8, itb, cams, exhaust... G50/03 or RSA G50/05? Mostly enthusiastic street driving.
between those 2, /03 gives better acceleration, /05 better mpg & more relaxed cruise. The difference is small but noticeable, both are in one of the charts above
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Old 11-30-2018, 08:41 PM
  #50  
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Lots of good analytical data, but for us mere mortals what would be good gear ratios in order to increase in gear acceleration in real world street driving, maybe keeping 1st standard and 2nd 3rd 4th closer in order to improve acceleration and keeping 5th standard for motorway driving?
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Old 11-30-2018, 09:52 PM
  #51  
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Bill,

Any chance you could plug this data into a thrust chart? The blue curve on the dyno:


The Following ratios:

More or less stock weight 964 - stock aero on 265 18ís at Rs height -10. Iím curious to see how different the thrust data is compared to the wheel torque data provided by the Shift RPM app. Also want to begin planning which direction to take with the engine.

Thx-

pete
​​​​​​​
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Old 11-30-2018, 10:09 PM
  #52  
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Originally Posted by AVI_8 View Post
Lots of good analytical data, but for us mere mortals what would be good gear ratios in order to increase in gear acceleration in real world street driving, maybe keeping 1st standard and 2nd 3rd 4th closer in order to improve acceleration and keeping 5th standard for motorway driving?
It all comes down to how you use the car. The stock ratios are pretty good balance for all around driving- traffic, backroads and highway. Itís a flexible gearbox.

If you donít see much stop and go traffic or starts on hills and feel you can do with a higher 1st then Iíd keep 5th shift all the lower gears up- similar to Spyerx.

If you want to keep 1st as is and are comfortable with a lower 5th then shift everything down to match first. If you want to keep 1st and 5th as is then personally I would probably just keep the 03 ratios stock/ or what I did and start looking for a 6 speed (I converted a 4wd box.)

It all comes down to your preferences. I spent a lot of time driving road and track just paying attention to what I liked and didnít like about the stock box. I would have a hard time increasing the gap between 1 and 2 however on the street a bit more of a gap between 4 and 5 wouldnít bother me because my spirited street driving never gets me into 5th. So given that Iíd rather shift 2/3/4 lower of my car was street only wanting to retain stock ratios in 1 and 5.

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Old 12-02-2018, 02:42 PM
  #53  
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Originally Posted by Peteinjp View Post
Bill,

Any chance you could plug this data into a thrust chart? The blue curve on the dyno:


The Following ratios:

More or less stock weight 964 - stock aero on 265 18ís at Rs height -10. Iím curious to see how different the thrust data is compared to the wheel torque data provided by the Shift RPM app. Also want to begin planning which direction to take with the engine.

Thx-

pete
Here's what I come up w/ for yours, I used stock 964RSA aero & 265/35x18 tires, I'd want taller 3-5

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Old 12-02-2018, 05:43 PM
  #54  
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Thanks! Thatís about what I expected. The plan with future engine mods Iíll aim to increase power at the higher end of the rpm range. Anyway to estimate how much of an increase would put match these ratios better. Iíd like 3rd to just kiss 4th at its max of 92mph.

The other part of th equation is reducing drag. If you could plug in realistic obtainable numbers in terms of engine power increase and lower drag and get a better result with the current ratios what kind of mods would I be looking at?

Your graohs are great tools! Did you make this program yourself? Thanks again- much appreciated.

Pete
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Old 12-02-2018, 06:20 PM
  #55  
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Here's your torque curve compared to other 964 & 993 engines(dashed line), your curve is dropping more rapidly at higher rpm. That's what you want to address. Could be intake or cams, probably not exhaust
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Old 12-02-2018, 06:52 PM
  #56  
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Great- thanks again. Mine is stock with G-pipe and SW chip. The dyno chart is not of my car but done by Steve so idealy I need to get my own info. The plan atm is to get some data to Steve and have him optimize the chip for my car then get it dynoed.

Hmmmm- intake is doable in the near future. Not looking to do cams yet. Wonder what intake options might help boost upper rpm power levels without hurting mid range....

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Old 12-02-2018, 11:04 PM
  #57  
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Ok, time for some blasphemy. We're having some good fun in this thread - so I'll ask... What about a swap car? Something turbo making 450-500 to the wheels, similar RPM (7k tops) and similar weight? I'm guessing the final drive of a /05 might be preferable?
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Old 12-03-2018, 11:04 AM
  #58  
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Originally Posted by jeff33702 View Post
Ok, time for some blasphemy. We're having some good fun in this thread - so I'll ask... What about a swap car? Something turbo making 450-500 to the wheels, similar RPM (7k tops) and similar weight? I'm guessing the final drive of a /05 might be preferable?
Generally the torque curves of a turbo motor are so different that they will very different gearing from a normally aspirated motor
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Old 12-04-2018, 06:39 PM
  #59  
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Alright, I need help. The gearing I had been considering would work well on the street. What I "feel" on track is I'd like 2-3-4 to be longer and tighter. Specifically longer in 2-3. The below is some data from a track I would drive the most. What I'm OK with is more shifting. What I'm not OK with is less pace as a result of it. What I would like is to be in the meat of the band.

Where I feel the current gearing is not ideal:
Between turns 2-3, 2 could be a little longer as 3rd to minimize getting to redline, it's really too short to get into 4th at that point then back to 3rd.
Section between 3-4, 2 is too short, 3 lugs. And due to the technical nature you really want to be in 1 gear until 4, then go into 4th from 5-6, staying in 3rd think is doable as max is about 90, but but you're so on boil its easy to unsettle the car
Turn 10, really want 2, end up in 3rd as 2 is short and getting on it is unstable out of 10 in to esses between 10-11

What Id been proposing is changing 1-4, leave 5 (there is 1 track Id use it on here, auto club)
1st - 3.154
2 - 2.176
3 - 1.526
4 - 1.174
5th - leave stock

So my question... is this stack going to give me what I want??? Or Bill, do you think I'd be better off with one of the other stacks?
I think I'll be going 3-4 more, or sooner, while 1 is longer, and closer to 2 which is good on street, reality is I'll never use 1st on track...

So confused!

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Old 12-04-2018, 07:50 PM
  #60  
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Originally Posted by Spyerx View Post
Alright, I need help. The gearing I had been considering would work well on the street. What I "feel" on track is I'd like 2-3-4 to be longer and tighter. Specifically longer in 2-3. The below is some data from a track I would drive the most. What I'm OK with is more shifting. What I'm not OK with is less pace as a result of it. What I would like is to be in the meat of the band.

Where I feel the current gearing is not ideal:
Between turns 2-3, 2 could be a little longer as 3rd to minimize getting to redline, it's really too short to get into 4th at that point then back to 3rd.
Section between 3-4, 2 is too short, 3 lugs. And due to the technical nature you really want to be in 1 gear until 4, then go into 4th from 5-6, staying in 3rd think is doable as max is about 90, but but you're so on boil its easy to unsettle the car
Turn 10, really want 2, end up in 3rd as 2 is short and getting on it is unstable out of 10 in to esses between 10-11

What Id been proposing is changing 1-4, leave 5 (there is 1 track Id use it on here, auto club)
1st - 3.154
2 - 2.176
3 - 1.526
4 - 1.174
5th - leave stock

So my question... is this stack going to give me what I want??? Or Bill, do you think I'd be better off with one of the other stacks?
I think I'll be going 3-4 more, or sooner, while 1 is longer, and closer to 2 which is good on street, reality is I'll never use 1st on track...

So confused!

What you want can be seen here, look at the red curves, compared to the blue. You want the red ones
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