Soo happy!! 3.90's are on!

[JTSVT]

That may be good advice, however, I'd like to ask how you came to that conclusion? What do you base it on?

Bump to that...Ill be spraying and was thinking about doing this next......More info folks...for us N20 guys 373's or 390's??

 

[WS6JJP]

well, i would think that with 600+ rwhp that your trap speeds would "out-do" 4th gear capabilities, although i havent really calculated anything out to prove it. Last time i was at the track before i had the KB (so it was around 100 hp less) the motor seemed to be getting real close to bumping the rev limiter as i crossed the traps. As i said in another post, i think the trap speeds had to be off that day because i was pulling 126-128mph with only 504rwhp, best E.T. was 11.2. This was at Norwalk (ohio) so elevation isnt a factor.

 

[CobraZb]

Wow this is interesting, I think I just might have to get some gears now. How much do gears normally run.

 

[Bob Cosby]

well, i would think that with 600+ rwhp that your trap speeds would "out-do" 4th gear capabilities, although i havent really calculated anything out to prove it. Last time i was at the track before i had the KB (so it was around 100 hp less) the motor seemed to be getting real close to bumping the rev limiter as i crossed the traps. As i said in another post, i think the trap speeds had to be off that day because i was pulling 126-128mph with only 504rwhp, best E.T. was 11.2. This was at Norwalk (ohio) so elevation isnt a factor.

Ok. Please don't take offense to this, but I would recommend putting more definative data with your recommendation. For example, with 3.73 gears and a stock-sized tire, 6500 rpm is good for 133 mph. With a 26" tire (common slick size), you can get 135 mph, and with a 28" slick, 145 mph.

Personally, I plan to bump the limiter (and my shift points) to 7000 rpm, thus I'm debating 3.90s or 4.10s with my KB and probably ~550-575 RWHP @ ~3600 lb raceweight.

Again - no offense intended.
Bob

 

[SWEET03COBRA]

I don't think there are too many people already trapping 135+ in the 1/4 so it seems like this gear change with some ET Streets make sense.

 

[BADASS03SVT]

like bob said...find a calculator online and do the math. think ahead of what you are going to do with the car because a gear change could really mess you up. as for the 3.90s if ur going to trap over 125 at the track..they are too much unless you are using a 27"+ tire

 

[black10th vert]

Wow this is interesting, I think I just might have to get some gears now. How much do gears normally run.

mustangtuning.com has motive 3:90s for 152 shipped. Ordering mine today.

 

[redstaf426]

all i have to say.. is It feels like i put on a lower pulley and gained 100X's of Torque..

car pulls soo hard.. im getting wheel hop in 2nd now.. with the nittos


well it was 11oclock at nite and cold as hell...

I was a big spectic when it came down to this... but u know what i said why not.. and did it.. and made a awesome descion..


dont knock it till u try it.. dont hate it till you drive a car with it!!!

driving a car with gears and being in a car with gears(projectzero's) made me think twice about keeping it stock.. his car pulls really hard with the 410s..

Lovin it!!

MArc

You know,after talking to projektZero about his 4.10s I'm kind of leaning towards the gears,but I also notice he has a hell of a time trying to hook up.what kind of tires are you running,ET streets,DRs??could you update us with your 60ft's times,thanks.

 

[03TorchRedCobra]

I am thinking of putting 4.56 gears in mine. If 3.90 is great why not go higher? Anyone have pros and cons with this?

 

[Bob Cosby]

like bob said...find a calculator online and do the math. think ahead of what you are going to do with the car because a gear change could really mess you up. as for the 3.90s if ur going to trap over 125 at the track..they are too much unless you are using a 27"+ tire

Once again, this begs the question; why are 3.90s too much if you're going to run over 125 mph? 3.90s with a 26" tire (common slick or ET street tire) will net you 129 mph at the factory 6500 rev limiter. I think 3.90s are a very good choice for those folks running just short of 130 mph - even better with the rev limiter bumped a bit.

Personally, and as stated earlier, I'd get the rev limiter bumped up to ~7000 rpm (peak HP is above 6000 as it is), install 3.90s (or even 4.10s) and call it a day.

 

[Bob Cosby]

I am thinking of putting 4.56 gears in mine. If 3.90 is great why not go higher? Anyone have pros and cons with this?

4.56s work great on N/A Cobra's because they have much less power to play with, and thus don't typically run the MPH that an 03/04 is capable of. You could get away with that gear at near-stock power levels, but I wouldn't do it. Once you start bumping up the power, you WILL run out of gear with 4.56s, assuming a reasonable rpm limit and a 26" tire. You could make it work with a 28" tire if you wanted I suppose, but highway rpm would be way on up there. For example:

4.56s w/26" tire @ 6500 rpm = 110 mph
4.56s w/26" tire @ 7000 rpm = 119 mph
4.56s w/28" tire @ 6500 rpm = 119 mph
4.56s w/28" tire @ 7000 rpm = 128 mph

 

[BADASS03SVT]

Once again, this begs the question; why are 3.90s too much if you're going to run over 125 mph?

right..i thought i stated unless you use a bigger tire than stock. :rockon:

 

[Bob Cosby]

Even a stock tire is good for 128 mph @ 6500 rpm.

EDIT: I'm not trying to be nitpicky, BADASS03SVT - but it might come off that way. Not my intention. Sorry.

 

[SWEET03COBRA]

Damn, so alot of you guys are running over 125? I hope I can say that some day.

 

[Black2003Cobra]

well, i would think that with 600+ rwhp that your trap speeds would "out-do" 4th gear capabilities, although i havent really calculated anything out to prove it. Last time i was at the track before i had the KB (so it was around 100 hp less) the motor seemed to be getting real close to bumping the rev limiter as i crossed the traps. As i said in another post, i think the trap speeds had to be off that day because i was pulling 126-128mph with only 504rwhp, best E.T. was 11.2. This was at Norwalk (ohio) so elevation isnt a factor.

For your case, the numbers do support your gut feeling. In theory, if you are currently trapping 127 mph on average w/ 504 rwhp, then with 600 rwhp you’d be trapping 127*(600/504)^(1/3) = 134.6 mph, (all else being equal.) So if you’re running 26” slicks and haven’t changed your rev limiter, the highest numerical ratio you could get away with is 3.73, (which tops out at about 135 mph in 4th as Bob said.) If you go with a 28” tire, then you could go with the 3.90’s, but the taller tire is canceling out the advantage (in terms of acceleration) of the “shorter” gear, and then some. So as mentioned, you really have to look at each situation case by case and work through the numbers to figure out what gear is best using the rule of thumb that Bob mentioned earlier.

 

[03TorchRedCobra]

Thanks for the input. I see that I need to do some thinking first. I have all the bolt ons to go fast. Sitting at 572 rwhp and plan to be above the 600 mark when I buy the new SCT MAF. Right now I have topped out the MAS. I already have problems in 1st and 2nd, so I have to go slow in those gears (on the street). I was hoping that with 4.56 I could just go past them real quick and use 3rd and 4th for most of the power range.

 

[BADASS03SVT]

Even a stock tire is good for 128 mph @ 6500 rpm.

EDIT: I'm not trying to be nitpicky, BADASS03SVT - but it might come off that way. Not my intention. Sorry.

np bob...are u doing this metally (on paper) or using internet calculators. i dont have that skill so im using the calculators...i guess they arent that great? i know in my car at 120 on 26" slicks im around 6000...maybe 6100 or so when i cross the traps. its high but my shift light doesnt come on which is 6200

 

[Bob Cosby]

http://www.camaroz28.com/calcs/rpmmph.html

Using the numbers you gave, 6000 rpm w/26" tire and 3.90s should be good for a calculated 119 mph - very close to what you're seeing. Increasing that to 6500 calculates to 129 mph.

 

[STREETREBEL]

For your case, the numbers do support your gut feeling. In theory, if you are currently trapping 127 mph on average w/ 504 rwhp, then with 600 rwhp you’d be trapping 127*(600/504)^(1/3) = 134.6 mph, (all else being equal.) So if you’re running 26” slicks and haven’t changed your rev limiter, the highest numerical ratio you could get away with is 3.73, (which tops out at about 135 mph in 4th as Bob said.) If you go with a 28” tire, then you could go with the 3.90’s, but the taller tire is canceling out the advantage (in terms of acceleration) of the “shorter” gear, and then some. So as mentioned, you really have to look at each situation case by case and work through the numbers to figure out what gear is best using the rule of thumb that Bob mentioned earlier.

I THOUGHT THE MORE GEAR YOU HAVE THE MORE
TORQUE MULTIPLIED! ALSO WITH A TALLER TIRE
THE BIGGER THE FOOT PRINT AND BETTER
THE TRACTION. :xpl:

 

[redstaf426]

I THOUGHT THE MORE GEAR YOU HAVE THE MORE
TORQUE MULTIPLIED! ALSO WITH A TALLER TIRE
THE BIGGER THE FOOT PRINT AND BETTER
THE TRACTION. :xpl:

The wider tire the bigger foot print and better traction,taller or shorter changes the gear ratio.That's a bad ass hood you got on your car,where did you get that.

edit:nevermind,see the :xpl: ,guess you were just kidding,still would like to find out about the hood though,thanks :beer: