Cobra rear gear ratio & springs

[ac427cobra]

Hey Guys:

Believe it or not I have finally nailed down a spare IRS for my car. It came out of an '03 Cobra with 400 some odd miles which will not require me to buy new half-shafts for my Torsen I will be installing.

Seeing the search function is down, we are unfortunately going to have to rehash this topic! :rollseyes:

My question is two fold. First, I'm going to set up this complete IRS in a different gear ratio than the stock 3:55 I am running now. I'm really leaning towards a 4:10 as I do not think a 3:90 will be that much of a difference? Any advice/input please?! :read:

Secondly, I will be going to a front coil over conversion and want to lower the stock configuration rear. I'm thinking a minimun of 1" to a maximum of 1-1/2". Should I buy lowering springs or shave equal amounts taken off of the top and bottom of some stock springs? What exactly is the difference between stock Y2K "R" rear springs and '03 Cobra springs?

Thanks for your help guys. I'm just trying to keep up with the rest of y'all!!!!

:thumbsup: :coolman: :beer:

 

[kevin]

are you planning on drag racing? if not, then maybe 3:73. you like road america and 4:10's will mean the high likely hood of being spanked like a red headed step child by the never feared Zoot crew

 

[ac427cobra]

Originally posted by kevin
are you planning on drag racing? if not, then maybe 3:73. you like road america and 4:10's will mean the high likely hood of being spanked like a red headed step child by the never feared Zoot crew

Drag Racing? R U Kidding?? I outgrew that when I was 17! :nono:

Road America is my "home" track. R U saying 4:10's are going to slow my car down? That sounds crazy?

Level with me here Kev!!!!:thumbsup: :coolman: :beer:

 

[kevin]

you'll get out of the turns faster but lose your mph on the straight with 4:10 as you top out your gearing

 

[ac427cobra]

Originally posted by kevin
you'll get out of the turns faster but lose your mph on the straight with 4:10 as you top out your gearing

Kev:

Right now I drive the whole track not getting any higher than 4th gear! Surely I won't even get out of fifth gear with 4:10's me thinks?

:thumbsup: :coolman: :beer:

 

[Cobra-R]

Bruce,
I am with Kevin. I would look at 3.73 or 3.90 at the most since RA is your preferred track. I bet Fred will have more to add, I think he has changed gears. I believe JoeJ even mentioned that his 4.10's were a little much for RA.

Are you just changing to coilovers in the front to lower the car? If so, do a search on Corner carvers, I believe you may do more harm than good geometry wise without changing the K-member that raises the A-arm mounting points.

In the rear you should be as concerned about spring rates as you are worried about ride height. If your going to do it, just go with coilovers and then you have adjustability and can change spring rates cheaply.

Brian

 

[Cobra-R]

Originally posted by ac427cobra
Kev:

Right now I drive the whole track not getting any higher than 4th gear! Surely I won't even get out of fifth gear with 4:10's me thinks?

:thumbsup: :coolman: :beer:

Bruce,
Another thing to consider is 4.10's going to effect you throughout the track. It might actually cause you to need to shift in places that you don't want to be shifting in. For instance: In turn five 3rd gear may be too low but the car may not pull the corner hard in 4th, or you may be going to 4th gear between 5 and 6 and then need to shift back to 3rd for 6 and back to 4th for 7. (hope that makes sense?)

In my 01 Cobra I installed 4.10 gears, while it was great in certain corners, it messed up others. On a mam or gingerman type track I can see them helping, but I really have my doubt whether the overall benefit will be worth it for RA.

Brian

 

[ac427cobra]

Brian:

Thanks for your knowledgeable input. You know how much I respect your opinion and appreciate your wisdom!


Here's the gig. ANY gear I go to, I will be shifting. I am already at redline in fourth gear with the 3:55's going into 1, 5 and 12. I'm also at redline in third gear going into 14. (Also, going through turn one I do not downshift anymore because I feel it is a waste of time and I'm pretty sure I can go through there hooting in low R's in fourth gear instead of all the screwing around of downshifting? Hence, it is my slowest turn on the track) So even going to 3:73's I'm going to be shifting?

3:90's IMHO are not going to make that much of a difference?

I'm changing to coil-overs and K-member on the front only (maybe long tubes to boot?). My focus is primarily weight reduction but the benefits of coil-overs is going to help, me thinks? I really don't like the way the lower single shear pivot point is set up on the rear coil-over set-up? Maybe I'm too anal about this? But to be honest with you, I'm relatively happy with my rear suspension since I did the Delrin bushings and UHMW cradle mount bushings! I just want to lower my center of gravity.

Trust me, I completely hear you on the shifting because that is what has prevented me from going to a different gear in the past. I have a mission right now, and that is to pass Black Death if it is the last friggin' thing I do!!! I'm going to own that Z06 next Spring!!!! :lol: :lol: :lol: This will be my "spare" IRS so it's not like it's going to be a permanent, irreversible change?

Still in my infancy in this tracking stuff!!! :thumbsup: :coolman: :beer:

 

[Flying Fred]

Originally posted by Cobra-R
Bruce,
I am with Kevin. I would look at 3.73 or 3.90 at the most since RA is your preferred track. I bet Fred will have more to add, I think he has changed gears. I believe JoeJ even mentioned that his 4.10's were a little much for RA.
Brian

As you know Bruce, I am a mechanical moron. But I will throw in my 2 cents on my experience with gears. I have been running 3.73s on the R for quite a while. I always upshift to 5th on RAs big straights - and also to 4th on 1-3 and 7-8. I take Carousel in 4th - and turn 5 in 2nd if I really want some serious pull. Turn 1 can be either 3 or 4 - depends on what I'm doing. The rest of the turns are usually in 3rd. Any gear change - be it to 3.73, 3.90 or 4.10 will make a difference in your shifting points (OK, no big surprise there).

Anyways, on to the real matter. My 03 has 3.90 gears which were recommended to me by Jeremy and Doug. It's too much for that car as I easily spin the wheels due to higher HP and torque. This winter Doug will swap rear ends on the 03 and the R. I think the result will be an improvement for both cars. As for 4.10s, I agree with Brian. It's too much. You might actually induce some unwanted wheel spin accelerating out of corners. BTW, remember Jeremy was topping out at the bridge with his 4.10s. OK, we don't have near the HP he does, but I still think it's too much. Believe me, you WILL notice a difference with 3.90s. You don't need to go overboard with 4.10s.

Hope my experience might be of help. At least there is more of that I can offer you as opposed to sharing my technical knowledge!

 

[ac427cobra]

Fred:

Thanks for your input as well. You need to give yourself more credit than you do. You might not have the mechanical ability to fix every part on your car but you know a heck of a lot more about cars than your average bear!!!!

:thumbsup: :coolman: :beer:

 

[scottmartin]

410 gears

i will chime in with my limited experience, ok? i have 410's in the r. i feel that on the bigger tracks like ra, mam, it is to much. on the smaller tracks like hallett and heartland i am ok. i am thinking about going to 373 this winter for next year. my skill and experience is minor compared to yours but thats my feeling. scott

 

[93SVTCobra]

I think you are going about this the wrong way Bruce. I look at the gear ratio a couple different ways. First of all is this going to be your only gear ratio or are you planning on switching between this gear and the stock 3.55? I see you mention that you are at redline going into a few of the corners at RA already which ideally is where you want to be (I'm not really sure which corners you are referring to but I am assuming they are the corners with longer straights based on the RPM and gear ratio). You really need to determine your speed at the end of the straight-a-ways and then work backwards using rpm and trans gear ratio to determine what the proper gear would be for that track.

We have two gear ratios for our AI car: 3.27 and 3.73. Granted we are working with a few less RPM's than the 00 R's but you need to really analyze each track you go to and the MPH you hit to determine what gear ratio is ideal.

 

[93SVTCobra]

Forgot to add comments on the Coil overs. Any reason why you only want to go coil over in the front? With 4 wheel coil over you can adjust your corner weights much more which is going to make a big difference! Are/Can you add a C/O kit to the factory Blistens or are you changing struts/shocks as well?

 

[ac427cobra]

Mark:

Thanks for chiming in here. As far as the complete spare IRS assembly goes, this will be experimental assembly that I want to make some changes to. If I'm going to the trouble of building up a spare IRS assembly I think it is only prudent to do it in a different gear ratio? What ratio? Good question? That's what I'm trying to figure out here? As Scott stated, 4:10's may be a little too much. But OTOH I think 3:73 won't be enough of a difference? So, right now I'm leaning towards 3:90's.

I guess I should have been a little more clear on the red line comment. I am just approaching red line only two places on the track. Going into 1 and 14. I'm right at 6,600. Two other areas are not quite as bad. When I'm going into 5 and 12 I'm only at about 6,400 or 6,500. So, no matter what gear I go to I will be shifting. I find it hard to believe I would run out of 5th gear even with 4:10's but I could be mistaken? IMHO there is no way I would run out of 5th gear with 3:90's?

I run a lot of different tracks and there is No Doubt it's hard to find a compromise for all of them?

At this time I plan on going to the full front coil-over system along with tubular K-member. I don't want to convert my struts. I hear what you're saying on the rear coil-overs but didn't want to bite off more than I could handle for a Winter project? It's just me working on the car!

I appreciate and respect everyone's input here. I'm just trying to get this tracking stuff all figured out! It is much more fun than watching the Big Boys run around in circles!!!!

:thumbsup: :coolman: :beer:

 

[Cobra-R]

Originally posted by ac427cobra


At this time I plan on going to the full front coil-over system along with tubular K-member. I don't want to convert my struts. I hear what you're saying on the rear coil-overs but didn't want to bite off more than I could handle for a Winter project? It's just me working on the car!

Rear coilovers are the easy ones to do, just remove the shocks and install new ones.

Brian

 

[ac427cobra]

Originally posted by Cobra-R
Rear coilovers are the easy ones to do, just remove the shocks and install new ones.

Brian

Brian I will have to weld reinforcing bars onto the top mounts because I did not reinforce that area (there was no need to) when I did the roll cage. I hear what you're saying it should be a pretty straight forward thing to do the rear at the same time? I have pretty much stuff on my Winter plate already and now I'm going to get a slightly later start seeing Fred twisted my arm to go to VIR!!! Woot!!!! :rockon: :rockon:

 

[Cobra-R]

I agree that reinforcements are a good idea, but I don't have and and actually don't know anyone that is running them. Hardly necessary in my opionion.

Brian

 

[Flying Fred]

Originally posted by ac427cobra
IMHO there is no way I would run out of 5th gear with 3:90's?

Based on my experience with 3.73s, you shouldn't have a problem running out of gear with 3.90s.

BTW, the reason I am putting 3.90s in my R is NOT because I think it's a better gear for that car. It's because I think it's a worse gear for the 03! In fact, the 03 will be getting a Torsen T2R installed in addition to the 3.73s coming out of the R. In other words, I'm swapping gears between my two cars because I think it will be a better combo for at least the 03, and perhaps both. Assuming I like the T2R in the 03, I will likely put one in the R at a later date. By that time I'll have a feel for how the 3.90s work in the R and decide whether to stay with them, or go back to 3.73s.

I may be a mechanical moron, but sometimes I come up with a good plan on trying things!:idea: I guess it's like the old adage that even a blind squirrel sometimes finds an acorn!
:beer:

 

[BAD PNY]

Bruce

After reading all this I have a comment and a question.

The comment is how are you going to beat a Z06 with the R. We all know the superior car. lol

2nd is 5th in your car .80 to 1. Trying to figure out if your gonna drop to many RPMs with 3.90's or 4.10's.. IMO I think the stock 3.55 is a great all around gear. I would work on another 20 rwhp before I would mess with the gearing. Especially since you drive so many different tracks.

Mike

 

[Flying Fred]

Originally posted by BAD PNY
5th in your car .80 to 1. Trying to figure out if your gonna drop to many RPMs with 3.90's or 4.10's.. IMO I think the stock 3.55 is a great all around gear. I would work on another 20 rwhp before I would mess with the gearing. Especially since you drive so many different tracks.
Mike

Mike, I disagree. My 3.73s have been far better for my R (will see what 3.90s are like). If you don't have a 00R, I'm not sure what you are basing your opinions on.

Your comment about an extra 20 RWHP sounds wonderful in theory, but I' skeptical of it's practicality. Bruce already has changed the exhaust, etc and is probably about 380 RWHP like almost all the other 00Rs he runs with. Would you care to be more specific on how you get that extra 20 RWHP?