NA build with a IRS what gear and IRS mods?

01yellercobra

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Any of you guys ever use the stiffler stuff? The web bracing with rocker and subframe connectors and the spider setup? Looks really interesting too me after you guys are telling me you guys creased panels....
That's what I have on my 04. It was one of the first things I did after I bought it. They made a noticeable difference. And the jacking rails are awesome.
 

Lightning&Mach1

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I think I have a lot of experience that would help you.

Gearing to make your car as it sits now to work perfect at the track mph wise, a 4.56 is your gear. With revs to 7500rpm you will be ending the quarter mile at 125-127mph on a 26" tire. If you would need more mph the change it to a 28" tire it would more you to a 132 or so mph.

Now 4.30 gears would be more street friendly. Revs to 7500rpm and a 26" tire you could trap 135mph. Then 140+ mph with a 28"tire.

Doing a k-member and a arms are a nice mod to do. I personally love the maximum motorsports, because with non offsetting a arms it moves the front tires center line 3/4 forward. Centering the wheel in the wheel well much better. Also a k-member makes for more space to work on things in the engine. And if you have to remove a passenger side header to drop your 3650(Unless you have the very very nice built 3650 with the removable bell housing). Then also just the better front suspension geometry that is built into the MM k-member and a arms.

As for IRS and drag racing. I'd like to say I am one of the few that have 100% made up their mind that I will never swap it out and that I'm drag racing with the IRS till I die in my Green 99 Cobra. Proper tire choice, clutch choice, and clutch technique on the launch is all what is going to help axles live. I have a 16" ccw drag pack for my car. You should run nothing but a bias ply tire for at the track.

FTBR delrin bushing kit was my very first mod to my completely stock 99 cobra. SFC or the stiffler stuff would be a great mod to do. I don't know how needed at the track, but to make it spin clean on the street and kill wheel hop they are a must. A 03/04 cobra front diff brace is good, there is also the Kenny brown ones out there. A nice Diff cover would be a very good thing to do(I run the not made anymore FORE cover). The newer ford racing cover for the IRS is a very nice piece. Bruce at FTBR also sells a solid rear diff mount that also moves the IRS pumpkin down 1in. That 1in improves pinion angles and the halfshaft angles.

My IRS is fully built as I went ahead and made the big investment of DSS Pro-level Halfshafts. I'm still under a one year warranty on them, so I've added a good about of power to really test the halfshafts in the warranty period :).

My point of breaking a 03/04 cobra halfshaft was on a torquey N/a setup. Never had the car dyno but I'd say it was a good 360-370rwhp with 4.56 gears. Anyways first pass I cut a 1.56 60ft on a 16in M&H 11.5x26 cheater slick. Next pass I got more aggressive on the launch and broke a halfshaft. My clutch choice was a little aggressive for my power level, so I blame it on that some as I feel I shouldn't have broke one. But I was launching at 6k rpm or so. NO clutch dumping was done either. Since I knew that I want to stick with the IRS 100%. I invested in the top DSS halfshafts.

Making a 15" fit in the back would be a good move as you would get that much more sidewall to help protect things.
 

RX1Cobra

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I had a crease on the passenger side quarter panel centered right over the wheel well. I had SFC's, but they were cheapies I had a shop weld in. I noticed it one day while waxing the car.

That's exactly where mine are. I'll put SFC on one day. Car is hardly driven and I don't beat the crap out of it anymore so I'm not that worried.
 

01yellercobra

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That's exactly where mine are. I'll put SFC on one day. Car is hardly driven and I don't beat the crap out of it anymore so I'm not that worried.

I drove mine hard. It was hard not to with the engine set up I had in it.

When I bought my 01 it had 51 or 52K on it. I had the SFC's put on within the first couple of weeks. I bought my 04 with 97K on the clock and it never had SFC's put on until I put them on. I noticed a big difference in sounds in the interior between the two. My 04 has the typical buzzing around the radio bezel and a couple rattles from the back seat. My 01 was pretty quiet. I'm sure part of it is that I took care of my 01 and I think until now my 04 lead a fairly hard life. But I think SFC's helped with the buzzing and rattles a lot.
 
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old01cobra

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Lightning@Mach1.... From your experience is 460rwhp and 390rwtq with a 4.56's or even 4.30's enough power to actually hit 130ish in the quarter?

This is my first post on here and you guys have been awesome. The suspension stuff is really falling into place now. I'm getting a great list going.
 

RX1Cobra

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Lightning@Mach1.... From your experience is 460rwhp and 390rwtq with a 4.56's or even 4.30's enough power to actually hit 130ish in the quarter?

This is my first post on here and you guys have been awesome. The suspension stuff is really falling into place now. I'm getting a great list going.

IMO not in a full weight car. You make a little more peak power than me but not much. If I wasn't on the limiter think the best I'd see is 120, if everything worked out perfect.

I'm a true full weight car though. Spare tire still in, stock K member, clutch, hell even the stock shifter. I also don't live at the track.

When I went I didn't even warm up my drag radials. Was afraid to deadhook and break something.
 

Lightning&Mach1

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Yeah full weight I don't see 130 happening. I think 122-125 sounds close though. My car's weight is down to about 3425 or so with me in it. Still pretty car for a IRS. I call my weight reduction factory sometimes, because I deleted mostly all the same stuff a 2000 Cobra R has for weight reduction. :)

As long as your 3650 that you have in the car has the better overdrive a .62. The 4.56 gears will honestly not be that bad on the street, but if you like to autocross and take some nice curvy roads sometimes. Then 4.30's would be the best choice. Granted my rpm window when I had my 4.56 gear was only 7k-7200 and my power was already dead by then.
 

old01cobra

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Yeah full weight I don't see 130 happening. I think 122-125 sounds close though. My car's weight is down to about 3425 or so with me in it. Still pretty car for a IRS. I call my weight reduction factory sometimes, because I deleted mostly all the same stuff a 2000 Cobra R has for weight reduction. :)

As long as your 3650 that you have in the car has the better overdrive a .62. The 4.56 gears will honestly not be that bad on the street, but if you like to autocross and take some nice curvy roads sometimes. Then 4.30's would be the best choice. Granted my rpm window when I had my 4.56 gear was only 7k-7200 and my power was already dead by then.


Quick question maybe you will know. I know the 03-04 cobras with top mount blowers don't like pulls past 4th gear do to EGR temps and heat soak concerns. I went ahead and ordered the 4.56 gears for now. My question is when I wanna play above 120mph me being NA with no EGR and not blower really don't have to worry about the 03-04 issues correct?

I mean do the math final drive with the 4.56 in fifth give me a same final drive as the 3.27 to in 4th. So that whole excessive heat detonation thing really won't apply to a NA motor.
 

01yellercobra

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Quick question maybe you will know. I know the 03-04 cobras with top mount blowers don't like pulls past 4th gear do to EGR temps and heat soak concerns. I went ahead and ordered the 4.56 gears for now. My question is when I wanna play above 120mph me being NA with no EGR and not blower really don't have to worry about the 03-04 issues correct?

I mean do the math final drive with the 4.56 in fifth give me a same final drive as the 3.27 to in 4th. So that whole excessive heat detonation thing really won't apply to a NA motor.

The EGR isn't functional during WOT. The issue with the 03/04's is the heat generated under load in 5th and 6th. Along with tight piston to wall clearances. The pistons get hot, swell up, and sieze in the cylinders. As for pulling past 120, mine seems to like it just fine. You just can't do it over and over. I might do a run, let it cool down a couple miles, then hit it again.

I'd treat your set up the same way. You probably won't have issues using 5th with the 4.56's. I just wouldn't do back to back to back runs. I'd give things a chance to cool down a little in between.
 

1Slowfocusst

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Unless you wanna grind hell out of car I'd stay with 16 or bigger. These are 15s with 26" Mickey Thompson ET Pro' .. runs consistent 10.6 quarter mile


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Lightning&Mach1

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Do you know which overdrive gear is in your 3650? The 01 cobra's came with a .68.

2002+ 3650's came with the .62

Either way you'll find out when you hit fifth gear, its going to fall on its face in a race. It'll look like you hit the brakes lol
 

old01cobra

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Do you know which overdrive gear is in your 3650? The 01 cobra's came with a .68.

2002+ 3650's came with the .62

Either way you'll find out when you hit fifth gear, its going to fall on its face in a race. It'll look like you hit the brakes lol

Promotion said its out of a 04 Mach. So its the .62. I just figured it be close to the final drive as the 3.27 with a 4th 1:1 ratio. As the 4.56's with a .62 would give me a 2.80 final.
 

old01cobra

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always nice reading about N/A cobras and irs.. love it !

I've been poking around with the turbo stuff as a lot of these guys on here are unloading setups. I honestly think I'm going to leave it NA at this point just because it seems like everyone in the world has a blower or turbo and I just like being slower LOL.

You listed Modded IRS what do you have done?
 

WIKD32V

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I've been poking around with the turbo stuff as a lot of these guys on here are unloading setups. I honestly think I'm going to leave it NA at this point just because it seems like everyone in the world has a blower or turbo and I just like being slower LOL.

You listed Modded IRS what do you have done?
all FTB bushings and solid rear mount, frpp diff cover, ftb rear bumpsteer ,etc
 

old01cobra

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Alright update...... Went all out with the tax return.
Went team z for the coilovers, k-member, caster plates and subframe connectors as well as the bumpsteer kit.

Got all the stuff from full tilt boogie for outback and went 4.30 gears for now

Went with Tokico D-spec struts on all 4.

So question! What spring rate would you guys recommend for outback to match the coilover rate of 12 inch 200lbs. Ive got H+R race springs currently and the factory set in storage still (should I cut a 1/2 coil off, keep the race springs in or get something a little softer to match the fronts?)

Thanks you guys
 

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