NA build with a IRS what gear and IRS mods?

[old01cobra]

I read numerous posts on this and nothing really fits my build. I'm not sure what too expect out of this build in a quarter mile setup. I did a BB/S with 03 heads and it made 460rwhp and 390rwtq. It pulls 400+hp from 5400 too 7400 before its starts to fall Im running out of air again and I'm not cutting up the Fr500 intake anymore. The TQ is 300+ from 2800 rpm all the way too 7400+ when I cut the pull.

I need some help on gearing and IRS setup, as well as the K-member stuff. This isn't going to act like a Pullied bolt on cobra or any blower car. I did a highway pull with a friends vmp 2012 coyote and he layed down 540rwhp through a Auto with 3.15 gears and the only time he pulled was when I was shifting. I know this things got some potential as I am still running the 3.27 gears with no suspension work done at all the benefits of a NA build I guess, no parasitic loss and heat soak.

So regardless I don't know what too expect in regards too trap speed with this. I know what 4.10s, 4.30s and 4.56s will get me in the MPH at the top of 4th but what will the car actually pull. I just need someone to chime in with some similar experiences. What gear? What k-member and coil over rate? I'm keeping the IRS so what upgrades (spring rate, bushings, halfshafts are really needed)? Can I get buy with 15inchx8's wheels for slicks or would I need 10 inchers etc. 26inch tire 28 etc.

All knowledge is welcome and is thanked in advanced........

 

[01yellercobra]

What are your plans for the car? Drag strip, corner carver, street beast. We need that info to give input.

At the very least you want to upgrade all bushings in the IRS. Upgrading half shafts seems to depend on who you talk to. At the very least I'd upgrade to 03/04 units. I snapped a stock 01 shaft getting on the freeway. Running slicks will help the half shafts live. And if it hops get off the throttle. In order to run 15" rims you have to grind the toe link mount and possibly the caliper. Run 16" rims and you won't have to worry about anything.

Springs and gearing will depend on what you're doing with the car. I have Maximum Motorsports coilovers and K member under my car, but my focus is canyon carving. I rarely hit the strip.

 

[old01cobra]

Its just a toy. Had the thing since new bought it out of high school. Been this long to save up for the build, well till I actually pulled the trigger.

It'll see the strip every now and then and maybe some auto cross. I live in a rural/suburban area with interstates close so it really doesn't matter it'll see whatever roads I drive through. It'll be more geared towards strip though.

Whats your opinion on Tokico D's struts and shocks? I was thinking about those with either 175lb or 250lb coilovers upfront with a matched spring outback. I just don't know how far too push the suspension upgrades, I mean go through Kenny Brown or M+M you could be pushing 6K+ dollars. Do I really need all that stuff? Kenny Brown makes rear upper and lower control arms for the IRS they'll brace the IRS subframe etc.. is all this really needed or justifiable?

As far as gearing I was leaning towards 4.30's till I get tired of the NA aspect and bolt on a YSI or 76mm turbo setup. Figured with 4.30's it should give me 125ish if I cross at 7K or later push too 7500 and I should have enough for 135ish. Is the 125 ish impractical with the power level I am at? If so, maybe Ill just do the 4.56 then? That'll give me 120ish at 7K or just shy of the 130 in the future at 7500. It'll be a little lighter spare out, maybe a UPR as its light, rear seat delete etc so slightly lighter. Keeping the 26inch tire and running it through a promotion 3650.

Side note nice rides. That old one how did the 323 like and hold up too the F1? In general how was the 323 in the long run just wondering what to look out for also what kinda numbers did it make?

New too this even though Ive poked around since 2012 so sorry for the 20/20 questions LOL.

 

[Brutal Metal]

26 inch tire height with 4.30's. If your doing a gear change a new stronger Diff cover is a no-brainer or at the least a brace, I use the Billetflow one. If your onsidering changing out all the bushing skip right over poly and go Delrin. I wouldn't bother with a K-member. Switch out the struts and shocks with some take off Bilsteins unless you just have money to burn to do coilovers.
As far as halfshafts what year is your IRS? If a 99 like mine you have the weaker 28 spline shafts while 01-04's have the 31 spline. If you keep your launch rpm low and ride the clutch out instead of just popping it at 5K you'll limit the shock. I'd attend to a part like that if and when it breaks.

 

[01yellercobra]

I'm running 300lb/475lb springs on my 04. That's with the Bilstein HD's. It rides nice and I can live with it for a couple hours at a time. I've never used Tokico's, but I've heard good things about them. I'm just a Bilstein fan.

As for suspension, this is just my opinion, but no, I don't think you need all that. I lived with a stock K member for years. The only reason I have a MM currently is because it came on a parts car I bought. And to be honest I have issues with it and it'll probably come off in the future. But it does handle great. Even with old school 555's I can make myself nervous on off ramps and interchanges.

For the IRS just do the bushings and brace the diff as Brutal mentioned. I used the Billetflow piece in the past with no issues. I currently have the FRPP cover and like it as well. I don't know of anyone that runs the Kenny Brown control arms or braces. So I'd spend the money elsewhere.

The 323 loved the F1A. I built it for boost though with 9:1 compression. The F1A never hit the dyno, but that engine laid down 496/469 on a Mustang Dyno with a D1 at 12psi and 12 degrees of timing. The F1A made it a monster. Some times I miss it. I still have the shortblock for future use.

 

[Brutal Metal]

I'm running 300lb/475lb springs on my 04. That's with the Bilstein HD's. It rides nice and I can live with it for a couple hours at a time. I've never used Tokico's, but I've heard good things about them. I'm just a Bilstein fan.

As for suspension, this is just my opinion, but no, I don't think you need all that. I lived with a stock K member for years. The only reason I have a MM currently is because it came on a parts car I bought. And to be honest I have issues with it and it'll probably come off in the future. But it does handle great. Even with old school 555's I can make myself nervous on off ramps and interchanges.

For the IRS just do the bushings and brace the diff as Brutal mentioned. I used the Billetflow piece in the past with no issues. I currently have the FRPP cover and like it as well. I don't know of anyone that runs the Kenny Brown control arms or braces. So I'd spend the money elsewhere.

The 323 loved the F1A. I built it for boost though with 9:1 compression. The F1A never hit the dyno, but that engine laid down 496/469 on a Mustang Dyno with a D1 at 12psi and 12 degrees of timing. The F1A made it a monster. Some times I miss it. I still have the shortblock for future use.

Nice writeup, I think the OP has a decent bit of advice to work with from these posts..

 

[olgreydog7]

I have the stock K member, but I have MM control arms, coil overs, and the entire FTBR kit on the IRS. I run 4.30s, but I have a T-56, so it's not much more gear than stock depending on what gear you are in. I haven't ever taken it to the track, so I don't know what my trap RPM would be. On the street, it lugs a bit if the RPM drops to about 1100, but she pulls like a train and lights the tires easily. I run a Sullivan and the cams are 232/238.

 

[old01cobra]

Thanks you guys with all the info thus far. Ill keep the K-member for now wait till I pop a halfshaft upgrade the bushings out back brace the diff run the 26inch and 4.30's.

Ill convert too coil overs with some aftermarket A-arms and Ill try the Tokicos as Ive heard great things too.

Im not a chassis guy I can do engines and trans so I appreciate all the advice otherwise I would've spent more than needed!!!!

 

[RX1Cobra]

I have a pretty similar setup and power level (Eaton though). I have 4.30s and run Nitto 275/40/17 NT05r's. At the track I'm sitting on the limiter in 4th gear before I cross the line. Trapped 117 each time. My car's limited at 6800 though.

Original owner here also, got mine when I was 20. Stock halfshafts, diff cover etc. Only suspension mods are springs, 00R diff brace (03 wasn't out yet) and subframe bushings. Car hooks pretty good besides 1st gear.

 

[01yellercobra]

Ie a pretty similar setup and power level (Eaton though). I have 4.30s and run Nitto 275/40/17 NT05r's. At the track I'm sitting on the havlimiter in 4th gear before I cross the line. Trapped 117 each time. My car's limited at 6800 though.

Original owner here also, got mine when I was 20. Stock halfshafts, diff cover etc. Only suspension mods are springs, 00R diff brace (03 wasn't out yet) and subframe bushings. Car hooks pretty good besides 1st gear.

That reminds me....

OP- Look for the 03/04 brace that goes under the diff. It has support tabs that the 99/01 doesn't have for the pinion. I think a couple of companies made an aftermarket version, but I can't remember off the top of my head.

 

[old01cobra]

Will do slo984now thank you.

RX1cobra 117 at 6800. I'm winding mine out too 7500 rpm if need be you're making me lean towards 4.56's now and if I run outta RPM on the top end I could always step up too a 28" tire. Id hate too do the 4.30's then wish I did the 4.56's when I could do the 4.56's and make 4.30's with a simple tire height change.

What is your spring rate RX1cobra similar too slo984now's 300/475 lbs?

 

[trxcobra]

Interesting stuff in here. OP sounds like you have a sweet motor setup! I am running a 5.0 stroker with Cams/PSR intake and made a hair over 400whp, but not a ton of torque ~330lbs.

I do not track my car, just a street cruiser with 4.10s, Bilstein struts + Eibach sportline springs, BF IRS brace, 03/04 crossmember brace and upgraded bushings. Never touched the half shafts (knock on wood). For what it's worth, I am very happy with my setup as a fun street car

 

[olgreydog7]

Are you running any kind of chassis bracing? If not you should look into the rear shock tower brace and full length subframe connectors.

 

[trxcobra]

Are you running any kind of chassis bracing? If not you should look into the rear shock tower brace and full length subframe connectors.

Not sure if this was directed at me or the OP - but I am curious on the rear shock tower brace. I do not have one, nor do I have a front tower brace either.
Worth picking up?

 

[RX1Cobra]

Id hate too do the 4.30's then wish I did the 4.56's when I could do the 4.56's and make 4.30's with a simple tire height change.

What is your spring rate RX1cobra similar too slo984now's 300/475 lbs?

I wish I had 3.55s now! Not sure on the rate, they're Eibach pro springs. I think, whichever set dropped the car less. I've had them so long can't remember.

I don't have subframe connectors but will probably add them soon. Can see a few tiny wrinkles in the back fender from chassis flex. My cars strictly a nice weather car.

Been the track 3 or 4 times in 16 years. From 13.3 @ 105 stock to 12.0 @ 117 now.

 

[old01cobra]

Man that sucks about the wrinkles. You're going to make me run out and check mine now LOL. Where do you see the wrinkles at?

 

[RX1Cobra]

Passenger rear quarter. They're hardly noticeable. You need to look down the side of the car to see them. Cars never been hit and they're not door dings. So that's what I assume they're from.

You would never see them unless I pointed them out. I only notice it from washing the car.

 

[olgreydog7]

I don't have the front strut tower brace. I run a Sullivan so I'm not sure if the ones for a KB blown Cobra will fit or not.

I did the rear tower brace and the subframes at the same time. HUGE difference in the feel of the car. It felt immediately more solid and planted. Even for street driving I highly recommend them. They are relatively cheap, especially if you can find a guy named Bubba who will weld them on for a 12 pack of Natty Light.

 

[01yellercobra]

Passenger rear quarter. They're hardly noticeable. You need to look down the side of the car to see them. Cars never been hit and they're not door dings. So that's what I assume they're from.

You would never see them unless I pointed them out. I only notice it from washing the car.

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.

 

[old01cobra]

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....