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Need Help With IRS Drag Setup

24K views 57 replies 18 participants last post by  ITSTOCK 
#1 ·
I'm looking to get my car back to the track in the spring to get some better ET's. When I went in the fall I couldn't get better than a 1.9X 60' and it also wouldn't hook up in second. I wasn't expecting too much since I was running Toyo R888's and not a drag radial, but I was hoping for at least 1.7-1.8. My current car is a whipple vert putting down 650/600. I used to have a ported eaton car with 100% stock suspension. With that car I could get 1.6.-1.7 with 275 Mickeys on stock wheels and 1.8-1.9 with regular 275 street tires.

Looking to get some help setting up my current car to transfer weight and hook better. I plan on switching to a drag radial, either a 315/35/18 Toyo TQ or 305/35/18 MT. It currently has adjustable front struts and single adjustable QA1 rear shocks. I'm not sure what springs are in the front, some sort of mild aftermarket lowering springs. The rears are stock springs with half a coil cut off. I'm looking for help tuning my current setup or suggestions on what suspension parts I should change to get this thing to hook up as good as possible on 18" drag radials. It's first and foremost a street car. It will only see the track a few times a year, but I don't mind a slight compromise in handling to get improved launches. Thanks :beerchug:
 
#2 ·
Sidewall height is your friend. I run a 325/40 M&H 18" Drag Radial and love them. I've ran less sidewall and I'd never do it again. To much of a chance of hopping and breakage. I ran 1 day at the track with my 6spd. and BFG Drag Radials and made 1 decent pass that was an 11.80 I think with a 2.3 Whipple at 660hp. The car hopped and I let out pretty much.

If you're going to run I'd get the tallest sidewall Drag Radial you can find or a 28" slick. You need that sidewall to flex and not hop. At least I think I said that right.
 
#3 ·
Sidewall height is your friend. I run a 325/40 M&H 18" Drag Radial and love them. I've ran less sidewall and I'd never do it again. To much of a chance of hopping and breakage. I ran 1 day at the track with my 6spd. and BFG Drag Radials and made 1 decent pass that was an 11.80 I think with a 2.3 Whipple at 660hp. The car hopped and I let out pretty much.

If you're going to run I'd get the tallest sidewall Drag Radial you can find or a 28" slick. You need that sidewall to flex and not hop. At least I think I said that right.
Thanks for the reply Posi! That's pretty much what happened to me. Bad wheel hop and let out then I'd try to get back on it as much as I could. Best I could muster was 11.68 @ 133. I went within 4 hundredths of that with freakin Sumitomo's in my old car with 150 less hp so I was definitely disappointed, lol. I'm not crazy about how a 28" tire looks with a 26" tire up front though. I'm sure it would hook better than a shorter one, but I don't think I'm willing to compromise on the looks quite that much.
 
#4 ·
Looking to get some help setting up my current car to transfer weight and hook better. I plan on switching to a drag radial, either a 315/35/18 Toyo TQ or 305/35/18 MT. It currently has adjustable front struts and single adjustable QA1 rear shocks. I'm not sure what springs are in the front, some sort of mild aftermarket lowering springs. The rears are stock springs with half a coil cut off. I'm looking for help tuning my current setup or suggestions on what suspension parts I should change to get this thing to hook up as good as possible on 18" drag radials. It's first and foremost a street car. It will only see the track a few times a year, but I don't mind a slight compromise in handling to get improved launches. Thanks :beerchug:
I'm not crazy about how a 28" tire looks with a 26" tire up front though. I'm sure it would hook better than a shorter one, but I don't think I'm willing to compromise on the looks quite that much.
I will just be honest with you here........you are pretty much screwed. You have a lowered car with stiff springs and you want to run a drag radial (a bad one at that with MT/Toyo) and are limiting yourself to a 26" tall tire.

Tires are the biggest single change to make, get those MT's that Posi mentioned, they are great. If you want to run a narrower tire get a 275 MT Pro. If you want to get into the suspension you need to change out those stiff lowering springs up front or the car will never transfer weight.

--Joe
 
#5 ·
If you can run a smaller wheel it would do alot. 17 or even a 16 inch wheel will give you more side wall without having to worry about fitment on the IRS. If you are willing to grind the rear knuckle using 15" wheel that much better.

Going with smaller wheels reduces overall rotating weight, give you more sidewall, and gives you more choices for tires. It's a win, win, win for cutting 60's. Your sig says you have a built irs, what exactly has been done? Also do you have subframe connectors or any bushings installed in the IRS?
 
#6 ·
Vehicle Tire Car Automotive lighting Automotive tire


Here's mine with the M&H 325/40 18 it's a 28" and hooks really well. On a 18" you will have to slip the clutch pretty hard.
 

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#7 ·
IMO a 15X8" wheel and an appropriately sized MT ET DRAG slick would make the biggest difference for you. Put some adjustable struts up front or try some cheap 90/10 lakewoods. Something that pops up easy, and resists slamming down easy to minimize front end bounce if the motor bogs a little, and on the 1/2 shift.
 
#8 ·
Hi guys, thanks for the responses so far. I'm not really looking for a full drag setup so no smaller wheels in the back and probably not going to go with a taller tire. More looking to maximize my current combo or maybe change shocks/struts and springs. I currently have adjustable struts and shocks, any suggestions on settings to get the best results? I think going to a 90/10 in the front would really help me, anyone have much experience driving those on the street in a cobra? Notice much difference in handling or braking?
 
#9 ·
90/10s suck on the street. Best bet for a street car would be a good double adjustable but they get expensive fast.

You're playing a game trying to hit drag radial tires with a clutch. Lots of parts have been broken that way.
 
#10 ·
Setting are pretty simple tight compression and tight rebound in the back to plant the tire when the car weight transfers. Tight rebound so the car stays planted.

Loss rebound in the front and tight compression in the front. When the car rises it doesn't want to slam back down and unsettle the car.

Best way to get a 18" tire to perform at the track is SLIPPING the clutch and I mine ride it like it owns you money. That being said my best time on 18" wheel with a 28" tall tire was a 10.36 at 136mph. That was with my double adjustables and dialed in suspension.
 
#11 ·
First of all, these guys are completely right you are going to need a taller tire and less rim diameter. The only "compromise" I can think of is if you got two 17x10 rims just like the 18's you have now and put a 315/35/17 drag radial like a nt05 or a Mickey Thompson. I'm not sure if you will get the result your looking for but most people will not know you switched the rear wheels and tires. Then you can put the 18's back on at your leisure. I have had mixed results with 17" drag radials, as far as how they hook. Once, on a very well preped track, I had to add air to a nitto drag radial to keep it from bogging off the line. Most every other time it's a mixed bag of frustration and a couple of good passes. The few times I have borrowed 15's it hooked every single time. Hope this helps, and best of luck...
 
#12 ·
OP, Please take this suggestion and realize there is a bunch of guys here that have been where you want to go and have all had to learn the hard way... I listened to the suggestions from a bunch of these guys and has really saved me thousands of dollars...

With that said, I've been where you are, my car was and is still a daily driver. First, your IRS is worth a pretty penny. Guys building kit cars/ replica AC Cobras will pay top dollar for it. I put in a solid 8.8, new suspension and a dedicated drag wheel set and went from 11s to 10s just from doing that and I had the same hp as you. If you do some strange single adjustables with 175lbs coilover springs you set it at one of the lowest settings for good weight transfer then you can turn the dial all the way to the other way and it wil stiffen up the front and I don't even have to use a front sway bar. The rear has Afco double adjustables w/ 150lbs coil overs, Baseline suspension outlaw kit with solid bushings. I have since changed to an auto and went with a 3.4 Whipple even with the drive train loss due to the auto it still made 630hp thru the auto and with MT 275 pro's I have been 1.39 60's and mid 9s.

The point here is that staying with the IRS limits what you can do and how hard you can launch the car. Also, there is no difference how the car handles with the solid 8.8 to the IRS.
 
#13 ·
IRS FTW:) Here's a slow motion video of my 1.44 60fts. I still run the stock 8.8 diff in my opinion the IRS doesn't hinder going fast.

 
#15 · (Edited)
IRS FTW:) Here's a slow motion video of my 1.44 60fts. I still run the stock 8.8 diff in my opinion the IRS doesn't hinder going fast.
I sincerly respect you and what you've done with your car but you can't seriously sit here and say the IRS doesn't hinder going fast. You have 1400+ hp and run 9.20s. If you had an SRA I bet you'd be mid-high 8s and if you added an auto to the mix, I bet 8-teens with a little seat time 7s .
 
#14 · (Edited)
If your looking for a tire to perform on a 17" rim I suggest the 295/45/17 MT. I have been 1.6's on this tire on a fairly unprepped track. Its just shy of 28" at 27.8" tall. very forgiving tire, and has a decent amount of sidewall for what it brings to the table on a 17" rim.

If you go with a slick, I like the 26" ET DRAG or 28", both in stiffwalls. They are like driving on a drag radials once up to speed, plus they have the added insurance of aborbing shock with the sidewall. I have been a best of 1.47 on a rather stock IRS with a KB and 6 spd into the 9.80's.

I have seen a handful of STOCK suspension cobra's with larger blowers go mid to low 1.5's out of 60ft with 315 DR's on the IRS and 6speed. Take into account you need the "ZERO ****S GIVEN" approach and have to drive the car with the chance of breaking it at any given second. In the end you could have a setup car ready to rip, and if the track isnt there or your driving isnt on par, its gonna not worth a damn. Learn to slip the clutch....

I have been 10.30's on a 275/40/17 MT DR on stock 17's with about 670whp. Its all getting out of the 1st 20ft...if it spins hard, hops etc..its not just gonna work.


With the above being said, I could go from having a semi consistent low 1.5, high 1.4 IRS to a VERY consistent 1.3x car with a properly setup solid (which I have ready to go in), plus drop about 70lbs off the cars weight in the process. I love the IRS, but it definitely has its drawbacks if your looking for a straightline approach.
 
#16 ·
Good luck with a radial and IRS at the track. Buy a cheap set of 16' Diamonds wheels and mount some 28" Hoosiers slicks on them. My best 60' is 1.44 on H&R race springs.
 
#18 ·
Thanks again for all the replies so far :beerchug: A couple people have talked about slipping the clutch and I completely agree. You have to know how to slip the clutch to get out of the hole on 17's and 18's. When I was last at the track I didn't necessarily spin right off the bat because I was slipping the clutch, but I could never actually apply full throttle in 1st or 2nd. Every time I'd try to ease into it the tires would eventually spin.

I think most of you are kind of missing my point though. I know I can put a taller tire and/or smaller rim to get more sidewall and the hook would be much better. I'm not disputing that one bit. I know there are cobras out there that have cut decent(1.6-1.7) 60' times on lower profile 18" drag radials though. I'm not chasing a particular ET, just want to set the suspension up to hook better on the street and track. I've had at least one 03 cobra or another over the last 10 years, but this is my first one with adjustable struts and shocks. It's got Tokico single adjustable up front and QA1 single adjustable out back. Curious what settings I should start with? I'd consider going to a double adjustable out back if anyone thinks it would help greatly. Double adjustable in the front is too expensive for me. Would also consider changing springs to something that might transfer weight better as long as they're at least slightly lower than stock(0.5-1") Let me know what y'all think.
 
#19 ·
For the track you want the fronts loose to transfer weight. I'd start out in the middle for the rears. I'm running d spec in front (200# springs) now and da Vikings in rear. Once I change rear springs I should be able to lower my 60's. Best is a 1.47 on that setup.
 
#22 ·
Sounds like you got your setup working pretty good. What do you have your D specs set at? I bet those double adjustable rears are really helping to to keep the weight transferred. I may have to check out those Vikings, they seem like a decent deal. What rear springs are you running now?

Imagine your car leaving like this. Stock motor, 3.4 whipple, setup solid axle.


Cobra IRS is not Supra IRS....if it was we would have some seriously fast IRS cars after 11 years of these cars being around, but just dont. I love my IRS btw but its garbage compared to a properly setup solid.
Haha, it would be great to leave like that, but that's not really what I'm after. It's primarily a street car that will see more back roads that drag strips.

I loved watching your videos back in the day. You know how to get it done with a 6spd and IRS that's for sure. I love my IRS too, it ain't going anywhere. It's one of the main reasons I don't have an 11-14. The 15's are looking more and more tempting all the time though. Ford did the best they could while being limited to the stock 4 link locating points. I think stock vs stock it hooks up way better than a solid in turns or a straight line in the 99-04 cars at least, but I've never driven a car with a drag oriented solid setup.
 
#20 ·
Those tokico illuminas are going to be tricky because they're single adjustible. You want the front to pop up fast, but resist slamming back down. The illuminas can't do that. They pop up fast, and they slam down just as fast. Which means if you get a mean bite, it's most likely unload a few feet out. Then it'll unload on again on the 1/2 shift.

However, with the right combination I'm sure you'll be able to find a happy medium. The one thing everyone has told you is that the tire is the most important part of obtaining a 60'. With a hard tire on a crap prep track you can waste years chasing your tail trying to tune everything to work in an inconsistent environment.

My recommendation would be to look at Hoosiers drag radials.
 
#21 ·
Imagine your car leaving like this. Stock motor, 3.4 whipple, setup solid axle.


Cobra IRS is not Supra IRS....if it was we would have some seriously fast IRS cars after 11 years of these cars being around, but just dont. I love my IRS btw but its garbage compared to a properly setup solid.
 
#23 · (Edited)
Many gave up on the IRS before even giving it a try. I remember watching Ken and Matt run 1.3 60's on the IRS 8 years ago and no one has done it since.

Stangman701 - I still have h&r race springs in the rear, I'm going to c/o's but I'm not sure what # spring yet.
 
#24 ·
I wouldnt waste your time on a DR you will end up breaking something in my opinion. I have over 75 passes on my stock halfshafts being bias ply tires are the key. My set up is simple stock shocks all the way around on HR race springs with FTBR bushing on a 26 inch et street ive been 1.48 sixty foot
 
#25 ·
Ive ran 1.5's with 335 hoosier drag radials on 17x10 replicas,qa1's, and drag bags. I think the biggest thing hurtin your short times are those springs,like someone else suggested. They look cool and are good for corner carving but horrible for weight transfer.
 
#27 ·
With H&R's and 28" slicks it took me close to 2 years to run a 10 in my vert. That's when it had the 2.3 Whipple at 22psi and made 660hp on full race gas.

It 60'd a 1.78 and went a 10.71@133 I believe power shifting the daylights out of it!
 
#29 ·
I'm about to put the H&R race springs back in mine, I went 1.44 at BG in '13. I switched to adjustable struts and coilovers up front and da shocks out back and went 1.47 at BG last year. I wasn't very happy to say the least, but I'm not giving up yet. Just wasn't what I expected.
 
#31 ·
funny how much difference there is in thought on what works...I'm tired of the H&R race springs and nitto 275 NT05rs on stockers... its just spin city on the streets... I was about to go buy some 16x10 bogarts till i saw how limited the tire selection is on the 16.. looks like the hoosier 28x14.5 QTP are the only real option..... its good to see the fast guys share their knowledge though, even if its still confusing...lol:good:
 
#32 ·
OP - I believe you and I were messaging back and forth on SVTP. With the IRS, slicks are your best friend. With anything, practice makes perfect.

On a side note, I'm a UPR/Viking dealer and Viking is releasing a VERY budget friendly DA Coilover strut for us. I got confirmation on Friday that there taking orders this week. That will be a great upgrade and a lot of folks have been waiting for these to be released.
 
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