dizwiz24

From time to time, I check out the C5 forums. I hear about guys in the 9's with the stock rear suspension.

What is different about that car that makes it possible to launch hard on it without breaking stuff?

Next question:

Why hasnt anyone on here figured out a way to make the C4's IRS work like that too ?

I dont know much about it, but I can tell you, with 100% certainty, its not impossible.

mnstrlt1

Well, the c5 has a significantly re-designed rear suspension geometry.

also the C5's tranny is located in the rear of the car. Coupled with a torque tube. don't be mistaken, several c5/c6 owners have distroyed IRS' due to wheel hop and other traction issues.

the suspension layout of the c4 is what makes the rear-end a bit of a problem. The half-shafts end up being a part of the suspension.

IRS suspension have proven to be a viable option in other applications. Short of using seriously large diameter sway bars and heavy springs to get the IRS to "work right" in a straight line, nothing is as consistent as a solid axle.

tpi 421 vette

If you run mid 10's or faster with a manual forget the irs. There are guys breaking irs parts with manuals running 12's. A auto trans car will be easier on parts, but they still wont make the irs last once you get close to the low 10's. And I have seen guys breaking irs stuff with auto's running 11's. A solid rear can be built bullet proof. I have never broke anything since doing the 9". There might be some guys running 9's with a irs, but I guarentee they have a maintance program on the irs. They would have to be tore down and rebuilt after so many runs. A solid rear in a 9 second car would be way more low maintance than the irs.

jhammons01

^^interesting...I never knew all this........

856SPEED

well,

If you want a straight line 1/4 mile machine; the Corvette in any era (from the 1963 model year on up) may not be your best available option......just my opinion......these cars are made for cornering first and foremost......they can do the straight line thing pretty well within their limits (11 seconds and better are normally not within their limits), but the solid axle is the way to go for all out 1/4 mile performance....

MK 82

There is the best answer. Why try to make the car do something it was not designed to do. Auto cross it. Road race it.

If you want a Drag Racer-start with something that came with a solid rear-preferably Ford 9 inch.

IMHO YMMV

Red Rocket

Have been fortunate the past ten years of serious drag racing my 396 manual LT1 of not having any major problems with the IRS. It seems like once you get the launch RPM over 360LBS of torque the breakage chances really go up in a C4.

Launch my manual at 2500 RPM's (360RWTQ in my 396). I never do a real burnout like everyone else either. Roll through the water and spin the tires moving forward. Run mid 11's with low 1.7 60'.

There is no doubt getting in the 10's would require a 4000 RPM launch and getting the 60' in the low 1.6's which would put the IRS on the edge.

dclafleur

I think it faces some of the same challenges as the high end drag radial racers. Softer launches and motors that make their peak torque later in the power band.

dizwiz24

my plans are to never go anything more grippier than 315/35R17 drag radials.

Thats my 'fuse'.

I have launched on nitrous, 275/40R17 BFG drag radials @ 22 psi and not had issues.

I just want to know why no-one makes a retrofit kit for the C5 parts that is allowing them to launch harder and more consistently than the C4.

Instead its always 'straight axle is the way to go!'.

If I wanted to run 7's. I can see that. However C5's are running 9's with IRS.

One day, once I get my bottom end built. I will have a supercharged machine capable of doing that.

Lets get some brains here together and figure out how to correct the IRS

The Green Rocket

If you do go 9's on your C4, make sure to get the half shaft safety loops http://www.dragvette.com/

The NHRA has a whole set of requirements related to drag racing with an IRS - all their safety rules were developed one accident at a time. The advent of the C5 saw the addition of rear upper control arms - every prior Corvette IRS essentially had the half shaft acting as the upper control arm. If you break your C4 axle, u-joint, or half shaft, then I can guarantee that at 100+ mph that you will be in for the dragstrip ride of your life. You can still break all those parts on a C5 - but at least your rear wheel won't be trying to make your car turn.

For the hard core C4 dedicated to drag racing with an IRS it is too bad that Dragvette does not make one of their 6 link kits for the C4.

Forgeting all the safety considerations, why would you want to limit your dragstrip launch with an IRS? Are you that stubborn? I'm not sure of ever seeing a 9 second car drag with any road race pretentions.

Thomas

Red Rocket

The only problem that I have with the newer vettes is when I line up against a new Z06 who drove to the track like myself. He has the same power and weight but can launch at 4000 RPM's and run low 11's/high10's on DR's. My 4.09 gears and 15" tires help some
but still at disadvantage.

RichS

One of my continuous problems was breaking the spiders or wearing out the clutches causing the spiders to pop. Also an occasional halfshaft breaking. This winter I was contemplating going solid out of total frustration. But I could not cut the car up to do it.

I installed the new locker posi, and Denny's Nitrous steel shafts. KNOCK on wood so far this season they have held up great. I have slowed the car a bit to run a 11.50 class, but the 60's average low 1.5s. In the fall I'll open it back up and try for some 10.7s and see how it holds up. This spring it went 11.2 @70%throttle

COPO

You got the money I will put ZO6 suspension under the rear of your car.

rklessdriver

There are a couple of reasonable things you can do to the C4 rear suspension.

1. Rear Camber Alginment.
2. Extend the outer rear suspension's Bump Stops.
3. Get rid of the rubber bat wing bushings. Use Poly or custom make some derlin or Alum bushings.
4. C-Beam Plates.

Beyond that you cryo the D44 case, Posi units, R&P Gears, halfshafts, u-joints, and stub axels. There are aftermarket D44 cases that are thicker/stronger from Neuman Car Creations. Regular D44 Spools can be fitted. Summers Bro's offers 31 spline stub axels w/matching broached brgs and re-splined hubs. A few folks have had billet stub axels mfgr'd.

At some point you can also build a pinion snubber bar to keep the C-Beam flex in check.
Will

MTVette

I agree with the posters above who talk of the carnage a strong engine can do to a C4 IRS. My 383 LT1 routinely gives me 60' times in the 1.5's, and in the last two years it has destroyed two half shafts, four U-joints, one wheel bearing, a D44 center section, and two transmissions. In fact, it's in the shop right now getting a new tranny - the 'bulletproof' racing transmission it had lasted just two years. Here's some photos of a few trashed parts.

thetoy

I broke a stub axle again last weekend where can a guy get the billet stub axles? And I would be willing to pay alot for a bullet proof IRS. I'm sure if I added up all the broken parts that I have in the corner of my shop I would be cheaper. I love to autocross the car so I'm unwilling to give up on the IRS rears.

383vett

I've been drag racing my 84 since it was new 26 years ago. I have broken countless halfshafts, spindles, ring and pinions, spider gears and burned out many posi clutches. The passenger's rear cargo hold still has a hole on the bottom from a flailing half shaft. In the interest of safety, I changed to a 12 bolt 4 years ago and have had no problems with the rearend since. In my experience, once the 60's approach 1.5-1.6 seconds, the parts will start flying. You can cryo and harden all you want, but it will happen. Fortunately, all my mishaps have happened on the starting line. But it only takes one 1-2 shift or 2-3 shift at a hundred or so to spell the end of the car or the driver.

tpi 421 vette

I cryoed everything,and it made no difference.

9 second 1/4 mile times out of a irs is asking alot.

dizwiz24

the c5 guys do it!!!

383vet: i love the wheelstand picture !

383vett

Thanks! As mentioned earlier, on the c4s, the halfshafts are an active member of the rear suspension geometry unlike the c5 and c6 suspension. On the later models, the halfshafts just transfer rotational power to the wheels. On the c4, the halfshafts have to provide power and also act as upper strut rods. That puts an additional load on the ujoints and halfshafts and increases the stress loads resulting in kaboom.