RVY

If your making at least 500rwhp I'd appreciate some help. If your unwilling to post, perhaps an E mail would to me be appreciated.
My toy for the past 5 years has been a glorified grocery getter here in central Florida. But I would like to make one last attempt at the local drag strip. I stopped @600 rwhp and could have added 200 more. But the 600 is useless at the drag strip as it is.
I priced out a Carroll's rear end assembly. However every thing including brakes, a Detroit locker and installation just about exceeds the value of the car. I don't mind 3 or 4 thousand for improvements. But within reason. At my point in life I may be pushing up Holly bushes before the job is done.

Any rear spring or shock suggestions or any other POSITIVE suggestions would be appreciated. Currently I'm looking at a set of M/T 3745 s radials mounted on 11 inch rims. A Dana 44 takes power from a 700R4 tranny.
PS When I hit third gear the power is awesome and the eyes shine!

dizwiz24

I am having great luck on bfg drag radial 2's 315/35r17.

As long as temp >60f, it will hold 1st gear at wot all day long on freeway entrance ramps (ie. Not as sticky as a preppd track).

this is a 93 6spd w stock 3:45:1 d44.

I also have drm relocated trailing arm brackets and relocated battery behind pass seat (for what its worth).

Ive heard the autos have a crazy high 1st gear ratio so may need to see if you have too much gear in it.

As for power, i made 510 rwhp and contiued to climb at 5400 rpm - where i stopped the run to make further adj t. Air fuel and spark advance. I have no doubt there is 530 rwhp in it at 6000.

if you do a search on c4 forced ind site, i have some dyno graphs (sept 2012?) That i posted..

I am on stock bottom end (ie. 350]) and i imagine you have at least a 383.

mnstrlt1

DRM relocation brackets would be a great option if you're lowered from the stock ride height.

I currently run Mickey Thompson ET street radial II, this compound was offered in a 315/35-17. This is a very soft compound tire, and even with 32psi, it holds very well. I'd drop the pressure down to 22psi at the strip and see how she holds, MT recommends running down to 18psi. I'd do increments from 22psi.

http://www.mickeythompsontires.com/s...StreetRadialII

However, MT also offers the ET street Radial in a 275/40-17, but the tire offers an impressive contact patch;

http://www.mickeythompsontires.com/s...ETStreetRadial

There are several options for "drag" only shocks, specifically valved for the strip. Also, some old school tricks, like disconnecting the front sway bar.

The first gear ratio on the 700r4 is 3.059:1, then it dumps down to 1.625:1 in second. So first gear is pretty short. I don't think the stock gear ratio in the d44 is going to be "too much".

Denny's driveshafts also has several offers for the c4 half-shafts,

http://www.dennysdriveshaft.com/c34_...lf_shafts.html

It should hold together behind an automatic, if you had a stick shift car and wanted to do clutch dumps on drag radials, I'd consider some other options.

BrianCunningham

Get some 32 spline stubaxles from SummersBrothers if you're going to keep the IRS

You're going to start snapping stubaxles if not

Orr89rocz

Its hard to get that much power to hook on the street in low gears. But at track a good set of drag radials like mickey et street 2's will hold fine. As long as prep was good

600+ on warm roads has a chance to hook. For turbo cars a boost controller that ramps in boost helps. Blower cars, a timing retard by gear or mph would be hot ticket for some additional power control for traction

Colder roads forget it. Have to use higher gears and higher speeds

RVY

Thanks for the reply. At the strip I light up MT ET streets as if they were street tires These were the 15 inch wrinkle walls. I have a boost blow off device which helps some what.
That first gear in the 700R4 creates my problem.

Orr89rocz

Either track wasnt prepped or you need some suspension work but an irs vette is not a drag machine, but still shouldnt spin a 15" et street

dizwiz24

I just looked a little closer at your post...

If you have a 3.45:1 dana 44 (vs. the 3.07:1 dana 36 that came w/ most auto's) thats your issue right there.

First gear on your car : 3.06*3.45 = 10.6:1
First gear on my car (6spd) : 2.68*3.45 = 9.25:1

Now... if you can get that thing to hook, then watch out

mnstrlt1

The second gear in the 700R4 really drops off that short first gear. With that said, I am surprised the OP is spinning MT ET's in a 15". Poor track prep? What's the stall speed? Trans brake?

rklessdriver

The C4 Vette IRS is a GREAT Drag Racing machine.... IF you know what your doing.

I am going to tell you what I know, what works for me and what I think of some mentioned suspension parts availiable for these cars. No BS and I'm not hiding anything about my 84 or what I have done to make it leave so well...

First thing. On the later model cars (89-96) GM changed the suspension. Everyone knows about the wider track width - but hardly anyone knows about the different brackets. The new brackets lowered the Anti Squat % that was built into the rear suspension. You need to raise the rear ride height about 1.5"-2" to get it back over 100% like it was in 84.

On my 84 I run a 28" tall rear tire which raises my cars ride height 1" to 1.5" taller than a stock 84... I also have the stock rear spring bolts bottomed out to raise the rear suspension another 1.5". Thats a total of 3" taller on the ride height.

Unfortunatly the DRM trailing arm brackets lower the AS % even more... They also place the Instant Center further forward.... They are totally the wrong thing to use for drag racing...

I do very much like the DRM camber arm brackets as they lower the inner pick up point for the camber arm so that the camber arm runs closer to parallel to the halfshaft. This reduces camber change across the suspension travel.. the eraly cars are terrible in this respect. The later cars are much better but the DRM brackets are about perfect IMO. That said I have never been able to find any used and I'm pretty cheap about some stuff.. espc when I can work around the problem.... Honestly I run the stock 84 brackets and just compensate for it by putting 1.5* negative camber in the rear end at ride height... then at launch the tire is pretty close to 0* camber.

Second you need a stiff rear spring.... the stiffest you can get. 84 Z51 rear spring is what I run.

Third you need real shocks to control all that spring rate.... Not some BS factory replacement stuff. I use Koni D/A SPA1 Alum rear shocks... $500 each and I had make new lower mounting brackets. You need the rebound cranked as tight as you can get it. Compression about 7 clicks from zero is my start point and then I adjust + - for track conditions.

Before the install of the Koni rear shocks I was having rebound problems with the stock Bilstine shocks... on a slick track the car would porposie after the tire broke loose.... I knew what the problem was but had to wait for the $$$ to cure it. For nearly half a season I raced on the stock 101,000 mile 1984 Bilstien Z51 shocks and the car ran great on killer track prep but on a slick track the car hopped on down the track like Flipper in the ocean.

Fourth I run extended suspension snubbers/bump stops. I have some from Energy Suspension (PN 9.9143) that I modified to fit.... Now when my car is squatted down on launch the half shaft is parallel to the ground... no angle at all on the inner or outer U Joints.

I run a 28X10.5S (Stiff wall) slick or a 275/60R15 MT Drag Radial on my 84. D44 IRS witha Yukon 3.90 rear gear and a spool. A1 Performance TH350 trans with a PTC 8" 4500 stall converter.

800+HP on nitrous.

I do run a progressive controller (LEASH Electronics) but use very little on a slick tire.... Single ramp, No delay, I typically start at 60% ramped to 100% in .5 second (yes 1/2 a sec). I did not have it at the start of the season and was hitting the car with everything right off the line.... My best 60ft ever actually came before I installed the progressive NO2 controller.

I have run a best of 1.247 60ft.

My average 60ft since I installed the Koni's is 1.27.... that is for 43 passes. FYI it's still under 1.35 if you count all season which is over 80 passes total. The car is very consistant.

The car runs equally well on the slick or the radial but the radial is much more track prep sensitive... The radial will also send my car up on the back bumper in a heartbeat if I don't chain the front end down (front suspension limiting straps). I don't usually need the front end limiters with the slick tire.

Biggest problem I see with your car is the 4L60 trans.... the steep low gear with all that power makes it hit the tire very hard for a very short peroid of time. Not much you can do about it without spending big bucks....

I like the tire your considering. Tall so it takes away some gear ratio. Radial so it's stiff sidewall but it's downfall is it's a 17" and has a short sidewall....

The biggest things you can change for free or cheap:

1) Ride height and Anti Squat. Just start jacking up the spring bolt.

2) Extended snubbers/bump stops. They were like $30 on Amazon and 20 mins time with a grinder to make them fit.

3) Rear Camber setting.... when you jack the spring up for taller ride height your going to add some negative camber to it just at the factory setting.... you really need a digital level to know how much (Smart Level is what I use).... Just spend some time on jack stands with a tape measure, the digital level and the spring/shocks disconnected to plot out your camber curve and see where you need to be to have 0* camber bottomed out on the bump stops.

I hope you can understand this and that it is helpful to you. Any questions just ask.
Will

RVY

Thank You
The rear spring and QA-1 adjustable rear shocks were about to be ordered when I received your E mail. I was confused about the rear suspension geometry/squat concepts. You clarified that for me. I no longer have the courage to run the ET streets (wrinkle wall),So the radials will be ordered. The snubbers were previously installed. I will send you an E mail on the results.
Randy

rklessdriver

What scares you about the bias ply ET Street?

They take a bunch of hit out of the launch... hit = shock that is transmitted to the driveline. Also a bias ply tire works best with a minor amount of slip/spin.... a radial works best when "dead hooked"... I will be first to tell you that dead hooked with any kind of power will eventually break something.

On the later cars the outer stub axle/spindle is a weak link. They are longer than the early cars and weaker. My 84 has had the stock ones in it for 4yrs of racing.... I just noticed after my last race that the yolk part where the U Joint cap is secured is getting loose but the shaft and splines are still arrow straight. The loose yolk could be from racing it crushed needles in the U Joint or from a few U Joint explosions or it just stretched out from yrs of abuse.

Now my 92 6spd has broken a few spindles.... only 487rwhp but a serious clutch and 315/35R17 MT radials. They always break at the step where its machined down.... the 6spd is hard on rearend stuff.... spent a ton of money fixing it after a track day....thats why I built the 84.

The U Joints are weak point as well.... I crush the needles out of them in about 70-80 passes in the 84 with the slick tire. The 275 radial can kill a U Joint in just one race but alot depends on how well the car is working. I have check U Joints closely after every race.... once they over 20 passes I get under the car in the pit box and check every couple of passes.

Just some more data points for you to consider. Best of luck.
Will

dizwiz24

Will, i have a ton of respect and learned a lot from your post..

One thing i dont get is why you dont like the drm relocated trailing arm brackets. I am running these in conjunction with banski rod end suspension and drm camber brackets.

Ever since doing those mods, the front end rises more when i get on it.

I cant quote you any hard numbers or anything, but i do believe that it is helping weight transfer (bilstein z51 shocks, stock 93 vert springs)

they arent dummies at drm. Though my only complaint is they dont care much about their c4 line of parts and are prob doing nothing to further improve upon them.

Btw..i love how you are running 1.2x on the irs. So many people ruin theirs because they dont do stuff like extend bump stops.

or drop the clutch at 5k on slicks on a mcleod twin disk non sprung hub clutches / aftermarket single mass flywheels.

Ill keep my irs. If i wantd a straight axle, i would have a mustang

This

rklessdriver

If you look at the DRM trailing arm brackets you can see that they spread the front pick up points further apart.

(1) This moves the Instant Center (IC) further forward (takes longer distance for the 2 imaginary lines to cross).

They also move the lower trailing arm link down closer to the ground.

(2) Since the car is still at the same ride height the Center of Gravity is in the same height/place... This reduces the Anti Squat (AS) percentage because the lower bar is now at a lower point - it has less leverge to rotate the CG.

Like I said on my 84 I increased the AS% by raising the rear ride height. Raising the rear ride height actually does (2) things at the same time. It increases AS % and it makes the IC height higher without moving it forward. Totally oposite of the DRM brackets.

I don't know what rear spring rate you have but it's probally pretty soft.... On my 92 (which has the soft ride suspension) the car has a ton of front end lift with the stock brackets. With the soft springs you get alot of suspension travel out of the front... espc with a stick shift. Looks impressive but in reality its alot of wasted motion that isn't transmitted to the rear tire.

I think alot of people mistake suspension motion/squat for "weight transfer"... While you are transfering weight, it's mostly being transfered on the springs.... and the springs absorb the force so your not transmitting that force to the tire... also as the suspension on a Corvette squats down in the rear you loose AS % and can't effectivley move the CG upward and to the rear .. this is the important motion or weight transfer in the classical drag racing sense that is needed to plant the tire in a drag car. Just raising the front end while dropping the rear end via spring compression isn't going to do it.

I would also say your experencing some more force transmittal via the heim joint rear trailing arms instead of the old factory rubber busings.

Just FYI AS % values and IC heights like the C4 Corvette has won't work with a solid rear axel.... This is because the suspension upright is isolated by a bearing on the C4 IRS and it can't transmitt 100% of the rear end ring gear force to the suspension brackets, then to the frame of the car.... because of this, C4 Corvettes need to run more aggressive AS and IC settings.... More aggressive IMO means the AS % is well above 100% and the IC is higher than the CG and the IC intersect point is behind to the CG.

Also what works on an automatic car isn't the same as a manual.... because the driveline force is far more violent in a manual trans car you can see where less AS, a further forward and lower IC could help "calm the suspension movement down".... which is IMO what you would want in road racing and what the DRM brackets do. Personally in drag racing with IRS I want as much of that that violent driveline movement transfered to the tire - automatic or manual.

As for the extended suspension bump stops.... lots of people don't think of them like this but I see them as another spring. Even poly has some compression and therefore "spring rate" to it. You need to account for that extra spring rate in your shock rebound setting. Another thing about the bump stops.... the softer your rear spring is the harder it's going to hit that bump stop.... the more rebound you need in the shock.

Man I did so many things wrong with my 92 when I first built the engine for it... lots of HP, monster clutch, 17" drag radials, soft ride suspension.... it broke at the drop of a hat and even playing around it was too fast to race without a roll cage. I started in fixing things a little at a time (roll bar, bump stops, stiff rear spring) but that stuff started to make the car no fun as a daily driver... and the stuff I needed to do was gonna cost a bunch of $$$ and there was no guarantee that it would still stand up to the HP I had after I was done.... I had to choose either having a drag race car or an all around street car. I choose to keep the 92 an all around street car....

But I so wanted some way, some kind of outlet to prove my ideas about IRS... Enter the 84. I broke alot of stuff in it as well but the car has always been a work in progress... only because I couldn't afford to built it all at once. I feel like the 84 has shown that my ideas work.

I have at least 1 more season racing the 84 on the IRS.

I am building a brand new 434 engine... I am shooting for 700-750hp normally aspriated and 200-400hp additional worth of nitrous. I'm into an easy $10K just in parts for this new engine. Currently waiting on some parts but I hope to have it on the dyno in Feb.

I just spent nearly $3,500 on a Chrome Moly 8.50 certified roll cage. Car should be done at the chassis shop next week.

The expense of these 2 things are why I'm still running the Stock IRS in 2014.

What I do for 2015 depends on how well the IRS drives and holds up to the new powerplant this season.
Will

qwiketz

Hey Will,

Great info! I learned alot from your posts. Too often people just assume that the dana 44 rear setup won't work just because they've broken something rather than taking a look at it and figuring out why it broke and fixing it.

I have a few questions. I've never looked or even thought much about my suspension since it's hooked decent in the past since I didn't have a converter.

Do you have any pictures of the bump stops? That's something I need to do.

Many of us have cars that are lowered slightly. So would simply going to a taller 28" tire help offset some of the negative effects of that at the track (assuming we can fit the tire under the car!)? Also, I can jack up the rear coil overs for track duty and lower for the street.

Thanks for the input!

rklessdriver

I don't have any pics of the Energy Suspension bump stops I modified to fit my 84... however I will have the 84 back from the chassis shop this weekend and I will take some pics and post them.

I really want you guys to understand what happens when you do certain things to the suspension like altering the ride height - either by tire size or just using the spring.

Go to this web site and download this free 4 link calculator.

http://www.patooyee.com/calculators/calculators.htm

Now I just went and measured my 92's suspension because its what I have here at the house. Now I have the rear spring cranked to raise the rear of my 92 to a 28.5" rear fender height. It has 315/35R17 rear tires which are 25.6" tall with a roll radius of 11.89".

From the ground the lower trailing arm measures 9.5" in the rear (on the suspension upright) and 13.5" front (on the frame).

The upper trailing arm measures 15.5" rear and 17.5" front.

A couple of important measurements that are the same on all C4 Corvettes.

The lower trailing arm is 12.5" long.
The upper arm is 11.0" long.
They are both set forward on the suspension upright 2.5" from the axle centerline.

For the Center of Gravity (CG) I use the camshaft height which is 18" on my car.

Now the program says my 92 has 241% Anti Squat (AS)... but we know IRS only actually has 50% of that, because of the isolated brg in the suspension upright... So my 92's actual AS is 120.5%.

The stock AS% on an early C4 is suposed to be 115%....

Just something to think about, play with and compare when you have the time to get under your car and take measurements.
Will

rklessdriver

Ok a little more food for thought and hard numbers to show the theroy of what I stated above - About how raising the ride rear height increases the AS%.

Taking my 92 as the example. Current AS% is 120.5%

If I were to only change the rear tire to something 2.4" taller (ie 30"X9" slick like NHRA Stock Eliminators run)...

(Roughly) the following changes happen:

Lower trailing arm now measures 12" in the rear (on the suspension upright) and 16" front (on the frame).

Upper trailing arm now measures 18" rear and 20" front.

The CG changes about 1/2 of the 2.4" tire height increase (because we are only jacking up the rear and the front stays at the same ride height).. CG now = 19"

Now the AS% is 133%

So from 120% to 133% Anti Squat with just by installing a taller tire.
Will

qwiketz

Hey Will,

So now that I think if it, all the fast guys with c4's all have older models. I'm thinking of you, Aaron, and that one red turbo vette that went 8.80's up in Canada years ago. Do you know of anyone that's cutting really fast 60's with the newer c4's?

Also, I read Brian's topic on stub axles on another forum. A member said that they often break because of lateral pressure outward as the car "squats" under pressure. Do you know if the stuf axles are the same on the early and later cars and does it go back to using a heavier spring to minimize that (the squat and therefore movement outward)?

rklessdriver

Sorry I have not been keeping up with this thread like I should.

I do know for a fact that the outer stub axels are different between the early and late suspensions.

The early cars stub axles are about 1" shorter over all length.

The way I see it the pressure on the stub axle is latteral INWARD. As the suspension tries to squat, the tire tries to gain camber (pushes in at the top) and the half shaft tries to maintain the static camber setting.

The stub axles is moving inward while the halfshaft is (mostly) static.

The area where GM added material to the later stub axles is behind the splines before it steps up in size to the U-Joint Yolk.... this is the weakest area, so no wonder why the later cars break so easily.

You have one other thing to take into account.

Slack in the inner stub axle to cross pin (side play) in the differential.... even just a few thousands allows the entire halfshaft/stub axels assy to slam into the cross pin placing a very high impact force on everything...

When ever i set up the D44 Trac Loks for racing I try and minimized the inner stub axels side play to .0005.

In a deal like my 84 where I have a spool, I used a section of alum tubing placed between the stub axles inside the spool so both of the the axles push against it instead of the end of the little 5/16 bolts I used to "retain" the stub axels in the spool...

I don't really know of any great 60ing later model cars.

I know for a fact the 6spd tranny kills any chance my 92 ever had of being a good drag car.... very tempting to put my TH350 and stall in it for a few track days....

I recently built a pretty good N/A 383 (462RWHP) for 93 ragtop's car and that car has gone some low 11's @ 126 mph with a really tight stall converter (foot braked barely 2000 rpm) and the car ran like a 1.60 60ft....

The car was dead hooked and bogged down well below it's TQ band on launch. Also his car has no suspension work, no extended bump stops or anything at all and still has the stock soft ride springs. It squats down alot on launch....

He just exploded some U-Joints a last week at MIR - which BTW I told him I didn't think thoses parts store greaseable U-Joints were long for this world behind that new engine... he had a ton of street miles and passes on them from before with his heads and cam combo and I knew they would be a problem with that new 383 in there.

But at any rate he does have a new 4400 rpm stall converter to go in it - Once we get it apart and the rear end damage fixed. The halfshaft flailing and bouncing around in there tore up alot of other stuff, so it's gonna take a hot min for us to source replacement parts and fix the damage.

I think with the new 4400 rpm stall, and some suspension work his 93 will 60ft well into the 1.40's but only time will tell how reliable it is.
Will

BrianCunningham

Nice read

I'm running all the DRM pieces
Explains why I couldn't get it to hook at the drag strip!