Rear End for Drag Racing
waiting for the info on that 9 inch IRS setup 
09-08-2010, 02:58 PM
#42
Team Owner
Do you think it's the 3 1/2 inch exhaust tips that give me away? Because it actually idles pretty smooth at 1100-1200 rpm.2007 picture out at the track before I decided to get the fender flares to cover up the big slicks. 295/17 fronts and 335/18 rear
09-10-2010, 05:57 PM
#45
Melting Slicks
As others said, stiffening up the spring rate will help so prevent breakage.. As you are running automatic, I would not worry too much about breakage. I used to break posi-cases (where the pin goes through the case) with 465 HP (when I had my 383 Stroker about 7 years ago). However, that was with slicks and stick shift.. With automatic, there's a lot less shock on the rear and if the rear spring rate is stiff enough. Less rear end travel will definetely help to prevent breakage. If you have fresh rear end components, a stiff rear spring solid spicer u-joints, you should be good to about 550 HP without going through parts.. Of course, nothing lasts forever and eventually, you will break parts but I'm sure that if everything is properly set up, you can get hundreds of passes out of the original components as long as you run automatic without transbrake.. It's not so much power that breaks things.. it's shock! For example, I'm launching at 5000 RPM with the transbrake with nitrous coming in immediately.. If I'd put a stock rear end in my car, it would grenade the first time that i'll let go of the transbrake button..
I'd say that you should go with about 400 - 420 lbs/inch rear spring rate (preferably composite spring to safe weight) and QA1 shocks, set to a very tight setting when racing.. As you will lose weight transfer in the rear, you will have to add weight transfer in front. This can be done through soft front springs (either '65 - '68 no A/C front springs (the originals and NOT the reproductions). The original front springs had about a 280 lbs/inch spring rate while all the reproductions have about 500 lbs/inch spring rate. You can easily tell if it's a original or a repro as the original springs are longer with thinner coils. If you can't find those springs, go with MOROSO Trick front springs. The 213 lbs/inch springs work on Vettes but about 1.5 coils will have to be cut off for the identical ride height of the original springs. In my case, 2 coils were cut off which lowered the front somewhat. Cutting coils also adds to spring rate.. With 2 coils cut off, my front springs went to approx. 250 lbs/inch. You also want to go with adjustable shocks and set them up to have minimum resistence for extention and maximum resistence for compression. That way you allow the front to come up easy to get weight transfer and to come down slowly so that the front won't bounce...
I'd say that you should go with about 400 - 420 lbs/inch rear spring rate (preferably composite spring to safe weight) and QA1 shocks, set to a very tight setting when racing.. As you will lose weight transfer in the rear, you will have to add weight transfer in front. This can be done through soft front springs (either '65 - '68 no A/C front springs (the originals and NOT the reproductions). The original front springs had about a 280 lbs/inch spring rate while all the reproductions have about 500 lbs/inch spring rate. You can easily tell if it's a original or a repro as the original springs are longer with thinner coils. If you can't find those springs, go with MOROSO Trick front springs. The 213 lbs/inch springs work on Vettes but about 1.5 coils will have to be cut off for the identical ride height of the original springs. In my case, 2 coils were cut off which lowered the front somewhat. Cutting coils also adds to spring rate.. With 2 coils cut off, my front springs went to approx. 250 lbs/inch. You also want to go with adjustable shocks and set them up to have minimum resistence for extention and maximum resistence for compression. That way you allow the front to come up easy to get weight transfer and to come down slowly so that the front won't bounce...
Grandsport got it right on. I have been through 3 rears,and it was always the same thing that broke,THE POSI CASE,Guys this is the #1 weak spot on our cars,the metal is too soft,it will egg out the the through pin hole and then break the retainer bolt that goes into the through pin and then the pin drops and then things go kaboom !!!!! A manual trans is very harsh on these cases.I didnt race my car at the track,just a weekend cruiser and hot rodding it every now and then.A stock rear will break quickly if raced at the track.The corvette shop around here was the one who told me all about this problem,these cars were not meant to race at the track.Other then the case being weak,its virtually everything else back there too But like everybody else has said ,they make parts to make the rear end alot stronger.This is what i have to do on my car ,when and if the economy ever gets better,
06-11-2019, 08:43 PM
#46
I absolutely Love that look and want to do similar if I buy a local 1979 C3 I'm looking at!!!
Blessings!
Will & Wendy,
N3YH & K3WMS
Last edited by Old Man Wolf; 06-11-2019 at 08:43 PM.
06-12-2019, 08:44 AM
#48
Le Mans Master
06-12-2019, 12:38 PM
#49
Old Man Wolf - I’ve done the same thing before. Old thread. Check out the Wheel & Tire combos sticky thread at the top of this forum and see if you find something more recent and to your liking there.
Lots of guys on here running aftermarket wheels.
Lots of guys on here running aftermarket wheels.
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Old Man Wolf (06-12-2019)
06-12-2019, 03:33 PM
#50
Burning Brakes
Another option is to check with Duntov for their racing rear
http://www.duntovmotors.com/Differentials_63-79.htm
Here's a video of one in my car after I broke 3 stock diffs.
http://s19.photobucket.com/albums/b1...t=01c64a2c.pbr
http://www.duntovmotors.com/Differentials_63-79.htm
Here's a video of one in my car after I broke 3 stock diffs.
http://s19.photobucket.com/albums/b1...t=01c64a2c.pbr
Since I have a TKO600 5-speed and 514 ft-lbs AT THE REAR WHEELS, I should beef it up.
Maybe I was just looking for another project?
06-12-2019, 08:41 PM
#52
Was the first thread I found after a google search on IRS performance & overlooked the date on it...
... sorry - didn't mean to rock the boat!
06-13-2019, 12:20 PM
#54
Burning Brakes
Oh I do want a 10 sec slip, and I know it's gonna take 1.50 or better 60' to get it. Eventually when I get the loot to completely R&R the rear end and rear suspension, I will hammer down on this biotch. For now, I just want to play on the street some with some decent tires that halfway hook up so I can do some 30 mph roll on racing. But before I really even start beating on it hard at all, I want to atleast do the halfshafts and loops.
I called a local drivetrain shop, they wanted $290 EACH to build 3" halfshafts, .083 wall with solid spicers and flanges. I can get them from Dragvette for $400. Prolly just go that route to keep it simple. I will get the loops from Tom if he still sells them, I couldn't find them on his site, gotta call him later.
I called a local drivetrain shop, they wanted $290 EACH to build 3" halfshafts, .083 wall with solid spicers and flanges. I can get them from Dragvette for $400. Prolly just go that route to keep it simple. I will get the loops from Tom if he still sells them, I couldn't find them on his site, gotta call him later.
06-13-2019, 01:54 PM
#55
QUESTION??
I UNDERSTAND THAT THE PURPOSE OF USING THE STIFF REAR SPRING IS TO ELIMINATE REAR SQUAT. WHAT PURPOSE DOES "ELIMINATING REAR SQUAT" SERVE? IS IT JUST TO GET ALL OF THE UNIVERSALS/HALFSHAFT ANGLE LINED UP, OR ARE THERE OTHER REASONS?
IN OTHER WORDS, IF THE REAR HALFSHAFT ANGLES ARE STRAIGHT UNDER POWER (SQUAT) WILL THIS SERVE THE SAME PURPOSE AS INSTALLING A STIFF REAR SPRING?
JUST TRYING TO GET IT STRAIGHT IN MY HEAD.
LOL
THANKS
BILL SR
I UNDERSTAND THAT THE PURPOSE OF USING THE STIFF REAR SPRING IS TO ELIMINATE REAR SQUAT. WHAT PURPOSE DOES "ELIMINATING REAR SQUAT" SERVE? IS IT JUST TO GET ALL OF THE UNIVERSALS/HALFSHAFT ANGLE LINED UP, OR ARE THERE OTHER REASONS?
IN OTHER WORDS, IF THE REAR HALFSHAFT ANGLES ARE STRAIGHT UNDER POWER (SQUAT) WILL THIS SERVE THE SAME PURPOSE AS INSTALLING A STIFF REAR SPRING?
JUST TRYING TO GET IT STRAIGHT IN MY HEAD.
LOLTHANKS
BILL SR
