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Old 12-26-2005, 01:20 AM
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Comp Cams 268XE cam replacement

Hi all, I have a problem. I just finished trying to get my 72 Chevelle to hook up and it was a difficult task. I have a .040 over 454 with 781 Oval port heads, a comp cams 268xe cam with about 10.2:1 compression. My problem is that I have WAY to much bottom end torque. Even though I have 295's on the back inside a 10 bolt with 3.42's, I send them up in smoke as soon as I try to launch hard. According to my desktop dyno I have about 500 lb feet of torque from 2000 - 4000 RPM. I think this is my "problem". I was wondering if I went to a higher duration cam with a little more lift if I could push the torque a little higher in the RPM band and make it a little more usable from off idle to about 2500 without smoking the tires to oblivion.

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Old 12-26-2005, 09:23 AM
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The notorious BBC and torque issue... Why change a cam to remedy a traction issue...? Might want to consider working the rearend area to get that good usable power to the ground... Steet tires other than DOT slicks just dont have the compound to deal with monster torque... Suspension changes (front and rear) can help but possibly some drag radials might help unless thats what you have...? But things like traction bars (slappers) or more intense modds possibly...? Also drag shocks in the front which help with weight transfer and upper bushings with the teeth milled off to allow more movement or urathane bushed pieces...?


Dont make the torque an issue work the problem...

Heck I run a BBC truck and with soft rear springs and DOT slicks and some shock work it hooks hard now... Before I had 295`s that were nothing but smoke monsters...

Last edited by Bumpstick; 12-26-2005 at 10:36 AM.
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Old 12-26-2005, 10:00 AM
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If that thing starts hookin up , that 10 bolt won't last long!!!
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Old 12-26-2005, 03:58 PM
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Sounds like a bigger cam to me would be good idea.Sounds cooler , less of a problem launching more topend.
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Old 12-26-2005, 05:03 PM
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Heck sounds more like bragging to me than a problem . I have not heard it put like that before. I think that's a problem everybody should want. I would just work on my suspension, new sticky rubber, and adjust the tire pressure. If you talk to some local drag racers you should get all types of tips to minimize tire spin.
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Old 12-26-2005, 09:13 PM
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Thanks for the reply's guys. I am concerned about getting the car to hook up hard on a 10 bolt like you said dgcantrellsr. I don't know if my 10 bolt will live for long launching a Heavy Chevy on a regular basis. I 'll look at some stickier tires and some suspension tips, but I'm thinking I may be searching for a 12 bolt after a 10 bolt fragging party
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Old 12-26-2005, 11:01 PM
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10 bolt strength

those 8.2 10 bolts are just fine as long as you dont run slicks and a transbrake. the weakest part is the spider gears. you could go to a powertrax if not already a posi. the only other problem is the pinion gear. factory gears are not as strong as aftermarket so if that is stock that should be changed too. i read in a magazine (car craft or hotrod) that you want the lower control arm to be as level with the ground as possible and the upper angle to intersect with the lower control arm at the front bumper. does that make sense?
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Old 12-26-2005, 11:48 PM
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If you want hook. Put on slicks and go to the track. I love running around blowing the tires off at 50 mph.
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Old 12-27-2005, 05:58 AM
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Quote:
Originally Posted by 1969NovaSS
those 8.2 10 bolts are just fine as long as you dont run slicks and a transbrake. the weakest part is the spider gears. you could go to a powertrax if not already a posi. the only other problem is the pinion gear. factory gears are not as strong as aftermarket so if that is stock that should be changed too. i read in a magazine (car craft or hotrod) that you want the lower control arm to be as level with the ground as possible and the upper angle to intersect with the lower control arm at the front bumper. does that make sense?
1969NovaSS, I have the Corporate 8.5" 10 bolt that I pulled out of a Buick grand Sport I believe. I liked it because I had heard that they were stronger then the 8.2 and it also had the bolt in axle's instead of the "C" clip type. I then installed a powertrax Lock Right in it. I like the performance of the 10 bolt so far, but am concerned about blowing it up with some sticky tire launches.
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Old 12-27-2005, 06:41 AM
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Does sound now like you built a good engine but are weak in the rearend dept...? My theory is to build to match and try to make it as bullet proof as possible... I do see a 12 bolt in your future with a true posi (Eaton or...?) among other good parts... I just recently upgraded to a turbo 400 and 1350 forged U-joints plus a new heavy wall driveshaft (balanced)... I had already built my 12 bolt with Eaton & Richmond and aftermarket axles... Now I`m not afraid to hammer the heck out of it... (or use that blue bottle I`ve been saving for a pretty day)
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Old 12-27-2005, 08:26 AM
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if the engine was built for the 268 , i wouldnt mess with the cam.

you have a traction issue,try some sticky tires.

if this is a street driven car car i think the 10 bolt will hold together fine. a drag strip vehicle you will have to go 12 bolt eventually.

big blocks are the cats meow. you built that thing for torque , wise choice.
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Old 12-27-2005, 08:49 AM
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8.5

the 8.5 is just as strong as a 12 bolt imo. I f you are going to run slicks just upgrade the axles and gears. there's guys running 10's w/ the 8.5's.
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Old 12-27-2005, 03:46 PM
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A little bigger cam with be a better match for the 10.2:1 cr. Plus it will give a few more rpms to move the car forward once it hooks up. Maybe a 280 cam would be the trick.
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Old 12-27-2005, 07:55 PM
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Quote:
Originally Posted by 1969NovaSS
there's guys running 10's w/ the 8.5's.
I am.

A T/A performance support/cover and aftermarket axles are a worthwhile investment.

As for the traction, Hotchkis or South Side Machine (SSM) has what you need to solve that issue. Lowered rear mounting points on the lower control arms and adjustable upper control arms. Get those in place and then you can start tuning for better launches.

Larry
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Old 12-27-2005, 08:50 PM
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In my opinion building a big block race car with an 8.5 or 8.2 is a waste of time and money. In time you will blow up that rear end and then you are still going to have to build another stonger one. Why not just do it right the first time....
Sell that little rear before it blows (it won't be worth much after) and do a built 12 inch or a Ford 9 conversion. Just put on the slicks and stop trying to hook that race car with street tires.
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