My car in sig hates the dyno...first month after the swap she broke a tailhousing on the second 3rd gear pull to 6400rpm. Made 325/339 unlocked with stock stall and stock ls1 intake/ported tb, cam headers, open cutouts...was peaking at 5600 and falling on its face. Running a mail order tune.

Added a self ported (mostly just cleaned up runners and removed casting flash) Fast 90/90, built trans, yank ss3600, and fresh plugs/wires and went for a dyno tune. First wot was a hair rich still but made 359/340 unlocked with cutouts closed. Peaked at 6000 and was riding out well to 6200+.

Couldn't finish tuning because the car ended up with a transmission case busted in 3 places, driveshaft snapped in half, hole in the floor, and ruined dual exhaust. Transmission had less than 2-3000 miles on the rebuld

Since then I rebuilt the trans, installed a thick walled 3.5" chromoly high speed balanced driveline with spicer solid u joints, and shimmed the trans tailhousing up 3/4-1" for less extreme driveline angle.

Tailhousing is -3* and can not come up any further, pinion angle is right between 0* and +1*

I really want to get the car tuned but cannot afford another failure. What else can I possibly do to make sure I'm safe? I've heard mixed reviews about tuning in 2nd gear. What about just ending the pulls earlier instead of pulling to 6400?

The consensus seems to be that the stock type thin walled 3" necked down to 2.5" low speed balanced driveline was the most likely culprit but I'm still nervous.

I do have a slightly cracked motor mount but the way the mounting brackets are it is nearly impossible and might be impossible to change it without pulling the engine at least partially out of the car.

 

If you have the drive line angles right and the appropriate drive shaft you should be all set. Also never put the transmission into neutral after a pull, always leave it in gear till the rollers are stopped.

Go out on the highway and give it a good pull and see if it vibrates. If it does fix the problem before the dyno, if not let it eat.

 

The pinion angle is going to kill you on the street, a -3 is a more common angle that produces better traction, but all setups are different...The cracked motor mount could be torquing the motor over at an extreme angle causing some problems.

 

I have been brave enough to hit 120+mph or 5500rpm in 3rd and felt nothing bad

what do you mean kill me on the street? car has been run like this for nearly 2 years and is basically daily driven. it is my understanding giving both the trans and the pinion the same angle is horribly bad and they should instead be as close to equal but opposite as possible so they cancel each other out

 

Not talking about top speed, yes you are right about the angle, but usually a negative pinion angle helps you from smoking the tires or wheel hop, but like I said, all setups are different, If you have been able to hook up with that degree then that's good..Don't know if you race from a dig or rolling..

 

ohh ok, gotcha

the car has traction bars and does not wheel hop anymore, hooks pretty good with nitto dr

well I have an appointment set up for tomorrow afternoon and must admit I'm nervous as hell because if it goes down again it will be down for a long time, but at the same time can't find anything wrong to signal I should have a problem and it would be nice to have a decent idle, not die so often, and pick up the rest of the power I have on the table

 

any other ideas or words of caution?

 

drive shaft loop?

If the thing comes apart again at least that will help keep your car from getting beat to death.

 

Stock d/s was repeatedly run above it's critical speed. Most likely, the failure began w/ the d/s taking a dump, and taking out the trans.
As for the "slightly cracked" mount. U R kidding about a dyno session anyway??

 

actually I wasnt...the engine does not move any more than it did when first put in I just noticed what appears to be a crack on one mount

 

if the car in your sig is the car in question, those old chevelles use more - pinion then a torqe arm f-body.
my dads chevelle(65) likes -5

 

well made a pull and didn't break anything...he got the a/f ratio at 13.2 and timing at 28* with no knock so we called it good and I was on my way

I'm curious to get to the track soon