Re: 2001 Pure Stock Drags
 

Pete

How much HP and Torque did your ZL-1 put out? Great job at putting the Bowtie's on top.

Jim Lerum

Re: 2001 Pure Stock Drags
 

Jim:

You are right on about the size of the ports, and the fact that the manifolds kill them! When I participated in the "Certified Stock" tear down this past week, I was the only Chevy car there on Wednesday, and I heard several people comment on how Chevrolet had "other intentions" when designing their hi-po BBC heads/ports. There was a 440-6, a 455 Stage 1, and Hemi also certifying that day, and they all commented on the seriousness (sp?) of the Chevy heads straight from the factory. BUT, the great equalizer is the crummy exhaust manifolds. That is one area the Hemi cars are definitely ahead of the game.

Re: 2001 Pure Stock Drags
 

I also think that the more compression that is run, the better the big ports function with the stock GM L-72, L-78, LS-6 cam. I think Pete's L-72 motor is a good example of why more compression is required. The lifters needed more lash to shorten the duration of the cam to fit the compression. I figure that the right dynamic compression should be 11.8 to 1. When you think of it, Pete's motor was running a lift of .480's after the lash was set to get the proper dynamic compression. Their are some good book out there that explain this very well. Pete I'm not picking on you as you have some great really quick rides, it's just that everyone is probably familiar with the really good article on your COPO dyno L-72 in MCR. Look forward to the ZL-1 dyno session. Which soon to be published issue will it be in?

Jim Lerum LS-6

PS: The 291 cast heads have 327cc ports which also hurt the low end port velocity for building torque. This right where we need to operate with the manifolds.

Re: 2001 Pure Stock Drags
 

Jim:

Tell me more about lash vs. duration vs. compression, etc. This could be very useful...

Re: 2001 Pure Stock Drags
 

Jim, The car was weighed just before we pulled the motor and right after to get a accurate comparison, same fuel,etc etc. It weighed about 200 lbs to the ounce less. I run UAP NAPA 50/50 gas shocks on all four corners, as were not allowed to run race shocks. Valve lash for the street so far is .035 on both intake and exhaust. I shift at 7000 every gear and it goes through the end at 7200. Second gear is really loose! But a fun ride! https://www.yenko.net/ubb/smilies/images/icons/laugh.gif
Peter

Re: 2001 Pure Stock Drags
 

Jim, I understand what your saying and I agree 100% and it all goes against everything I've done. These GM cams are rediculous and silly. Without giving it that much valve lash I pretty much had no brakes. It could'nt produce enough vaccuum to operate them. Also from going from .024 to .035 I picked up 30 lbs of cranking pressure. Bottom line was I could'nt launch the car with no brakes. Et and mph were not effected at all with the change.
Peter

Re: 2001 Pure Stock Drags
 

Really neat Peter. Thanks for the info on the shocks. Again I look forward to the article on the motor. Did Tom Shaw come to do the article on the dynoed motor?

Jim

Re: 2001 Pure Stock Drags
 

465 hp threw the stock exhaust manifolds! Sorry the rest of the facts will be coming out shortly in MCR. They followed along for the day at the dyno. The real story is when we put the headers on!
https://www.yenko.net/ubb/smilies/images/icons/laugh.gif
Peter

Re: 2001 Pure Stock Drags
 

Cool Pete, glad to see that the magazine has come back once again for some Chevy power dyno sessons. It will hopefully reillistrate that the exhaust manifolds on the big blocks are really restrictive because of where the power is made. It's not the average big block that other manufactures designed with low RPM torque in mind. The intake port design says it all, RRRRRRR PPPPPPP MMMMMM's. How much weight did the car drop when the ZL-1 was installed? What type of shocks do you use?

Re: 2001 Pure Stock Drags
 

Peter:

I would think that you would beable to use as much of the exhust duration and lift as you wanted. If you can't it's because the exhaust maniflolds are allowing too much reversion. Use a balance pipe just on the other side of your torque converter housing. You can get them from Jeg's for $35.00 US. The car will run considerable better 2500rpm and up.

Jim