i am doing a secondary delete tomarrow for....

[sammy]

oh ps i am going to do this to both my cars asap. car seems to have more spunk in the low to mid range .and one has confedance that they are indeed open all the way

[sjs]

Excellent post everyone, I sure learned alot! Thanks to Kevin for turning me on to this post. I never would have believed driveability would have improved until everyone here said it did. Ironically, the same SAE that all the Vette engineers belong to preaches the EXACT OPPOSITE of what everyone experienced in the real world. Their combustion theory - intake vs cam design states clearly that doubling the intake area cuts velocity and turbulence in half - thus reducing horsepower and torque under 4000 rpm. Same as the old school guys comparing tunnel rams and dual plane intakes under carbs. Also the original purpose of this system was to run like an L98 motor with gobs of torque down low then open up the are with the secondarys and larger cam lobes under them later. ... ????
But since everyone is finding out otherwise and the car runs better without this system in place it must mean the cams are not much different from the primary to secondary ports .... does any one else agree ??? Or does anyone make an aftermarket truly "dual personality" CAM with monster torque for the primaries and long duration on the secondaries to make a real monster out of this motor?

[Kevin]

you're welcoms sjs, we're all here to learn

[tomtom72]

http://www.zr1.net/forum/showthread....ghlight=shafts

sjs, you might find this thread an interesting read concerning cam shafts.



Tom

[Paul Workman]

Originally Posted by sjs

...But since everyone is finding out otherwise and the car runs better without this system in place...

One of the first things I did was yank the secondaries, and I have NO regrets. IMO, the throttle response is quicker - has to be, cuz there is no delay between the throttle plates opening and the secondaries being switched on; both are already on. WOT, according to my dyno brag sheet gave up nothing in the low/mid range**.

Drivability is better than before pulling the secondaries, actually. But, part of its manners now come from new (Accel) injectors, after it was discovered the replacements put in before I bought the car were NOS with the same suseptibility to alcohol as before, and after 3 seasons had started to go bad again. And, I give credit too to Marc Haibeck's calibration. He does some fuel modifications and ups the idle a bit to speed the air flow at idle a little. (He also changed the management of the cooling fans, which I like a LOT as well!)

So, combined with the new calibration, it isn't exactly clear (to me) what the reason for the better street manners is: sans secondaries or the cal?? But, none the less, I'm VERY happy with the delete in combo with the new calibration which also addressed some of the (high) idle issues known to the original factory cal for the 90 MY.

**Independent and revised I/O cam timing may well have a lot to do with not affecting the original torque curve at the low/mid range. Again, this is a variable that doesn't have bearing on a single cam, pushrod motor. (Like having your cake and eating it too!) I'm no expert to tuning DOHC LT5s, but Pete, Marc, Bob G (FBI gurus) are. From the graphs (make that "wallpaper"!) on display in Marc's office and the results at the track by Pete (especially), it stands to support the supposition that when it comes to predicting performance characteristics resulting from certain mods, those with pushrod experience exclusively are beyond their depth when discussing DOHC (LT5s). (Maybe the GM guys should go over to Ford to see what they're doing with a 5.0L these days!) These LT5s are very interesting power plants, to be sure!

P.

[PhillipsLT5]

I picked up torque & RWHP also, no driveability issues