Originally Posted by Staples (Post 987514)

I've posted an explanation on another thread, can't find it... here's a brief copied and pasted explanation.

The VVEL system in our cars and extremely aggressive at about a 300 cam duration;

Valve Overlap

"The portion of the operating cycle of a reciprocating engine in which, when the piston is passing TDC (top dead center) on the exhaust stroke, both the intake and exhaust valves are open. Valve overlap increases the efficiency of the engine operation by allowing the low pressure caused by the exhaust gases leaving the cylinder to help the fresh charge of fuel-air mixture in the induction system to start moving into the engine."

When you're pushing so much air into a car (forced induction) with an aggressive cam - there's air that isn't going to be used and is just going to pushed out of the motor and wasted because both the intake / exhaust valves are open at the same-time. Drop the cam duration, you'll have more time between the valve overlap process so when the air enters the head it will give the bottom end enough time to use that air for the combustion process, building more psi, creating more power.

Let me know if there's anything I'm incorrect about, but that's what I've gathered.

Originally Posted by Lug (Post 988163)

So in essence a more free flowing exhaust system could effect SC performance if you are using the VVEL system. That could explain some weired results we've seen in SC'ed cars so far.

Originally Posted by 1slow370 (Post 989854)

they don't run off back pressure, to much is still a bad thing as then you start to trap exhaust in the cylinder instead of more fresh air mixture. the breathing mechanics are complicated. basically what you want is enough duration and lift on the exhaust that the engine pumps out most of the exhaust gasses, but on our cars which are tuned for n/a the valve overlap between the exhaust and intake valves allows the now compressed air charge to escape with the exhaust before the valve closes. all that is really needed is to bump the intake cam timing backward to reduce the overlap but with vvel you have to do both or nothing or else you risk the valves hitting the piston due to the high lift.

Originally Posted by gleonard (Post 1283360)

sounds like you need new cam shafts all together with the cam lobes in different locations specifically customized for each individual car's set up. :eek:

Originally Posted by darron (Post 1284064)

Not with the 370z...the cams are essentialy tunable themselves just waiting on the good-ol-boys at GTM to finish crackin te system for it. CANT WAIT!!!

Originally Posted by Z eliminator (Post 1292730)

One "off custom intake ".
how can you claim those #'s with that intake, as the average customer will not have one on his car.
How much more did it make VS the stock intake ?

Originally Posted by Z eliminator (Post 1292730)

One "off custom intake ".
how can you claim those #'s with that intake, as the average customer will not have one on his car.
How much more did it make VS the stock intake ?

Originally Posted by NYBladeZ (Post 1293422)

In the end of it all, the real gains from F.I. be it SC or TT on the VQ37 will not be recognized until VVEL is cracked its that simple. When you are forced to deal with stock cats due to VVEL not allowing you to fine tune timing and fully utilized the compressed air you're just banging around fixing everything else except the real issue. Damn thing is that VVEL seems like a tuning rubix cube that no one has figured out yet but everyone says they are working on.

Originally Posted by Z eliminator (Post 1307814)

GTM just shipped my stage 2.
Will be here in about 10 days ( has to clear customs ).
the wait is over.