GTM 370z supercharger 550bhp/400 ft of Torque: The Masterpiece

Staples · 03-15-2011, 12:26 AM

Quote:

Originally Posted by BLM

Can someone with engineering knowledge give a layman's explanation of how the VVEL hinders the power output and how "tuning" it will benefit both NA and SC cars? I have a vague understanding of it but I know VVEL tuning and "cracking" the ecu has been a hot topic

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.

Lug · 03-15-2011, 11:54 AM

Quote:

Originally Posted by Staples

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.

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.

BLM · 03-15-2011, 12:00 PM

So then, LTH/TP + SC + VVEL <<< LTH/TP + SC + 'cracked' VVEL??

I get it now. These were tested with stock cats. More resistance to exhaust flow = more time in combustion chamber = best you can do with SC + VVEL. Sorry I had to write that out. Went to an engineering school but was not an engineer. Pretty much exactly what Mike said post #2.

Staples · 03-15-2011, 09:43 PM

Quote:

Originally Posted by Lug

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.

The supercharger runs off of backpressure, that's why more boost / power was made with the stock cats rather then longtube headers, reduce backpressure lose boost.

1slow370 · 03-16-2011, 04:47 AM

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.

gleonard · 08-26-2011, 03:57 PM

Quote:

Originally Posted by 1slow370

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.

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.

darron · 08-27-2011, 05:06 AM

Quote:

Originally Posted by gleonard

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.

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!!!

esfourteen · 08-27-2011, 09:04 PM

Quote:

Originally Posted by darron

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!!!

only the intake cam has VVEL

03-15-2011, 12:00 PM	#3 (permalink)
BLM Enthusiast Member Join Date: Feb 2011 Location: NJ Posts: 342 Drives: 2011 Silver M6 sport Rep Power: 16	So then, LTH/TP + SC + VVEL <<< LTH/TP + SC + 'cracked' VVEL?? I get it now. These were tested with stock cats. More resistance to exhaust flow = more time in combustion chamber = best you can do with SC + VVEL. Sorry I had to write that out. Went to an engineering school but was not an engineer. Pretty much exactly what Mike said post #2. __________________ K&N // GTM // BERK Last edited by BLM; 03-15-2011 at 12:03 PM.

03-16-2011, 04:47 AM	#5 (permalink)
1slow370 A True Z Fanatic Join Date: Aug 2009 Location: In the D Posts: 3,733 Drives: v8 74 260z ;) Rep Power: 7252	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. __________________ ANSWER PRICE LIST Answers - - - - - - - - - - - - - - - - $0.75 Answers (requiring thought) - - - - $1.25 Answers (correct) - - - - - - - - - - $12.50

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