VVT and turbo

[Brettsauto]

Ok, just building a low boost 20v st at the moment, It will have about 9.5:1 compression and 10psi boost. I have been looking at the camshaft timing of the std cams, the inlet cam timing with a non-activated VVT looks idea for a boosted application, and when VVT is activated , the timing changes to a massive amount of valve overlap, which for a N.A. application is good, but not so for boost. I was looking at fitting an adjustable inlet cam gear so so fine tuning can be done. This will eliminated the VVt. Yes I no all the pros of VVT, but in a boosted application it does not seem to be required, so feed back from people who have the experenice will be appreciated
The question is, have the people out there who have gone the turbo 20v route found no need for VVT or do you still use it?
Brett.

[Matt]

VVT with turbo is still good...

You'll find a better power curve, increased torque across the board.

[Gunner]

VVt turns back off at 6500 on a silvertop from memory, the window for it isn't very large. I wouldn't be concerned about the overlap, it doesn't have to be a bad thing. If you are using an aftermarket ecu, and your tuner is switched on he will know how to take advantage of the overlap, rather than let it hinder performance.

[SamsTA22]

R33 and R34 Skylines have a similar form of VVT as the 20v 4ages. It definitely improves the torque curve. AFAIK, its only really the exhaust side vvt tuning that changes significantly between N/A and turbo.

Also, even though the cam specs are identical, the vvt turns off a lot earlier in the rpm range on the turbo rb25's than the NA ones.

You can use an adjustable exhaust cam gear to reduce your overlap, if you want. You might see some improvement in boost response, too.

[Brettsauto]

thanks for the replies,
I have alot of experience with NA engines, and have built a few turbo ones as well , but this is the first with VVT, I will be using a Haltec SP1000, so no problem with controling the activation points, but it is a very basic form of VVT , ever off, very little overlap,Approx 6 deg , or on, approx 36 deg overlap( measured at the crank), which is not a massive amount for a N.A. engine, but still very large for a std cam 1.6 engine , and alot more then what a turbo spec (fixed timing ) performance cam would run. That is the beauty of moden engines and VVt in all it's forms. I was just thinking, In the case of the simple on/off VVT , people may have found it was not used to any great advantage in the 4age turbo situation, and if not I would have fitted a set of adjustable pulleys before hitting the dyno and fine tunning. So it looks like I will leave the VVT inlet and fit an adjustable exhaust before hitting the dyno.
thanks Brett.

[Sam-Q]

I know someone who has 270 degree cams and he picked up a lot of power when he got his VVT to work

[Matt]

Ill find some dyno graphs of 20psi and stock blacktop head for you. Vvt running is a great thing that you should keep.

[SR_andy]

Vvt and turbo is massive win, new pulsar runs vvt turbo. 9.5 comp ratio, 140 kw they are fast

[joeschmo_57]

^ yeah? How do they steer? 1.6 eh?