FI with VVT vs non VVT

[morris]

The question here is when going FI (turbo) with 1uz with VVT is there anything you need to consider differently than if you were doing it with a NON VVT engine.

 

[Peewee]

Tuning will be more painful.

VVTi's have a higher compression ratio.

Thats about all that springs to mind at the moment.

 

[morris]

Well I figure a set of those 8.5:1 pistons will solve the compression issue. Hopefully the tuning thing wont be too much of an issue give a good piggyback computer.

 

[TundraEddie]

Too much overlap due to camshaft timing may be a problem at higher boost levels. Right now I don't think anybody has a piggyback VVTi controller,it'll require a more sophisticated system compared to a VTEC/MIVEC controller (basically on/off control of cam profile changover)

 

[Peewee]

Overlap only happens at idle, so I don't think boost will be an issue there.

 

[chrisman]

pewee are sure it only happens at idle? i always thought that more valve overlap is better for hi rpm.. i could be wrong.. just wondering..

 

[Peewee]

I thought valve overlap was just for emmision purposes? ie, at idle, but I could be wrong?

 

[morris]

Well I guess I better figure out if the VVT is going to be an issue or not, its not one of those things I want to find out after the money is spent and the engine is built. I have succefully run 10 psi with a supercharger and no issues but I would want to go a good bit higher with a turbo and built engine.

 

[turboandrew]

Basic concern is controlling vvti. I plan on controlling it with AEM EMS (http://www.aempower.com). They support a pretty advanced vvti control on their EMS.

FWIW, there are a lot of turbo'd 2JZ motors running with overlap, and for high rpm it's no problem. Some even pick up boost in mid rpm (provided everything else was tuned for mid-high rpm, and the cams was the last thing to be done).

 

[morris]

So are you saying that you know for a fact that it has to be dealt with by using some sort of aftermarket computer setup? I was hoping that we could just ignore it and let the OEM computer continue to do its thing as far as it pertains to VVTI

 

[turboandrew]

well, yes you could do that. I'd prefer to just have control over everything

 

[verylost]

Morris,

Contact Lex Luthor on Clublexus. Even though he turbo'd a late model sc300, he will probably have some tips for you.
You may also want to contact some of the is300 tuners and see what pit stops you can avoid.

 

[TOBES]

Back to that valve overlap thing...

A certain amount is a good thing on a NA motor at high revs as, with both valves open and the piston passing TDC, the momentum of the exhaust gasses flowing out the exhaust port helps to pull the intake charge into the cylinder resulting in a better flow. Also when the intake air enters the cylinder, the overlap allows the remaining exhaust gas to exit leaving only the fresh charge. Without overlap the chamber would always contain some exhaust gas which will not burn a second time.
The aim of the engineers is to time the whole cycle perfectly to remove all the exhaust gas and enable the cylinder to be filled totally with the fresh air/fuel mix.
This is not so important on a turbo motor as the intake charge is under pressure and has less need of the assistance of the exhaust gas momentum. Turbo motors operate most efficiently with less overlap. Too much overlap results in the air/fuel mix passing thru into the exhaust system... not good for fuel economy, the environment or your nerves when it explodes in the exhaust system......

 

[urtwhistle]

just my 2 censt, i dont know 100% but most high spec turbo vtecs change there cams and disable the vtec.
might be soming to think about

 

[morris]

All good information thanks a lot I'd rather research this to death now than get burned later. Sometimes I get tired of going first.


Very lost I will check with him, I didnt know tha tthe 2jz had vvt Thanks.