been lookin through posts and its a debate ive heard many times b4, from certain shops, machine shop, and school, should u boost a VTEC motor. I hear that the overlap caused by VTEC, makes boost not as effective as if you go with a non VTEC engine... also if this is tru is it only for DOHC VTEC with the extra exhaust lobe or does it affect SOHC VTEC as well?

 

ok, overlap shmoverlap.
the ls is a great engine. but it cannot flow nearly as much as the vtec head, and the vtec kinda gives you the best of both worlds. low end with top end.

if thats the case, why is everyone making huge power (im not saying an ls is a bad idea, but setup for setup the vtec head out flows the ls) using the vtec head? there are even guys not using the vtec feature, but are using the vtec head. (vtec killer) to lighten the valvetrain.

 

More than likely you've been talking to hardcore 'factory turbo' guys. They may be right about overlap causing reversion...when you use a poorly shaped cast manifold with 1" runners. They are the same people using tiny turbos pushed beyond their limits, in which case the lower dynamic compression you get with more overlap means the turbo would absolutely fall on its face. Lossing dynamic compression with very high exh mani pressure means the turbo looses efficiency, and needs more boost to put the same amount air into the cylinder, something it can't do if its already maxed out.

Given the fact that people can easily make 400whp with a bone-stock 1.8L GSR or LS-Vtec, and then pick up another 25-50whp with ITR cams (higher overlap, higher lift) proves that its not a problem. "The proof is in the pudding"

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by HiProfile &raquo;</TD></TR><TR><TD CLASS="quote"> They are the same people using tiny turbos pushed beyond their limits, in which case the lower dynamic compression you get with more overlap means the turbo would absolutely fall on its face. Lossing dynamic compression with very high exh mani pressure means the turbo looses efficiency, and needs more boost to put the same amount air into the cylinder, something it can't do if its already maxed out.
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Exactly

 

thanx for the info think ill build the mini me then.

 

I am taking a Z6 cam for my D15B in to get the VTEC lobes' duration ramped a little.. giving me a better "boost cam".. thinking about making a plugin for CROME to be able to switch VTEC based on MAP, not RPM.... but it's a formidable task....

But for the mean time, it would be for a motor with VTEC set such that as I won't be in VTEC unless I am mashing on it (VTEC load Threshold setting in ROM) It is a good stop-gap for now, but I want to tie it into boost. Plus it will create a nice idle, and low end characteristics.

Good Idea... I am just wondering if the lack of VTEC on the exhaust side would hinder performance....