civicboy1128

Goes like this...

Built GSR, LS tranny, enough fuel for whatever, and a PTE SC6152. This turbo seems just a touch too laggy. Boost starts kicking in around 4300-ish. That's just initial spool. I've done various things to get better boost response. Got rid of the crappy cast manifold and bought a pretty nice Mynes Ram Horn and what not. A little better, but not satisfied yet.

I was wondering... if my VTEC is kicking over at 4800 rpm, mid-spool of my turbo... it seems like the climb in boost slows down just a hair when the VTEC engages. Would it be beneficial to retard the VTEC engagement to say...5k or 5200 to help boost climb to it's peak, open the wastegate, and then have the VTEC come on? Does this even matter?

Can anyone provide any insight to using VTEC with a boosted application. It just seems to me that when the VTEC is kicking in, my turbo has to keep working to push up to max boost.

Anyone?

TheShodan

iTrader: (14)

VTEC doesn't work that way. It will not really assist in the characteristics of INITIAL spool. You have to understand that you're running a turbo that was over 65lbs/min in a small displacement engine. The best ways to combat this are 1) actually get a slightly smaller turbocharger or 2) look at changing gearing in the transmission. (This part though, depends upon where you're feeling this "late spool".)

civicboy1128

I know VTEC doesn't excite quicker spool. If anything, it might even sacrifice initial spool if the VTEC came online during those pre-boost spools. It's liks putting in a lumpier cam... low-end might suffer a little, but you pick up a little mid and lots up top. At least, that's my experience.

This is why I was curious if the VTEC point switches over too soon, that granted it flows more air, but will it cause the turbo to have a moment of continuing it's huff to create boost. Where as, if it were retarded to engage a few moments later, once full boost has been established, then the larger profile cam slips into place and better end-mid range is felt as it pulls on in to the high-end of the gears.

Also, a trans is one thing I have looked into getting for the shorter gear and better boost response.

DaveF

have you looked into a boost controller ?

have you had the car on the dyno, to "optimize" the vtec enguagement point ? so there would be no dip or spike in power when vtec occurs ?

the ls trans will make any car feel sluggish/slow. id get that out of there asap, or at the least, swap to a 4.4 final drive.

civicboy1128

Got a GReddy Profec B Spec II right now. Still dialing in the high boost to get rid of the slow boost response because of a too fast actuating wastegate. Should have it finished up by tonight, for solid 20 psi on the SC6152. It feels strong at that boost level with no knock.

But ultimately, that's what I'm trying to figure out; When I should have my vtec engage? I know I read that it engages TOO soon and it will cause a dip in power before it picks up again, and such. But right now I don't have the money to put it on a dyno and am trying to get a 'by the seat of my pants' tune for 20psi with decent AFR's, giving me a good base to start from when I hit the dyno with some 110 octane.

Is there a sort of general rule of thumb that goes with vtec engagement points and boost?

TheShodan

iTrader: (14)

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by civicboy1128 &raquo;</TD></TR><TR><TD CLASS="quote">
Is there a sort of general rule of thumb that goes with vtec engagement points and boost?</TD></TR></TABLE>

No. Not really. Many have engagement a bit lower than stock, but this is when the dyno really helps. A good "touch up" tune along with your boost controller will really assist you with your goal, albeit as I've said you can't expect too much due to the large size of your turbo.

civicboy1128

Yea, I understand this thing is pushing the limits of a street friendly turbo, but it gives me good gas mileage with all the lag too. Anyway, I'll chyme back in after tonight with what progress we've made after another few cruises and tweaks to the tune. I definitely picking up a different transmission too.

Turbo-charged

changing from the cast log manifold to the tubular manifold can change your optimal vtec engagement point by 1500rpm or more. put the thing on the dyno before you go throwing more parts at it.

civicboy1128

As it being 1500 sooner would be ~ more optimal or 1500 later?

LastGenEK

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by civicboy1128 &raquo;</TD></TR><TR><TD CLASS="quote">As it being 1500 sooner would be ~ more optimal or 1500 later?</TD></TR></TABLE>

You need to put it on the dyno to know for sure it sounds like your street tuning it which is fine and im not douting your knolledge at all But there are lots of factors especially that turbo because its not very common!