Hey guys. Someone posted the following message on clubsi, and I was wondering if anyone here has heard of this?

"I have heard talk of when running a turbo vtec that when the vtec kicks in it creates irregular exhaust patterns, therefore irregular boost. Anyway, is this documented? Anyone else heard of this? And if i get a turbo, how can this be fixed if it exists."

Also one of the replies was this:

"I have heard that for the split second that vtec is kicking in it screws with your boost pressure. But after that split second it's all good from there."

.........Anyone hear of this?

 

not true. at all.

 

its funny how people just make things up when they know nothing about cars, then try to pass them off as truth.

 

I have heard something along those lines. I dont personally think it is true. All the person told me was "I disconnected my vtec at the track and I ran better times, The vtec makes your car slower with boost, so dissconnect it"

my suggestion to you is take it the track, run it with and wtih out vtec.

 

its so obvious its b/s, its not even worth the time to try and see if theres a difference.

people who say these things need to end themselves.

 

i know a buy with GST eclipse, and when he heard that i was putting a turbo on my Prelude, he was like "I hope that dumbass disengages his VTEC, otherwise he'll blow it up." well, it won't be long, and he'll be the one looking like the dumbass when my POS Turbo Honda smokes his ***.

 

A large over lap on a high boost application has a tendancy to blow the intake charge out the exhaust. Hence loss of power potential in vtec. I dont know off hand the over lap on a GSR cam, when the extra lobe engages, but this is what they are probably refering to. If your not running high boost (just street drivin) I wouldn't worry about it to much.

 

I don't have my helm handy right now but i think the h22 has 20 degrees of overlap at TDC and 40 at BDC. This overlap as stated before causes you to blow boost out the exhaust. Adjustable cam gears can help dial out the overlap.

 

 

Exaaaaaaaaaaaaaaaaaaaaaaaaaaaactly...

 

ACTUALLY, the positive unflux pressure of the cam gear to timing belt vtec lobe ball bearing joint adds side pressure to your secondary lobe and causes overboosting, for all of you who dont speak turbo that means leave it to the professionals.

 

VTEC is better. I remember that the big rumor for a while was that it didn't work well with boost, but I've seen dyno graphs of turbo cars gaining 100hp or more in the top end when VTEC is ON.

I realize that 'in theory' alot of overlap is bad for boost, but if the charge air is being blown out the exhaust, then the turbine is being spun more, so it makes more boost, correct? This sounds a little retarded, I admit, but there might be something to it...and in any case, if you dialed it out with cam gears you'd be all good.


[Modified by ion_four, 1:47 AM 9/27/2002]

 

yeah, I've never heard anything about vtec being better to be disengaged when running high boost or a turbo in general. Actually I've never heard anything negative about vtec at all. Only good things...

I've been in the imort scene for 4 years, and I would think with all the reading I do, and people I have talked to who are in it as well, that I would have at least seen, heard, or read something on this vtec vs. boost/turbo topic mentioned in this post, but haven't.

 

dont be mean..not everyone there are total *****

 

.This can be a serious problem with a turbo motor since the charge will burn in the exhaust raising temperatures of the exhaust valves, turbo, and cat. Potentially destroying them or heating up cylinder temps enough to cause hot spots and preignition.

Streetcars with moderate boost 8psi and below may still suffer but not as serious as a track cars that see's 20psi+.

 

theoretically, when vtec is engaged when boosting a lot you will experience 'overlap' where the intake valve is opened while the exhaust valve is still open. But that can be eliminated easily with tuning.

 

At a race in Houston earlier this year we ran two 9.0's at 164 and we had a problem with the vtec solenoid staying on so we unplugged it in the pits. The next run we forgot to plug it back in and the car went 10.1 at 140. I guess you could say vtec is bad for turbo, right

 

VTech phones and Turbo are the BOMB!!

 

Vtech (larger lift and duration) not a bad thing at all. Overlap different story.

 

well, i'm not saying it's completely true, but when i got dynoed (dyno pics are thanks to VTC_CIVIC aka DAVE) i noticed that i was spiking pretty bad. AFTER i took of my turbo, and i looked over the dyno sheets, i realized it was spiking exactly where i had my VTEC set to kick through my VAFC at 4800rpms. i thought it was pretty intresting info, but is it just a fluke?

this was d16y8 on greddy td04 kit w/ vafc hack and spiking 12-14psi.









[Modified by 98civicEX, 7:14 PM 9/29/2002]


[Modified by 98civicEX, 7:17 PM 9/29/2002]

 

Vtech phones have the fastest speed dialers made

 

The little dip you have at 4.8k is vtec kicking in and it would probably work better at around 4.9 or 5k. The rest of the run is just screwed up. You have some sort of fuel or ignition problem. That's not the result of vtec.

 

98civicEx- I doubt that's just a fluke. On a single cam you cant really adjust out the overlap like with a dohc. It might just be a fuel thing or something else not related to overlap. Try turning the vtec off and run it on the dyno $ome more to see what it does.

 

do you think it was too much fuel? this was w/ 440cc injectors as well...i couldn't figure out why i was spiking. stock ignition btw.


lol, wish i could, the turbo was taken off already..i never noticed it was spiking where i had my VTEC set at until after i took the turbo off...if only i knew earlier then i could of ran it w/o VTEC.


[Modified by 98civicEX, 7:50 PM 9/29/2002]

 

I know where the "turbo is better with NO VTEC rumor came from"

Its in the Endyn Supercharger FAQ. Its been there for years, and probably been hit 100,000 times and read.

He says the engine runs better without VTEC. Basically. "VTEC is disabled on my supercharger kit...blab blab blab" LOL

In my opinion, that is the dumbest FAQ I have ever read.

yeah right...VTEC is not good on a forced induction car...

LOL

Time to wake up.

Jeff