Can somone explain how turbo-vtec works

[TomTom]

im just curious as to what happens when you turbo a vtec engine

the vtech kicks in at 5500rpm, the turbo kicks in at say around 3500rpm, both kick in is this putting extreme pressure on your engine?
meanwhile when you turbo say a b18b it is just straight turbo kick in and no vtec to engage.

[legendboy]

works the same. no difference. vtec turbo is harder to tune cause it uses 2 cam profiles rather than one.

[redline]

Originally posted by legendboy
vtec turbo is harder to tune cause it uses 2 cam profiles rather than one.

[rage2]

First, you need to understand what VTEC is and what it does. VTEC is a 2 stage variable valve timing system. There are 2 cam profiles, one for low rpm's to maximize torque in that area, and the other one "opens up" to maximize torque in the high rpm region. Unlike the higher end variable valve timing systems such as BMW's which allows infinate amounts of lift/duration, the VTEC system only allows for 2 cam profiles.

In a low pressure turbo system, the VTEC cam profiles are used to maintain the same torque curve shape as a N/A VTEC engine, only difference is the torque curve is higher. In a high pressure turbo system, the VTEC system is disabled because the high lift cam at high rpms do not work well with high boost. What happens is the valves are still open during compression stroke, so the boosted mixture escapes before the valves close, therefore robbing you of power at high rpms. Since the low rpm cam profile doesn't exhibit this behavior, VTEC is disabled to use the low rpm profile across the entire powerband. Of course, the proper scenario would be a custom ground cam for low rpm and high rpm turbo operation, with the VTEC system intact, to maximize power across the entire power band.

As for tuning, there would be just 1 curve to tune... regardless of what cam profile(s) you'll be running, the load would be identical for that profile, and you would change the fuel maps based on your cam settings.

[TomTom]

thanks your the man rage
confused the crap outa me so you must know what your talking about lol.
so is it good to bad to turbo a vtec engine?

[rage2]

Turbo's always good, regardless of engines. VTEC gives you more tuning flexibility, you can use single or dual cam profiles, or custom grind 2 profiles...

[RCBVtec]

Holy crap rage... how do you know all this stuff??? That is very insightful... good to know for future reference

[legendboy]

Thanks for clearing that up for me too

[rage2]

Originally posted by RCBVtec
Holy crap rage... how do you know all this stuff??? That is very insightful... good to know for future reference

I just make shit up, use big words, in hopes of confusing everyone.

[choweyt3t4]

Originally posted by rage2


I just make shit up, use big words, in hopes of confusing everyone.

yeah right then how do explain the knock you took away from my full throttle runs.rage is the man!

[buh_buh]

Originally posted by TomTom

so is it good to bad to turbo a vtec engine?

turbo + vtec =

[Voodoo Child]

Rage,
I've done some serious research on turbo's for my ITR but have never heard of anybody dis-engaging the vtec. With the B18C5 running high compression, it is recommended to decrease the compression ratio so not to cause too much stress on the engine.
Would you say a turbo itr would be able to keep the vtec?

VC

[redline]

Originally posted by Voodoo Child
Rage,
I've done some serious research on turbo's for my ITR but have never heard of anybody dis-engaging the vtec. With the B18C5 running high compression, it is recommended to decrease the compression ratio so not to cause too much stress on the engine.
Would you say a turbo itr would be able to keep the vtec?

VC

yes you would and dumb if you do disable it.

turbo + vtec all the way!!

[rage2]

See what I mean by just making shit up?

Seriously though, you would have to look at the torque curve after turbo'ing... because high lift cams do NOT work well with high boost turbo systems. Lowering compression, that's a totally different subject. Personally, I've never done much research on how agressive the cams are on a VTEC engine. On the Porsche 968 engine (a project I was doing research on recently), the high lift cam profile on the Variocam system (same as VTEC, 2 stage) has to be disabled, otherwise the torque curve drops harsh at higher rpm's. This effect starts happening after around 12psi of pressure.

[redline]

differnet engine like differnet things. I will see if i can dig up some dyno charts but with a turbo honda when vtec engages hp and tq raise crazy fast...

[redline]

http://www.hondata.com/dyno372turboimportbuilders.html

http://www.hondata.com/dynogsrturborocky.html

vtec is 5600

[redline]

not turbo but one sick n/a civic

http://www.hondata.com/dynoericksracingrc.html

[Superesc]

wow, between 5600 and 6000 it goes skyhigh!!!!! (first link)

[LUDELVR]

Originally posted by rage2


I just make shit up, use big words, in hopes of confusing everyone.

Not me! I understood everything that you said! Had a dictionary beside me the entire time!! haha So after reading all of that........at what temperature should you preheat the oven and then when do you hit record on the VCR hmmm....maybe I didn't understand!! haha

[Superesc]

hmm lets put this in Leo's terms!

VTEC is like 2 girls with 2 different profiles, and Turbo is like You, Some people think you plus 2 girls are a big no no, 'cause the 2 girls can cause a lot of high and varying tensions!! But in your reality, 2 girls plus you is very good, good compressions, after 5600 bumping around, you get REAL high, but it only last for 400 bumps more.... then it levels off and you can have a smoke... if you do smoke...

Does this make sense???????