VTEC engagment for tuned members

themiller13

New Member
Engine Is a 98 GSR, PO claims it has been decked. Current Modifications include:
-Oil Ported head (LOL jk)
-Injen SRI
-Comptech 4-2-1 with a 2.25'' collector
-Custom made 60mm piping from header back with 18" resonator and an N1 can
-IAB system removed
-No AC or PS
-Neptune Demon 2 RTP full street tune

When I went to get my setup tuned, the Tuner set the VTEC engagement to 5150 RPM. But after some reading, I want to play with it in the window of 4500 to 5200 and see what the butt-dyno claims to feel the best.

So I'm curious what you guys with a tuned ECU and a set up close to mine are engaging your high lobe cam at to give myself an idea of where I should be looking for the smoothest crossover and most power. Google searches only brought up what people argued the stock engagement was.

Thanks
 
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Nick_C78

New Member
The engagement really depends on cams mostly. Your engagement sounds right for oem cams.


Btw, whats an oil ported head?
 

Muckman

Not a M0derator
WTF is an "oil ported head"? That doesn't make any sense.

I assume GSR cams because you didn't specify. Im confused why the tuner would RAISE the VTEC point from 4800. That's unusual but still within reason.
Without the dyno graph you can't easily determine where the engine likes the cross over. Its possible with those modifications the engine wanted the higher engagement point.

Supposedly if you put the cross over higher it will "kick" harder only because at that rpm the engine is under VE on the low cam thus under producing. But some customers want that distinctive sound rather than more mid range power and smooth power delivery.

Usually you don't lower the engagement unless you are moving a good amount of more air by either more displacement or forced induction. And obviously different cams will have their own profile. Neither is the case here.

If you had a wideband you could street tune both low cam up to 6000 and high cam down to 4000 to a static AFR of 12.0:1. Then simply compare the fuel values in the same rpm columns on both tables. The higher fuel values indicate which cam profile moves the most air at a given rpm. That's a cheater way of establishing engine VE.

In conclusion you probably shouldn't touch it unless you have a way of A.) tuning with a wideband and B.) scientifically measuring the difference such as at the track or a G force accelerometer.
 

themiller13

New Member
My mistake on the Oil port. when I had the VC off i noticed some Dremeling marks around the Oil Drain tubes in the head so I made a dumb assumption there.

It still has stock GSR cams.

Muckman, I do have a wideband in the car and I'm pretty sure I can get my hands on an accelerometer as well through. I will test both of these methods (with science) and report back.
 


themiller13

New Member
Nick_C78 said:
How about...you put it on a real dyno :)
Click to expand...
I plan to, the guy who tuned my car is assembling a chassis dyno that he purchased. Once he has it assembled and everything I'm handing him the keys again for a dyno tune.
 


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