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Guest JB88

Modify VTEC for Constant 4 Valve Operation

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Guest JB88

Has anyone out there modified a VTEC VFR to run with 4 valves per cylinder constantly? The earlier VFRs without VTEC had better bottom end grunt. It would be an interesting experiment to see if a VTEC VFR could be modified to operate with 4 valves per cylinder and see what the performance would be like between idle and 6,800 rpm after mapping the fuel injection on a dyno. Any comments?

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I believe that the vtec does give a 6th gen more low end grunt. Two valves per cylinder usually gives you more low rpm torque but chokes the engine at high rpm. Its really late where I am but I recall it has something to do with keeping back pressure or static pressure high enough through the exhaust system which is why you don't want to just open an exhaust wide open without making other changes to the engine because it decreases low rpm torque. I'm sure one of our engine experts will be along to explain further or correct me soon. If vtec cuts low rpm torque then why would honda put it on the bike? That's kinda dumb.

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Members Dutchgixxer and rvf750rr have done this mod. Here is a dyno chart of rvf750rr's de-vtec before and after the mod:

post-4608-1299782628.jpg

There is hardly an increase in low end torque.

post-3961-1299773118.jpg

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Most (if not all) torque/hp runs on dynos are done with full throttle (come to think of it why would one do anything else), but what it would be really interesting to drive the 2-4 valve conversion at normal throttle openings to FEEL the difference in the bottom end. It's the responsive feel to minor throttle openings that really impress (to me). For example my 750 Shadow had less peak torque than my VFR but what a great push at initial throttle openings....

My hunch is that the light throttle grunt and the lower noise are the prinicple reasons for the VTEC (might even throw in pollution in the mix, if I was guessing...come to think of it I AM guessing.... :blush: ).

Brian

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A m8 of mine on another site had this done over here. I'd need to ask him how it went though. I have a feeling he changed it back to stock operation.

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A m8 of mine on another site had this done over here. I'd need to ask him how it went though. I have a feeling he changed it back to stock operation.

yes I seem to remember someone on the UK forum doing this - personally from experiences of 3 vtecs and 3 fi's. The pre-Vtec has a better midrange punch, just where you need it to be smooth, but that's where the VTEC is and gets annoying - although I think I could put up with it better on the later models, much smoother.

Plus the fueling on my 00 VFR is far far superior than the stutter fest of my 6th gens

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Guest ElTigre1

Well, maybe it's just me, but I don't know from the graph which one is before and which is after. Also, seemingly related, in what year did they tweak the VTech?

Members Dutchgixxer and rvf750rr have done this mod. Here is a dyno chart of rvf750rr's de-vtec before and after the mod:

post-4608-1299782628.jpg

There is hardly an increase in low end torque.

post-3961-1299773118.jpg

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post-4608-1299782628.jpg

Dyno proof how VTEC destroys the linear curve of the V4... why just look at that unwanted

bump in the power band... mercy Honda...

VTEC... Vacillating Torque Engine Compartment... worked on heavy cars

but it's a failure on light bikes...

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Well, maybe it's just me, but I don't know from the graph which one is before and which is after. Also, seemingly related, in what year did they tweak the VTech?

I expected everyone to recognise the power curve of a VTEC in stock trim :happy: the blue (more linear) curve is from the tweaked VTEC. It also runs higher rpm, no valve float was measured up to 13K rpm.

This was done less than 2 months ago.

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I dont understand how you have a HP increase after Vtec hit if both pulls were using 4 valves anyway.

After the engagement, there is no difference, so why are the charts different? I take it the electronic used to allow Vtec were disabled, not the actual removal of the actuating system, so you cant blame it on a parasitic loss caused by the hardware. Something is not right.

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I dont understand how you have a HP increase after Vtec hit if both pulls were using 4 valves anyway.

After market exhaust & rapidbike module.

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Guest JB88

Members Dutchgixxer and rvf750rr have done this mod. Here is a dyno chart of rvf750rr's de-vtec before and after the mod:

post-4608-1299782628.jpg

There is hardly an increase in low end torque.

post-3961-1299773118.jpg

I also don't understand the graphs. VTEC only affects operation of the engine below 6,800rpm. Above 6800rpm with all things being equal an engine running with VTEC and without it should give the same power curve unless other modifications were done at the same time and this would invalidate the comparison anyway. Also, regarding another comment regarding dyno runs being done at full throttle. The gas analyser on a dyno can be used to map fuel mixture for all throttle opening and engine rpm combinations in order to maintain optimum mixture under all operating conditions. Cheers JB.

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Guest JB88

I dont understand how you have a HP increase after Vtec hit if both pulls were using 4 valves anyway.

After market exhaust & rapidbike module.

Ok, that explains the difference in power over 6,800 rpm. I wonder what difference you would get if you made those modifications first, mapped the fuel injection for optimum performance and then rigged the engine to run on 4 valves constantly and then mapped the fuel injection for that. My view is that VTEC is mainly for noise and exhaust emmissions, does nothing to improve performance and just adds a lot of complexity to the engine. JB

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Ok, that explains the difference in power over 6,800 rpm. I wonder what difference you would get if you made those modifications first, mapped the fuel injection for optimum performance and then rigged the engine to run on 4 valves constantly and then mapped the fuel injection for that. My view is that VTEC is mainly for noise and exhaust emmissions, does nothing to improve performance and just adds a lot of complexity to the engine. JB

You would probably see a curve that almost matches the 2nd run after the modifications. I see the peak hp on the 2nd run about 107 hp which is typical with a tuned VTEC VFR without the VTEC modification you were asking about. The first run looks like a stock VFR base line curve. Even the torque curve looks normal with typical gains with a properly mapped PCIII/V or similar product.

So in a nut shell running all 4 valves all the time doesn't look to gain you anything more than what you would get from the usual performance mods and tuning based on what I see in the graphs. Of course you can do the mods and have it tuned and then do the VTEC mod yourself and compare them. :fing02:

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1) Is there any VIDEO proof of this?

2) What was the process for disabling the VTEC?

(ie. hacking the electronics/solenoid or cracking open the engine and engaging all 4 valves mechanically)

Is there a thread write-up on any of this?

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God yes, would someone PLEASE, once and for all, dyno a bone-stock VTEC back-to-back without/with VTEC engaged all the time and report back with charts and graphs?

And don't forget the AFR to go along with.

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God yes, would someone PLEASE, once and for all, dyno a bone-stock VTEC back-to-back without/with VTEC engaged all the time and report back with charts and graphs?

I agree... once and for all let's see what the unwanted bump in an other wise perfect V4 power band looks like on paper...

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1) Is there any VIDEO proof of this?

2) What was the process for disabling the VTEC?

Is there a thread write-up on any of this?

1) Don't know.

2)) Replacing valves and valve buckets.

MF topic

He'll be doing the same mod to another engine that will be overbored and fitted with lighter pistons.

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I dont understand how you have a HP increase after Vtec hit if both pulls were using 4 valves anyway.

After market exhaust & rapidbike module.

I seem to have missed a memo; what's the Rapid Bike module like to deal with? I've pulled up some info on the thing via Google, is this thing easier or harder to deal with vs. the Power Commander? Besides a lower price, why would I or wouldn't I want a Rapdi Bike module?

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Would it be easier just to get a 5th gen? laughing6-hehe.gif My VTEC doesn't kick in ever. And the cam chain tensioners never need adjusting. No valve float...laughing6-hehe.gif

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Would it be easier just to get a 5th gen? laughing6-hehe.gif My VTEC doesn't kick in ever. And the cam chain tensioners never need adjusting. No valve float...laughing6-hehe.gif

/fail - move along...nothing interesting to see here. :beatdeadhorse:

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I dont understand how you have a HP increase after Vtec hit if both pulls were using 4 valves anyway.

After market exhaust & rapidbike module.

Well there we go. Apples and oranges comparison.

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1) Don't know.

2)) Replacing valves and valve buckets.

So finally is there a way to do this electrically I'm interested by having a switch to disable the VTEC when I'm on track with my Viffer.

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Has anyone out there modified a VTEC VFR to run with 4 valves per cylinder constantly? The earlier VFRs without VTEC had better bottom end grunt. It would be an interesting experiment to see if a VTEC VFR could be modified to operate with 4 valves per cylinder and see what the performance would be like between idle and 6,800 rpm after mapping the fuel injection on a dyno. Any comments?

Why not try the larger Tube headers and fatter Map of the 98-99 first? :cool:

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