This is a hypothetical, just something I've been kicking around in my head for a while and now that I'm not riding all the time...
Hypothetically if someone wanted to modify a 6th/8th gen bike to be "always" in VTEC (always running on 4 valves per cylinder), how would you do it?
The best way to get rid of the rough VTEC transition is to always run in VTEC!
5 hours ago, lazyeyeThis is a hypothetical, just something I've been kicking around in my head for a while and now that I'm not riding all the time...
Hypothetically if someone wanted to modify a 6th/8th gen bike to be "always" in VTEC (always running on 4 valves per cylinder), how would you do it?
The best way to get rid of the rough VTEC transition is to always run in VTEC!
When I checked my VTEC's valves, I more or less realized that is what one is doing during the clearance check procedure. There used to be a good online guide to it, but it's now a dead link. The attached youtube video, despite the annoying music which is too loud over the narration, is a decent "how to" for a VTEC valve check. The reason the cams have to come out and go back in 3x is that the 8 VTEC valves must be set to work at all times to check their clearance. That is done by removing the VTEC buckets and the internal latching mechanism and pinning it closed with a shim, then replacing the bucket/latch assembly back over the valve. During non-VTEC operation, the latch is open and the valve stem rides up through the open latch inside the bucket, leaving the valve closed. When the spool valve closes, oil pressure is diverted in to a spider web of 8 passages to the VTEC valve lifter bores, pushing the latches closed so that when the bucket comes down (it goes up and down using a lighter, secondary spring regardless of VTEC engagement) the latch contacts the valve stem pushing it open. Theoretically it would be possible to place the shims in that manually latch the VTEC latch mechanisms close and leave them in - thus forcing all 8 valves open all the time. This came up in another post a while back and I think it was pointed out that latching the valves closed that way could cause some oil pressure issues if the oil has no where to go. The more I thought about it, it seems as though that once the latch closes by pressure the oil doesn't have anywhere to go, anyway. It just drains out the bottom of the VTEC bucket. Besides, the passageways are very small (a good reason to keep oil clean on a VTEC btw) and wouldn't seem to make up much of the circulating oil's volume. I may be FOS on all that, so if someone knows definitively, chime in. The other downside is that more reciprocating mass is added to the VTEC portion of the valve train. The shims are about 6mm in diameter and only about 1/8 inch to maybe 3/16ths in thick, so they're very small. Hard telling if there would be any long term effects to this. So to do this, in the valve procedure, it would be 1. Remove the cams 2. Install the shims on the 8 VTEC valve latches 3. Replace the cams. 4. Check all 16 valves - adjust as needed (by removing cams) 5. Replace cams and ride. There are numerous unknowns in all this - but theoretically it's possible.
https://www.youtube.com/watch?v=XEimE9DptP4
The other way would be to install a 2nd VTEC solenoid, grounded and connected to the ECU through the normal connector. The ECU wants to see that before it will fire the engine so it must be in place. This is only to fool the ECU in to thinking that it's actually actuating the VTEC valves. Then, set up a switched 12v source (or maybe 5v? - you'd need to check for that) to the installed VTEC solenoid in the "V" and allow the switched power to open the solenoid and keep the VTEC passageways pressurized at all times. That would be a simpler approach - so either mechanically or electrically. You would need to remove the throttle bodies to get at the spool valve connector. I don't know of anyone who's ever done either in practice (for full disclosure I did not) but either seems plausible. Going the spool valve route would be the most easily reversed if it turned out undesirably.
Regardless, it would seem there are going to be some tuning issues to be sorted as the airflow below 6,400/6,800 rpm will be changed. That could either be a dyno session with a P.C., or letting a Rapid Bike do it automatically while you ride. The latter is slick - plugs in just like a P.C. but is way more capable. It uses the 2 stock O2 sensors on a VTEC and changes parameters on the fly to a target AFR while the P.C. only uses a set tune and does not change. Autotune is available for P.C., but is a manual process vs the automatic one with RB. Out of the box the RB tune is outstanding for a VTEC and just gets better as you ride it - I've been very pleased with it.
If you do this, please do a write up - AFAIK you would be the first to do so and post it publicly.
As always, YMMV
Thank you for the info. It sounds like going about it electronically (with the solenoid) would be the more feasible route. I've had the opinion for a while that the VTEC would be better if it were a switch on the handlebar, like a "sport mode" switch (as opposed to something done to meet emissions standards).
Anyways the idea of making the V4 into a 4-valve all the time engine came up discussing performance bikes (Panigale V4, RSV4) and theoretically how to build-your-own Honda V4 superbike using a VFR as a base. I'll keep this in mind if I ever acquire an extra VFR and a few thousand bucks to waste 😄
The juice wouldn't be worth the squeeze.
The Honda engineers do a great job. I truly believe if you aren't happy with the VFR's performance then it's just not the right bike for you.
Running all 4-valves full-time gives horrible low-end.
4 hours ago, DannoXYZRunning all 4-valves full-time gives horrible low-end.
Have you done it or know someone who has?
1 hour ago, SamuelxHave you done it or know someone who has?
I feel like this is just a safe assumption. With 4 valves open at lower rpms the air velocity is a lot lower seing as there is more area to flow, meaning you would lose the advantages of the two valves which hive a higher air flow velocity due to the smaller opening area which causes the air charges momentum to actually fill the cylinder with more air/fuel charge. thus giving better low end performance.
On the converse, at the higher rpms you want the flow to be as unrestricted as possible as the induced drag on the faster flowing air through just the two valves would end up choking off the amount of air charge you can get.
Which is why V-tec is such a great concept. you get the best of both worlds - kinda.
Even simple things like lengthening or shortening the velocity stacks can have a major change in engine performance.
Fluid dynamics (compressible and non-compressible flow)and how it relates to engine performance is such a fascinating topic!
6 hours ago, SparkieThe juice wouldn't be worth the squeeze.
The Honda engineers do a great job. I truly believe if you aren't happy with the VFR's performance then it's just not the right bike for you.
My 2014 is staying stock. This was merely a hypothetical. I realize even IF someone did this and made it work, it wouldn't be an RSV4.
9 hours ago, DannoXYZRunning all 4-valves full-time gives horrible low-end.
You mean like a 5th gen VFR800...???
I've read some (now dated) articles that debate why Honda put the VTEC system on the 6th gen (I'm not sure there's ever been a definitive answer). There are obvious benefits of using 2 valves / cyl at lower RPM to improve intake velocity. Some however have contended that it was for emissions compliance, some say for bragging rights, or for showcasing engineering/technology prowess or other reasons. Looking at 5th and 6th gen engine specs, the two share near identical bottom ends - the same bore and stroke, same C.R., highly similar cam timing (2deg diff on the intake cam (non-Cali)), the 5th g has about .7mm more exhaust lift than the 6th and intake lift is nearly identical. The engines will directly bolt one in to the other, the only mods needed are dealing with the VTEC solenoid and the difference in the cam covers holding either 6th gen coil packs or the 5th gen HT leads. In short, the engines have slightly different characteristics and yet are highly similar in most ways - except for the VTEC. Regardless, riding a 6th gen and a 5th gen back to back does not give me any seat of the pants indication that the VTEC's purportedly higher intake velocity at low(er) revs gives it noticeably more grunt in that range than a 5th gen. Maybe the dyno graphs show it's true, but in practice any difference is, IMO negligible in everyday riding. Probably more important than the 4 vs 2 vales / cyl question is how each is tuned - fuel delivery, how intake airflow is managed and header design. 5th gens run just fine on 4 valves / cyl so there's no question it can be done with that basic V4 layout.
My personal belief is that if one is doing this, it's for the challenge and enjoyment of it, to overcome any obstacles and to have the only one (or at least the 1st) of its kind. It's hot rodding for bikes. Only the owner would know it's there - no telltale signs from the outside. To me a more interesting mod would be rather than make the VTEC run on 4 valves per cylinder all the time would be to swap a 5th gen motor to an 8th gen and get rid of the VTEC altogether (along with its added complexity and more difficult valve adjustments) to obtain constant 4 valve operation. Once the two main mechanical hurdles were overcome, the only remaining task would be tuning, and a Rapid Bike will do that plug and play right out of the box. It's been done on 6th gens, there isn't any reason that it couldn't be done on an 8th. To each their own. In some way or another most of us make our bikes our own - some in small ways, other in much bigger ones. For me that's what makes it interesting. YMMV.
My friend Makota San previous job was Chief Engineer Honda R&D who
invented Honda's VTEC... he calls VTEC "his baby" and recalls his boss
being super skeptical of the idea working at all...
Makota San also worked on the NR500 oval piston racer and he plans to
visit the Busy Little Shop some day because I have 2 cylinder blocks
off the NR500 that I packed out of Japan in 1981...
[image: gallery_3131_5511_17541.jpg]
Makota San down on cannery row...
[image: gallery_3131_5511_48694.jpg]
In my opinion VTEC stands for Vacillating Torque Engine Compartment... it worked on heavy cars
but it proved to be too radical on light bikes... 50% hate the bump in their powerband whereas 50% don't
mind the bump and favor the added gas mileage...
Honda has got to admit that their auto VTEC is a resounding success whereas the motorcycle VTEC has been a dismal failure...
12 hours ago, DannoXYZRunning all 4-valves full-time gives horrible low-end.
Negative Danno... if you ever get lucky enough to test hop Mr.Honda's race bred V4 it will
re calibrate the seat of your pants with its bottom end plod, midrange drive and top end rush...
Quote Fast Bikes
"In view of the modest stock HP claims, we didn't expect particularly
startling grunt from the engine as most of the manufactures have been
claiming 125BHP as a matter of course for their 750 replica
superbikes. Quite unexpectedly, the RC45 forced us to think again;
it's HP combined with formidable torque in the middle gears and the
extraordinarily clean and rapid response provided by the fuel
injection system make an explosive mixture which measures more like
130RWHP through the only barometer which really counts- the seat of
your pants."
[image: 07IOMRC30RC452.jpg]
[image: 07IOMRC30RC451.jpg]
4 hours ago, TerryYou mean like a 5th gen VFR800...???
While there's subtle differences in cam specs, it may or may not make big difference with/without VTEC? Might make 6th-gen worse than 5th?
1 hour ago, BusyLittleShopNegative Danno... if you ever get lucky enough to test hop Mr.Honda's race bred V4 it will
re calibrate the seat of your pants with its bottom end plod, midrange drive and top end rush...
I'll have to try RC30 and RC45 some day.
9 hours ago, SamuelxHave you done it or know someone who has?
I've done it on Honda VTEC and Toyota VVTi cars and it's pathetic. Turns engine with wide flat torque-curve into a 2-stroke with nothing in bottom-half of RPMs and then it ramps up quickly in top 3rd. Then you hit redline before it's done any work and have to shift into molasses bottom-end.
Since VTEC on bikes hasn't been as dramatic between 5th & 6th, maybe disabling it will result in nothing anyway.
If the VTEC transition is bothersome it is due to being in the wrong gear for the conditions.
Just my $0.02...the VTEC transition on my 2004 was a little rough but not terrible. I installed a PCIII and O2 sensor eliminators and it smoothed out completely. Well, except once in a while, for some reason after riding through rain I would get a jumpy transition. I just learned not to let it transition in a turn after a rainstorm.
I think removing VTEC is an intriguing thought and possibility, but I was happy with my 6th gen's engine, especially installing the Power Commander. If you go pursue this, I'm sure we'd all love to see the work and read about the results. 🙂
With a rapid bike its barely noticeable. Now my new fireblade kicks in like vtec now that is very very scary compared to my vfr800.
1 hour ago, VFR750F3With a rapid bike its barely noticeable. Now my new fireblade kicks in like vtec now that is very very scary compared to my vfr800.
Indeed. R.B. is light years ahead of P.C. V. It just works - they really got it right. I still haven't successfully installed the RB software on my laptop though . . . :comp13:
Terry, 11/18/2020 at 1:55 AMYou mean like a 5th gen VFR800...???
I think he meant running 4-valves full time on a Vtec engine that wasn't designed for it. I can't imagine that going well at all.
For anyone who wants a non-Vtec VFR-engined bike, there are indeed earlier versions which run beautifully on 4 valves throughout, and they are fabulous engines. However, the Gen6/8 Vtec versions of the VFR are better in almost every other way, so you'd have to do some serious farkling to get the best of both worlds, like fit a 5th Gen engine into a 6th (or 8th) Gen frame.
Now if only someone had done that..... :wink:
TBH, the 8th Gen engine on my VFR800X Crossrunner is about as good as I could imagine a Vtec engine getting. The transition is really smooth yet gives the added urgency we all love, the torque curve around the 5k rpm range feels much better than the 6th Gen and overtakes in 6th gear are quiet rapid with plenty of pull from around 70mph. The fuel mileage is also excellent and along with all the other improvements, you'd have to really want to do some serious engineering putting a 5th Gen engine into a newer model.
But I remember my 5th Gen days, I loved that bike and I can understand why current owners can be very protective of their bikes and not want to move onto a newer model with the dreaded Vtec.
6 hours ago, SkidsFor anyone who wants a non-Vtec VFR-engined bike, there are indeed earlier versions which run beautifully on 4 valves throughout, and they are fabulous engines. However, the Gen6/8 Vtec versions of the VFR are better in almost every other way, so you'd have to do some serious farkling to get the best of both worlds, like fit a 5th Gen engine into a 6th (or 8th) Gen frame.
Now if only someone had done that..... :wink:
I can think of 5 6th gens running around powered by a 5g GDC motor. Literally everything bolts right up - as mentioned previously sorting the ignition is the most difficult part of the swap. Oddly, the 5th and 6th gear ratios are 1 tooth different between the two - the 5g has a touch more torque multiplication at speed. It would seem equally as doable on an 8th gen - and my trick knee tells me it just might be possible on a Crossrunner, too! :smile:
1 hour ago, CogswellI can think of 5 6th gens running around powered by a 5g GDC motor. Literally everything bolts right up - as mentioned previously sorting the ignition is the most difficult part of the swap. Oddly, the 5th and 6th gear ratios are 1 tooth different between the two - the 5g has a touch more torque multiplication at speed. It would seem equally as doable on an 8th gen - and my trick knee tells me it just might be possible on a Crossrunner, too! :smile:
I thought there were issues squeezing the motor in? Cam covers somesuch.
Anyway, I quite like the gas mileage on my Crossie and the Vtec is really nice when it kicks in.
Now how's about a 1200 engine in a....... :goofy: :beer:
4 hours ago, SkidsI thought there were issues squeezing the motor in? Cam covers somesuch.
Anyway, I quite like the gas mileage on my Crossie and the Vtec is really nice when it kicks in.
Now how's about a 1200 engine in a....... :goofy: :beer:
Now would that be something!! I don't know of anyone brave enough to attempt that - possibly someone with tremendous fabrication skills - maybe Seb? :cool:
The 5G heads are about 1 1/2inch shorter than a VTEC's. Could very well be some clearance issues particularly on the rear head putting a VTEC in to a 5G frame, but then who would want to do that?? HighSideNZ did a fabulous write up about his 5th gen engine build project that he put in to his VTEC - lots of photos. I recall him mentioning that he had it in and out so many times he'd gotten it down in to the range of a few hours to do it - pretty impressive. Mite still be saved here - IIRC it was in 2014.
I wish we had the Crossrunner here - I've never seen one in person.
10 hours ago, CogswellI wish we had the Crossrunner here - I've never seen one in person.
Well when this whole pandemic is over and we can travel again, when you pop over for your next European holiday, drop in for a coffee and you can have a ride!
The whole turning on VTEC all the time I believe is a moot point.
The porting/cam timing is so similar between the 5th and 6th Gens that the bottom end power difference is not really an issue.
The conversion I did was one of the best additions to the 6th Gen I think I've done.
Honda did the VTec for one reason and one reason only. Emissions and EURO compliance.
7 hours ago, HighSideNZHonda did the VTec for one reason and one reason only. Emissions and EURO compliance.
That's 2. :wink: 😆 :beer:
Cogswell. The difference in head height between the 5th and 6th Gen is 16mm not 38mm with the 5th Gen being the shorter.
Cheers
Phil