Finally got a '98 and '01 VTR in at my shop and took the chance to measure the camshaft lift on both bikes. Surprisingly enough (or maybe not at all) there is no difference. As for the duration... . Engine numbers for both bikes have been checked at the Honda Interactive Network website and match the VIN's from each bike.

'98 Intake Cam


'98 Exhaust Cam


'98 Engine Number


'98 VIN

 

'01 Intake Cam


'01 Exhaust Cam


'01 Engine Number


'01 VIN

 

I'm not surprised.

 

Well a couple of issues.

First, there is no way to actually know if either one of those engines has had a cam change somewhere in their past.

Second, you really need a set of "vee" blocks and a dial indicator to get really accurate reading for this type of measurement.

Then "if" the cams are the same what happened to the HP.

5 of them were lost somewhere. Add in the fact that by the published dyno charts the later models not only make less power they also make their peak power at a lower RPM. Both of these suggest than there was a cam change.

Now I'm not sure how Markus (Tweety) did his measurements but he did see a difference in the samples he tested.

So I guess it's believe what you want but I still would like to know why the power dropped. In order to get an extra 5 HP out of this engine takes quite a bit of time and $$ so what did they do to lose that much power?

 

I have a related question to this... how much does cam profile shape play into the performance? As in, you could have those exact same measurements on the two different cams, but the "egg" shape could be much wider on one than the other.

Actually, it would seem that the shape of the egg would be most important if I'm visualizing it correctly. The longer length that inderocker measured is just how far the valve is pushed down (likely the same on both motors, otherwise parts would be hitting) and the shorter length is just the diameter of the circle when the valve is closed (also likely the same on both motors, as the cams are the same distance from the shim buckets on both motors). It's the shape of the transition between the two that would control speed and duration of the valve lift. Just thinking aloud here...

 

Could it be that one lot of measurements were taken including losses from the alternator and the water pump, the others without. It would have looked good on the brochures at the launch and could be corrected later on??

 

No that is not the answer as the numbers I have seen and based my questions on were done on the same dyno and the numbers were at the rear wheel.

 

I did it with a dial... However, I didn't have a suitable V-block or otherwise suitable way of holding it perfectly, making my measurements less than perfect... What I found however was that the lobe was at different angles, and different width... If the total measurement end to end is the same, like indie measured, I have no idea...

And there is no way of telling if the two I measured had at one time had the cams swapped either, so there is no more certainity there...

 

guys he only measured lift here of course there could be some duration differences (egg) maybe where the power went. this thread is only telling us that the lift is the same throughout the years, assuming no cam swaps.

 

SO wait, you're telling me that they changed the Superhawk cam profiles, and late model bikes lost horsepower? Do I have that correct or backwards?

 

Did you measure the base circle? how did those compare?

 

Yes, that is the general discussion. There are no concretes on if there is a difference, so it's an ongoing discussion, but if you search old threads you will find it.

It could be b/c of a variety of things, EPA/Euro emissions, HP restrictions, ignition advance, etc, but it was noticed that the Hawk seems to have lost 5hp on certain dynos after 1998. The part # is the same, and Honda didn't make any note of it, but the best guess as to where the HP loss could have come from is the cams, as there doesn't seem to be any other reasonable explanation.

Hence the comparison of measurements of the cams.

 

You need to measure the duration. I think that could be done with a dial indicator and a degree wheel.

But if you confirm that the cams are the same, I'd have to change my signature.

 

Well actually it was 2000 when the power loss happened (which by coincidence is also when the RC51 came out)

And any magazine test you see from that time on rates a SH at 100hp
the '97, '98 & '99 put out 105hp

In fact in '97 &'98 it was part of the ad campaign..... one more HP than a 916....

and it's not just the loss of power, it is also that the peaks for both HP & torque are at lower RPM and the only way I know to do that would be to run a different cam profile.

If someone else can explain how to do that without changing the cams, I would sure like to hear it.

 

Just a thought here, because I think you're onto something with the whole egg-shape deal. The shape of the cam surface represents a sin/cos curve with the y being the position of the valve along x where x is the surface area of the cam. not sure on all the individual variables, but that's the basic principle. You could use these curves to determine the differences between any of the cams.

 

There is a myriad of ways. Timing advance curves, changes to the manufacturing process in the exhaust which could have left restrictions in the headers, changes to the cyl head manufacturing process which could have led to smaller ports. I could go on and on. But without actually measuring thing, like you point out, there is no real way to tell.

 

I would measure the cam timing with them mounted in the engine and a degree wheel on the crank. Measure the crank angle at .040" lift on the open and closing sides and calculate the lobe center and duration. There may be a small change in the cam phase angles, which you won't see by measuring the cam lobes.

I'm guessing there is no difference between the early and late cams.

 

Well what I can add right now is I do find it a bit strange that both the intake cams you show are on the low side, while still in the "service limit" they are both out of "spec"

The service manual states that the intake cam should have a lobe size of 40.08mm - 40.24mm with a service limit of 39.78

So a bike with the cams having 40.24mm lift would have right around .010" more lift than a cam with 40.00mm of lift.

So I guess it is still unknown but 5 HP disappeared somewhere.

The smaller ports or exhaust system is not the answer. The timing did change in '01 when they changed the ECU but they added more advance (which is why the FP fixed advancers don't work well in later model VTR's)

and even if any or all of these things were true, I could see less power but the 500RPM or so drop in the peak power just doesn't make sense in any of those cases.

Not that I really care as mine has always dyno'ed at over 105 HP but it is one of those things that I would like to figure out.

Hell maybe Honda spent more time and installed "matched" cams (where both cylinders revived the exact same amount of lift) on the earlier bikes and then just fitted whatever to the later ones.

I just don't know but like I have stated the drop in the peak RPM for both HP & Torque usually happens when something changes in the cam timing or lift.

 

It would be interesting to see if they made a small change. For the amount of change and a decrease in HP/torque, its hard to see any justification.

 

That is why I had the thought that they might have done a better job of "matching" the lift on both cylinders on the early models.

 

Ok, in my search through the parts fiche after a thought of how things changed...They changed the gears on the cams...or rather cam timing??? It looks like this is something that got updated and it is shown as a standard part for some but an update for other years. Changing timing can change power significantly without changing the cams themselves.

 

+1
My old '86 CB700SC Nighthawk S had a screaming top end, but in the midrange it was a dog. I never did it, but there was a fix documented in "Motorcyclist" magazine where you could drill a new locating hole in the cam sprockets to retard the valve timing slightly and thus beef up the midrange torque.

Of course, there's always variable valve timing, which works great on cars, but I've heard it can be upsetting in corners on VFRs with VTEC.

 

Ok so did the later models get the increased torque as a trade for the HP?

 

I've never heard anyone say that the torque curve changed. It's flat as a table top, from the charts I've seen.

 

That's what I was talking about with cam phase angles. It has to be measured (or is most easily measured, without any other fixturing), with the cams in the engine, relative to the crankshaft angle, from top-center.

they may very well have decreased the overlap between intake and exhaust cam timing, to increase the midrange torque and decrease the top end torque - which would correspondingly decrease the peak HP number - not a bad compromise.

 

Well just like the cams, if you do a reverse search or where used search they list the same cam gear for all years.....

 

If you want to, you can slot the cam gears and advance the exhaust cams a few degrees, for more overlap. I bet you'll get more peak HP, but you'll pay for it in the midrange.

It's easy to do, but you should degree the cams before and after and document the change.

There's a lot of speculation and not a lot of measurement and documentation going on...

 

When I looked at the individual years only some showed an updated part. The early years were the ones that showed it, later ones showed it as a standard part.

 

The site I looked at shows "14321-MBT-F20 (replaces 14321-MBB-000)" for all years.

Honda, ATV Parts, Scooter Parts, Motorcycle Parts,CRF,CR,MX Parts, Goldwing parts

Also if you use the Ron Ayers "where used" tool it shows the same thing for both numbers (that they are for all years).