vfr 800 vtech (one exhaust hot / one exhaust cold ----WHY?

[muffadog]

ive got a 2002 vfr 800 vtech, can anyone tell me why the right hand exhaust always stays very cool and the left exhaust very hot?
Its really bugging me.

[loply]

Sounds very strange.

Is it firing on all cylinders? I suppose you would know if it wasn't.

As far as my practiable knowledge of bikes goes; If the exhaust pipe isn't warm it's safe to assume no exhaust gas is passing through it. And since the pipe is the only thing the cylinder is capable of exhausting into, that suggests a potentially serious issue like the cylinder just not firing.

But I'm working on theory here.

Check the spark plugs for those cylinders are working.

If it isn't the spark plugs, maybe an exhaust valve problem or fuel injector problem?

[muffadog]

Thanks for the reply, I have got no idea why it's like this, it pulls like a train and I'm sure its not missing, I wonder if all the vtechs are like this?

[John]

It's got VVT hasn't it ?

Don't know if that makes any difference or not? But I think the bike uses only 2 cylinders when not using much throttle, then uses all of them when you open it up?

I'm probably totally wrong though.
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[cagiva gezzer]

I was thinking along johns lines.

The VTEC means that below around 7000rpm only half of the valves are working. If each exhaust valve has its own header, then only half of the headers would become warm below the point where VTEC kicks in.
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"because one stroke isnt enough and four strokes waste two"

[MarJay]

I think you are all thinking too complicated here.

If you think about it, the twin exhausts on a VFR800 Vtec each come from different banks of cylinders in order to make the pipe routing simpleish.

There is a longer distance to travel from the front bank to the pipe than there is from the rear bank of cylinders.

Maybe its just that the gases from the front bank have time to cool before they reach the pipe? or that the front bank of cylinders is more exposed to the air (being that the radiator is split and on either side of the bike) enabling better cooling?

I doubt that each valve has different pipe routing...
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British beauty: Triumph Street Triple R; Loony stroker: KR1S; Track fun: GSXR750 L1; Commuter Missile: GSX-S1000F
Remember kids, bikes aren't like lego. You can't easily take a part from one bike and then fit it to another.

[G]

I don't know if this is the case here, but most twin pipe systems havea a 4->1->2 system, or similar. If that is the case then maybe one of the pipes has got blocked up to some degree, some how?

[Kickstart]

Hi

If it was a real problem with the exhaust I suspect the engine would run badly.

Never seen how the late VFR exhaust is put together, but as the VTEC system opens valves at higher revs it is possible that each exhaust valve has its own port and header (with a totally different length to the normal valve), and then stays fairly seperate.

However this is very much a guess and I am not even certain that the VTEC system works on the exhaust valves.

All the best

Keith
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[KevTM]

I've had a Civic VTi and i'm pretty clued up with Honda Cars as i'm a bit of an enthusiast.

The VTEC on my car kicked in around 5.5k, redlined at 8k.. what it does is a solenoid engages a 'middle' lobe on the camshafts which then gives the cams higher lift i.e. makes them more aggressive. Basically you have a driveable, economic car for everyday driving, but once you open it up it's sheer power, and great fun.

Anyway not sure if this is how it works on bikes.

The NSX is a V6 and i know when you're just cruising it only uses 3-cylinders and when you put your foot down it obviously used all 6 cylinders and again it also has VTEC, but i don't think VTEC has anything to do with it not using the other 3 cylinders. Again, it's for economic reasons - Maybe the bike incorporates this sort of technology?

then again, i could be deadly wrong!

[MarJay]

KeV6,
Yep unfortunately you are wrong.
As far ask I know, the Vtec system on the VFR800 Vtec is a small oil pressure actuated shim type thing that activates a second exhaust valve in the cylinder head. I'm not sure if this also affects one of the inlet valves as well. I think it does.

The head is designed as a four valves per cylinder design. One of the exhaust valves always works, and as far as I know, one of the inlet valves always works, so that below 7000rpm it is a two valve per cylinder design.

Over 7000rpm a small oil pump is started that pushes the little shim thing into position above the valve stem. this activates the other two valves. This effectively turn an 8 valve head into a 16 valver.

As I said, AFAIK, I think I have an explanation in a magazine somewhere so I might look it up if I can be bothered!

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British beauty: Triumph Street Triple R; Loony stroker: KR1S; Track fun: GSXR750 L1; Commuter Missile: GSX-S1000F
Remember kids, bikes aren't like lego. You can't easily take a part from one bike and then fit it to another.

[KevTM]

Ah right.. it works in a completely different way to the VTEC system on cars then... learn something new everyday!

[Demonic69]

My old Gixxer used to run with 1 hot and 1 cold, and that was waaay before Vtec
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