The Fixer

Some people in racing that build 16V V8 motors (and do not have the luxury of having a dyno on hand) have been very successful advancing or retarding their cams a few degrees carefully to dial in for maximum power output for that given profile.

I recently read about American 16V V8 motor builders (oval track racing) doing this with great results.

I have a 450CC 4-stroke Yamaha racing quad (yfz) and rotating the cam 1 tooth makes a very noticeable power increase.

All the serious racer of this particular machine do this as soon as they get the chance. So naturally having to do my TB soon i got to thinking.

Anyway, first being sure that there is no piston to valve interference.
The oval track racers do what you'd expect, setting #1 piston at TDC and using the starter to crank the motor,
they move the cam a degree or two at a time in each direction while checking cylinder pressure on #1.
Once they determine which direction higher cylinder pressures are observed,
they go in that direction a degree at a time as pressure builds until the pressure begins to drop and then back it off a degree.
This would maximize engine power.

I was curious if any US 16V owners have tried this as many in racing have done with much success.

Not advocating, I'd be very cautious to try this. But I was curious what the
much more experienced 928 Motor Heads around here thought.

AO

The problem is they are not adjustable per se. Carl at 928MS sells a cam advance key to advance the cams by 2* or 4*.

James Bailey

Much was done years ago.....they even had some adjustable modified sprockets (which usually broke
result was minor changes somewhat like what I lifted from a well known camgrinder's site....

."Advanced Cam Position: If your intake happens to come out with .100 gap, and the exhaust with say .080 gap, your cam is in an advanced position. In this position, the came will produce more low-speed power or torque. However, there might be a slight loss of power at high RPM.
Retarded Cam Position: If, on the other hand, the intake came out with .080 gap, and the exhaust at .100, your cam is in a retarded position. In this position, there will be some loss in low-speed torque and power, and probably some subsequent gain in high-speed power. "

Sounds like the gains for the Quads is the FEEL of more low end torque...which makes sense.

Porken played around a LOT with 16V cam timing much has been written about it.

123quattro

When I bought my car it had one cam off a tooth on the passenger side pulley. I fixed it when I changed the timing belt. Seat of the pants power and driveability felt identical.

danglerb

First step in performance is to go with a non stock cam, which includes the ability to tweak the timing any way you want doesn't it?

The basic advantage I see going with the 16v is the lower cost of messing with cams and valves. If you plan to leave those stock then its a no brainer to switch to 32v motors for performance.

atb

No such thing as a free lunch in changing cam timing, you just get to decide where in the power band you want your dessert.

crushingday

I wonder how a vario-cam ala the 968 would feel.

James Bailey

Very, Very EXPENSIVE !! It was tried and became way more trouble than it might have been worth...project got changed but only after much effort to make it work.

Hilton

Its been done - go read www.928sg.com (Sterling's car - he's since dropped the variocam and is doing something else to the car)

slate blue

But why was it dropped? What was the problem? In theory there is only positives (except cost) and it should work.

As to the cam position, retarding will lose you power everywhere, advancing will gain it. These cams need a better exhaust and need to be advanced.

Imo000

I think the problems were the locking bolts for the cam gear kept moving or something similar to that.

The Fixer

Thanks, i was thinking the same.
While doing there TB why couldn't the cams be advanced a tooth on the belt?

slate blue

A tooth on the timing belt will be way too much, you need a kit like Porken made back a decade or so. That is what I have and it works well. The offset keys may work but again no adjustment, may not give the results you desire.

Strosek Ultra

First fine tuning of the cam timing has a much greater effect the hotter cams you have. Changing the timing one tooth is 15 crankshaft degrees. Usually one never change the timing more than half that value.
Åke

The Fixer

Why can't anyone give me a straight answer??! LOL, I couldn't resist.

Thanks slate blue and Strosek Ultra.

That's the info i needed. My math was way off, i figured 5 degrees on a tooth. -Matt