Timing Belt And Performance

[BlexusGS]

I did some searching here on this site and on the net and have not found any real solid evidence. Is there any correlation between a warn timing belt and performance? I was told a while back that the timing of a vehicle has to do with performance and how the engine runs (obviously). If your timing is off (retarded) then you will have poor performance, right? Now, as the timing belt becomes old and worn over the years (miles) it should stretch, right? If the timing belt stretches doesn't that !Removed! the timing therefore resulting in poor performance?

The reason for the question is because I have a 2000 GS400 with about 75K miles on it; the performance doesn't feel like a 300HP car should be... mostly sluggish off the line; no wheel spin no matter what I do (stock wheels/tires, traction control off, power mode "on"), nothing. Any ideas??

Thanks guys,

Nick

[SRK]

The is no doubt that a stretched timing belt will !Removed! the camshaft timing, and in fact the right bank will be retarded more than the left bank. I installed a new chain on a Mercedes V-8 a few years back, and the right cam was about 5-6 degrees retarded and the left only 1-2. The engine ran noticeably smoother with the new chain.

That said, the amount of power loss due to cam timing will be very small. The real test for your car is to drive it down a dragstrip and see what the numbers are, or take on a car with known performance data.

Either is fun.

[GuyTelefunken]

I would have to wonder if the VVT-i would compensate fo any change in length of the timing belt. Using data from the camshaft position sensor and the VVT sensors the ECU could theoretically compensate for any small error in the timing belt length and still position the camshafts as desired.

[SRK]

I wonder about that too, but I think the VVTi system changes angle from a given point, not a set point. In other words it assumes the cam belt is installed with the marks "straight up" and then procedes from there. It may be like an old distributor which adds and subtracts timing from the starting point given it, correct or not.

It would be interesting to know for sure.

[GuyTelefunken]

I gonna' lean towards the Japanese mind for perfection and say, I bet the ECU knows exactly where each camshaft is.

Here is the poor translation found in my service data of how the VVT sensors work.

It seems to me that the rotational angle of each camshaft would be in reference to the position of its sensor, not in reference to the angle of the crankshaft. Does that make sense?

VVT_i.pdf

[SRK]

Makes perfect sense. It seems that Lexus uses a camshaft position sensor, which must be similar in operation to a crank position sensor. With that, the ECU knows the true position of the cam in relation to the crank.

You be right! Lexus strives for perfection.... where have I heard that before......?

[BlexusGS]

Thanks guys, I guess my theory is out the window. I just thought that my poor performance could have been related to the timing belt. Thanks for your help!

Nick