Hi Richard,
no problem with your summary.
I see you have an auto, so will be familiar with the cold morning
"lack of power" I was referring to.
The dyno study I refer to was on my disco with a new timing belt
fitted approx 3700km prior to the study. Like you I was surprised at
the amount of improvement, but found it very reproduceable.
The real test is not how hard it is to pull the old belt off, but to
measure the position of the injector pump and cam shaft variation with
the engine locked at TDC- see how much anti clockwise movement you can
get on the pump and camshaft. Remember that when you're doing this,
the engine isn't under load, so you are looking at minimums, when it
comes to the amount of retardation.
I have never seen a belt that wasn't stretched and that didn't cause
both the injector pump and cam shaft to be retarded. This is what
causes the deterioration in performance with the belt. The gears
simply keep the timing the same, irrespective of the engine speed etc.
Given the loading at the lower revs, until the turbo comes in, is why
the difference is so marked.
It doesn't take much retarding of the injector pump or cam shaft to
have an impact on the performance, so the comparison with geared
timing is pretty elementary. I had heard a lot of anectedotal comments
on the gears "extra performance" which was why I had the dyno study
done at the local technical college. We actually did the study on 2
vehicles (my disco and a low km defender) and the results were the
same.
The 27% is not the amount of belt stretch, but rather the improvement
in power. As you can see from the graph it is a peak, and happens at
the lower rpm range. I don't know the maths to calculate the timing
belt variance needed to give X degrees variation on the pump, but
remember that it is both the camshaft and the pump that are retarded.
All the gears are doing is maintaining the timing with the constant
geometry of gears as compared to the variable nature of belts. Even
timing chains vary with time, and with the timing belt the effect
simply happens sooner.
Hopefully this answers your questions, but if not just keep sending
them.
Cheers
Phillip
On Thu, 8 Sep 2005 20:05:37 +0100, "Richard Brookman"
<
[email protected]> wrote:
>so Phillip Simpson was, like...
>> Hi Michael,
>> I'm the bloke in Australia who "went to bat" for the Zeus
>> gears when they were attacked on the forum.
>
><snip>
>
>> you will see that dyno data on the improvement in performance (about
>> 27%, and fuel improvement is around 12%).
>
>Phillip - I read all your comments on this a while back (hope I wasn't too
>rude when I summarised it in an earlier post). What puzzles me is why a
>vehicle with timing gears is said to perform so much better - in performance
>and economy. There is a certain relationship between cam, crank and
>injector pump which a newly-fitted belt will maintain, and presumably the
>gearset will keep this relationship. How can a gearset improve on a new
>belt? I can see a gearset maintaining the settings better than a belt over
>time as the belt will wear and stretch (although when I took the old cambelt
>off my 300Tdi it was a bit of a wrestling match, so it can't have stretched
>much!) - but not by 27%. What do the gears do that a belt can't?