I'm up on my soap box
Would work great if you could drive with no load on the engine at exactly
4000 rpm all the time.
What is optimum for one particular condition may not be optimum for another
condition, since the distributor has only two primitive advance control
mechanisms - vacuum and centrifugal advance to adjust for all possible
timing needs. The factory curves and initial timing settings on a
non-emissions distributor are as close to optimum as the engineer could
determine for the stock engine (within the severe limitations of the
advance mechanisms).
Now-days we have computers that can instantaneously adjust many things
(including timing) at the same time to account for damn near everthing
including, but not limited to barometric pressure, fuel mixture, throttle
position, engine load, vehicle speed, engine temp, ambient temp, coolant
temperature, etc without relying on something as simplistic as pulling
against spring tension. This means that many things (including timing
curves) can be controlled very precisely without any mechanical
limitations. This is why todays engines can put out about twice the
horsepower as the same size ones were putting out in the late 70s while
pulling down better fuel mileage, better emissions, and having better
driveability.
Getting a car to perform correctly is just not as simple as setting initial
timing to a generic setting or optimizing efficiency for a given condition
on a given day. The whole picture must be taken into account.
This is the reason many performance mods are disappointing. When I was 18
I bolted a lot of expensive pieces together in a Ford engine and expected
it to be fast. It was a dog - dead as a doornail below 3000 rpm and bent
pushrods at 5500 rpm. Took me 2 years of frustration, experimentation, and
additional parts to get those original pieces to work right (yes, they
finally did). I've been a lot more conservative with street engines since
then.
My advice is the following:
Verify what you have (the whole engine) is working properly first before
trying to change anything, and then don't change much at a time unless
someone has a proven formula for a set of mods. If you're determined to
change the timing, how about advancing the timing 2 degrees at a time -
drive it - keep a log for each setting and then decide the best place for it.
By the way, the distributor in my Sprite had no advance at all when I
purchased the car - the weights were stuck due to age, rust, etc. All I
did was disassemble it, clean it up, verify the advance curve, set initial
timing to factory specs and I think it works great, even with the
performance cam and header.
Les
At 10:56 AM 5/29/98 +0800, you wrote:
>I seem to recall that the "How to be a Home Mechanic" course I went to
>about 20 years ago recommended just using a vacuum guage to do your timing.
>
>Basically, you set the idle to about 4000rpm and then turn the distributor
>until you get the highest, steady reading. I've given it a go and it seems
>OK (but I wouldn't know if it is optimal).
>
>Has anyone got a view (as if you haven't!) on this method?
>
>Greg
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>>Set yor timing at speed not idle. Most of the books call for 35 deg @
>>4000 rpm, I find that 37-38 deg is about all you want to go for total
>>advance at 4000 rpm. As to what this is at idle depends on the
>>distributor and points dwell it can vary a lot. My bug-i with 948cc and
>>mechanical advance distributor is static timed at 12 deg BTDC with a
>>points dwell of 60 deg to get 37 deg @4000rmp total advance.
>> Crash
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