Interesting quote from Ohio Tom, Distributor Mod.

[beetlenut]

[raygreenwood]

[mark tucker]

many people set idle timing way to low thus the carb idle screws are almost useless...as is the tuner. if it's not all stock why should the timing be stock.... because some moron says so.

[raygreenwood]

[beetlenut]

[raygreenwood]

[Frank Bassman]

Very opportune thread.

So the benefits of the right amount of timing (idle and elsewhere) can most effectively be seen using a vacuum gauge.

The V8 guys with radical cams shoot for highest manifold vacuum at idle. (Often in the 8-10 in hg range for big cams. Stock cams can go as high as 22 or 23 inches!)

(And shorten total advance to not overadvance.)


Strong idle vacuum helps a LOT with idle quality with use of accessories like AC compressors.

But I also hear tuning for best idle vacuum is not necessarily what a tuner's goal should be. The response through rpm range is more important.

My question is: is there any reason why, IF it is possible, we shouldn't tune for best idle vacuum AND rpm response? Is there a benefit to having less than maximum possible idle vac?

-Frank

[raygreenwood]

Best idle VACUUM reading.....benefits what?

Not saying you are incorrect at all.....simply asking what the higher (really lower)...vacuum reading benefits?

Why I ask.....is again....with different/certain systems and applications like the early injection systems....having extra vacuum at idle is not really of benefit.

But having slightly higher idle and more complete combustion.....through slight ignition advance coming off idle is.....because it affects the airflow that we need for fuel mixture metering.

So.....on a range of injection systems ....especially those that are metering volumetrically.....its nice to have a slightly higher idle moving more airflow.....yet not so high that it is starting mechanical advance before its necessary.

I can see vacuum being a good tool to measure where you are. Just wondering what the specific benefits were beyond use as an indicator. Ray

[67rustavenger]

Wow! I am so glad I started this thread.

There is so much gold here. Everywhere you turn you find a huge nugget!

Thanks for participating team. Keep the comments coming.
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[j-dub]

So if you kept track of your rpm while you were increasing your initial timing with the engine idling by twisting your distributor, you would find that as timing increases the idle speeds up. This will continue up until about 22-28 degrees, all engines will vary. Another way to say this is that the torque is increasing as you are increasing the timing until the point in which it does not increase any more, hence the rpm stopped increasing.

One rule of thumb, as a starting point, would be to find this rpm and then cut it in half. The point of not running your idle timing at the best torque setting is so that you have torque in reserve when you rev your engine as to take off from a stop.
Also don't forget the other part of idle timing is to get your throttle plates in the right position if you are running carburetors.
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[balljoint]

[Vanapplebomb]

[oprn]

[spencerfvee]

most guys buy a after market distributor . put it on there motor .and set the timing .and wonder why it runs the same as a stock distributor . lol i dont know what the big deal is on setting up a distributor to run 12 or 14 degs. intal. i have been doing it since 1969 . mostly using a Mallory distributor. that came with a key. that made it easy to set the Mallory up. to run 12 to 14 degs. intal. . i have seen a lot of the china distributors being sold now a days as replacements for the 009 distributors . that are junk.the timing jumps all over the place .when you try to set the timing . the points dont last long .and the parts break on the china distributors . thats why you see good used German 009s selling for over $100.00 . spencerfvee

[oprn]

In actual fact most of them don't run as good as a stock distributor!
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[FreeBug]

[raygreenwood]

[mark tucker]

I use weeker springs, bending in the arms still has about the same curve, they are just way too stiff. I susaly use the msd or mr gasket curve kits for almost every dist. but yes some do need the arms moved for addvance limits or knotch the weights if they are the limit contact. there are many ways to recurve dist. but knowing what your engine needs and giving it that....is priceless and there is no bees knees pretty dist with a blue tag that fits what your engine needs. no slick moron selling stuff out of his basement never seeing or knowing anything about your engine claming his is the one and only and the best,and only he can supply what your engine really needs. but you may need his junk dist to show off how stupid you are.there are many out there. he is after a exspurt sails man.( no this is not refering to you, so dont get your painties in a wadd, this could be any of many clueless morons buying & selling the bees knees.)( good thing they have wings!!!

[Alstrup]

Hello.
What Ray, - and Tom said. We have been doing this for 40 years, but somewhere back in the late 90´s it sort of disappeared probably due to the lack of interest invintage cars in that period.
When you begin to work with optimizing the ignition timing, you need to have AT LEAST a quality timing gun with a retard function, so you can veify your correct timing.

Almost any ACVW engine can handle a more aggressive timing curve than the stock delivered, - unless you insist on running on moonshine.

Optimizing the timing curve can be the difference of a fair running engine and a great running engine.

Finding out where the engine in question optimizes power, - and efficiency wise is kinda difficult to do on the street, but possible if you invest a lot of hours and some hardware into it. Here a chassis dyno, along with a professional engine master comes in handy.

Ignition timing is very effected of the entire ignition system from coil to wires to plugs. After that cylinderhead shape, deck height and even the quality of the valve seat job has an effect. (Basicly mix quality and vortex areas in the chamber)) I have seen medium tune engines with the classic blue Bosch and 009 "screamer kit" that needed nly 0,7 mm plug gaps to run well at all times and needed 33 degrees advance at WOT to optimize hp and torque wise. The very same engine with a better and more precise distributor, a 60 KV high insulated coil, MSD Super conductor wires and plug gap increased to 1,0 mm. optimize at 29 degrees AND pull a solid 3,5 hp and 5 Nm more. (This particular engine was a 1776 displacement, so no monster motor) and it was no slouch to begin with, ending at 125 hp and 177 Nm torque.

The optimization of the timing curve is most interesting in the idle to about 2200 rpm area, because that´s where most engines (with cam swops) are "off cam" So there you have a lesser quality combustion mix and so the engine needs more time to burn the mix decent.
This is also where the beloved 010 & 019 comes back into the picture, because on low compression large cam duration engines the initial timing advance becomes even more on its place. It is not uncommont o see a low compession engine with say an FK8 cam and 8-1 CR want 28 degrees of timing already at 2000 rpms to run even fairly well.

So, yes, as I have stated before, for the average tuner, the ignition system is one of the most overlooked areas in engine tuning. The old term "A spark is a spark" simply does not hold water, and have never done. (Pun intended)

If you live in CA and have a smog regulated vehicle there is only so much you can do. But if you are willing to invest some time and a little money in it even those engines can be optimized quite a bit and still pass the smog test and visual inspection with flying colours. I am aware that some people call it bending the rules. I call it using what ever knowledge there is available to improve both emission, cooling, performance and longlivety. BUT, that´s a whole different chapter which we shall not stray into here.

Back to main topic
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[jpaull]

I was just about to say a few things of what Alstrup mentioned.

You can get away with alot more if you have a powerful spark. As appossed to someone that is just playing with a bosch blue.

California smog is required for 1976 and newer. 1975 and older can do whatever they want.
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