A Question of Timing

Guy · Post by **Guy** » Mon Nov 01, 04 11:52 am

I am thinking of locking out the distributor on my Barracuda to get rid of the mechanical advance. I am using an MSD pro billit without vacuum advance, MSD 6AL ignition, and I am just about to fit a MSD multi step retard unit as well. I was going to lock the timing at 35 degrees and use the start retard feature in the MSD unit to retard the ignition a further 25 degrees during start up, does this sound feasible the car see some street action but with the 4.10 rear gears the rpm is nearly always faily high I am not bothered about fuel consumption being affected as it consumes it nicely now thanks

I was also going to use a micro switch on the shifter to activate the retard box a further two degrees when in third gear as I have been told this will also help the top end of the vehicle, again does this sound right

Dave-R · Post by **Dave-R** » Mon Nov 01, 04 1:29 pm

Seems a complicated way of doing something the dizzy does simply. I have never heard of retarding the timing to increase efficancy or power before? Quite the opposite.

Advance is not just for MPG. The faster the piston speed (up to a point) the sooner combustion has to start otherwise the combustion pressure peak occurs too late.

The dizzy you have is completely adjustable as you know so why not use it?

You don't want any dizzy advance at idle. The carb throttle should be completely closed so you are on the idle circuits only with no advance in the dizzy.

You want around 12-14 degress MAX initial timing at idle though.

Timing advance should be starting just above idle speed as the transfer slots on the carb are being uncovered and the main jets start to work.

You want all your timing in at 2500 to 3000 rpm. Above this rpm you want 35 - 42 degrees total advance. Depending on fuel and cylinder pressure. Most mopars run fine with 35 degrees total advance but you may find you can run more.

You can get automatic ignition retard units that work with knock sensors. In this case dial in something like 42 degrees and the unit will automatically retard the timing only as much as you need to get rid of knock.

If you ALWAYS pull away from a standstill at WOT (which I doubt you do) locking the timing will work fine. But this car is no Top Fueler.

I would be interested to learn more about how retarding the ignition at the top end will increase mph.

Guy · Post by **Guy** » Mon Nov 01, 04 5:25 pm

I dont know why it is meant to give more top end Dave it was something I had heard in a conversation maybe i got it wrong it would not be the first time.

Dave-R · Post by **Dave-R** » Mon Nov 01, 04 5:48 pm

Well if you find anything out let me know. I am always looking for new info.

I know where you are coming from with this idea of retarding the ignition. I just think the mechanical advance does a good job of it and we know it works. So why mess with it?

Have a look at this product. You might find it interesting.

http://www.hughesengines.com/features/p ... ept_03.asp

Guy · Post by **Guy** » Mon Nov 01, 04 10:13 pm

A very neat and clever bit of kit that is

Anonymous · Post by **Anonymous** » Tue Nov 02, 04 3:11 pm

Wow, that looks like a great bit of kit. The Victor has trouble with fuel distribution, this could help a lot. My only question is, how can it tell which cylinder is causing the problem if the knock sensor is plugged into the block drain plug? (I'm guessing water drain plug?)

Anonymous · Post by **Anonymous** » Tue Nov 02, 04 3:29 pm

I'm guessing the oil drain plug? Automatic delay box. cool. I have no use for one but feel the need to own one

Anonymous · Post by **Anonymous** » Tue Nov 02, 04 3:31 pm

OK I actually read it properly this time

Coolant drain plug...

However to answer your question about how it knows....

"Since it uses only one knock sensor, you may be wondering how it can figure out which cylinders are knocking. Actually, it's easy. When the unit makes a spark, it listens to what happens. If it hears a knock, it knows that it's the cylinder that just fired, and that this cylinder won't fire for two more revolutions. When the knocking cylinder comes up to fire again, the unit dials in the appropriate retard FOR THAT CYLINDER ONLY. The unit does this as each cylinder goes by, building up a different retard curve, if needed, for each cylinder."

Cool huh

Kev · Post by **Kev** » Tue Nov 02, 04 4:05 pm

Doesn't it cost more than your Victor is worth, Bratfink??

Anonymous · Post by **Anonymous** » Tue Nov 02, 04 9:09 pm

Probably.

I guess you wouldn't be well advised to use this on a car equiped with a CAT converter then? Since 2 missed sparks would put unburnt fuel into the exhaust system. But I guess a more modern car with a CAT may well have it's own form of knock sensor in the ECU?

Kev · Post by **Kev** » Tue Nov 02, 04 10:34 pm

Well I filled me cat up on the Beemer when I had starting flooding problems and it still passed it's emissions....

Holly · Post by **Holly** » Tue Nov 02, 04 10:36 pm

It wouldn't miss, just retard per cylinder as needed, IIRC Audis had a system that worked in exacly the same way in the late 80's or early '90s (ie. single knock sensor).

Kev · Post by **Kev** » Tue Nov 02, 04 10:39 pm

Doh

I've been suckered into answering a BratFink question when he hadn't read the post correctly

Anonymous · Post by **Anonymous** » Wed Nov 03, 04 8:06 am

Doh Doh!

It was a bit ambiguous in it's wording. So actually it won't miss 2 sparks :tongue8:

Anonymous · Post by **Anonymous** » Wed Nov 03, 04 10:02 am

what I'd taken it to mean was that there are two further strokes of the cylinder in the cycle before it has to fire again. It "listens" on the power stroke, then theres the exhaust and charge stroke before its compression stroke and the ignition fires towards the end of the compression stroke so thats two strokes or one full rotation. No sparks are missed.

Was what I thought anyroad.