MSD Pro-Billet advice please

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Allan Robinson
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MSD Pro-Billet advice please

Post by Allan Robinson »

Guys
I have just ordered a PN 8548 MSD Pro-Billet distributor for my Rover 4.6 engine which is sitting in my Dax Rush (740kg). It has 9.75:1 compression and a Stealth cam. According to Des Hammill a 4.6 requires 28 degrees of total advance, so rather than wait for it to arrive then have another delay while ordering additional springs and bushes I thought I would get ahead of the game.

Can anyone offer advice with the following questions:
1. What range of advance stop bushes come with this distributor?
2. If a 28 degrees bush is not included, is it just a matter of a bit of maths (difference between supplied bushes) and modify one of the larger ones?
3. What RPM should I be looking at for setting total advance?
4. Which advance springs works best?

Thanks in advance
Allan



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Re: MSD Pro-Billet advice please

Post by JP. »

As I remember mine..

All parts came in the box.

I have it set, 25 degree total advance + 13 at idle makes 38 total all in at 4000rpm.
Have the mechanical advance come it at 1200rpm so if you have a hot cam you won't have idle issues caused by the mechanical advance comming in to soon.

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Re: MSD Pro-Billet advice please

Post by Robrover »

On my 4.6 I had Performance Ignitions build a Scorcher (Bosch) dissy with a custom advance curve. Total mechanical advance is 30 degrees all in by 2,800rpm. Idle set at 10 degrees with vac advance disconnected. Vac advance then connects to the "always on" port (ie non timed manifold vacuum) on the Edelbrock.

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Re: MSD Pro-Billet advice please

Post by sidecar »

I run a programmable MSD 6530 unit along with a MAP sensor, my Lucas dizzy has had all the guts removed and an MSD pickup fitted, the dizzy is 'locked' out, it has no bob weights fitted at all, the advance curve is controlled by the MSD unit.

I guess you would call my engine a 'stage III' tune, my tests have shown that the engine wants around 18 to 20 degrees at idle but I think that if the advance curve just ran on from that point it would really be too advanced for most of the rest of the curve. Idle is an 'odd ball' state of affairs for the engine, the VE is really low at this point as the throttle is 99% shut. The idle timing can tell you something about the timing required at say 1200 RPM which is around 300 higher than my idle. At first glance if my engine needs 20 degree to idle well you would think that it might need say 22 at 1200 RPM and this would be true if the engine was running at 1200 RPM but with the throttle 99% shut. The problem is that at 1200 RPM the throttle could be 99% shut or 100% open, this will have a MASSIVE affect on the VE of the engine and therefore the burn rate of the charge. (The aim of any ignition advance is to try and get peak cylinder pressure to occur at 14-20 degrees ATDC). So at 1200 RPM my engine could need 22 degrees advance OR a lot less. I have set my system up so that the MAP system can pull out around 12 degrees of timing, this means that if the throttle is wide open the timing will back off from 22 down to 10 degrees for this RPM.

In my opinion if you don't run some sort of 'load sensor' (vac advance) on a road car you are going end up with a big compromise with regards to the timing. The problem is that many of the vac canisters that you can buy might not suit the engine that they are being used with, even the adjustable units are limited.

If you drill through some of my old posts you might find me stating that you don't need a vac advance system, well I've changed my mind! The more I learn about ignition timing the more I think that you do need vac advance on a road car. There are loads of things that effect the flame speed and therefore how much advance is required in order to get peak cylinder pressure at the right time in the power stroke but the mains ones are the RPM of the engine and the cylinder pressure before the plug fires, the lower this pressure is the more advance you need, the VE of the engine determines this pressure and the main controllable thing that sets the VE is the throttle!

My engine runs 28 degrees at 4500 RPM but as the VE is dropping off above these revs due to the heads and manifold not being able to flow well enough I add another 4 degrees advance from 4500 up to 6000 RPM which is my rev limit which makes 32 in total at WOT, my setup could theoretically run 44 (12+32) degrees at 6000 RPM if the manifold vac was high, i.e. the throttle was virtually shut.
Last edited by sidecar on Fri Mar 23, 2018 5:19 pm, edited 1 time in total.

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Re: MSD Pro-Billet advice please

Post by DaveEFI »

I'd always assumed on a dizzy, the vacuum advance was only for economy, not power. Older racing engines usually disconnected it.
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Re: MSD Pro-Billet advice please

Post by sidecar »

DaveEFI wrote:
Fri Mar 23, 2018 12:53 pm
I'd always assumed on a dizzy, the vacuum advance was only for economy, not power. Older racing engines usually disconnected it.

People state that the vac system is for economy and in a sense that it true however it would be better to say that the vac system allows the timing to be set both for best power and economy whilst being sensitive to the load that is being placed on the engine. In other words if the throttle is just cracked open you still want the engine to make the most power it can for that throttle setting and that will require more ignition advance than at WOT for any given RPM.

A racing engine is really operating at WOT for most of the time or at least the driver is trying to get to WOT as often as possible therefore it is much easier to set the ignition system up to cope with this. Lets say at WOT and at 1500 RPM the engine wants 14 degrees of advance, that easy to do, then at 2000 RPM at WOT it wants 18 degrees and so on up to peak RPM where you then set the peak advance. You could probably get quite close to the required figures by messing about with the bob weight springs.

With a road engine the above figures may still be OK for operating at WOT but they will be way too retarded for part throttle settings, the bob-weight-only advance curve will then just run the engine hot and effectively waste fuel because the power strokes will not be operating as well as they could do if the peak cylinder pressure was happening at the right time in the power stroke, the peak cylinder pressure will occur too late in the power stroke.

On the flip side if you set the advance curve up from idle to peak revs for a 'just cracked open' throttle setting then it would be way too advanced for any RPM when the throttle was on the floor.

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Re: MSD Pro-Billet advice please

Post by sidecar »

Its funny in a way the this thread has started now as I have been thinking about going over my ignition setup over the last few days, this afternoon I started the process by finding exactly how much advance my engine wants at tickover, this is easy to do as all you have to do it twiddle the dizzy around whilst listening to how the engine responds. My engine wants 30 degrees of advance on tickover. I have worked on two small block Chevy engines that wanted over 30 degrees at tickover. On the face of it this seems odd as my engine will only want around 28-32 all in at peak revs at WOT.

The MSD 6530 takes some getting your head around because it actually adds retard not advance! I have currently set my static advance to 46 degrees, the MSD then 'adds' 16 degrees of retard to bring the total advance at tickover to 30 degrees. The MAP system is adding 0 degrees of retard at the vac level generated at tickover (about 18" of mercury). The MSD then progressively adds less retard as the rev go up which in theory would allow the total advance to go up to 46 degrees but that the same time the MAP system has been setup to add 14 degrees of retard if the vacuum in the manifold rises to around 10" of mercury, it has added all 14 degrees of retard at 7" of mercury, this means that the total advance can be pegged back to 32 degrees or climb to 46 degrees depending on the vac level in the manifold. I need to run some more tests to see what vac level my engine pulls when cruising at say 50MPH but from memory it is around 11" of mercury which means that the MAP system will not be adding 14 degrees of retard.

Er, I seem to have hijacked this thread! sorry! To the OP, are you running a vac system? Regardless of that you will want the all in advance figure at WOT to be around 28-32 degrees at 4500-5000 RPM, the idle figure will depend a lot on the camshaft fitted and whether you are running a vac system.

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Re: MSD Pro-Billet advice please

Post by Allan Robinson »

Having searched the internet I have found an MSD instruction sheet for a Pro billet dizzy which answers some of my initial questions.

There are 5 advance stop bushings supplied giving max advance curve of 18, 19, 21, 23, 25, 28 + initial advance. So if I want 10 degrees at idle and 28 degrees 'all in' I will require the Black 18 degree bush + my initial advance of 10 degrees. Well thats how I read it at the mo.

What I am not clear on is how to select the RPM that I want the total advance to occur. From previous threads we have 2800 rpm to 4500 rpm. From the MSD advance curve graphs 'all in advance' can be selected anywhere between 2800 to 5500 by the changing the springs. Any thoughts?

In historic posts it has been stated that an Edelbrock performer carbs does not work well with a vac advance. I to agree and have have found that my car is much more responsive without vac advance than with it. In my case with vac advance performance has been quite unstable although I have never been able to provide a reason why.

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Re: MSD Pro-Billet advice please

Post by sidecar »

Allan Robinson wrote:
Sat Mar 24, 2018 10:17 pm
Having searched the internet I have found an MSD instruction sheet for a Pro billet dizzy which answers some of my initial questions.

There are 5 advance stop bushings supplied giving max advance curve of 18, 19, 21, 23, 25, 28 + initial advance. So if I want 10 degrees at idle and 28 degrees 'all in' I will require the Black 18 degree bush + my initial advance of 10 degrees. Well thats how I read it at the mo.

What I am not clear on is how to select the RPM that I want the total advance to occur. From previous threads we have 2800 rpm to 4500 rpm. From the MSD advance curve graphs 'all in advance' can be selected anywhere between 2800 to 5500 by the changing the springs. Any thoughts?

In historic posts it has been stated that an Edelbrock performer carbs does not work well with a vac advance. I to agree and have have found that my car is much more responsive without vac advance than with it. In my case with vac advance performance has been quite unstable although I have never been able to provide a reason why.
I used to post up that the Edelbrock carb does not work too well with a vac advance system, to be more precise it does not work too well with some of the Lucas vac canisters that are fitted to Rover engines. There are at least 4 different vac canisters, they all look the same but the numbers stamped on the canisters indicate that they are different. The first number (from memory) indicates the vac level that the canister starts to operate, the second number indicates the vacuum level required in order to fully operate the canister, the last number is the number of distributor degrees (not crank degrees) that the canister can add to the timing. As an example you might see the following on the canister...'5 10 8' Some of the Lucas canisters are totally unsuitable for use with the Edelbrock carb but it all depends on your engine and what vacuum is pulls on tickover and whilst operating in 'cruise' mode.

I have read that genreally a vac system will be connected to a non-timed port and it should add all of its advance at idle, if the engine pulls 12 inHg at tickover then the canister needs to be 'all in' at 10 inHg, if the canister requires 12inHg to be all-in then the timing will 'bounce' in and out and that will make the idle very unstable! (I've seen this on a SBC). If the engine wants lets say 20 degrees advance at tickover and the canister adds lets say 15 degrees at the crank then the static timing would be set to 5 degrees and the vac system will add the 15 degrees required to obtain 20 degrees in total. If the engine then needs lets say 30 degrees at WOT then the bob weights need to be able to add 25 degrees in total. (30-5). The vac system should not be adding and extra advance at WOT, however it can add more timing at high vac levels, in this case it could add an extra 15 degrees to the 30 making a total of 45 degrees.

With regards to your setup I think that you will need to do some testing on your engine in order to say at what RPM the all in figure is obtained, with regards to what the RPM should be then somewhere around 3500 will be safe enough. People often try to get the all in figure in as early as possible but really without hours on a dyno its all a bit of guess work (and I admit to using guess work too!) The aim of any timing system is to get the peak cylinder pressure to occur at 14-20 degrees ATDC, if it arrives earlier or later than this the engine will not be operating at its best. This is why the 'advance until it knocks then back it off a couple of degrees' is total rubbish. With this method the engine might go into detonation when the peak cylinder pressure arrives at lets say 6 degrees ATDC so the timing is backed off so that the peak pressure arrives at 8 degrees ATDC, the engine does not detonate because the pressure is now below the detonation threshold but the con-rod still does not have the correct angle to apply maximum force on the crank. (Imagine the con-rod at 12 0 clock, you could push the piston down as hard as you like but it won't cause any rotation of the crank!)

Allan Robinson
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Re: MSD Pro-Billet advice please

Post by Allan Robinson »

Thanks Sidecar for a very comprehensive explanation and will follow your advice and use 3500 rpm as a target for all in advance. I'm pretty sure the dizzy does not come with a vac canister therefore will continue to run without one for now until such time I fancy experimenting with one again.

I have just completed the cam run in on this V8D 4.6 long engine and now need to complete a further 500 mile of engine break in before I can explore the full range of the engine revs.

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Re: MSD Pro-Billet advice please

Post by sidecar »

Don't be too gentle on the engine otherwise you will never get the rings bedded in before the bores glaze. I am a firm believer in giving the engine 10 hard acceleration runs with a few minutes of cruising in between each run to allow the rings to cool down, once you have done that the engine will be 95% run in. Then just drive the car around and try to vary the load on the engine for a 100 miles or so, it will then be run in!

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Re: MSD Pro-Billet advice please

Post by minorv8 »

I have a 4.6, Merlin heads and EFI with Haltech ECU. The ignition is wasted spark setup. I run 20 degrees at idle, 30 degrees total up to max torque rpm (about 4500 rpm) and 32 degrees from 5000 rpm onwards. We gained quite a lot power with that extra 2 degrees on rolling road. With dizzy setup I had less advance at idle and 30 degrees total, all in at about 3000 rpm.

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Re: MSD Pro-Billet advice please

Post by sidecar »

minorv8 wrote:
Mon Mar 26, 2018 5:55 am
I have a 4.6, Merlin heads and EFI with Haltech ECU. The ignition is wasted spark setup. I run 20 degrees at idle, 30 degrees total up to max torque rpm (about 4500 rpm) and 32 degrees from 5000 rpm onwards. We gained quite a lot power with that extra 2 degrees on rolling road. With dizzy setup I had less advance at idle and 30 degrees total, all in at about 3000 rpm.
That's interesting stuff, I only guessed that the engine might want more than 28-30 at RPM figures higher than 4500 RPM. I spoke to the bloke that used to gas flow JE Development heads years ago, I said that most 4.6 engines could do with more than 28 degrees advance but the issue was that they would run into detonation around peak torque RPM so with a bob-weight dizzy it ended up being a compromise. I guess your system is similar to the MSD 6530 that I run in that you can program in any curve that you like.

My engine will idle OK with 20 degrees advance but I can hear it running better with 30 degrees, using a vac system means that this is not an issue because if/when the vac system drops the extra advance, the timing then backs off 14 degrees that the vac system added.

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Re: MSD Pro-Billet advice please

Post by Allan Robinson »

I have been reading Des Hammill 'How to power tune Rover V8' for a guide on 4.6 distributor ignition timing. This is where I found the values 10 degrees of initial timing and 28 degrees 'all in' stating that larger engines require less advance than a smaller one. In fact my previous 3.9 ran very well with 15 degrees of initial advance.

Reading the previous threads I am so surprised to find such high values of initial advance. Is there a particular tuning mod that has necessitates these high initial timing requirements?

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Re: MSD Pro-Billet advice please

Post by sidecar »

Allan Robinson wrote:
Mon Mar 26, 2018 6:37 pm
I have been reading Des Hammill 'How to power tune Rover V8' for a guide on 4.6 distributor ignition timing. This is where I found the values 10 degrees of initial timing and 28 degrees 'all in' stating that larger engines require less advance than a smaller one. In fact my previous 3.9 ran very well with 15 degrees of initial advance.

Reading the previous threads I am so surprised to find such high values of initial advance. Is there a particular tuning mod that has necessitates these high initial timing requirements?
The cam duration has alot to do with how much advance the engine requires at tickover, a long duration can mean that the cylinder is not well filled at low RPM and even has exhaust gases sucked back into it, this will then require more advance for the engine to run well.

Having said that the standard engine probably runs with moer advance than people think because Rover quote figures with the vac system disconnected but you then connect it to a non-timed port which will add at least another 12 degrees.

It is a very easy test to see what the engine wants at idle, just start the engine and slowly advance the timing whilst listening to the engine, the revs will start to rise but at some point the rate that the rev rise will drop, any further advance will hardly make the revs rise at all and teh engine might go lumpy, just before this happens is the advance that the engine wants at idle.

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