Question on ignition advance for increasing RPM

[stevieturbo]

Racing engines ain't really worried about economy.

yes they are.

Fuel is weight, no need to be carrying more than is needed. And squandering fuel is wasting power too. And there is the safety aspect of carrying excessive amounts of fuel.

And some racing, you have a limited supply of fuel, or refuelling stops take a long time...they need to be minimised.

So economy is very often an important factor.

[garrycol]

Of course vac advance or retard must not be all that relevant to a dizzy system as the mechanical system is because some cars do not even have vacuum advance or retard. My 24v 3.5 RV8 in my 101 does not have vac advance and neither does my Haflinger - neither has it so must not be all that important.

I think the other reason many people tend not to run vac' advance is because they see race engines not using it and think it must be better without stoping to think that a road engine has to work in a much broader range of conditions. Of course it also means it must be 'cooler' which may be even more important.

My RV8 and Haflinger are not race engines and not modified - they are as built by the manufacturer ie the manufacturer decided they did not need vacuum advance and the RV8 in the Land Rover pulls like a train from idle with plenty of torque.

[DaveEFI]

Racing engines ain't really worried about economy.

yes they are.

Fuel is weight, no need to be carrying more than is needed. And squandering fuel is wasting power too. And there is the safety aspect of carrying excessive amounts of fuel.

And some racing, you have a limited supply of fuel, or refuelling stops take a long time...they need to be minimised.

So economy is very often an important factor.

It was a bit of a throwaway comment. More to the point is them spending much of their time at full throttle.

[minorv8]

I had a 4.6 engine with Merlin heads that I ran with wasted spark ignition. CR around 10.5:1 and healthy hydraulic cam. Total advance ignition was 30 degrees, that is what the engine was happy with. On rollers the power peaked at about 5600-5700 rpm and then started decreasing. Just for fun, we put another 2 degrees advance above max torque rpm and gained quite a lot. The power curve stayed flat all the way to about 6200 rpm. Advancing another 1 degree to 33 degrees gained nothing but did not loose anything either. But to be safe we dropped back to 32 degrees total advance.

So, on some engines you may gain something by having more advance above max torque rpm. Mine liked it. But this is something that you simply can´t achieve with mechanical distributor with weights and springs.

[GDCobra]

Of course vac advance or retard must not be all that relevant to a dizzy system as the mechanical system is because some cars do not even have vacuum advance or retard. My 24v 3.5 RV8 in my 101 does not have vac advance and neither does my Haflinger - neither has it so must not be all that important.

I think the other reason many people tend not to run vac' advance is because they see race engines not using it and think it must be better without stoping to think that a road engine has to work in a much broader range of conditions. Of course it also means it must be 'cooler' which may be even more important.

My RV8 and Haflinger are not race engines and not modified - they are as built by the manufacturer ie the manufacturer decided they did not need vacuum advance and the RV8 in the Land Rover pulls like a train from idle with plenty of torque.

I guess we have to be careful to separate 'need' from 'want' (or nice to have). Arguably you could run the engine without any variation in advance at all, just a constant advance value (in fact on a previous thread someone mentioned that they could run their EDIS based system at a constant 10° and it ran just fine), for whatever reason whoever built/manufactured your engines decided to omit load based advance, presumably this was done on a cost vs benefit basis. Does that mean that there is not benefit to be had, for most engines the answer seems to be 'no' but there may be something specific about your engines that would result in only a limited benefit, difficult to say without any background.

Worth bearing in mind that the load based advance will have limited effect on the pulling like a train capability as this would indicate using a lot of throttle opening hence vacuum advance being removed anyhow.

As I say I think the initial focus should be on getting the RPM based advance sorted for WoT (and simlar) conditions then adding the vacuum advance for a bit of finesse at part throttle and idle.
The idle condition is particularly important to me as lower underbonnet temp's are very nice to have.

[GDCobra]

I had a 4.6 engine with Merlin heads that I ran with wasted spark ignition. CR around 10.5:1 and healthy hydraulic cam. Total advance ignition was 30 degrees, that is what the engine was happy with. On rollers the power peaked at about 5600-5700 rpm and then started decreasing. Just for fun, we put another 2 degrees advance above max torque rpm and gained quite a lot. The power curve stayed flat all the way to about 6200 rpm. Advancing another 1 degree to 33 degrees gained nothing but did not loose anything either. But to be safe we dropped back to 32 degrees total advance.

So, on some engines you may gain something by having more advance above max torque rpm. Mine liked it. But this is something that you simply can´t achieve with mechanical distributor with weights and springs.

Another engine which makes me jealous! Would love that in my car.
Interesting information though and does indicate that at least some engines benefit from a little more advace and the RPMs continue to rise and every little helps.

[garrycol]

Arguably you could run the engine without any variation in advance at all, just a constant advance value (in fact on a previous thread someone mentioned that they could run their EDIS based system at a constant 10° and it ran just fine), for whatever reason whoever built/manufactured your engines decided to omit load based advance, presumably this was done on a cost vs benefit basis.

That was me - but is a different engine to the 24v 3.5RV8. I have a 4.6 in now only got to the stage of having the ignition running on edis - yes runs fine on fixed 10° when driving around but I have not pushed it to higher revs where it no doubt will make less power than it should.

As I indicated before the lack of vacuum advance on the two engines I mentioned are not modified engines - they are as built by Land Rover and Styer Puch. My point is to simply highlight that vacuum advance is not necessarily all that important as some manufacturers do not have vacuum advance as designed.

Cheers

Garry

[DaveEFI]

I have the BL manual for my SD1. It gives advance curves for all the variants. And that alters between 3500 carb, 3500 injection, and TP. So would guess any alteration to CR, flow etc, is going to need a different optimal curve. But setting for max power etc is one of the easier things to do on a rolling road.

If you can find the maker's advance details, it's not difficult to draw the graph on your computer, and translate that into figures to create a starting map for a programmable ignition system. At least that base map should be safe, unlike some you'll find online.

I, too, have EDIS driven by an MS2. If you disable SAW, the performance suffers noticeably - as does the MPG.

If you already have an injection RV8 and are considering a mapped ignition system, I'd think of the future. Going for an ignition only system like MegaJolt will be fine - but using an MS etc in ignition only mode would reduce the amount of wiring etc if you later decide to do fuel too.

[DEVONMAN]

[
Dave EFi wrote.
If you already have an injection RV8 and are considering a mapped ignition system, I'd think of the future. Going for an ignition only system like MegaJolt will be fine - but using an MS etc in ignition only mode would reduce the amount of wiring etc if you later decide to do fuel too.
[/quote]
I agree that's probably a good plan, but in my case I progressed from Holley Carb with dizzy to Holley TBI with dizzy and now use Megajolt/EDIS8 with the Holley TBI. This set up also has a 4 channel MSD box in circuit to give a massive spark.
For the next build I will probably go MS or maybe a self learning TBI.

[DaveEFI]

Not quite clear what you mean? You're using EDIS and also a 4 channel MSD box? Can you describe it?

[DEVONMAN]

Not quite clear what you mean? You're using EDIS and also a 4 channel MSD box? Can you describe it?

The 4 outputs from the EDIS8 go into the MSD DIS-4 box which sends 4 stronger signal to the coilpacks. The MSD version of the normal Ford coils can be used to further enhance the spark and allow much larger plug gaps to be used. The MSD box sends a high voltage (300v-400v)to the coil primaries.

[DaveEFI]

Interesting - never heard of that before. Any real difference in practice? I'm already running 0.035 with EDIS. Last time I checked. One disadvantage with EDIS is it decides the dwell for the coils. Which according to the MS boys is important. The ability to set it for best results. I've got LS1 coils waiting to be fitted along with an MS3 and full sequential. When I get round to it.

[stevieturbo]

MSD stuff isn't the most reliable.

I've had a few of their boxes fail over the years.

Although with modern coils....a lot of that stuff is pretty much defunct although a lot still like to use it. Most decent modern coils will have no problems at all with say 2-300hp per litre.

That said, if it's a single coil and dizzy.....given the reduced time available for charging and between cycles.....using all the tricks you can to add ooomph to the coil can help.

With coil per cylinder, there's a lot of time available.

[DEVONMAN]

Interesting - never heard of that before. Any real difference in practice? I'm already running 0.035 with EDIS. Last time I checked. One disadvantage with EDIS is it decides the dwell for the coils. Which according to the MS boys is important. The ability to set it for best results. I've got LS1 coils waiting to be fitted along with an MS3 and full sequential. When I get round to it.

Good luck with the fully sequential project. It would be too much of a change for me given that I am set up for TBI.

[DEVONMAN]

MSD stuff isn't the most reliable.

I've had a few of their boxes fail over the years.
(quote.)


Agreed. Consequently I have a plug in loop cable to bypass the msd if necessary.