3.9 timing

CastleMGBV8 · Post by **CastleMGBV8** » Sat May 23, 2009 2:46 pm

No instructions? if not try down loadat

http://www.loco4fomoco.com/MalloryAdvanceCurveKit.pdf

Kevin.

bones · Post by **bones** » Sat May 23, 2009 5:25 pm

the keys are for the total advance,they are used to set the total advance limit, this mallory has been set already to 24 deg, how does 2 brown springs sound or orange and grey

rich

CastleMGBV8 · Post by **CastleMGBV8** » Sat May 23, 2009 6:10 pm

Rich,

The brown would appear to bring total advance in a little early, I would try a pair of the orange springs which would give total mechanical advance all in at 2700 RPM which is what Pete recommends.

You can set the static advance to 8-10 degrees and run the engine without vacuum advance or set it to no more than 5 deg and disconnect when racing.

Kevin.

bones · Post by **bones** » Sat May 23, 2009 8:06 pm

Hi Kevin, i run it without vacuum, so the orange springs should be ok then ,ive also got the timing set at 12deg at the moment but im going to try 14deg to see how that is,and try 10deg

rich

CastleMGBV8 · Post by **CastleMGBV8** » Sat May 23, 2009 10:08 pm

Rich,

You don't really wan't more than 34 degrees of total so 10 Static + 24 mechanical = 34 deg which is what a 3.9 should run best at.

If you look at the graph you will have 16-17 deg by 1500 RPM with the static set at 10deg.

Kevin.

bones · Post by **bones** » Sat May 23, 2009 11:39 pm

well ive put the orange ones in for know to see how it goes, will test it sunday night as im out most the day.

rich

sidecar · Post by **sidecar** » Sun May 24, 2009 4:58 am

CastleMGBV8 wrote:Rich,

You don't really wan't more than 34 degrees of total so 10 Static + 24 mechanical = 34 deg which is what a 3.9 should run best at.

If you look at the graph you will have 16-17 deg by 1500 RPM with the static set at 10deg.

Kevin.

Personally I'd run a bit more than 10 degrees static, as you wind on more advance with the engine ticking over you will hear the revs pick up, this must indicate that it 'wants' more ignition advance. You do have to be careful though, if you just used this method to find the ideal static timing is would end up at round 18-20 degrees. This is because the cylinder pressure is very low due the the carb being shut. It sends the VE down the pan. If you did run say 20 degrees when you floored the throttle the VE would go up and the timing figure would be too high. I'd go for 12-14 but you will than have to tweak the dizzy so that it only gives 22-20 mech advance, thus giving you the 34 all in at 2700-3000 RPM

Even if you do only go for 10 it is still better than the 6-8 that Rover set them up to, just not quite as good as it could be!

You can see that getting the damper pointer to point to zero at TDC is mega important!

Pete

bones · Post by **bones** » Mon May 25, 2009 1:39 pm

ok ive used the orange springs and adjusted the mechanical advance to go no higher than 22deg and static is 12deg and it seems to go ok .It still needs some little bits of tinkering ,but the test will be in june , thanks for the help and advice all,

rich

jefferybond · Post by **jefferybond** » Wed May 27, 2009 10:25 am

CastleMGBV8 wrote: You can set the static advance to 8-10 degrees and run the engine without vacuum advance or set it to no more than 5 deg and disconnect when racing.
Kevin.

Why? Vac advance has no effect at WOT (ie. racing), so why disconnect it?

I'm amazed at all the comments on this topic to forget about the vac advance. Without it, light throttle response and economy both suffer! To be fair, it will have no benefit when racing, but no downsides either.

I limit my 3.5 to 34BTDC at 3500rpm (WOT), but my vac advance can go to about 48BTDC at light throttle (using megasquirt-n-spark extra).

Jeff

sidecar · Post by **sidecar** » Wed May 27, 2009 10:59 am

jefferybond wrote:
CastleMGBV8 wrote: You can set the static advance to 8-10 degrees and run the engine without vacuum advance or set it to no more than 5 deg and disconnect when racing.
Kevin.
Why? Vac advance has no effect at WOT (ie. racing), so why disconnect it?

I'm amazed at all the comments on this topic to forget about the vac advance. Without it, light throttle response and economy both suffer! To be fair, it will have no benefit when racing, but no downsides either.

I limit my 3.5 to 34BTDC at 3500rpm (WOT), but my vac advance can go to about 48BTDC at light throttle (using megasquirt-n-spark extra).

Jeff

You may well be amazed about the comments on using no vac but the fact of the matter is that it does not work with and Eddy 500 carb!

("Bones" stated that he is using an Eddy 500 on the first page of this thread)

Well to be precise it does not work with the 500 carb unless you restrict the static advance to a really low figure which sort of defeats the whole object somewhat.

Running 48 degrees total advance may well be great but with the 500 carb (and possibly even with the SU's) the vac advance still adds too much extra timing on top of the static even when the throttle is opened and the vac in the manifold is reduced. If you are running a decent amount of static then the engine will kick back.

Rover cocked this up which is why they specify really low static figures such as 6 degrees. No engine has combustion chambers that are so good that the mixture will burn within 6 degrees of crank rotation, let alone a 50 year old design.

The tests that I've done with my old 3.5, my 4.6 and my mates, 3.5 and 3.9 showed that they all run smoother and harder with no vac, a decent amount of static and the full advance all in around 2700-3000 RPM. They all run an eddy carb.

jefferybond · Post by **jefferybond** » Wed May 27, 2009 11:23 am

sidecar wrote: You may well be amazed about the comments on using no vac but the fact of the matter is that it does not work with and Eddy 500 carb!

Well to be precise it does not work with the 500 carb unless you restrict the static advance to a really low figure which sort of defeats the whole object somewhat.

Well I am running an edelbrock 500 carb with vac advance and it's fine. I know I'm running mapped ignition now, but originally I was using the original opus 35DE8 dissy with vac advance and it really was fine.

Obviously the megasquirt improved things by allowing me to run more advance at idle, but still keep to 34BTDC at WOT, but it ran pretty good before that.

sidecar wrote:
Running 48 degrees total advance may well be great but with the 500 carb (and possibly even with the SU's) the vac advance still adds too much extra timing on top of the static even when the throttle is opened and the vac in the manifold is reduced. If you are running a decent amount of static then the engine will kick back.

Yes, running a 'decent' amount of static will be hard with a crappy mechanical distributor, but that's a shortcoming of the distributor, not a problem with the eddy 500 carb surely?

Actually, one thing you can do is keep the static timing pretty low (eg 6 BTDC), but use the NON-TIMED vac port on the carb (against everyone elses advice!). This will give a good advance at idle, but the low static setting will keep the max advance in check.

One reason they don't leave the factory like this is because it reduces the exhaust temperature, and means you might get more unburned HC out the back! Reducing the manifold temperature is probably a good thing for most of us.

Jeff

sidecar · Post by **sidecar** » Thu May 28, 2009 8:19 am

jefferybond wrote:
sidecar wrote: You may well be amazed about the comments on using no vac but the fact of the matter is that it does not work with and Eddy 500 carb!

Well to be precise it does not work with the 500 carb unless you restrict the static advance to a really low figure which sort of defeats the whole object somewhat.
Well I am running an edelbrock 500 carb with vac advance and it's fine. I know I'm running mapped ignition now, but originally I was using the original opus 35DE8 dissy with vac advance and it really was fine.

Obviously the megasquirt improved things by allowing me to run more advance at idle, but still keep to 34BTDC at WOT, but it ran pretty good before that.

sidecar wrote:
Running 48 degrees total advance may well be great but with the 500 carb (and possibly even with the SU's) the vac advance still adds too much extra timing on top of the static even when the throttle is opened and the vac in the manifold is reduced. If you are running a decent amount of static then the engine will kick back.

Yes, running a 'decent' amount of static will be hard with a crappy mechanical distributor, but that's a shortcoming of the distributor, not a problem with the eddy 500 carb surely?

Actually, one thing you can do is keep the static timing pretty low (eg 6 BTDC), but use the NON-TIMED vac port on the carb (against everyone elses advice!). This will give a good advance at idle, but the low static setting will keep the max advance in check.

One reason they don't leave the factory like this is because it reduces the exhaust temperature, and means you might get more unburned HC out the back! Reducing the manifold temperature is probably a good thing for most of us.

Jeff

I bet when you were running the lucas dizzy with vac and the eddy 500 carb you were not running much static advance and possibly stiff bob weight springs, that could be why the setup did not kick back.

It may be possible to set up the ignition and use the vac system whilst it is connected to the non-timed port but it would require quite a bit of experimenting. My vac canister added 14 degrees to the timing so the static would have to be set at 0 degrees. I don't think that the Rover lumps like much more (if any) advance than this at idle. This is fine until you floor the throttle at say 1500 RPM, the vac then disappears and so will all the advance. The bob weights may have started to add some back at 1500 RPM but I don't think it will be that much. (Infact mine would have added about 10 by then) so the total addvance might be 10 assuming that the vac canister is now adding nothing.

Like I said it might be possible to set it up this way but I've done more than enough messing about with the setup that I've got now to start all over again.

One last thing, if the vac canister springs a leak and stops working, you would be left stranded!