Trying to set timing!

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paulsv8manta
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Trying to set timing!

Post by paulsv8manta »

Hi guys, this is doing my head in!
I’m trying to get the engine running somewhere near perfect.
The engine is a 3.5 flapper EFI with ported heads and a 3.9 cam with a 4CU ECU.
Looking at my bottom pulley clockwise, I have 5 marks which I presume is ATDC then a Larger mark which must be TDC then 5 more marks which again I presume is BTDC. That’s it nothing else is stamped on the pulley, I don’t know what value each of these marks are (in degrees).
I have a timing light but what good that is I’m not sure because if I set the light up to the first or second dash on the pulley (BTDC side) engine is running rough as hell and the vacuum gauge which is reading manifold vacuum is like 10”
(ATDC) (TDC) (BTDC) (Presumed)
ꞁ ꞁ ꞁ ꞁ ꞁ │ ꞁ ꞁ ꞁ ꞁ ꞁ
So I’m going by ear, the further I go moving the light to the right the sweeter the engine is running, the rev’s increases to a certain point then I back off, the vacuum is now reading 15” and its rock steady. There’s no way I can hear the engine pinking as the exhaust is to loud!

Currently the timing light is flashing on the first mark (BTDC end) it could go further but it’d be off the scale.

Currently I’m running the engine in, so far I’ve covered 250 miles with the rev’s limited to 2500 rpm with the aim of increasing rev’s by 500 rpm every 500 miles, I’ve heard that’s a good method.
So I’m running scared not knowing if the engine is happy or not.

I'd appreciate any feed back. Thanks.



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Re: Trying to set timing!

Post by DaveEFI »

Easy to make a timing strip on your computer and print it out, then glue to the vibration damper. To give you a scale in degrees. But on my SD1 EFI, it is already marked in degrees.
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Re: Trying to set timing!

Post by sidecar »

Some sort of degree tape on the damper is always a good idea but you have to ensure that the TDC mark really is at TDC. The pointer can be out by several degrees. A piston stop and some maths and patience is required to get the tape setup correctly.

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Re: Trying to set timing!

Post by ChrisJC »

As long as it's not pinking, I wouldn't worry.
I never bothered with the timing marks as you couldn't see them through the rats nest of belts.
I just adjusted the timing until it didn't pink. Never had any issues.

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paulsv8manta
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Re: Trying to set timing!

Post by paulsv8manta »

Hi guys thanks for the input, I've checked top dead center and the pointer does match up with the center line on the pulley. What I don't know is what value each of those marks are is it 2,3 or 4 degrees per dash?
What I also don't understand is how do you set the timing on the engine? Surely the timing light will only tell you what the engine is set at - how many degrees its at. If the manual tells me to set it at 2 degrees BTDC yeah I understand you can use the timing light, but if the engine sounds like a bag of nails at this setting are you going to use your ears to get it sounding better by increasing advance which is what I have done, or is there another way?

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Re: Trying to set timing!

Post by sidecar »

The marks are 2 degrees apart, If the manual states 2 degrees BTDC that will be with the vac canister disconnected, it will idle like a bag of spanners when running with this figure so I suspect that the vac canister will add around another 12 degrees as soon as you plug it back in, i.e. its not connected to a 'timed' port. The vac system will push the timing figure at idle up to around 14 degrees, it will run pretty well with this setting. The all-in figure will be around 36 degrees, in at around 3000-4000 RPM when the vac system is disconnected. At High RPM when the bob weights are all in and with the vac system adding its figure the total timing could go up to around 48 degrees BTDC. As soon as the vacuum level drops when you floor the throttle the timing would back off to 36 degrees.


Advancing the timing until it pinks then backing it off is a really bad way of setting the timing, its all to do with when the peak cylinder pressure occurs (after the plug fires), peak pressure needs to occur at 14-20 degrees ADTC on the power stroke, the likes of Ricardo Engine Development worked this out years ago, if the timing is set too advanced but not so advance that that the engine pinks peak pressure might occur at say 8 degrees ATDC, in this case the con-rod and crank are not at the best angle to convert the pressure into torque. In the example I have just described someone might advance the timing another 2 degrees and then the engine pinks, they back the timing off 2 degrees and then they think they have found the optimum timing figure, they haven't because the timing is still too advance, its just not so advanced that it is pushing the engine into detonation.

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Re: Trying to set timing!

Post by gd302 »

You can mark them yourself with some white paint, just mark some key points such as tdc and 10 btdc etc, no need to do them all. I’m guessing you will end up somewhere around 12 btdc.
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Re: Trying to set timing!

Post by DEVONMAN »

sidecar wrote:
Thu Nov 15, 2018 9:04 pm
i.e. its not connected to a 'timed' port.
Maybe I'm wrong but I thought the vacuum can on a flapper distributor normally uses a timed port.
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Re: Trying to set timing!

Post by paulsv8manta »

Hi Sidecar,
Thanks for your advice, So had another look at the timing today, and set the timing to 14 BTDC with the vac disconnected and adjusted the tick over by the idle adjustment screw on the plenum to 700 rpm, the adjustment screw is almost screwed right in albeit a ¼ of a turn.
It feels a bit better; the only little hitch is after driving it, the tick over went up to 1100 rpm not sure what the reason for this would be.
Just realised reading your post I should of set the timing to 2 degrees then reconnect the vac hose!”
Rechecked the timing with the vac hose connected and it had only increased by 2 degrees to 16 BTDC at tick over. The vac unit is brand new and I had cleaned and oiled the dizzy (35DLM8) internals a couple of months back.

(If the manual states 2 degrees BTDC that will be with the vac canister disconnected, it will idle like a bag of spanners when running with this figure so I suspect that the vac canister will add around another 12 degrees as soon as you plug it back in, i.e. it’s not connected to a 'timed' port.)

Sorry I’m not sure what you mean by a “timed port” are we talking where the vacuum hose take off is e.g. ported vacuum or manifold vacuum?
Regards
Paul

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Re: Trying to set timing!

Post by DaveEFI »

The vacuum port from the dizzy is positioned so that with the throttle closed it sees the intake side of the throttle so little vacuum. Open the throttle and it sees engine side. If it saw engine side at idle vacuum would be high, so it would go to maximum advance.

On my SD1 EFI, idle timing is 8 BTDC. With a dizzy, if you change the idle setting, you'll also change the maximum advance figure. Which might result in detonation.
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Re: Trying to set timing!

Post by sidecar »

I don't know the setup of Rovers EFI system and how it relates to the ignition timing, really Edelbrock 4 barrel carbs are my 'thing'.

If your timing is only advancing 2 degrees when you connect the vac pipe then I would say that the port that you are connecting the pipe to is not really seeing any significant vacuum whilst your engine is at idle, in other words you are connecting the pipe to a timed port. (Or it is a non-timed port and there is something wrong with your vac advance system). You can check that the vac system is working by removing the distributor cap and sucking on the pipe that is connected to the canister, you should see the base plate inside the dizzy move, it should spring back when you remove release the vacuum but it should not creep back if you maintain the vacuum in the pipe.


I have read that the whole idea behind 'timed' ports was to keep the ignition in a retarded state whilst the egine is at idle, the retard timing reduces NOx levels in the exhaust but the engine is not running as effeciently as is could if it had more ignition timing. With the timed port the idea is that when you place a small load on the engine the port is exposed to manifold vacuum which advances the ignition system so that the engine is running with the timing that it really requires, if the engine is placed under a large load the vac system backs off the 'extra' advance the it has added to the timing. A non-timed port is subject to manifold vacuum even when the engine is idling.

If your vac system is not adding timing at idle then there is no way that the timing should be set to 2 degrees, the tickover would be very rough!

Like DaveEFI say's the idle timing is one thing but the total timing must also be taken into account, really I am suprised that knowbody can give you the standard timing figures for your engine.

My engine is far from standard (4.6), I run around 30 degree at idle which is quite a lot but my engine has 'told' me that this is what it wants! 14 degrees of the 30 degrees is supplied by my vac system so we can work out that my 'static' timing is actually 16 degrees. My total all-in figure is 32 degrees (when there is no manifold vacuum) but my total all-in figure can go as high as 46 degrees if the vac system adds its 14 degrees. (i.e. A high vacuum level in the manifold). My setup is far from standard and is only possible because I run a programmable MSD ignition system.

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Re: Trying to set timing!

Post by DaveEFI »

I'd guess the amount of advance you can run at idle with a mechanical dizzy is restricted by the amount of advance you can allow when cranking to prevent kickback. No such restriction with a programmable system.
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paulsv8manta
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Re: Trying to set timing!

Post by paulsv8manta »

Ok guys, sorry for the delay in getting back but the ignition module blew again! that's the second one in three months!

So, I've now set the timing at 2 degrees BTDC with the vac disconnect. When I plug the vacuum hose back in, the timing jumps to 18 degrees BTDC, and when I raise the rpm to 4000 the timing moves up to 36 degree BTDC.
Looking at the Vacuum gauge it has lost about 2 Hg and its rock steady at this setting and the engine seem ok.
When started from cold the tick over is 1200 rpm and drops to around 800 when warm, I've had to wind in the air bypass screw all the way closed to get the rpm down to around this figure, it still seems a little fast.
Thank again guys :)

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Re: Trying to set timing!

Post by sidecar »

Thanks for the update on your progress. the vac canister must be connected to a non-timed port which I think is good, your vac system can add 16 degrees to the timing which is reasonable.

The 36 degrees all-in figure is also reasonable as long as none of this timing advance is being added by the vac system, in other words at 4-4.5K rpm you want to see 36 degrees advance whilst the vac hose is disconnected from the vac canister. If this is the case then your bob-weights must have a sweep of (36-2) / 2 which is 17 degrees. Your total all-in could go up to 52 degrees when the engine is under very little load but at high RPM (36+16) which is also fine.


So to sum up,

Your static timing is 2 degrees
Your vac system can add 16 degrees
Your idle timing with the vac system connected is 18 degrees
Your bob-weights have a sweep of 17 degrees at the dizzy, 34 at the crank
Your all-in at low vac levels (WOT) is 36 degrees
You all-in at high vac levels is 52 degrees

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Re: Trying to set timing!

Post by SuperV8 »

paulsv8manta wrote:
Sun Nov 25, 2018 8:17 pm

When started from cold the tick over is 1200 rpm and drops to around 800 when warm, I've had to wind in the air bypass screw all the way closed to get the rpm down to around this figure, it still seems a little fast.
Thank again guys :)
Have you removed the water jacket plate under the throttle plate part of the plenum? I did and had trouble get the idle low enough - only to find one of the 4 holes used bolt this small ali plate had broken through to the inlet so a simple bolt filled up this hole and enabled correct idle speed.
Also have you set the throttle plate gap with feeler gauge?
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