Distributor and Ignition timing on twin 40s

Could someone tell me the type of distributor and Ignition timing to have with twin 40's on 1.8 8v DX engine.

Also what are you doing with the vacuum outlet?

We've always used the original distributor. Timing will need to be set during the tuning process.

If you're talking about the vacuum feed to the distributor then I've always blocked it off and left the ignition and timing set without vac advance.

Ian

borednow said

We've always used the original distributor. Timing will need to be set during the tuning process.

If you're talking about the vacuum feed to the distributor then I've always blocked it off and left the ignition and timing set without vac advance.

Ian

Thank you Ian, how did you block it off? Been told I could use a T piece on to brake servo?

Is there any advantage or disadvantages to setting the timing without vac advance?

Erm, I think we may be at cross purposes here maybe.

From the manifold you should have a vac feed to the brake servo.

If your cars are compatible they will have vac advance take off just behind the butterfly. This is where a vac advance for a car needs to be taken from. If you try and take a vac advance from a manifold it does not really work too well as the vac isn't related to the carb.

Apparently.

To block off the vac advance on the dizzy just use some pipe and a bolt and clamp in the end of the pipe.

By setting the timing you are exactly sure what the ignition is going to do. If you rely on the vac advance you don't.

This is keeping it simple of course. If you want to get into position sensors and ecus then I can't help I'm afraid.

Ian

borednow said

Erm, I think we may be at cross purposes here maybe.

From the manifold you should have a vac feed to the brake servo.

If your cars are compatible they will have vac advance take off just behind the butterfly. This is where a vac advance for a car needs to be taken from. If you try and take a vac advance from a manifold it does not really work too well as the vac isn't related to the carb.

Apparently.

To block off the vac advance on the dizzy just use some pipe and a bolt and clamp in the end of the pipe.

By setting the timing you are exactly sure what the ignition is going to do. If you rely on the vac advance you don't.

This is keeping it simple of course. If you want to get into position sensors and ecus then I can't help I'm afraid.

Ian

AHH right under understand thank you.



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borednow said

…

If your cars are compatible they will have vac advance take off just behind the butterfly. This is where a vac advance for a car needs to be taken from. If you try and take a vac advance from a manifold it does not really work too well as the vac isn't related to the carb.

Apparently.
…

Apologies for the thread hijack, but I'm interested in this comment. I've got 1.8 GTi (DX engine) and have fitted an Audi throttle body (std mod) but it doesn't have  a vacumm take off on it (unlike the stock one). I'd read that you could instead take the vac advacne pipe off of the brake servo pipe tee'd from the line to the MFA. Your comment would suggest this isn't ideal. Keen to understand where this comes from. Is it because the vacuum is more immediate off the TB (would make sense).
I've also got a 16v WUR (that requires a full refurb) so that owuld probably benefit the same as the dizzy advance  would.

I can see where a vac take off would go on the TB - it's just not drilled through (or have the nice little pipe sticking out - but that can be recified!). If I;m going to do it, I;d rather do it before I put the engine back in.

Cheers,

J

To be honest there are a few different thoughts on the vac advance take off thingy.

BTW I have a mate who has some Dellorto twin 40's and they have a vac advance take off on the carbs. I also have a set of Dellorto twin 40's and mine don't have a vac advance take off.
Webers are even wider ranging as they were made specifically for some engines and cars and some were made for 'tuning applications' and for putting on any engines.

I used to know a lot more but my brain has emptied the info into the trash file and left me with only bits on the different carbs.

Anyhoo.

Vac Advance. Right.

The 'usual' thought process is that you need one as the original carb has one. But the vac advance on the carbs comes just in front or behind the butterfly. This way the vacuum created by the air entering the carb creates a vacuum, which is then linked to the dizzy, if using multiple 'barrels' ie twin carbs have 4 barrels then each would need a link to the dizzy. In that way you create an average vacuum signal to the dizzy. If you only go from one carb you would be relying on the carbs being perfectly balanced and acting exactly the same in all scenario's. This never happens.

If you take a feed from the manifold then it's a lot different to the actual carb created vacuum. There's a lot more volume and to create the vacuum takes longer and it's different to the one created by the carbs.

I have a derby which is the standard 1272cc engine, with an exhaust/manifold and Dellorto twin 40's.
I have mk1 golf with 1400cc twin cam polo engine with bike carbs on it.
Brother in Law has a cabby with the 1800cc with some cam mods and other bits and bobs running Weber twin 40's.
Mate has a 2000cc pinto in a kit car with twin 40 dellorto's.

In the case of each one we have all put the vac advance onto the manifolds and when they have gone for tuning the first thing the tuner have done is remove the vac advance and block it off.

We have also all used different tuners and rolling roads due to time/distance and in my case 'can't be bothered to drive all that way' .

I was always told it wasn't needed as the timing  can be set for the power band.

That being said I have another mate who swears his 1400cc twin cam needed the vac advance and has never had any trouble with it.

So use it or don't.

If you are going to use it then I'd suggest drilling and tapping an extra feed into the manifold as this is what is usually done. I'd suggest not tapping into the brake feed. In case of leaks for one and secondly when the vacuum is building or being used in the brake booster you ignition timing will be all over the place I would think.

Most manifolds can be drilled and then tapped for a vac feed to the ignition without too much trouble.

Please note here chaps, I am NOT an expert!!!!!!!!
My knowledge comes from doing it and talking to tuners and old skool mechanics.

When it comes to throttle bodies etc I have no clue at all, not been there or done that. But I suppose the ideas still stand? Perhaps a throttle position sensor may be needed along with a 'no diz' set up?

Good Luck

Ian

yes you can run the vacuum from the brake servo hose on your car, this is where it goes to on lots of other MK1/2 golf no problem.

the reason you can have trouble doing this on a car running twin carbs is the brake servo hose will only be connected to one cylinder, rather than to all 4 cylinders together as it is on a standard engine as said above in lots more detail. some have worked round it by plumbing the servo connection to all 4 inlets. but yeah, not something you need to worry about as you're running a standard inlet

Thanks for the insight chaps! Didn't really fancy taking a drill to the throttle body (even thought the hole is 50% there).