SVA turbo timing?
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John S.
- Posts: 750
- Joined: Tue May 01, 2007 10:37 pm
SVA turbo timing?
Am I over or under thinking this? It seems simple that I could use a single vacuum advance distributor with the mechanical advance limited to 25 degrees. The vacuum advance would aid drivability and advance to factory settings, past 25. Then when it matters, the vacuum would drop and only mechanical advance would be applied????
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Buggsy
- Posts: 1457
- Joined: Tue Jan 01, 2002 12:01 am
Re: SVA turbo timing?
Yes, your thoughts are correct. Just make sure of two things. Use ported vacuum, not manifold vacuum. If you don't know the difference, look it up somewhere. Also, make sure you have no vacuum to the distributor at idle, or it will defeat the purpose of having a SVA. I don't know what carburetor you are using, but you may have to drill a couple tiny holes in the throttle plates to achieve this.
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Buggsy
- Posts: 1457
- Joined: Tue Jan 01, 2002 12:01 am
Re: SVA turbo timing?
I've been running this set-up since 2001 with my turbo and it works perfect. Follow these directions step by step and you will love results, and the DVDA or SVDA costs about thirty bucks.
1. Set the timing where the car idles the smoothest with no vacuum hoses connected. Spend some time going back and forth with the carb adjustments and timing until it idles great. Don't use a timing light until your done, and then check it for future reference. You'll be somewhere between 10 and 16 btdc, and it will vary depending on your dynamic compression.
2. Limit your centrifugal advance. Bend tabs, put in a stop, whatever. Guys do it different ways. The more initial advance your using, the more you'll need to limit centrifugal advance. You want to end up with 24 degrees total when revved up in the driveway. Sorry, but you'll have to take your distributor in and out several times, and take the distributor apart several times to get it just right.
3. Hook up the outer vacuum nipple , DVDA, or the only vacuum nipple, SVDA, to ported vacuum. Ported vacuum and manifold vacuum are not the same thing, so do some research so you know the difference. If your kind of carb does not have ported vacuum, do something else, because ported vacuum is what makes all the difference. Use a vacuum can for multi-throttle plate carbs. This is just a canister with two nipples and a pin hole size opening in one of the nipples. This will smooth out the pulses to the vacuum diaphram on the distributor. Ported vacuum will provide an additional 8-12 degrees advance. So at light throttle openings, you'll have, hopefully, 36 degrees total advance, which is great for mileage and drivability. If you can find a distributor with more vacuum can movement than 12, use it.
4. Under boost, ported vacuum goes away as soon as you open the throttle all the way, and you end up back at 24 total advance, which is where most agree you want to be. So it doesn't retard per say, it just looses part of the advance under boost.
5. Pitch the points and install a Pertronix or similar. Pitch the blue coil and by any quality hot rod coil and a matching coil ballast resistor if the ignition unit calls for it.
1. Set the timing where the car idles the smoothest with no vacuum hoses connected. Spend some time going back and forth with the carb adjustments and timing until it idles great. Don't use a timing light until your done, and then check it for future reference. You'll be somewhere between 10 and 16 btdc, and it will vary depending on your dynamic compression.
2. Limit your centrifugal advance. Bend tabs, put in a stop, whatever. Guys do it different ways. The more initial advance your using, the more you'll need to limit centrifugal advance. You want to end up with 24 degrees total when revved up in the driveway. Sorry, but you'll have to take your distributor in and out several times, and take the distributor apart several times to get it just right.
3. Hook up the outer vacuum nipple , DVDA, or the only vacuum nipple, SVDA, to ported vacuum. Ported vacuum and manifold vacuum are not the same thing, so do some research so you know the difference. If your kind of carb does not have ported vacuum, do something else, because ported vacuum is what makes all the difference. Use a vacuum can for multi-throttle plate carbs. This is just a canister with two nipples and a pin hole size opening in one of the nipples. This will smooth out the pulses to the vacuum diaphram on the distributor. Ported vacuum will provide an additional 8-12 degrees advance. So at light throttle openings, you'll have, hopefully, 36 degrees total advance, which is great for mileage and drivability. If you can find a distributor with more vacuum can movement than 12, use it.
4. Under boost, ported vacuum goes away as soon as you open the throttle all the way, and you end up back at 24 total advance, which is where most agree you want to be. So it doesn't retard per say, it just looses part of the advance under boost.
5. Pitch the points and install a Pertronix or similar. Pitch the blue coil and by any quality hot rod coil and a matching coil ballast resistor if the ignition unit calls for it.
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John S.
- Posts: 750
- Joined: Tue May 01, 2007 10:37 pm
Re: SVA turbo timing?
Thanks, I currently have a 6al, pertonix coil and a limited advance 009. But, a flat spot with the single drla.
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BFB
- Posts: 5
- Joined: Sat Aug 06, 2022 3:24 pm
Re: SVA turbo timing?
This also depends on whether its draw or blow through, if its draw through then you cant use any of the carbs vacuum ports whether manifold or ported. Also manifold vacuum does work very well for this set up as you can get away without limiting the dizzy. Say if your dizzy has 25° of mechanical advance and 12° of vacuum advance , if you set initial timing to 10° and have manifold vacuum youll have 22° at idle. But if you set initial timing to 0° , use manifold vacuum then youll have 12° at idle and a total of 25° at WOT, doesnt matter whether you have 0 vacuum or 10lbs of boost in the manifold because the vacuum pot doesn’t register positive pressure, unless its a DVDA.
Or run -2° initial timing and with manifold vacuum youd have 10° at idle and 23° at WOT.
Only issue with this way is that when you crack open the throttle your vacuum drops and you have a similar stumble to if you run an 009.
Far as manifold vs ported, theres nothing wrong with 20° of timing at idle matter of fact the more duration you run the more timing it calls for, same if you have larger ( hemi type ) chambers. And originally vehicles went from manifold to ported for emissions reasons not because manifold vacuum didnt work.
If i set one up like this I’ll run manifold vacuum and limit the dizzy, done this way you do have higher initial timing but it doesnt have the 009 stumble , and its limited under boost.
Also, if you pop the metal window out of the dizzy you can bend the tabs without removing the distributor which lets you make adjustments and check with a timing light. Hard part is getting the metal tab to stay back in the dizzy after your done.
Or run -2° initial timing and with manifold vacuum youd have 10° at idle and 23° at WOT.
Only issue with this way is that when you crack open the throttle your vacuum drops and you have a similar stumble to if you run an 009.
Far as manifold vs ported, theres nothing wrong with 20° of timing at idle matter of fact the more duration you run the more timing it calls for, same if you have larger ( hemi type ) chambers. And originally vehicles went from manifold to ported for emissions reasons not because manifold vacuum didnt work.
If i set one up like this I’ll run manifold vacuum and limit the dizzy, done this way you do have higher initial timing but it doesnt have the 009 stumble , and its limited under boost.
Also, if you pop the metal window out of the dizzy you can bend the tabs without removing the distributor which lets you make adjustments and check with a timing light. Hard part is getting the metal tab to stay back in the dizzy after your done.