I haven't seen this information anywhere on the net so thought I'd post my findings. I tee'd a vacuum gauge between the carb and distributor to see what vacuum you get under different driving conditions. Engine is a Scat 1776cc with standard head and C25 cam. Carbs are Kardrons tapped for vacuum signal. Dissy is a new 034 SVDA.
Constant <2800rpm - 0"HG
Constant 2800rpm - 5"HG
Constant 3500rpm - 7"HG
Constant 4000rpm - 9"HG
Initial acceleration - 5"HG for about 1 second then 0"HG
Constant accleration - 0"HG
Decceleration - 0"HG
All on dead flat straight road. Any whiff of throttle above what it takes to hold a constant speed will change all this and reduce the vaccum. So if you want to take advantage of the vacuum advance for fuel economy you need a rock steady right foot.
Kadron Vacuum
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Max Welton
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Re: Kadron Vacuum
Out of curiosity, how much advance does your distributor add for 5 " of vacuum?
Max
Max
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Spydaman
- Posts: 16
- Joined: Sat Feb 08, 2003 12:01 am
Re: Kadron Vacuum
Not sure yet. That's this evenings job to measure advance versus vacuum. I've seen it quoted here http://www2.cip1.com/ProductDetails.asp ... 905-205-ZB but this isn't where my dissy came from so want to double check.
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Marc
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Re: Kadron Vacuum
It's supposed to take about 8" of vacuum to get 5° of advance out of an SVDA - and they're capable of up to 12°, so you won't see the full benefit without a ported vacuum source that can provide about 15" at high RPM/light load.
The centrifugal component of the SVDA's curve provides 22-25°, about the same as the all-centrifugal 0 231 178 009 but with an important distinction - while the 009's advance is "all in" by ~2500 RPM, the SVDA comes in slower, peaking at ~3800.
Therefore, if your gearing puts your cruising RPM at ~31-3300 (typical with stockish tire height) and there's only 6" of vacuum, the total advance is about 20° more than the initial setting - under these conditions, the much-maligned 009 will actually yield more advance than the SVDA.
I used to do a consistent daily commute of about 20 miles each way, about half of which was highway speed and the rest on surface streets. With a stock 1600 and gearing for 3000RPM @60MPH, I found no discernible difference in mileage or operating temperature when I switched back and forth between an SVDA and an 009 - the H30/31PICT carb I was running just couldn't pull enough vacuum to get full advance out of the SVDA until nearly 4500 RPM. But on my trike I'm usually at or above 3500 RPM on the highway and have a legit 34PICT-3, so the SVDA's worth having.
The centrifugal component of the SVDA's curve provides 22-25°, about the same as the all-centrifugal 0 231 178 009 but with an important distinction - while the 009's advance is "all in" by ~2500 RPM, the SVDA comes in slower, peaking at ~3800.
Therefore, if your gearing puts your cruising RPM at ~31-3300 (typical with stockish tire height) and there's only 6" of vacuum, the total advance is about 20° more than the initial setting - under these conditions, the much-maligned 009 will actually yield more advance than the SVDA.
I used to do a consistent daily commute of about 20 miles each way, about half of which was highway speed and the rest on surface streets. With a stock 1600 and gearing for 3000RPM @60MPH, I found no discernible difference in mileage or operating temperature when I switched back and forth between an SVDA and an 009 - the H30/31PICT carb I was running just couldn't pull enough vacuum to get full advance out of the SVDA until nearly 4500 RPM. But on my trike I'm usually at or above 3500 RPM on the highway and have a legit 34PICT-3, so the SVDA's worth having.
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FJCamper
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Re: Kadron Vacuum
Hi Spydaman,
Good info. It is important to me because I had been planning a simple water induction system for dual Kads using their vac ports.
Jeff Lain at KaddieShack and I talked this over, and he was generally aware of the vac fluctuations you've mapped out precisely, and I decided to use pressured and metered water injection through the ports rather than straight vac pickup.
However, I'm not posting about water injection, I'm posting about the value of the SVDA vs the 009. It still comes down to "it depends." The best we can advise our VW friends is the SVDA/Kad combo is better in the overall than the 009/Kad combo. The cam is a big variable. As a matter of fact, too much of our recommendations and criticisms of our parts and experience is actually guided by one or more unseen variables, and we argue with each other about it!
FJC
Good info. It is important to me because I had been planning a simple water induction system for dual Kads using their vac ports.
Jeff Lain at KaddieShack and I talked this over, and he was generally aware of the vac fluctuations you've mapped out precisely, and I decided to use pressured and metered water injection through the ports rather than straight vac pickup.
However, I'm not posting about water injection, I'm posting about the value of the SVDA vs the 009. It still comes down to "it depends." The best we can advise our VW friends is the SVDA/Kad combo is better in the overall than the 009/Kad combo. The cam is a big variable. As a matter of fact, too much of our recommendations and criticisms of our parts and experience is actually guided by one or more unseen variables, and we argue with each other about it!
FJC