Honey, I Shrank the Parasitic Vacuum Connections
07-22-2003, 09:47 AM
#1
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Honey, I Shrunk the Parasitic Vacuum Connections
Over the last year, I have removed almost all the vacuum lines to the throttle body, except the brake booster, heater controls, and the cold start.
This helped mightily with snap acceleration, and maximized access to the engine verily.
The only thing left was the cold start system:
With an L-Jet system, I found you need the cold start fuel injector to start easily (it only squirts for a few seconds
), even when it's hot out (it'll start without it, but you have to crank it for a while).
However, the air bypass valve can be replaced with positive foot displacement.
Since I have a foot, and it is a finely adjustable one, all I need is this:
I had a spare rear fuel rail, so I had #4 connectors brazed on, and a Teflon hose made to length.
The rear cylinder head plugs are 16mm oil drain plugs, reusing the aluminum crush washers.
Total cost <$50.
The front vacuum connection on the plenum, normally used for the A/C idle speedup bypass, was formerly the mounting point for the cold start injector on the K-Jet systems.
I cut out a simple aluminum plate with matching gaskets to permit installation of the cold start injector.
The 1/8" thick plate covers the 3/4" hole in the plenum.
The two threaded holes in the plenum match the mounting holes on the injector.
This has no beneficial effect on performance, other than weight, and a slight electrical load removed.
But, this is art to me!
I had to turn out the idle screw a few turns, to compensate for the air that flows through the cold air bypass valve even when the engine is warmed up.
*Update*
~thread~start~
This helped mightily with snap acceleration, and maximized access to the engine verily.
The only thing left was the cold start system:
With an L-Jet system, I found you need the cold start fuel injector to start easily (it only squirts for a few seconds
), even when it's hot out (it'll start without it, but you have to crank it for a while).However, the air bypass valve can be replaced with positive foot displacement.
Since I have a foot, and it is a finely adjustable one, all I need is this:
I had a spare rear fuel rail, so I had #4 connectors brazed on, and a Teflon hose made to length.
The rear cylinder head plugs are 16mm oil drain plugs, reusing the aluminum crush washers.
Total cost <$50.
The front vacuum connection on the plenum, normally used for the A/C idle speedup bypass, was formerly the mounting point for the cold start injector on the K-Jet systems.
I cut out a simple aluminum plate with matching gaskets to permit installation of the cold start injector.
The 1/8" thick plate covers the 3/4" hole in the plenum.
The two threaded holes in the plenum match the mounting holes on the injector.
This has no beneficial effect on performance, other than weight, and a slight electrical load removed.
But, this is art to me!
I had to turn out the idle screw a few turns, to compensate for the air that flows through the cold air bypass valve even when the engine is warmed up.
*Update*
~thread~start~
Last edited by PorKen; 07-19-2004 at 11:28 PM.
07-22-2003, 09:53 AM
#2
Now you've gone and done it..... 
The boys from Weissach are on their way to Oregon right now. I'd take the car and hide
Either way, I like the thinking. Low $ HP gains through system refinement.
I hold the belief that less is more.
The boys from Weissach are on their way to Oregon right now. I'd take the car and hide
Either way, I like the thinking. Low $ HP gains through system refinement.
I hold the belief that less is more.
07-22-2003, 10:26 AM
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Yeah, I had removed all that same stuff on my 79 when I was trying to isolate vacuum leaks. I even was running without the cold start valve. Out hear in California it doesnt get cold enough to really need it. It started all the time for me. I did like running without all that vacuum stuff, however I need to have it smogged out here and was afraid of what the tester would say. I did fix all my vacuum leaks. They were mostly caused by old brittle vacuum lines that had cracked or even were broken. That did not entirely fix my problems though. The real problem was that defective green wire that came from Porsche. What a pita.
07-22-2003, 07:51 PM
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Scott C - I agree, only drag around what you need!
T_MaX - thanks again, by the way, how much am I paying you now? You need a raise.
Curt - After I bought the car (ran super rich) I replaced every hose and sensor I could (including the AFM), tuned it totally stock, then went for a voluntary emissions test (car already had tags), passed, then started taking things off! (All the testable parts can be reinstalled in a day.)
Injector install detail:
It fits, just!
T_MaX - thanks again, by the way, how much am I paying you now? You need a raise.
Curt - After I bought the car (ran super rich) I replaced every hose and sensor I could (including the AFM), tuned it totally stock, then went for a voluntary emissions test (car already had tags), passed, then started taking things off! (All the testable parts can be reinstalled in a day.)
Injector install detail:
It fits, just!
07-22-2003, 08:18 PM
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Fellow Oregonian, I salute you!
After all that I read about the L-jet, I popped the hood and thought,
"I don't think it needs all this, does it?" I am now jealous of your
vacuum system, and will begin doing the same to mine. Let me know
if it passes emissions, it just might. Mine runs lean, and produces
almost the limit of NOx, so I'm very anti-spiderweb. Cool!
After all that I read about the L-jet, I popped the hood and thought,
"I don't think it needs all this, does it?" I am now jealous of your
vacuum system, and will begin doing the same to mine. Let me know
if it passes emissions, it just might. Mine runs lean, and produces
almost the limit of NOx, so I'm very anti-spiderweb. Cool!
07-22-2003, 09:26 PM
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Wolfmaniser - Howdy!
Funny, when I had it tuned stock, I had borderline NOx too.
The biggest culprit for a large air leak is the gas tank vent system. The carbon canister (which lives above the wiper reservoir), weighs a ton, and there is huge tangle of hoses coming to and from this beast. I removed the whole lot, and vent the tank at the rear.
Removing the unnecessary vacuum lines increases the reaction of the flapper in the AFM, which richens the mix. When you accelerate the flapper overextends briefly and acts like an accelerator pump in a carb.
Note that the biggest restriction to high vacuum is, funny enough, the Vacuum Limiter! The saucer shaped dealy on the side of the TB is supposed to burp air when you let off the throttle on deceleration, to help burn any gas that has already been injected. (By '84 I think only the manual cars have the limiter) Anyway, if you remove say, the gas tank vent line, the vacuum limiter will make the idle go up and down, up and down, because you are past it's preset limit.
When I go for a retest I would have to reinstall at least:
Cat and stock exhaust
Air pump (for visual)
Reconnect O2 sensor
Retard line to distributor
PCV hose
PS: I kinda wish I had an '80, cuz then I wouldn't have to do the roller test!
Funny, when I had it tuned stock, I had borderline NOx too.
The biggest culprit for a large air leak is the gas tank vent system. The carbon canister (which lives above the wiper reservoir), weighs a ton, and there is huge tangle of hoses coming to and from this beast. I removed the whole lot, and vent the tank at the rear.
Removing the unnecessary vacuum lines increases the reaction of the flapper in the AFM, which richens the mix. When you accelerate the flapper overextends briefly and acts like an accelerator pump in a carb.
Note that the biggest restriction to high vacuum is, funny enough, the Vacuum Limiter! The saucer shaped dealy on the side of the TB is supposed to burp air when you let off the throttle on deceleration, to help burn any gas that has already been injected. (By '84 I think only the manual cars have the limiter) Anyway, if you remove say, the gas tank vent line, the vacuum limiter will make the idle go up and down, up and down, because you are past it's preset limit.
When I go for a retest I would have to reinstall at least:
Cat and stock exhaust
Air pump (for visual)
Reconnect O2 sensor
Retard line to distributor
PCV hose
PS: I kinda wish I had an '80, cuz then I wouldn't have to do the roller test!
Last edited by PorKen; 07-22-2003 at 09:47 PM.
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07-22-2003, 10:46 PM
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Porken writes >The biggest culprit for a large air leak is the gas tank vent system. The carbon canister (which lives above the wiper reservoir), weighs a ton, and there is huge tangle of hoses coming to and from this beast. I removed the whole lot, and vent the tank at the rear.
Hmmmm. I have replaced all the other hoses except the ones to the carbon canister. In looking at the vacuum diagram, it appears that there is a vacuum set up that draws excess fumes from the tank through the canister and into the air filter. What are the symptoms of a leak on the canister side? It is not at all clear how these interact with the rest of the vacuum system. Do canisters wear out? How would you know? The shop manual say exactly squat on all this.
Hmmmm. I have replaced all the other hoses except the ones to the carbon canister. In looking at the vacuum diagram, it appears that there is a vacuum set up that draws excess fumes from the tank through the canister and into the air filter. What are the symptoms of a leak on the canister side? It is not at all clear how these interact with the rest of the vacuum system. Do canisters wear out? How would you know? The shop manual say exactly squat on all this.
