20b In A Glc
Senior Member
Joined: Sep 2002
Posts: 5,542
From: Vanderhoof,BC(Canada)
Originally Posted by Jeff20B' date='Dec 8 2003, 05:16 PM
I finally have time to set up the camera today. I'll take some pics in a few minutes.
I spoke with Gary at Atkins and he said the idea to use their 20B manifold in NA form with a carb on top won't work very well.
I spoke with Gary at Atkins and he said the idea to use their 20B manifold in NA form with a carb on top won't work very well.
Thread Starter
Senior Member
Joined: Nov 2001
Posts: 2,284
It's because the carb would be in the middle and the front and rear rotors would tend to run lean. The aluminum tube idea would work better.
Heh, I don't know if I'm just tired or what, but the picture of the SC manifold on the 20B in the plane seems like it would work ok with a carb on it. Then again, that 20B had a turbo on it, so the AF mixture was being pushed into the ports because the inside of the manifold is always under pressure (to some extent). I think that's how they were able to get away with it. Also, the injectors are at the very top of the tubes, giving the AF mixture a really long set of runners before it enters the manifold. Mine would be lucky to fit a carb spacer of up to 5" tall. It would be sorta large inside too. Can you say low velocity? Would it even be a problem? Maybe.
Imagine a carb square bore funneling down to a rectanglular hole 7" by 2 5/8". Gary said I'd have better luck with injectors in their stock holes (primaries) with a throttle body. Get this; whether it's supercharged or not, it doesn't matter. Infact, the engine could be run on just the primary injectors with a supercharger. I think the injectors would need to be larger than 550CFM, but it's not too hard to get larger ones. The reasoning is that the AF mixture gets heated as it gets compressed in the manifold. If the fuel could be injected below the SC's rotors, it would have a cooling effect in the manifold. Gary mentioned other benefits, but I don't remember them right now.
Anyway, I then mentioned the aluminum tube idea, and he said it would work better than their manifold for preventing as bad of a lean condition. He even recommended a place nearby that could do the work to the LIM. It means a lost sale for his supercharger bussiness. He also said I should install an O2 sensor. I'd better install one now (or atleast the bung) so I won't have to later.
I can't think of anything else, so here is the pic of the 20B in the plane with the long intake runners.
Heh, I don't know if I'm just tired or what, but the picture of the SC manifold on the 20B in the plane seems like it would work ok with a carb on it. Then again, that 20B had a turbo on it, so the AF mixture was being pushed into the ports because the inside of the manifold is always under pressure (to some extent). I think that's how they were able to get away with it. Also, the injectors are at the very top of the tubes, giving the AF mixture a really long set of runners before it enters the manifold. Mine would be lucky to fit a carb spacer of up to 5" tall. It would be sorta large inside too. Can you say low velocity? Would it even be a problem? Maybe.
Imagine a carb square bore funneling down to a rectanglular hole 7" by 2 5/8". Gary said I'd have better luck with injectors in their stock holes (primaries) with a throttle body. Get this; whether it's supercharged or not, it doesn't matter. Infact, the engine could be run on just the primary injectors with a supercharger. I think the injectors would need to be larger than 550CFM, but it's not too hard to get larger ones. The reasoning is that the AF mixture gets heated as it gets compressed in the manifold. If the fuel could be injected below the SC's rotors, it would have a cooling effect in the manifold. Gary mentioned other benefits, but I don't remember them right now.
Anyway, I then mentioned the aluminum tube idea, and he said it would work better than their manifold for preventing as bad of a lean condition. He even recommended a place nearby that could do the work to the LIM. It means a lost sale for his supercharger bussiness. He also said I should install an O2 sensor. I'd better install one now (or atleast the bung) so I won't have to later.
I can't think of anything else, so here is the pic of the 20B in the plane with the long intake runners.
Thread Starter
Senior Member
Joined: Nov 2001
Posts: 2,284
Pics are coming tomorrow. I snapped a bunch and I'll upload them in the morning. 
I posted this on the other forum, but I'm going to post it here too for more coverage (with some added text).
This manifold stuff is still on my mind. The info I found out from my conversation with Gary today has had a chance to sink in.
Ok, the way I see it, I have two main choices right now. The first choice is to use an Atkins 9" supercharger intake manifold (no SC at this time due to lack of funds). The other choice is to modify my stock 20B LIM.
The Atkins manifold:
I could build a carb spacer to mate the carb to the manifold. The manifold opening is 7" long by 2 5/8" wide. The carb square bore is 3 9/16" by 3 5/8" (essentially a square).
Do you guys think I'd have a lean-running condition in the front and rear rotors if I were to build a square-to-rectangle carb spacer at least 6" tall? The height of the spacer will mimick the height of the supercharger. Maybe it would work better if I added a flow director/deflector inside to help guide the AF mixture fore and aft a little better. Thoughts?
Modified LIM:
I'd find an aluminum pipe anywhere from 3" to 4" diameter by around 14" long. Then I'd slice it lengthwise, cut six holes lengthwise in one piece, shorten the LIM, weld the piece with the six holes to the LIM and clean up the runners a bit, then weld the other piece back on with a carb adaptor on top. Two end caps, and it's done.
This idea has an open plenum beneath the carb, with stock (shortened) runners leading into the ports. Is this idea any better than the other one for preventing a lean running condition? Mind you, the carb will have less area beneath it for the AF mixture to sort of 'spread out' than with the SC manifold.
I obviously know very little about intake manifold theory and design, so building my own from scratch is not an option. Please give me your input. Thanks.
I posted this on the other forum, but I'm going to post it here too for more coverage (with some added text).
This manifold stuff is still on my mind. The info I found out from my conversation with Gary today has had a chance to sink in.
Ok, the way I see it, I have two main choices right now. The first choice is to use an Atkins 9" supercharger intake manifold (no SC at this time due to lack of funds). The other choice is to modify my stock 20B LIM.
The Atkins manifold:
I could build a carb spacer to mate the carb to the manifold. The manifold opening is 7" long by 2 5/8" wide. The carb square bore is 3 9/16" by 3 5/8" (essentially a square).
Do you guys think I'd have a lean-running condition in the front and rear rotors if I were to build a square-to-rectangle carb spacer at least 6" tall? The height of the spacer will mimick the height of the supercharger. Maybe it would work better if I added a flow director/deflector inside to help guide the AF mixture fore and aft a little better. Thoughts?
Modified LIM:
I'd find an aluminum pipe anywhere from 3" to 4" diameter by around 14" long. Then I'd slice it lengthwise, cut six holes lengthwise in one piece, shorten the LIM, weld the piece with the six holes to the LIM and clean up the runners a bit, then weld the other piece back on with a carb adaptor on top. Two end caps, and it's done.
This idea has an open plenum beneath the carb, with stock (shortened) runners leading into the ports. Is this idea any better than the other one for preventing a lean running condition? Mind you, the carb will have less area beneath it for the AF mixture to sort of 'spread out' than with the SC manifold.
I obviously know very little about intake manifold theory and design, so building my own from scratch is not an option. Please give me your input. Thanks.
