varible manifold duel plane manifold to single
02-09-2003, 10:06 PM
#1
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varible manifold duel plane manifold to single
As some of you amy know im currently designing a varible cam system for a sbc. I was screwing around on desktop dyno changeing the durations adn lift as the cam would as if varible and i noticed i would gain and aditional 57 hp at 7000 rmp and 38 ft/lbs at 2000rpm by going between dual plane for low rpms to single pletum for high rpm. Do you think it is posible to accieve this by machining the plentum divider so throtle plates go into it. They would have to be vertical so they dont block the fuel and air coming from the carb. This should allow the pulses to pull from the other plentums therfore acting as a single plane. Do you think a system like this would work well? Has anyone ever though of this before or seen it?
Last edited by turb0racing; 02-10-2003 at 02:11 PM.
02-10-2003, 02:22 PM
#2
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Some thoughts:
1) Dual planes are not necessarily better than single planes for low-mid torque. Basically dual planes are used to give a stronger signal to the carb in order to mix fuel with air at part throttle. They are called 180 degree manifolds, because the cylinders that are paired fire at 180 degree intervals.
2)A properly sized single will work extremely well from low 2000 range up. Single plane manifolds tend to have more even runner lengths and shapes than dual planes. Surprisingly, many singles have longer runners than duals, and tune well. Most dual planes have different length runners for different cylinders, and very different flow characteristics because of their less than straight shapes. That's why they suffer at high rpms.
2) Look inside the plenum of a dual plane. Just opening up the wall will give you a stepped plenum with the same convoluted runners. That's not a single plane manifold by any stretch.
3) There have been dual planes with cut down plenum dividers in the past. They didn't help much.
4) If you want a NA, carbureted 350 to run well from below 2500 to power peak at 7000, and get good average hp and torque values, you are asking a lot from any one manifold. A good single plane will do the job. Of course, one with the optimum size and length runners probably isn't a shelf item.
5) There might be some merit in having a controllable door between the plenum sides; GM did just such a thing on the '93 era 4.3L V6 Vortec. A butterfly opened and closed at a couple of rpm points to change the plenum volume. Of course this was a MPFI engine.
6) I'm not sure there is a current dual plane which will flow enough air to feed a 7000 rpm power peak 350. 6000 perhaps, but a good single will still beat it.
7) If you want a dual plane to perform better, consider treating the engine as 2 V4's, and port and cam them as required to work with the manifold runners. That's not reinventing the wheel either.
8) Out of the box can be good, but understanding what goes on inside the box should come first, IMO.
1) Dual planes are not necessarily better than single planes for low-mid torque. Basically dual planes are used to give a stronger signal to the carb in order to mix fuel with air at part throttle. They are called 180 degree manifolds, because the cylinders that are paired fire at 180 degree intervals.
2)A properly sized single will work extremely well from low 2000 range up. Single plane manifolds tend to have more even runner lengths and shapes than dual planes. Surprisingly, many singles have longer runners than duals, and tune well. Most dual planes have different length runners for different cylinders, and very different flow characteristics because of their less than straight shapes. That's why they suffer at high rpms.
2) Look inside the plenum of a dual plane. Just opening up the wall will give you a stepped plenum with the same convoluted runners. That's not a single plane manifold by any stretch.
3) There have been dual planes with cut down plenum dividers in the past. They didn't help much.
4) If you want a NA, carbureted 350 to run well from below 2500 to power peak at 7000, and get good average hp and torque values, you are asking a lot from any one manifold. A good single plane will do the job. Of course, one with the optimum size and length runners probably isn't a shelf item.
5) There might be some merit in having a controllable door between the plenum sides; GM did just such a thing on the '93 era 4.3L V6 Vortec. A butterfly opened and closed at a couple of rpm points to change the plenum volume. Of course this was a MPFI engine.
6) I'm not sure there is a current dual plane which will flow enough air to feed a 7000 rpm power peak 350. 6000 perhaps, but a good single will still beat it.
7) If you want a dual plane to perform better, consider treating the engine as 2 V4's, and port and cam them as required to work with the manifold runners. That's not reinventing the wheel either.
8) Out of the box can be good, but understanding what goes on inside the box should come first, IMO.
Last edited by OldSStroker; 02-10-2003 at 04:37 PM.
02-10-2003, 03:29 PM
#3
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1 thing there OldSStroker, in the paragraph 1) you said "Singles tend to have more even runner lengths and shapes than singles." You got me a little confused as to which one has the more even runner lengths and shapes. 
02-10-2003, 04:42 PM
#4
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Location: Upstate NY
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Originally posted by 72Demon
1 thing there OldSStroker, in the paragraph 1) you said "Singles tend to have more even runner lengths and shapes than singles." You got me a little confused as to which one has the more even runner lengths and shapes.
1 thing there OldSStroker, in the paragraph 1) you said "Singles tend to have more even runner lengths and shapes than singles." You got me a little confused as to which one has the more even runner lengths and shapes.
Thank goodness for the edit mode.
02-10-2003, 05:40 PM
#5
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Join Date: Jul 1999
Location: Tx
Posts: 128
Before you get too serious about designing variable length manifolds I'd suggest some reading material. Theory of Engine Manifold Design... there are 2 volumes. The 1st deals primarily with the mathematical modeling and volume 2 is more design oriented. Those two books should be required reading material for anyone looking to design an intake on this level. Once you've read it, come back and ask some questions.
Take care
Take care
02-10-2003, 07:48 PM
#6
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Join Date: Nov 2002
Location: NY long island
Posts: 137
Thanks for the book recomendation. I havent seen an in depth intake book till now. I found it at amazon, 508 pages, thats alot of reading!
Last edited by turb0racing; 02-10-2003 at 07:51 PM.
. Does anyone have it that i can buy it off, or borrow (leaving a cash deposit).
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