Jon the owner of CHI is suppose to be by my shop either tuesday or wednesday. I am going to ask him about the intake sounds we are hearing. It's to bad we had another engine to get dyno'd, otherwise we could have left Dan's engine on the dyno and let Jon hear it.
You can play the video for him. Also tell him that the spacer plates should have tapered port holes, big side to the manifold, small side to the head. This will provide two barriers to reversion pressure waves.
The Cobra TB on the EFI setup is rated at 1089 CFM, and should be adequate for this motor, but the air intake has a 90 degree bend and other restrictions. I will have to investigate that when I get it in the truck.
The 1089 CFM flow of the Cobra TB is specified at 28" of H2O. When I convert that to 1.5 in Hg to compare it to a carb, it becomes 793 CFM. That is still adequate, but we measured about 2 in Hg in test for the TB vs 0.8 in for the carb. An Accufab TB will flow much better than the Cobra TB, but I need to find and fix any other pressure drops.
The 1089 CFM flow of the Cobra TB is specified at 28" of H2O. When I convert that to 1.5 in Hg to compare it to a carb, it becomes 793 CFM. That is still adequate, but we measured about 2 in Hg in test for the TB vs 0.8 in for the carb. An Accufab TB will flow much better than the Cobra TB, but I need to find and fix any other pressure drops.
I just found that the Demon carb used in the Dyno pulls is rated to flow 933 CFM @ 1.5" Hg. It seems to be flowing even better with 680 CFM @ 0.8" Hg.
I know that o lot of people were following this thread, so I want to let them kn ow the outcome.
CHI claims that the Intake Manifold problem is the result of the modifications that I made to it. I don't buy into that answer, and they haven't offered a specific reason for that answer. I believe that since this is a 351C intake, that the spacer plates make the tubes longer and reduce the RPM range of the Ram Tuning, also the 434 cu inch motor pulls the same air at 5500 RPM, that a 351C pulls at 6500 RPM. The air is reaching sonic velocity at the RPM range where we see our problem. Reversion pressure wave propagate easlily at sonic velocity.
In other words, the manifold should have shorter tubes with larger diameter.
I tried to get an unmodified CHI Intake to prove my point, but the are none available in the US. My motor is now being crated for shipping. After all 511 HP and 532 ft-lbs torque are not bad numbers. I will install it in the truck and put my EFI setup on it. If in the future I can get better air flow from the EFI air intake, I'll consider changing manifolds if I run into this problem. The Lightning MAF that I am using is only good to 540 HP, so I can't get much more out of it anyway.
So, what else could have been tried to confirm this theory? If a 2" carb spacer were used and the pressure wave happened at the same rpm would that have eliminated anything?
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There was a 2" carb spacer on it. The modification was the clover pattern was cut out of the Dominator 4500 series carb mount, and a Weiand 4500 series to 4150 series spacer/adapter was bolted onto the manifold. One of the reasons this was done was to raise the EFI Plenum above the distributor mounted in the front. The other reeason was because my original intent was to put a 460 EFI Upper section onto the Dominator manifold. This didn't work due to a clearance problem.
In any case the Weiand adapter has an open throat area with radiused edges, and should supply a smooth transition from carb to manifold. The CHI 4150 intake does not have a cloverleaf, but an open throat.
A short adapter may have been a better way to go then. It could have reduced the plenum volume and I don't think the smooth transition helped it any. There was basically a reverse taper in the Weiand part... correct?
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I believe that since this is a 351C intake, that the spacer plates make the tubes longer and reduce the RPM range of the Ram Tuning, also the 434 cu inch motor pulls the same air at 5500 RPM, that a 351C pulls at 6500 RPM. The air is reaching sonic velocity at the RPM range where we see our problem. Reversion pressure wave propagate easlily at sonic velocity.
In other words, the manifold should have shorter tubes with larger diameter.
So how does the CHI intake compare to an old 351C Torker? I would believe the Torker has shorter runners but not sure if those are larger diameter. It is shorter. The plenum could be increase with a 2" spacer.
A short adapter may have been a better way to go then. It could have reduced the plenum volume and I don't think the smooth transition helped it any. There was basically a reverse taper in the Weiand part... correct?
The taper is large on the 4500 side, and small on the 4150 side.
I think that this makes a case for a manifold made for a 10.3" deck height.
So how does the CHI intake compare to an old 351C Torker? I would believe the Torker has shorter runners but not sure if those are larger diameter. It is shorter. The plenum could be increase with a 2" spacer.
--J
A 351C Torker intake could be a good alternative to a CHI intake, but it still needs spacers, which lengthen the tubes by more than 1". With a short duration intake valve, like my cam, the longer tube causes the pressure wave to hit a closed intake valve.
A 351C Torker intake could be a good alternative to a CHI intake, but it still needs spacers, which lengthen the tubes by more than 1". With a short duration intake valve, like my cam, the longer tube causes the pressure wave to hit a closed intake valve.
I'm using a Torker on my 400 with Price spacers and a 1" carb spacer. Carb is a Street Demon 850 VS. With the 1" spacers, what is the total runner length on a CHI intake? I can measure mine from outside but a carb and head get in the way of measuring the inside
I'm using a Torker on my 400 with Price spacers and a 1" carb spacer. Carb is a Street Demon 850 VS. With the 1" spacers, what is the total runner length on a CHI intake? I can measure mine from outside but a carb and head get in the way of measuring the inside
I don't have the motor here yet, it will be coming soon. I'll chech the length of the runners then.
I don't have the motor here yet, it will be coming soon. I'll chech the length of the runners then.
Understand. BTW, after looking at the CHI intakes, I'm betting the Torker has shorter runners even with the spacers. Do you know how much shorter you need the runners to be? I've been looking for calculations online to help me determine the plenum volume and runner length for my 408ci motor when I go EFI. Like you, I plan to use a EEC-IV with a Tweeker. Dizzy will be aftermarket Windsor EFI with C gear. Intake may be built off a 351C tunnel ram base like some of the aftermarket GM intakes.
Understand. BTW, after looking at the CHI intakes, I'm betting the Torker has shorter runners even with the spacers. Do you know how much shorter you need the runners to be? I've been looking for calculations online to help me determine the plenum volume and runner length for my 408ci motor when I go EFI. Like you, I plan to use a EEC-IV with a Tweeker. Dizzy will be aftermarket Windsor EFI with C gear. Intake may be built off a 351C tunnel ram base like some of the aftermarket GM intakes.
Talk to TMI about EFI spacer plates. That may save you from modifying the manifold. You could even use a 351C dual plane intake, if you wanted.
Talk to TMI about EFI spacer plates. That may save you from modifying the manifold. You could even use a 351C dual plane intake, if you wanted.
Since the Price spacers add an inch to the C intake, I've thought about having them make me a set to adapt one of those cool "big box type" supercharger manifolds for the 5.0. That would add 2" to the runner length while still giving me a fairly large plenum. Runner diameter is my concern.
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