intake manifold differences

[92gmc]

why did GM make a dual plane and a single plane intake manifold.

Would a non-EGR dual plane make better torque than a single plane (like it would on a gasser), or is there really no reason to have made a dual plane in the first place ??

thanks

[5.7L oldsdiesel]

The intakes found on the LL4 6.2L HD emission engines are the intakes that increase power.These have no EGR.They allow much more airflow.

[BC Clark]

I read somewhere in the Q&A's that a member did a study on the two and determined that between the two manifolds the dual plane made a little more power at low end and the single plane made a little more at high end. This does follow the gasser rule but maybe not to the same extent since you are not delivering a fuel/air charge. Here is some real world data that I'm pleased with. I swapped the single plane EGR manifold on my daughter's '88 Jimmy with a dual plane non-EGR manifold I found on E-bay and MPG went from 18 to 22! Running the second tank now to verify but I can tell this one is better as well. I did have to grind the lugs a little by the water outlet and the Glow Plug controller. One other thing I noted, for the first couple of full throttle runs just after the swap a lot of dusty grey-brown crud came out of the exhaust. Sorta like the carburetor days when you used to say "I'm blowing the carbon out" as an excuse for a full throttle run. :D

[92gmc]

Originally posted by BC Clark:
Here is some real world data that I'm pleased with. I swapped the single plane EGR manifold on my daughter's '88 Jimmy with a dual plane non-EGR manifold I found on E-bay and MPG went from 18 to 22! Running the second tank now to verify but I can tell this one is better as well.good info !

When you did this swap was the EGR functional ? I wonder how much benefit is from the EGR delete and how much from the single to dual plane ?

[BC Clark]

That's kind of an interesting part. The EGR was not functional, vacuum tube removed and port capped. But the diaphragm was still attached and sitting in the middle. It's possible the valve could have been leaking. Also the EPR valve line was still attched to the solenoid, I removed that as well. Actually I removed the vacuum from the solenoid pack, so there is only vacuum being applied to the MAP sensor, HVAC damper doors, and the cruise control. This year did not have a vacuum valve for the transmission, TV cable and TPS only. The Service Engine light stays on all the time. I think the computer is expecting the vent solenoid to relieve the vacuum on the MAP sensor so I may play with that later, but right now I sure like how it's running!