TBI on a dual plane Manifold??

[racprops]

New question: I am being told I should run a dual plane intake manifold under my Throttle Body Injectors.

I am told that such a intake will improve my engines torque at lower RPMS like 1500 to 2500.

I am building a 383 for low RPMs at 1800 for highway crusing.

So what has any of you guys found out: Is this a good or bad idea??


Thanks.

Rich

 

[PlayingWithTBI]

Are you saying a dual plane manifold with an adapter plate for your TBI? You should be OK as long as you don't go with too high of a rise. The higher the rise the less low end torque you get.

 

[c1500deathtrap]

Are you saying a dual plane manifold with an adapter plate for your TBI? You should be OK as long as you don't go with too high of a rise. The higher the rise the less low end torque you get.

I thought it was higher rise=longer runners=better low end torque.....

 

[PlayingWithTBI]

Bigger/longer runners take more volume to obtain proper flow, thus higher RPMs.

 

[Schurkey]

The OEM manifold is a dual-plane. So, yes, it can be done.

Long runners = low(er)-rpm torque. Consider the ancient Chrysler "Long Ram" manifolds, where each carb was mounted outboard of the opposite-bank valve covers. 30 inches of runner gave a tuned torque boost around 2800 rpm.

https://www.allpar.com/mopar/sonoramic.html

You must be registered for see images attach

Starting point for ram tuning is: N x L = 84,000, where N is the desired operating rpm and L is the length of the runner in inches.

Longer length lowers RPM for torque peak.

Larger cross-section tends to raise RPM for torque peak; not by "tuning", but simply because it slows velocity of the mixture--and the cylinders fill better when appropriate velocity is maintained. Put another way, increased cross-section "supports" higher RPM.

The torque boost of a typical "dual-plane" intake is due to the increased velocity through the throttle body and runners, more than the longer runners.

 

[CrustyJunker]

The OEM manifold is a dual-plane.

This is the big thing. ...The rest of Schurkey's explanation is also correct!

Each TBI barrel literally feeds the opposing bank of your engine. [edit: on the outer cylinders, see below for more information] Added bonus, your factory intake does a great job at keeping torque up because the ports are small and runner lengths are decent.

Flow-for-flow your intake manifold port velocity will increase because of the cubic inch increase. That should help contribute to that super low end torque you're looking for.

Mind you I'm talking the mildest of street stuff here, not getting creative. If we're talking specifics of cams, different heads, that's a whole 'nother world of things.

Happy truckin'.

 

[Schurkey]

Each TBI barrel literally feeds the opposing bank of your engine.

Each TBI barrel feeds two "inner" cylinders on one bank, and two "outer" cylinders on the opposite bank. This can be seen by looking at the shape of the runners of the upper plane--it's usually very obvious that it's feeding two cylinder of each bank, outers vs. inners.

1 and 7, (Outer cylinders) 4 and 6 (Inner cylinders) will be fed by one "barrel" and one plane of the dual-plane intake.

2 and 8, (Outer cylinders) 3 and 5 (Inner cylinders) will be fed with the other "barrel" and plane.

Most two-plane manifolds have some amount of cross-feed between the two planes, either there's a notch machined into the metal of the divider, some cast- or machined-hole in the divider, or a gasket that's open between the "barrels". The amount of cross-feed varies from zero to "considerable" depending on the engineer's intent.

A "two-plane" manifold is not the same as a cross-ram, where the intake runners are arranged bank-by-bank even if sharing a single carburetor. The Mopar manifolding pictured above uses a "Left" carb that feeds the "Right" bank, and a "Right" carb that feeds the "Left" bank--with some amount of crossover between the two systems.

 

[95nProgress]

It's been a while but I clearly remember that when I went from the common dual plane intakes (stock & Holley) to a single plane (Weiand 7525) on my TBI it was a tremendous improvement. None of that single plane low end loss that you hear about when using carbs because of the TBI. I would highly recommend a low rise type single plane over any dual plane for a TBI specifically if your doing your own programming.

Brian

 

[CrustyJunker]

Uhh, I knew that.

Curse my memory, I did port a couple of these intakes...It's been awhile. Edited post for lack of information / poor information. Sorry everyone!

Those Chrysler Cross-Rams used a pretty big balance tube. Actually a pretty creative system. The only crossover visible on my TBI intake was maybe a 3/8" x 1/2" open notch between the throttle bores. I think there were bigger notches in the bores where the EGR came back in. Learned a lot running water through the intake after the port jobs!

Anyway, I'll stop littering this thread. Good info in here, though.

 

[Erik the Awful]

If you have MotorTrend access, Engine Masters did a dual-plane vs single plane dyno comparison.
https://www.motortrendondemand.com/detail/intakes-for-torque-vs-horsepower/0_ys6o01oy/

If I were building a nasty street engine, I'd go single plane, but for any daily driver or towing application, dual plane. If you're planning on running past 5000 rpm on a regular basis, a single plane is worth it, otherwise stick with a dual plane.

Don't bother wasting money on an "air gap" manifold. Once it heat soaks the air gap does nothing.