Intake Manifold Selection for MPFI
 

I currently have a 355 with the Howards (111145-10) retro roller cam, 110 LSA .510 in, 525 ex with 1.5 roller rockers (Scorpion) the operating range is 1500-5600 which I am very happy with. Moving on, heads are Dart 180 SHP 64cc (Part Dart 127121). Intake is a Edelbrock Airgap performer 1500-6500 RPM Range. Have installed a Holley Terminator some time ago and it is great. I also run Hooker super comp side pipes. I recently installed a dual sync distributor for the addition of running CNP with LS7 coils. Everything works great. Have a TKO 5 speed with a BB 308 rear. The combination is perfect for my cruiser and I keep up with C7's all day long without any issues. About 2K RPM at 70 MPH. So my question is; I am wanting to go to MPFI using the Holley Terminator controller (which is a Holley HP). My problem is I don't understand the relationship between a dry runner intake (MPFI) and a wet intake (TBI). The CFM or RPM range has me confused. I only see MPFI manifolds starting at 2200 RPM (Holley). Most start at 3000 RPM and go up. I want the intake manifold to compliment my current cam and heads while using the benefit of MPFI. My dilemma is will a broader RPM MPFI intake cause my combination to go out of wack? Will as an example an intake manifold (MPFI) with a power band of 3000-7000 be okay without having to change the cam or cylinder heads? Would I just be loosing a little low end torque? Does the same theory apply to a TBI intake vs a MPFI intake, meaning are the RPM ranges the same or are they actually identifying an air flow vs an air/fuel flow. I should also mention that these MPFI manifolds are all open plenum and the runners appear to be slightly larger than the current Airgap. I would also be using a 1000 CFM throttle body. Not because I need that much but because that is where most manufactures start at. The Edelbrock Airgap on it now is a dual plane with the center cut down (This is the way they come) and a small 1/2 in spacer sitting on it. If I loose some lower torque That won't really matter to me. I don't race the car but do some spirited driving with with the big boys. I hope I have provided enough information to get a good answer. I have built engines in the past being careful to match parts to get the best performance from the engine, I don't want to screw up my current setup by having an intake manifold that has runners to large for what I want.

Two larger runner isn't so much an issue with multi-port fuel injection. with the wet air flow, the gasoline will fall out of suspension if the air starts flowing too slowly. That's not an issue when there's no gasoline in the air in the first place. So single planes are much better mpfi setups.the loss of low RPM torque with a big single plane is mainly from the liquid gasoline running down the sides of the intake runners instead of being in suspension in the air where it belongs.

NEVER run a duel plain manifold with a TB full injection. Always run a single plain. if you do not, you will have problems.

So, you have throttle body injection with a dual-plane and want to switch to multi-port. That isn't recommended, but it can work. You could machine bosses into that intake and keep it for that matter, but that is rather overkill.

You generally can go with "more" intake on a port injection setup compared to carburetor. A carburetor needs airflow speed to operate the venturies to meter fuel, where EFI does not. Still, you do want to watch the matching somewhat because the intake runners do have some effect on cylinder fill. I believe Holley does have an EFI manifold that has an rpm range starting at 2000 rpm.

+1 To what everyone else said.

Most MPFI intakes you see are going to be single plane as you've seen and as everyone else has already explained. That's largely because there isn't the significant loss of low-end torque with port injection and a single plane as there is with a carb (Lionel's description is great); you also get more even airflow cylinder to cylinder with a single plane. Having said that there's two factors that decrease low end torque when moving from a single plane to a dual plane intake -the first Lionel already mentioned (airspeed at low RPMs) the other is via intake wave tuning- longer runnners' harmonics cause the wave tuning effect to be effective at lower RPMs -this you WILL still lose going from a dual plane to a single plane.

IMHO, your low RPM combo is better matched to a dual plane intake, but as you've seen, there's not really any off-the-shelf Dual plane intakes setup for multi-port. There are a few places that will let you mail them your dual plane intake and have them convert it do mult-port.

Also if you've got the Holley Terminator / Dominator / HP with the dual sync and the LS7 coils, don't forget to switch to SEQUENTIAL multi-port for a minor boost in low RPM torque and MPG in the settings menu. (I think the holley default is bank-to-bank).
-Your setup and my setup are ending up at very similar places: I've got a Holley HP on my SBC, with sequential multi-port and LS-coils, but I went with a Vortec Cam sync sensor instead of a dual-sync distributor, and the 60-2 crank sensor for crank timing.
I am very much interested in torque, so I went with a long-runner FIRST fuel injection intake and a roller cam that's pretty similar to yours. https://firstfuelinjection.com/


Adam

Going from a large intake port outlet to a small head intake port IS a problem you want to avoid. -You either want to gasket match the head to the intake, or get an intake with a port that takes the same gasket as your heads. (If I remember right DART has an "SHP" branded dual and single plane intake that should be a perfect match for those heads..)


Adam

Not to throw the thread off topic, but in my reading I have found that dual-plane intakes work just fine with TBI as long as the plenum divider is not full.

But that's just a hack to "emulate" a single plane!

It's not that hard to add fuel injector bungs to your present intake. Summit and Jegs both sell them. Or, you might keep an eye out for an Accel/Lingenfelter Super Ram or TPIS Big Mouth intake for sale, although you'd have to buy used as they don't make them any more. Both of those intakes are based on the GM L98 TPI intake manifold, but have shorter, wider runners compared to the GM piece. The GM TPI intake makes GREAT torque down low, but it's done by 4500 rpm. The TPIS and Lingenfelter intakes are good to about 6000 rpm.

NO... no it does not

the runners are different lengths, and this racks havoc on TB systems.

Isn't the factory TBI manifold dual plane?

TBI's were stuck on carb intakes originally. And TBI is more carb-like as it is wet air in the intake runners.

Look at what GM, Holley and Edelbrock do.

TBI: GM had them on dual planes....CCC Qjets are kinda like TBI. Ebay search TBI manifolds, they're all dual planes.
MPFI: GM's new ZZ6 uses a single plane, Holley and Edelbrock use single planes.

terminator base
 

I don't know if other systems have this issue, but the Holley Terminator may need a spacer to be used on dual lane manifolds. If the MAP sensor doesn't get an adequate signal there may be tuning issues, so a 1/2" spacer has been proved to take care of this. The factory TBI units were probably designed to draw from both sides of a divided plenum dual plane. Just a thought, if you get a TPI/Stealth TPI wiring harness for the Holley HP ECU, you could un plug the Terminator wiring and plug the fuel line fittings and use it as your throttle body vs spending for a dedicated throttle body. That may save you enough to pay to have a dual plane welded with injector bungs for your MPFI system.

Ironically, modern OEM MPFI intakes like the LS use long runner lengths. I believe the LS intake has an 11 inch runner length, for example. The short runner intakes are used because they're easy to tune, not because they're superior.

OEMs use long runners to build enough low end torque to run down the highway at 1,200 rpm and get good fuel economy. Probably not the primary goal of a C3 build.

The OP says he's running a dual plane intake now and he's happy with its performance - just wants to switch to MPFI.

"If you read my thread here concerning my own experience using a dual plane with TBI, you'll see I didn't find the dual plane, I used, to be an issue for a year - even with a much more radical cam than a GM crate motor comes with (increasingly more radical cam designs cause increasingly more fuel reversion than stock cams). However, I did eventually spot issues after reading all the sparkplugs and a MAP failure. I then found numerous benefits, that weren't readily apparent, after changing the intake to a single plane Victor Jr.."

http://www.cpgnation.com/forum/threa...e-plane.25871/

"My 406 small block Chevy, with turbo 400 in a 1986 Pontiac TA, made 490 horsepower with an air gap (tall) dual plane intake and the 2.0 throttle body, and ran well with the exception of a few things. It could not idle under 950 without issues, it would surge at times in gear while driving at low pedal pressures, and the engine ran warmer than it should. I also had to replace the MAP (due to fuel reversion) a few weeks before changing my plugs - roughly after a year. The plugs I checked always looked good - until, after year of use, I removed all to replace them. I immediately noticed they were showing signs of uneven fueling - with some showing signs of too hot a heat range and others looking correct. I then decided to install a single plane intake - whether or not it would hurt low end torque.

With the install of the single plane, I was immediately able to feel more power from
idle to top end. There was actually an unexpected increase in low end torque. With the engine cylinders fueling more evenly, I also found I needed to go two heat ranges colder with my sparkplugs and the ECU adaptive learning corrected the A/F a few tenths leaner at idle and cruise. I dropped my idle to 700, and all surge disappeared. The engine idled perfectly and vacuum improved at idle to a 62-65 MAP reading. I had never been able to see that higher vacuum MAP reading anywhere below 950 with the dual plane. My fuel mileage also improved with the change, and the engine now averages running about ten degrees cooler. My top end horsepower also improved to just above 500, and the car is stronger throughout the entire power band - the exhaust no longer had any un-burned fuel smell, and it actually sounded quieter at idle.

Tossing the dual plane and changing to the Victor Jr. single plane was the best thing I could have done. The car now has street manners like an OEM - just with a lot more power requiring light pedal use. There is zero doubt the 2.0 Throttle Body performs much better with a single plane. I never had the erratic operation at higher RPMs like others have had using dual plane intakes, but the difference in my car running a single plane is very noticeable for the better.

TBI just works better with a single plane intake. The best advice is to only use dual plane intakes with carburetors. They were designed to work with carburetors - not fuel injection."


http://www.cpgnation.com/forum/threa...alplane.26264/

None of which is relevant since the OP stated he wants to go with MPFI, NOT TBI.

there is no stock vehicle that I am aware of that does NOT use a single plain manifold on any FI... even 4cyc Hondas..

but I am sure you know better... :-)