[Blackmamba]

I’m looking to run multiport injection on my 671 set up, this maybe an issue maybe not is the fact that the BDS intake doesn’t divide each cylinder, one intake manifold runner supports two cylinders.. is there a way around this or maybe I know some make their own blower manifold out of a dual quad set ups .. I don’t think welding in runner dividers would work bc of the fact it could distort the manifold…what are you guys doing to do this?..thanks

[Scott65]

I don't know the best way to do what you're trying to do, but have you considered the effects of loss of charge cooling without the fuel coming through the blower with the air? Are you looking at mechanical fuel injection or electronic? With electronic you can probably run a batch fuel strategy and make it work. Low rpm will probably be the problem area, I'd guess.

[Blackmamba]

I planned on running a few injectors up top I do realize cooling, I want to do electronic injection.. I also realize the complexity of this and it is out of my wheelhouse but that never stopped me before.. and thanks for the help and or insight it’s def going to be a project

[JLMounce]

It's clearly done in the OEMs to run MPI with a positive displacement blower/supercharger. I agree that if you can't get away from common ports, a batch fire port injection setup is likely best, but I still worry about distribution, especially under boost.

If I was running a traditional blower design like a 6-71, I personally wouldn't even consider port injection because of the loss of cooling effect from the fuel atomizing in the blower itself. The rotor design of these units is as such that they are extremely inefficient, with most of the charge compression happening in the intake, rather than in the blower case. You need that rapidly atomizing fuel to help bring the charge temps down if you're not running some type of intercooler.

Based on that, from an EFI perspective, I'd recommend one of the many throttle body applications, sized properly for the amount of power you're wanting to make. Heck I'd upsize your needs by 30-40% and run e85 if it's widely available in your area.

[Blackmamba]

I realize some of the issues, I may just run injectors up top and get the best tune I can with that and call it a day..I do run a meth kit now which works but it only comes on in boost as I’m sure you know how those work ,it wouldn’t come on all the time to keep rotors cool enough while either idling or light cruise bc this is just a street car

[Blackmamba]

Jlmounce thanks for some insight about fuel injected below and or above blower i def overlooked that aspect..

[Blackmamba]

No E-85 here at least at the pump, I drive it a lot so I wouldn’t want to convert yet

[Blackmamba]

Thanks Scott. Yea batch fuel I was thinking about but didn’t get too far into I’ll look more into it now I have a checklist that I’m goin go thru to narrow down my direction

[JLMounce]

Originally Posted by Blackmamba

Jlmounce thanks for some insight about fuel injected below and or above blower i def overlooked that aspect..

No worries. If you follow what the OEMs do, it's pretty easy to track what they think is good, efficient and reliable.

Not only have they completely stopped using roots style blowers in general, they utilize air to water intercooling directly in the intake, along with sequential port, or now direct injection.

You have to go back to cars like the Ford Thunderbird and the GM 3800 Supercharged equipped w-bodies of the early to mid 90's to see roots style blowers without intercoolers. In these cases the blowers ran tiny amounts of boost, 5-7psi is all.

That's directly related to the efficiency of a roots style blower. It's rotors move air to the intake manifold where it compresses before entering the combustion chamber. It's really inefficient and creates a lot of heat. Modern positive displacement supercharges like a Whipple, TVS etc are screw blowers that compress the air charge in the case itself, more like what you see from a turbocharger or centrifugal blower's compressor housing. The newer style blowers still aren't as efficient as a turbine compressor though.

Old school stuff that used carburetors (or throttle boy injection) overcomes some of that heat production by the cooling effect of the fuel atomizing in the fuel/air charge. Going with port injection, you lose that completely, regardless of whether it's batch fire or sequential.

If you follow the track guys that run screw and traditional roots style blowers, they all run mechanical fuel injection above the rotors. Almost always it's a wet supercharger.

[Blackmamba]

JLMounce very informative on where different types of superchargers create boost/pressure I never new, if that’s true the old school stuff pressurizes the intake and whipple type pressurizes the blower case itself? Well that changes some thought and possible direction, and I see how that would influence fuel and it’s delivery

[JLMounce]

That's correct. The roots blower typically uses an intertwined three bladed rotor that acts simply as an air pump. It moves air from above it's inlet, to an outlet directed towards the intake manifold. There, whatever the engine can't ingest creates "boost" There's a small amount of compression of the charge that happens as a net result, but it's efficiency in compression (and thus ability to not become heat) is more dictated on the amount of boost being created and how the intake manifold's plenum is shaped.

The term is called "adiabatic efficiency." The higher the efficiency, the less heat that gets generated from the compression process.

The screw blower on the other hand uses an intertwined screw design that compresses the air between the screws, in the case, before moving the charge to the intake manifold. The benefit being higher adiabatic efficiency and the fact that you're sending compressed air to the combustion chambers, increasing charge density over what is possible with a roots blower.

This is all not to say that the roots blower isn't good or shouldn't be used. They are robust, reliable and known to produce power. Otherwise people wouldn't buy them. But yes, you want to keep in mind heat management with these things and I believe that a carb or throttle body injection system on these is best for a street car. Others may have better or different ideas than I do, but for this kind of deal, I like the KISS methodology.

[Blackmamba]

Well again this explains a lot that the intake charge is created at different places from the charger itself until it gets to top of the piston..I’ve been messing around with these blowers for about ten years and never dawned on me about the placement of the condensed air charge..I know the old school stuff is inefficient and I think that’s part of the fun even tho it creates issues…like I said if this is all true which I’m not doubting you it’s just new to me its making me rethink….much appreciate the insight.. so this being said it prob won’t make much diff in driveability bc all the fuel whether injected or squirted in the top it’s all the same by the time it get to just before the valve opening, and if port injection is a goal better of with a diff system to take advantage of all the possibilities port injection has to offer..making sense

[Scott65]

Yours is a scenario where "the juice isn't worth the squeeze" for mpfi. It could be done, at least a hybrid version. But you'd want probably either 50% of the fuel coming in the topside, or constant water/meth injection. No real gain in precision fuel delivery like that. And that assumes you could have dividers welded in to separate the injectors for said precision. Now if you wanna open up the discussion a little, you could take a modern Ecu and control a tbi(or 2) and gain serious timing control and add in some safeguards for afr protection and temperature safeguards for manifold air temps. That could be money well spent, that would move up with a change to a Whipple and mpfi later...

[Blackmamba]

Scott65 that’s the scenario I’m at at this point, would rather do a diff setup with a system I could get the most out of rather then trying to reinvent the wheel and prob would have issues..I was looking into the DIS msd coil overs system for now bc I would like to have better ignition control, I do run a BTM, and start retard but would like more ignition control so I was looking at the DIS

[Scott65]

If you're interested in individual coils, and also later going to some form of mpfi, there's probably better long term ways to do it. An MS3X will drive 8 coils sequentially, and handle all your ignition timing duties, and be able to drive 8 injectors sequentially later on when your ready. Will allow for boost control, fuel pressure and oil pressure safeties, afr safeties, traction control, and a whole lot more. And I'm sure there are other similar options as well.

[Blackmamba]

Scott65, the only distributor I found was the one from msd/Holley the dual sync one is this the only one? I’ve been looking at ecu’s but wasn’t sure there are many options, I’ll look at the one you mentioned bc I’ll prob move to efi in sometime… I appreciate you guys info much needed

[Scott65]

You don't have to have a distributor per se... Or you can use a dual sync, or you can turn a distributor into a wheel arrangement that can be read for sequential, OR (and I think this is best) you can turn a distributor into a cam sync and add a crank wheel. Check out my thread here for the last method, and how I did it.
https://forums.maxperformanceinc.com...d.php?t=820018
Be forewarned, it's lengthy. I used two different versions of a cam sync, the last one is a lot nicer and close to the end of the thread. Both worked well.

[Blackmamba]

Thanks for your guys help and knowledge it def helped me in making a more informed decision.. Scott65 and jlmounce…much appreciated