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Big Block MPFI Intake Manifold Choices with L88 Hood
Moving to MPFI this winter and am looking at my intake options.
Running a Merlin II big block with iron rectangle port heads. I'm installing an L88 hood and would ideally like to add the airbox as well.
Possible choices I have found:
holley strip dominator
pros: perfect fit with the L88 hood
cons: injector bungs and fuel rail bracket modifications will be required, 30+year old design
Height: Front 4.77", Rear 6.16"
Edelbrock Victor Jr EFI
pros: already has injector bungs and fuel rail kit, more modern design
cons: *maybe* fits under the L88 hood without an airbox?, but would need to be angle milled to fit with airbox
Manifold height: A-5.90" & B-5.90".
Holley EFI intake: similar to a Victor Jr with the same pros/cons, also a little cheaper
Height: Front 5.96", Rear 5.96"
RPM Air Gap
pros: modern design, some say it will fit under the L88 hood even with an airbox
cons: modifications required for injector bungs and fuel rails. Dual plane design which isn't recommended for MPFI, questionable that it will fit without further mods.
Manifold height: A-4.45", B-6.0"; Carb pad height: 5.22".
Are there any others that will work?
I know several members out there are using the intakes above. If you were to do it over, would you use the same intake?
dont we need more information such as what cam you are running, it's rpm characteristics would greatly effect whether going with single plane or dual plane intake.
In addition rear end gearing and what type of trani and if auto what stall speed to get a better idea about your car.
dont we need more information such as what cam you are running, it's rpm characteristics would greatly effect whether going with single plane or dual plane intake.
In addition rear end gearing and what type of trani and if auto what stall speed to get a better idea about your car.
I'm really more focused on what will fit under the L88 hood and what can be easily converted to EFI by adding injector bungs and fuel rails. I think the available choices are pretty limited.
My plan will be to do the MPFI conversion this winter using my existing cam/heads and then upgrade them in a year or two to better match whatever intake I have installed.
Currently the engine has the low-rise LS6 intake, Holley Terminator TBI, Merlin iron rectangle port heads (I believe 345 cc), and a comp cams XE262H cam.
This engine is for the street so doesn't need to be high-revving. It has a 4-speed muncie and 3.55 rear end.
looking up the height of the original L88 intake I came up with 5.5" and also came up with the Air Gap fitting with no problems. The link below discusses the Victor Jr. I realize you intend to change the cam in the future but the current cam has a completely different rpm range, much lower, than any of those single plain intakes. https://www.corvetteforum.com/forums...se-wanted.html
dont we need more information such as what cam you are running, it's rpm characteristics would greatly effect whether going with single plane or dual plane intake.
In addition rear end gearing and what type of trani and if auto what stall speed to get a better idea about your car.
I have always heard EFI doesnt need the dual plane because it doesnt use vacuum to draw the fuel from the TB. So a dual plane becomes a restriction to EFI, right?
FWIW, I have an Edlebrock RPM Air Gap and it fits fine with my L88 hood. It might even fit with a standard hood. It is fairly low. Not sure on the others.
I will say the reason I went with a throttle body (Holley terminator) instead of MPFI was because of exactly what you are looking at. I did not want a single plane for the street and ended up with the Terminator for my BBC. The problem with the terminator and a BBC is that it is good to around 600hp. More than that and you likely need to go to MPFI.
Easy to get past 600HP or in that range with a BBC (even without power adders), which I am sure is why you are where you are...
The RPM Air Gap would be a challenge though to modify for fuel bungs. The angle on the ports don't lend themselves easily to fuel bungs.
Last edited by 73racevette; 09-08-2017 at 03:40 PM.
I have always heard EFI doesnt need the dual plane because it doesnt use vacuum to draw the fuel from the TB. So a dual plane becomes a restriction to EFI, right?
Not quite, but I will leave this alone to not thread jack.
FWIW, I have an Edlebrock RPM Air Gap and it fits fine with my L88 hood. It might even fit with a standard hood. It is fairly low. Not sure on the others.
I will say the reason I went with a throttle body (Holley terminator) instead of MPFI was because of exactly what you are looking at. I did not want a single plane for the street and ended up with the Terminator for my BBC. The problem with the terminator and a BBC is that it is good to around 600hp. More than that and you likely need to go to MPFI.
Easy to get past 600HP or in that range with a BBC (even without power adders), which I am sure is why you are where you are...
The RPM Air Gap would be a challenge though to modify for fuel bungs. The angle on the ports don't lend themselves easily to fuel bungs.
I'm neutral on the single vs dual plane debate. Most MPFI setups do seem to be single plane, but that could be because the runners tend to have the same angle and are easier to convert.
That's good to know that the Air Gap will definitely fit. I agree it would require a bit of work for an MPFI conversion due to the differing heights and angles of the runners.
That's the reason I created the thread. I know any of the intakes I listed will work, just not right out of the box. I talked to one machine shop who thought that angle milling the Victor Jr which would involve filling in and redrilling the carb mounting holes, would be more work than drilling/welding injector bungs to the Holley Strip dominator. But I also don't want price to be the only determining factor. If the Victor Jr is that much better than the Holley or Air Gap then I'm willing to have the work done.
Don't know all of your constraints, but you might consider a throttle body setup like the terminator as an option. Makes the intake manifold a bit easier.
Don't know all of your constraints, but you might consider a throttle body setup like the terminator as an option. Makes the intake manifold a bit easier.
That's what I'm running now. Nothing wrong with it, I just want to go all in with MPFI.
not sure if you spoke with an ordinary machine shop or a place that specializes in manifold efi conversions but may want to check this place for info on particular manifolds.
It was flat milled, but I should have milled an angle. I needed to cut the plastic ring between TB and air cleaner base (came w/ Holley) to get the right angle.
When I cut the intake I lost the mounting hole for the IAT sensor which wasn't a big deal. I got another sensor that is push mount instead of threads and put it in the air cleaner base.
Another issue with the oval-port Holley intake is that it's for peanut heads so I had to port it to match my ovals.
Even with all that I think fixing the Holley intake was less work than starting with a non-EFI intake and adding bungs & rails.
I have a MassFlo conversion which uses a Victor Jr intake modified with injector bungs. No way does it fit under the L88 hood even with drop base air cleaner. I ended up doing a lot of custom work to the underhood air box and increasing the scoop height by 1.5" to give the right clearance. I did not mill the intake flange which certainly would help some. Also the newer EFI systems seem to have better rail and injector packaging now so you might have better luck on fit.
I thought I would close out this thread with my final choice. I ended up going with the RPM Air Gap, getting the injector bungs welded and the divider milled down. I think the end results look great.
Old vs New. I see why they call it the pancake intake:
While waiting on the intake I had too much time to think. So I decided to pull the trigger on a new roller cam while I was at it!
I vote for the Strip Dominator intake. I was able to fit that intake under my L88 hood without issue. The Strip Dominator performed fine around town and especially at the track...one of my favorite intakes.
*edit* didn't realize you had already selected an intake haha, by the way those are some nice welds.
Last edited by bence13_33; 01-22-2018 at 11:46 AM.
one guy to talk to is Mesa Balancing in Miami FL area. he did an extensive thread on his head and intake work on Offshoreonly with an extensive bit on efi conversion in a single plane, think it was a Brodix, but photobucks blew all the pics out.
Last edited by derekderek; 01-22-2018 at 08:36 PM.
09-08-2017, 11:44 AM
Big Block MPFI Intake Manifold Choices with L88 Hood
