SBF Edelbrock RPM 2 Intake - Airflow & Porting

[SRS_Chris]

Has anyone had a SBF Edelbrock RPM 2 EFI intake on their flow bench after porting? The lower seams to flow fairly well, but the upper is giving me fits at the moment. I am flowing through an AFR 185 head and the upper is seriously choking the system. I have the lower flowing very close to the limit of the head, but when I attach the upper airflow goes away. I have a clay radius on the inlet of the upper (in place of the TB), but it doesn't help. I have made sure that the port cross-section is uniform from the upper-lower mating face into the upper as far as I can reach, but it just doesn't want to move air. Any advice?

[groberts101]

Welcome to the world of 5.0 EFI type manifolds. Those particular "bent manifold" designs are generally aimed at improving runner length for increased torque production.. not necessarily for all out power production. Just too many twists and turns for the lower rpm street versions to make big airflow numbers to match a better heads flow capability. Really can't see that manifold not hitting 260-280 cfm with decent porting but depending on what you're looking at doing here you might need to step up to the Victor EFI version if you want/need those higher peak airflow numbers.

What cfm number does the connected manifold flow in comparison to the head port?

[SRS_Chris]

I can get the lower to come really, really close to the head (~280 cfm on my bench) with some mild work. But the issue is when I attach the upper and re-test. Airflow is dropping off to the mid-230's. I can't get into the runner entry without cutting the back of the plenum off, which isn't an option on this project. Am I missing something here?

[mag2555]

The typical clay radius of about a 1/2 a 25 cent peice will not do the trick for getting the air flow turned into the runners of most any duel plane's shollow Plenum, even though the air is not at its max velocity.
Think more along the lines of a 2 inch to 4 inch tall velocity stack who's smaller ID then the Plenum makes for a far more gradual turn into the front and read of the Plenum.

I guess what I am trying to say is that as best as you can when everything is bolted up, no less for testing you want a Venturi shape , as in speed things up, then slow it down!

Also in regards to guiding air mass / flow always remember that once your trying to turn air flowing at more then some 10 to 15" of H2O ( and it's fps velocity), air flow approaching a bend / turn of more than 15 degrees will just sheer way !

This is another reason why I have always Said for ever that there should be specific off the shelf Carbs for race usage that have bigger somewhat slower flowing bores for the side that bolts over the shallow side of a Manifolds Plenum!

[EDC]

The upper can only be improved by cutting it open. Removing the two mounting hole posts in the upper and use a fastening method that holds it down inside the plenum helps but they screwed the pooch on the transition/floor from the upper plenum to the lower runner entrances. Too sharp of a bend there versus the Holley Systemax II upper.

There was a similar issue with the TFS intake discussed here: http://www.hardcore50racing.com/vbullet ... hp?t=61042

Good luck!

Ed

[xr4x4ti]

I have also had the theory that a big issue with these kind of intakes is that the radius of the runners as the make the turn from vertical coming out of the lower to horizontal is to small. In the case of the RPM 2, in order to keep the height down and have room for the triangular shaped upper inlet plenum/diffuser the bend is really tight reducing the effective cross section of the runners.

Plus what Ed said, the air can't take the turn from the upper diffuser to the runner entrance. I have been meaning to tackle one of these intakes for a while. I have one on my turbo 331 SBF, but I have been spending all of my time trying to get the power I have now to the ground before adding anymore.

Tim

[mag2555]

You only need 1/8" of Carb gasket to seal it to the Plenum so cutting back the gasket area on the Plenum to this point will help to form a better turn into the Plenum.
Every 1/32 of a inch can make a difference!

[SRS_Chris]

You only need 1/8" of Carb gasket to seal it to the Plenum so cutting back the gasket area on the Plenum to this point will help to form a better turn into the Plenum.
Every 1/32 of a inch can make a difference!

I appreciate what you are saying, but this is an EFI application. I understand that the principles of airflow are the same, but just making sure we are on the same page here.

[SRS_Chris]

Based on what I have read above, it sounds like my hands are more or less tied here when it comes to making the upper work. I will finish the lower and see what gains I can find with the upper. I will report back soon. In the meantime, if anyone has any suggestions to make this upper work better I am all ears.

[turbo2256b]

I have run the Victor 5.0 EFI intake on my 302 which now has dual quads on it. Big issue with it is port is raised about .285 over factory location. Took about 400.00 in machine work to match ports up if heads were using factory location. Without the machining about 1/4 or so of the roof of the port was blocked which was also blocking part of the spray pattern of the injector. I like the intakes with the plenums that could be opened up and modified better than the tapered style of the newer ones.

[mag2555]

Do you have room for a 1" spacer under the Carb?

[EDC]

Do you have room for a 1" spacer under the Carb?

This is a long runner EFI intake he's working with.

[F-BIRD'88]

Wow, a very convoluted flow path. Someone should-could make a different upper
EFI manifold/plenum with a more direct flow path, say (could be) with two air control throttle bodies.
Make the (tuned) runners length adjustable with add able runner spacers to +/- the tuned length of the runners. Bolt it on the ported lower EFI and it would rock.

Might stick out above the hood of a Mustang but it would flow a LOT OF air
and resonate at higher rpm for more power potential.
If the ported lower flows that much, there is lots of potential.

[mag2555]

Thanks, I have been missing that fact!

[turbo2256b]

Pics of the Victor 5.0 EFI