In general terms the RPM dual planes are decent intakes. In some applications they are taller than stock intakes, and cause hood clearance issues, problems with Shaker assemblies and some "Ram Air" set-ups.
I would also add that fitment of the Edelbrock intakes these days is hit and miss.....FULLY expect to get the grinder out for some set-ups!
Most applications do not need or benefit from an aftermarket intake manifold, despite what you may read in the magazines. Same deal with carburetors, distributors, camshafts, etc. Keep in mind that the aftermarket industry is here to serve us, and magazines must promote aftermarket parts, or it all goes away. You will NEVER read once where a factory iron intake, or q-jet will outrun aftermarket parts everyplace, even though we have done this on many occassions, on the dyno and at the track testing parts. Not a big deal to me, my mission in life is NOT to outrun shiney aftermarket parts, just to show folks that you can run as fast or faster with stock parts, if using them is among your goal(s) for the project.
For decades folks have been tossing out factory iron intakes and factory carburetors to install aftermarket aluminum intakes and carburetors, just to loose or make no more power than the factory parts.
Several years ago we tested 3 intakes back to back on the dyno on a pretty stout 428 Pontiac engine we built here in our shop.
The engine was topped with unported aftermarket aluminum heads flowing apprx 260cfm. A 236/242/110 custom ground hydraulic roller cam was installed, compression ratio at 10.6 to 1. We tested a factory 1971 Pontiac HO intake, stock aside from gasket matching and opening it up to two big holes/same size shape as the Edelbrock RPM intake. My own iron intake, which is modified in the same manner, and a port matched Edelbrock RPM intake were also tested.
The HO intake made 487hp.
The RPM made 491HP.
My own iron intake made 497hp.
The RPM intake actually pulled peak power down by 200rpm's. The 500hp engine just didn't want or need that much runner volume for the power level. (Make sure to read the last sentence again, this testing was done on a 500 HP engine, which also produced over 540ft lbs peak torque!!!)
Keep in mind that larger runners increase plenum volume and reduce port velocity. If the engine is getting enough air with smaller runners, then larger runners do not always make more power. They can also shift power curves, narrow up the power curve, and make less "average" power as well.
How many little tiny 350 engines do you see with HUGE intakes sitting on them, feeding factory iron heads and some sort of "high performance" aftermarket camshaft?
I'd bet my next pay check most of them made or make LESS power than the factory intake.
I also did some pretty extensive intake manifold and spacer testing a few years ago, at the dragstrip. It took several outings, and at that time my car was powered by a 455 engine making about 500hp.
I tested several single plane intakes, Holley Street Dominator, Torquer I, and the Edelbrock Performer and Performer RPM, against my modified factory iron intake.
We also obtained and tested a newly released Tomahawk intake (single plane).
The testing was done over several weeks, and each intake was raced on at least one outing, and another one swapped on for as many runs as we could get in. Then it was left in place, made another outing, and raced at least 3 runs, swapped in another one, left it on for another outing, etc.
It took some time and quite a few runs as I had to average numbers and take weather and track conditions into account.
When the smoke cleared and the dust settled, the quickest (ET) run from all intakes was made with the iron intake in place!
The only intake that ran faster in MPH was the newly release Tomahawk intake. It was a solid 2mph faster on the top end of the track, but gave up so much starting line (.09 seconds) and mid-range power that it went slower in elapsed time.
When you read this, consider that this testing was done on a mid-11 second street car, that is deadly consistant at the track.
That testing was extended to spacers as well, 4 hole, fully open, semi-open and fully divided. All on the iron intake. The quickest runs were made with no spacer at all, fastest MPH with a semi-open spacer.
So much for intake and spacer testing, my engine still uses a "modified" factory intake, even though the new engine makes quite a bit more power than the old one. I use the stock parts because they work, and the look you get from folks who wonder by in the staging lanes who gander at the q-jet sitting on the stock intake, then at the ET, then back at the carb/intake......PRICELESS!!!......Cliff
PS: I attached a pic of the plenum mod to my factory intake...
