Dyno lessons about RPM intake
 

I just had an engine on the dyno and was able to do some testing/comparisons.
First thing is, it really does make great torque and when setup right the horsepower is pretty good.
We compared it to a northwind and the RPM was by far better below 5300 after that the northwind was better but avg from 4500-6000 the RPM was still ahead.
Finally don't be afraid to try spacers on the RPM. My engine liked it everywhere in the rpm range.
Wish i could've done more test but ran out of time.

Thanks for posting, and with the purpose you have built your motor for it’s the average numbers that are more meaningful in whatever rpm range said motor will spend the most time in .

Motors of 430 cid and up with high flowing heads and duel plane intakes just love more plenum volume that the spacers give especially above 4500, yet it does not harm the bottom end torque numbers for the most part.

Thanks, I agree spacers are a easy horsepower adder and really a must for maximum power for these higher horsepower engines. I'm hoping to find time to test a few I have, one inch open, 2 inch open, one inch Wilson tapered 4 hole and a 2 inch HVH Super sucker..or a combination of the one inch spacers.

For each intake can you post the numbers at a lower RPM (example start of the dyno pull), the numbers at the peak torque RPM then the horsepower number at peak power RPM.


Another example of the Performer RPM intake compared to a single-plane intake.
Both intakes port matched to the heads in use, with half-inch open spacer and a HP950 carb.
4.210" stroke / 462 CID

RPM intake 580.2 HP at 5800 rpm (peak) and a Victor intake 600.9 HP at 6000 RPM (peak).
RPM intake 589.1 ft.lbs. torque at 4400 RPM (peak) and the Victor 595.1 ft.lbs. torque at 4700 RPM (peak).
Down low, the Performer RPM with 491.2 ft.lbs. torque at 3500 RPM and the Victor intake 487.0 ft.lbs. torque at the same 3500 RPM.


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From 4500 to 5000 the RPM averaged 20 more tq, 5000-5500 they were basically equal, from 5500-6000 Northwind was 10 averaged 10 more tq

"The Edelbrock Performer RPM continues to impress me as a 6,000-rpm and under choice. As a dual-plane, the manifold produces more usable torque in the midrange with some of the larger-port heads than do most of the single-plane designs. At 5,700 rpm on a 455, and 6200 rpm on a 400, the party is just about over; but below these levels, it seems to increase the average torque output handsomely."

Pete McCarty
Nov/Dec 1997 PE magazine


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Yes on the above and it needs to be paired with a larger then a 750 cfm Carb also.

What carb were you using?

Spacer on an RPM?….I can BARELY get the hood closed with an RPM and a paper thin gasket….lol

Dual plane usually makes more low end Torque.
Pontiac had a stock 400 that made 400 tq at 2400 rpm.
Iron intake, 2 Bbl.
Yes Engineers before us did some homework..

I've back to back tested the RPM against T-II's with 1" spacers on them for years and even thru the Victor into the mix on occasion.

At the track I've tested the RPM against a T-II, Street Dominator, and Tomahawk and with and without spacers. I've done the same testing against my factory iron intake. The track reflects exactly what we see on the dyno. The car runs quicker short times and give up some top end charge. In most cases the best ET are with the dual plane intakes even though you may run 2mph faster on top end with a Tomahawk using a 1" spacer, for example. For the most part we are just shifting power, not really making more of it as ET's are always pretty close with the extreme spread less than a tenth and most runs usually just a few hundreds of a second difference.

The T-II, Street Dominator and Tomahawk require a 1" where the RPM does not. If you try to test one of those single plane intakes w/o a spacer you are probably going to get your feeling hurt. Well, at least on any 455 or larger build capable of making over 500hp or so. Adding spacers to the RPM is hit and miss. They typically do NOT like fully open or 4 holes spacers. The best I've tested on them to date were fully divided or semi-open (allowing the rear openings to see a good bit of each other).

I will also put a warning out there about the RPM. I had one custom try to use on over 700hp and he kept spinning the same rod bearing. Can't remember at the moment which one, but one of the runners in the RPM is chopped off a bit where another one lays over it so may have been leaning out that cylinder.

After pulling the engine twice to find the same rod bearing toast and the rest in good shape he switched to a single plane intake with a spacer and never had any more issues........FWIW.....

So far everytime i have tried spacers on a rpm the engine responded very very well (both 400 and 455), open spacers has worked great for me.

I'd imagine the issue for many would be hood clearance...add spacers and try and cobble up air cleaner assemblies.

Cliff I would venture a guess that the cylinder in that motor you speak off the repetitively failed the rod bearing would have been feed off of the Manifolds shallow Plenum.

My 505 at peak power rpm the Tomahawk intake without a carb spacer was down 4.8 horsepower compared to a 1-inch open carb spacer.
At peak torque rpm the Tomahawk intake was down 5.9 ft.lbs. torque without the carb spacer.


4.210" stroke / 462

Holley Street Dominator intake with runner & plenum work by Dave Bischop

No carb spacer:
577.9 hp at 5700 rpm, 581.0 ft.lbs. at 4400 rpm.

With 1/2" open spacer:
589.4 hp at 5600 rpm, 589.0 ft.lbs. at 4600 rpm.

With 1" open spacer:
589.8 hp at 5700 rpm, 590.8 ft.lbs. at 4400 rpm

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Hoods suck

I’m honestly considering a super 400 hood or something just so I can fit in a tapered spacer on my RPM

When my engine was dynoed I was undecided on carb. So it was tested with a shop dominator and 2” spacer. Was good for 579hp at 5900 RPM.

IM always left wondering how much either A. Power, or B. RPM I’m giving up. Probably a little of both.

LOL dad did the same thing. Couldn't believe what the spacer did for his engine so he didn't want to take it off. Ended up buying a raised GTO hood from Glasstek to fit everything under the hood.

On my flow bench the rpm has issues of some runners robbing flow from other runners ,mainly the upper plenum.beleive it or not the lower plenum runners flow real good

i ran a t2 with a 1 inch open spacer on my 65 gto, then decided to try an rpm. then decided to try the spacer on the rpm. now i have a tiny little dent in my hood from the air cleaner stud. i need a good reminder that i am stupid every now and again, and that dent is in the perfect spot to remind me pretty often ...

"I'd imagine the issue for many would be hood clearance...add spacers and try and cobble up air cleaner assemblies."

Correct, the RPM is too tall right to start with to clear the hood on most of these vehicles and REQUIRES "cobbling" with Ram Air and Shaker parts. We are over here in the "Street" section so the owners of most of these cars haven't taken a saws-all to the hood yet to clear most of these parts.

I'd also add here that IF you find yourself adding a drop base air cleaner or move the air cleaner lid closer to the carb you are killing off a LOT of power with some set-ups.

NO ONE tests any of that stuff unless they are racing the car and have a car that will hook and run the numbers right to start with. I've tested everything out there that will bolt under my factory Shaker hood and you do NOT want to know what I've found with many of these parts, especially drop base air cleaners, funky flow thru lids, spacers, etc.

I've actually tested 4 spacers back to back at the track on both single and dual plane intakes with Q-jets and Holley carbs. Like running a fully open spacer on an RPM. I couldn't make a clean pass with one even though it pulled really hard on top end. It induced a "stumble" or hesitation going quickly to full throttle that wouldn't tune out. Keep in mind when reading that comment that most folks are looking to "feel" the secondaries "kick-in". I'm tuning for no felt transition whatsoever, just smooth/seamless power from idle to the shift point. That deal will run quicker ET and MPH every single time.

We tried it on another car we were running that day (private track rental) and it did the same thing. Sort of puked on itself for a second then pulled hard thru the gears to the finish line. Both cars LOVED the semi-open spacer in contrast, divided across the front and open between the secondaries. They also ran very well with a Tomahawk, 1" open spacer and 850DP carb even though they lost a little 60' we were seeing a solid 2mph on top end and very close in ET.

So you really never know with any of this stuff what's going to be the best in actual vehicle performance once you leave the dyno room and get the vehicle on the track. For bragging rights on a dyno sheet we usually top the engine with a T-II, 1" spacer and 850cfm Holley and lighten up the dyno a bit so it can rev.

If it's a higher end "race" engine just bolt a Victor/Dominator on it and hand that dyno sheet to the new owner......FWIW.......