M1 vs. RPM

I built a 512 for my Super Bee last year, and here are the basics:
.040 over 400 block.
Source 4.25" stroke bottom end with the lighter crank and upgraded rod bolts.
TF 240 heads, Scott Brown solid lift cam, Hughes 1.5 rockers.
10.6:1 compression.
I read a bit on intakes before I chose one, and then put out the word looking for an M1 or a Holley Street Dominator.
A friend thought he had a SD, and it ended up being a Performer RPM, so I picked that up. Then I found a screaming deal on an M1 single plane. I put the M1 on, but got to talking with Cab Burge and he says the RPM would be a better choice.
What do you all think? I am pretty sure the M1 gives me more hood clearance with the N-96 air box, but I know an RPM will fit, I had one on the previous 383 that was in it.
It's going in my '69 Bee, 4-speed, 3.54 Dana. Suspension will be switched over to either Assassin Bars or Cal-Tracs once I get it all back together.

Imo, the rpm will be much more responsive and street friendly with those 3.54 gears. You have them both so its easy to try them both. But I think for the street you will like the RPM best. It might even be the best choice for the track as well since you have a 4 speed and not a mild stall vert with a automatic.

M1

ITS A 512 CI MOTOR

two inch spacer help out with a 850 carb

I have ran the M1 on my 512 (400) for going on 4 yrs now. Throttle response is a non issue. It is great at low, mid and full.

Last yr I switched to a 4500 version of the M1, no loss of throttle response on the street but it is .12 faster in the 1/8. I hope to get to run some 1/4 mile times this yr.

With the 512 there is so much low end torque I dont think you will notice any let off by running a single plane.

PHR did a B series intake shootout a few years ago that you’ll find if you google it. It suggests that those two make similar HP up top, but the RPM will offer a much broader torque curve and better power down low. With 3.54 gears and especially in a big street-heavy B-body, what you need is midrange torque. My sense is the RPM makes more of the meat your car needs. I run one on my 452” B motor. Last fall I added a short 1/2” open spacer and blended the top of the intakes carb-pad in an effort to open up more plenum volume to each cylinder. Although I didn’t do a back to back test, I noted that the car felt like it wanted more RPMs and made better top end power. It went faster but the air was good, so...??

On a 512 go with the M1. On my old 440 with 3.55's I had the same question . There was almost no difference at the the track or on the street between the two intakes.

Very true.

I guarantee neither will fit under my hood with a 2" spacer.

I was hoping someone had some real world experience with it. I was thinking the torque should be a non-issue, but I was concerned about the 3.54's.

What gear do you run?

Thank you.

I run 4.10’s with a 28” tire. I’ve toyed with the idea of an M1; I’d be interested in your results if you were able to do a back to back test.

I'll see what I can figure out. I'd like to switch them on the same trip to the track and see which one performs.

I run a small Comp Cams Mech, grind XS282S. Like Stealthwedge67 I also run 4.10 and 28" tires and my car is 4000lbs.

Going to try and get something closer to 29" tall tire. The convertor on my car is tight enough that when I drive on the street that when I left off the brake it moves w/little slippage. On the track when I mash it it flashed to 4500. That is a little higher than I wanted. Was wanting closer to 4-4200. I shift at 5500-5600. If I'm running 1/4 I cross the stripe at 6100. I wont return my convertor because its too conmsistent. But I will be trying one another one from PTC that is a tad tighter to see if I can even out the shift points and finish line rpms.

The edelbrock is a great intake, my brother runs it in his Cuda w/the same cam I do. Only difference is his is 446CU and I'm 512. Which ever you chose you will like. The 512 is a great set up.

I was planning on going with a 29-30" tall tire. I plan on driving it a lot, so I will be attempting to keep the revs down. 295-65/15 is my tire of choice, but it is only available in drag radials and the super expensive flame-tread Mickey Thompson tires.

Really don't see why a RPM would even be mentioned on a 512?

Von, the RPM is a great intake for the street No matter what C.I on anything that has less than a all out solid roller cam with 440 size port heads
I've dyno tested multiple RB and B motors with a bunch of different intake, the RPM is the best over all for low RPM HP and torque, especially with light part throttle driving below 3500 RPM
I haven't done any same day at the track tests on BB 440 intakes in a long time so no valid feedback on that

Fathers Roadrunner:
Going from an RPM to M1 produced cleaner and more consistent plugs for all the cylinders on his pump gas, FT cam 440. With 3.23 gears and a 9” convertor it still kills the tires on the street.
He went to a Holley SD but swapped to a larger cam at the same time. It was a 12.0-12-teen car with the RPM and smaller cam. With the single plane and larger came it’s an 11.90-11.98 car @ 112-113 car.
91 octane
3900 pounds


My Coronet:
On my 505 with Eddy RPM heads, flat tappet, 93 octane I went from the INDY 2D dual plane to an M1 4150 ( STD port )
I’ve hit 11.05 ( peddling on top end ) and 11.06 and some other 11.0’s @ 120-121 ( Close to 122 once ) with 3.54 gear and the single plane.

Couple of the passes have been 6.99 and 6.98 in the 1/8 with the M1

11-teens and some 11.20’s with the exhaust still on and the M1 but 118 to high 119 mph

Does pull 24 MPH from the 1/8 to the ¼ on some of the passes.
While bracket racing, I noticed that peddling on the top end with the single plane does shave off et as much as peddling with the dual plane.

3840 pounds with head pipes and mufflers off.
3900 pounds with mufflers and head pipes on.
Sixty foot has been 1.54 best and as high as 1.58 with M1 and 3.54 gear
Flat steel hood.

FWIW

Mike

I still venture that overall...a RPM is a choke on 500 plus inches, unless we are talking a super heavy/pulling type application.

Silver,

Exhaust is costing you a solid tenth, (maybe .15) , it looks like?

My wagon, 4600lbs, 526 inches, unported rpm heads, 10.6 compression, mild cam. 2600 stall, 3.73's.
had a rpm w/ 850 holley. ran ok. changed to an M1, and a 1000cfm 4150 quick fuel carb.
HOLY CRAP. a difference of night and day. car feels like an animal now.
go with the M1.

Do you think the 150 CFM bigger carb. didn't help?
I haven't seen or heard of any BB Mopar, B or RB , that didn't go quicker and faster with a bigger carb

I'd say some. But considering the actual flow difference between a 850 and 1000, is not near 150 cfm, ,I'll say not that much.

Yea, the coronet did seem to like the open exhaust.
The exhaust system is full 3" to the bumper with Flowmaster's
I guess the cam is somewhat healthy so i've been told


When i went open header i also put on 16" extensions
But i just used 3-1/2" for the extensions as thats the collector size.

You need to remember that not all carbs. of the same CFM size built by a different company flow the same, some flow more and some flow less as another company same size rated CFM
The true test is either on the same bench the same day tested by the same tech or tested back to back to back to the original carb. at the track within 1.5 hours of each other at the track tracking the weather changes and adjusting for that
I had three carbs flow tested by the same tech on the same bench within 30 minutes of each other, one barrel at a time and the B.G. Stage # 3 modified Holley 750 CFM flowed 1020 CFM The stock Holley 950 HP #80496 flowed 880 CFM and the stock Holley 4781-2 850 CFM D.P. flowed 880 CFM also
The B.G. was the fastest of the three at the track

IMO You’re kidding yourself. These two manifolds are very very close by all accounts including Dyno tests. Going from a standard 850dp to a quickfuel 1000 is light years. I’d guess the difference in that swap is 90% carb. In fact, In a heavy wagon, I wouldn’t be surprised if you’re still leaving performance on the table with the single plane.

Lightyears?

I don't see lightyears. Just my .02...

On my junk...i saw exactly .07 difference between a 40 year old 800dp and a high dollar carb 950 carb. Just my experience.

Yes. I know...every combo is different...

If we're talking 4150 to 4500, then I would agree, no doubt.

Fair enough. Do you still have the RPM? Just like I mentioned to Ohio, I’d love to see a back to back test with no other changes with these two manifolds.

Sorry to hijack one more time, but...Silver was is the LSA of your cam?

I can say we had a pretty good comparison on my sons Dart between the RPM and the Holley street Dominator. But his eng is only a .030 over 400 (406 cubes). But you could really see the RPM was much better in the 1/8 and 60 ft. I know in the 1/4 he ran at that time 11.59 @ 117 with the SD and 11.55 @ 116 with the RPM. The single plane SD had more mph in the 1/4 but the RPM still had the better et. And you could see in the timeslip how the RPM won all over in the 1/8 and how the SD was coming on in the 1/4 but ran out of realestate. So if had a bigger eng like a 499 or something then the SD may have won in the 1/4 with an eng with more cubes and torque. Course much depends on the combo as we all know. I run the Indy dual plane on my 493 and it looks to have larger ports then the RPM. I do want to try a single plane one day but a friend I know with a combo very close to mine ran 10.98 with the Indy Dual plane and then he switched to a single plane (Victor I think) and ran a 10.90. So he picked up almost a tenth. But then he took his 850 DP off and went to a Dominator and then ran 10.60's as it really liked the more carb.
So to me it all depends on the combo as the dual plane is better down low and may be faster in the 1/4 on some combo's until you have enough eng , gear and converter so the single plane will be the best and fastest. Ron

Sorry to hijack one more time, but...Silver was is the LSA of your cam? [/quote]


No worries bud,
.585/.600 1.5 rocker
260@50-268@60
109 lsa
104-105 installed

I would definitely run the M1 single plane on that motor.

Love the SuperBee by the way!

run the M1 and a good annular booster carb, best of both worlds???

500+ inch motor = single plane intake.

My only on track comparison that might be somewhat relevant here was on a mid 11 sec stock stroke 440 combo in a 3700 lb cuda. I tested the RPM vs. a Holley SD and the timeslips were almost identical.

Merely because Cab and I talked about it the other night and I respect his opinion and experience a great deal. Just getting some opposing views on it. I feel that the M1 is the best fit for my car, but I would like to put them both on and do some street duty with both and possibly find time to do a same day shootout with both intakes.

on the street my 512, max wedge ,Indy 400-2 ran great, 3.54 gear.