Hot Rod Forum banner
1 - 14 of 14 Posts

·
Registered
Joined
·
46 Posts
Discussion Starter · #1 ·
Building a new engine for my monte. But im down to the intake and cant decide on whether to buy an rpm performer or rpm air gap...

Here's the set-up...

350 bored. 40
completely balanced rotating assembly (9.7 compression )
906 vortecs... Completely reworked
750 holley vac secondary
lunati voodoo 268 (227/233 @50)
1.6 roller tip rockers
msd distributor
dacco 2200-2500 converter
turbo 350 trans
3.08 rear (soon to be 3.42)


looking for the best intake for my set up. Hoping for around 375 to 400 horses... But more concerned wit best intake. Any experience as to which performs better would be greatly appreciated...
 

·
Registered
Joined
·
12,338 Posts
why not look for a used intake and w/e is best price is the best intake for you.If you find an older airgap,before you install it check the divider,,,there is a certain amount to machine in the older intakes that have a full divider.watch the video thats posted comparing the 2 intakes.that intake works better with the 1 5/8 header s.The bigger tube headers are for more horse power.
I think you will come close to the hp you are looking for.
not sure where the video is,but it is posted here somewhere
 

·
Registered
Joined
·
4,018 Posts
RPM Air gaps suck.

Slow warmups. Takes 30 minutes before the carb starts to act right when temps drop below 60.

Pain in the *** as everything seems to fall under the carb (in the "air gap" space).

Get the regular RPM.
 

·
Registered
Joined
·
5,391 Posts
I like the look of an air gap intake - but the basic idea of it is to keep the air fuel charge cooler. Really? impossible as the residence (cooling) time from air entrance into the carb to the combustion chamber at any rpm is measured at the third decimal point of a second. If it looks nice, the price is right, then the air gap will be your best bet. The positive effect is that these intakes tend to straighten the air flow as they are a bit higher.
 

·
Registered
Joined
·
15,631 Posts
Building a new engine for my monte. But im down to the intake and cant decide on whether to buy an rpm performer or rpm air gap...

Here's the set-up...

350 bored. 40
completely balanced rotating assembly (9.7 compression )
906 vortecs... Completely reworked
750 holley vac secondary
lunati voodoo 268 (227/233 @50)
1.6 roller tip rockers
msd distributor
dacco 2200-2500 converter
turbo 350 trans
3.08 rear (soon to be 3.42)


looking for the best intake for my set up. Hoping for around 375 to 400 horses... But more concerned wit best intake. Any experience as to which performs better would be greatly appreciated...
Performer RPM with no air gap. If this is a daily driver and air gap in winter is a PIA and the excess fuel you have to choke in to get it to run just kills the pistons, rings and bore by washing out the already thin lubrication at the top of the cylinder. Unless this is a race mahine that only comes out on summer Saturdays and Sundays the air gap just isn't the way to go. Or can buy the air gap then move to southern Arizona, Nevada, or California where it's sunny and hot most of the time.

I can assure you that the regular Performer RPM with everything else you've done will on an engine dyno deliver from 380 to 410 horses.

Bogie
 

·
Registered
Joined
·
5,391 Posts
Another vote for the RPM sans air gap. The two make basically identical power if the plenum divider is cut the same on the RPM as it comes on the air gap.
I'm thinking an open spacer will accomplish the same. What they are doing is balancing the air flow pulses - and quite frankly, for day to day low and mid throttle operation that will detract from low end performance, idle and even a bit of gas mileage if my engine is an indicator. Might as well have a Victor type IMHO:eek:

Aluminum open spacer - gone now, replaced by a phenolic 4 hole version(but no photo):


Dave W
 

·
WFO
Joined
·
5,030 Posts
The 1" x 3" notched plenum divider of the RPM AG falls in between an intact plenum divider of a dual plane and an open spacer on a dual plane. It allows some of the benefits of a single plane but w/o all of the downside. In my experience using an Edelbrock C3B w/its cut out for the secondary throttle blade of the Holley 3 barrel extended out to a little over 3.5", it performs right in between an open spacer and no spacer or "notched" divider of a dual plane. This also seems to be the trend w/the RPM vs. RPM AG. An unmodified C3B is shown below, left. An RPM AG below, right. Below them is an RPM w/o AG, left and a Vic Jr, right.




An open spacer on a dual plane will increase plenum volume- something that a notched plenum doesn't do, and this is part of the reason why an open spacer/dual plane often falls in between an open plenum and a standard dual plane w/o an open spacer in performance. Also there's no added carb height when using a notched plenum divider like there is using a spacer. The added height of the spacer can help allow the air/fuel to make the turn into the runners w/less deflection of the a/f when it hits the plenum floor at high rpm.

So it's hard to directly compare the Vic/Vic Jr. w/a notched RPM intake or an open spacer on a dual plane (not that anyone is) because of the runner lengths and added overall runner/plenum volume of the Vic that combine to raise its powerband over an RPM w/an open spacer or an RPM AG.

As far as cutting the RPM like the AG, because the carb height and runners are basically the same between the two intakes, that mod will make their top end output equal for all intents and purposes. Not saying that's the thing to do in every case- just saying that if the same powerband as the AG is wanted, it can be had by notching the divider. For the right engine and vehicle combo (low gears, higher stall speed, light weight, more track than street, etc.) notching the plenum (or adding an open spacer) can help more than it hurts. But for the majority of street driven vehicles, I think the non AG w/the plenum left as-is, IS the way to go.


FWIW, I have always had better performance from a divided spacer on a dual plane (not always a 4-hole spacer). The spacer below I made from marine grade plywood for a 455 Pontiac engine running a Performer (this was before there was an RPM Pontiac intake). It picked up the quarter mile ET over a tenth, which was also pointing towards the engine wanting more intake and carburetor. Being wood, it acts as an insulator much better than metal and most other denser materials.

 

·
Registered
Joined
·
46 Posts
Discussion Starter · #12 ·
Thanks for all the advice. I live in north Mississippi, we get cold weather and snow every now and again. I thought that I should run the air gap because it was along the RPMs as my cam. My cam is from 18-6200. But I don't want to sacrifice any low end torque by using too big of an intake..
 

·
WFO
Joined
·
5,030 Posts
Thanks for all the advice. I live in north Mississippi, we get cold weather and snow every now and again. I thought that I should run the air gap because it was along the RPMs as my cam. My cam is from 18-6200. But I don't want to sacrifice any low end torque by using too big of an intake..
The RPM won't sacrifice any appreciable amount of bottom end- especially compared to an open plenum intake. Both the RPM Air Gap and the RPM w/o air gap have the same 1500-6500 rpm advertised powerband.

IMHO the real debate here is whether the RPM w/Air Gap or w/o air gap is what you'd want to run. My vote is for the RPM w/o air gap. This is doubly so if you plan on driving in cold weather.
 
1 - 14 of 14 Posts
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top