BBC dual plane intake which one?

[bowtie72]

I am trying to choose a intake manifold for my 396 I built. Are the rpm air gap manifolds good? Should I stick to low plane? Cam is the small thumper comp cam. 279 stock otherwise. Let me know your experience. New any better than used?

[geezer#99]

EDelbrock performer rpm would work.
Air gap intakes don't work well if you need some heat in your intake which is needed if you run at all much when it's cooler temps.
That's a lot of cam for 'stock otherwise'!
What's your elevation and how 's your timing curve.

[bowtie72]

I was thinking the air gap would be a problem with cold starting/driving. The thumper cam is mainly for sound not much on the performance side. Driving will be between 6-7k elevation. Timing curve will have to be adjusted as the carb etc. is tuned

[geezer#99]

On timing with that cam, think up near 20 initial if possible.
What's your compression ratio?

Do the timing first and you likely won't need to touch the carb.

[bowtie72]

Compression should be 9.0-9.5

[geezer#99]

You got way more cam than your compression likes so timing might be tricky.
You'll need to experiment.
And it'll be much easier for tuning if you don't use an air gap intake.

[James the III]

I'd not use the air gap.. nor would I use the rpm..
I'd use the performer.. It's a 9 to 1 static compression bbc.. and the dynamic compression will be in the dumpster.. with that cam.. it's gonna be a fuel pig with no balls.. you don't want an intake (performer rpm) than moves the power up the rpm range.. Stick with the performer, and trash can that faux cam..

[DieselSJ]

Originally Posted by James the III

trash can that faux cam..

Best advice in this thread.

[geezer#99]

He can't trashcan that cam. He thinks he needs the racous rumpty rump sound.
And I suggest the rpm because with that cam he'll need to move the rpm band up a bunch.
It'll be a bandaid but better than trying to maintain any semblance of street low rpm manners with a little performer intake. He'll need to run it at higher rpm to get it to run well at all. Mights well feed it with an intake and carb that likes to run well above 3000 rpm.
At least he lives at higher elevation which lets him run mega more timing without detonating itself to death.

[Port&PolishMan]

Good Porting gets 30 HP & 40 Tq. - Engine Breathes Easier . .

No Power Robbing Cam - Spring Load Drag . . If Your running
higher Lift Cams

[James the III]

Originally Posted by geezer#99

He can't trashcan that cam. He thinks he needs the racous rumpty rump sound.
And I suggest the rpm because with that cam he'll need to move the rpm band up a bunch.
It'll be a bandaid but better than trying to maintain any semblance of street low rpm manners with a little performer intake. He'll need to run it at higher rpm to get it to run well at all. Mights well feed it with an intake and carb that likes to run well above 3000 rpm.
At least he lives at higher elevation which lets him run mega more timing without detonating itself to death.

Wrong..
low static compression 9 to 1, with that cam it's dynamic compression is low8 or high 7's..
then add in the thin air.. at his 7-8000 ft elevation..
This is going to run as good as a 540 cid bbc with peanut ports
Welp, the 540 with peaports might run better..

heck a 307 2 barrel will outrun it


he has 3 choices..
run it and hope he likes it as it farts,coughs,etc
or trash can that cam and get one that works with his combo of parts
or keep the cam and get 11to1 static compression..

I get the wanting the cool, thump thump.. but that goes out the window when a tired 150k mile small block.. walks it.. and you can't catch it..
That sir is not cool.. A rat should eat a mouse, not run and hide from it.

[geezer#99]

What you mean 'wrong'!!
I don't disagree with your summary. All I'm saying is he has the cam, it's not the right one but in order for it to work he needs all the help he can get. That's where an rpm intake works. No sense choking it more with an intake that runs out of breath right where he's gonna need it to start working.
Likely the only choice is to make a doorstop out of the thumpr but... he wants the sound of the wild idle.
At least keeping it he'll maybe learn a bunch about tuning.

[James the III]

Originally Posted by geezer#99

What you mean 'wrong'!!
I don't disagree with your summary. All I'm saying is he has the cam, it's not the right one but in order for it to work he needs all the help he can get. That's where an rpm intake works. No sense choking it more with an intake that runs out of breath right where he's gonna need it to start working.
Likely the only choice is to make a doorstop out of the thumpr but... he wants the sound of the wild idle.
At least keeping it he'll maybe learn a bunch about tuning.

If I compress sea level air the oxygen in the cylinder is much more than the same engine running at 7-8000 feet above sea level..
So, a low compression engine, sucking in thin air (oxygen) will be a royal turd..
Now that cam, that to get that rump rump bleeds off cyl pressure (compression) only dropping the dynamic (real world compression) even lower..
So no compression to make power, a cam that bleeds what little it did have off, and high elevation from sea level thin oxygen air.. will not be pumping much air through the engine.. It's an air pump.. the more oxygen and fuel the more power.. to get that thin air, no compression to run you'll be dialing the fuel way back.. and less fuel+less air= turd

[61K10]

The guy wants the rump rump sound so be it. either manifold probably won't make much difference anyway (yes James you disagree) So it's slow but sounds good. Wait till he bolts it up to his auto trans--------

[DieselSJ]

There are other ways to get rumpety-snort without going to a long duration cam. Find a shorter duration with a nice tight lobe center and he'll get his sound and it will be much more fun to drive.

[Ironangel]

I'm running a Weiand 2P-180 (PN#8001) For BBC on my 69 L34 396 and like it. I like it ALOT!...That is if your running a spread bore carb...I'm running a Comp Cam 268H cam and like it alot as well...Loose the Thumper! If you want a motor, especially a BBC that sounds awesome? Boost the CR with a set of closed chambered heads and 3" pipes...The Weiand intake above is a dual plane intake. The 268H cam for BBC has a mild lope at low idle but more importantly makes it's power at low rpm so a set of low budget old school closed chambered heads can work their magic before running out of breath..."just sayin" PS. I'm ridin with Geezer on going for the rpm's. The dude (OP) already has two strikes with a Thumper and an Air Gap..."Wind that Mutha up!" :P