Im interested in the effects of the plenum size on performance.
I understand the difference between and a single plane and a dual planed that a smaller plenum essentially increases signal to carb and also the 180 design alternates the firing order stopping the effects of overlap so to speak.
Typically single plenums are quite a bit bigger than the dual plane BUT what happens when you have a dual plane with an approximate plunum volume of 38cc of per side versus a low rise single plane with a total plum volume of 76cc.
Bearing in mind that on the dual plane whilst each plenum is smaller it is also operating on only one side of the carb.And on the single plane whilst it is bigger it is acting on the whole carb.
Ie the 2 sides of the dual plane at 38cc total 76cc acting on the whole carb.
Whilst the single plane also has 76cc acting on the whole carb.
so is there really much of a difference? if they have the same effective plenum volume?
And under 400rpm what effect if any on torque does the cut out on the plenum have ? as in the performer rpm
Splitting the plenum increase air velocity which works better at lower rpm.
The cut out short circuits the split which improves high rpm flow rate by allowing the engine to draw from both sides of the carb which reduces restriction.
Thats the jist, there will be long drawn out explanations I'm sure but thats the engineering effect.
X2 with Chuck and Hcompton. Here's my real life example that backs up what they are saying and what I've witnessed. The effects of the GM's TPI intake on torque and horse power. Defining the TPI as having small runners, by any true performance application, and that are EXTREMLY long (almost 17 inches) : torque below 3500 RPM's that is 100+ft/lbs higher than any other intake on the market and a top end that hits a wall right near 5000 rpm's that is the worst of any intake on the market. It is extremely common to see a build with one of these intakes have number that make low HP&high torque, i,e, 275HP at 5000 and 360 ft/lbs at 3300. This makes for a great daily driver/tire burner and a not so good E.T. at the strip.
Intakes should be purchased for application and included with that are the cam and carb. Putting together the correct combination for you're application is key to getting the performance you're after.
Hi , thans.
I ask because Ive got a 427 bbc with a 227/235 cam @50.limit to 6000k.Pure street use. Low end seems a bit poor - off idle etc and Ive got a low rise single plane on it. An old holley street dominator. WAs wondering on fitting a dual plane ( maybe rpm) to improve low end.
But on looking at the plenum volumes they are as I mentioned above.If you add the 2 sides of the dual together its about that of the holley street dominator.
Of course , the runners on the holley are much shorter - maybe 60% shorter...any thoughts?
Also , my wideband gives me an air of 12.2 at idle - too rich - what am I aiming for on a holley 750
A dual plane should be a bit better off the bottom. Regarding throttle response, the AFR at idle isn't urting your performance, but rather as long as it stays in the mid to high 12's when you stab it is more critical.
its a 4 speed stick so no converter. seems slighty sluggish idle to 2000k. Or maybe less slugguish but drivability is an issue. Pulling off in 1st seems like I've got to give it more rpm then I would like to get it going. Im figuring this is down to the intake I'm using.With a bbc id expect enough torque to almost put it in 2nd and lift the clutch with no throttle and pull off gently.
driving in general is ok , off 1500 giving it some throttle seems good. But lets say Im trundling around at 1200 rpm and i go WOT i get a bog and 9-10 reading on the AFr - too rich.
Wheel spins for a second then bogs. Theres power there but its bogging down.
The engine was dyno'd and It hit 380hp somewhere around 5700 and 420ftlbs at 4400.
We did expect more after the build a few years back but there you go.
No dyno figures idle to 2500 where i feel the problem is.
Heads are iron , nicely ported , 2.06 and 1.72 valves btw.10:1 compression.
As its street car i guess i want fast acceleration idle to 5500
any thoughts..?
tallest intake i could fit would be a performer rpm.
Almost any dual plane is going to be better than the rotten low-rise single plane you have now.
Performer RPM would be a great choice, I would not be surprised to see it pick up 35 ft/lbs at 1800-2000 rpm and be much more drivable at low rpm than what you are using now. Weiand Street Warrior would also be good if you can find one.
Street Dom, Torker, Torker II, Weiand Accelerator, Offenhauser 360° are all about the same....a poor intake design all around, made back in the day just to clear low hood lines and feed into the public perception that it would be better than a dual plane for upper rpm power....but they really weren't very good at all.
Was the cam degree'd in when installed?? Or just dot-to-dot??
ok , I'm sold on the dual plane.
Does a dual plan improve effective compression over a single plane then? as its 180 and every other cylinder fires on each side of the intake? reducing cam overlap in a way?
The plain Performer has a spreadbore carb bolt pattern and will require an adapter to fit the Holley Squarebore carb you have. Making it within 1/8" of the same height as the Performer RPM
I'd use the Performer RPM.
I think you'll need a drop base air cleaner to get it under the stock hood of your '73 Camaro though, if you don't already have one.
check your cam thats its not flat? I took a performer off a warmed up 454 and used a Victor Oval port. I picked up 4/10s in the 1/4 with nor notice able loss of bottom end. Something is way wrong with your tune at low rpm.I think my 454 was around 400 hp but the tires broke loose very easily. I had aan auto though.
what effect does the notch have on the performer rpm on low rpm?
vs the performer ?
Bearing in mind the holley adaptor for the performer essentially adds a small notch - albeit smaller than the rpm notch
ok , so perfromer is not getting the thumbs up!
Looks like rpm for me , no room for anything bigger , please all keep your comments coming
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