Plenum Volume

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Fast01

Fast01

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Does anyone know the plenum volume if the Indy big block tunnel ram? From what I'm reading, it seems to be a bit small and benefits significantly from spacers. I'm on the fence with buying one and really don't want to have to apply bandaid fixes to make it work. Thanks!
 
.....or, if someone's got one, maybe you could give me the length, width and height of the plenum and I'll do the math.
 
I wouldn't call spacers a band aid. They are a tuning tool. There is nothing wrong with using spacers to change plenum volume.
 
yellow rose said:
I wouldn't call spacers a band aid. They are a tuning tool. There is nothing wrong with using spacers to change plenum volume.
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Height issues
Vision issues
?Personal dislikes?
 
I'm not too concerned about height and have always run some sort if spacer, but there's only so much volume to be gained by adding a spacer without it being 10 inches tall. Lol! The spacers are definitely a good tuning tool, but there's only so far you can go with 'em. In doing some research and looking at the pics of the manifold, the plenum does look to be real small. I read somewhere on the internet (so it must be true) that the plenum volume, optimally, should be around the displacement of the engine.....it doesn't look to be anywhere near 517".....maybe half that. Of course, there are a lot of guys,a lot smarter than me on here and hopefully they'll chime in on this!
 
Fast01 said:
I'm not too concerned about height and have always run some sort if spacer, but there's only so much volume to be gained by adding a spacer without it being 10 inches tall. Lol! The spacers are definitely a good tuning tool, but there's only so far you can go with 'em. In doing some research and looking at the pics of the manifold, the plenum does look to be real small. I read somewhere on the internet (so it must be true) that the plenum volume, optimally, should be around the displacement of the engine.....it doesn't look to be anywhere near 517".....maybe half that. Of course, there are a lot of guys,a lot smarter than me on here and hopefully they'll chime in on this!
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LOL , wow , if 10" x5" = 50, how big would a 517" plenum be ? Think I MIGHT HAVE MISSED SOMETHING ON THAT!
 
Lol! The 10 inch tall comment was a joke. The point was, for arguement's sake, a spacer with a 5x5 opening at 2" tall, you're gaining 50 cubic inches of volume (LxWxH=volume) times 2 is 100 cubic inches gained. That's all fine and good if the original volume is in the ballpark. Now again, I'm far from an expert and could be way off on this plenum volume thing, but I've read that the Indy is real small and if max benefit is to be had by matching the plenum volume to engine size, I'd like to be close. I could space the whole top plate up to gain more volume than throttle body spacers would provide.
 
You are right about the general rule of thumb being plenum volume should roughly equal engine displacement, on a normally aspirated racing motor. This prevents the engine from bogging during closed to wide open throttle transitions, like on the start line in drag racing. It also allows better top end power when maximum air volume is required.
Increasing the plenum volume can sometimes decrease air velocity, which in turn limits throttle response and messes with A/F ratios at lower RPMs. Point being, if you spend a significant amount of time at WOT, or need the motor to react quickly from idle to WOT, lots of plenum volume is good, but not so good if it comes at the expense of velocity.
Plenum volume is much less important if you are using any sort of boost.

Hope this helps.

Garry
 
Garry in AZ said:
You are right about the general rule of thumb being plenum volume should roughly equal engine displacement, on a normally aspirated racing motor. This prevents the engine from bogging during closed to wide open throttle transitions, like on the start line in drag racing. It also allows better top end power when maximum air volume is required.
Increasing the plenum volume can sometimes decrease air velocity, which in turn limits throttle response and messes with A/F ratios at lower RPMs. Point being, if you spend a significant amount of time at WOT, or need the motor to react quickly from idle to WOT, lots of plenum volume is good, but not so good if it comes at the expense of velocity.
Plenum volume is much less important if you are using any sort of boost.

Hope this helps.

Garry
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Garry,
Yes, that helps a ton, thank you! I'm glad I'm thinking in somewhat the right direction. I understand the trade off with the velocity issue and figure if i can get on the low side of my displacement I shouldn't hurt velocity too much and can then fine tune with spacers if needed. I think i failed to mention this is a MPI set up, so there's no booster signal or anything to worry about and adding or removing spacers won't be as much of a chore.
 
Fast01 said:
Garry,
Yes, that helps a ton, thank you! I'm glad I'm thinking in somewhat the right direction. I understand the trade off with the velocity issue and figure if i can get on the low side of my displacement I shouldn't hurt velocity too much and can then fine tune with spacers if needed. I think i failed to mention this is a MPI set up, so there's no booster signal or anything to worry about and adding or removing spacers won't be as much of a chore.
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SO , HOW WOULD A SINGLE SQUAREBORE INTAKE ACCOMPLISH THIS? IMPOSSIBLE !
 
famous bob said:
SO , HOW WOULD A SINGLE SQUAREBORE INTAKE ACCOMPLISH THIS? IMPOSSIBLE !
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I don't know myself but since we're talking about tunnel rams here, how the hell does your shouting CAPPED reply, apply?

Even if Gary is running a single 4bbl. & not antunnel ram dual quad, wouldn't the idea of larger smaller plenum still be in effect?
 
Famous bob, I don't think getting the plenum volume in a typical squarebore intake to equal the engine displacement is likely. We have been talking about a tall "tunnel ram" style intake, designed for high rpm operation.
As a quick example, lets say an intake has eight 2.5 inch diameter runners, each 10 inches long. Just those runners alone displace almost 395 cubic inches. If individual runners are not used, the volume grows even more quickly.
70855angled_left.jpg


The interior volume (total 3 dimensional volume, LxWxH) of the manifold can approach the CID of the engine, and in fuel injected applications, it's even easier to get very large plenum volumes. Look at a current Pro-Stock intake and you'll see what I mean. Here is a pic of John Gaydosh's 2016 Pro Stock intake. It's easy to see how that could be 500 cubic inches.

ProStockEFI-01.jpg
 
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rumblefish360 said:
I don't know myself but since we're talking about tunnel rams here, how the hell does your shouting CAPPED reply, apply?

Even if Gary is running a single 4bbl. & not antunnel ram dual quad, wouldn't the idea of larger smaller plenum still be in effect?
Click to expand...
Yeah, I hit the caps button quite regularly by mistake, pay no mind to it. I can`t type worth a ----, and don`t want to delete and start over! A lot of times I just quit the post .
 
Garry in AZ said:
Famous bob, I don't think getting the plenum volume in a typical squarebore intake to equal the engine displacement is likely. We have been talking about a tall "tunnel ram" style intake, designed for high rpm operation.
As a quick example, lets say an intake has eight 2.5 inch diameter runners, each 10 inches long. Just those runners alone displace almost 395 cubic inches. If individual runners are not used, the volume grows even more quickly.
View attachment 1715079484

The interior volume (total 3 dimensional volume, LxWxH) of the manifold can approach the CID of the engine, and in fuel injected applications, it's even easier to get very large plenum volumes. Look at a current Pro-Stock intake and you'll see what I mean. Here is a pic of John Gaydosh's 2016 Pro Stock intake. It's easy to see how that could be 500 cubic inches.

View attachment 1715079487
Click to expand...
See ur point, but I think streetcar mostly now, my heavy dragracing days are gone. 1 fourbarrel intakes only, but see the need for big volumes on big motors. I need more on mine !
 
Garry in AZ said:
You are right about the general rule of thumb being plenum volume should roughly equal engine displacement, on a normally aspirated racing motor. This prevents the engine from bogging during closed to wide open throttle....

Garry
Click to expand...

OK, then let me ask about a single 4bbl. engine? I have in front of me a MP W2.
In order to figure out plenum size it is HxWxD correct? And then X's 2 for the suggested engine size that it should feed?
And somewhat less for a street/strip engine, less for a street engine, etc...

Runner length is left out because it is seen as an extension of the intake port?

Thanks
 
Plenum size is generally regarded as the total air volume in the complete manifold, from the carb mounting surface to the intake gasket, including the air volume in the intake runners. Nothing gets multiplied by two though. Maybe I misunderstood your post?

Here is a good article on the subject:
Tech Feature: Custom Racing Intake Manifolds - EngineLabs
 
Nope, sounds good so far.

I don't have any material/tools to calculate runner volume. The plenum would be a close calculation because of the pyramid shape it has.

I was just thinking of this post & wondering how well, or not, a single 4bbl. is on top of *** displacement sized engine. Also in a street, street strip & full race application.
 
Hey Rob!
I'm not familiar with the runner shape of that manifold, but in figuring runner volume you can get close using the L*W*H for a rectangular runner, 3.14*Radius squared*H for a round runner and 4/3*3.14*R1*R2*R3 for an oval. Obviously the curvature and taper of the runner will be difficult to factor in. As for a pyramid shaped plenum, L*W*H/3.
Anyway, back to the Indy tunnel ram issue. In doing more research it seems that even Indy feels it's undersized as they offer a plenum spacer to raise the top plate by 1/2". Go figure!
 
Oh, and you could get a burette or graduated cylinder, seal up all the runners and fill the thing with fluid to get an accurate idea of total volume. Kinda like ehen you cc a cylinder head only bigger
 
Fast01 said:
Oh, and you could get a burette or graduated cylinder, seal up all the runners and fill the thing with fluid to get an accurate idea of total volume. Kinda like ehen you cc a cylinder head only bigger
Click to expand...

I did think of that. But, IMO, I think it's more trouble than it's worth. It seems to run into the low 10's high 9's in A bodies. Good enough for me.

Yes yes yes, back to the tunnel ram.
I have one of those awaiting better days to come!
 
rumblefish360 said:
I did think of that. But, IMO, I think it's more trouble than it's worth. It seems to run into the low 10's high 9's in A bodies. Good enough for me.

Yes yes yes, back to the tunnel ram.
I have one of those awaiting better days to come!
Click to expand...
I remember waxing a couple of tunnel ram hemi`s back in the day w/ a rat roaster, talk about volume !
 
In case anyone besides me actially cares, i found somewhere on the net that the Weiand tunnel ram (I have already) has a total volume of 549 cubic inches. Well, i went out to the garage and took sime very rough measurements and came up with approximately 522 cubic inches. Just found it coincidental and interesting.
 
Sooooo, I guess I won't be able to purchase that intake from you then huh?!

LMAO

549 in plenum?
 
Because of plenum volumes of single 4 stuff, it's almost impossible to get the carb to big, as long as you compensate for it.
 
Not just plenum, but total volume. Still, pretty funky that it's right at the volume I'm looking for. Anyway, don't rule it out just yet Rob. It may still be more economical money wise and tome wise, to get the indy and modify it to suit my needs......I'll let you know.
 
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