Why is our stock lower intake so poor?

Pablo94SC

Registered User
I'm really having trouble figuring out the math on this one. Let me explain. According to a few different posters, our stock lower intake flows between 200-215cfm per port when port matched to the heads. Now, that is definitely lower than some of the better heads out there, so I understand wanting to match the flow of the heads. But that still doesn't take into consideration the fact the best M90 out there flows less than 900cfm. Here's what I see...

200cfm * 6 ports = 1200cfm potential flow
- 900cfm blower output
------------------------------
300cfm of potential left on the table

Sure, opening up the lower may make things flow better, but we're talking about a positive displacement blower that can't outflow the parts we currently have. Now, an AR or M112 might be able to max this out, but it appears to me that our stock lower intake doesn't necessarily need more volume, only some modifications to better direct the air. Make sense, cause all this talk about how crappy our lower intake is (in regards to flow) sure doesn't make sense to me.
 
My wife just painted the kitchen and we need to change them all ,so when you're done I have plenty more. I'm sick of wiring after the garage.
Alan
 
Can we please get back on topic here?

PS: Damon, the outlet is changed and working fine. You're buying dinner.
 
yea in my kitchen............wait a minute, we're supposed to be talkin about the intake. :p

i think the most we can do with what we've got is port match, smooth up some rough edges and maybe remove the air divider. not much we can do with that hunk of metal sitting on top. take that off and u'll have plenty of room to work with :D

has that actually been proven to give any more flow? -removing the air divider ?
 
yea in my kitchen............wait a minute, we're supposed to be talkin about the intake. :p

i think the most we can do with what we've got is port match, smooth up some rough edges and maybe remove the air divider. not much we can do with that hunk of metal sitting on top. take that off and u'll have plenty of room to work with :D

has that actually been proven to give any more flow? -removing the air divider ?

You can opened it up like this:D
 

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Not sure if it's really a good idea to remove the air divider triangle. I think it's there to provide a more even distribution of air to each of the cylinders.

David
 
Not sure if it's really a good idea to remove the air divider triangle. I think it's there to provide a more even distribution of air to each of the cylinders.

David

Exactly. If anything, I think there needs to be some more dividers in their to distribute the air more evenly. My opinion is the reason the #1 and #4 cylinders generally blow when the head gaskets fail is because they run lean due to lower intake design.

But no one has mentioned flow. I still don't see the lower intake being a restriction on flow until an AR or M112 is used. Even then, do those blowers outflow 1200+ cfm?
 
I think the reason for the rear cyls blowing is because of the lack of water flowing through those passages. If there was a relief from the rear of the head to the front passage, you could get more timing and power.

Chris
 
Not sure if it's really a good idea to remove the air divider triangle. I think it's there to provide a more even distribution of air to each of the cylinders.

David

I agree with David N.

But the shape and size can be changed to improve air flow.

I have ran both stock height and raised manifolds with-out
and with the triangle. The best working manifolds had a
different shape/size triangles & vains.

I have worked a bolt-on top manifold over the last couple years.
I finished it up this past summer. this has been a big help in making
changes during bench testing.

And the manifold that I am going to us for my final build, was one of
the first two raised manifolds built by Charles Warner. It was
built and sold to Jim Demmit. I thought it would be nice to
update a stock casting with some history behind it.

I have a final size and shape my manifold/plenum size. I bolted
the plenum on my car. It ran better across the rpm range.
But my blower whine noise has been cut in half.

Thanks Randy
 
But no one has mentioned flow. I still don't see the lower intake being a restriction on flow until an AR or M112 is used. Even then, do those blowers outflow 1200+ cfm?

All the intake valves are not open at the same time. So your 1200 CFM is quite a bit off. Some are on the intake stroke, compression stroke and exhaust stroke, so the "flow" potential of the manifold does come more into play. If you've got heads that flow 240 cfm on the intake, but the manifold can only support around 210 cfm, then you're leaving performance on the table and the manifold is a restriction point. And it is by no means the only restriction point in the intake system either, but it is a cruitial one as it occurs right at the intake runners on the heads. I don't have all the information in front of me right this instant and I'd have to research it a little to get it all, but the M90 does support the flow of the heads in stock and mildly ported form. In more extreme ports, the heads are capable of outflowing the potential of the M90 (the reason that boost drops) thus requiring more OD on the supercharger.

The problem with the manifold is the angles that the air intake has to make to enter the intake runner. The simple fact that the air has to make several turns right before the runner creates turbulence reducing flow. The volume has never really been in question, but the angle of the air path has been. The manifold should smooth out the air flow into the heads, and ours does not do that. That is the biggest issue with our manifold. It creates turbulence where it should be smoothing the flow.
 
Exactly. If anything, I think there needs to be some more dividers in their to distribute the air more evenly. My opinion is the reason the #1 and #4 cylinders generally blow when the head gaskets fail is because they run lean due to lower intake design.

But no one has mentioned flow. I still don't see the lower intake being a restriction on flow until an AR or M112 is used. Even then, do those blowers outflow 1200+ cfm?

I started modifiing manifolds for my car to get linear air flow.
This is the main problems with the manifold. I never raised a manifold
for more plenum/air volume. But a larger manifold/plenum area was
the end results from raising a manifold top to help straightin the air
up some. The IC plenum & IC plenum bolt flange hole was inlarged
to help in linear flow to rear manifold port openings. Not just to
let more air enter the manifold.

Modifiing a manifold ,I now look to get balance & linear air, then more CFM.
When dealing with a stock sc bird castings.

Randy
 
Chris,

That can easily be solved by tapping the rear of the heads and running a bypass line between the two heads. I've looked into this quite a bit and I'm pretty sure it can be done without loss of structural support in the heads.

007 -

True enough, but if the new heads that are in the works take car of this issue (angle of entry), do we really need a redically redesigned lower intake, specifically one that requires a raised hood? I think we should easily be able to achieve 240cfm or greater flow per port in the lower intake with only slight modification. Increased width and port size should allow better flow numbers, especially if the floor of the intake resides deeper in the valley.
 
Chris,

That can easily be solved by tapping the rear of the heads and running a bypass line between the two heads. I've looked into this quite a bit and I'm pretty sure it can be done without loss of structural support in the heads.

Ok, how is this going to improve cooling? What structural support? :confused:
 
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