Exh. flow #'s "with and without a pipe"

[fishy68]

I've seen flow numbers posted for various heads on a few different sites. Sometimes I see it state "without exhaust pipe" and "with pipe" and without the pipe the numbers are lower. I can only assume that with no pipe it acts like the intake would with no guide to straighten the air. Is this true? If so is there any way to estimate how much difference there could be or is every head different? Reason I ask is when the guy flowed my heads that I ported he said the exhaust flow was a little weak compared to the intake. He didn't use any type of exhaust pipe on it though and after seeing the statement with and without pipe I'm wondering if the flow numbers might actually be better than what he said they were.

 

[rumblefish360]

I can only assume that with no pipe it acts like the intake would with no guide to straighten the air. Is this true?


Reason I ask is when the guy flowed my heads that I ported he said the exhaust flow was a little weak compared to the intake. He didn't use any type of exhaust pipe on it though and after seeing the statement with and without pipe I'm wondering if the flow numbers might actually be better than what he said they were.

Yes, it is true. The air just explodes out of the exhaust port and tumbles around. The pipe on the end helps keep that train a rollin on by quickly.

If so is there any way to estimate how much difference there could be or is every head different?

I'm not sure about that. I would imagine each head is different, but the calc's have to get goofy on it.

Flowing with a pipe helps the port flow more air. This is a different way of testing the port with the pipe. If your used to this, you can choose a cam based on it, but it wont be the same cam as with the specs on the port without the pipe.

You'll end up with 2 different cams.

Just ask the guy how he flowed the heads. What was used on the ports entrance and exits. Bore fixture size, radiused clay exit.

You know what, BJR has a flow bench. PM him and ask him to reply here and what he does or how it's done and how others may do it.

 

[crackedback]

Flowing with a tube is more "real world" to me.

Does your car have an exhaust system or headers on it?

I don't own a vehicle that dumps exhaust straight out of the port. Having a tube on the exhaust more closely replicates operational parameters.

 

[rumblefish360]

CB, most mag's and shops post numbers without a pipe, right?

This is what I have come to judge a head by and use to figure out a cam to suite the need. Though, I like the idea of real world better.

 

[crackedback]

It would be nice if there was a standard to judge results.

 

[hilbillyconques]

i dont know about all the reasons but i thought i would post my 440-1s that i sent to modern cylinder head the numbers on the left is where he flowed them when i sent them to him and the other numbers are after his port work . it also shows with and with out tube.

 

[fishy68]

Thanks for all the replies guys. It sure would be easier to have a standard flow measure but I imagine that all the variables like Rumble mentioned affect things so to get good comparable answers everybody would have to go by a standard and probably isn't going to happen.

Hilbilly thems some nice numbers. That ought to wake up a sleeping giant.

 

[rumblefish360]

WOW! Hillbilly, thanks. That is a cool sheet showing with and W/O a tube.
(Welcome aboard by the way.)

 

[moper]

The reason you have clay radii on the intake port is to get the air to act more like air flowing thru an intake. It makes the air use the whole port for the test, not just the center. On the exh side, the entry is determined by the bore size (adaptor) and the valve and seat. Remember the exh is pushed out by the psiton, so that part is accurately simulated by the standard setup. So you will see a lot of numbers with no pipe, as it would only lower the result. Kind of like flowing with a carb at WOT and intake in place. It's much more accurate, but it doesnt sound as good and doesnt work with accetped formulas as well. It's just accepted that you dont need anything on the exh side. If you were running exhaust manifolds, the manifold should be in place because there is no scavenging. But if you run headers, the reduction in flow the tube may show will be offset by the scavengin affects of the header design. That may be why it's accepted... They basically even each other out. The difference would be huge if they revers flow the exh side. I know some guys do the intake in reverse to check for seat angle stuff and to reduce reversion at lower speeds, but I dont think I've heard of anyone doing the exh side.

 

[mopar1962]

the push of air into and out of the engine is known as swept volume.