Cylinder Head flow rates

[jogi730]

Look forward to seeing those
CHeers
Chris

[S2central.net]

I should have some flow figures this week for my cylinder head that has had extensive work done.

Yes - before and after figures I hope... And some nice photos are always nice - polished exhaust ports - mmmmmm

[jogi730]

Well I have had my cylinder head reworked now.
At 12mm valve lift I have the following figures;

Before After

Intake 121CFM 150CFM
Exhaust 88CFM 123CFM

Not entirely sure what this means, but I have been told I should be very pleased with these figures, especially the exhaust side as that had already previously had some work carried out.
Cheers
Chris

[S2central.net]

WOAH - those are some seriously good gains... especially so on the exhaust side. Can you post a pic of the ports Jogi ?

Have those CFM figures been normalised for ambient temp / press by your flowbench man ?

Also - do you have figures at any other valve lifts for a more complete picture

[jogi730]

Hey, that's a bit testical - you're asking the wrong man here!
These are the only figures I have atm. Hoping to drop engine off for reassembly next week so can hopefully take some pics and maybe get some more figures.
Chris

[LHD_Kid]

Hey, that's a bit testical - you're asking the wrong man here!
These are the only figures I have atm. Hoping to drop engine off for reassembly next week so can hopefully take some pics and maybe get some more figures.
Chris

I have also been speaking with "some people..." It is not just "the numbers", ie flow rate that is important.... it is also "how" it flows, combustion chamber shape / profile... there are many more variables than just the flow rate, although it does look like you have had some very impressive gains - especially as it was a head that had already received some work....

Chris

[G60Rallye]

They sound like huge figures Chris................

My head made 134cfm on the inlet and 120 on the exhaust.

[JP]

Not to rain on anyones parade, but it'd be interesting to know what bench that was tested on and at what pressure drop. Currently I can only assume it was tested at 10" using the starting figures as a guideline.

Likewise what bore adapter was used as you get overinflated figures if the bore adapter is much larger than the cylinder bore you are going to run on the engine. I've seen it happen on the CNCHeads figures that are published on their site where their intake figures are as much as 20% higher and exhaust as much as 30% than the actual figures measured on a properly callibrated bench.

Also be interesting to know what the valve and throat sizes where as the intake figure mathematically is implausible due to the discharge co efficient relative to the corresponding skirt area of even over sized valves.

I've got flow figures on file done on a digital flow bench which has been compensated for ambient pressure and temp and of the top of my head can confirm intake is around 190cfm at 450thou lift @28" pressure drop (converted figure as original measurement was taken at 10" which tends to yield slightly lower values as turbulance cant be overcome that easily especially on the exhaust side) can't remember standard exhaust of the top of my head though. Unfortunatelly the files are on another computer so will have to post them up at a later date.

Putting that aside it isn't about peak flow but total area under the curve gains/curve shape and port velocity. Heads with less measured cfm but correctly adjusted port velocities can produce more power and deliver it smoother especially on a FI engine when correctly matched to the ramp rate and lift of a cam profile.

[jogi730]

This guy comes highly recommended and knows what he is doing - read LHD Kid's post.
We have both seen his work.
Ultimately as always, we shall see how car performs.
I don';t want to get too carried away as I have gone through more false dawns that bread and butter, but I have some great help on this including Repo!
Chris

[zlobo]

we only did a test on the intake side of my 3b head with a full radius funel intake.
what pessure are you running the flow test?

[mcandmar]

Any pics Jogi? Were they standard sized valves or oversize? Multiangle valve seats, or anything else done?

Also what cams are you using? The specs your posted were @ 12mm valve lift which seems a lot.

Cheers, Mark.

[jogi730]

I will post what I find out next week. This is what I have been told so far.
Chris

EDIT I will be using 3B adjustable cams as supplied by Repo (pics in my project thread.
They worked well enough when I ran the t34

[JP]

we only did a test on the intake side of my 3b head with a full radius funel intake.

Those figures are pretty much spot on of what I'd expect to see on a multiangle valve seat with back cut valves, the standard ones tally up aswell.

Saying that my favourite reason for overinflated figures is the missing spark plug trick which I've seen on a lot of US figures easily spotted with the ridiculously high 5othou lift figures. Which is why a full curve is always nice.

Looking forward to the full spec though.

[Jamo]

http://www.motorgeek.com/phpBB2/viewtopic.php?t=28489#338569&sid=d09b0651310522007869863f072af7cf

[JP]

^^^^^ lol looks like someone didn't take into account the discharge co efficient of the orifice plate in the bench when flowing that head. As the metering plate will have a 45 degree sharp cut on it which means when you blow though it for exhaust measurements you end up with a .62 discharge co efficient which yields nice and accurate results.

Whereas when you suck through it it becomes ineeficient and the discharge co efficient can drop as low as .48. Obviously if you are not compensating for the drop you end up with seriously overinflated figures as shown on the intakes on that thread.

Obviously if the plate is installed upside down then the exhaust figures become over inflated.

I'll make a point of hooking my laptop up to the telly tonight to dig the standard figures out of a 3B (broken screen).