333pg333

Note that you have the stock intake port at just under 200 cfm at .5 lift Sean. Remembering that the stock head is meant to have 188cfm max (perhaps anecdotally?). Wonder what that lift that was at and was it at 28" Mercury? Seems to me that the stock head would continue to flow more at a higher lift also. Maybe that 188cfm was at a lower lift or pressure?

V2Rocket

I'm diggin' the CATERPILLAR yellow...

Voith

Are these done in exactly the same parameters and can be compared?

Does this mean that mild ported 951 head with stock valves will match/outflow 2.7 head with bigger port and valve at full lift?

V2Rocket

Looks that way, would make things easier if you implemented that Koeniggsegg electric-valve thing, but peak lift is only a small portion of the lift cycle...look how much more the 2.7 flows at "mid-lift" which is a longer period of open valve...

Maybe you could grind a cam with "rounder" lobes instead of "pointy egg shaped" to make the most of high-end lift...

Voith

I wonder if 951 port with 48mm (2.7) valve&seat would make the same bulge on 3.0 mark..

refresh951

Interesting looking at throat to valve ratios. The stock 951 has a ratio of 0.88 and the 2.7 head has a ratio of 0.92. The seat on the 2.7 is thinner than the 951 head. To compensate the 951 has an additional cut on the seat as shown below:



I wonder if they used a thicker seat for heat purposes or just learned more moving forward and improved the design. This makes a significant flow difference especially at lower lifts.


The stock intake port numbers are pretty solid for a fresh head. I have flow data from several sources. All these were benched at 28" H2O

That is the MM head which has now been sold.

Yes, all at 28" H2O. Yes indeed, a mildly ported stock 951 flowed essentially the same as the 2.7 head at high lift. I am pretty sure if you clean up the throat area on the 2.7 head, it will pick up nice gain but the head I tested is not mine. Also, the seat design of the 951 head may flow better at high lift (see above). The lower lift numbers on the 2.7 are very special and should not be discounted. I would definitely use this head if I did not want to retain the ceramic liners on the exhaust ports.

Pretty sure that is a no. The velocity is significantly less in the huge 2.7 intake port.

Voith

I mean if only lower portion is enlarged, to accommodate larger valve.. I guess velocity would still be retained since the upper portion would be left as is?

How did you port your head to fit bigger valves you have in the head you are using now? SI 47mm intake valves if I remember correctly?

Something like this, only enlarged where is needed to fit larger valve seat:

Dave W.

The stock cam has .473" of lift. That's probably where it was tested.

I agree that the easy way to get more flow is to use a cam with more lift.

Van

That big expansion in volume will cause a decrease in velocity, causing a loss in momentum of the air particles and turbulence.

Think of it more like a doorway to a building with lots of people trying to shove through. If the people are orderly, more of them might be able to get through a small doorway in a fix amount of time than a large doorway where people are pushing and shoving and bumping into one another. Working on the choreography of the people moving will have a bigger result than just increasing the size of the door.

Voith

I understand this, but stock valve and port was designed for 2.5L engine and performs at a certain air port velocity and air mass per displacement in given time/cycle. Lets call it a golden standard.

When increasing displacement, there must be a point where stock port and valve becomes a goose neck, thus bigger valve and bigger port must be used to get proportionally the same (or more) amount of air per unit of displacement.

So, how to achieve golden standard with more displacement?

I was searching the net on the subject and found this, is this true? (right part)



If it is, then if bigger valve is fitted, the rest of port would need to be enlarged to the same proportion in order to retain the same properties (as stock 2.5L) but accommodate more displacement. (more volume @ same velocity)

Van

Yeah, I'd buy that diagram. Makes sense on the cross sectional area. And, your throttle body has to have 4x the cross sectional area into the intake plenum.

On the left side of that diagram, it doesn't show the effect turbulence has... That can help correct some of that rich/lean problem. Have you heard about "wet flow" testing? They use a fuel injector that sprays a liquid that shows up well under a UV light, and they can "see" how the fuel and air swirls into the cylinder at different valve lifts. http://rehermorrison.com/tech-talk-4...de-your-motor/

Voith

Interesting stuff, thanks.