20vST Valve Guide Bosses in Inlet and Exh Ports. X? Cozmo?

[85AW20v]

Has anyone done any flow bench work on a silvertop head and knows what the difference is in flow with the guide bosses as standard and then removed? I'm starting on assembly of another silvertop for the AW racecar - 3 litres of oil for 90km of racing is a bit much. Just wondered if it's worthwhile removing the protrusions or just leaving it as is. Anything else I should do to the head before it all goes together?

[85AW20v]

Anybody have any ideas? Not even Dr X or Cozmo?

[10k 20v]

pm redmist/daniel as he's played with them on a bench

[RedMist]

Unfortunately we did F all with guides. Common practice is to take back the inlet but leave the exhaust. I have no idea as to how far to take back and shape the inlet guides as we didn't flow it. Exhaust guides rid the valve of heat so stop you burining the valves on the exhuast side. Graham A Bell had some good rules of thumb in his book "4 stroke performance tuning" however both my copies are out on loan.


We did play with tulip valves and valves of differing sizes. They made bugger all difference, generally a small flow loss in the 20 valve.
Again this is only flow, I couldn't tell you how it affected swirl, tumble or velocity.

[vvega]

i removed mine
there bloddy long on a blacktop so didnt feel id have any issues
thre are some pics on here somewhere of my blacktop heres simon

ill se if i can find them

v

[vvega]

[CozmoNz]

now, just file it out to one giant port .


ROAR 12 valve powa!

and why you put my name in this threads subject... stop poking me

[RedMist]

Noted that you have shaped the sides of the inlet port. Why? The only flow problems we found with the blacktop was an increase in pressure about an inch from the intake manifold face on the top of the port. (flowed with the mainfold in place).
Also the port deviders were awful, they forced a majority of the flow through the center port. Is this why you shaped the sides of the port?

I never developed a blacktop race engine. So we didn't bother attempting to work the head.

You have obviously cut back the guides on the inlet, what did you do to the exhaust?
Have you also altered the shape of the port at the inlet manifold face?

[vvega]

most of the work i did was to get the flow to come down over the valve rather than accross the top of it this involed changing the very shallow rad that was over the valve to deeper shape
i believe that this increases tumble
air just skimming the top of the valve and heading over to the ex side of the bore IMO cant be good for swirl or tumble and its still a very focused flow
whereas making the vavle disperce the flow into the clyinder sould give a more disrupted and even cylander fill

the sides where just cleaning off the flashing and yes a little bit or boundry layer work
the exhaust guides hung down quite low and i felt they added a large restriction to the exhaust flow thought the outer port is bigger than any other 4age the attuall valve pocket is smaller
i just tried to open that to be equivalen
unfortunatly the gude had to go...in saying that there very long internally

i aiming to get 250+ kw out of this head so every little bit counts
i dont wanna just do it with massive amounts of boost

this is just my way of doing the head
and been the fact there is no real testing around with blactop heads and flow im just having a play

v

[vvega]

ill tri to take some more dicrip pics of my working later for you redmist

v

[RedMist]

Fantastic!! I'm sure many here would appreciate it.

Pity your not making an NA enigne. I would be interested to discover whether or not the direction of mix over the valve to induce tumble works. After all the included valve angle of the 20 valve is relitively narrow anyway (compared with the 16 valve). But a least you have something holding fuel in suspension with tumble, are you going to offset the valve in the port to attempt to promote swirl as well?

I don't quite agree with your removal of the exhaust guides, unless your going to change the valve material. A hot spot such as an exhaust valve can promote detonation. But hey its one of those many things with an engine, the increase in flow may add a benefit over the increased risk of detonation.

Please detail your work and present it here... I for one am MOST interested.

[vvega]

i have been looking tinto ceramic coating the valve faces and combustion chamber so hopfully det issues wont be to great
alternate valve selection is very minimal at present

v