Head porting .....

[Machineman]

They say if you dont know what u doing while porting you will damage the swirl and make it run like crap which i understand but why when the ports have so much carbon build up the still run great ?

 

[morpwr]

Swirl?

I think the swirl is only a small part of the combustion process. it is mostly about the squish, just like a two stroke. Squish helps mix up the fuel and the air. Tight squish good running engine.

 

[Machineman]

Swirl is also more used at low rpm ?? I read somewhere butcher porting will hurt the low end more so high

 

[Ranch]

low speed + low boost, = poorer cylinder filling. 'swirling' helps the filling part, think of hammering a square peg into a round hole. when the air charge is 'spun' into the cylinder, it helps 'fill' the dead corners. The harmonics of impulses within the plenum all the way through to the top of the piston is a pretty complex dynamic.
You're correct, 'hogging' out a port tends to hamper low end..
But when you have choked down runners, they tend to really speed up charge flow, which actually helps the cause.. up to a certain point... but eventually will be a limiting factor after a certain CFM.

Think of a funnel. Have you ever noticed sometimes when filling a gas tank while using a funnel, that sometimes the fluid will 'swirl' down the funnel? (and quite fast too) But the next time it might just fill up and 'glug-glug'..
When dealing with NA engines, a system could be designed around the amount of air expected to flow. Now when dealing with engines that can run anywhere from zero boost, up to (insert your boost here) It gets complicated on dialing in the 'perfect' setup, one that suits both low end, and wot operation.

 

[turbovan+tdi]

That's a myth that n/a engines require a different porting job than boosted engines. I have friends and know people who port engines etc, have flow bench's and boosted flow bench's and when push comes to shove, the best porting job for an n/a will be perfect for a boosted engine. Free up the choke points and keep the velocity up and its a winner. You won't lose bottom end and will gain up top.

Example is my 2.5 Caravan engine with a Lotus head, stock, the air would stall over .325" lift and my engine would run out of steam at any boost at around 5800 rpm. Ported with a boosted bench, my new high lift cams wouldn't cause the air to stall and I made power to 7500 rpm, and my bottom end torque was miles better.

 

[keaton]

They say if you dont know what u doing while porting you will damage the swirl and make it run like crap which i understand but why when the ports have so much carbon build up the still run great ?

If you are going to do a DIY head porting, clean up the the casting flash. stay off the top of the runner, smooth out the bottom radius to the port, gasket match the inlet & intake manifold. call it a day

 

[morpwr]

some is good

just fixed my 06 brm I bought. Widened the exhaust from the gasket surface back into short turn radius. Made radius as big as possible. Widened and flattened floor into short turn radius. Three angle valve job. Cut into intake swirl bump from bowl side to angle air up towards valve. Used a 1 hole gasket with .041-.042 piston stand out. This gives good squish action. Engine runs great. Best of the 3 BRMs we have. Very smooth motor, starts right away. Don't need to go crazy just help the air out alittle.

 

[Ranch]

That's a myth that n/a engines require a different porting job than boosted engines. I have friends and know people who port engines etc, have flow bench's and boosted flow bench's and when push comes to shove, the best porting job for an n/a will be perfect for a boosted engine. Free up the choke points and keep the velocity up and its a winner. You won't lose bottom end and will gain up top.

Example is my 2.5 Caravan engine with a Lotus head, stock, the air would stall over .325" lift and my engine would run out of steam at any boost at around 5800 rpm. Ported with a boosted bench, my new high lift cams wouldn't cause the air to stall and I made power to 7500 rpm, and my bottom end torque was miles better.

So, was it the port job, or the new high lift cam or a combination of the 2 that gained your increase?

 

[turbovan+tdi]

So, was it the port job, or the new high lift cam or a combination of the 2 that gained your increase?

Both, if I'd put those cams in my stock head the engine would have gone flat. Having a boosted bench is pretty cool because you can see how it will react with boost vs a flow bench which just measures vacuum, which isn't a bad deal either.