LS1 heads

[TK]

Testing was done on a SF600 at 28" - not mine, I can't quite justify the cost of a bench for now - maybe in 6 months.
I'm looking at an Aussie bench - for the same price as an SF you can get em with a full electronics package that can do port mapping - handy.

I wouldn't take it as a dig - it's much the same as any good head porter would do - cept I bet you woulda got caught on the short turns, they be tricky bastards unless you've done 2V clevos & know what a turn like that will do, cut em back & the flow will just plummet.

[Calibrator]

Try doing a 8v VW head the short turns are also a tricky. I havent looked at a LS1 head with an eye to porting yet so I cant say what I would have done with the short turns
300 was ok but couldnt pull much more than 20" on a decent head.
I was doing heads back in the early and mid 90's so I am sure the flowbench technology has moved on enormously

[TK]

Yeah, the newer benches can pull a lot of air.
The one I'm looking at can pull 400cfm at 28" - that's a fuckload of air.
You realy do need a big bench with modern stuff - even some 4-banger stock valve heads can go over 300cfm & you really do want to be testing at 28" for everything - if only to keep your brain straight on what the figures mean.

[TK]

I was just thinking about heads/port shapes etc this morning & realised something.
I know why I usually get flow fairly spot on on the first or sometimes second attempt without owning a flow bench.
It's because, when it comes down to it you don't really need a flow bench - they are only really usefull to confirm that you haven't screwed anything up, if you know what you are doing you can figure out the right shapes/sizes for various parts of a port without ever flow testing it.

There are several key things that'll determine if a head will work or not, regardless of what the flow bench says.
Flow bench figures are just a small part of the equation.

Things like valve size to throat size ratio, cross sectional area, seat angles, chamber angles etc are far more important than what the bench says.

ie - a big bowl compared to valve size can flow large numbers on a dry flow test, but add wet flow to the mix & things go to shit - if you size the bowl to the valve, cut the bottom angles & chamber angles to suit the lift & ramp rate of the cam to be used, size the ports to achieve optimum velocity & cut the short turn to suit the bowl shape, lift & ramp rate then the head will make power.
A properly shaped & sized port with the correct valve size for the application can make a lot more power with lower flow figures than a huge flowing head that gets even 1 of the key things wrong.

[Calibrator]

I was just thinking about heads/port shapes etc this morning & realised something.
I know why I usually get flow fairly spot on on the first or sometimes second attempt without owning a flow bench.
It's because, when it comes down to it you don't really need a flow bench - they are only really usefull to confirm that you haven't screwed anything up, if you know what you are doing you can figure out the right shapes/sizes for various parts of a port without ever flow testing it.

There are several key things that'll determine if a head will work or not, regardless of what the flow bench says.
Flow bench figures are just a small part of the equation.

Things like valve size to throat size ratio, cross sectional area, seat angles, chamber angles etc are far more important than what the bench says.

ie - a big bowl compared to valve size can flow large numbers on a dry flow test, but add wet flow to the mix & things go to shit - if you size the bowl to the valve, cut the bottom angles & chamber angles to suit the lift & ramp rate of the cam to be used, size the ports to achieve optimum velocity & cut the short turn to suit the bowl shape, lift & ramp rate then the head will make power.
A properly shaped & sized port with the correct valve size for the application can make a lot more power with lower flow figures than a huge flowing head that gets even 1 of the key things wrong.

Yep
Its just a measuring device just like a dyno all they can do is help point you in the right direction but your findings still have to be proved empirically.

I used to run 2 VW Golf rally cars the engines were as identical as I could make them yet the one with the highest flow figures and I am talking small amounts here always made slightly less power and torque than the other. We could never prove which way was better as the drivers were totally different.

But both of them were the only VW's that could run with or beat the Toyotas in that class.

I reckon head porting is as much or a bigger black art than header building