Head work gains.

[harrison]

How much extra power can be acheived with a porting job ? ALL of my carburetted engines have been flow benched, ported, and swirl polished,for more power.(Merlin heads on big block Chevy, 911 heads, Edelbrok heads on Small block Chevy,etc.,and most importantly the heads on VW bug 4 cyl. 2016cc Dual 48 mm Weber carbs). \"/ Forced induction engines don't see as much gain from porting. Unless you are 8,000 HP +. (Dragsters)

[London Lad]

I suspect they are pretty good already on the R8 but I think that a good porting job will always be needed to get the most out of any exhaust or filter mods.

[Josh@ECS]

The gains in a full port job depend entirely on how optimal to original port design is, how thick the casting is and how aggressive the other engine mods are (bored,stroked,cammed and how far). The old American head designs are terrible and benefit from reshaping and smoothing more than opening up to a larger size. The VW heads tend to have a good balance between design and optimum air flow so flow can improve...just not dramatically. Ferrari heads ever since the 50's were cast fairly thin so there's not enough material to make a large gain, on the other side Honda heads have a great port design and have thick castings so you can quite often do a full port job and nearly double the CFM. The greatest benefit I've seen to porting heads on a forced induction engine generally is an improvment in effeciency so the system can run cooler and/or on a slightly lower boost pressure reducing stress.

[harrison]

Good summary Josh. Porting on aircooled engines really does help with overheating.

[Josh@ECS]

Thanks, it's always good fun to talk engine physics. I've seen gains as little as 20 CFM and gains as high as 100 CFM after a proper port job. I'm sure the most noticable gain in the air cooled vw/porsche stuff you've done has been easier tuning/more efficient combustion or increased torque due to the increase in efficiency. My 1.8l VW watercooled heads gain very little cfm from a port job, and cost much more to do than the Hondas but the ability to run a more aggressive turbo/supercharger setup afterwards pays off.

[London Lad]

A lot of the benefit of port work on older mass production engines was due to the fact that the inlet and exhaust manifolds didn't line up with the ports in the head perfectly, as they came from the factory.

[harrison]

I have heard of people picking through new raw head castings to find the best castings.Sometimes they are cast in two pieces and aren't quite perfectly alinged in the casting seams.(G M V8 heads)

[mlpor]

How much extra power can be acheived with a porting job ? ALL of my carburetted engines have been flow benched, ported, and swirl polished,for more power.(Merlin heads on big block Chevy, 911 heads, Edelbrok heads on Small block Chevy,etc.,and most importantly the heads on VW bug 4 cyl. 2016cc Dual 48 mm Weber carbs). "/ Forced induction engines don't see as much gain from porting. Unless you are 8,000 HP +. (Dragsters)

Having once gone through this exercise & spent 3 days in a machine shop watching and talking with a guy porting my head, I'd say what "can" vs. what ussually "is" gained is rarely ever measured or quantified with any dyno "before" vs. after results. I watched flow number on a flow bench rise, then abruptly fall to worse than stock with the small removal of just a tiny additional amount of material (we brought a junked head to experiment with first before starting on the real thing.)

But enough of that, if you're looking for a good place to start on gathering information, I found Dave Baker's Puma Racing site helpfull and full of a lot of interesting infomation http://www.pumaracing.co.uk/cflow.htm on trying to improve flow HTH

[Josh@ECS]

Just like in any aerodynamic situation every angle and contour inside the port directly effects the air's speed and turbulence, an understanding of HOW significant an angle or contour is based on it's position in which port is critical. Since CFM compared to displacement and RPM is a direct calculation for an engine's efficiency and power output...and cylinder head flow is the most critical aspect in an engine's operation...if you measure an increase in CFM you can calculate a target horsepower gain. The you then have to overcome intake/exhaust design,camshaft profile, fuel tuning and air temp/density to actually realize the benefit in the real world.

Stan Weiss has a website with a table of proven data to use as a guide for the ideal CFM to look for when porting a head and at what valve lift it was measured. It lists numerous different engines.