Exactly.

Easy to see why Hondae make power at high RPM in naturally-aspirated form.

 

<p>Sorry for the delay. Here's some flow bench data. The head is a 1999 BP4W. Flow bench done at stock and after a mild port and polish job done on the same cylinder of the same head. I had 1 cylinder with a noticable core shift on the exhaust side but all the other ports seemed to have minial core shift. I think the core shift was on cylinder 4 and I flowed cylinder 1.</p><p>For the port job I tried to follow Mike Keegan's advice in this edmund article shown below. Minimal enlarging of the intake port was done. The short side radius was cleaned up, bowl transition smoothed out and casting surface polished. The exchaust side I did a mild port enlargment focusing on the roof and the same throat details mentioned above. I have no installed or dyno'd any HP changes due to this port job.</p><p>Keegan Engineering Head And Porting Tech - 1997 Mazda MX-5 Miata Long-Term Road Test</p><p>&nbsp;</p><p>&nbsp;</p><p><img src="http://cimg3.ibsrv.net/gimg/www.miataturbo.net-vbulletin/926x563/80-graph_2_9b74f193b879f29dae9e30ff6d49249858a2ca9e.j pg" title="" /><br /><br /><br /><br /><img src="http://cimg1.ibsrv.net/gimg/www.miataturbo.net-vbulletin/1023x684/80-table_0c69e034bbf344a28794761f8f04c9011633ca7b.jpg " title="" /><br />&nbsp;</p>

 

So, looks like focus on the exhaust port? Looks like you stayed within measurement noise on the intake.

BP4W and BP05 exhaust ports are basically the same, aren't they?

 

I'd like to see pics of the work. He basically shows no gains on the intake. Given how bad the stock head is, you should be able to see improvements with good porting and unshrouding. His low lift flow did increase, which is good, so he did something right.

 

This pics shows the areas where I cut on the head. Around the seats there's an edge from the factory, I remove it/blend it to the chambers. Also unshrouded the valves. And bowlwork too.

 

<p>I ended up not deshrouding the valves. The gap from the oem head gasket to the cylinder bore was very minmal around some areas so I decided to play is safe and and not touch that area.&nbsp;</p>

 

Thanks for taking the time to post the flow chart and table!

 

You're making 200whp NA? That's a good figure. Mind sharing some more engine specs?

Cheers

Earlysport

 

Specs are around if you search my tag name.

Basically 11.5 ish : 1 compression, Crowler rods, E85, Modified Skunk2 Intake & 70mm tb, 310deg custom cams, very ported BP-05 head, oversized custom valves, custom headers and 3" aluminium exhaust. 218HP at the hubs @ 8300.