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Poly A Block Head Street Porting
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PolyJ
Posted 2022-05-18 10:24 PM (#621590)
Subject: Poly A Block Head Street Porting



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Posts: 137
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Location: Denver, Colorado, USA

I'm making progress on the 390 stroker poly A-block build. I finished street porting the head and intake manifold runners, and the heads are at my machinist's having 2.02"/1.60" race valves and new guides installed. He's going to make the 70° seat cut and give the heads back to me so I can blend the bowls and finish the porting job before he goes back in and finishes the valve job. I wrote up a porting tech article for those who want to follow along or are interested in street porting A-block heads since they flow really well when street ported: https://poly318.com/poly-cylinder-head-porting.html

I also modified the intake manifold to open up the plenum and gasket-match it to the Offenhauser cross-ram adapters. The intake required a lot of material to come off the runners to match the gasket. I also epoxied up the exhaust crossover. A complete description of the work is at https://poly318.com/poly-intake-manifold-porting.html

 

 





(intake_runner_ported.jpg)



(Exhaust_ported1.jpg)



(head_ported_intake.jpg)



(manifold2_gasket_marked.jpg)



(Manifold_Ported_resized.jpg)



(Manifold4b.jpg)



(manifold4a.jpg)



(Manifold_Ported1_resized.jpg)



Attachments
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Attachments intake_runner_ported.jpg (166KB - 109 downloads)
Attachments Exhaust_ported1.jpg (225KB - 110 downloads)
Attachments head_ported_intake.jpg (181KB - 103 downloads)
Attachments manifold2_gasket_marked.jpg (224KB - 107 downloads)
Attachments Manifold_Ported_resized.jpg (141KB - 108 downloads)
Attachments Manifold4b.jpg (197KB - 111 downloads)
Attachments manifold4a.jpg (184KB - 110 downloads)
Attachments Manifold_Ported1_resized.jpg (124KB - 109 downloads)
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Powerflite
Posted 2022-05-18 11:20 PM (#621593 - in reply to #621590)
Subject: Re: Poly A Block Head Street Porting



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Keep in mind that once you start opening up the intake manifold at the carb mounts, that you can no longer run the original WCFBs on it. They won't seal all their ports properly.

Nice job on the head porting. Were you able to do a flow test before and after?

Edited by Powerflite 2022-05-18 11:22 PM
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PolyJ
Posted 2022-05-19 12:34 AM (#621596 - in reply to #621593)
Subject: Re: Poly A Block Head Street Porting



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Posts: 137
10025
Location: Denver, Colorado, USA

Powerflite - 2022-05-18 9:20 PM Keep in mind that once you start opening up the intake manifold at the carb mounts, that you can no longer run the original WCFBs on it. They won't seal all their ports properly. Nice job on the head porting. Were you able to do a flow test before and after?

Thanks. Correct on the WCFBs. If I ever ditch the cross-ram setup, I'd run the dual AFBs with adapter spacers that would seal. I don't care for WCFBs compared to AFBs, AVSs, or Holley 4150s.


Unfortunately, I don't have a flow bench, didn't want to spend the funds on building one, and didn't want to pay someone to flow them and deal with the hassle, so I'm utilizing my experience and the knowledge I've gained from others. I probably should have built one twenty years ago when I first started fooling with porting small block Chevy heads. From a handful of flow charts that Gary Pavlovich gave me, factory A318 heads flow 187 cfm intake 147 cfm exhaust at .55" lift, and hand-ported heads in the fashion I'm performing with 2.02"/1.60" valves flow 219/164. These ported numbers are from Greg Douglas of Douglas Porting Service, and Greg and I have had some good discussions about where to focus my attention. Hekimian Racing put together a CNC porting program for the A-block head that gets a whopping 266/211 out of them! I've designed the 390 build to produce around a modest 430 HP, 470 TQ at 6,500 rpm to get the '56 scooting, so the hand porting should be enough to get me there. If I were going for the high end of a 390 build at 600 HP, I'd send the heads to Hekimian for a CNC job.

I have five other A318 engines and therefore sets of heads, and Gary P. and I have been kicking around the idea of an experiment with me taking a set, lapping in the valves, installing stiffer springs for my cam, and doing a little heads-up comparison at the 1/4 mile. I'd run my ported heads with large valves one week, swap the heads out for the factory unmodified heads with 1.84"/1.56" valves, and go back to the track the following week. We ended up in an hour-long conversation about then pulling the factory heads, porting them but maintaining the small valves, and going back to the track to see how they compare to the larger 2.02"/1.60" valves with porting. Aside from time, this adventure would cost me a second set of valve springs and four sets of head and intake gaskets, but it would provide great information.

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