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On what ?
 

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It depends on what head to a degree, obviously some heads are better than others. Most are designed as N/A heads and could stand some help on the exhaust side. On a turbo engine you can't just use a monster exhaust lobe like on a blower/N2O combo to help exhaust all the extra gas from the power adder. Since we are driving the turbo with this gas causing higher back pressure the exhaust lobe is very critical for top Performance with as little reversion as possible. This is where the port comes in. If you can make the exhaust port more efficient then you may be able to reap the benefits of the better flowing port and/or even run less exhaust duration depending on your goals. IMHO the exhaust port and cam lobe is more important than the intake on a turbo application so if you can improve it I would. However you can do a lot with refining the port shape keeping the valve size the same. I have a set of AJPE SBC heads that flow 325+ cfm using only a large stem 1.650" valve. Hope this helps.
 

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This is the port I'm talking about. Valve size is 1.65" and flows 325+cfm straight off the CNC. I am going to do a little blending and buffing to avoid any kind of build up on the tool path ridges. It may pick up a few cfm from this hand work.
 

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Thanks guys. I'll post more pics as it comes together. The block is past due and hopefully be done soon, I have everything else to put it together except bearings I'm ordering today. It will have twin 94mm turbos and be capable of 3500cshp reliably. It has a lot of internal changes to make this possible which is a big part of why the block has taken so long to machine.
 

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I have 1.5s in my high ports that go 272 cfm. Its the total design. The old boss 302 heads had a 1.7 and can barely poot out a pulse:rolleyes:
 

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This is the port I'm talking about. Valve size is 1.65" and flows 325+cfm straight off the CNC. I am going to do a little blending and buffing to avoid any kind of build up on the tool path ridges. It may pick up a few cfm from this hand work.
Big Baller :p
 

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any advantage to bigger port and valve on exhaust side??
There was a thread a few years back . One guy claimed .3 and 4mph on a valve size change. I think he went from a 2.48 EV to 2.52 EV using the same cam. It's kinda a hot button issue when you involve professional head porters and the given guide lines to developing a good head for an application.
If you feel your combo could use more exhaust flow maybe get with a cam designer. Maybe some duration or lift will reveal what you expect.
In short just get a good sound head if you're just turning laps and concentrate on the chassis set up. A well lined out chassis is worth 300 hp,IMO.
 

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Since I have already crashed the OP's thread, I might as well post the other pics. My apologies to the OP.

 

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Couple more pics. Chambers are softened, damn near a hemi.



 

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This is the port I'm talking about. Valve size is 1.65" and flows 325+cfm straight off the CNC. I am going to do a little blending and buffing to avoid any kind of build up on the tool path ridges. It may pick up a few cfm from this hand work.
No need in buffing the heat will smooth the port.:p
 

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Beautiful for sure....but SBC?
Yes SBC and still on 4.400" bore centers so the engine is legal in all classes that allow billet heads and/or blocks.
 
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