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Author Topic:   exhaust port on a 305
28 T
Dirt Full Roller

Total posts: 30
posted May 29, 2005 09:25 PM  
I have a set of 305 heads in the exhaust port there is a small bump like the head of a rivet I hear it has somthing to do with slowing up the exhaust should these be, could these be smoothed out or leave them alone?

beachracing
Dirt Forum Racer

Total posts: 94
posted May 29, 2005 10:03 PM  
Port match it to your header, the bump is probably casting made there, but can be removed. Which casting# is your heads. Exhaust ports are where you can really make a difference on stock heads. smoothing the exhaust port, giving it a slight d shape with the flat edge horizontal, and matched closely to header, and gasket. The area behind the valve is important, and the exhaust port floor radius, if done properly will help in letting the heads breath better at higher rpms.

28 T
Dirt Full Roller

Total posts: 30
posted May 30, 2005 11:38 AM  
Thanx Beach the heads are 416's I have a set of 882 and 993 but i'm thinkin 416 for compression.

[This message has been edited by 28 T (edited May 30, 2005).]

beachracing
Dirt Forum Racer

Total posts: 94
posted May 30, 2005 02:12 PM  
416 can be opened up to a degree, but be careful not to get into the water jackets. Port match the gasket to port entry, then taper it somewhat, and then smooth the short side radius just behind the valve seat. Be careful not to hit the seat.

Panky AMCA 21
Dirt Roller

Total posts: 11
posted May 30, 2005 03:09 PM  
Another area of real benefit is the short turn radius,(the turn on bottom of port on the transition to bowl area) lay this turn over a little and widen the turn a little. a simple rule of thumb is when you want to turn the air, slow it down first, also remember that the bigger you make you port opening the slower the air will flow at low rpm ,great for massive rpm or big lift cams but terrible down low, keep it at a reasonable size for air speed, on;y remove metal from areas that are restricting the air flow.
hope this helps.

[This message has been edited by Panky AMCA 21 (edited May 30, 2005).]

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