exhaust valve porting

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Aug 20, 2007 | 02:02 PM

hollenjoe

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exhaust valve porting

HI, Im running a dyno simulator for my 400, and im finding that porting the exhaust valves to the same size of the intake valves in a stock milled head would give me like 150 more horse power ( stock valves: int 2.04" vs ext 1.66"). Is it posible to port the exhaust valves in a stock head to 2.04" ? IN my dyno says it wont affect that much low end torque, what would the consequences be ?

Aug 20, 2007 | 02:40 PM

packlet

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From: Berkeley

pretty sure the physical layout in the cylinder head prevents making the valve openings any bigger than 1.72 or so. even if you could cram a bigger valve in there, it would be so close to the cylinder walls so as to shroud itself and not provide better flow.

you're better off improving flow though the exhaust ports in the cylinder head. experiment with your head flow exhaust numbers in your dyno program to see what i mean...

Aug 20, 2007 | 07:08 PM

danlee

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Dyno sims do not predict physical limitations. The cylinder walls shroud the exhaust valves, so that there is not much improvement in flow above 1.65" in exhaust valve diameter. All aftermarket heads limit the exhaust valves to about that size for this reason. Opening the port and increasing the short radius of the bend, remove any flashing, and polishing the port will give your as much flow as you can get.

Aug 20, 2007 | 11:42 PM

Matts72

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Don't underestimate what Danlee is saying, this exact procedure is what I do to all of the 2v heads and it makes a world of difference.

Aug 21, 2007 | 12:32 AM

Fordication

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From: Spring Texas

So you are saying that staying with the stoock head and porting and polishing it makes a real difference? What else can be done with the heads if the valves are already maxed out to get better performance? ED

Aug 21, 2007 | 06:32 AM

danlee

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From: Delaware

There may be some benefit to using a larger intake valve. Don't polish the intake ports, just clean up any flashing and work on the bend radius.

Aug 22, 2007 | 05:50 PM

hollenjoe

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So I should increrase my exhaust valve to 1.72" and enlarge/polish my exhaust port in the head nad whats increasing the short radius of the bend? what´s the bend ? sorry for my ignorance

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Aug 22, 2007 | 06:27 PM

danlee

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Quote:

Originally Posted by hollenjoe

So I should increrase my exhaust valve to 1.72" and enlarge/polish my exhaust port in the head nad whats increasing the short radius of the bend? what´s the bend ? sorry for my ignorance

There is no advantage to increasing the size of the exhaust valve.

The short radius is the radius of the bend of the port between the valve seat and the outlet of the head. This is a sharp bend. You want to reduce the shapness of this bend, so that exhaust will flow smoothly around the bend.

Exhaust wants to follow a straight path and not bend.