When I tear my motor apart I plan on street porting it, and I was wondering if it would be benificial to make the exhaust ports bigger then the normal street port, for example, lets say I street port my intakes, and use a bridge port template for my exhaust would it be better then just using street port exhaust? I know low end torque will suffer, but will other things be thrown outta wack, is it even worth considering? I'm basicly looking for a middle ground between SP and BP, a nice high end pull, but have the peak power below 8k, a cool lumpy idle, but at least some power and torque on the low end and good mid range response. Any thoughts?

 

I recommend spending some time in the engine building section over at NoPistons. Wealth of experienced info over there. Enlarging the exhaust ports will NOT give you the lumpy idle. It will reduce the overlap of intake porting done, providing the exhaust system is upgraded to match the porting.

 

Say what? Enlarging the exhaust ports upwards WILL increase overlap. What you said doesn't really make any sense.

 

There a two types of streetports. Many just extend the closing edge of the port which increases port timing but doesn't provide any additional overlap. You can also extend the opening edge of the port which will give you more overlap without having to resort to a bridge port. You just have to make sure you leave enough support for the corner seal. This combined with a nice size exhaust port will give you plenty of overlap, a nice brappy idle and great performance. The other alternative would be to do a secondary bridgeport.

 

True enough, I'm tired and thinking in one dimension, sideways, and not up. Thanks for the correction.

 

One could also widen the ports (intake) as well as the above mentioned, just leave enough there for the corner seals to ride on. Solid corner seal recommended.

 

I always knock out the exhaust sleeves on all my motors. I dont see any problem with it nor overheating.

 

do not make the exhaust port close any later than the street port template or you will have no low end for street driving. your power will just begin at 7000rpm with a race port template.

 

If you look at the Racing Beat street exhaust template, and you place it next to a 12a stock port.... its almost twice the size of the stock port.

I say thats more than enough to begin with

 

12A's suffer from VERY tiny exhaust ports. Compared to a 13B, these look like a dime sitting beside a quarter. Yes, there is that much difference.
Widening the exhaust will improve flow, without changing the port timing.
Porting up will increase overlap. Porting up too far, and the lower end suffers.
Porting down is bad, unless you are going turbo. Hurts power with N/A, but spools turbo's faster.
The real "Art" of porting, is matching the exhaust to meet the needs of the intake. Stock, the 12A exhaust ports do not meet the needs of the intake, above ~6K or so, and it just gets worse the higher you try to go.