The 44 blends in nicely... Just a reshape of the chamber is all thats needed.
Everytime I see a huge intake valve and huge welded port I just grin and walk a way..
1.8 valve sizes...
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HAM Inc
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Ron I'm sure we could improve the exhaust to the point that the 1.7 intake port would become the weakness. Considering that the 1.7 &1.8 ex. ports were designed to be restrictive for emissions purposes there is a lot of room for improvement. The ex. port can be opened up to accomodate a 40mm valve. But shrouding factors become an issue, so such large exhaust valves would only realize their full potential on large bore engines, (like Jake is currently building). And logically once the displacement is opened up the intake will have to be improved over the stock 1.7 specs. to see any gains.
It's true that there are worse things than having an exhaust port that is capable of outflowing the intake. However, in that situation the loss of scavenge effect due to a drop in port velocity will hurt low speed torgue.
Some relationships between port runner cross section area and valve diameter are well established for all normally aspirated engines. Port cross section should be around 80% of the valve diameter. Exhaust should be between 75%-90% of the intake, depending on a multitude of factors such as valve placement in the chamber, port shape and efficiency, RPM's, header quality, cam specs, chamber efficiency, dynamic compression ratio, etc.
a 2.0 intake port is 35.6mm in diameter. 80% of 44mm is 35.2mm. By upping the valve size from 42mm to 44 we're allowing the port to see its full potential without a lot of porting. A 38mm ex. valve is 86% the size of the 44mm valve. Ex. port improvements keep the balance between in. and ex. about right. This is a textbook example of proper valve sizing. Upping the revs to high sustained RPM's with a very aggressive induction system such as twin 48IDA's and high compression ratio could justify going over this, as would larger displacements.
Remember that all engines love port velocity, and that carries out through the exhaust system (which is why primary pipe sizes & length and collector opening AND volume is so critical to tuning.) The extreme cylinder pressure during the blow-over period is the reason exhaust don't need to be as large as intakes, which only have atmospheric pressure to work with.
Len
It's true that there are worse things than having an exhaust port that is capable of outflowing the intake. However, in that situation the loss of scavenge effect due to a drop in port velocity will hurt low speed torgue.
Some relationships between port runner cross section area and valve diameter are well established for all normally aspirated engines. Port cross section should be around 80% of the valve diameter. Exhaust should be between 75%-90% of the intake, depending on a multitude of factors such as valve placement in the chamber, port shape and efficiency, RPM's, header quality, cam specs, chamber efficiency, dynamic compression ratio, etc.
a 2.0 intake port is 35.6mm in diameter. 80% of 44mm is 35.2mm. By upping the valve size from 42mm to 44 we're allowing the port to see its full potential without a lot of porting. A 38mm ex. valve is 86% the size of the 44mm valve. Ex. port improvements keep the balance between in. and ex. about right. This is a textbook example of proper valve sizing. Upping the revs to high sustained RPM's with a very aggressive induction system such as twin 48IDA's and high compression ratio could justify going over this, as would larger displacements.
Remember that all engines love port velocity, and that carries out through the exhaust system (which is why primary pipe sizes & length and collector opening AND volume is so critical to tuning.) The extreme cylinder pressure during the blow-over period is the reason exhaust don't need to be as large as intakes, which only have atmospheric pressure to work with.
Len
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Plastermaster
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cool! So its not 100% a matter of having the smallest possible valve for the port, but almost. Too large and there are shrouding probs, but too small and there is still some restriction. Interesting what you wrote about Cylinder presure and exhaust. We all know what goes in must go out, and we all know how Jake is about exhaust, 
I once had an engine builder recomend or at least OK running stock heater boxes on a 2110 T1 I was considering with 40X35 heads. He sad the exhaust just gets forced out anyway. While in real world application this was wrong, there is a slight amount of truth to it, and I guess this is why I E ratios are not optimally 1:1.
Thanks for your thorough and informative replies Len. But remember, this head porting stuff is supposed to be some kind of secret black magic.
Ron
I once had an engine builder recomend or at least OK running stock heater boxes on a 2110 T1 I was considering with 40X35 heads. He sad the exhaust just gets forced out anyway. While in real world application this was wrong, there is a slight amount of truth to it, and I guess this is why I E ratios are not optimally 1:1. Thanks for your thorough and informative replies Len. But remember, this head porting stuff is supposed to be some kind of secret black magic.
Ron
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MASSIVE TYPE IV
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