Can i put oversized valves wihtout porting??

 

No

Even if you could, you wouldn't want to. It would destroy your flow rates.

 

Knutz,i was talking whit sam coe performance and he said that i could put oversized valve without porting would be actually better but he also said (with a blended valve seat) what is a blended valve seat??

 

I don't mean to step on Sam Coe's toes, but I dis-agree. With stock sized ports, the mixture velocity would be high, when it reaches the over sized valve[and the blended valve seat] it would expand and slow at the point of enlargement. This would cause the mixture to "back up" on the port side of the valve. In the simplest of terms, a blended valve seat is porting the head from the valve seat into the port, to smooth out the cut needed to install the large valve seat. It may allow more flow than stock, but would not flow as well as a ported head with stock size valves, or over size valves and port work. The port work needs to be done carefully to get good flow. Too much material removed makes the valve a serious restriction, creating high preasure on the port side of the valve. My personal motor is stock size valves and port work.

Both is best, but if you can only afford port work or over sized valves, I would go with the port work.

Keep in mind, although a ported head with over size valves will flow great numbers, unless the rest of the motor is built to need it, you could experience a serious loss of bottom end power. If the cylinder doesn't create enough vacume at low RPM to demand the volume the port can supply, the velocity will be too low to sufficiently fill the cylinder, and the bottom end power will suffer.

 

Thanks for the info Knutz.

 

I have had good results going to 1.0mm O/S valves with a stock engine configuration. A 1.0mm increase with a properly developed port gives you enough to make a nice increase throughout the lift curve without making a huge area change (which will cause the aforementioned dreaded drop in velocity). A good head porter knows this and will make the mods keeping this in mind. Measuring port volume and specific cross sectional areas before making any changes will give the porter an idea of where he can go without making big sacrafices in velocity.

If your head porter has done these heads he probably has some concrete results to show you, or customers he can refer you to. It is difficult to analyze someones work in a discussion forum, especially if the people discussing it haven't seen or used his product. There are a lot of wrong ways to go when porting cylinder heads, but it doesn't mean that everyone makes the same mistakes. You can't asume that the porter will remove too much material, anymore than you can assume he's going to give you the head that's going to make you go 400mph at Bonneville. Ask your guy some more specific questions, and maybe for a referral to a customer, and ask about their combinations. Is there a longer duration cam being used, more compression, higher rpm range? You have to know what you're after, and if that's what he can give you.
MP

 

Thanks MP..

 

dswolf,as a side note my freind had samcoe do a 720 kit to his motor,he has called many times and gets the same guy,i think his name is matt,same guy i talked to when i ordered fortin gears,anyway he doesnt know much,when asked tech questions he always seems to have stupid answers.he said their 720 kit was 102mm bore,plus 5mm stroke,my buddie just got his parts back and the cylinder measures 103mm,he still hasnt ckd stroke,but the sales man doesnt seem to know what hes selling.hopefully the guy building the motors knows more than the guy answering the phone

 

Thanks Derby..