Should I widen my intake port?

[TheBaldKiwi]

Hello,

Are there any downsides to widening the intake port? From the factory the port is already as wide as it can be on the outside, however I notice that it tapers down to a much smaller hole when it meets the inside of the cylinder. The last mod I did to my engine was trimming the piston skirt and I had fantastic results, so the next mods I am looking into are raising the exhaust port around 1mm and widening the intake port.

 

[machanic]

It could swallow your piston, with that said be careful and don't square the top of the port leave it rounded or crowned and yes there are performance gains with port cleaning up of casting flash matching gaskets and intake port and transfer ports.

 

[FurryOnTheInside]

Yes, go for it!

No, I did a lot of reading about simple port improvements and everything I read about this was positive.
I think the only possible downside is if you go too far and expose the ring ends, or you tear the intake gasket when you remove the intake and don't have a spare one handy.

I can't say I scientifically tested the gains from this mod; it needs the supporting mods to really get full advantage anyway, of course. I just put my faith in the more scientific members' experiences/ opinions and did this mod (more like correction?) right from the beginning. I have widened the bottom of my intake port window (making it a more trapezoidal shape) to about 25mm (measured on thin paper around the inside of the cylinder).

 

[TheBaldKiwi]

Yes, go for it!

No, I did a lot of reading about simple port improvements and everything I read about this was positive.
I think the only possible downside is if you go too far and expose the ring ends, or you tear the intake gasket when you remove the intake and don't have a spare one handy.

I can't say I scientifically tested the gains from this mod; it needs the supporting mods to really get full advantage anyway, of course. I just put my faith in the more scientific members' experiences/ opinions and did this mod (more like correction?) right from the beginning. I have widened the bottom of my intake port window (making it a more trapezoidal shape) to about 25mm (measured on thin paper around the inside of the cylinder).

Alright cool. So you widened the bottom of your port and pretty much left the upper part untouched? I guess that would take the rings snagging out of the picture.

 

[Street Ryderz]

Widening the ports at the window(cylinder) is one of the easiest and most noticeable gains to be done.I've seen Britt Vanegas's 70 plus cylinder and the exhaust port width is 3/4 of the bore width the sides of the port overlap the transfers and the intake is also huge.Now I dont recomend doing this to that degree because there is alot of other stuff done to make it work and it doesn't last long but it can be done to extreams you would not normally think possible.It's not uncommen to see port widths in the mid 20's myself the intake is 23mm and exhaust is 27mm I found (for my set up) those widths to work very well and still be streetable having enough torque to pull through numericaly lower gearing and make good power through out.IMO these engines are run normally under charged meaning that the a/f ratio interduced to the cylinder is anemic (not sufficaint) witch creates heat quickly doesn't carry enough oil for protection and just doesn't work efficaintly.Here is a pic not the best it's hard to see the difference unless you hold a stock one to compare but for those who do this you can tell.

 

[FurryOnTheInside]

Alright cool. So you widened the bottom of your port and pretty much left the upper part untouched? I guess that would take the rings snagging out of the picture.

Yeah, just the bottom "corners", made the port more like a rounded trapezoidal shape, like a chunk of chocolate that's been sucked on for a few minutes.
I read a bunch of other people's port widening measurements they kindly posted on the forum, Jaguar, Steve Best, Street Ryderz and others; picked a figure in the middle and just did roughly that.
Idk why only the bottom, I guess piston speed or something.
I lowered the bottom of the intake just barely, then widened the top of the exhaust to about 25.5 or so, redirected the transfers, and got a very fast bike compared to the 25mph stock builds we read about (I have a generic eBay engine). Doubt it's as fast as it could be, I've done no scientific testing on my first build, but it really goes.

 

[TheBaldKiwi]

Widening the ports at the window(cylinder) is one of the easiest and most noticeable gains to be done.I've seen Britt Vanegas's 70 plus cylinder and the exhaust port width is 3/4 of the bore width the sides of the port overlap the transfers and the intake is also huge.Now I dont recomend doing this to that degree because there is alot of other stuff done to make it work and it doesn't last long but it can be done to extreams you would not normally think possible.It's not uncommen to see port widths in the mid 20's myself the intake is 23mm and exhaust is 27mm I found (for my set up) those widths to work very well and still be streetable having enough torque to pull through numericaly lower gearing and make good power through out.IMO these engines are run normally under charged meaning that the a/f ratio interduced to the cylinder is anemic (not sufficaint) witch creates heat quickly doesn't carry enough oil for protection and just doesn't work efficaintly.Here is a pic not the best it's hard to see the difference unless you hold a stock one to compare but for those who do this you can tell.

Very informative. When comparing those pictures to my stock cylinder, I can clearly see the ports are opened up quite a bit. Once I get all my porting tools together I will definitely widen up my ports.