I installed a dt reed valve with boyesens as a stand alone mod and I had way more bottom end torque. I don’t know if it was the bigger reed windows or the boyesens or the fact that the reed valve changed the crankcase volume slightly. Maybe a bit of all 3 but surprisingly other people don’t rate this mod for the ct motors. It does take a bit of hogging out to get it to fit.

A friend of mine who does a lot of 2 stroke tuning said he’d give me a larger Yamaha RD reed to try, he pretty much said what you did so I’ll give it a shot. One question I have about that article was the port shapes. I retained my exhaust ports oval shape, just raised it. The intake port is also oval shaped and is already at the height called for in the article so left it alone. What did you guys end up doing? I’m hesitant to square them off like they’re shown. I figure I can always go back and do that later if that’s what I need to do.

What measurements did you get with the degree wheel

Always good to post that as other people with different cylinders can compare.

Keep them oval. More efficient. Square exhaust ports are not good.

I widened my intake port as far as I could and put lower boyesen ports in as per the book. All those ports are doing is making the reed valve intake full duration. It was technically power ported before hand.

Don’t know if the rd reeds fit think the bolt holes are different. Give it a go. If not dt175 do and blaster do too but jo way the blaster cage fits in the cylinder. That’s my next job to weld up the intake flange on the ct cylinder so I can fit a blaster reed and 34mm tmx flatslide. I have to fix my transfer ports a bit more though before I do that. I stupidly angled the transfer port roofs and I lost a bit of bottom end torque.

Port shape affects power... oval is more "mild" opening... Squared off is more abrupt opening and will give you more power. Square is also bigger. The exception is if you widen an unbridged exhaust to the max a careful elliptical shape "eases" the ring back into the cylinder allowing you to widen more than if you had a square port. Proper chamfer is critical either way.

Hmmm... by memory, on the main intake you need to lower the bottom of the port quite a bit. Top of the port stays the same. I'd be surprised if stock port was lowered enough unless someone ported it.

If the article you guys are talking about is the one I think it is, it was written by a guy that won a National MX title in the 250 class... on a 175. Shoemaker is his name I think... International Cycle was the shop.

Fun stuff and I'm very "old school" but modern porting has come a long way... a pro could probably do a better job with modern techniques... someone like Rich or Meis...

I did not change the stock CT2 reeds. For the time this was an awesome modification. Most of the performance (in my opinion) came from the cylinder porting.

I did a porting map of my cylinder, the exhaust port is 27mm, 51mm from the top, the large transfer port is 39mm, 51mm and the intake is 42mm, 87 from top.

What are the port durations in degrees didn’t you say you used a degree wheel?

The exhaust duration is 188 degrees, I’m not sure of the other ports. I’ll check them when I’m putting things back together

The CT2 article I'm thinking of shows lowering the intake to 91mm with a sort of big bevel and "fingers" to help the skirt support in the center.

Top of intake port should be at least the stock height of the transfer ports... Has cylinder been bored? The top of the intake port drops as the bore gets bigger. If yours is 42mm... should be at 41 if map in article is correct.

Aux transfers drop as bore gets bigger too... should be verified as being at least 41mm.

Port widths also can change as bore gets bigger...

Details are important... +/-1mm can make a noticeable difference in power. Intake is important on the CT.

Also, I would call the stock ports "square" with large radius corners as the important opening and closing edges are straight across. The elliptical or oval port design, for say the exhaust, would have the upper edge higher in the middle and lower at the sides, gently curved. That curved design gives a more gradual port opening and closing. "Square" or straight across tends to be better for power as I said before. Each has its place.

Find a good 74-75 mx175 top end and 28-30 mm carb. You wont have to do any porting. I use a pvl ignition. Mine is on an AT1mx bottom end. It has power from the bottom up.