Vintage Dirt Bike Q & A
https://vintagedirtbikeforums.alp-sys.com/

More MR175 porting
https://vintagedirtbikeforums.alp-sys.com/viewtopic.php?f=21&t=2950		 Page 1 of 1
Author:  Endo58L [ Thu Feb 17, 2011 10:23 pm ]
Post subject:  More MR175 porting
The transfer timing was altered and a piston fed boost port was added. A Sudco intake manifold for a 36mm Mikuni was matched to the cylinder. (Yes Ray it's thin at the gasket mating surface, but it works).

Attachments:
175 Intake manifold.JPG
175 Intake manifold.JPG [ 34.79 KiB | Viewed 3276 times ]
175 Piston port4.JPG
175 Piston port4.JPG [ 25.19 KiB | Viewed 3276 times ]
175 Piston port5.JPG
175 Piston port5.JPG [ 24.76 KiB | Viewed 3276 times ]
175 Boost port 3.JPG
175 Boost port 3.JPG [ 37.49 KiB | Viewed 3276 times ]
File comment: Stock MR175 cylinder
MR 175 Intake.JPG
MR 175 Intake.JPG [ 36.49 KiB | Viewed 3276 times ]
Author:  rayivers [ Sat Feb 19, 2011 9:29 am ]
Post subject:  Re: More MR175 porting
Coll,

Quote:
(Yes Ray it's thin at the gasket mating surface, but it works).

Hey, that's all that matters. :) Check out the gasket surface surrounding the top two bolts in the CR250 head in my other post.

How much did you open up the intake port? The engmod2t software says it flows about 32.2mm equivalent I.D. in stock form, and I've removed .5mm from each vertical edge (33.2mm I.D.) in case the software's a little off. My other motor also had the port lowered 2mm, for 34.5mm I.D. I'm using a 30mm Keihin.

I modeled 10mm and 12mm conventional passage-fed boost ports - the software won't do piston-fed - and got about +1hp starting at 8,000 rpm. I'm using a 9,000 rpm redline, though; if you rev higher, the gain is greater. I believe the piston-fed port works better than the conventional type in some ways, since 1) a large quantity of otherwise-wasted charge under the piston crown is utilized, 2) refreshing this charge every cycle keeps the piston cooler, and 3) very little flow / velocity is 'stolen' from the main transfers, since the under-piston volume is somewhat separated from the main crankcase volume.

At some point I'll upload port diagrams to my Photobucket account and paste links, as the diagram text looks horrible when resized.

Ray
Page 1 of 1 All times are UTC - 7 hours [ DST ]
Powered by phpBB® Forum Software © phpBB Group
https://www.phpbb.com/