11.56 sec 1/4 mile Commando motor with Narley ports

Just got this email from Garth in Australia. So far he's the only one I know of for sure who has been using the "Narley ports" specs (HD XR750 port design). Some modern parts and designs in these motors.

Hi Jim
She is flying! Just won the Phillip island classic and sidecar was first in class and held together also. Also ran it quarter mile 11.56 seconds , not bad for an old bomb!
Garth

I'd happily have a go with either one!

that hack has to be fun...

Do you know what stage of the port he created and any idea what the MPH was in the 1/4 mi?

Probably the quickest Norton 1/4 mile in Aus? Go on, shoot me down.....
Would have looked good at the nostalgia drags at willowbank last weekend !

Jim have you heard anything on Mark Parkers BSA special?

Garth didn't spell out the dimensions he used or the MPH at the end of the 1/4 mile. You can see from the machining photo photo that they are wider but he did not make them bigger top to bottom. He didn't weld up the port floor but started with small ports and shaped them closer to the easier version of the "Moved Narley ports" which is the combined steep down draft of the Norton port blended into a smooth radius leading up to the valve - which is possible because the larger 43mm valves move the port closer to the intake manifold. When he didn't weld the port floor I realized that others were going to do the same so I drew up plans on how to do this most effectively to mimic the efficiency of late style XR750 ports. To do this right you have to start with 28.5mm ports and relocate the bolt holes near the spark plugs ala 850 for the larger bores that accept larger valves. I have photos of the bolt hole re-locating available now - courtesy of Ken Canaga. Too many photos to post here.

Here's how the the XR750 port near the valve is blended with the original Nort small port.


The result is similar to below



A photo of Garth's machining. Its not necessary to weld up the manifold bolt holes. There is just enough room with the stock layout. But welding them allowed him to make them just a little wider and keep the vertical dimensions tight. Its important to keep the port oval shaped throughout the head and not go completely round till you get near the carb end of the manifold. Note the weld filling between the ports. You can't see the outsides near the spark plugs but there is weld there as well.


The last I heard from Mark Parker he was happy with the results and was getting better flow and performance than ever before.

More news from Garth.

He doesn't have the top speed on the 1/4 mile run but top speed on a long straight is 140mph
A strong head wind can bring that down to 135MPH