Norton intake ports compared to Harley XR 750 (2013)

Joined
Aug 5, 2015
Messages
44
Country flag
I've finally been doing some data runs with the BSA with the Harley style port, I've only done a few runs just to experiment with jetting. With more air flow through the same carbs it seems to need smaller jets. It's making about 85HP on the data logger, which is the best it's ever been. The graphs show acceleration in first and second gear and show the exact differences between jet sizes. These are 230 black trace 240 red trace. I did try 220s which perform almost identical to 230s. I have a C/ratio 5speed in the A65 now which has excellent ratios.

The 1st and 2nd graphs equate to accelerating between 30MPH and 98-99MPH. It's just rolling on the throttle at 30MPH.

 
Joined
Nov 26, 2009
Messages
2,329
Country flag
Congrats on your successful results Mark.

One thing I've been wanting to do is drill a couple conical shaped holes in the bottom of the port floor, install the valve temporarily and poor some molten aluminum into the port to build up the floor. The conical holes would lock the floor in place. You could even insert a temporary rubber floor, ram in some casting sand, remove the temp rubber, replace the valve and then pour in the molten alum. You might have to come 1/2 way each direction with the rubber pieces. Its just an idea and has to be worked out but it could lead you to a raised alum port floor and you could carve in the direction of KR 750 "cobra head" (Narley) ports from there.

Nascar ports below
 

xbacksideslider

VIP MEMBER
Joined
Aug 19, 2010
Messages
1,886
Country flag
Mark - awesome work, thanks for the detailed report and pics. Thanks to Jim too, again.
We should all appreciate that it can be as if you are doing two jobs to put together this kind of post.
 
Joined
Aug 5, 2015
Messages
44
Country flag
I did this head with a smallish version of the ovalport, it's to suit 34mm carbs and has 42mm inlet valves. With seats cut manifolds on and with a little radiused entry its working surprisingly well. It outflows the stock head by about .200" valve lift. It out flows a 38mm round port head with 44.5mm valves. It's going on a LSR 750 A70 configuration engine and flows a little over 160CFM according to my bench.

We should have some dyno figures on it sometime soon. And maybe some speed results if Chris gets it to a venue.

It's pretty simple to cut this size port into a BSA head, it doesn't break through anywhere and just has epoxy to raise the floor. The port is quite small and would probably work fine on a 650.

 
Joined
Nov 26, 2009
Messages
2,329
Country flag
What's interesting is the ridge leading up to the guides that you can see in your photo above. You can see how much work has been done. It would be great to have a better way to raise the port floor than by building up with epoxy. I've been working on this and its not easy.
 
Joined
Dec 23, 2010
Messages
663
Country flag
Very nice work Mark. If the '69 Lightning I had many years ago had been fitted with a cylinder head like yours & a five speed box, I would still own it today. I always thought it was lacking in low down torque for a four speed 'box.
Martyn.
 
Joined
Aug 28, 2012
Messages
119
Country flag
jseng1 said:
What's interesting is the ridge leading up to the guides that you can see in your photo above. You can see how much work has been done. It would be great to have a better way to raise the port floor than by building up with epoxy. I've been working on this and its not easy.
You can make the floor raising part in body putty or 2 parts if needed so you can get them out. Use the part or parts to make simple sand cast replicas. They are small enough that even if you haven't done sand casting you can pull it off cheap and easy. Epoxy the parts in and secure with a couple small screws where you can find a good spot for. No I haven't actually done this yet but I think its a good way to make a major change without welding.
 
Joined
Jun 30, 2012
Messages
9,794
Country flag
What I don't understand is why you are looking at a motor which revs to 9000 RPM safely, for inspiration about porting motors which only rev to 7,500 RPM safely. If you increase the revs, you increase the horsepower, however if you cannot increase the revs, you must increase the mid-range pulling power. You are probably going in two different directions. Short stroke is good, however the rider has to live with it and if you haven't got the gearbox, you haven't got the bike. Are the XR750 Harleys you refer to on dirt, or are they road racers ? - the power requirements are different.
 
Joined
Jun 30, 2012
Messages
9,794
Country flag
It is not horsepower which makes the Aermacchi 350 the fastest 350 single cylinder four-stroke race bike of the 1960s. It is the complete package. It probably developed less horsepower than the 1958 7R AJS.
 
Joined
Aug 5, 2015
Messages
44
Country flag
The advantage of this port design is that it can be applied in various size ports to suit your configuration. And engine size. My BSA is 883cc with 160CFM, power falls off by 6500, using this shape I can have around 200CFM with a port of the same volume and power is good to higher RPM. Smaller ports workout the same, a std volume ovalport flows around 140CFM instead of 110 and the A65s std 74mm stroke allows higher RPM, especially in a 90degree configuration. With the same port volume I doubt it will lose midrange. So the study and application of this is well worth the experimentation.
 
Joined
Nov 26, 2009
Messages
2,329
Country flag
edgefinder said:
jseng1 said:
What's interesting is the ridge leading up to the guides that you can see in your photo above. You can see how much work has been done. It would be great to have a better way to raise the port floor than by building up with epoxy. I've been working on this and its not easy.
You can make the floor raising part in body putty or 2 parts if needed so you can get them out. Use the part or parts to make simple sand cast replicas. They are small enough that even if you haven't done sand casting you can pull it off cheap and easy. Epoxy the parts in and secure with a couple small screws where you can find a good spot for. No I haven't actually done this yet but I think its a good way to make a major change without welding.
I'm thinking about making rubber port molds, removing the molds and cutting the bottom of the rubber mold to raise the port floor. Drill two large diameter holes through the cylinder head port floor (later to be filled with molten aluminum when the head is upside down). Replace the port molds with the raised floors, fill the floor gap with water and freeze it solid. Remove the molds and pack casting sand into the ports before the ice melts. Melt the ice. Warm up the head, dry out the sand & pour in molten aluminum. Details such as sprues need to be worked out but the alum would fill up the drilled holes (conical shape) to lock the aluminum shoe in place and you could shape the new port from there. I'll find out if this works when I try it. I'd rather just weld up the floor but space is too tight for most welders.

Fortunately they had metal shops when I was in high school where I learned aluminum sand casting.
 
Joined
Jun 30, 2012
Messages
9,794
Country flag
Mark, you have posted a reply with port flows stated in CFM. I suggest that measurements off a flow bench don't accurately represent what happens when the port is operating on the bike. The fact that noise is emitted from the inlet tract indicates that sonic conditions are involved. My 850 pulls hard from 4000 RPM and if I am not careful, will go straight through the roof. That means I usually keep it boiling between 6000 to 7000 RPM, where the torque is greatest, and every gear-change is a race-change. Moving the power band higher means you are trying to turn the motor into something it will never be without big money - reliable and very high revving.
 
Joined
Aug 5, 2015
Messages
44
Country flag
acotrel said:
Mark, you have posted a reply with port flows stated in CFM. I suggest that measurements off a flow bench don't accurately represent what happens when the port is operating on the bike. The fact that noise is emitted from the inlet tract indicates that sonic conditions are involved. My 850 pulls hard from 4000 RPM and if I am not careful, will go straight through the roof. That means I usually keep it boiling between 6000 to 7000 RPM, where the torque is greatest, and every gear-change is a race-change. Moving the power band higher means you are trying to turn the motor into something it will never be without big money - reliable and very high revving.
I just putt around on the road, but It's fun experimenting. When I do data runs with the 883 I try to shift at about 7500. The 750 version by 8500
when we were messing with it.

The flow bench just gives an idea of how easy air can move through the head. For a given port volume if one flows appreciably more then I expect the velocity is higher which is a plus. If there is an edge that air is tearing off I think that is where some noise comes from. I do not think these ports ever get to any sort of limiting sonic speed.



I had one configuration that was noisy and pulsed, as in the manometer wouldn't stay steady, it was not good for higher lift flow, but the bike went really good till about 6200 but that was it. It also was very noisy in the induction.

Exhaust configuration can pretty easily determine the power curve you get. Big bore headers on the 750 gave excellent power from about 5500, std headers made it very streetable but lost a little top end.

When you're actually riding the bike you find out how theoretical potential sits with reality.
 
Joined
Jun 30, 2012
Messages
9,794
Country flag
I use a 2 into 1 exhaust system with header pipes that are small enough in diameter to have no step ate the end of the exhaust port. You might expect it only improve power at the bottom end of the rev range. Not so - if I am not very careful, it will go straight through the top. The timing of the exhaust cam makes a difference and an earlier inlet opening also helps. I don't think you could operate this way with petrol, the methanol fuel I use solves a lot of heat problems.
 
Joined
Jul 8, 2011
Messages
2,668
Country flag
acotrel said:
sonic conditions are involved.................... and ............... I usually keep it boiling between 6000 to 7000 RPM, where the torque is greatest,............................
Does your motor also blow smoke under these sonic conditions?

Unless you have a screamer of a short stroke Norton twin; your peak torque will have occurred well before 6,000 RPM
 
Joined
Jun 30, 2012
Messages
9,794
Country flag
All I know is that there is so much torque that I have a problem avoiding over-revving. And every time I have raised the overall gearing, the bike has gone faster coming out of corners. It is very deceptive. I'm used to a short stroke Triumph 500, so I really feel that heavy crank doing it's thing. I would not have thought my bike would accelerate from a standstill in 5th gear and almost put me through a fence, but it happened and I am used to race bikes. Acceleration out of corners is not a problem , however maintaining it over very long straights is. The gearing I'm now running is absurdly high.
I had a similar experience with a two stroke, years ago. I'd made chambers which made the motor too torquey. The bike accelerated like a blur coming out of corners, but ran out of puff halfway down the straights. Back then I didn't have a decent range of sprockets, so I simply fitted better chambers.
 
Joined
Dec 14, 2017
Messages
26
Country flag
You can make the floor raising part in body putty or 2 parts if needed so you can get them out. Use the part or parts to make simple sand cast replicas. They are small enough that even if you haven't done sand casting you can pull it off cheap and easy. Epoxy the parts in and secure with a couple small screws where you can find a good spot for. No I haven't actually done this yet but I think its a good way to make a major change without welding.
The screwed in insert method is reliable and works well either side. I did this firstly with fabricated stainless parts, and then simple sand cast aluminium pieces, 30 years ago when playing Mazda Wankels. They had an inconel insulator in the exhaust that was often removed to make way for timing/width changes to the serious detriment of port volume.
 
Joined
Jun 30, 2012
Messages
9,794
Country flag
How mch racing development did the Harley factory ever do ? If I was going to copy a port design, it would be Aermacchi 350, NOT a Harley shape.
 
Joined
Mar 12, 2013
Messages
300
Country flag
How mch racing development did the Harley factory ever do ? If I was going to copy a port design, it would be Aermacchi 350, NOT a Harley shape.
I take it you've never heard of Dick O'Brien?

Perhaps your liking for Aermacchi ports explains why your Triumphs were such abominations !
 

WZ507

VIP MEMBER
Joined
Dec 26, 2013
Messages
479
Country flag
How mch racing development did the Harley factory ever do ? If I was going to copy a port design, it would be Aermacchi 350, NOT a Harley shape.
Harley has worked in earnest on flat track racing engines for well over half a century, from the WR (pre-1952 flathead), to the KR (pre-1970 flathead, 12 Championships in 17 years of production) to the XR (introduced in 1970), and won more flat track national championships than all the other marques combined. With respect to the modern era of flat track, i.e., circa 1970 through present, Harley actually had a much better idea than the Aermacchi, they copied the BSA Goldstar head/port design, and then, using both internal and external personnel (Axtell, Augustine, et al) continued researching and improving it from 1970 through most of the last century. Although the XR’s run is now essentially over with the introduction of Indian’s 750 Scout last season, on certain tracks the XR is still a very formidable foe, but extraordinarily costly to maintain and find replacement parts for. So yes, the Harley factory did a bit of racing development.
 

Top