Intake manifold and port

I use an air tool as below. Only $15 at harbor freight.


Intake manifold and port




Use with cartridge roll and mandrel as shown below. A small diameter roll and longer mandril will get around the guide without having to remove the guide. Takes longer than if the guide is removed and there is some hand finishing required but I've done it. Can hand finish right next to the guide with abrasive paper wrapped around a needle nose pliers.

Intake manifold and port


Intake manifold and port


Use machinist caliper and micrometer to measure IDs being careful not to go too far.

Intake manifold and port


Intake manifold and port


Its all about craftsmanship and patience.
 
I would not raise the roof of the port near the valve guide. You can end up with a split and the valve guide becoming loose in the head.
My motor is an 850 and the ports are 30mm. I use 34mm Mk2 Amal carbs and blend the first 10mm of the port in with a smooth curve, When a motor is running and you can hear the ports, what is happening is sonic. What happens under those conditions is different to what happens at lower gas speeds. I suggest the whole system from bellmouth to the end of the exhaust pipe resonates when the motor is revving higher than the threshold. The cam and exhaust system set the threshold. When you ride the bike, you can usually feel when the system begins to work, When you race , the only time your revs go really low is when you are balked in a corner - so poor gas flow then does not matter. - You just slip the clutch to get the revs up. The problem comes when you try to optimise the gearing to suit the circuit. If the inlet ports are too big, you become forced to used the bike in a different way
 
Before you wear your finger out, these are what I use with air tool above. They come in different diameters and grit. MSC supply


Intake manifold and port
 
jseng1 said:
I use an air tool as below. Only $15 at harbor freight.

Use with cartridge roll and mandrel as shown below. A small diameter roll and longer mandril will get around the guide without having to remove the guide. Takes longer than if the guide is removed and there is some hand finishing required but I've done it. Can hand finish right next to the guide with abrasive paper wrapped around a needle nose pliers.

Use machinist caliper and micrometer to measure IDs being careful not to go too far.

Its all about craftsmanship and patience.
Click to expand...

Thanks for the tips. I'm measuring the shape and dimensions inside of the venturi with a small bore gauge, and guesstimating what is happening around the guide with my artist's eye.

I already have enough material removed prior to the guide at the end of the venturi section. What I don't have is a mildly raised roof there. I doubt I'll be raising it much. I just want to get a minor hump on the sides at the end of the venturi just before the base of the guide smoothed down some more. Essentially matching the transition out of the venturi into the bowl right around the guide at the roof. After looking at it some more, I can do it with my fingers and sandpaper/emery cloth. It'll just take about 10 more hours at the current speed I'm doing it.

I've got the craftmanship and patience. Slow and steady. I could use a metal high speed rotating finger to speed things up though.
 
Schwany said:
Thanks for the tips. I'm measuring the shape and dimensions inside of the venturi with a small bore gauge, and guesstimating what is happening around the guide with my artist's eye.

I already have enough material removed prior to the guide at the end of the venturi section. What I don't have is a mildly raised roof there. I doubt I'll be raising it much. I just want to get a minor hump on the sides at the end of the venturi just before the base of the guide smoothed down some more. Essentially matching the transition out of the venturi into the bowl right around the guide at the roof. After looking at it some more, I can do it with my fingers and sandpaper/emery cloth. It'll just take about 10 more hours at the current speed I'm doing it.

I've got the craftmanship and patience. Slow and steady. I could use a metal high speed rotating finger to speed things up though.
Click to expand...
The widest part of the port should be around the guide because the guide is the restriction. Also go with a higher arch so the flow gets directed downward onto the valve. That way the charge uses the complete diameter of the valve to enter the combustion chamber (rather than blowing across it). Something towards the radical Nascar intake port shape shown below.
Intake manifold and port
 
This A65 port does this. It's 34mm and you can see the oval entry at the head, the oval means the top run can go under the spring pocket and be straight and curve over. The point is to get this high either side the guide and get a nice turn onto the back of the 42mm valve so the valve flows properly. The charge has no option but to follow this curve. If it dips under the spring seat area and goes back up the charge jumps off the wall and stuffs up. The floor is raised for a nice turn down and the port is widened to allow volume through unhindered. I can take the valve out and plug the guide hole and it flows less. If I go smaller, 30mm, I can increase speed a lot, but kill off cfm. Speed with the 34mm is around 400fps and best cfm with 42mm valve around 178cfm. An engine needs cfm and port speed to have volumetric efficiency at higher rpm. That is over filling the chamber beyond the swept volume. What cfm an engine needs for its displacement to produce maximum hp at 7,000 varies according to its VE. As does its hp at those rpm. I can see that's what you are talking about. The speed uses that energy to force the charge into the cylinder, the more it does that the more charge it requires.

Just to illustrate as engines can make up to 127% VE if done right. With a VE of 100% 140cfm makes 72hp @ 7,000 but increase the VE to 125% at 7,000 it will make 91hp, but will require 175cfm and what will enable the overcharging of the cylinder is speed in the inlet port to force that charge in. So, the port becomes very central to achieving that. Though it is not the port alone.

What the high VE does is increase hp at lower rpm and make the engine very responsive. People hear the race engine at a meeting and think it has a super light flywheel when in fact weight has been added. Last year this period 3 outfit qualified 2nd fastest out of outfits up to Period 6, 1000cc and 750 multivalve 4 cyl. And period 3 1250cc Vincent etc. Yet it is 745cc with a rev limiter set at 7,000.

So, I based a big port on Jim's pictures of the XR750 oval port 38mm on an 883, with very decent hp from my big A65. But I did not get the instant response of the smaller versions I have done since. I can get within 5 or 10cfm of that 38mm head using the same 44.5mm valve and 34mm runners and carbs, so the 883 you open the throttle and initially it jumps then it feels hollow till it gets rpm up a bit, then is really good, a 750 with the 34mm ports and carbs is more instant response and feels more alive. The 42mm valve and a little less flow measures the same speed and seems to go as well.

Intake manifold and port
 
mark parker said:
This A65 port does this. It's 34mm and you can see the oval entry at the head, the oval means the top run can go under the spring pocket and be straight and curve over. The point is to get this high either side the guide and get a nice turn onto the back of the 42mm valve so the valve flows properly. The charge has no option but to follow this curve. If it dips under the spring seat area and goes back up the charge jumps off the wall and stuffs up. The floor is raised for a nice turn down and the port is widened to allow volume through unhindered. I can take the valve out and plug the guide hole and it flows less. If I go smaller, 30mm, I can increase speed a lot, but kill off cfm. Speed with the 34mm is around 400fps and best cfm with 42mm valve around 178cfm. An engine needs cfm and port speed to have volumetric efficiency at higher rpm. That is over filling the chamber beyond the swept volume. What cfm an engine needs for its displacement to produce maximum hp at 7,000 varies according to its VE. As does its hp at those rpm. I can see that's what you are talking about. The speed uses that energy to force the charge into the cylinder, the more it does that the more charge it requires.

Just to illustrate as engines can make up to 127% VE if done right. With a VE of 100% 140cfm makes 72hp @ 7,000 but increase the VE to 125% at 7,000 it will make 91hp, but will require 175cfm and what will enable the overcharging of the cylinder is speed in the inlet port to force that charge in. So, the port becomes very central to achieving that. Though it is not the port alone.

What the high VE does is increase hp at lower rpm and make the engine very responsive. People hear the race engine at a meeting and think it has a super light flywheel when in fact weight has been added. Last year this period 3 outfit qualified 2nd fastest out of outfits up to Period 6, 1000cc and 750 multivalve 4 cyl. And period 3 1250cc Vincent etc. Yet it is 745cc with a rev limiter set at 7,000.

So, I based a big port on Jim's pictures of the XR750 oval port 38mm on an 883, with very decent hp from my big A65. But I did not get the instant response of the smaller versions I have done since. I can get within 5 or 10cfm of that 38mm head using the same 44.5mm valve and 34mm runners and carbs, so the 883 you open the throttle and initially it jumps then it feels hollow till it gets rpm up a bit, then is really good, a 750 with the 34mm ports and carbs is more instant response and feels more alive. The 42mm valve and a little less flow measures the same speed and seems to go as well.

Intake manifold and port
Click to expand...
Mark - how do you raise the port floor?
 
I was at a race meeting a few years ago, and my friends were racing a featherbed frame with a 500cc pushrod Matchless engine. I happened to see inside the inlet port and it was absolutely huge. I said tothe guys 'why don't you get a two-valve Jawa speedway engine and you would start where you have finished with the Matchless engine ?'. The bought two Jawa engines, and almost immediately beat one of Ken McIntosh's new Molnar-engined Manx Nortons.
I made the same mistake with my first race bike. I was seeking more torque, so I enlarged the inlet ports. I did similar with wheels, I wanted better handling and better rubber, so I replaced the 19 inch wheels on my Triton with 18 inch. It made the bike exhausting to ride. It is a mistake to look at a more recent Japanese bike and base what you should do with an old bike, on that. A Manx Norton is radically different from a Japanese two stroke, and in some ways better.
With my Seeley 850, I use 34mm Mk2 Amals, but the ports are carefully tapered for the first 10mm. Inside, they are 30mm.
When mistakes are made when using methanol fuel, it is much more forgiving.
 
Is not seat of the pants testing less accurate ? And no matter what values you get from the flow bench
does not the dyno really tell the tale? I'm just asking, no knowledge do I possess. And most of this stuff is not road use but race track needs. What about those of us looking for better efficiency and less hot spots in a road bike?
 
Onder said:
Is not seat of the pants testing less accurate? And no matter what values you get from the flow bench
does not the dyno really tell the tale? I'm just asking, no knowledge do I possess. And most of this stuff is not road use but race track needs. What about those of us looking for better efficiency and less hot spots in a road bike?
Click to expand...
Seat of the pants can tell you if a modification brings a significant result. It may also show response at part throttle that a dyno doesn't see, because dynos tend to be measuring wide open. But with a dyno at least you have an easy measure. And it puts a number to a result. You definitely get an idea from a flow bench if you understand you are dealing with two important variables not one. Cfm is important but so too is gas speed in the inlet. It's very applicable on the road and efficiency is the holy grail. Because what's nice is an engine that responds strongly and is very willing at the slightest hint of throttle. That will go nuts with wide open throttle. If efficiency is up and it overfills the cylinders your actual dynamic compression ratio also goes up. If it overfills to 120% which is 120% VE, 9.5-1 turns into 11.4-1 and this can be from midrange and up, and a 750 can punch like a very strong 900. There is one way to make hp, burn more charge. You can do that with a bigger displacement, more rpm or higher VE. The last is more satisfying because the engine is more alive, it also seems to use less fuel.

So that port I showed above is on a fairly std spec A65 670cc. That averages around 70mpg ridden virtually every day. I do need to dyno it just to see what it makes.

The floor of that port is built up with JBweld Jim. I rough the alloy up and make it clean and have never had it come off. The curve of that needs to keep the air following it, if too sharp I think it comes off it. Which can cost around 10cfm. The valves and ports tend not to get carbon in them.

Intake manifold and port

Intake manifold and port
 
Someone inadvertently found that lip in the intake port caused by a mismatch in carb to manifold diameter, gave more power. Probably due to break up of the boundary layer, resulting in a greater charge density,
Flow with a turbulent boundary layer "fills " a channel more than that with a laminar boundary layer.

Slick
 
Last edited:
mark parker said:
Seat of the pants can tell you if a modification brings a significant result. It may also show response at part throttle that a dyno doesn't see, because dynos tend to be measuring wide open. But with a dyno at least you have an easy measure. And it puts a number to a result. You definitely get an idea from a flow bench if you understand you are dealing with two important variables not one. Cfm is important but so too is gas speed in the inlet. It's very applicable on the road and efficiency is the holy grail. Because what's nice is an engine that responds strongly and is very willing at the slightest hint of throttle. That will go nuts with wide open throttle. If efficiency is up and it overfills the cylinders your actual dynamic compression ratio also goes up. If it overfills to 120% which is 120% VE, 9.5-1 turns into 11.4-1 and this can be from midrange and up, and a 750 can punch like a very strong 900. There is one way to make hp, burn more charge. You can do that with a bigger displacement, more rpm or higher VE. The last is more satisfying because the engine is more alive, it also seems to use less fuel.

So that port I showed above is on a fairly std spec A65 670cc. That averages around 70mpg ridden virtually every day. I do need to dyno it just to see what it makes.

The floor of that port is built up with JBweld Jim. I rough the alloy up and make it clean and have never had it come off. The curve of that needs to keep the air following it, if too sharp I think it comes off it. Which can cost around 10cfm. The valves and ports tend not to get carbon in them.

Intake manifold and port

Intake manifold and port
Click to expand...
That looks like a lot of fun while looking good at the same time..
 
Schwany said:
I don't have any plans to do anything in excess and will probably do less material removal than what is in your Axtell port diagram. Baby steps really. Ports are now 30mm right at the entrance then blended into the smaller existing diameter. Most of what I'm doing is using the fickle fingers of fate and emery cloth around the guides.

Anybody ever raise the intake floor with JB Weld and live to tell about it? :)
Click to expand...
Yea, I do on BSA twin heads, one a Championship winner in 2020. Use a cutter and make it rough and clean for it to key to. What I find is that raising the floor can reduce flow so widening the port is necessary to restores the flow. And the whole deal works better. It's deeper in the bowl and the top runs up either side the guide and down onto the valve in one curve or straight and curve right from the entry, the port cannot aim up and then go down under the spring area then back up at all or it kills flow and speed. The charge forces against this curve so must turn down, the walls go out either side the guide and back into the valve. On a BSA head it's necessary to make the port transition to oval as it enters the head to keep it low and allow a smooth fast top run, yet still allow flow. This head is shown part done and the 27mm port goes from 108cfm to 34mm and 178cfm. It's for a 750 so should punch hard all the way to 7,500.

Intake manifold and port


This is a different head and manifold but shows the oval shape at the head interface. You can see the height it goes up into the bowl but not the width at the guide. Usually, it is said a straight port flows best, but in this case with such a low entry it must turn the charge down squarely into the back of the valve or the valve does not flow, aiming across the valve uses part of it only. That is why the floor is raised to assist that turn.

Intake manifold and port
 
texasSlick said:
Someone inadvertently found that lip in the intake port caused by a mismatch in carb to manifold diameter, gave more power. Probably due to break up of the boundary layer, resulting in a greater charge density,
Flow with a turbulent boundary layer "fills " a channel more than that with a laminar boundary layer.

Slick
Click to expand...
There was a story from the BSA gold star competition shop
They had a 350 Goldie motor on a Dyno
"The carb was removed before tea break and when they came back and apprentice accidentally fitted a carb from a 500
When they ran the motor again there was a big jump in power "
I've read this several times, or versions of this stot
 
baz said:
There was a story from the BSA gold star competition shop
They had a 350 Goldie motor on a Dyno
"The carb was removed before tea break and when they came back and apprentice accidentally fitted a carb from a 500
When they ran the motor again there was a big jump in power "
I've read this several times, or versions of this stot
Click to expand...
As it is sucking rather than blowing in against the lip it may not do much, but the bigger carb will flow more, allow more air in. I don't know if this was a GP carb or something else, but it looks like the carb size was restricting it. Open the port size to the bigger carb and it would likely drop power, unless that port runner was also a restrictor.
acotrel said:
I would not raise the roof of the port near the valve guide. You can end up with a split and the valve guide becoming loose in the head.
My motor is an 850 and the ports are 30mm. I use 34mm Mk2 Amal carbs and blend the first 10mm of the port in with a smooth curve, When a motor is running and you can hear the ports, what is happening is sonic. What happens under those conditions is different to what happens at lower gas speeds. I suggest the whole system from bellmouth to the end of the exhaust pipe resonates when the motor is revving higher than the threshold. The cam and exhaust system set the threshold. When you ride the bike, you can usually feel when the system begins to work, When you race , the only time your revs go really low is when you are balked in a corner - so poor gas flow then does not matter. - You just slip the clutch to get the revs up. The problem comes when you try to optimise the gearing to suit the circuit. If the inlet ports are too big, you become forced to used the bike in a different way.
Click to expand...
On a BSA head the port can be raised either side the guide because there is sufficient metal in that head, I don't know about a Norton. But you need to leave metal leading up to the guide in the centre so as not to go into where the spring sits. If you put a sharp ridge up to the guide the air may go across it and cause problems so blending that so it's a lump not a wing allows better flow. When I had my 883 BSA running just over 12-1 compression it definitely made that loud sonic noise when the throttle was opened, it sounded so nice.
 
mark parker said:
As it is sucking rather than blowing in against the lip it may not do much, but the bigger carb will flow more, allow more air in. I don't know if this was a GP carb or something else, but it looks like the carb size was restricting it. Open the port size to the bigger carb and it would likely drop power, unless that port runner was also a restrictor.

On a BSA head the port can be raised either side the guide because there is sufficient metal in that head, I don't know about a Norton. But you need to leave metal leading up to the guide in the centre so as not to go into where the spring sits. If you put a sharp ridge up to the guide the air may go across it and cause problems so blending that so it's a lump not a wing allows better flow. When I had my 883 BSA running just over 12-1 compression it definitely made that loud sonic noise when the throttle was opened, it sounded so nice.
Click to expand...
I'd assume the story was about GP carbs
 
baz said:
There was a story from the BSA gold star competition shop
They had a 350 Goldie motor on a Dyno
"The carb was removed before tea break and when they came back and apprentice accidentally fitted a carb from a 500
When they ran the motor again there was a big jump in power "
I've read this several times, or versions of this stot
Click to expand...
I use 34mm Mk2 Amals on 30mm ports with the first 10mm of the ports tapered. I don't know why I did that, but I must have had a reason. I probably think about Commando engines a bit differently. When I first bought the 850, I thought that being a Norton, with their racing history - it would probably be OK. But the crank lookes horrendous, and I never really believed in it until I started to develop it. I trusted the part of the inlet port from the valve guide to the valve seat to be pretty correct. From experience I knew what happens when the inlet ports are too large. After tuning and gearing, I now believe the rod to stroke ratio to be very good.
Top end power is not so relevant as some people might think , as long as the motor pulls very strongly, somewhere within its usable rev range. The gearbox is the torque converter. Dynos run on torque. Because I have not got a dyno, I choos an ignition advance to suit the fuel ans the compression ratio, then jet to get the fastest acceleration on a race circuit. If you have a dyno, you can get the jetting pretty right using an oxygen probe then while the bike is running on the dyno, adjust the ignition timing to get maximum torque.
If you alter the port shape during development, you are almost back to square one. In most cases, you cannot add metal inside the port.
Another thing to consider is at TDC on the non-compression stroke, the inlet and exhaust valves are both open, and the exhaust and inlet tracts affect each other. Fitting a megaphone to an exhaust, in place of a silencer without retuning can burn a piston.
 
I did not know it, but where I worked when I built the Seeley 850, I could have had a billet crank made out of the best alloy steel in Australia, at very low cost. I would have had a different approach to tuning, and raced the bike much earlier. My mind was on other things. With a billet crank of similar dimensions to standard, I could make my motor much faster down the straights.
 

Similar threads

elefantrider
Intake Manifold Cap Screws
Replies
10
Views
323
ilikevelos
I
D
Inlet manifold balance stubs.
Replies
17
Views
538
Schwany
Schwany
Anvill
Mikuni single manifold inner bolts
Replies
4
Views
466
Larry S
Larry S
jseng1
More power with more intake length
2 3
Replies
46
Views
3,431
acotrel
acotrel
jms
1967 Atlas Carbs and Manifolds
Replies
3
Views
315
marinatlas
marinatlas
Back
Top