Inlet upgrade?

Wow,
Looks like you have been busy with induction changes.
I too think the longish inlets between the filters and throttle bodies may have a negative impact.
You can always cut down the inlet hoses if their length seems to be hurting performance.
But the small plenum of the stock airbox is a real restriction, your mod has to improve things somewhat.

Just as a comparison, on the Triumphrat forum, some members replaced their Bonneville airboxes with foam sock filters that bolt directly to the carb inlets (on the carb version Bonnies.) Bikes ran way lean and required re-jetting, and produced instant HP increase throughout the RPM range.

I would imagine once the 961 ECU adapts to the new filters, you'll see better throttle response. You already have decatted, free flowing exhaust right?
The only downside will likely be noticeable intake roar.

Will you be testing the final setup on a dyno?
 
BritTwit said:
Wow,
Looks like you have been busy with induction changes.
I too think the longish inlets between the filters and throttle bodies may have a negative impact.
You can always cut down the inlet hoses if their length seems to be hurting performance.
But the small plenum of the stock airbox is a real restriction, your mod has to improve things somewhat.

Just as a comparison, on the Triumphrat forum, some members replaced their Bonneville airboxes with foam sock filters that bolt directly to the carb inlets (on the carb version Bonnies.) Bikes ran way lean and required re-jetting, and produced instant HP increase throughout the RPM range.

I would imagine once the 961 ECU adapts to the new filters, you'll see better throttle response. You already have decatted, free flowing exhaust right?
The only downside will likely be noticeable intake roar.

Will you be testing the final setup on a dyno?
Click to expand...
Intake roar a downside????????
 
TonyA said:
Hot Rod Norton 961 : PHASE 1 , not finished , more trimming and fitting needed.

Inlet upgrade?


Inlet upgrade?


Inlet upgrade?


So far so good. I was trying to form an intake runner with the black hose . I think this is going to work good ! Making it look nice will come later , once I know its worth the effort .
Click to expand...
Just out of curiosity, can the air box be removed without removing the rear wheel?
can the air box come out by unbolting one end of each shock and lower the swing arm enough?
 
TonyA said:
Hello Iwilson , Your work inspired me so to speak. I have ordered a oil breather like the one you fitted and will give it a try.
Click to expand...
Hi Tony, the catch can itself is just there to prove visually the plumbing before it works. Judging by the lack of oil in it you could just route it back into the airbox. In terms of the air filters if you prefer the look (and I quite like it), I wouldn’t get to hung up on whether it’s faster or not, we’re talking about an air cooled push rod engine after all, if you’re chasing hp you’ve bought the wrong bike!

Needless to say (and I’ve been a bit quiet lately), mine is 100%. Starts perfectly, winter or summer, hot or cold without any idle control! Just goes to show the engine is quite good once you remove the design flaws (balance pipe between the throttle bodies). Should probably do a post with the pile of bits I ended up removing to make it run well!

I’m just thankful the clutch etc has not given me any problems! Touch wood....
 
iwilson said:
Hi Tony, the catch can itself is just there to prove visually the plumbing before it works. Judging by the lack of oil in it you could just route it back into the airbox. In terms of the air filters if you prefer the look (and I quite like it), I wouldn’t get to hung up on whether it’s faster or not, we’re talking about an air cooled push rod engine after all, if you’re chasing hp you’ve bought the wrong bike!

Needless to say (and I’ve been a bit quiet lately), mine is 100%. Starts perfectly, winter or summer, hot or cold without any idle control! Just goes to show the engine is quite good once you remove the design flaws (balance pipe between the throttle bodies). Should probably do a post with the pile of bits I ended up removing to make it run well!

I’m just thankful the clutch etc has not given me any problems! Touch wood....
Click to expand...
This adds to the confusion..
I was told that one of the running problems was due to the fact that there wasn’t a balance pipe between the injectors.
An ECU company told me this!
 
MAK said:
This adds to the confusion..
I was told that one of the running problems was due to the fact that there wasn’t a balance pipe between the injectors.
An ECU company told me this!
Click to expand...
They lied... Search my previous posts, they include pictures... It’s not a balance pipe so much as a pipe to split the air from the idle air control motor. Trouble is it allows one cylinder to steal fuel from the other. I posted a number of videos using industry standard wideband AFR senors to document the issue. I can tell you Norton and Jenvey were quite surprised by the results....
 
Voodooo said:
I mean on a commando. Can the air box on a commando be removed without removing the rear wheel / tire.
Click to expand...
I have been waiting for an answer on this too anyone? - in the manual it says to do so plus hugger. Probably a good opportunity to clean off surface rust which seems to form where the hugger bolts on.
 
iwilson said:
we’re talking about an air cooled push rod engine after all, if you’re chasing hp you’ve bought the wrong bike!
Click to expand...
Dunno about that.
Sure, a 4 cylinder, DOHC 1000cc sport bike will respond better to improved induction, mainly owing to better head/combustion chamber design.
But don't discount the effect of just a few more ponies from an obsolete pushrod twin with better breathing.
Better throttle response, better acceleration.
Both worth the effort.
 
Clive said:
I have been waiting for an answer on this too anyone? - in the manual it says to do so plus hugger. Probably a good opportunity to clean off surface rust which seems to form where the hugger bolts on.
Click to expand...
Unless someone has found a trick that I missed then yes wheel and hugger off.
There is a pic of rust below the hugger in 961 Birthday thread over in the rebuilds section.
 
BritTwit said:
Dunno about that.
Sure, a 4 cylinder, DOHC 1000cc sport bike will respond better to improved induction, mainly owing to better head/combustion chamber design.
But don't discount the effect of just a few more ponies from an obsolete pushrod twin with better breathing.
Better throttle response, better acceleration.
Both worth the effort.
Click to expand...
Not saying you can't, just that the platform is a little limited. Not only is it an air cooled pushrod engine but there's not a lot of fiddling available given you really need a programmable ECU and the knowledge to drive it in order to optimise any mechanical adjustments. Opening up the throttle body size will actually decrease throttle response as you'll be losing volumetric efficiency (i.e. torque) at part throttle settings as well as reducing part throttle control (small throttle movements will lose precision as small changes in the butterfly will lead to big changes in air flow).

Throttle butterflies are very non-linear in operation. You get a very large increase in air-flow as they initially open, this rapidly reduces as the butterflies continue to open. So by fitting larger throttle bodies you lose ability to have good throttle control which is so important when you're cornering or low speed maneuvering. You lose torque because switching to a larger throttle body means the engine is ingesting air at a lower velocity at a given throttle opening reducing the volumetric efficiency i.e. the amount of air you can fill the cylinder with (higher velocity air increases the ram effect) - less air = smaller bang = less torque.

In saying that the key question is whether or not the current 38mm throttle bodies are the optimum size and are there any restrictions before or after the TB which are smaller than the new throttle body size. Unless you have access to bunch of different throttle bodies it would be quite an expensive exercise and you would need to remap the ECU on a dyno each time. Personally with this particular bike, I place improving reliability above improving hp as I find the bike has 'enough' as is.
 
Last edited:
BritTwit said:
Dunno about that.
Sure, a 4 cylinder, DOHC 1000cc sport bike will respond better to improved induction, mainly owing to better head/combustion chamber design.
But don't discount the effect of just a few more ponies from an obsolete pushrod twin with better breathing.
Better throttle response, better acceleration.
Both worth the effort.
Click to expand...
And don't forget the reason we bought a 961 rather than an oh-so-capable sportbike-San - the fabulous looks of the beast!

Maybe you could accuse me of wanting my cake and eating it but in the 961 I got the looks, the handling, the name and acceptable performance. I just want an extra dusting of icing sugar and a cherry on the top........
 
iwilson said:
Not saying you can't, just that the platform is a little limited. Not only is it an air cooled pushrod engine but there's not a lot of fiddling available given you really need a programmable ECU and the knowledge to drive it in order to optimise any mechanical adjustments. Opening up the throttle body size will actually decrease throttle response as you'll be losing volumetric efficiency (i.e. torque) at part throttle settings as well as reducing part throttle control (small throttle movements will lose precision as small changes in the butterfly will lead to big changes in air flow).

Throttle butterflies are very non-linear in operation. You get a very large increase in air-flow as they initially open, this rapidly reduces as the butterflies continue to open. So by fitting larger throttle bodies you lose ability to have good throttle control which is so important when you're cornering or low speed maneuvering. You lose torque because switching to a larger throttle body means the engine is ingesting air at a lower velocity at a given throttle opening reducing the volumetric efficiency i.e. the amount of air you can fill the cylinder with (higher velocity air increases the ram effect) - less air = smaller bang = less torque.

In saying that the key question is whether or not the current 38mm throttle bodies are the optimum size and are there any restrictions before or after the TB which are smaller than the new throttle body size. Unless you have access to bunch of different throttle bodies it would be quite an expensive exercise and you would need to remap the ECU on a dyno each time. Personally with this particular bike, I place improving reliability above improving hp as I find the bike has 'enough' as is.
Click to expand...
Wilson,
I don't disagree with your analysis, but don't forget that the 961 head was originally designed to work with 39mm FCR carbs. Smooth bores that will flow a hell of a lot more air than the 38mm Jenvey TBs. Some would say that 39mm smooth bores flow as well as 44mm TBs. I hate to once again mention the Triumphrat forum, but folks there have done 44mm Keihin TB conversions for the Hinckley Bonneville motor with phenomenal results. The ports on the Bonnie motor where designed for 36mm Keihin CVK carbs, and later the 36mm TBs.

They buy 44mm Keihin TBs (from the Triumph street triple) off eBay, then cut down the linkages to fit 2 TBs between the Bonnie's intake ports. The Bonnie's EFI is able to operate the the TB's and injectors with a Power Commander. If you read the posts there, the results are massive low RPM torque, and lots of HP up around 8500RPM. Stock red line is 7500, so they have to tweak the ECU with a tune. Some have opened the ports, and added cams and 12:1 pistons, those machines get 100HP. Not bad for a 65HP stocker.

I do think a modest improvement can be gained on the 961 from better induction especially if the exhaust has already been addressed with a free flowing system, and the airbox is replaced with less restrictive filters. I think the Unifilters have small velocity stacks inside the filter housing to improve flow into the TBs. If the final build is Dyno-ed to achieve the right mapping/APR, I'm pretty sure 6-8HP increase (8-10%) should be possible, with improvements throughout the entire RPM range. Not a massive increase in performance, but still noticeable, and enjoyable.
 
Clive said:
I have been waiting for an answer on this too anyone? - in the manual it says to do so plus hugger. Probably a good opportunity to clean off surface rust which seems to form where the hugger bolts on.
Click to expand...
Richard 7 & dad told me 5 years ago , “ back wheel has to come out “ to remove air box
 
Clive said:
And don't forget the reason we bought a 961 rather than an oh-so-capable sportbike-San - the fabulous looks of the beast!

Maybe you could accuse me of wanting my cake and eating it but in the 961 I got the looks, the handling, the name and acceptable performance. I just want an extra dusting of icing sugar and a cherry on the top........
Click to expand...
I fell in love with the same cake. Saw it, clocked that famous name and put my readies down. Did’nt even taste it first! Another 8-10% more sprinkles on top would be awesome!!
 

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