Inlet upgrade?

Remember the Beechcraft Starship. Buy them back and scrap and remove all worries...sounds like the same deal. Business is business.
 
But to return to the tuning theme my track time was interesting - It inspires confidence in the corners but is never going to be 'flickable' especially with spoked wheels but it is down those straights where I just need that bit extra maybe 20bhp to enjoy track days?

The two first areas used to be head mods and cam swap.

There are companies who offer to reprofile your cams - if you could work out the clearance to piston and be confident with the spring rate this could be interesting but this is normally just moving the power under the curve around. What you gain at the top you lose at the bottom. Only 5 gears becomes a problem.

Not much could be done with the head other than a bit of flowing and fettle with the air box. The intake under the seat always looked a bit suspect....
Or of course there is forced induction. Something similar to the Thruxton setup is in the thousands (cost of a second hand Triumph 650) and a bit messy. I need to get that electric supercharger built.......
 
If you’re serious, I believe Ollie Thiel offers a big bore. And the CR could be raised at the same time. He also does Dynajet PC fitting and set up. He may have looked at cams too, I’m not sure, but he’s definitely the man to speak to.

But I wasn’t really joking when I asked “I do wonder what hitherto well hidden foibles would be unmasked if the 961 was tuned for more oomph...?”

You may embark upon a long road of constantly discovering, and re-engineering, the next weak link.

I can’t remember if you have ABS? If not, I’d definitely give the CF wheels a go and invest some paddock time in trying to dial in the suspension.

Having a bike slower than the herd can be fun cos you’ve got nothing to prove or lose! More importantly, it can be a great way of improving your riding by focusing on late braking, maintaining corner speed and general ‘race craft’. A bit like Peter Williams did !
 
Fast Eddie said:
Having a bike slower than the herd can be fun cos you’ve got nothing to prove or lose! More importantly, it can be a great way of improving your riding by focusing on late braking, maintaining corner speed and general ‘race craft’. A bit like Peter Williams did !
Click to expand...
Yup - wise words indeed sir. What's going round in my head is;

1 for road or dry novice track day use the bike is more than adequate.
2 I'm trying to convince myself that a 1980's CRMC Jap bike is really the sort of classic bike I'd like (can afford to buy and repair) to get some track experience. (MZ racing?????????)

And yes mine was one of the first ABS.

But I'm still thinking about that (non ebay fake) electric supercharger.......
 
Indeed, an early 80s bike is about as cheap as decent racing gets I think. And I don’t think you even have to worry about repairing them!
 
Clive said:
Yup - wise words indeed sir. What's going round in my head is;

1 for road or dry novice track day use the bike is more than adequate.
2 I'm trying to convince myself that a 1980's CRMC Jap bike is really the sort of classic bike I'd like (can afford to buy and repair) to get some track experience. (MZ racing?????????)

And yes mine was one of the first ABS.

But I'm still thinking about that (non ebay fake) electric supercharger.......
Click to expand...

I don’t know what the “UK Club Thundersport, Golden Era Superbike series” actually is, but it looks like it would be fun on this (I had one of these as a track bike once, huge fun):

2000 SP-1 race machine For Sale | Car and Classic

2000 SP-1 race machine For Sale
www.carandclassic.co.uk www.carandclassic.co.uk
 
Fast Eddie said:
I don’t know what the “UK Club Thundersport, Golden Era Superbike series” actually is, but it looks like it would be fun on this (I had one of these as a track bike once, huge fun):

2000 SP-1 race machine For Sale | Car and Classic

2000 SP-1 race machine For Sale
www.carandclassic.co.uk www.carandclassic.co.uk
Click to expand...

Sorry to pollute this thread but:

SP-1 is a way cool unit. An RC51 with factory WSB Honda Superbike race kit.
I had an RC51 way back in 2001, and they are great bikes.
Power on top, midrange, and lowend, everywhere.
The motor is magnificent.
The only place they couldn't match a Duck was in tight curves.
I noticed in your link owner states that he removed the lash gears from the cam gear drivetrain.
That bike will be LOUD when starting cold.
The RC51 has a set of marvelous cam gear drive trains - one for front cylinder, on for rear.
Beautiful Honda engineering.

Inlet upgrade?
Hosted on Fotki

If I where you and 20 years younger again, I would go for it.
And don't forget to write a race diary, here on the forum.
 
A little ‘off track’ machine wise but a mate of mine is having way too much fun on the track with a well sorted CBR250RR. Paid very little and the thing is a screamer, literally! Sounds like a 650 to me. Would love to try that rather than risk turning my pristine Norton into a mangled piece of modern art! Then it would have to spend the rest of its life in the living room!
 
Ta all for for advice. Having seen some very expensive carbon fibre clad machinery disintegrate after accidents at Donnington recently I think this is the way to go - this could be a dangerous time coming up with some spare time on the computer over Christmas - we're planning a house sale and I'm waiting for an insurance payout from a cycle accident....
 
Are you referring to these?
Will they fit on to the intake ports of the 961's head?
the 40's are only 2mm larger than the stock TBs.
Don't know if it would be a very worth while mod.

Inlet upgrade?
Hosted on Fotki
 
There is somebody selling new 961 Jenvey bodies and injectors complete for £225 (or offers)

www.ebay.co.uk

Jenvey 38mm Throttle Body / Bodies - MCT Norton 961 - New Old Stock - NOS | eBay

<p>Jenvey 38mm Throttle Body / Bodies - MCT Norton 961 - NOS. Condition is "New". Dispatched with Royal Mail 2nd Class </p><p>Brand new / new old stock throttle bodies built by Jenvey for norton bit suitable for any bike or car that requires 38mm tb’s.</p><p>Will post better pictures soon.</p>
www.ebay.co.uk
 
Last edited:
cliffa said:
There is somebody selling new 961 Jenvey bodies and injectors complete for £225 (or offers)

www.ebay.co.uk

Jenvey 38mm Throttle Body / Bodies - MCT Norton 961 - New Old Stock - NOS | eBay

<p>Jenvey 38mm Throttle Body / Bodies - MCT Norton 961 - NOS. Condition is "New". Dispatched with Royal Mail 2nd Class </p><p>Brand new / new old stock throttle bodies built by Jenvey for norton bit suitable for any bike or car that requires 38mm tb’s.</p><p>Will post better pictures soon.</p>
www.ebay.co.uk
Click to expand...
That's got me thinking........with machining and new butterflies....job done?
 
Al's#5 said:
That's got me thinking........with machining and new butterflies....job done?
Click to expand...
That's what Triumph Twin Power did to the 36mm throttle bodies on the old Bonneville model.
Gave a nice improvement in flow going from 36 to 38mm.
Not enough metal on the TBs to go any further though without compromising the strength of the TB unit.

May have a problem port matching the new 40mm TBs to the 961 head.
Might need to open the inlet end of the port a bit.
 
BritTwit said:
That's what Triumph Twin Power did to the 36mm throttle bodies on the old Bonneville model.
Gave a nice improvement in flow going from 36 to 38mm.
Not enough metal on the TBs to go any further though without compromising the strength of the TB unit.

May have a problem port matching the new 40mm TBs to the 961 head.
Might need to open the inlet end of the port a bit.
Click to expand...
Just to kick this around a bit more, I noticed the offset at the head end, taper from inlet to head with the butterfly at 40mm leaving the outlet at 38? Armchair engineering at the moment!
 
It all depends where the bottleneck is.

IF the TB size IS the bottleneck, then an extra 2mm will make a very worthwhile difference.

IF it is NOT the bottleneck, best case is it will make no difference at all and the worst case is it’ll slow down the intake charge velocity and make things worse at low / mid rpm.

Interestingly, Kenny Dreer specced 39mm FCRs for these engines originally. Being flat slides, these would flow better than a butterfly of the same size. So perhaps the 38mm TB is under sized ?

Unless you want to embark upon a trial and error experimentation exercise, I’d suggest finding a good flow bench guy to test the relevant flow and velocity of head and TB and ascertain whether or not it can be improved.

Personally, if I were removing the stock TBs, I’d definitely go the FCR route as it would also remove a lot of other known 961 foibles.
 
Last edited:
Al's#5 said:
Just to kick this around a bit more, I noticed the offset at the head end, taper from inlet to head with the butterfly at 40mm leaving the outlet at 38? Armchair engineering at the moment!
Click to expand...
Seems rather strange to taper from 40 to 38mm within the throttle body itself, but if true it may work.
Anyway, if money is no object, go for it, and report back.
 

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