Turkey or more turkey ^ ^

NKN · Aug 9, 2016

from 880cc-where-can-one-buy-one-t23677-15.html

lcrken said:
[...] Using the 93 mm stroke along with 79.5 mm bore would give you a 923 cc engine without the need to sleeve the cylinders. That would probably make a really nice combination for a street Commando.

Ken

Did anybody ever tried that combo? Less stress on the barrels with more torque at the end due to the bigger stroke. Sounds nice to me, what do you all think about it?
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Danno · Aug 9, 2016

Lengthening the stroke on an already long-stroke 360-degree twin will increase vibration and piston speed, the latter of which will probably have to be accompanied by a reduction in rpm limit, which would negate any power gains. Likely it's been tried and abandoned as an improvement.

lcrken · Aug 9, 2016

Danno said:
Lengthening the stroke on an already long-stroke 360-degree twin will increase vibration and piston speed, the latter of which will probably have to be accompanied by a reduction in rpm limit, which would negate any power gains. Likely it's been tried and abandoned as an improvement.

That sounds reasonable, but there are several successful 1007 race bikes that are working quite well with the 93 mm stroke, so it can't really be too limiting. My guess would be that with the larger displacement, the peak horsepower is limited by how much air the head will flow, and that it reaches that limit at a lower rpm than where the ring friction would limit it. You can raise the head flow limitation some by running a really long duration cam, with lots of overlap, and that will let you make more power at the top end of the power band, but that usually makes the bike almost unrideable in the slower parts of the track. You are probably correct about the longer stroke increasing the felt vibration, but that doesn't seem to have been a problem to the riders racing these bikes. I ran an engine with a 91 mm stroke Nourish crank and 80.5 mm bore in my race bike for a while, and didn't have any problems with vibration, but it was an isolastic chassis, which really does reduce the felt vibration.

I think Steve mentioned a couple years ago that there were racers who had quite successfully used the 93 mm stroke crankshaft with 81 mm bore, which would give you a 960 cc motor without having to go to the special 1007 cases, cylinders, and head mods, and I know there have been, and still are folks using the 83 mm bore of the 1007 with shorter strokes to raise the usable rpm range. Lots of mix and match possibilities with the parts now available.

Ken

Ken

comnoz · Aug 9, 2016

Well, that is the combo in my engine. And I love it. Jim
Actually it's 92mm stroke.

Danno · Aug 9, 2016

Ken, as you know, parameters for streetbikes and racebikes are worlds apart.

And Jim, that monster of yours is so much different than anything else, it just can't be compared. You should be selling the hell out of whatever you've put into it, but apparently not many could afford it or there'd be a ton of people lined up to have one of their own. Just guessing, how much would you say it would cost to build that motor/transmission wEFI for a customer?

NKN · Aug 10, 2016

comnoz said:
Well, that is the combo in my engine. And I love it. Jim
Actually it's 92mm stroke.

And what would you recommend for camshaft, CR, manifolds, carbs and advance timing for it?

comnoz · Aug 10, 2016

NKN said:
comnoz said:

Well, that is the combo in my engine. And I love it. Jim
Actually it's 92mm stroke.

Click to expand...

And what would you recommend for camshaft, CR, manifolds, carbs and advance timing for it?

First off, there is no mechanical torque advantage gained by using a longer stroke vs a larger bore. The increase in torque applied to the crank by a longer stoke is exactly the same as the increase in torque applied to the crank by a larger bore.
Midrange torque vs high rpm power is solely determined by tuning and friction losses.

I found the grind spec for the crank that's in my bike. It is a 91.8mm stroke. The stroke was determined by the need to offset grind out the big dent in one of the journals made by a broken rod.

I would recommend a fairly mild cam on the street. Lift is good, but duration just raises and narrows the powerband.
I run a Webcam #312a with the duration reduced by a 4" radius grind on the lifters.

For street I wouldn't go over about 9.5 compression unless you have a better source of fuel than I get here.

When increasing the capacity by increasing the stroke, instead of the bore, there is less need to increase the breathing ability of the head to get a power gain. [of course bigger valves will help]

IE, If you build a 920 by boring only and do not increase the valve size then you will get a bump in the midrange torque but the horsepower peak will barely change.

If you build a 920 by increasing the stroke with no valve size changes, then you will get a torque gain up to the horsepower peak.
This is because the lazy induction pulse from a longer stroke is easier to handle with smallish valves.

I limit the revs to about 6500 on my motor although I have revved it to 7500 on the dyno just to see where the HP peaked. HP peak was at 7200.

34 or 35mm carbs on a Fullauto or ported RH10 head work well. 1.5 OD exhaust pipes.

I am running a pretty well developed stock head with 1.5mm oversize intakes.

Since the bore diameter is close to stock then the timing advance needed will be close to stock.

Note that this is for a street motor.

When looking for maximum power for a race motor then a big bore is the better deal. It gives you more room for bigger valves and less high rpm friction loss than you would see with a stroke increase. Jim

comnoz · Aug 10, 2016

Danno said:
Ken, as you know, parameters for streetbikes and racebikes are worlds apart.

And Jim, that monster of yours is so much different than anything else, it just can't be compared. You should be selling the hell out of whatever you've put into it, but apparently not many could afford it or there'd be a ton of people lined up to have one of their own. Just guessing, how much would you say it would cost to build that motor/transmission wEFI for a customer?

One Million Dollars....

Danno · Aug 10, 2016

comnoz said:
Danno said:

Ken, as you know, parameters for streetbikes and racebikes are worlds apart.

And Jim, that monster of yours is so much different than anything else, it just can't be compared. You should be selling the hell out of whatever you've put into it, but apparently not many could afford it or there'd be a ton of people lined up to have one of their own. Just guessing, how much would you say it would cost to build that motor/transmission wEFI for a customer?

Click to expand...

One Million Dollars....

That's kinda what I was thinking.... :lol:

The other thing to consider, for all those considering these bore/stroke dimensions, is that any engine is greater than just the sum of it's parts and that all the components have to work together for best result. How much does the fuel injection contribute to proper combustion and power production? What crank, cases, rods and pistons are necessary to make the whole thing work?

NKN · Aug 10, 2016

comnoz said:
NKN said:

comnoz said:

Well, that is the combo in my engine. And I love it. Jim
Actually it's 92mm stroke.

Click to expand...

And what would you recommend for camshaft, CR, manifolds, carbs and advance timing for it?

Click to expand...

First off, there is no mechanical torque advantage gained by using a longer stroke vs a larger bore. The increase in torque applied to the crank by a longer stoke is exactly the same as the increase in torque applied to the crank by a larger bore.
Midrange torque vs high rpm power is solely determined by tuning and friction losses.

I found the grind spec for the crank that's in my bike. It is a 91.8mm stroke. The stroke was determined by the need to offset grind out the big dent in one of the journals made by a broken rod.

I would recommend a fairly mild cam on the street. Lift is good, but duration just raises and narrows the powerband.
I run a Webcam #312a with the duration reduced by a 4" radius grind on the lifters.

For street I wouldn't go over about 9.5 compression unless you have a better source of fuel than I get here.

When increasing the capacity by increasing the stroke, instead of the bore, there is less need to increase the breathing ability of the head to get a power gain. [of course bigger valves will help]

IE, If you build a 920 by boring only and do not increase the valve size then you will get a bump in the midrange torque but the horsepower peak will barely change.

If you build a 920 by increasing the stroke with no valve size changes, then you will get a torque gain up to the horsepower peak.
This is because the lazy induction pulse from a longer stroke is easier to handle with smallish valves.

I limit the revs to about 6500 on my motor although I have revved it to 7500 on the dyno just to see where the HP peaked. HP peak was at 7200.

34 or 35mm carbs on a Fullauto or ported RH10 head work well. 1.5 OD exhaust pipes.

I am running a pretty well developed stock head with 1.5mm oversize intakes.

Since the bore diameter is close to stock then the timing advance needed will be close to stock.

Note that this is for a street motor.

When looking for maximum power for a race motor then a big bore is the better deal. It gives you more room for bigger valves and less high rpm friction loss than you would see with a stroke increase. Jim

Waow, thanks for spending your precious time for that complete answer.

comnoz said:
IE, If you build a 920 by boring only and do not increase the valve size then you will get a bump in the midrange torque but the horsepower peak will barely change.

Jim

Well not really looking for horsepower peak, rather go for a bump in the midrange, but can't understand changing the valve size without changing the valve seat size. Do you have to recut them? What is the technical advantage or how does it work?

comnoz said:
I limit the revs to about 6500 on my motor although I have revved it to 7500 on the dyno just to see where the HP peaked. HP peak was at 7200.

Jim

Remember the HP number? ^ ^

comnoz said:
34 or 35mm carbs on a Fullauto or ported RH10 head work well. 1.5 OD exhaust pipes.

I'm planning on a Fullauto, but which carbs should I choose like Amal's are going to 32mm only? And i do like Amal's look. Did you already try to bore Amals?

I am going for a stree bike, not a race one.

comnoz · Aug 10, 2016

NKN said:
Well not really looking for horsepower peak, rather go for a bump in the midrange, but can't understand changing the valve size without changing the valve seat size. Do you have to recut them? What is the technical advantage or how does it work?

>>>With a short duration cam you can install 1.5mm oversized intakes on the stock seat after re-cutting. Larger than that requires a new seat and re-angling the guide<<<

comnoz said:

I limit the revs to about 6500 on my motor although I have revved it to 7500 on the dyno just to see where the HP peaked. HP peak was at 7200.

Jim

Click to expand...

Remember the HP number? ^ ^

>>>77<<<

comnoz said:

34 or 35mm carbs on a Fullauto or ported RH10 head work well. 1.5 OD exhaust pipes.

Click to expand...

I'm planning on a Fullauto, but which carbs should I choose like Amal's are going to 32mm only? And i do like Amal's look. Did you already try to bore Amals?

>>>Amal concentrics can't be bored that large.

Amal MK2s are/were available in 34. A pair of new ones were on e-bay last time I looked.

keihin FCR's are available in 35mm.

Mikuni 34mm carbs can be fit but they will be splayed out because of the width which makes air cleaners tough.<<

I am going for a stree bike, not a race one.

comnoz · Aug 10, 2016

Danno said:
That's kinda what I was thinking.... :lol:

The other thing to consider, for all those considering these bore/stroke dimensions, is that any engine is greater than just the sum of it's parts and that all the components have to work together for best result. How much does the fuel injection contribute to proper combustion and power production? What crank, cases, rods and pistons are necessary to make the whole thing work?

I am running a stock crank that has been offset ground a little over .1 inch undersize. It has been reworked with a nodular iron flywheel and a pin fit through the big end to regain some of the strength lost with the large amount that has been ground off.
Custom Carrillo rods fitting Hyundai bearing shells. [ex-racebike stock]
Custom JE pistons [also ex-racebike stock]
Stock cases, stock barrels with sleeves.
A cylinder head with a lot of time in it that has been duplicated in the Fullauto head [except for the valve size and hand work to optimize the ports]
The fuel injection does not make more peak horsepower than big carbs would. It just lets you gain the advantage of big carbs without the low speed fueling issues you would get from big carbs.
The throttle bodies are 42mm with butterfly valves, so they flow about like 40mm carbs. Jim

Danno · Aug 10, 2016

Is that offset grind enough to make the stroke increase? Doesn't seem like a lot. I realize the difference is double.

comnoz · Aug 10, 2016

Danno said:
Is that offset grind enough to make the stroke increase? Doesn't seem like a lot. I realize the difference is double.

If I could have removed .100 all from one side that would have given me an additional .200 stroke. That would have been a 5mm increase.
Since I had some cleaning to do all the way around I ended up with a 2.8mm increase.

Danno · Aug 10, 2016

comnoz said:
Danno said:

Is that offset grind enough to make the stroke increase? Doesn't seem like a lot. I realize the difference is double.

Click to expand...

If I could have removed .100 all from one side that would have given me an additional .200 stroke. That would have been a 5mm increase.
Since I had some cleaning to do all the way around I ended up with a 2.8mm increase.

Then, (I'm guessing), a 1.4mm spacer at the cylinder base? Do you have to use longer pushrods?

comnoz · Aug 10, 2016

Danno said:
comnoz said:

Danno said:

Is that offset grind enough to make the stroke increase? Doesn't seem like a lot. I realize the difference is double.

Click to expand...

If I could have removed .100 all from one side that would have given me an additional .200 stroke. That would have been a 5mm increase.
Since I had some cleaning to do all the way around I ended up with a 2.8mm increase.

Click to expand...

Then, (I'm guessing), a 1.4mm spacer at the cylinder base? Do you have to use longer pushrods?

No spacer, The difference is made up in pistons and rods. Jim

worntorn · Aug 10, 2016

It sounds strange but over on the Triumph forum the hot setup is to tear off the factory electronic fuel injection and mount big old carbs. Those that believe in this claim many extra HP and have the usual suspect dyno charts to prove it.
To my way of thinking it's a pretty big step backward to remove perfectly good efi in favour of carbs. Ignoring peak HP numbers, modern efi engines just run better than those old carburettted engines ever did.
Remember all those 1960s car dieing at every stop light as the weather got colder and the choke wasn't quite on
enough?
Or stalling out in the summer heat because the choke was stuck on? Engines always in need of a tuneup and on and on....
My two modern bikes with EFI run just like modern cars. Turn the key and go.
Then there is the advantage at high altitude.

The carbed bikes sometimes exhibit a bit more "character"

Glen

Fast Eddie · Aug 10, 2016

worntorn said:
It sounds strange but over on the Triumph forum the hot setup is to tear off the factory electronic fuel injection and mount big old carbs. Those that believe in this claim many extra HP and have the usual suspect dyno charts to prove it.
To my way of thinking it's a pretty big step backward to remove perfectly good efi in favour of carbs. Ignoring peak HP numbers, modern efi engines just run better than our old carbuerated engines ever did.
Remember all those 1960s car dieing at every stop light as the weather got colder and the choke wasn't quite on
enough?
Or stalling out in the summer heat because the choke was stuck on? Engines always in need of a tuneup and on and on....
My two modern bikes with EFI run just like modern cars. Turn the key and go.
Then there is the advantage at high altitude.

The carbed bikes sometimes exhibit a bit more "character"

Glen

True Glen, but if they are removing 'built to a price' mass produced injector units designed for 'general use' and are replacing them with high end stuff like Keihin flat slides AND are setting them up properly AND are fitting them to tuned / modified motors... then I'd say it makes sense.

worntorn · Aug 10, 2016

I talked with a fellow Triumph owner today about this. He got into the whole TPUSA thing and ordered all the expensive stuff for the changeover for his T100. He went also went with their high compression and hotter cam setup. After running like a watch with the stock EFI the hotrod carbed motor ran like a bag of shite. After much dyno tuning and months of fiddling and several thousands of dollars it runs better ( but not as good as before) but does make 6 more peak hp than stock.
He wishes now that he had left it stock with EFI.
Just one report but I wonder how many others have done the same but don't want to admit that it didn't work out so well...

Glen

Fast Eddie · Aug 11, 2016

worntorn said:
I talked with a fellow Triumph owner today about this. He got into the whole TPUSA thing and ordered all the expensive stuff for the changeover for his T100. He went also went with their high compression and hotter cam setup. After running like a watch with the stock EFI the hotrod carbed motor ran like a bag of shite. After much dyno tuning and months of fiddling and several thousands of dollars it runs better ( but not as good as before) but does make 6 more peak hp than stock.
He wishes now that he had left it stock with EFI.
Just one report but I wonder how many others have done the same but don't want to admit that it didn't work out so well...

Glen

Oh dear!

Bet he wishes he'd just bought a new 1200!

Turkey or more turkey ^ ^

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