Top End of an 8000 rpm 750 Breganzie Twin

sfcpiet said:
It's a challenge... much the same as climbing a mountain.  And just as rewarding if things work out as you planned.

Since the very beginnings of motorisation, petrolheads have tried to get the bloody things to go ever faster.  Why not take something old and out-dated but with a bit of potential and unleash it?  A CBR600 may be quicker than anything that rolled out of the gates in Breganze, but chasing (and maybe even catching) one on a Laverda triple is a whole lot more fun. :D

piet
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On the money, Piet. But even better if the person you catch knows you have a big horsepower deficit! (smileys not working on this computer:-(((
 
I'd guess Piet is considering the diameter at the beginning of the port, probably same as carb diameter, for comparing it to the reference straight tube. Smaller cross sections, bends, nooks and crannies inside the port are considered then by the overall percentage value derived from flow bench results, which is to be seen as a qualitative rather than a quantitative figure, I assume.

Wondering that no one mentioned the influence of combustion chamber shape so far? It looks like there has been an evolution taken place in the past, moving from hemispherical chambers to flat, lentile shaped chambers with large squish areas. Probably Keith Duckworth paved the way for this with his ingenious DFV F1 engine. To squeeze appropriate valve sizes in there, this "modern" shape of combustion chambers seems to be followed by rather small angles between inlet and exhaust valve, 4 valve heads and short stroke/big bores. Seems like most modern high performance bike engines are following somehow that route.

Altering the combustion chamber looks a difficult job on a 4-stroke to me, at least if you want to do anything more than reshaping the piston crown. Easier done on 2-strokers, I did this once on one of my old smokers to a great effect. Went from a domed piston/hemispherical cobustion chamber w/o squish and 1:7 c/r towards a flat piston/circular squish surface chamber and 1:9 c/r. Results have been quite astonishing. Without altering ports or exhaust, power and torque figures increased by nearly 20%, fuel consumption cut down by 25%! Carbie needed smaller jetting and engine runs way cooler now than with the old design.
 
MotoJouni said:
And what if the port has different diameter on the other end that is the case very often at least? The numbers you said needs calculations to power of two. If the channel is only for 2mm bigger on the other end it will do a notable error to your calculations if this is not taken in account. For example a port of 34mm diameter and 36mm diameter has a difference of more than 10% on area of the port. Many times the difference is far bigger. There was something strange or something I don't understand in your numbers in the way I understand them. Just trying to understand what you mean, for shure you have used more flow bench than I (almost non) and very big respect for that.
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FFS sake MJ, you need to start somewhere.  So you start with what you have and go from there!  If I measure the port and get a (theoretical) result of 3m?/min and my straight tube shows that 15m?/min is possible, how am I to know how "good" my resulting 5m?/min is?  I've almost doubled what I had, but am nowhere near what is possible.  I measure what I have BEFORE I start and compare with what is do-able, and then measure what I have achieved, if I alter port diameter or not.  Of course if I'm working on a 30mm port and compare it to a 40mm tube, I may as well lay down and watch telly, that is fighting windmills...

piet
 
Altering the combustion chamber looks a difficult job on a 4-stroke to me, at least if you want to do anything more than reshaping the piston crown.
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Yes - did this one about 30+ years ago - the work was easy - but the heat treatment after it warped like crazy was a tad more complicated!! - regards - Phil



 
Very nice Phil. Trouble with doing the bathtub conversion is that there's a lot of other stuff needs doing to match. Crown shape, advance curve....and the underhead shape of the valves becomes more critical than you'd think too.

These days getting a lot more power out of old motors is somewhat easier. Most of the period information is now in the public domain - and accessible thanks to the interweb thingy. Given say, Pop's setup for a Suzuki as a starting point, it's easy to first duplicate that with better parts thanks to modern CNC - then improve on what was done in period. generally with better materials now available it finishes up more reliable too....

Not necessarily cheaper though.....
 
Finally got my 1440p PLS display working again. Haven't read all your comments but look great. I need to DRAW my Valve Train configuration for an 8000rpm Breganzie 750SF and take PIC's then upload. Give me TIME.

PHIL: I'm dissuading a SOHC TWIN Mill's with a Cam Follower No DOHC 3 or 4 CYL's.
 
The (Red) OX is slow but the earth is patient. (To misquote somebody)  :LOL:
 
Rabbit Proof Fence - Don't give me that when I have Inginote Northern Natives as very close friends.

Perhaps you will appreciate these  PIC's from an old Bregazie Northern Ontario Rider:
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Don't ask why I put up with that little Poodle She-Wolf in the Bush - Other words she loves me and I can't get rid of her. Really I want a Wolf or a Bear. What the Hell. She has to learn about Porky Pines, Skunks, Wolf Packs, Foxes, Beavers, Water Moccasins , Snapping Turtles  ... etc. I'm  not about to train another Bush Dog but she has the heart with no lash - Don't matter how Big a Bush Dog is.

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I tend to forget about Bregaqnzie's in my old age. Doesn't mean I don't care anything about them because the Breganzie SF played a big part in my life.
 
well hell! going on a canoe trip to Aintry? better watch out for the mountain men, they like a nice mouth....
 
well hell! going on a canoe trip to Aintry? better watch out for the mountain men, they like a nice mouth....
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What you can't see the Belgium Browning FN Parabellum P35 9mm in my Belt - Never fired it once in the wildness against  animal's as they scene I have no fear. CDN Gun laws are a Farce.
 
Dellortoman: Would love to have you show me your Tasmania as I would my Cambrian Shield but unfortunately we're getting too old and can't afford it.

PS: Fuck the Jeep - It Works - Wish I could afford a Land Rover - LOL
 
Had 2 Landrovers and 2 Range Rovers over the years. Remember them all fondly. Had one Jeep - would never buy another. Cheaper to stand in mud and rip up hundred dollar bills.
 
I owned one Land Rover back in the mid 60's when I was about 17 and no one wants to hear the sad demise of that vehicle - It still haunts me.

Who torched my Land Rover at Shawmere!!! Unfortunately I will never know.

Jeep parts are realitively cheap in North Amarica and cost reflecttive as long as you are handy with a wrench. Jeeps can crawl but not nearly as well as a Leyland Land Rover. I agree Davo - Muddy water eventually fucks a Jeep.

I promise I will get back to you regarding the 8000rpm 750 SF valve train but I have to ensure my spec's are accurate - Can't find the original spec's to compare with the mod's. Thought I had it when I opened this thread but it`s been too long. I need help on the original spec`s - The Mods will be my input.
 
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