Exhaust For Lightly Tuned 750

I very much doubt they were doing it for a living CK. Like most things in this small town if you want something done you have to do it yourself.
It's something I would've done and I'm old!!!
 
Always interested in SF/C exhaust discussions. A dark art that can provide huge gains or losses

My 2 lira's worth: 5/C, SFC crank & valves, 750cc, 10:1 CR, ported head and factory 2/1 for years. I simply couldn't ride the unbaffled 2/1 on the road from day 1 (or the track - got chucked off a Philliip Island track day by the Vic Ducati Club president for exceeding the day's db limit of about 83!!). For ages I ran it on the road with a tapered baffle inside the mega, but retaining about half the effective area of the reverse cone; that worked really well and only seemed to reduce top end a tiny bit. Was still too loud though, so in later years I added a muffler with the same tapering baffle concept and a reverse cone on the end of the muffler - the motor still breathed well but not the crispness of an unbaffled 2/1. I tried a parallel baffle muffler (no reverse cone) - it was nice and quiet but definitely killed the mid and top end.

Took the bike through rego with that motor running std SF headers into Contis (no crossover) - it felt like a 350. For the new motor (880) and similar setup to above I'm experimenting with smaller initial headers (gas velocity) into an X pipe and tapered system, expanding from the X at (from memory) 42mm ID to 52 at the muffler opening with the last 400mm wrapped perf. Purely experimental. I can easily change to two separate pipes or a 2/1 or a triple style central collector rather than the X. One day I guess I'll find out o_O
 
my experiance of "high comp" pistons over the years is that they NEVER give the claimed compression ratio, eg 9.5:1, or 10.5:1 etc etc
if correctly measured after instalation, this was mainly on Matchles/AJS and BSA twins, straight six Jag's, Rover V8's but also Laverda triples (never did mess with the engines of the laverda twins much)

2 into 1 or 2 into 2 ?? the "noise" is a contributing feature of the "feel good" factor, the dyno tells you if what you feel is what you are getting, normally they are not one and the same thing. 4C cams "feel" more pokey than F1 but the truth is different.

CLEM
 
MarnixSFC said:
Generally speaking, any tuned Lav750 will perform better with the SFC 2 into 1. Once you put a silencer in it, you instantly lose midrange power. In my experience, the best solution is to place an additional absorption damper at the end of the SFC megaphone.

I think Piet’s experience with the 2 into 2 silencer was based on a particular SFC (Georg Kühnert) that was intensively ported and with a modified combustion chamber shape too.

What worries me a bit are the 10,5 : 1 pistons. If you have real 10,5 compression then with an SF type head detonation is very likely to occur.
In case you have pistons from an Electronica SFC, those will only give a 10,5 compression in combination with an (all aluminium) Electronica cylinder head. If you mount them in combination with an SF head, you end up with less compression than with standard SF pistons.

Marnix
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Hi Marnix. I used a true (measured) 11:1 CR on my SF - I was running it on "Super unleaded" and Avgas (50/50) ratio. Never had any detonation or pinking - I had modified the cast skull head to "unshroud" the valves and a few other mods that i thought would aid better flame spread. Once it was back in normal road use I added another base gasket and it runs a true 10.1:1 ratio. The pistons are forged Ducati 750SS ones and I used the SFC 2into 1 exhaust with a home made baffle that got me through scrutineering. - but probably not these days. Whilst it was being raced I used B10EV plugs too. - regards - Phil

Just read some more posts! - I used 6/C cams but with a different rocker radius to reduce the overlap. Bike pulls from 2000 - 8000RPM and is a pleasure to ride - even in traffic!
 
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Paul Marx said:
What are you looking for, noise or performance? SFC type 2/2 is probably good and a bit less noisy than the 2/1 which puts out 120 dB. Don't forget that in both cases, you need to junk the centre stand and that a Norton weighs 40 kg less. You need to be a good rider above all else.

Paul
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Not an either/or proposition - I don't mind noise to get more area under the curve.
 
MarnixSFC said:
Generally speaking, any tuned Lav750 will perform better with the SFC 2 into 1. Once you put a silencer in it, you instantly lose midrange power. In my experience, the best solution is to place an additional absorption damper at the end of the SFC megaphone.

I think Piet’s experience with the 2 into 2 silencer was based on a particular SFC (Georg Kühnert) that was intensively ported and with a modified combustion chamber shape too.

What worries me a bit are the 10,5 : 1 pistons. If you have real 10,5 compression then with an SF type head detonation is very likely to occur.
In case you have pistons from an Electronica SFC, those will only give a 10,5 compression in combination with an (all aluminium) Electronica cylinder head. If you mount them in combination with an SF head, you end up with less compression than with standard SF pistons.

Marnix
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Good info, thank you Marnix. The engine was just built by Wolfgang, I doubt the pistons are actual 10.5:1, but I'll set the ignition curve carefully (Ignitech) and watch for detonation.
 
sfcpiet said:
Was simply a ported Electronica head Marnix, can't remember any combustion chamber alteration, valves remained stock. Don't think Georg would have been willing to have that head welded, I waved the magic wand over the valve seats... ;) Apart from a DMC ignition and the oiling/filter system, the remainder of the engine was stock. The beast pushed out a very healthy 85hp with over 80Nm, still on 750cm³. Can't remember the revs, but the porting was overall very sucessful!

Our findings were established on the Moto Witt dyno. Engine breathed best on 5C cams and stock 2-2 exhaust with X-tube. 6C gave only a modest increase at the very top of the rev range and only with the 2-1, the 2-2 would strangle them. 5C made more torque low down and provided the more pleasurable riding experience. Imho, the 6C and 2-1 are track only, whereas the 5C and 2-2 are equally at home on the open road. Both are a right bitch in traffic, especially when coupled with the CR gearbox. I rode that bike through rush hour Birmingham/UK once (on the way home from Baskerville, '92(?) ), a truely distressing experience, and I was a lot fitter then!


piet
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Hi Piet,

I remember it well, eventhough this was done 30 (!) years ago. I remember Georg telling me about handing the head to a flower who did his magic on the head, but that he returned it after dyno testing more than once because he still wanted more power. What was done to it I don't know and I never had the chance to feel the bike myself, but it was, and still is, the only time I heard of a favourable result with the silenced system as being superior to the 2into 1. Except Rob Bradbury I should add.
Come to think of it, pics of the 1974/1975 SFCs being raced in their heyday with silencers are pretty rare, and they didn't do that because of the nice sound they made.

By the way, Georg's bike was a US model 1974 SFC that he got as a derelict around 1991 in exchange for his gorgeous Harris 570cc racer.

Another variable is the silencers. You don't find original SFC silencers very often, they usually are replicas. Many replica silencers were cut up slash cut SF silencers with 40mm access. The originals are surprisingly light weight and quiter than the replicas. If memory serves, Uwe Witt had replica SF/SFC silencers made by Bos in Holland at the time which were a little crude looking, but worked quite well on the SF.

A thing I didn't mention is that Andrighetto is selling very nice db-killers that turn your megaphone into a Conti type silencer. Such a pipe can easily be placed, the only thing you have to do is drill a 6mm hole in the megaphone to secure it. It actually works quite well that is to say that performance feels very similar to the 2 into 2 system, but mounting it is a matter of minutes and you of course retain the cool looks of the 2 into 1. I also tried them in the megaphones of the 8000 batch SFC with similar result.

Marnix
 

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MarnixSFC said:
Hi Piet,

I remember it well, eventhough this was done 30 (!) years ago. I remember Georg telling me about handing the head to a flower who did his magic on the head, but that he returned it after dyno testing more than once because he still wanted more power. What was done to it I don't know and I never had the chance to feel the bike myself, but it was, and still is, the only time I heard of a favourable result with the silenced system as being superior to the 2into 1.

By the way, Georg's bike was a US model 1974 SFC that he got as a derelict around 1991 in exchange for his gorgeous Harris 570cc racer.

Marnix
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I know... I collected the box with the SFC from Düsseldorf airport and delivered the Harris back in the same box. ;) Georg swapped with Tim Parker. A bit later Tim had destroyed the crankcase of the Harris (Daytona iIrc), I salvaged a used item from the extensive Moto Witt stock for him. That bike had a 580cc motor built by Augusto Brettoni, made slightly over 80hp.

The SFC wasn't at all bad, just disassembled in large bits. It went together pretty drama-free and ran soon after recieving it. Various lube issues caused Georg to considerably re-work the cam oiling system, it was absolutely reliable after that. I lost track of the bike after Dirks' passing in 2016.

I've got photo prints of the unpacking of the SFC somewhere, when and if I find them I'll scan and post.

piet
DSC03305.JPGDSC03304.JPG
 
The bike was between Georg and Dirk with Jost H. who lived close to Düsseldorf. Jost sold it as far as I know for a very low price to Dirk. I had one ride-out with Jost when he had the bike and we gave it a blast on the A555 down to Bonn, me on my 1200 Jota with roughly 110 HP, him (being much, much lighter than me) on the 750 SFC. I had a hard time keeping up with him under acceleration, although my Jota really runs nicely and has lots of torque...

Also not sure where it went, I think Dirk's brother sold it at some point in time. I know that he wanted serious money for it but absolutely don't know any more details really.
 
Nice to see a recent photo of the bike. The silencers were apparently ditched for a 2 into 1 at some point. Apart from the oil cooler to cam cover connection I wouldn’t have recognised it as Georg’s former SFC..

Marnix
 
MarnixSFC said:
Nice to see a recent photo of the bike. The silencers were apparently ditched for a 2 into 1 at some point. Apart from the oil cooler to cam cover connection I wouldn’t have recognised it as Georg’s former SFC..

Marnix
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Jost entered the bike in a couple of Bikers Classics events, as well as the german VfV Classic Races. He rarely rode it on public roads, so I guess he opted to make as much noise as possible... :rolleyes:

piet
 
Was that oil-cooler mod done by blinded original fittings and a new oil outlet somewhere at the case? Maybe due to a new crankcase for some reason? Cool oil to the head is the good idea.
Cheers
Michael
 
Indeed interesting! Seems to be a modded right side cam and primary engine cover. More pics and technical background?
Regards
Gerald
 
sfcpiet said:
Jost entered the bike in a couple of Bikers Classics events, as well as the german VfV Classic Races. He rarely rode it on public roads, so I guess he opted to make as much noise as possible... :rolleyes:

piet
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Then I clearly did not recognise it at Spa.. he clearly opted to free some more horses in the midrange! ☺️

Marnix
 
Gerald said:
Indeed interesting! Seems to be a modded right side cam and primary engine cover. More pics and technical background?
Regards
Gerald
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Direct oiling to cams and rockers via bored camshafts. Enlargened oil pump with 15mm wide teeth. Oil filter incorporated in lines to cooler. Stock '74 cases modified for cooler take-offs. The crank was modded to fit the Electronica primary cover and ignition, which was swapped for a DMC... of course. ;) Not much really, but it took months to execute properly.
MarnixSFC said:
Then I clearly did not recognise it at Spa.. he clearly opted to free some more horses in the midrange! ☺️

Marnix
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Georg rode the bike on public roads only, including several holiday trips to Italy, it was fitted with the 2-2 and 5C cams. This engine showed almost identical midrange with both 5C and 6C, so he simply didn't bother with the 6C and the extremely anti-social 2-1. 6C offered a slight advantage at the very top of the rev range only. As already stated, this engine breathed very well, and nobody ever accused it as being too quiet!

piet
 
Here you go, Marnix.

Georgs' '74 SFC imediately after unpacking at the Moto Witt premises in the Cologne Rhine harbor, must be around 1988-89.


img20221209_15305039 (2).jpg.

A OR600 and a SFC1000 in the crate for a backdrop. The one and only SFC600 is just visible in the RH background.

piet
 
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