Laverda 750 SFC 1974 replica

carby size depends a lot on what you are going to do to the head, no use bolting on a set of 38mm carbs to a small valve 750 head for example
but figure you are planning on doing some porting work considering you have come this far

in general, smaller the carb (to a point) the better the acceleration, larger better for wide open throttle so keep that in mind but as above port work and head modifications plays a big part in the size selection

photo attached is of a set of Mikuni RS 40mm carbs bolted onto one of the 270 degree Twisted Twins, 880cc, massive Phil Todd port job, works great
we machined our own billet inlet manifolds to match the port shape which was far from circular, filters are DNA OVI type, fit the available space perfect


 
Redax thanks for quick lesson about carbs size and acceleration. I didn't know that until this moment :D

So about engine 900ccm custom con rods (approx same weight as carillo) i have big valve head exhaust valves will be same size intake valves 44mm. original valve seat will be taken out. The hole where original seat was will be welded and reshaped for nice mixture spread and valve seats will be like in newer bikes so just a ring. Head will be lowered and porting will be also done .

I was trying to install screen today  (banghead) (cuss) i will take some pictures tomorrow for comments because i don't have idea in what position must be mounted because on pictures there is different screen position on every bike :D  Where do you buy rubber between fairing and screen? laverda paradise or somewhere else?

Than i still don't know what headlight to use (i have gor few headlamps but all are to flat at he front :D) and more important how to mount in. Is headlight rubber that laverda paradise sell good for any headlamp?

And now i have to find rs carbs on ebay :D  http://www.ebay.co.uk/itm/Mikuni-RS38-Flat-slide-Carburettor-Aluminium-Ford-Cross-Flow-Intake-/271799485116?pt=LH_DefaultDomain_3&hash=item3f488302bc  those are correct ??
 
ludiluka said:
Where do you buy rubber between fairing and screen? laverda paradise or somewhere else?
Click to expand...

I use 20mm self adhesive black foam strip! Cheap and cheerful:
http://www.ebay.co.uk/itm/NEOPRENE-SPONGE-FOAM-SELF-ADHESIVE-STRIP-5MTR-3MM-6MM-10MM-THICK-/121388027214?pt=LH_DefaultDomain_3&var=&hash=item1c434a4d4e

absponge2_zps3f01efb5.jpg
 
Hi Luka - We used a 40mm carb size on Steve Elliott's 880cc SFC (180?) - at the time it was tested by the top UK dyno house and was the 2nd most powerful 4 stroke twin in the Uk at the time - (early 1980's). I used 40mm on my 870 twin - but I did a really fancy head job - beautifully calculated and tapered to work so well - it was crap! That was why the head that Red got was almost a copy of Steve's - really just a couple of big holes for the inlets. The idea was to weld a stub to head to avoid the difficult job of sealing the inlet manifolds - but Red has got over that problem very neatly.

    You say you will be using a 44mm inlet valve - I found that this will only just fit in the cast iron skull and leaves no room for a separate seat unless you put in a deep seat then face it off to the flat part of the head where the liner spigots fit - not a lot of room for error!! - Perhaps this shot may help clarify what I mean -  best of luck - sounds interesting - Phil
 

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@phil, redax

hoping to ask no secrets, but what is the peak output power (estimated, wished or real)
for the 880 motor (in approx. hp , kw) compared with a smooth prepared engine with 72 hp?

m

 
Hi Michael - a difficult question to answer properly. On our rolling road water brake - we used to average around 46bhp on an SF2. This dyno was set to give the same results as the dyno that Steve Elliott's SFC was tested on. Steve's made 74.5bhp @ 6000 &6500 RPm. We still had the original SFC 2 into 1 exhaust and I think we would have increased the power with a larger bore one.

  You can read anything you want into dyno figures - a variance of up to 20% is easily possible  between different dynos- especially with the "accelerometer" type that doesn't hold a motor under load for a while. The main use for a dyno is so the operator/tuner can see the comparison of "before & after" work - Regards - Phil
 
redax5 said:
photo attached is of a set of Mikuni RS 40mm carbs bolted onto one of the 270 degree Twisted Twins, 880cc, massive Phil Todd port job, works great
Click to expand...
Did you have the flow bench when you did this job, Red? Wondering how the head worked on the bench.
Quentin
 
phil37 said:
The idea was to weld a stub to head to avoid the difficult job of sealing the inlet manifolds - but Red has got over that problem very neatly.
Click to expand...

well that is just great, no one told me that, would have been so much easier to weld a couple of scrap pieces of pipe on to the head than designing and machining custom inlet manifolds
:D


 
Piranha Brother 2 said:
Did you have the flow bench when you did this job, Red? Wondering how the head worked on the bench.
Quentin
Click to expand...

no, flow bench came later, and we have not machined a valve vernier calibrated opening mechanism for a 750 yet either
bit of work involved in that and have front ends to build now



 
phil37 said:
Hi Luka - We used a 40mm carb size on Steve Elliott's 880cc SFC (180?) - at the time it was tested by the top UK dyno house and was the 2nd most powerful 4 stroke twin in the Uk at the time - (early 1980's). I used 40mm on my 870 twin - but I did a really fancy head job - beautifully calculated and tapered to work so well - it was crap! That was why the head that Red got was almost a copy of Steve's - really just a couple of big holes for the inlets. The idea was to weld a stub to head to avoid the difficult job of sealing the inlet manifolds - but Red has got over that problem very neatly.

    You say you will be using a 44mm inlet valve - I found that this will only just fit in the cast iron skull and leaves no room for a separate seat unless you put in a deep seat then face it off to the flat part of the head where the liner spigots fit - not a lot of room for error!! - Perhaps this shot may help clarify what I mean -  best of luck - sounds interesting - Phil
Click to expand...

Thanks for photo

About valves head work will be done by moto officina because i don't have equipment for this job  original cast iron combustion chamber will be taken out of the head. Than he will weld (fill) the hole where cast iron was and than he will redesigned shape of combustion chamber and than he will make new seats for valves + lower complete head for higher compression ration Porting will be done by me or him we have to discuss about this step i have experience with ''porting'' on high preformance 125ccm sportbikes only(cagiva mito )

Hope that i understood you correctly and explain things  ?

What about carbs is 38mm good compromise ? and are those correct rs carburetors http://www.ebay.co.uk/itm/Mikuni-RS38-Flat-slide-Carburettor-Aluminium-Ford-Cross-Flow-Intake-/271799485116?pt=LH_DefaultDomain_3&hash=item3f488302bc
 
hi phil,
you?re right with the interpretation of "raw" power and dyno-testing.
i just wanted to have a number to deal with.
thanks
m
 
Hi Luka - understood OK - make sure head is properly heat treated afterwards - we did a lot of welding on one at Motodd (see Photo) a long time ago and it was so soft before heat treatment. - Those e-bay carbs look Ok - if price stays lowish! - regards - Phil

 
Hi Luka,

Failing to find the proper profile for (disc brake) SFC fairings, I had the correct type trimming made. See pic.
Selling it at ? 27,50 plus postage per fairing.

Marnix
 

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v2ventiler said:
@phil, redax
hoping to ask no secrets, but what is the peak output power (estimated, wished or real)
for the 880 motor (in approx. hp , kw) compared with a smooth prepared engine with 72 hp?
m
Click to expand...

we ran House's 880cc x 284 degree Twisted Twin on the Dyno and it pulled 82hp
only ever did the one Dyno session with that engine, felt we had a lot more power to find with different exhaust systems and also wanted to play with cam timing
that engine had an old set of 36mm Dellorto's on it


 
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