I need air

M

Mingh

Hero member
Although i didn't intend to do any changes to my 3c, a ride on the restored gavin spencer bol d'or replica changed my mind slightly. It was with my mechanic for some time. After he reversed all the mistakes and bad engineering, the engine now is a dream. With light cranks, carillo's, hi comp pistons, standard cams and a wild 3-1 mega it snarls and barks, pulls fiercely and very lineary from all revs and doesn't have the brutality of a jota that makes it not very relax in today's traffic. I loved every minute on it.

I don't want to open pandora's box and won't split the engine for crank balancing, carillo's or hi comp pistons, so i'll stick to the basics of improved breathing. Keeps the budget under control and makes for reversible changes if ever needed.
Currently my bike is full stock, incl air filter, stock dellorto's, 36mm headers pipes on a flattened 60 mm 3-2and  jota lookalike exhausts. Probably stock cams, no idea about jetting.

Where i want to take it: a bit more oomph would be welcome, particularly between 2500 and 5500 revs. So: what can be achieved with open bellmouths or k&n's, better jetting, more open exhaust and different cams? Any advice on combinations of these that are known to work? Or is it going to boil down to a session on the dyno?

Thanks

Btw the gavin spencer endurance replica was returned to original condition and was sold a couple of days ago. Lucky owner. I hope he gets the hang of the fontanas...finnicky buggers. In the 20 k test ride they surprised me a couple of times, . I'll try to upload a clip of it revving
 
Hi Mingh,

first of all I would check if your bike has all the power it was intended to have from the factory. Have seen 99,8% of all changes at the exhaust going into the wrong direction, killing midrange and/or top peak power. Happened to all my bikes until I went to experts to get it fixed...

Next: overhaul your carbs. New gaskets, jets, needles etc. and proper adjustment of float levels and synchronization do release a lot of hidden torque and power... We have had bikes in the workshop in the 90's that came in with no more than 60 HP and went out with 74HP or more after fixing the issues...

Then you could simply start with different cams. Depending on if your bike has A11, 4/C or what ever in, I would start with either a 4/C, an Axtel or - preferably - a P1 180. I think Keith still makes them?!? They give better midrange (some even top-end) by reducing bottom end torque.

The next step would involve at least some engine work. Easy to find torque is by increasing compression and/or volume of the engine. Having the engine open, you could consider some serious head work involving larger inlet valves, new seats and guides, larger oil-pump etc. etc. . To finish that off, you will need to adjust carbs accordingly and set the exhaust to the right level. This can increase the torque to over 100 Nm at the rearwheel and accordingly 100HP or more without to much rocket science. After that, it gets really tough...

so - depending on what you aim for, you should talk to someone who has done it before, like OCT, Keith, or according people in holland or belgium. They can help you. But first make a concept, just doing one little step makes you hungry for the next one, believe me...  :D
 
Thanks already.

What i'm intending is a 'stage 1' tuning. Open inlets, better exhaust and if it helps carbs. I'm not going down the line of pistons, valve size, rods or crank. Good suggestion to get the carbs a thorough once-over.

I'm actually looking for known combinations of inlets, cams, exhaust that actually work.

You're absolutely right on working with reputable people only. My mechanic (oldskoolmechanics in antwerp) has dozens of laverdas among his customers and has fixed the engine of my old jota greatly. The new owner attested this as well.
 
In that case I would do the following:

-Carbs overhaul, no need to go larger if you only aim for torque/midrange
-P1 180? cams from Keith or some 4/C cams if not yet installed
-Bin the collector and let an expert make a good one or at least alter the existing one to the right shape. the original one and most of the aftermarket ones I have seen do cause issues in midrange.

You should see an increase with the a 4/C of 8 - 10 Nm in midrange and from there on, with the right collector setup for sure some more torque in midrange... With the 4/C, the bike should be at around 80 - 82 HP (rest correctly configured and set up...). With the Collector adjusted, maybe even 85. That is as far as it can get without opening the engine any further.

Airbox or not will not make a significant positive difference in torque I assume, but it looks nice...  :D
 
Laverdalothar said:
With the 4/C, the bike should be at around 80 - 82 HP (rest correctly configured and set up...). With the Collector adjusted, maybe even 85.
Click to expand...

Are you talking rear wheel or crankshaft HP Lothar? My Jota's best dyno run was 76.2 RWHP, which is about as good as I can get it with standard factory spec innards (4C cams and HC pistons).
Changing from 32mm Dellorto 32 to 36mm Mikuni made no difference to maximum power, but gave slightly better mid-range and improved fuel economy. I suspect that's due to better fuel metering rather than carb size.
 
Dellortoman said:
Are you talking rear wheel or crankshaft HP Lothar? My Jota's best dyno run was 76.2 RWHP, which is about as good as I can get it with standard factory spec innards (4C cams and HC pistons).
Changing from 32mm Dellorto 32 to 36mm Mikuni made no difference to maximum power, but gave slightly better mid-range and improved fuel economy. I suspect that's due to better fuel metering rather than carb size.
Click to expand...

Cam, I am refering to crank or clutch power. Rearwheel is - in average - roughly 8% less. Add 8% to your numbers and that's roughly what crank/clutch power is. where do you get to? right, roughly 82HP...  ;)

The midrange you found is due to the better atomization/vaporization the Mikunis have compared to the Dell'Ortos. Dell'Ortos were good carbs for their time but when the RS came on the market, the PHF were 20 years old - at least...

So - yes, Mikunis can improve the midrange additionally, but they come at roughly 1.100? total cost if you take used ones. New ones, you spend a total of at least 1.300? with dual twist grip, new manifolds, bellmouthes etc. etc.
 
OK,thanks Lothar. That makes me feel better. My poor old Jota (nearly 100,000 km) is not yet a sick and feeble old thing like its owner. It's about where it should be in the power range.

However, I don't understand the point in quoting engine or clutch HP when the only thing measurable is at the rear wheel.

I know that manufacturers used to quote engine power as part of their advertising blurb back in the days when pimply faced kids (I wish I was one of them) were buying new Laverdas. But surely now we've gone beyond the advertising hype. It's the power that the tyre transmits to the road that is the only thing that matters. It's is the only parameter that is universally comparable between all bikes, no matter what the power train system - chain, shaft, toothed belt, whatever.
 
I agree, however, if you tune an engine, very often you do that without measuring the RWHP BEFORE you tune it. So - the only comparable figure after the tuning is what was actually in the papers, and that is clutch or engine power...

Also - very often people refer to RWHP although the dyno puts out a calculated figure that also incorporates the drive chain loss, just because the measurement was done with the rear wheel on a dyno-role. Typically, all graphs that show HP AND Torque are done by disengaging the clutch at the top rev and measuring the drive chain loss, calculating the engine power. That is the reason I always ask HOW the actual process was when someone states Rear wheel horsepower...  ;)

It is btw. interesting to see what difference 630 chains compared to 520 ones make on REAL RWHP... or a badly greased chain compared to a freshly greased one...
 
Mingh,

Reckon the best bang-for-buck course, assuming the engine is still mechanically sound, would to bring the carbs up to scratch (needles, needle jets, linkage bushes, slides, and maybe a bit more), ditch any filter in the airbox, but keep the empty airbox (to keep intake roar to an acceptable/bearable level, and to keep the rest of the bike rearwards of the carbs clean) and fit the stock big-bore collector (cheap as chips, as everybody now knows it don't work :D).  All chains should be checked on their condition, same for the clutch rubbers and both chain tensioners.  Once the engine is carefully set up, you should notice a considerable difference.  If the budget allows, there is no way of getting around a set of hi-comp pistons and a pair of C4 or equivalent cams.  I think that's about it, without spending mega-bucks and whole winters in the workshop.  Valves, porting, lightening, larger carbs etc can drive you close to bankruptcy once the bug bites.

As you well know, a freshly overhauled crank allows the engine to spin a lot smoother... smooth engines make more power to begin with.  It's basically deciding how far gone the engine already is, and how much is to be/can be spent.

piet
 
great input Piet

To me the engine feels still ok at the core. starts fine, has good idle and isn't extremely noisy. When the day comes that the engine is shot, i already know who'll get the crank job :-)
 
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