Corsa - exhaust choices

Fordychap

Fordychap

New member
Location
Forest of Bowland, NW England
I posted a pic of the “new to me” Corsa - the second of these I have owned in the in the “Out and About” section.
I also inadvertently started a thread regarding the exhaust - so this is the question repeated (hopefully better phrased) to ask for experiences and advice from the Laverdisti “hive mind” on here.

The Corsa is fitted with a 3 into 1 but I find although it’s good and loud, I think the mid range is a bit lacking.
The downpipes appear standard size.
I want to consider putting twin Jota pipes on the bike and would ideally favour mid range torque over top end - more suited to a life on the road. I doWant to use the Corsa not wrap it in cotton wool.
I have an unused Cox 3-2 collector box and some spare headers (standard).
What would you do?

I will consider all suggestions including downpipe size, exhaust supplier, inlet rubbers/ sizes and either for the standard carbs - jet sizes or needle positions as a starting point...
I just want a relatively quick, nice sounding (but not deafening) Corsa with plenty of mid range.
Ta. IMG_0955.jpeg
 
Fordychap said:
What would you do?
Click to expand...
I would spend the money at a good dyno centre who'll tune the flat spot out.

If you were able to see the Air/fuel graph youd likely see it running rich/ lean and thats the usual reason for the flat spot.

Very likely come away with a motor that runs better than it does now overall.

What your effectively doing by changing the exhaust is trying to tune the carbs and if it happens that it runs better, great and if not, you're back to the same place.

Cheers Rob
 
Heres a screen grab showing a bike fitted with dellortos that were so far out of tune, it took 3 pulls/ re-jets to get to this point dyno pull #51.

There you see the spike in the af graph (super lean) and subsequent loss of power.
 

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Sir Sidney Ruffdiamond said:
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Thanks for the video - yes, that's more the sound I remember... it probably sounds stupid to change it out and go for a system with twin Jota pipes and removing the 3 into 1, but since getting the Corsa was about nostalgia - while I am still able to, then maybe that twin Jota pipe "bean can" sound is all part of it.... ?
An interesting thing the memory and the human psyche....
 
Jota Rob said:
Heres a screen grab showing a bike fitted with dellortos that were so far out of tune, it took 3 pulls/ re-jets to get to this point dyno pull #51.

There you see the spike in the af graph (super lean) and subsequent loss of power.
Click to expand...
Wow. That's one heck of a lean spike on the #51.
What exhaust system was that running?
I can do some stuff before I get it to a dyno - which might reduce the demand for dyno time and shuffling back and forth with different setups.
I don't have a rolling road here to put it under load, but can go slightly beyond the basics when setting carbs up, as I can now analyse the fuel air ratio (LambdaKing Monitor) and properly balance the carbs with a decent set of electronic vacuum gauges (these use almost infinitely variable damping which helps enormously to get reliable readings).
Jetting and needles I can also do - but it's one heck of a lot easier to start with a known combination of kit that's identical t something that works well on another bike than to do "a suck it and see" series of tests.
All experiences or results with the various options like down pipe diameters, inlet rubbers, collector box types/sizes and the Dellorto settings (jets needles and notch positions) using Jota exhausts would all give me a head start...
 
Jota Rob said:
I would spend the money at a good dyno centre who'll tune the flat spot out.

If you were able to see the Air/fuel graph youd likely see it running rich/ lean and thats the usual reason for the flat spot.

Very likely come away with a motor that runs better than it does now overall.

What your effectively doing by changing the exhaust is trying to tune the carbs and if it happens that it runs better, great and if not, you're back to the same place.

Cheers Rob
Click to expand...
That's helpful - particularly once I get the bike kitted out the way I want it - so it may well be a dyno trip once I have the setup I would like to end up with actually on the bike.
I was debating if moving to Mikuni Carbs would be enough of a difference in all round practicality and reliability to make it worthwhile, or if the Dellortos set right would be OK.
I never had any problems with my first Corsa on the standard Dellorto carbs - but that was in the 80's and things have moved on.
Just trying to get to a point where I can get an easy, reliable Corsa I can use - and probably back to using two Jota pipes rather than the 3 into 1.
 
Fordychap said:
Wow. That's one heck of a lean spike on the #51.
What exhaust system was that running?
I can do some stuff before I get it to a dyno - which might reduce the demand for dyno time and shuffling back and forth with different setups.
I don't have a rolling road here to put it under load, but can go slightly beyond the basics when setting carbs up, as I can now analyse the fuel air ratio (LambdaKing Monitor) and properly balance the carbs with a decent set of electronic vacuum gauges (these use almost infinitely variable damping which helps enormously to get reliable readings).
Jetting and needles I can also do - but it's one heck of a lot easier to start with a known combination of kit that's identical t something that works well on another bike than to do "a suck it and see" series of tests.
All experiences or results with the various options like down pipe diameters, inlet rubbers, collector box types/sizes and the Dellorto settings (jets needles and notch positions) using Jota exhausts would all give me a head start...
Click to expand...
Its starting with an unknown entity, 3 x 38mm dellorto phm on a tuned motor.
I would say in this case, the exhaust system was irrelevant, could have been 3 into 3. I bought a box of new parts and built 3 carbs with no data.

Sounds like you have some useful equipment to play with, especially if you can use it while mobile but either way, you might dial it out if you go that route, good luck.
 
Fordychap said:
I notice you have swapped out the clutch and brake master cylinders too - something I will consider, as both are pretty stiff and not that good to use all day.
On my last Corsa I used some AP master cylinders and levers - but these look different... are they the smaller piston later Brembo ones (Guzzi) ?
Click to expand...
I believe they are Triumph ones - they were on the bike when I got it - Grant would know
 
Been covered previous here, standard factory exhaust had the correct "physics" ( especially so the factory big bore collector, a relative term ) for best overall engine operation on the CR motors. Various novel notions only reduced the tractability of this very refined variation of the 120 motor series. Witnessed many a poxy improved exhaust setup on owners Laverda in the day(s) Perhaps this may assist or no, j.
 
iis_iis said:
Been covered previous here, standard factory exhaust had the correct "physics" ( especially so the factory big bore collector, a relative term ) for best overall engine operation on the CR motors. Various novel notions only reduced the tractability of this very refined variation of the 120 motor series. Witnessed many a poxy improved exhaust setup on owners Laverda in the day(s) Perhaps this may assist or no, j.
Click to expand...
Assists greatly. Cheers. D
 
I’m in agreement with Rob that you spend a bit of time tuning out the flat spot. I know the factory didn’t always get everything right but when they chose to offer an alternative to the ‘restricted’ standard exhaust on the Corsa it was a 3 into 1. AFAIK it was based on the TTF1 exhaust and it worked well enough on Ray Peacock’s Corsa I raced in 1985, and also on the SFC1000 I owned (and raced) in the late eighties.
I perhaps should also say I had Jota exhaust cans on my Corsa, but it was more a case of that was what was fitted on the bike when I bought it rather than me choosing to fit them. Obviously the factory couldn’t sell them with Jota cans as they had to meet the new EU regs, although I’m not 100% sure how they got round the regs with the 3-1.
In my opinion, the Corsa is the factory’s road going version of the TTF1 and as that had a 3-1 if you’re going to fit a different exhaust to standard it should mirror the pukka factory bike. I also think it looks right for the bike.
But whatever my opinion it’s a case of ‘horses for Corsa’s’ 😜
 
Thanks for that response, Andy.
I’ll take a long hard think before I do anything different to what’s currently on the bike. I have the whole winter to consider and do stuff.
If it’s okay with you - might PM you for additional info. Phil has already given some good tips.
Your experience clearly is much more relevant and recent than mine. I only raced the 500 and 750 before short stint on a 1200 in endurance. I didn’t build it either - just fixed/maintained/rebuilt it with others.
It was very different to Corsa although we ran a three into one on that bike as well. We used Mikuni carburettors that came from a Yamaha I think. Seemed to stay in tune better than Dellortos and used a bit less fuel which helped!
Also used Alfa GTV “surface” spark plugs too - but don’t remember if they had much effect!
 
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