Difference between C7 & C4 power delivery
- Thread starter Jota Rob
- Start date
No data Rob, just seat-of-the-pants dyno...
C7 definitely lacks low-end grunt but comes alive around 5000, quite a bit more so than the C4, see my trackbike aka The Iron Pig. C7 also prefers to run un-baffled, C4 doesn't seem to mind much at all. Both will rev as far as you're brave enogh to take it, or the rev limiter sets in, power peters off after 7750-8000 anyway.
The Pig has seen quite bit of use over the years and so far nothing extraordinary has revealed itself under the cam cover. It's a re-phased 120 RGS engine with HC pistons, head converted to CR spec and running 36mm Dells.
piet
C7 definitely lacks low-end grunt but comes alive around 5000, quite a bit more so than the C4, see my trackbike aka The Iron Pig. C7 also prefers to run un-baffled, C4 doesn't seem to mind much at all. Both will rev as far as you're brave enogh to take it, or the rev limiter sets in, power peters off after 7750-8000 anyway.
The Pig has seen quite bit of use over the years and so far nothing extraordinary has revealed itself under the cam cover. It's a re-phased 120 RGS engine with HC pistons, head converted to CR spec and running 36mm Dells.
piet
Dyno run, 7C Cams, 1160cc, Dual valve springs, 42mm Inlet valves, 33mm Exhaust valves, Gas ported Ross pistons, 38mm Mikuni carbs, 13.4 CR, ported Inlets, welded up Exhaust ports, race fuel 103 octane, 3.8% oxygenated
This was Dyno run 29 out of 55, we did make slightly more power by the time we were above 50 runs but not much, 134.6 hp was our best
Run 29 was after we modified the 3-1 again but we also increased the length of the angled Inlet manifolds by 20mm which gave us a 13hp gain through the mid-range and removed the flat spot we had there
Inlet manifolds are tapered 36mm at the head to 38mm at the carbs
Held power curve through to 8,700 rpm, set our 1st shift light to come on at 9,000 rpm, 2nd shift light at 9,250 rpm, rev limiter set at 9,500 rpm
This was October 2018, since then all I have done to my race engines is to keep modifying them to get them to be reliable
Been a big learning curve
Mule 131
This was Dyno run 29 out of 55, we did make slightly more power by the time we were above 50 runs but not much, 134.6 hp was our best
Run 29 was after we modified the 3-1 again but we also increased the length of the angled Inlet manifolds by 20mm which gave us a 13hp gain through the mid-range and removed the flat spot we had there
Inlet manifolds are tapered 36mm at the head to 38mm at the carbs
Held power curve through to 8,700 rpm, set our 1st shift light to come on at 9,000 rpm, 2nd shift light at 9,250 rpm, rev limiter set at 9,500 rpm
This was October 2018, since then all I have done to my race engines is to keep modifying them to get them to be reliable
Been a big learning curve
Mule 131
81 Jota, 1045cc, 4C cams, 36mm Mikuni carbs, Jota pipes, Ross pistons, Redax/Ignitech ignition
Dave Roberts
Dave RobertsHi Piet,
Is this your yellow bike that I saw earlier this year?
Do you run single valve springs ?
Were C7 ever used from the factory on road bikes eg formula mirage/ others?
Cheers Rob
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Extremely impressive results, thanks for sharing both the dyno charts.Dyno run, 7C Cams, 1160cc, Dual valve springs, 42mm Inlet valves, 33mm Exhaust valves, Gas ported Ross pistons, 38mm Mikuni carbs, 13.4 CR, ported Inlets, welded up Exhaust ports, race fuel 103 octane, 3.8% oxygenated
This was Dyno run 29 out of 55, we did make slightly more power by the time we were above 50 runs but not much, 134.6 hp was our best
Run 29 was after we modified the 3-1 again but we also increased the length of the angled Inlet manifolds by 20mm which gave us a 13hp gain through the mid-range and removed the flat spot we had there
Inlet manifolds are tapered 36mm at the head to 38mm at the carbs
Held power curve through to 8,700 rpm, set our 1st shift light to come on at 9,000 rpm, 2nd shift light at 9,250 rpm, rev limiter set at 9,500 rpm
This was October 2018, since then all I have done to my race engines is to keep modifying them to get them to be reliable
Been a big learning curve
Interesting , all if it.... the gain from extending the inlet manifolds.
I'll have to get a baseline in the new year and see what I have with C4.
Cheers Rob
Rob,
Iron Pig shown below, you might remember it from Spa. Built on a small budget using up lots of surplus stuff, so engine spec is not as impressive as Reds'. But we managed to shed quite a bit of weight, so it goes quite OK. Double springs, 980cc, 40.5/34mm valves. Intention when building was to participate in a newly founded class allowing only 18" wheels, etc, all keeping to a classic theme. Cut-off date for bikes basis was '76, hence the re-phasing to 180°. The set of C7 laying around suddenly became rather useful! RGS motor used as a basis, mainly because it is structurally a lot stronger than the MkI... and there was one laying under the bench.
Racing class never really took off and a rule change to wire wheels only killed it for me anyway. No way I was going to put my life on the line using bicycle wheels... they couldn't stand up to my riding style on the road, didn't want to imagine how they behaved on the track.Yellow is my road bike, originally a '74 3C. 78mm forged Asso pistons, C4 cams, double springs, RGS head, 40.5/34mm valves, RS36 carbs, factory 3-1 headers into 750SFC silencers, lightweight crank, CR gearbox, latest DMC32 ignition with twin plugs. I feel more at home on this than on the Pig... it has evolved a bit since the pic was taken. Recent quick 'n dirty dyno run (mate had a newly-installed dyno and needed something with a bit of power to try it out) showed 90 rwhp, more than enough to get you into trouble with. Pulls like a train.
Not aware of any C7 factory fitted road bikes, these cams were always offered as a competition/racing option. Noise restrictions would have prohibited their legal use in most of Europe anyway. Formula Mirage was a dealer special, UK seemed to be rather lawless back then.
piet
Piet
I do indeed remember the orange and blue bike from 2009. I think Werner was the rider there.
Yes, I get the spoked wheel thing, a bit heavy for my liking but aesthetically
.
Im off to look under the bench incase I've any 120 motors doing nothing .
Dynos all read so different, i believe that dyno is probably very Conservative because I know how well your bike goes.
Do double springs require different retainers/bases ?
I do indeed remember the orange and blue bike from 2009. I think Werner was the rider there.
Yes, I get the spoked wheel thing, a bit heavy for my liking but aesthetically
.Im off to look under the bench incase I've any 120 motors doing nothing .
Dynos all read so different, i believe that dyno is probably very Conservative because I know how well your bike goes.
Do double springs require different retainers/bases ?
Yes, inner springs need to be supported and need the correct load on them
I used PAC-Alloy dual valve springs made for some Honda car engine and then we machined our own spring seats and top retainers
Uses the standard Laverda collets
Will only work with the later 81 model and later RGS/RGA/SFC Cam buckets which have a larger ID and shorter length and thus are lighter which is a bonus
We have them anti-friction coated hence the finish, believe I have a set in stock in my race engine spares but can source more and easy to machine the seats and top plate as we have them CNC programmed
dual springsI've ridden the Pig on occasions, Willi takes it to most of his track days. Hoping to roll it out at the Nürburgring next August, big Laverda special event has been announced. Hoping to have the '73 works racer running by then too. If all goes well, I'll be able to present a surprise bike as well!Piet
I do indeed remember the orange and blue bike from 2009. I think Werner was the rider there.
Yes, I get the spoked wheel thing, a bit heavy for my liking but aesthetically
Im off to look under the bench incase I've any 120 motors doing nothing .
Dynos all read so different, i believe that dyno is probably very Conservative because I know how well your bike goes.
Do double springs require different retainers/bases ?
Yes, I was a bit disappointed at the read-out, especially after feeling this motor going so much better than the old, worn-out donk you experienced in Spa. That had shown 95 at the clutch, different dyno though!
piet
CLEMTOG
Hero member
ALLEDGEDLY Rob, some of the Slater Formula 1000/1200's did have 7C cams, might have only been one, maybe more???? They also had bodywork made from a bed sized piece of thick wet fibreglass dropped on to the naked machine from ten foot, then left to set before drilling holes for the indicators, The Astralirs were nice though, I never could trust them, far too light, but OK an a TZ250. Maurice in Aus bought mine, or was it Batto?
CLEM
CLEM
Is that a closed event ? Im looking to do something/s in Europe next yearHoping to roll it out at the Nürburgring next August, big Laverda special event has been announced. Hoping to have the '73 works racer running by then too. If all goes well, I'll be able to present a surprise bike as well!
I only use Dynojet 250i which I think is what Red uses. At the end of the day it matters to you only. I've got no experience outside of that brand.
I'll go back to the same place as before, they've done my brothers bikes and a few Laverdas as well.
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Weekend 22-23 August 2026, I'll get back to you as soon as I know more! Apparently 4 x 20 minute Laverda-only demo runs on the GP course. Home game for me.
piet
geoffr
New member
- Location
- sheffield England
The Formula 1200 Mirage with the lovely bodywork was advertised as having 7C cams and HC pistons never saw any performance figures other than claimed 150 top whack