Cylinder head marking

[Ian Short]

Ian, if you are looking for efficiency, modify your head to the CR-specs. I had the head of a project engine at a specialist for head tuning and he found basically 5 things that kept the original 1000 Jota head (same as the RGS Head) from breathing as it should:

1.) the valve seat ring protrudes into the inlet channel, building a "step" in the inlet channel. the 40,5 or 41mm valve seat rings are larger and hide in the material of the channel, so that they do not have that step
2.) the valve size of the inlet valve was 39mm, he suggested 41mm
3.) the valve stem is relatively thick and the valve guide also protrudes into the inlet channel quite much; a shorter guide (that is longer at the top below the tappet cup) would help on the flow
4.) overall inlet channel diameter to narrow (was 32mm) and not optimally shaped
5.) combustion chamber not optimaly shaped, sharp edges should be smoothed out to reduce heat nests.

There was much more he said is not ideal but he said that between a standard 3C/3CL head and the possible optimum, there are easily 10 HP found - on each cylinder (assuming carburation and exhaust are in sync with the head!). And he was right... records show that even with the standard 1000 SFC engine, just different carburators and Exhaust, we had 110HP on the 1000 SFC compared to the claimed 84HP of the RGS. To be fair, a lot of it was the Exhaust, which is crap on the RGS/1000 SFC. It kills midrange and limits peak power.

Thank you for that Lothar, I'm not in a hurry to do any engine work to my RGS unless it's required. It still surprises me to no end at how sensitive some engines are to exhaust systems and how the factories paid so little attention to it. Harley's in particular suffer from this.

The same friend who does my head porting for me also does all of my dyno work as well (Dynojet 150 inertia dyno). We had my RGS on the dyno a week or so ago and we got 71hp @ 7000rpm at the rear wheel. Carbs were acting up a bit and I didn't want to take it much higher until I calculated piston speeds and found out the big end and roller diameters. There is little doubt in my mind that 82-83 @ 8000rpm rear wheel horsepower is correct for a stock RGS. We also feel safe spinning the RGS up to 8500rpm. As an aside I was also quite surprised when I calculated the rod/stroke ratio at 1.97:1.

The pic below is from the Superflow Manual and illustrates how much velocity (over 60%) can be lost/disrupted in the valve and valve seat area.

 

[Laverdalothar]

Thank you for that Lothar, I'm not in a hurry to do any engine work to my RGS unless it's required. It still surprises me to no end at how sensitive some engines are to exhaust systems and how the factories paid so little attention to it. Harley's in particular suffer from this.

The same friend who does my head porting for me also does all of my dyno work as well (Dynojet 150 inertia dyno). We had my RGS on the dyno a week or so ago and we got 71hp @ 7000rpm at the rear wheel. Carbs were acting up a bit and I didn't want to take it much higher until I calculated piston speeds and found out the big end and roller diameters. There is little doubt in my mind that 82-83 rear wheel horsepower is correct for a stock RGS. We also feel safe spinning the RGS up to 8500rpm. As an aside I was also quite surprised when I calculated the rod/stroke ratio at 1.97:1.

The pic below is from the Superflow Manual and illustrates how much velocity (over 60%) can be lost/distupted in the valve and valve seat area.

The RGS officially had - I think - 86HP (engine). Assuming losses of at least 10 HP in the primary, gearbox and secondary chain, you could expect something like 76 - 78HP on the rear wheel (without clutch correction factor).

My 1000 SFC put out roughly 100HP at rear wheel (with the change of the exhaust and the carbs, it was already 105HP crank = 95HP rear wheel), so does the Jota, which makes it roughly 110HP @ crank, maybe a bit more - not sure.

 

[Ian Short]

The RGS officially had - I think - 86HP (engine). Assuming losses of at least 10 HP in the primary, gearbox and secondary chain, you could expect something like 76 - 78HP on the rear wheel (without clutch correction factor).

My 1000 SFC put out roughly 100HP at rear wheel (with the change of the exhaust and the carbs, it was already 105HP crank = 95HP rear wheel), so does the Jota, which makes it roughly 110HP @ crank, maybe a bit more - not sure.

All hp numbers that I present will be SAE corrected at the rear wheel, with 45psi in the tire (45 psi compensates for tire wrap around the dyno drum). I'll also try and give the more important torque value as well however some of the ignition systems don't play well with the tach input on the dyno.

Note - this dyno pull only went to 7000rpm, unfortunately I only have the mph scaled at the bottom. Next time I'm at the shop I'll see if I can get a copy with rpm on the x-axis.

 

[Laverdalothar]

Hi Ian, was first irritated by the 108 number, thought that is the Power-Output... Then I saw it's the speed...

you may add to this roughly 1,4% to get to European HP, which does not make much of a difference though. I think, with a bit of tweaking and a run beyond the 8.000 RPM you should see something like 75 - 76HP at the rear wheel, which is fairly normal for a RGS.

 

[Ian Short]

Hi Ian, was first irritated by the 108 number, thought that is the Power-Output... Then I saw it's the speed...

you may add to this roughly 1,4% to get to European HP, which does not make much of a difference though. I think, with a bit of tweaking and a run beyond the 8.000 RPM you should see something like 75 - 76HP at the rear wheel, which is fairly normal for a RGS.

This spring I wil have the RGS back on dyno, once I go over the carbs and check valve clearances and I will have a decent number to present of a stock RGS (albeit Jota mufflers). I also have my '96 Buell S1 Lightning, '03 Harley Street Tracker, Dad's '85 S2 Mille and my buddy's '95 Guzzi 1100 Sport to be dyno'd as well. It may happen before the new year but I'm in the midst switching heads on my '03 Tracker right now.