RGS Head - Rebuild to Stock or to Corsa/SFC Spec?

More power Baby, it's always a good thing. WARNING more power is additive and expensive. Guess how I know. But as it's within Factory Spec it's probably a reliable option, it's not like you're reinventing the wheel way out in experimental land, that's really expensive territory.
 
Hi Kristian
My suggestion:get your original cylinder head refurbished and spend the money on a set of new carburetors: Mikuni and buy a good ignition system and always run the best sports tires.

Br
Peder
 
Hi Kristian,

First of all: what is your desire and what your budget? If it's a bit more power (roughly 10HP/Nm can be achieved if everything is right; with the right exhaust even more...), but it comes at a cost (as allways).

The 41mm Inlet do help the bike to breath a lot better. Reason being is that the bigger seats do move the edge of the top of the seat ring into the aloy of the inlet port, wich reduces resitance. Also, the bigger opening does help to breath a lot better. This is compromised by - if existing - the original exhaust design. F.e.: my 1000 SFC put out 97HP with the original Exhaust (which is roughly 10-12HP more than an RGS with the same cams and I think also the same compression), had a HUGHE dent in the power-curve in midrange though but ran nicely. When I changed the exhaust to a one-off-designed one from SR-Racing in Germany, the dent was removed, torque was massively improved (from 65 to 80 in midrange) and the top end gained another 7 HP!

Dyno-Run SFC 1000 with SR-Exhaust and Keihin FCR.jpg

So - once you are "on the hunt" for improvements, you are soon running into restrictions and will need to spend more money to free up existing power.

Also keep in mind that you are filling the cylinders better, which might cause more stress to the crank/big end bearings. Depending on how old your engine is in terms of millage and wear, you might want to consider work there, too, at least in the future...
 
While you're at it, twin plug the head. The ignition will need retarding. I think it's a very underrated modification.

Cheers,

bazzee
 
Soft seats on an RGS head are unusual? 'Tulipping' valves less so.
Twin plug heads does little to increase absolute power output in my experience. Red gets more out of his single plug motors than the 98hp from my twin plug TT1 replica 😊
Money would be better spent on RS 36 carbs which do improve mid range. Porting also worthwhile if done by proven expert!
 
If memory serves, ksoholm has already installed RS36 carbs. My guess is he's just looking for that extra bit of reliable power - if available - while he has the head off. As to "soft seats" on the RGS, I had to replace all of the valve seats on my '83 as the valves were sinking so far into the head I ran out of shim options. Replaced all the valve guides, valves and springs at the same time.
 
Laverdalothar said:
Hi Kristian,

First of all: what is your desire and what your budget? If it's a bit more power (roughly 10HP/Nm can be achieved if everything is right; with the right exhaust even more...), but it comes at a cost (as allways).

The 41mm Inlet do help the bike to breath a lot better. Reason being is that the bigger seats do move the edge of the top of the seat ring into the aloy of the inlet port, wich reduces resitance. Also, the bigger opening does help to breath a lot better. This is compromised by - if existing - the original exhaust design. F.e.: my 1000 SFC put out 97HP with the original Exhaust (which is roughly 10-12HP more than an RGS with the same cams and I think also the same compression), had a HUGHE dent in the power-curve in midrange though but ran nicely. When I changed the exhaust to a one-off-designed one from SR-Racing in Germany, the dent was removed, torque was massively improved (from 65 to 80 in midrange) and the top end gained another 7 HP!

View attachment 86994

So - once you are "on the hunt" for improvements, you are soon running into restrictions and will need to spend more money to free up existing power.

Also keep in mind that you are filling the cylinders better, which might cause more stress to the crank/big end bearings. Depending on how old your engine is in terms of millage and wear, you might want to consider work there, too, at least in the future...
Click to expand...

Thanks Lothar; yes, I'm a big fan of not opening cans of worms. I'm still pondering whether to open the bottom end.

Mine only has 34K miles, has Mikunis, stock headers and crossover with Jota "silencers", Witt ignition. Ran very well, 86 HP at rear wheel on a Dynojet 200i last summer.
 
Laverdalothar said:
Hi Kristian,

First of all: what is your desire and what your budget? If it's a bit more power (roughly 10HP/Nm can be achieved if everything is right; with the right exhaust even more...), but it comes at a cost (as allways).

The 41mm Inlet do help the bike to breath a lot better. Reason being is that the bigger seats do move the edge of the top of the seat ring into the aloy of the inlet port, wich reduces resitance. Also, the bigger opening does help to breath a lot better. This is compromised by - if existing - the original exhaust design. F.e.: my 1000 SFC put out 97HP with the original Exhaust (which is roughly 10-12HP more than an RGS with the same cams and I think also the same compression), had a HUGHE dent in the power-curve in midrange though but ran nicely. When I changed the exhaust to a one-off-designed one from SR-Racing in Germany, the dent was removed, torque was massively improved (from 65 to 80 in midrange) and the top end gained another 7 HP!

View attachment 86994

So - once you are "on the hunt" for improvements, you are soon running into restrictions and will need to spend more money to free up existing power.

Also keep in mind that you are filling the cylinders better, which might cause more stress to the crank/big end bearings. Depending on how old your engine is in terms of millage and wear, you might want to consider work there, too, at least in the future...
Click to expand...
Lothar,
Is this rear wheel horsepower of crank shaft? Also, is the SFC 1000 motor as factory or are cams and carbs different?

Impressive numbers for an antique two valve motor.
 
I think the F 1 cams are standard at the RGS, the cams with more lift are P 1. The difference to Corsa and SFC are the bigger valves.
 
I have an F1 cam grind dialled in to work correctly in my 3c, love its broad range of performance right through the rev range. Comprehensive porting plus big valves and and big bore exhaust and Mik carbs and I have zero complaints with my engine performance.
 
IAG said:
Agreed, great grind for stock RGS but considering all the mods done to your bike Megacycle offers a 120° F-1 grind w/ a little more lift than stock-. Cam # 584-X9
Click to expand...

I think that's a P1 grind, by all accounts not a great street cam - and Megacycle no longer show them as available.
 
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1200ts said:
Lothar,
Is this rear wheel horsepower of crank shaft? Also, is the SFC 1000 motor as factory or are cams and carbs different?

Impressive numbers for an antique two valve motor.
Click to expand...
Well, I hate that question as everyone understands something different when you say "rear wheel HP"...

It was measured on a https://www.amerschlaeger.de/ P4 dyno, which measures loss of the drive train and calculates engine power. The measurement was done at the rear wheel, yes, but I think with correcting factors. If yours is a stock RGS with "just" Mikunis, the 86HP are measured absolutely the same way, I am sure, as an RGS rarely has more than 85HP engine power. 85HP engine power equals roughly to 74- 75 REAL rearwheel power. So - if your engine hasn't been modified before, has stock cams and compression, stock rgs head and either stock exhaust or exhaust with "Jota" cans, there is barely a chance it does 86HP at the rear wheel really. And then, there is DIN HP, HP, etc. etc. ...

Oh - and yes, my engine was 100% standard as from the factory at that time. The only change on the first run were the Keihin 39mm carbs (with a tappered inlet to the head's 36mm inlet). On the second run, it had the SR-Racing exhaust in addition as the only modifications.
 
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I cant say I was chasing power as such on my 79 Jota, but after buying an unused RGS head from the Slaters 120 show engine a few years ago, Richard and Clem doing the spannering, Keith Nairn recut the valve seats to 3 angle, some mild port work, cam wheels drilled( as was clutch, and balanced), billet cam blocks, sachse /red ignition, latterly full crank rebuild, an awful lot of shit in the near full slingers, new bespoke Arrow rods, barrels bored to 78mm, new pistons, RS36 Miks. New gearbox. It really is a delight, so much torque, then screams with the C4 cams.Now against all I have said before, and i guess because of the brakes on my Husky 701sm and Honda SP1, I am feeling the need for sharper front brakes.Anyway those mods strike a great balance, front forks re worked, wheels wearing Contis as Keith suggested, and now tubeless. Looks standard..but a long way from...divine🙂
 
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