Power piston kit

[richie moore]

hi phil the answer to the cylinder size problem is yes it can be done i did 2 cylinders today and took them out to 93.995 no problems just a long time to hone

 

[Phreaky Phil]

hi phil the answer to the cylinder size problem is yes it can be done i did 2 cylinders today and took them out to 93.995 no problems just a long time to hone

Thats good news. I will email you and can get some prices etc.

 

[AliBaba]

hi ali

Hi Richie!

The graph was only meant as a comment to your claim "800 to 1000 kit will give about 43 to 45 bhp.enough said."

not wanting to put a damper on your graph but your torque curve is not good . you should always aim for a flat torque curve not mount everest.

No hard feelings
Personally I think that to see if the curve is good or not you need to look at the intensions for the rebuild. For this rebuild there were three important factors:

1) Max price 1250€ (all inclusive)
2) More then 75 Nm at 3500RPM
3) Still road-legal (this means that max power can only be increased by 10% from the BMWs claimed max power (50hp))

Sure you can disagree with one or more of the points above, and you didn't know the story when you posted your reply, but I think I achieved what I tried to do. With a flatter torque curve this wouldn't have been possible.
The drop at 2600RPM is also gone now.

if you look at my results you will see the torque is in ft/lb when you do the conversion it comes out to 78 nm the same as you but my torque curve is much flatter at 5200 rpm mine still has 74 nm.

Yes, I haven't seen your curve but we have the same max-torque and you have 10% more at 5200RPM. It would have been interesting to also know the difference in price....

when i do a few bits to my long rod kit i have in more than 104 nm at 5500rpm and still have 76 nm at 7000 rpm. your hp is also in din which is 1-2 more than my sae you also have no correction factor that i can see.

That's impressing, it should be approx 80hp at 5500rpm.


I'm not saying that the Siebenrock R80 to R100 kit is the best you can get. But I think it can be a good and cost-effective base for a rebuild. The initial cost is also low because you can re-use the carbs and you don't need to modify the heads.
You (or at least I) will never reach 80hp with the kit but it will still leave a R100 in the dust behind you.

Anyway I have collected and machined some parts through the winter and in a few weeks I will remove my Siebenrock-kit and gain a flatter torque-curve. This will surely come in conflict with point 1 and 3 above.... Life is dynamic.

 

[richie moore]

hi ali good to see you are going for a flatter torque curve . the hp figures i quoted for your kit are the norm that i see from that kit with nothing else modified on the dyno that i always use . i have ridden a few bikes with this kit and on the face of it they go well but once you are over 5000 rpm they tend to run out of puff. maybe siebenrock will develope an 18 speed gearbox so you can keep it between 3000 and 4000 rpm just joking. my latest engine i cant dyno yet because i cant get the clutch to hold it so i am having some special clutch plates made i will keep you informed. ps i still think a stock r100 is better than a stock r80 with your kit fitted from the dyno results i have.

 

[AliBaba]

My point about the R80 to R100 kit is that if you have a R80 it might be more cost-effective to spend 1250€ on a solution based on the Siebenrock-kit then multiple the sum for cylinders, carbs, pistons, cylinderheads etc.
If you have a R100 then the situation is different.

I roughly sketched my curve into your dyno-chart (green standard R100, red your pistons and blue is my setup):
Yes, I know it's not exact science, but it gives an overview.

 

[richie moore]

hi Ali all very interesting but you dont have a before and after dyno graph if you look at wreford miles dyno graph you will see that it makes 43.6 hp and 46ft/lb of torque with the same kit as you but with a hi torque cam and that is about the same as i have seen. even jim cray only got 62.5 ft/lb with a1070 kit modified heads twin plugs and dellys and you are telling me you have 57ft/lb with your kit at the back wheel. are you sure the dyno hasnt callculated the losses and given you the crank hp and torque because from all the bikes i have run the losses are about 18% and as if by magic you take 18% off your results and you have about the same as wreford miles.

 

[AliBaba]

I don't have a before and after graph, but I have something better.
This graph includes the graph posted above and a graph from a run with a standard R80 the same day. Both bikes are newly serviced, have newly overhauled carbs, same tires etc.

The dip in the R80-graph between 3000 and 3750 RPM is probably caused by an y-pipe. I do think that the y-pipe gives a bit more on top but it messes up the midrange.

Yes, we are talking about rear-wheel measurements, calculated crank-values are not interesting.
To make it clear, the upgraded bike has a few other modifications, that's why the price of the rebuild was almost 1.250€. The bike is still running well 50kkm after the rebuild, it has 220kkm total.

 

[richie moore]

hi Ail the gains you have are good shame they are not on the same bike. but you do have other mods my graphs only shows a piston change and motobins removed the top two curves for his sales data which were the air filter mod and the long rod kit. you must know by now that tuning is like climbing a ladder and with the piston kits i have they will give you a leg up. the long skirt piston will put you on the first rung and the long rod kit will put you on the second rung and you can then make all your other mods.i have an engine running the long skirt pistons and a few other mods that has 67hp at the wheel and 53ft-lb at2500rpm increasing to 6oft/lb at 5400 rpm and still making 50ft/lb at 7000rpm and all for less than your cost. my point being it is very dificult to make good hp on your kit the piston crown is just the wrong shape. i would always go down the road of secondhand cylinders. heads and carbs put some better pistons in and go from there.

 

[Deleted account 111026]

Some useful information on modifying standard pistons for improved squish.
http://moragafalconers.org/BMW_Pistons/

 

[AliBaba]

As you probably know the Siebenrock-kit is pretty popular even if a lot of people is talking negative about it. The reason I posted a comment here is that I'm bored of people talking negative about the kit because it works well and it's reliable.

i would always go down the road of secondhand cylinders. heads and carbs put some better pistons in and go from there.

If you can make a kit for the R80 which has the same or better performance for the same price then you have the opportunity to make lots of money.

Recently I have bought second-hand carbs and cylinderheads. The price of this parts including rebuild was high and I also had to buy new control-cables and quite a few other parts. But probably you have better source for parts and better discount on new parts then I have.

 

[Beemerboff]

The Siebenrock kits were originally marketed as a 800 hop up kit and they claimed extra power and torque due to better use of the squish band area, when using 800 heads. Some photos I have seen of the original kits show squish bands similar to Falconers pistons in the link above.

They now market kit to go with 1000 heads and hi comp pistons for the low comp R100 GS and others. The hi comp 9.5 ? to one pistons for the GS do not have the squish band and are a different shape to the head. There are other small details I am not happy with either. I havent run the bike with them yet - the guy overhauling my box and driveshaft buggered them both, there is a 14 month wait for court time and I have to keep the evidence intact.

No instructions are enclosed relating to head / squish band clearance or shape, barrel or ring clearance, or bore finish for the rings.

IMHO that is all information that is required before I can get the full benefit from the pistons, particularly the squish set up.

This is the gap in the market that I think Ritchie is trying to fill, providing not only the best quality components but also the expertize and advice to enable them to be fitted correctly so that you can be certain that they perform as well as they are designed to, rather than relying on a lucky fluke.

And in my experience you just dont get it with the alternative products.