siebenrock big bore kit 98,00mm

bernardofeio

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hello

does anyone have a comparison graph comparing big bore kit std and touring?

on the touring the compression ratio is smaller. Conrod has less 0,5 mm that should reduce the compression ratio from aprox 11,0 to 10,00 (151,0 to 150,5)

what should be the expected difference in performance in a airhead engine?

thanks mates!


:beerjug:
 
I fitted one to a friend's G/S and it made a big difference. Loads more go.

Needs the high top gear conversion as well IMO. The stock bike is short geared as it is.
 
thanks

my question was regarding " graph comparing big bore kit std and touring Kit"
 
Main difference seems to be one is out of stock and the other is worth more than my bike!
And the 5% difference a hi top makes isn't noticeable on a properly tuned bike, better just getting someone who can tune it for you.
 
A 11:1. compression ratio is really high for an airhead engine, unlikely to work without pinging, even with dual plugging.

I think that you need to check your figures.

I think that the 1070cc Seibenrock kit, the instructions recommendation going down the dual plug route. I seem to remember that the CR on this kit is 9.5 : 1. I used dual plugs on it.

Airheads engines tend to ping on compression ratios greater than 9.5, this is due to various factors including the wide bore of a 1000cc twin, and modern fuels are generally of a lower octane rating than the 4/5 star fuel used in the 1970. This was why bmw reduced compression ratios as the use of lower octane fuel became more widespread in the 80s and 90s.

Modern engines can run high compression ratios because they have better designed combustion chambers, and much better control of ignition and fuel supply than the crude OEM ignition and carbs.



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Power claims are on the Siebenrock site , and are quite impressive, around 80 PS and over 100 nm of torque.
At this level the kit is probably not DIY, and would be better fitted by someone who has the experience, equipment and ability to check and set the squish/ piston/head clearance, dial in the cam timing and set the ignition and jet the carbs on a dyno.
Probably no point is fitting it without a high flowing air box and exhaust either, so with fitting and tuning I could end up costing nearer twice the list price and you would end up with more power than the bike could handle without the same again spent on upgrading the forks,shocks, frame and brakes.
A cheap old brick (K bike }would be a lot cheaper and probably better too!
 


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