how to increase r100 power

[RGregor]

Originally Posted by Nath87

I'm thinking about making a cafe racer out of a r100/7. I would like the bike to have more than stock 60 hp and 54 lbft torque is it possible to get much more horsepower out of the old air heads with out making them over heat?

Hi!

Getting more than 60hp out of an R100 engine is easy.
But first of all you should decide where in the rpm range your engine should be stronger. Low - medium - high rpm?
That will affect the direction you' ll have to take and prevent you from building an engine you won't like.
Then you should consider that your talking about tuning an engine that is nearly 40 years old.
How many miles has it already run? No sense to try to tune a worn out engine.
Blueprinting an engine is no bad idea as a starting point for improvements.
And of course the question about the budget you have.

Any chance to ride a modified / tuned beemer?
That gives you a better impression of what you might get than anyone can give you here with words.

[bikerfish]

Originally Posted by orangebear

my dad use to run a 79 r100/7 and said he use to sit at 90mph on long runs and said the top speed was great even tho the bike handle bad. i thought the book top seep for one was like 130ish mph

my /7 wouldn't do 130 if it was dropped out of a plane!

[chasbmw]

A R100 would do something in the region of 105-110, on the speedo, which in most cases is around 10% optimistic, not that bad for an engine producing less than 50 RWHP. Handling tends to get interesting at speeds over 110, even when the bike is set up correctly

[Uncle Pollo]

Loose 20 pounds ... instant power to ratio gain.

[Uncle Pollo]

Originally Posted by chasbmw

A R100 would do something in the region of 105-110, on the speedo, which in most cases is around 10% optimistic, not that bad for an engine producing less than 50 RWHP. Handling tends to get interesting at speeds over 110, even when the bike is set up correctly

Nah .... it does fine.


I had cars that behaved worse.

[Uncle Pollo]

Originally Posted by supershaft

I think the cam wins out simply because most people aren't very good at jetting!

I trying my hand at jetting and so far it is easier than changing a cam.

I vote for different carbs and get already with the learning to jet program.

[supershaft]

I think you might be one of the blessed ones UP. IMO, I think for most changing the cam is way easier. Besides, most bikes need all those oil leaks fixed and a timing chain to boot. It's a perfect time to do it. I would guess in my experience that nine out of ten people that would consider doing either job would be way better at renewing the cam. Getting them to run decent is hard enough for a lot of people. Getting them running real good is not in a lot of people's cards.

I just thought of a good way to decide where to go first. It would depend on how you ride your bike. If you are one of those types that rarely revs their bike above 5k rpm, get the carbs first. If you are one of those that almost never rides below 4k rpm, get a 336 first. IMO, if you are the former type, you might consider switching to Norton or Moto Guzzi. Beemers are engines that need to be reved. My advise is to not fight it. Besides, they handle WAY batter with the revs up! 336's make everything better from 2500rpm on up past red line with very little trade off before that rpm.

[Uncle Pollo]

What about those pesky staintunes and that box thingy replaced with the crossover h pipe?

[supershaft]

I am planning on welding up some of my own minus the crossover sometime in the not too distant future. IMO, the front crossover gets that job done well enough. Stepping up the pipe just one size will get you from the header to the muffler.

[Uncle Pollo]

In your experience ... what the box does achieve?

[Voltaire]

I knocked 5 seconds off my February best time around a local track during quailifying....only changes since then was swap the 2 into 1 for std headers and Norton Pea shooters, trumpets on the Dells and an Ignitech ignition ...oh and I took off the Norvill fairing.
Rev limiter is set to 7500 and did not hit it in 4th on a slight inclining hill.
I found I could pass the 1975 1000ccHarley I could previously not get past...and pass a Commando on the corners but he took me on the straights....
I just about got past a hotted up 1000 cc BMW ridden by a former racer....70 and still going strong....
Man some of those old blokes and shift.
Shame it poured with rain today....
They called a halt later in the day.....yeech.
Thinking next build up an 1000 with Moorespeed pistons, some port work, more comp, balanced ,same 336 cam and some 40 mm dells..... that would probably do the biz.

[supershaft]

Originally Posted by Uncle Pollo

In your experience ... what the box does achieve?

It's an exhaust plenum. It fools the exhaust into thinking it's longer. Typically as well as in our case the 'longer' exhaust helps sub peak torque power. In our case IMO, mostly from just off idle to about 2500rpm. Right where I don't care about anyway. I have got plenty of juice there to get up a few revs higher where you can start loading the engine without it bucking and shuddering like they do if you load them much down there to start with. (In the upper gears, of course.)

[RGregor]

Originally Posted by supershaft

IMO, the front crossover gets that job done well enough.

My experience is different.
By switching from one crossover (pre 81 headers) to two crossovers (R100CS) I gained a max of 4 hp at high rpm.
Without any losses at low rpm.
The dyno confirmed information from a technical article I have found. Authors were engineers from Zeuna-Staerker (the company building the exhausts for BMW). It said the front crossover would increase low-rev torque, the second one high-rev torque.
Regarding the fact that literally no race bike from the 70ies had crossovers at all (e.g. PJs bike has none, too) it would be interesting to test the other configurations as well.

[Bluethumb]

Sorry guys but virtually every time a "how do I get more h.p.?" thread starts up all I see is "IMO or my experience, or ... The seat of my pants tell me, or my experience is" I never see any data. I don't understand why not. In dealing with mechanical engineering, why is there no real data to back up all these experiences? I think it's awesome that someone says their motor revs faster, that's great. But what does it actually prove? Fantastic job passing that bike you didn't pass last time, but what if on that day his bike was out of tune?

On the hotrod car threads I follow those guys talk data. They can tell you by doing "XYZ" that it will gain you 10 h.p. for example. Cycle magazine shows a performance gain when ever they compare different exhausts on a bike, showing real gains and losses for each system tested.

Theses horsepower threads on this forum makes amusing reading. But in terms of specific and hard data, helping someone to make informed decisions, there just ain't much substance. Not to yank anyone's chain, but a few that post the most, and with the most suggestions never offer any hard data, e.g. dyno runs. A few post with real info, but there sure is a lot of opinions thrown around with nothing backing them up.

When someone's getting ready to go out and pour easily a couple of thousands of dollars, be pretty cool if they had some real info to go on.

[supershaft]

I am just the opposite. The entire concept of 'real data' concerning this topic cracks me up. First hand reports are just, if not more, informative IMO. Sure, if we all used the same dyno under the same conditions with the same operators and had all of our bikes setup just the same but guess what? We don't. I am all for using dyno runs for tuning what I have right in front of me. I am for reading other's dyno reports but IMO you are a fool if you think they are gosple. Real world? That's my gospel. Real data? I take that with a grain of salt. Real world through the eyes of others? I take that with a grain of salt too but that doesn't make it any worse than 'real data'. Try not to forget that a lot of 'real data' is selling something.