Posted: Wed Apr 15, 2015 5:45 am
That sounds good. I feel some velocity stacks coming on! What injun? Sohc or dohc?HerrFlick wrote:
....... My CB750 Four cafe engine is the next on the list
www.boxertrix.com
The UK-based forum for BMW's sportiest Boxer motorcycles
http://w.boxertrix.com/phpBB2/
R1100S Intake Ram Tubes.
Page 4 of 4
Posted: Wed Apr 15, 2015 9:22 am
Sohc. "The" CB750 Four. Currently a pile of bits on the slab..Corvus wrote:That sounds good. I feel some velocity stacks coming on! What injun? Sohc or dohc?HerrFlick wrote:
....... My CB750 Four cafe engine is the next on the list
Posted: Wed Apr 15, 2015 5:43 pm
Referring to data next to pictures. Doesn't seem to be any valve overlap? Are the btdc and atdc mixed up or is that really it? Maybe I'm getting confused.HerrFlick wrote:That's the only way I can understand it too Corvus. The AF ratios showed the mixture was not leaning out at all.Corvus wrote:Cool!HerrFlick wrote:
Oh absolutely right.
It's when you've got more cylinders to play with you can use these tricks to make things much more betterer.
The gains on your torque curve graph looked healthy enough, with surprisingly little loss of max power.
Regarding effect on AF ratio, this phenomenon doesn't really seem to be interfering with actual air flow or the various devices monitoring mass flow. Just making sure that what air and fuel mixture does find its way in there is not allowed to be pushed back out. Keeps it tightly packed in there. At the rpm zone in question. Is that a fair comment?
Funny thing is that the 'S' has smaller valves than the 'GS' yet makes more power. Huh?
When the GS tubes are put on an RT there's an 8 hp loss at the top end and not quite the same torque gains.
I can only explain this by the gas speed in the 'S' being higher than in the other engines.
In light of this it's sort of sad to see so much money being spent on exhaust systems, air filters, porting power commanders etc for not a lot of gain when the root cause of the problem was in the intake runners. Thing is, had a mate not put me on the RT forum I wouldn't have found this and I'd be out there spending big too. LOL.
I would imagine putting The Choobs on a bike with all the other stuff done would really bring it to life.
One Trixter, SL Parry (?), already had Lennie's sprockets when he fitted The Choobs a couple of years ago. Reckoned all hell broke loose at 4k rpm.
Hoping to fit my rocket sprockets v.soon.
I used the same concepts in the intake manifold on my 928 S4 Porsche. Got similar results. It was the same story there: ppl spending $$$$$ to get OK results but running into a ceiling where, for the money spent the gains weren't all that great.
I'm lucky to have stumbled across this stuff because let me make the 1100 and the 928 so much more fun for not many $$$. My CB750 Four cafe engine is the next on the list
Posted: Thu Apr 16, 2015 3:13 am
No, you're not. Very similar thing with my 928 Porsche and other current cars/bikes. I think it's something to do with lowering emissions, but it's doesn't seem to be lowering power.Corvus wrote:HerrFlick wrote:Corvus wrote:
Referring to data next to pictures. Doesn't seem to be any valve overlap? Are the btdc and atdc mixed up or is that really it? Maybe I'm getting confused.
My understanding is that the commonly accepted measure of valve timing is using 1mm (40 thou) of opening, but after a bit of googling the current figure is 0.050" for 'advertised' duration'.
A couple of years back I saw the BMW spec for the R-engines and they appeared to use a 'strange' lift number. Can't find it now.
Maybe I was confusing it with the SAE standard of 0.006".
Either way the overlaps are still quite low.
I got my R engine info from 'motorcyle specs.za'.
Cheers
HF
Posted: Thu Apr 16, 2015 6:13 am
Thanks again HF. Very informative.
Went a looking for more info and this link seems good (for laymen like me).
http://www.enginebasics.com/Engine%20Ba ... iming.html
I once went onto the motorcyclespecs site for bore and stroke info on a Honda 600 single. Took a little head scratching before I realised they had the two numbers the wrong way around! Not saying that's necessarily the case here but I'm now a bit more wary of their info.
Cheers
Went a looking for more info and this link seems good (for laymen like me).
http://www.enginebasics.com/Engine%20Ba ... iming.html
I once went onto the motorcyclespecs site for bore and stroke info on a Honda 600 single. Took a little head scratching before I realised they had the two numbers the wrong way around! Not saying that's necessarily the case here but I'm now a bit more wary of their info.
Cheers
Posted: Thu Apr 16, 2015 6:36 am
Haha. Great minds.Corvus wrote:Thanks again HF. Very informative.
Went a looking for more info and this link seems good (for laymen like me).
http://www.enginebasics.com/Engine%20Ba ... iming.html
Cheers
Posted: Thu Jun 25, 2015 5:56 pm
I followed this thread with a lot of interest, and recently found a set of second hand GS1100 "tubes" off a write of bike. Picked them up at a great price, so decided to try the mod... Why not?
Unfortunately, I cannot report back that I am experiencing similar results. In fact, the engine feels rougher and slightly "uneasy" with the GS tubes.
To be fair though, I live in Johannesburg, and our altitude here is 1700 meters above sea level, or roughly 5000 feet. It was for this reason I was really hoping that this mod was going to work by "forcing" more air into an already air disadvantaged situation.
I don't feel like now playing around with different chips. Bad luck I suppose.
Going to have to whip them out to get my old girl back to normal
Unfortunately, I cannot report back that I am experiencing similar results. In fact, the engine feels rougher and slightly "uneasy" with the GS tubes.
To be fair though, I live in Johannesburg, and our altitude here is 1700 meters above sea level, or roughly 5000 feet. It was for this reason I was really hoping that this mod was going to work by "forcing" more air into an already air disadvantaged situation.
I don't feel like now playing around with different chips. Bad luck I suppose.
Going to have to whip them out to get my old girl back to normal
Posted: Sun Jul 05, 2015 9:49 am
Hi Fellow 11S Trixters.
Health issues have abated such that today I've been able open Herr Flick's throttle in anger on mountain roads for the first time since adding full bellmouth profiles to the intakes of the GS intake runners that I fitted a couple of years ago.
I wasn't sure if I should expect any noticeable performance improvement over that which I gained by fitting of 'basic' longer GS intake tubes. Perhaps 'marginal' at best, but at least I'd know in my own mind that I'd made every effort to improve airflows according to the best available theories.
Well I wasn't disappointed.
While the engine pulled with all the extra low-mid range torque previously achieved, once the revs passed 5000 or so, an extra urge set in through to 8000 rpm. Wheeee. Verrry satisfying seat-of-the-pants stuff.
Atm - not in a position to do a dyno test - but as I've outlined in previous posts / threads re your outlay vs performance gain - you can virtually take performance gain as a 'done' thing (and proven), and so IMHO you can approach the idea of an anticipated performance c/- these refinements in the same manner: very low cost; easily reversed; unlikely to be disappointed.
Cheers.
Herr Flick.
Health issues have abated such that today I've been able open Herr Flick's throttle in anger on mountain roads for the first time since adding full bellmouth profiles to the intakes of the GS intake runners that I fitted a couple of years ago.
I wasn't sure if I should expect any noticeable performance improvement over that which I gained by fitting of 'basic' longer GS intake tubes. Perhaps 'marginal' at best, but at least I'd know in my own mind that I'd made every effort to improve airflows according to the best available theories.
Well I wasn't disappointed.
While the engine pulled with all the extra low-mid range torque previously achieved, once the revs passed 5000 or so, an extra urge set in through to 8000 rpm. Wheeee. Verrry satisfying seat-of-the-pants stuff.
Atm - not in a position to do a dyno test - but as I've outlined in previous posts / threads re your outlay vs performance gain - you can virtually take performance gain as a 'done' thing (and proven), and so IMHO you can approach the idea of an anticipated performance c/- these refinements in the same manner: very low cost; easily reversed; unlikely to be disappointed.
Cheers.
Herr Flick.