Yamaha TRX850 Enthusiasts Forum

Well, curious what the keihin reds will do with bottom and top.....

Well from memory length of bellmouths has to play with powerband mmmmm now was it longer for lower rpm.. shorter bellmouth length for powerband in the higher rpm rev range.
Bit like porting a speaker cabinet ..Different size port hole and tube length in a cabinet tuning it to different frequencies either more mids or a subby bottom end... be interested to here how things scrub up as such.. was only lookin at some reds the other day myself with dyno time just round the corner...funny that...

I wouldn't be suprised if those red jobbies are more so for a four cylinder higher reving motorcycle tho round the 14/15 rpm mark now i think about it tho. Notice how the blue bellmouths are pretty close to the length of the short end of the bellmouths in the std airbox(ones inside the std airbox finish curved tho with a longer top edge and shorter bottom edge )..

Could this be to give the best of both worlds..good low mid with the longer top bellmouth (2.5-5000rpm) and with the shorter bottom bellmouth a better mid-high(5-7.500rpm)... or did those morpiene tablets affect my brain a bit tooo much...

cobbadiggabuddyblooo wrote:I wouldn't be suprised if those red jobbies are more so for a four cylinder higher reving motorcycle tho round the 14/15 rpm mark now i think about it tho. Notice how the blue bellmouths are pretty close to the length of the short end of the bellmouths in the std airbox(ones inside the std airbox finish curved tho with a longer top edge and shorter bottom edge )..

Could this be to give the best of both worlds..good low mid with the longer top bellmouth (2.5-5000rpm) and with the shorter bottom bellmouth a better mid-high(5-7.500rpm)... or did those morpiene tablets affect my brain a bit tooo much...

R1 is a good ex of variable length, long in low revs and short up top.
I´m at 16/40 now and bike pulls like insane from 3k so i thought it would be interesting to see what these do for the top.
Also, "artsi" in here who made a model of the engine gave me an "optimal" inlet measurement and it was shorter than the blues.
...but i bought blue as well as i broke mine a couple of months back....

Running 16/40 myself at present still with the 60 series tyres. Had the fcr's with the std airbox and headers with staintunes without restrictors in and found 8700 was the limit in top gear. Fitted the blue bellmouths the other month and wooo hoooo.. 9000rpm in top and I backed off....yeeeesssss... Just got the bike back yesterday from pipemasters who manufactured a stainless big bore 2 into 1 big bore system for me with a megacycle muffler I had rolled up with a 57mm outlet so can't wait to get it on the dyno to and out for a fang to see how it goes....still in plaster after a scaphoid operation right thumb...

This guy has palyed around with different bellmouths.

http://www.tuning-fibel.de/motorrad_tun ... ha-trx.php

280 mms total inlet length was his optimum, which is 40 mms longer than the standard bellmouths for the TDMRs (at least I think this is what he compares with?) 300 mm gave even more in the midrange, but then he started to loose power from 7700 RPMs.

HansJ wrote:This guy has palyed around with different bellmouths.

http://www.tuning-fibel.de/motorrad_tun ... ha-trx.php

280 mms total inlet length was his optimum, which is 40 mms longer than the standard bellmouths for the TDMRs (at least I think this is what he compares with?) 300 mm gave even more in the midrange, but then he started to loose power from 7700 RPMs.

Cheers for that!!
220 was optimal according to the modeling, well see what happens!

Yer the length on the blue bell mouths is only 200mm ... Would love to read the article on that web page tag you gave but...mmmmmm.. it's written in...mmmm indian or spanish or german or italian ..well to put it plain and simple not cobbadigga language no offence
So ultimately with horsepower peaking around the 7500/8000 rpm I can understand the 280mm being a good choice for a length of bellmouth.

cobbadiggabuddyblooo wrote:Yer the length on the blue bell mouths is only 200mm ... Would love to read the article on that web page tag you gave but...mmmmmm.. it's written in...mmmm indian or spanish or german or italian ..well to put it plain and simple not cobbadigga language no offence
So ultimately with horsepower peaking around the 7500/8000 rpm I can understand the 280mm being a good choice for a length of bellmouth.

Do you measure blues and carbs then? Should go to the inlet valves...

No just measured the actual length of the blue bellmouth to the carby as such

Killerwhale wrote:Well, curious what the keihin reds will do with bottom and top.....

Well, here are the findings....
Inlet with the reds on are 260mm and moves power about 1000rpm´s.
With the blues bike pulls clean from 2k rpm and reds it´s pretty much useless under 3k rpm.
....although, reds made the bike pull like a MF straight to the rev limiter....and i have the TPS mod so i guess just under 10k.
Don´t know about usability but i like trying things out....

Killerwhale wrote:Inlet with the reds on are 260mm and moves power about 1000rpm´s.
...

Interesting. What's the total length with the blue ones then? I measured mine, and I have approx. 280 mms, but that's for the Mikunis, and mine are not in cheap plastic

HansJ wrote:

Killerwhale wrote:Inlet with the reds on are 260mm and moves power about 1000rpm´s.
...

Interesting. What's the total length with the blue ones then? I measured mine, and I have approx. 280 mms, but that's for the Mikunis, and mine are not in cheap plastic

Heya mate...
Reds are 35mm and blues are 50mm so 275mm would be correct....although i measured to the valvestem and i don´t know how accurate that is.... I´ve heard that the mik´s have better low/mid so this might be the reason!?

...and...there are fine metal one´s to buy wich also protects the main air jet etc. so i will probably go that way in the end....

Funny that was just thinkin how you went with your reds.. but much as i thought in responding a little moreso in the higher rpm. Thanks for the info tho on optimum length.. Now just got to find someone to whip some together(bit hard with a limited budget. ) Wonder if they can just plastic weld and extend the blue ones As for the main air jet and with the foam sock i made to go over the bellmouths..I cut a small foam block to sit down between the sock and carb(over jet) to give it filtration.. another budjet saving device..