Bell touches on ducting and the like for aircooled go karts.Originally Posted by B.Crump
Long Haired Yobbo
Bell touches on ducting and the like for aircooled go karts.
Heinz Varieties
Scooter boy
iv only got as far as blue printing the motor in the book i might skip ahead and take a look at it cheers
Forum whore
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Dynode a couple of the team bikes yesterday. We had a laser temperature gun to see if we could get some idea of the average exhaust temperature.
Blair lists the average exhaust temp and BMEP for a road bike as something like 360 degrees C – 5 bar BMEP, enduro 500 – 8 bar, motorcross 600 – 9 to 10 bar and GP racer 650 – 11+ bar.
From this I expected that the more power the hotter the exhaust, but we had one bike with an exhaust temp less than 300 that made 2hp more than a bike with a 560 degree exhaust.
On the bike with the 560 deg exhaust, thinking we had it tuned wrong we advanced the ignition 3 deg. The ex temp dropped and so did the power. Same with the main jet, bigger jet cooler exhaust and less power so it looks like we had it right first time.
My guess is that the engine with the hotter exhaust develops a higher BMEP but at much lower revs than the higher hp engine. Unfortunately the dyno could not pickup the engine rpm so we don’t know for sure. Interesting though.
High BMEP is everything, but it looks like a high BMEP (hot exhaust) at low rev's can equal less HP than a lower BMEP (cooler pipe) at much higher revs.
Hope to get back to the dyno tommorow
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Long Haired Yobbo
Do you know which one would win in a drag race? (maybe a short one for buckets)
Heinz Varieties
Highway Biker
I would suggest try the midsection of the pipe. Not sure what it will be like with a laser temp gun as I normally use type k thermocouples inserted into the exhaust system. However, the temperature difference between engines in the midsection is much smaller compared to front of pipe.
Exhaust gas is not a great method of comparing engines anyway as one engine might make its power with a low delivery ratio and a high trapping efficiency and another will make its power with a high delivery ratio and a low trapping efficiency. The two engines might be making the same bmep at the same revs but will have a different exhaust gas temp. However, as a means of checking fuelling and ignition timing on an engine that you have some experience of it can provide a useful guide.
No8 Wire Extraordinaire
of my very limited understanding is that temp can vary a heap & should only be used as a baseline. Measurements on EGTs are typically done at 4-6" from piston face.
the bike is then set up best it will go & measured. If it is then run at a track & the temp is lower than baseline tuning is preferable. Too cold will be rich.
. . . Or it could be lean, but the difference is it will likely get hot, then cool down as the heat energy moves from the pipe into the piston. So you have to watch for the temp change to get an indication.
Fitted an EGT this week so aim to get on dyno on sunday.
Don't you look at my accountant.
He's the only one I've got.
Forum whore
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At the BOB today Avalon made one of the Team Bikes (NedKellys) look good, gaining a second place in a support race and setting the second fastest PB time in the BOB race itself before retiring with a broken engine mount.
The thing I like most about buckets is all the great people you meet.
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In the riders seat
When I raced Karts guys were going away from EGT as they reckoned quite often by the time you'd noticed your engine was already toast
They were all swapping to Det counters
"If you can make black marks on a straight from the time you turn out of a corner until the braking point of the next turn, then you have enough power."
Forum whore
Hi Kickaha, my interest in exhaust gas temperatures gathered while running the bike on a dyno, is so I can design a more effective pipe.
I can understand what you mean about monitoring the EGT while racing but I don't know anything about using a Det Counter, probably time for me to learn, have you used one yourself?
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Forum whore
By using a laser temperature gun on the dyno I had hoped to get an idea of the average exhaust gas temperature. It was not that easy as the temperatures along the pipe varied greatly, they also varied between runs and no doubt were hotter inside the pipe than on the outside.
On the dyno yesterday I measured the midsection temperatures as 160 deg C on my bike and 180 deg C on another ESE bike that’s making another 1.5 RWHP than mine.
Interestingly the best runs were often cooler than other rich/lean or over advanced/retarded runs. Generally the first pull in a run was cooler than the second and the third pull in a run was hottest. And as the power went up the final "best run" midsection temp was down compared to other lesser runs.
Another difficulty is this dyno only graphs RWHP against road speed so I have to work backwards to find RPM. From the RWHP + Estimated Transmission Losses and RPM I have been able to estimate the BMEP at 120 psi or 8.3bar and this suggests an average exhaust pipe temperature of 500 deg C.
The estimated crank HP at 10,000 rpm, 8.3bar BMEP and 500deg C accord well with Blairs pipe formulas and allow me to re-evaluate the porting to better suit the RS pipe.
The RS's exhaust timing won't work properly for the GP even though we are using an RS pipe as the GP engine does not have the same trapping efficiency or exhaust port time area and average exhaust gas temperature as the RS125.
I now know there is little point in using the same exhaust timing as the RS on the GP, and I have to work out a new one to suit the new motor/pipe combination.
In back to back runs with the new RS pipe and the old RM one it was found that they both made the same power at much the same RPM but the RS pipe gave much more useful over rev and now that we have the carb thing sorted I am keen to develop this GP-motor/RS-pipe combo further as I think it has real potential.
After the good showing by Avalon at the BOB Team ESE are very much looking forward to Taupo.
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gypsy
you stupid man...... Avalon makes ANY bike look good!!!
especial if she is standing next to it.....and even better when she is riding it....
what a ride so far!!!!
Forum whore
Sooo True......
Highway Biker
Those temperatures for your midsection are well below what the actual midsection gas temperatures are likely to be - typically 400 degC plus.
Not surprised that cooler temps are associated with your better runs as that particular rs pipe has a tuned length that is far too short for your exhaust port time area / exhaust duration setup - 814 mm on the rs. If you get a chance try the 15mm spacer I had suggested in a previous post. Just out of interest, what sort of ignition timing worked best.
I would also give some thought to trying a milder closing point on your disc valve - 85 degrees is typical of gp aprilias. On homebru discvalve racers a milder timing can be better all round. Try 75 deg atdc.
In the riders seat
Haven't used one myself as they were a pricey bit of kit, K14 had one on his RS125 so he would be able to tell you about them
"If you can make black marks on a straight from the time you turn out of a corner until the braking point of the next turn, then you have enough power."
Forum whore
I will put a degree wheel on the crank and measure the ignition timing, my guess is that its about 14deg BTDC fixed. Retarding it with the RS pipe did not seem to improve the over-rev past peak power like I expected, previously it had done so on the RM pipe but the RS pipe has plenty as it is.
One of the Team ESE bikes is running an inlet that closes at 76deg ATDC and an Ex that opens 80deg ATDC with 70% bore width, trans open 114 ATDC and an RM spec pipe for 20RWHP, it runs quite well and is relatively easy to ride.
I measured the tuned length from the piston face on the GP with the RS pipe to the end of the convergent cone at 825mm, the exhaust tract on the air cooled barrel is 55mm. I think this is a little longer than the RS cylinder but could be wrong as its hard to measure the chamber accurately.
Like you suggest I will make up a series of spacers to try. All my modeling with Blair’s formulas suggests the pipe could be longer, like up to 900mm TL with different scenarios.
Looking at Blair’s formulas and using what I think the BMEP currently is (8 bar) I have come up with a new plan to try with the RS pipe.
From what I have measured, the RS125 transfers open 116 and Exhaust 86 Deg ATDC
My plan is to modify the GP125 transfers to open 114 and Exhaust 81 Deg ATDC 75% bore width for peak power at 11,000 rpm using the RS pipe.
Sure a longer duration means a longer pipe but a lower average ex gas temp like we are getting in the GP calls for a shorter pipe.
Using Blairs formulas and my estimated BMEP but at a higher rpm the above arrangement evens out producing higher HP than my current 20.
Anyway that’s the plan, and I would like 24 RWHP (26 at the crank) for Xmas. I can see your spacer idea being very useful.
I notice that in the top of the RS125 cylinder exhaust port, it is heavily angled down at the port window, is this a good idea?
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