View Full Version : Calling all port tuners

RS50 Jeff
05-16-2003, 10:07 AM
I am port mapping my Malossi 68 kit this weekend for a near future port job. It is a race only application, so I want to actually change the port timing instead of just doing a clean up. Question is is there an optimum tuned RPM range I should shoot for? Would 9.5-10k be to steep? I try not to let the revs drop too much under that anyway. Also every tuning source I come across says that radical porting and the like will shorten top end life. What exactly is likely to fail? One last thing, what is a good high rpm pipe? I have an Arrow but I've heard it called a midrange pipe. Would hate to do a kick-ass port job only to lose my power in the pipe. Any info would be appreciated.

05-16-2003, 10:23 AM
Time to open up the wallet and get a Jolly Moto Pipe. When you are turning higher RPM and producing more power it is going to wear the rings much faster. Basically you are going to have to check the rings, piston, and bore for wear more frequently. If it is for race use you might want to check them after a race weekend.

05-16-2003, 11:14 AM
Hey JJ i think i have a lead on the shipping (i hope) :S

micah apriliaforum com
05-16-2003, 12:21 PM
I would personally raise the exhaust port to about 20mm from the top of the cylinder and do what you can to raise the schnell ports as well (side exhaust ports). My Malossi was cut to 20mm and with the Jolly Pipe and a 21-24mm carb kit will do 14 bhp. I am shooting for 19bhp by the end of the year I am just too bust right now to play with my own bikes much at all.

tiba karotsu
05-19-2003, 04:50 AM
for a race only application go for 130 transfers 126 boost & 190 to 196 degrees ehaust port durations but you'd better have a true race crank, JM, MHR or Gianelli pipe, close ratio gear box & inner rotor digital ignition.

shoot for a 10,000 to 13,000 rpm powerband with the peak revs hitting 14,000+ 'coz that's the only way you can get power out of a 68cc bike. for a twisty course Micah's ports are the way to go as they're a bit milder than what i run on my scooter.

ring life? you can forget about getting longevity out of them rings 'coz mine only lasts as far as 15km of hard drag race use & that includes testing. that's what you get if you stay up above 14,000 revs every run.

05-19-2003, 05:23 PM
I;ve got nothing but time on my hands out here now. If you want any help with the formulas, etc send it this way...
I've got the team sticker ready to go....



RS50 Jeff
05-20-2003, 07:39 AM
Thanks for the insight, fellas. I still haven't got the jug off yet. I need to yank it and bring it to work so I can look at it on my breaks.
Mark- Appreciate the offer. I got the Bimotion freeware off of the macdizzy site. I need to do the measurements and just plug them in. You obviously don't have a problem with LAN out there if you can get this site. I had a hard time with time outs when we were in port! If you get a chance, send me a check for the TP75- it would really help the race effort. Talk to ya later. Any chance you can scan the sticker?

05-20-2003, 11:59 AM
"for a race only application go for 130 transfers 126 boost & 190 to 196 degrees ehaust port durations "

Durations are a good thing but where do you start the proccess? OR
When do you think the exhaust port should open (Degrees ATDC) 76 to 84 ?

Interesting footnote:
The 1994 production Aprilia 250 that Chris D'Aluisio ran in the 1994 AMA 250 races came with an Exhaust Opening 'EO' of 84, which is only one degree "racier" than a stock RD350 of over 20 years ago, despite the fact that the company's printed literature calls out EO 81.

How long of a blow down period (the period during which only the exhaust port(s) is open)? This is very important. 30 to 35 Degrees?

Exhaust Opens at 80 Degrees ATDC
Blow Down for 30 Degrees ATDC
Transfers and Boost Ports Open at 110 Degrees ATDC
Transfer and Boost Ports Duration 140 Degrees
Transfers and Boost Ports Close at 110 Degrees BTDC
30 Degrees for pressure wave
Exhaust Closes at 80 Degrees BTDC
Compression,Combustion,We start over.

What do you think?

Steve Guynes