Frits i am going to copy and paste the info about blowdown i used. its a bit long winded and the english is a bit poor. its aimed at mopeds with variators.
blowdown timing
Blowdown is best set up using a % of your transfer port timing as a base guide.
For single EX-port kits you want the top of your EX-port to be flat in the center of the top of the port. This flat area with shod not exceed ether 50% the combined with of the transfer ports or exceed 55% of the EX-port with. This will be close to 1/3rd=33% of the bore if you have good wide porting.
Blowdown tuning starting points for single EX-port kits.
16% to 17.5% of transfer timing with stock or weak hitting pipes up to 8,500RPMs with 154deg to 165deg exhaust.
17.5% to 18.5% Good timing for strong pipes working in the 7,000RPM's to 9,200RPM rang with 164deg to 170degs exhaust.
18.% to 19.% Hard hitting pipes working in the 7,500RPM to 10,500RPM rang with 168deg to 174degs exhaust.
18.5% to 19.5% This is near the max for most one speeds with clutches engaging in the 4,000 to 5,000RPM rang,
With hard hitting pipes working in the 8,500RPM to 11,000RPM rang with 172deg to 178degs exhaust.
This is the end of the road for 90% of the one speeds, now entering the variomatic zone.
19.5% to 20% Is for big pipes working the 9,000RPM to 12,500 with EX-port timings of 176deg to 180deg.
20% to 20.5% If you don't know what your doing just stop, this is for 178deg to 187 EX-port timings Spinning 10,000RPM to 13,500+RPM.
Exhaust timing:
138-150: Stock on most Mopeds to keep you under 30 MPH.
151-161: Low RPM powerband timing.Good for low & mid rang torque power, up to 7K-8K RPM rang.
162-168: Very usable timing. Good mid rang torque & power up to 8K-9K RPM range.
169-175: Best all around power band timing. Good upper mid rang torque with hi RPM power up to a 9K-10K RPM range.
176-182: Gives weak power under 5K, good power at 7K, and will rip from 8K up peaking from 9K up to a 10.2K-11.2K RPM range.
183-187: Gives no power under 5.5K very weak upper mid ranger, some power at 7K, good at 8K, starts to rip from 9+K, pulls to the 11.5K-13.5 RPM range.
188-198:Very limited use. Almost no torque with a narrow high high RPM power band at Pro use racing high revs.
Old single EX-port timings chart/notes.
Blowdown of 16 to 20: Stock on most Mopeds to keep you under 30 MPH with the best MPG.
Blowdown of 18 to 22: Low RPM powerband timing.Good for low & mid rang torque power, up to 8K-9.5K RPM rang.
Blowdown of 20 to 24: Very usable timing. Works best with weaker hitting pipes. Good mid rang torque & power up to 9K-10.5K RPM range.
Blowdown of 23 to 26: very good all around Wide power band timing. Will work with most pipes. Strong upper mid rang torque with hi RPM power up to a 9.5K-11K RPM range.
Blowdown of 25 to 27: A good pipe is a must. Best all around power band timing. Riper upper mid rang torque with hi RPM power Wide power band with a big power hit. Best power for everyday use up to 10K-11.5 RPM
Blowdown of 26 to 28: Low power under 5K, Good mid range. works best with pipes that peak hard in the 8K to 11.5K range fading/topping out at 12K This the max for most street set ups.
Blowdown of 28 to 30: Works best with a tuned variomatic or shifter engine, Very low power under 6K. Weak mid rang under 7.5K. The power band starts to get narrower and more peaky. needs a HIGH RPM pipe. gives the best power in the 9k to 12+K rang, will pull past 13.5K with some set ups.
Blowdown of 30: At this point 99.% of you will just have a door stop. Very narrow power band. No power at RPM's under 8K, higher power at high high revs. You will fry most one speed well tuned clutch's to be able to ride with a blowdown as high as this, You need a well tuned variomatic or shifter engine that can spin over 14K.
Blowdown of 32+: Way too high for any 1 speed or 2 speed automatic. This is only ride able at the race track on the very very best tuned variomatic shifter engine.
As a rule of thumb, a blowdown higher then 25deg isn't for everyday use on an automatic with full clutch engagement under 5,000RPM. Don't go higher than 22deg if you don't know what you're doing
Now for the split/twin and three port exhaust with these you can have the flat area of the top of the EX-ports that is two times wider in the flat zone. So now it's close to 66%=2/3rds of the bore instead of one 1/3rd with the single port exhaust that's 100% more area. With 100% more flow area with we need less blowdown timing to mach the wider area cross section.
Blowdown tuning starting points for split/twin and three port exhaust port kits.14.0% to 15.0% of transfer timing with stock or weak hitting pipes up to 8,500RPMs with 156deg to 165deg exhaust.
15.0% to 16.0% Good timing for strong pipes working in the 7,000RPM's to 9,200RPM rang with 164deg to 170degs exhaust.
15.5% to 16.5% Hard hitting pipes working in the 7,500RPM to 10,500RPM rang with 168deg to 174degs exhaust.
16.0% to 17.0% This is near the max for most one speeds with clutches engaging in the 4,000 to 5,000RPM rang,
With hard hitting pipes working in the 8,500RPM to 11,000RPM rang with 172deg to 178degs exhaust.
This is the end of the road for 90% of the one speeds, now entering the variomatic zone.
17.0% to 17.5% Is for big pipes working the 9,000RPM to 12,500rpm rang with EX-port timings of 176deg to 180deg.
17.5% to 18.0% If you don't know what your doing just stop, this is for 178deg to 187 EX-port timings Spinning 10,000RPM to 13,500+RPM.
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me again
using the above info i went for 176 126 and my moped reaches 65 mph and has max power at 9250k rpm and revs to 12k
with the doppler original pipe i get the following hp curve.
[Vous devez être inscrit et connecté pour voir cette image]is any of the copy paste useful or is it wrong?