Transfer ports

[bandanshee]

Maybe the answer to this is on the forum already but I could not find it. anyway, my machine has a port-job that is very similar to the racelogic stage 3 setup, with a few changes. When I did the porting, I raised the exaust ports by almost 2mm from stock, in addition to widening them out alot. I did not do any real work on the transfers except for the lower case area. The quad is fast now (t5s, +4 timing, milled head), but it is a little pipey, and doesnt seem to rev-up quite as well as a stock machine! (the low rpm throttle response just sucks). I am wondering if raising the tranfers by 1mm or so would give me better response and maybe smooth out the power band. At first, I thought that the lack of response was coming from jetting or compression, but both of these are dead on (about 150 for compression, and jetting is on the lean side of perfect). I ran FMF fatties with this motor before I got t5's and the same thing happened with both pipes. This is not to say that the machine is not fun to ride or a pain to ride. The porting was basically free and gave an insane power increase, but im always looking for ways to improve things!

[lowriderb]

your best bet would be to degree it and find out what the durations of each the transfers and exhaust are, then figure out what the blow down is.

 

you also want to look up what roof angles people have had best luck with (there was a big thread on it a long while back on planetsand)

 

then figure out the width of the exhaust relative to the bore (73% is about the max for a reliable set up that wont eat rings)..

[bandanshee]

Currently, with the ex. 28.0mm from the top and the transfers 43.0mm from the top, that is 190 and 120 degrees, so blow down is around 35. This seems a little high to me, but I am not sure. I just think that this could describe why it runs like it does- I have heard that too much blowdown can cause a motor to be peaky and not as responsive off-idle.

Also- as far as the ex port width goes, the bore is 65.0mm and the width is 48mm, so Im pretty safe here (about 73.8%). how does the blown down duration sound?

[Indubitably]

I'm guessing this is just kind of an all around port, but the transfers should be a little higher. I've always liked to set my blow down at 32-33 degree's or so. I wouldn't mess with the exhaust anymore. Hope this helps.

Pete

[Leadfoot350]

I'm guessing this is just kind of an all around port, but the transfers should be a little higher. I've always liked to set my blow down at 32-33 degree's or so. I wouldn't mess with the exhaust anymore. Hope this helps.

Pete

 

 

t-5s like around 188-192 and a 124-128 trans. I like to stick with 70% of the piston size for width. Did you make the bottoms of the transfers even with the piston at bdc?

[bandanshee]

I cut the transfers today. Had to be real careful because I dont have a 90 degree tool, I just use a dremel flex shaft and some small-diameter coarse cutting wheels.Took my time and it worked very well. the tranfers where raised 1mm to bring me to 125.5, and that puts me at 32.5 for blow down. should work well. It's nice creating horsepower instead of buying it. (At least when you are a poor @@s in college!)

The wide ex port doesn't seem to eat rings too bad. The rings are probably 60 hrs old and are in perfect shape, the gap is well within specs. Thanks for the replies.