Dear Diary: Fabrizi 50mm bore portmap/Port timings

[DirtyE]

its got a coat of oil in it, might just be a line from that.

[DirtyE]

Here is a pic of a spreadsheet my friend from the Netherlands BigBNRG sent to me:

If you have a portmap, this spreadsheet will calculate timings for you! Now to find ideal "street race" timings.

[DirtyE]

My measurements were from the paper. I will get in my cylinder soon with digi calipers and get exact measurements. Then I have to hunt for desired street race port timings, and modify the cylinder accordingly.
The other day I printed of the following port map, all a/c of course:
-Polini evo
-Malossi MHR 47.6
-Hebo manston
-Stage6 racing

From these maps I can at least examine timings. There are variances though, due to stroke and squish. The Fabrizi head is of a higher volume, so it requires a smaller squish.

From the pic, you can see the difference in the combustion chamber varying from the MHR for dio head and the Fabrizi head.

[DirtyE]

I got bored(no pun intended). No height adjustment, no width increase in bore percentage, just more area I suppose. Its a start. Now to make the other side symmetrical and polish. Im gonna raise exhaust to 185 degrees and leave the transfers at 125.

[DirtyE]

2 sides. too tired to finish tonight

[DirtyE]

Getting to the finer details. Im most out of room due to cylinder studs. I have to wait til I get my crank back in the cases before I can truly know how much to raise the exhaust port. Assuming the squish fabrizi gives me with the specs sheet, I can raise it by 5 degrees. Its very difficult to reach the area near the cylinder wall to chamfer and even them. Once I get it all polished it should look more "even". Right now that different cuts on the metal are reflecting differently.

[kauaianman]

I got bored(no pun intended). No height adjustment, no width increase in bore percentage, just more area I suppose. Its a start. Now to make the other side symmetrical and polish. Im gonna raise exhaust to 185 degrees and leave the transfers at 125.

raise exhaust to 185 deg.?

what crank are you going to use?

what degrees are you getting now without raising the exhaust port?

nice job.

[DirtyE]

Stock fabrizi timing is 180. This timing is shown in the above spreadsheet with the factors of 41.4 stroke, .6 squish (based on fabrizi manual), and distance measured and confirmed from the top of the port to the cylinder deck.). I wont raise the port until i can confirm these numbers; for now they are based loosly on what is expected when cylinder is mounted. Also, i inserted a stroje of 80mm which i believe is correct. Id like to go higher than 185 but ill be running a modified c16 pipe. Malossi crank. I am trying to suit my cylinder to the modified c16. Im relying on some advice from my coach through this process bigb(bram), and with his back ground I trust him fully.

Im willing to send a copy of the spreadsheet if anyone would like to use it for running numbers on thier cylinder in particular. Id like to run the numbers on the mhr and corsa cylinders too. Numbers dont lie, and we could all discover what the timings are that make the corsa more desirable over the mhr. With having vertical cylinders the pipe length is increased, so I was not overly surprised to see low exhaust timing. Im leaving my transfers alone (just lining the ceilings up)@125 to increase the blowdown a little and put a little more emphasis on that fly c16 pipe!

[Wheelman-111]

Greetings:

180 degrees? I don't understand. To me that's all the way down... Can you explain? Following with interest.

[swimmingfree]

DirtyE
i have a question for you..... buy razing the the port the timing dont you need to mill the head as well???
swimmingfree

[DirtyE]

180 is a mild duration. 185 is in mid-race area. Race motors are 190 plus. Raising exhaust ports raises peak power to a higher rpm. Too high and the cylinder is useless (heat or wear, maybe mixture entering or leaving too soon/late). I have spoken with the bigb before doing anything to this cylinder, hes been coaching me through adjustments, and I've been learning a lot, but I am just learning.
here is a link to his blog which may explain things better:

http://bigbnrg.blogspot.com/2011/05/por ... r.html?m=1

[DirtyE]

No swimminfree. Raising exhaust simply means your exhaust port opens sooner. It raises rpm power, at the cost of heat and wear. You'll see mina and piaggio race motors like polini evo and such with exhaust timings of 190 plus. They can do that on those bikes because there are pipes designed for high rpm power (c21 c30 from yasuni and such). There is no point in a cylinder with those timings/rpm for dio cause there are no pipes to make power up there. Its due to the legnth of the dio pipes mostly, and the angle at which the pipes bend to route itself out.

[swimmingfree]

thank you for the info... boy hope spring gets up here so we can see how the motor runs....
who the weather on your side of town ??? we got about 1 foot of snow last night....
swimmingfree

[DirtyE]

For further reading, you can google chapter 3 of Bells book and download it in pdf format. Although somewhat irrelevant now because of better expansion pipes its still a good read.
search 2 stroke exhaust porting in google and scroll down til you see a link to the download.

[DirtyE]

Greetings:

180 degrees? I don't understand. To me that's all the way down... Can you explain? Following with interest.

Your maybe thinking of ignition timing? That would make sense if ignition timing was 180 after TDC. So many things timed. Port duration, opening, and ignition. An advance key old be an example of changing that timing. Usually 3 degrees. With ignition timing I would think it would be more beneficial to have a nice aftermarket curved cdi than using the advance keys though, a quality cdi will not advance over the entire spectrum 3 degrees, it will adjust.