That would make a big difference. The flex shaft adapter and handpiece is very slim.
Husqvarna 55 Rancher Open Port Porting Job
- Thread starter Peter White
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Agreed...not the perfect setup but way better than the dremel motor in the bore......patience is necessary...
Peter White
PAW
OK. So, I know you all haven't slept well waiting for my timing numbers, so I broke out all the stops in getting the degree wheel setup. Here is a picture of the degree wheel on the saw.
And the timing numbers I have calculated are as follows...
Intake Opens 71 degrees BTDC
Intake Closes 71 degrees ATDC
Exhaust Opens 104 degrees ATDC
Exhaust Closes 104 degrees BTDC
Transfer Opens 134 degrees ATDC
Transfer Closes 134 degrees BTDC
So, any comments on those timing numbers? That is without base gasket. Intake numbers are relative to the piston skirt, the Exhaust and Transfers are relative to the piston dome. I only looked at one of the transfers - I assume the other is the same. My eyes were going buggy looking through the exhaust port at the transfer with a flashlight!
And the timing numbers I have calculated are as follows...
Intake Opens 71 degrees BTDC
Intake Closes 71 degrees ATDC
Exhaust Opens 104 degrees ATDC
Exhaust Closes 104 degrees BTDC
Transfer Opens 134 degrees ATDC
Transfer Closes 134 degrees BTDC
So, any comments on those timing numbers? That is without base gasket. Intake numbers are relative to the piston skirt, the Exhaust and Transfers are relative to the piston dome. I only looked at one of the transfers - I assume the other is the same. My eyes were going buggy looking through the exhaust port at the transfer with a flashlight!
Chris-PA
Where the Wild Things Are
That gives a "blow down" (angle between exhaust and transfer) of 30deg, which seems unusually high. I'm not sure what you mean by "relative to the piston dome" - the timing you are looking for is where the port just cracks open or just closes.
I find it is more accurate to measure the duration and divide by 2 for the timing from TDC, as it has to be symmetrical. I turn the crank so that the port is just opening, and set the wheel to zero. Then I rotate the crank until it closes again and read the duration angle. This skips having to figure out where TDC is and associated errors.
Peter White
PAW
I meant from the top of the piston. And I did record the angles where the top of the piston (or bottom of the skirt for the intake) just opened or closed the port. I recorded both numbers just to be sure I had TDC right at zero, which I did, because they are the same number. But your way does skip that whole step of setting TDC at zero! These are the numbers after doing my preliminary port work. I unfortunately did not record the stock numbers. I noticed high blowdown, too, compared to some numbers I have seen. Looking for some input on what additional work might be in order.
Peter White
PAW
So, another way to write the port timing I measured would be as follows....
Exhaust port is open for 152 degrees
Transfer port is open for 92 degrees
Intake is open for 142 degrees
Romeo mentioned a good number for exhaust opening is 170 degrees in one post on Rancher 55 mods. I would have to raise my exhaust port 9 degrees to obtain this. It would also lower the blowdown from 30 degrees to 21 degrees. What would that do to power/powerband? Won't raising the exhaust port lower my compression ratio?
Exhaust port is open for 152 degrees
Transfer port is open for 92 degrees
Intake is open for 142 degrees
Romeo mentioned a good number for exhaust opening is 170 degrees in one post on Rancher 55 mods. I would have to raise my exhaust port 9 degrees to obtain this. It would also lower the blowdown from 30 degrees to 21 degrees. What would that do to power/powerband? Won't raising the exhaust port lower my compression ratio?
drf255
BAD CAD
I wouldn't raise your exhaust because of the compression reduction, as you've pointed out.
You can lower your exhaust port, but you need to measure the piston skirt to make sure you don't free port at TDC.
Brad knows better, but from everything Ive read, those big open transfers should flow really well and need less blowdown than they have.
You have the benefit of that central ring pin. I'd slightly raise the transfers and slightly extend towards the intake. You probably don't have alot of meat there though. Be careful you don't going though. I use a cheap, but effective, caliper to measure the thickness of the wall.
You're gonna wind up with an angled transfer entry instead of square. Some say that makes a difference as well.
The thing with all saws is that although some general rules may apply, some saws just work better with something that won't work on others.
You can lower your exhaust port, but you need to measure the piston skirt to make sure you don't free port at TDC.
Brad knows better, but from everything Ive read, those big open transfers should flow really well and need less blowdown than they have.
You have the benefit of that central ring pin. I'd slightly raise the transfers and slightly extend towards the intake. You probably don't have alot of meat there though. Be careful you don't going though. I use a cheap, but effective, caliper to measure the thickness of the wall.
You're gonna wind up with an angled transfer entry instead of square. Some say that makes a difference as well.
The thing with all saws is that although some general rules may apply, some saws just work better with something that won't work on others.
I would not raise the exhaust. I would raise the transfers and add some intake. I'm thinking something like 104, 122-124, 78.
old-cat
Fir Man
Here's a very valuable set of porting tools
http://www.ebay.com/itm/50-Piece-DI...157?pt=LH_DefaultDomain_0&hash=item20f913608d
Get your pointer in there for the big view then go to the right side, top. There are two burrs with 45 degree inside angle.
PERFECT for making inside exhaust port bevels!
http://www.ebay.com/itm/50-Piece-DI...157?pt=LH_DefaultDomain_0&hash=item20f913608d
Get your pointer in there for the big view then go to the right side, top. There are two burrs with 45 degree inside angle.
PERFECT for making inside exhaust port bevels!
Rx7man
Cattle Rubbing Post
If it's too hard to raise the top of the transfer port, take a file and notch the piston where the transfers are by 1 or 2 mm on about a 30* angle to get them to open a little earlier... I do the same for the exhaust as well, so if I screw it up, I only need another piston, and don't need a new jug
Rx7man
Cattle Rubbing Post
Here you can see what I did.. wasnt the neatest job, but you get the idea
Chris-PA
Where the Wild Things Are
I have tried this too, but it certainly disrupts the squish band. The saw I did it on had maybe 0.040" squish anyway, so I figured it was not such a problem. I re-did that engine with a new piston and reduced squish, and left the transfer timing alone (BD was at 22deg). It ran much better the second way.
I'm still skeptical of the 30deg BD measurement - it just seems very large even for a stock saw. Has anyone else seen angles this large before?
Rx7man
Cattle Rubbing Post
I haven't had all that many saws apart.. but usually they're somewhere around 20* blowdown.
The saws those pistons were in were about .020" squish... On a closed transfer port design it's VERY hard to do anything to raise the top of the transfer port (keeping them balanced, etc), so this is about the only solution to it... If you mill off the whole piston, your squish band goes way back up, and if you mill off the bottom of the head you're back to where you started. On the exhaust side I make a much steeper angle now than on the transfer side.
The saws those pistons were in were about .020" squish... On a closed transfer port design it's VERY hard to do anything to raise the top of the transfer port (keeping them balanced, etc), so this is about the only solution to it... If you mill off the whole piston, your squish band goes way back up, and if you mill off the bottom of the head you're back to where you started. On the exhaust side I make a much steeper angle now than on the transfer side.
Why would that be?
Rx7man
Cattle Rubbing Post
Just hard to get the tooling into there and do a good job, especially in the smaller bore engines... The open transfers give you room to work from the bottom of the jug
Peter White
PAW
Wow, I appreciate all the input. Actually, I am thrilled to get the feedback! Thanks, to all.
Mine is an open port design, and I am willing to try and raise the transfers. Worst case, I pork the cylinder and buy the Meteor kit, which I may do anyway! I will give it a whirl and we'll see how it goes. I can easily raise the intake as Brad suggests, too. Old Cat, I just ordered that kit and will try those bits for the open transfer raising. Not sure why blowdown is so high, but I am very confident in the accuracy of the numbers I measured. I will check again tonight - no update means I got them right the first time!
Mine is an open port design, and I am willing to try and raise the transfers. Worst case, I pork the cylinder and buy the Meteor kit, which I may do anyway! I will give it a whirl and we'll see how it goes. I can easily raise the intake as Brad suggests, too. Old Cat, I just ordered that kit and will try those bits for the open transfer raising. Not sure why blowdown is so high, but I am very confident in the accuracy of the numbers I measured. I will check again tonight - no update means I got them right the first time!
Chris-PA
Where the Wild Things Are
Hey it could well be. I've not seen that many numbers really.
Rx7man
Cattle Rubbing Post
That's nearly bang on what I set my buddy's Jred 920 Super at and he loves it. The exhaust was 101*, Transfers were 122*, intake was 78*... On my 'experimental' saw it was 92, 114, and 85, and it's a little bit too peaky power.. doing it over I'd go 95/118/82 or so, but the flow rates are a big factor there as well... With mild transfers the saw ran like a turd, but once I did massive work to them it got a lot better throughout the RPM range with no change in the timing
Peter White
PAW
OK. Based on the cumulative skepticism on my blowdown numbers, I went back and rechecked those timing numbers. It turns out my assistant Igor incorrectly read the dial! Below are the right numbers, and I put them in the proper order, too. I was 10 degrees off on the transfer number. So, blowdown is 20 degrees, not 30!
Exhaust Opens 104 degrees ATDC
Exhaust Closes 104 degrees BTDC
Transfer Opens 124 degrees ATDC
Transfer Closes 124 degrees BTDC
Intake Opens 71 degrees BTDC
Intake Closes 71 degrees ATDC
So, it seems like a little raising of the intake is in order. I wish I could tell how thick the remaining walls are. I am going to have to flare the intake port on the inside, as I can't make the intake snorkel much thinner than I already have. I could go even wider on the ports on the inside, but I would need to flare them. Should I just leave well enough alone in that regard? Thanks, everyone, for all the help. It has been fun learning this.
Old cat, I got those bits, and you are right - those reverse angled bits will be great for port chamfering!
Exhaust Opens 104 degrees ATDC
Exhaust Closes 104 degrees BTDC
Transfer Opens 124 degrees ATDC
Transfer Closes 124 degrees BTDC
Intake Opens 71 degrees BTDC
Intake Closes 71 degrees ATDC
So, it seems like a little raising of the intake is in order. I wish I could tell how thick the remaining walls are. I am going to have to flare the intake port on the inside, as I can't make the intake snorkel much thinner than I already have. I could go even wider on the ports on the inside, but I would need to flare them. Should I just leave well enough alone in that regard? Thanks, everyone, for all the help. It has been fun learning this.
Old cat, I got those bits, and you are right - those reverse angled bits will be great for port chamfering!
Chris-PA
Where the Wild Things Are
I wondered where Igor had gotten to - he works with me from time to time, but he don't see too well.
I would just flare the intake on the inside if you want to go wider. There is plenty of area/volume in the port throat - take a look at the intake and the carb venturi. I often don't go more than about 55% and find great gains that way - there are less issues with rings getting into the port and less problems with believing.
