Checking Port Timing With Degree Wheel

[robertg]

My 4mm stroker crank arrived today so I checked the port timing with a degree wheel. I used a 61X cylinder that I had that had the exhaust port raised slightly, I think 1mm. The exhaust port opens around 87-88 deg and the transfers open around 114-115 deg. So the exhaust duration is 184 deg and the transfer duration is 130 deg. How would this thing run with this port timing? I think the stock exhaust duration is 179 deg.

Also my crank is about 1.5 deg out of phase, Is that a problem?

 

[SUPERTUNE]

Most of the time the cranks are NOT out of phase that much...as most of the out of phase degree readings is from the degree wheel not running true enough to the crank center line and will give a false reading.
What are your intensions with this motor, explain in more detail the rest of your combination of parts.... your too vague as to what your trying to build.

 

[robertg]

Most of the time the cranks are NOT out of phase that much...as most of the out of phase degree readings is from the degree wheel not running true enough to the crank center line and will give a false reading.
What are your intensions with this motor, explain in more detail the rest of your combination of parts.... your too vague as to what your trying to build.

I think the degree wheel is a little wobbly so I will recheck it again.

What I am doing is building a 4mm stroker motor for my Superjet. I am looking for low end power. I know I should send it out to get ported but I am cheap. I have a stock 61X cylinder, ported 61X cylinder, stock 701 62T cylinder and a ported 760 62T cylinder. I want to check the porting with all of them with a degree wheel to see which one would work the best. I know I am going to have to get my domes machined also

From what I have read it sounds like the port timimg is not that bad on my ported 61X cylinder, I just wanted someone to confirm that.

I am going to use a limited chamber and dual 46mm Novi carbs. I have an aluminum flywheel and a MSD Enhancer. I may get a programmable ignition but I am not sure. I want to run pump gas.

 

[SUPERTUNE]

The blowdown is way too short for me, on this one you stated. I like a better hit off the bottom for freestyle/freeride motors. I also like CC's for making power (start w/85mm big bore sleeves for 61x casting).
P.S. Don't use the ported cylinders, use stock cylinders to start with when building stroker motors, then port for your target rpms. Resleeving un-ported cylinders is the best way to go as you can install sleeves where you want them.

 

[robertg]

After doing some more checking the crank is definitely out of phase at least 1.5-2 degrees. The PTO side comes to TDC around 182 degrees after the mag side.

It is kind of difficult to see exactly when the transfers open because of the port chamfering. I double checked everything and it seems like they open at 115-116 degrees. That would make the blowdown 29 degrees.

 

[robertg]

I measured my 760 with a stock crank and the exhaust port opens at 85 deg and the transfers open at 120. That would make the blowdown 35 deg. I didn't measure a stock 61X but I read the exhaust opens at 90 deg so the blowdown would be 30 deg.

I am thinking if my exhaust opened at 86-87 and transfers opened at 119-120 that would be all right. Now I understand why you say you should re-sleeve unported cylinders.

I think I am going to buy that book on two stroke tuning by Gordon Jennings. It would be easier to send my clyinders out to get ported but I wouldn't learn anything that way.

 

[SUPERTUNE]

Well I wouldn't want to buy all my porting stuff over again, way to much $$. I just keep buying stuff every year and now have a ton of porting stuff now...

 

[Powder]

I think I am going to buy that book on two stroke tuning by Gordon Jennings. It would be easier to send my clyinders out to get ported but I wouldn't learn anything that way.

I don't know about that. There is a reason people pay me to do my job, because I have spent the time specializing and mastering the skills needed to be the best at it. (no it isn't porting that's for sure) For that same reason I pay other people to do jobs they have spent time mastering. Could you port it on your own, sure. Will you get a better end product having a master do it, without a doubt. I rather spend the money and get it done right then try two, three, four times to get so-so results. just my .02

 

[douglee25]

I don't know about that. There is a reason people pay me to do my job, because I have spent the time specializing and mastering the skills needed to be the best at it. (no it isn't porting that's for sure) For that same reason I pay other people to do jobs they have spent time mastering. Could you port it on your own, sure. Will you get a better end product having a master do it, without a doubt. I rather spend the money and get it done right then try two, three, four times to get so-so results. just my .02

Been there, done that, for sure. Catch 22 as always.

Doug