Port Timing & Duration Specifications

[Matt_E]

He wasn't talking time area....this was only degree (time) duration.
195Deg duration isn't that far out if you go with a curved roof shape.
It's not uncommon in freestyle X cylinders to have the roofs raised a bit.

 

[ATS_Scott]

Chris, I already PM'd these to you but thought I'd share with everybody else. These are from a 6mm stroker, T cases and cylinder. 85mm bore.

85.5° ex port opens
119° Transfers open
EX duration...194°
127° transfer port duration.
So blowdown is 33.5°

I also traced the ports with a sheet of paper and pencil. So these are approximate dims.
Ex port is 66mm at widest
Transfers closest to ex port: 36mm wide
secondary transfers: 30mm wide
boost port:23.5mm wide
all transfers and boost ports are 19.5mm tall
Ex port is 37.5mm tall

The exhaust port has about 2.5mm concave shape to the top then tapers to a 20mm radius to the bottom.

 

[#ZERO]

Chris, I already PM'd these to you but thought I'd share with everybody else. These are from a 6mm stroker, T cases and cylinder. 85mm bore.

85.5° ex port opens
119° Transfers open
EX duration...194°
127° transfer port duration.
So blowdown is 33.5°

I also traced the ports with a sheet of paper and pencil. So these are approximate dims.
Ex port is 66mm at widest
Transfers closest to ex port: 36mm wide
secondary transfers: 30mm wide
boost port:23.5mm wide
all transfers and boost ports are 19.5mm tall
Ex port is 37.5mm tall

The exhaust port has about 2.5mm concave shape to the top then tapers to a 20mm radius to the bottom.

Your right at the limit with that port timing and I imagine that engine would run great on the top end. I'm surprised that the stroker crankshaft and porting would give that much duration compare to the stock 760 specs. If you're going to use that engine for freestyle you will need to alter the port timing a bit. You could remove the sleeves and mill the cylinder bottom a bit but you would have to re-machine the domes. Also those pistons look like they don't have much more room before the rings are exposed at TDC. They really did some porting on that engine because the stock 760 cylinder has a 44.75mm wide exhaust that's 32.15mm tall and the transfer ports should be 12.3mm tall. Here are some pictures of the Big Bore LA-Sleeve dimensions which are very similar to the stock 760 sleeve so you can compare them.

 

[#ZERO]

This is from an e-bay item, that I thought was interesting, especially the bit about the transfer roof angles being up and opposing to keep the mixtures in the cylinder, although I don't understand how they can be both Up and Opposing.

61x with 760 sleeves:

Please note I just measured these pistons and cylinders and they are 85.5 mm bore. There is still plenty of room for more bores since these are the aftermarket 760 sleeves. I have had several questions about the specs on these cylinders, so here they are. The sleeves are from Watcon and were installed at Watcon. All finish porting was done here in house, these were the cylinders off of my personal boat. The exhaust ports are 185 degrees, transfers are 120 degrees. The transfer roof angles are up and opposing to keep the mixture in the cylinder for maximum low rpm performance. The exhaust port has a upside down bell shape with a semi flat top, actually matched to the dome of the piston. This makes the power come on hard and abruptly. The bottom of the sleeves are very high to allow maximum flow to the tranfers. The exhaust port widths are set to about 75% of the bore diameter, as far as I feel safe going for this application. The port times are lower than a race boat because this was setup for freestyle. Normal Superstock cylinder are anywhere from 194-198 degree exhaust port timing, 125-127 degree transfer port timing and flat angles for flat top pistons. I know everyone has there own opinion on this subject, but these are the specs I used. I ran the B Pipe with this cylinder along with a girdled head with 35 cc 760 domes, and a advent ignition. Thanks for looking.


http://cgi.ebay.com/ebaymotors/ws/e...Track=true&ssPageName=VIP:watchlink:middle:us

That cylinder would run pretty well for freestyle use with those specs.

I'm surprised to see that the transfer ports are angled upward because the sleeves I received from Watcon had a flat roof angle. I guess Randy is making the angles on the sleeves after they have been installed during the porting process. The Northwest sleeves are almost completely identical to the Watcon sleeves but the NW sleeves are already angled upward on the transfers on the top and bottom. Also the Watcon sleeves have a wider flange for better o-ring sealing and the auxiliary transfer ports are wider compared to the NW sleeves.

 

[freestylegeek]

Here's the porting specs for stroker:

RAD 76mm crank (8mm stroker)
Kawasaki KX500 rods (134mm long)
81.5mm Kawasaki pistons

Exhaust port opens at 83.5º
Transfers open at 117.5º
Exhaust duration 193º
Transfer port duration 125º
So blow down is 34º

I didn't get a chance to do a port map the last time I had it apart, but I'll probably do one this winter.

 

[#ZERO]

Here's the porting specs for stroker:

RAD 76mm crank (8mm stroker)
Kawasaki KX500 rods (134mm long)
81.5mm Kawasaki pistons

Exhaust port opens at 83.5º
Transfers open at 117.5º
Exhaust duration 193º
Transfer port duration 125º
So blow down is 34º

I didn't get a chance to do a port map the last time I had it apart, but I'll probably do one this winter.

I'm guessing that’s a non-P.V. Lamey cylinder with those long rods and Kawasaki pistons. I know that the Lamey cylinder can be order in different heights; do you happen to know how tall the cylinder height is?

I'm building a 5mil stroker with flat top pistons using the Northwest sleeves right now and I'm trying to decide where to put my port timing. Here are the measurements taken at with the sleeves installed at different height levels. I would use the regular dome top pistons but it would require me to install a spacer plate at the bottom of the cylinder. So I'm using the Riva flat top piston because they are 3.88mm lower then the standard Yamaha pistons. I'll have to machine the bottom of the cylinder down a few millimeters and possibly re-machine the squish band depth on the flat top domes. Here are the measurements taken with the engine on a degree wheel with the Northwest sleeves at different heights.

86° Exhaust Port Opens
117° Transfer Port Opens
188° Exhaust Port Duration
126° Transfer Port Duration
30° Blow Down

87° Exhaust Port Opens
118° Transfer Port Opens
186° Exhaust Port Duration
124° Transfer Port Duration
30° Blow Down

88° Exhaust Port Opens
119° Transfer Port Opens
184° Exhaust Port Duration
122° Transfer Port Duration
30° Blow Down

89° Exhaust Port Opens
120° Transfer Port Opens
182° Exhaust Port Duration
120° Transfer Port Duration
30° Blow Down

90° Exhaust Port Opens
121° Transfer Port Opens
180° Exhaust Port Duration
118° Transfer Port Duration
30° Blow Down

 

[freestylegeek]

I'm guessing that’s a non-P.V. Lamey cylinder with those long rods and Kawasaki pistons. I know that the Lamey cylinder can be order in different heights; do you happen to know how tall the cylinder height is?

I believe it's 126.5mm tall.
My pistons stick through the top 1mm, and I have my domes cut to accept that. my squish is 0.050". Yes, it is a non PV Lamey cylinder.

 

[michael950]

Did you ever get your motor back together, or is this the required research to do so?

 

[WaveDemon]

figured I'd add this here.

Hey Tim here's the port timing duration specifications for the 66e GP800 cylinder.

90° Exhaust Port Opens Power Valves Closed
78° Exhaust Port Opens Power Valves Open
117.5° Transfer Ports Open
120.5° Boost Port Opens
181° Exhaust Duration Power Valves Closed
205° Exhaust Duration Power Valves Open
126.5° Transfer Duration
120° Boost Port Duration
27.5° Blowdown Time Power Valves Closed
39.5° Blowdown Time Power Valves Open

The 60T GP1300 P.V. cylinder should give some interesting specifications because all the ports are lower by about 1.5mm

I'll have the specifications for the 60T cylinder real soon.

 

[BROSS]

With the northwest sleeve can you run round top pistons? Or just flat top? I have LA bigbore sleeves, and havn't used them yet, the guy at LA Sleeve told me the sleeve had port timing close to the 61x sleeve.... I guess he is a salesman....

 

[SUPERTUNE]

Close? Yes, 62T, 64X cylinder timing!! Not 61X port timing, I have the blueprint sheet from them and the sleeves.

 

[BROSS]

Like I said, he may have been a salesman. But will a round top piston work in the Northwest sleeve?

 

[robertg]

Like I said, he may have been a salesman. But will a round top piston work in the Northwest sleeve?

Yes, I am using NW sleeves with my 4mm stroker with round top pistons.

 

[#ZERO]

With the northwest sleeve can you run round top pistons? Or just flat top? I have LA bigbore sleeves, and havn't used them yet, the guy at LA Sleeve told me the sleeve had port timing close to the 61x sleeve.... I guess he is a salesman....

The guy at LA sleeve told me the same thing about their big bore sleeves.:17: I found out they're almost identical to the 760 sleeves and the only difference is the exhaust port is a little wider and the bottoms of the sleeves are a bit thicker to accept larger bore sizes.

All the big bore sleeves will work with OEM dome pistons but some require modification to the ports and height changes of the sleeves to get the port timing in the desired range. If the big bore Northwest, Watcon, R&D or Riva sleeves are to be used with the OEM dome style pistons and a stock stroke crank. All transfers will need to be raised approximately 2.5mm (varies due to your desired port timing) and the deck surface will only require light machining to match the sleeve tops to the deck surface.

When I started making my big bore stroker engine, I used a set of cases bored to the sleeve diameter plus a few thousands and partially assemble it with an 83mm piston, as in the picture above. I used a clamp on dial indicator on top of the piston to determine the TDC positioning of the degree wheel. You can rotate the crank five degrees forward and back using the dial indicator to find the centerline. I checked the port timing with the sleeves at stock cylinder height 119.0mm plus 0.5mm for the base gasket thickness then raised or lowered the sleeve with shims to obtain my desired port timing and duration specifications. After boring the cylinder casting to accept the sleeves with an interference fit, I checked the height of the ports to determine where the ports would line up (this can vary depending on the outer sleeve diameter and if the cylinder has been ported or milled down.) If you're not happy with the blowdown time, port timing or duration of the sleeve with the workable limit of the cylinder, you can alter the length of the sleeve ports, change the counterbore depth, machine the cylinder height or install a spacer plate (top or bottom of the cylinder) and machine the domes squish band depth, all depending on what type of engine you're building. All this and more needs to be determined before you start any machining on your cylinder or else you'll end up with a nice looking paperweight for your desk top.

 

[1550]

Hi, i bought used cylinder from Ebay half year ago, it have broken sleeve. I just mapped those specs, so what you think. Im thinking replace those sleeves with stock 62t 760 sleeves. It is in size 85,5 and i think i need to fill that exhaust little bit when i think use 84,5 or 85 pistons.


Exhaust duration 193º
Transfer port duration 129º
boost port duration 124º

 

[#ZERO]

Hi, i bought used cylinder from Ebay half year ago, it have broken sleeve. I just mapped those specs, so what you think. Im thinking replace those sleeves with stock 62t 760 sleeves. It is in size 85,5 and i think i need to fill that exhaust little bit when i think use 84,5 or 85 pistons.


Exhaust duration 193º
Transfer port duration 129º
boost port duration 124º

The duration specs you listed are way over the limit for freestyle use and the exhaust ports are way too wide.

If you're going to use that engine for racing it will be okay but if you're looking for a freestyle setup you'd be better of just selling back on eBay.

 

[timoNZ]

Hey #0,

Thanks for your pm it helped alot, have you got your 5mm stroker motor running yet? I would be keen to hear how it goes As I am going to start a similar motor project. What one of the 4 port timings you listed did you end up using?

Cheers

Tim

 

[1550]

What is good duration specs for freestyle?

Yes i know and think also that it is Racing Superstock cylinder, and that exhaust port is like 71% of piston diameter. I just want to do some experiments with that cylinder. What ou think will it hold if i put some material in exhaust port. Also i found out that exhaust port is like in cylinder 2420 mm2 and in exhaust flange it is 2220mm2, if i understand correctly that exhaust flange should be 1,1-1,3 times bigger in area than cylinder side port.

Cylinder side i meant in sleeve and ex flange is where exhaust manifold connects.

Sorry mine bad english.

 

[brett]

you guys are core.

 

[kevbo]

Most modern two-strokes that are designed to use a pipe will have ports larger than the header. These Yamahas were not originally intended for a tuned exhaust so the header is larger than the port on stock cylinders.