Port Timing & Duration Specifications

[#ZERO]

I'm starting a data base on port timing - duration and blow down time specifications on some different engines.

Here are the specifications for the 61X-701 cylinder sleeve.

90.5° Exhaust Port Opens
121° Transfer Port Opens
179° Exhaust Duration
118° Transfer Duration
30.5° Blowdown Time

Here are the specifications for the 62T-701 & 63M-1100 cylinder sleeves.

89° Exhaust Port Opens
121° Transfer Port Opens
182° Exhaust Duration
118° Transfer Duration
32° Blowdown Time

Here are the specifications for the 62T-760 and LA-1588 BB cylinder sleeves.

87.5° Exhaust Port Opens
120.5° Transfer Port Opens
185° Exhaust Duration
119° Transfer Duration
33° Blowdown Time

Here are the 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


I'm still trying to find some more specs on different engines.

I did a search and didn't come up with much and I'm hoping that someone might have this information printed in a manual.

Cylinder angles:

 

[Mouthfulloflake]

interesting.

where do you find these specs?

or are you mapping them yourself?

 

[WaveDemon]

interesting.

where do you find these specs?

or are you mapping them yourself?

I"m pretty sure he is. :Banane09:

 

[Crab]

Much better than my 752 Kaw.


Exhaust opens at 84
transfers open at 120
boost port at 123
boost closes at 237
transfer closes at 240
exhaust closes at 276

192 degrees of exhaust duration
120 degrees of transfer
114 degrees of boost port.
__________________

 

[#ZERO]

I found some of the information from HPT-Sport and MacDizzy to confirm my own calculations.

I've been using a degree wheel with a dial indicator and digital calipers to take the measurements. I shim the sleeves between the cases and take the measurements at 119.48mm height. The cylinders are 119mm and a compressed base gasket is around .48mm thick. Then use a small .003" feeler gage on the piston top to measure the port timings. Also I've been trying out different big bore sleeves at various heights and an assortment of cranks and pistons.

 

[waxhead]

Man i hope they put the 760 cylinder on the new superjet
those port specs are way better for racing

and the ports line up as well

 

[Mouthfulloflake]

#0,

I could loan you a stock 701 62T ( raider I think) if you would like to map it?

 

[#ZERO]

I could loan you a stock 701 62T ( raider I think) if you would like to map it?

It should be the same as the 760 with just a smaller bore size.

 

[WaveDemon]

It should be the same as the 760 with just a smaller bore size.

don't start assuming chris... :smashfreakB:

 

[Matt_E]

I think the 701T sleeve may be a bit different. I have noticed the exhaust roof on the sleeve hangs lower than the casting. About 2mm or so.

 

[#ZERO]

don't start assuming chris... :smashfreakB:

I suppose your right......... maybe I should be checking the port timing on the 6M6 cylinder as well.

If you have any old 63M, 65U, 66V sleeves lying around, I'd like check those too.

 

[jura]

Sorry, deleted.

 

[Matt_E]

Chris, I think your blowdown for the 760 T cylinder is off by 0.5 degrees

 

[#ZERO]

Chris, I think your blowdown for the 760 T cylinder is off by 0.5 degrees

The blow down time starts when the exhaust port opens and shuts off when the transfer ports open.

121° - 87.5° = 33.5°

 

[Matt_E]

Yes, and by what you posted for specs:
87.5° Exhaust Port Opens
120.5° Transfer Port Opens

The blowdown should be 30.0 degrees.
Perhaps your Tx opening is off?

 

[#ZERO]

Yes, and by what you posted for specs:
87.5° Exhaust Port Opens
120.5° Transfer Port Opens

The blowdown should be 30.0 degrees.
Perhaps your Tx opening is off?

Your right... I have numbers written down all over the place and my second measurement came up with 120.5 on the transfer ports with a new 760 sleeve.

The 61x has a flat roof angle on the sleeve and the 760 sleeve has a 1mm angle upwards, which will be lower each time the cylinder is bored out.

A bored 760 sleeve should have the 121° and a 33.5° blow down time because the ports are angled upwards.

I wanted to show less of a difference between the 61x vs. the 760 sleeve for that reason.

 

[#ZERO]

Sorry, deleted.

I found those porting specification very interesting. ??????

I was told about the same thing from some other well known engine builders.

They like to run their freestyle engines around 123° ~ 124° with a maximum being 127° on the transfer port duration and 184° ~ 193° with a maximum being 195° on the exhaust duration.

 

[deanz]

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

 

[Matt_E]

Up as in angled upwards, and opposing as in the flow jets are opposing each other.

 

[adet16v]

I found those porting specification very interesting. ??????

I was told about the same thing from some other well known engine builders.

They like to run their freestyle engines around 123° ~ 124° with a maximum being 127° on the transfer port duration and 184° ~ 193° with a maximum being 195° on the exhaust duration.

If this port timing you are referring to is for X cylinders than there is some roof raising involved...:thinking:

195° is 10° more than a stock T cylinder correct? and 16° more than the stock X cylinder?

From my mediocre knowledge of 2 stroke theory there are two ways to obtain the time area required to make the desired power in your target rpm range or powerband...

1. Widen ports (increasing area)
2. Increase the height (thus increasing duration)

Both increase the time-area....

My impression was that #1 was more for freestyle or 'low end power' and that #2 was for racing or 'top end' power.

Thoughts? or correct me if I'm wrong :shrug: