port timing

[MercMyles]

I just bought a used 260 powerhead from a guy and some body has " HOME-PORTED" IT,worst job Ive ever seen,was wanting to check factory port timing specs to see if this is piece of junk block or maybe I can still save it,without resleeving every-hole.Are these specs available anywhere??

[tlwjkw]

Think this is it.

http://forums.screamandfly.com/forums/attachment.php?attachmentid=140541&d=1198826769

[wrechin2]

That one has standard 200HP transfer and booster port timing but has 1.550 exhaust???? All the 200's I have here are 2.215/2.175 angled with the booster/finger measuring 2.175 and some 2.200 with 1.600~1.610 exhaust and that is multiple blocks. Some of the blocks have straight transfers. I Have gotten where I measure porting and deck height and write them down on a sheet before I cut them. Those specs are basicly a 200 with high exhaust. Custom port map maybe?

You also have this one floating around for many years that is the 260 specs. Notice the 2.120 transfers and booster/finger port timing. These are cut straight. Dale Eaves said he has cut them both ways and have never seen a noticable difference in the angled or straight. ON the 330 HP they are cut at the angle.

http://i50.tinypic.com/a0ibtz.jpg[/IMG]

[tlwjkw]

Think it came from John from awhile back. Didn't "tag" it...............

[wrechin2]

When I right clicked to save it in my "MERCURY INFO" it came up as 200HP file name.... If you right click on the link and chose save target as, it automaticly shows 200HP.

The one above is Johns also I believe. I know the 330Hp is.

[Raceman]

If you're tryin' to measure port timing on a block that's already been hacked on, it's important to know whether they also decked the block. Although block decking DOES NOT alter port timing, it will give you an inaccurate measurement. (for instance block decked .020 would make you think the port timing is .020 higher than it actually is)

[wrechin2]

If you're tryin' to measure port timing on a block that's already been hacked on, it's important to know whether they also decked the block. Although block decking DOES NOT alter port timing, it will give you an inaccurate measurement. (for instance block decked .020 would make you think the port timing is .020 higher than it actually is)

:iagree::iagree::iagree:I hear so many people say if you deck a block it will effect port timing. NO. It will effect the measurments. If you use a Degree wheel it WILL BE THE SAME. The only time you will change it is if you alter the piston like the 2.4 I am building, I have decked the block .027 and the pistons .027. That will effectly raise the port timing as the piston is .027 shorter and ALL ports will open .027 sooner same as grinding the ports. If the engine is together you can measure the deck to piston relation and see what it is and see what the normal is. By looking at the piston, you can tell if it has be shaved. Jay will know what is the normal height for that engine.

[Raceman]

Yeah, we had a REAL HEATED debate around here several years ago with some guy gettin' totally outta' whack and callin' names 'cause he was just sure that deckin' the block raised the port timing. When it was suggested (by me:reddevil:) that he didn't understand basic 2 stroke theory he got downright insultin'. Years ago, when I usta' be basically the ole' Bubba at the bike shop that I like to po' mouth now about screwin' up outboards, I'd always measure the port timing with a degree wheel, 'cause back then the cyls would get cut top OR bottom, run with or without gaskets and all kinds of other stuff that would cause the measurments to vary.

[wrechin2]

Common sense tells ya that the relationship between the piston and ports stay the same reguardless of what you do to the top of the block/ cylinder. The deciding factor is if you alter the piston height as I have done.

Like the "O" ring blocks 200's, the pistons are .045/.044 below the deck , all I have measured, but the degree of crankshaft relation that the ports open are going to be the same or VERY CLOSE to a gasket block with the piston .004 below the deck. When measuring the porting with a caliper, subtract the .044/.045 and the porting will measure the same as a gasket block, there again very close. They both also both use a 38CC head whether they use a gasket or "O" rings because the addition deck makes up the volume of the missing gasket.

I don't use a degree wheel, but I do measure my piston to deck height before I tear down and figure it in to what porting I am using and they vary alot from .008 below to .0015 above on the ones I have kept records on. For what I do, I feel it is good enough as many variances I have seen in mercury FACTORY stuff. I had a date stamped 94 2.0L (replacement verticle for 88 XR2) that the porting was .005 from each other starting at 1.540, the next was 1.535, 1.530, ECT. I just stood back and said HUH???? Then I cut them all to 1.595 and was done with it.

[Jay Smith]

With a stock deck the exhaust should be ( under the shelf and flat with the deck) as high as 1".565" to as low as 1".595" that was the ones I fool with daily measure... They all have different chamfers, from .030" to .050" according to if it was Monday or Friday at Mercury on stock engines..One that been cut who knows?

Jay

[wrechin2]

Those Mercury "CLOSE TOLERANCES AGAIN!! " :D:D

[MercMyles]

I guess Im old school I like to check port timing with degree-wheel,but all this info has been helpful,Does the factory manuals give you any timing #s,and I guess this is a ? for Jay Smith what is the best port champher to have for performance,and what is the safest degree of overlap for intake/exhaust so your not blowing all the intake back out of the exhaust

[Jay Smith]

I like about a .030" chamfer at a fairly high angle and I also "Square Off" the top "horizon" a bit . I have a 105 degree air grinder with a cone shaped fine cut rotary file and it seems to get it where it works out OK, I then use a 320 grit small cartridge roll the finish off then use Maroon grade then Grey grade fine scotch bright material...The ports on a Drag are very close to as much height that is usable and the 260's have a ton of torque.. For a heavy bass rig the 280 with a 1".625" port is the king of the bottom torque of the 2.5's IMO...If you quized 10 folks about how they port you would get 10 different opinions about what works..

If your rig is SUPER light and your Drag Racing a nice map would be a 1"510" - 1".500" under shelf at exhaust with the .030" chamfer and a 2".070" boost port all measurements off stock deck... I have a Bro that uses the degree wheel and a light to check ports, works great for him , guess I'm a "war baby" and do things different...

my .02

[wrechin2]

If you quized 10 folks about how they port you would get 10 different opinions about what works..

guess I'm a "war baby" and do things different...

my .02

:iagree::iagree::iagree:I'm right here with you.

[sschefer]

Those Mercury "CLOSE TOLERANCES AGAIN!! " :D:D
:D:D:D:D:D:D How dare you! Merc Engineers had to work overtime to meet the accounting departments predicitve failure rate expectations. I think at one time they had it within 3 days of warranty expiration.. Amazing engineering if you ask me.:cheers:

[MercMyles]

Hey Jay,when your measuring your ports are you reading the top or the bottom of the champher to get your measurement,or so if your figuring a .030 you could split the difference at .015,I know like you said everybodys got their own little thing.If it produces the power like you want your going in the right direction,.ALL the guys I know get carried away and kill off all their torque.

[wrechin2]

You measure the port from the highest flat portion, then the chamfer is measured from the deck to where the angle ends into the cylinder. If you measure 1.580 then 1.550 to the end of the angle, then you have a .030 chamfer