O-ring head block

[gonefishing_68]

How much taller is a o-ring head block than a standard block? I'm wondering how much it changes port hight?

[Jay Smith]

AH,
The only late model 2.5 blocks that are different in the deck heights that I know about are the 240 EFI Sport Jet( there may be more motors with this set up that I'm not farmiliar with ) ( the SJ motor is .040" taller because the "O"ring head seats with a flat or no built in head squish band , no recess to form the squish is machined into the head like the rest of the late model HIGH PER. "0" ringed headed Mercurys ( not sure about the stock fishing motors ) the Sport Jet block deck being .040" lower creates the squish as at TDC the crown is -.040" in the deck ! ) Also a garlock gaskeded Drag motor's pistons pertrudes .004" out of the deck ( Thats the reason they come with a series #44 gasket that are thicker) , if you run a thin head gasket ( 260 style ) on a garloc type gasketed Drag and really turn it up ( 10,600 + ish ) the rod streach will cause the piston to kiss the head, ( been there and seen it happen a bunch ) 260's piston are recessed .004" in the deck, they ALLl have the same length rod, crank stroke and piston crown height as each of the motors I have talked about if I havent been hitting the crack pipe ! LOL...........!

Good luck and Happy Holidays......

[us1]

How much taller is a o-ring head block than a standard block? I'm wondering how much it changes port hight?


Different deck heights will not affect the port timing if thats what you mean by height. Piston height, rod length and stroke are what affect port timing and of course grinding the port opening.

[2-Stroke]

Just pulled the heads off of my 2001 XR6 fishing motor and there is NO squish band in the heads, so it must be built into the deck height

[steve]

1999 and newer fishing motors with Oring'd heads , the Opti blocks and the 240 jet ( maybe the smaller jets too, not sure) all have .040 added to the deck. Another way to do it, the 280 has the squish built into the head for instance. The guys with the Oring'd blocks seem to be winning in the DSRA in the stock class BTW.

[gonefishing_68]

So on the 2000 and newer fishing motor you would need to subtract .040 from your measurement when porting?

[gonefishing_68]

Or would that be add to it?

[steve]

On an Oring block a 1.610" exhaust port on a gasketed block becomes 1.650 so you ADD .040. A transfer goes from 2.200 to 2.240 etc. If you have a stock 200 or 225 or 240 jet then the ex should be around 1.650 and the tranfers should slope from 2.240 about .030" or so . But remember, if you port the block, you are likely going to want to add compression some time later and you will need a set of heads thats Oring'd and smaller chambered. You'll have to make those. You cannot add a gasket and tight heads or you'll have a huge squish band. Much easier to change to gaskets if you are already going to port it. You have a wide selection of head cc's available that way. Just an opinion.

[gonefishing_68]

So you would want to deck the block .040 while it was down?

[steve]

I would , if its an Oringd block. If you like the Oring idea after you deck it, you can always buy the new factory O ring'd 21 or 26cc heads that have the squish built into them and not use a gasket. But you cannot run those heads with the block you have without cutting .040' off. Otherwise you have .040 in the block and .040 in the head + another .010+ or so for the piston height for squish = .090" which is probably 4 to 5 cc worth of trapped fuel thats never burnt. For a 21cc head, thats 20% of your charge! It would kill your hp and it would also not cool your pistons as much.
Unless you want to always stay with the heads you now have, or plan on having someone do all the fancy cutting on them in the future, I'd deck the block. Much easier.

[gonefishing_68]

Thanks Steve.