Cross Flow Options.....

[spucky]

Hi, I am in the middle of a 1988 90 HP Johnson rebuild. I have found a junk 1983 140 Evinrude powerhead that I got a bubble back and related parts off, also the heads. I noticed that the center web in the exhaust cavity on the 140 is milled out below the last angle brace in casting. The head chambers are very different from the 90's. And there are obvious differences in the porting. I am a machinist, and can modify as required. Looking to get the most out of it without losing low end power. I have a 1979 115 block and heads also. How would you use this hardware, and or cut metal to improve this old motors output? If I use the 90 block it will be .020 wiescos, usually deck the block about .006 to correct out of flat on block. Will be getting boysen reeds, it has 1 3/16 carbs.

 

[Dhadley]

Re: Cross Flow Options.....

Copy the 140 porting. They all use the same centerline on the intakes so all you need is the ball end cutter that matches the 140 intakes. See how the edges go right up aginst the web?<br /><br />Match the exhaust. Should be the same deal.<br /><br />You can cut the center exhaust web if you like to match the 140. Use the 140 exhaust gaskets. Use the inner and outer exhaust manifolds. Dont use the exhaust stuffers.<br /><br />Dont mill the block. Use the 90 heads to break it in and get your baseline. Surface the heads slightly only if necessary. <br /><br />Make sure you use the 31 series pistons. What are you using for a finished bore size?<br /><br />Boyesens are a good idea. Use the 115 carbs. Target 6000 rpm with an average load.<br /><br />What hull?

 

[spucky]

Re: Cross Flow Options.....

Thanks for the response, I will match the 140 ports.<br /><br />I will leave out the stuffers, looking at them it would seem they would get very hot and no real way to sink heat into the block or exhaust cover. One of them looks like it sagged.<br /><br />If I use the 140 cover gaskets without the stuffers, it looks like large areas of gasket will be unsupported in the cavity, do you cut this off?<br /><br />I have been "decking" these because the cyl are usually sunk into the block about .005, and out of flat. Worry about getting a good ring seal on head gasket.<br /><br />I am getting the 31 pistons, do you know whats different about them? I do my own bores, and go on the high side 3.521" for .020 overs. 3 of the 4 cly in this block are ok, but out of round, will cut them all. You can see areas in the wall where the rings are not touching. <br /><br />The boat is an old 1979 Grady White runabout measures 18' 6" down the centerline, has moderate deadrise, and 4" reverse chines. The boat was floatation waterlogged, and is gutted for new transom / stringers etc. In its waterlogged condition it would reach an indicated (speedo) 33 mph with a sick 115. ( 1 60 psi cyl.)<br /><br />I read a while ago about cutting the intake to siamese the intake tracks? Cant remember if it was a crossflow post.<br /><br />Have no fear of rpm, hoping it will pull 17" of pitch. How high will the stock ingition sys function? Do the reeds have any tendency to float at high rpm?

 

[Dhadley]

Re: Cross Flow Options.....

If the exhaust stuffers have sagged its most likely because of abnormal combustion heat from lugging, wrong plugs or using high test fuel or a combination when previously ran.<br /><br />You can trim the gasket if you like. We usually do. <br /><br />I wouldnt cut the deck unless its absolutely necessary. And then as little as possible and only if your sure it hasnt been cut before. If it has been cut before and it has to be cut again use the thick head gaskets.<br /><br />The 31 series pistons are coated. 3.521" is perfect. No less.<br /><br />Sounds like a neat boat. As long as there's no major hook it should respond well.<br /><br />Yes, the intake can be cut but I would wait and do that after the initial baseline is set.<br /><br />The stock reeds will give up around 6200 to 6400 rpm or so. The Boyesens will carry it right thru 7000+. The stock intake will give up about 6900 or so. The stock porting is good to about 7400.<br /><br />I doubt you will see any of those rpms unless the boat is very light and it has a pad bottom. You'll probably end up in the low to mid 6K range. <br /><br />Neat project. Have you given any thought to a jackplate? Whats the main use going to be?

 

[spucky]

Re: Cross Flow Options.....

Ok, I will try not to cut the deck. <br /><br />How big is too big with Wiesco's? I have another block I missed the dia on, honed out 3.567 on the .064 size.<br /><br />Is the piston coating a heat shielding? I have used a set last fall noticed they are dark on dome.<br /><br />She's an old boat, but the bottom is straight with no hook or rocker. Will try to keep it that way putting it back together. No pad or any late model trick stuff.<br /><br />You are right about expected load, it will be an rpm limiter. The tag on hull says rated to 175 HP.<br /><br />Never used a jack plate, other than easy X ajustment does it give some leverage for lifting the bow with setback?<br /><br />Main use will be to embarass late model 4 strokes on similar hulls. And a little fishing, all in the salt. Have been without my own boat for a while, need to get back in it. <br /><br />I will finish the engine in mid oct, prob wont get to use it till spring. <br /><br />Thanks for your help on this, I appreciate your knowledge. Hope things are getting better down there. We are to fly to Wally World (Orlando) in 16 hrs, the flight for today was cancelled. Hope we dont meet Ivan.

 

[Dhadley]

Re: Cross Flow Options.....

Man, 3.567 is really on the large side for the .064 os pistons. It should still work as the wear tolerance is .004. It'd be interesting to see how it worked and for how long. I have a feeling it may last longer than we think. <br /><br />Good luck on your trip. I'd call Dizzy World to see whats left before coming. Charley was fierce, Frances was relentless. Dont want to (cant) even think about another one next weekend.