Best heads for OMC Crossflow?

[JeffR]

This is a great site. I've learned a lot.

I have a 1988 Johnson 175 hp. It's stock except for Boyesen reeds. I'd like to add some punch and believe a set of heads should be next. Which ones? I've read the older 235 hp or 200 hp heads are what I should look for. This will be for recreational use and often I'm stuck using 87-89 octane gas. I'm at high altitude so premium is only 91 octane.

What year heads are best and part #s would be great. Thanks much!

[BarryStrawn]

1980 235 heads #325638 and 325639 are the best bolt on big bore heads. I've never tuned on a late 175 but these are fine on the 235 with pump premium.

The ones in the picture have been cut .030 and polished. Stock the chamber should be about .028 deep on the intake side. Good luck finding a pair but you may be able to get one side new from your Johnson Evinrude dealer.

[racer]

I recently found a couple new sets and have one set left.714-827-7920

[235spd liner]

just slipin in on this i have #323873 #323872 on my motor and i have a set of #328326 #328327 witch ones are better and how much can i mill on 93 octane thanks spd liner

[racer]

235, the 323872 are the better ones on a 3.5 bore engine

[Hooty]

I don' tink dem duckbill boats is urgley!

http://home.attbi.com/~jehart1/wsb/media/68666/site1050.jpg

c/6

Hooty

[235spd liner]

racer thanks for info how much can i mill my psi is 125 now thanks hooty my boat is not ugly any more i was not meaning the duck bill i was meaninng the gel coat but it is panted yellow now

[B.Leonard]

Where are you finding these NOS parts? Outside the US? :rolleyes:

By the way, are you coming to Instigator's party (Rumble)? I could use a good crew chief :D

-BL

[racer]

BL I gave away enough secrets but some have to remain. Seriously, because I have been doing this so long people call me now and then wanting to sell parts.

[B.Leonard]

That 150 compression sounds high and that gasket thickness sounds way off as well. Remeasure both.

Better yet, CC the head and compare those numbers. The compression gauge is prone to error when measuring max compression for a particular combination (port heights, cranking speed, elevation etc.). The compression gauge is good for measuring variances between cylinders on the same motor.

The thickest crossflow gasket I've seen is the Sierra at .055". The Pro Marine's come in at .050". I have seen a stock gasket at .035" but I have no idea where to get a set of those new.

-BL

[Jeff_S]

I have a 1981 175 horse Johnson that has the old "bath tub" heads on it. Compression is 110 lbs approx. on all cylinders. I have a pair of the heads laying around like Barry Strawn has pictured above, the ones that are supposed to be off of a 235 horse. If I swapped out heads for the "good" ones with having them cut, what type of performance gains could I expect? The motor runs really good right now, but I hate to leave horsepower just laying around. Also, the higher performance heads had one hole that must've had a broken ring in it at one time. The inside was pretty pitted up. I sanded it down and got rid of a lot of the pitting, but the bigger pits I just rounded the edges. Will it hurt to run it like this? I wish I could post a picture of it, but it is the only hole like this, the rest are fine.

[B.Leonard]

You'll notice a good bit more midrange punch/acceleration. Very little if any rpm increase. The exhaust will sound a little crisper all around.

Just clean the burrs off that cyl and clean up. The pits won't cause any problems. Make sure your timing is set between 24-28 and you're running good 92/93 octane gas (not a mix of 87 and a couple gallons of 93).

-BL

[racer]

Jeff your 1981 175 is a 3.5 bore engine and the heads Barry posted a pic for are from a 3.625 bore. The haed you want is from a 235 but a 78 or 79 # 323872 if the pits are deep I would not run them.

[BarryStrawn]

Just to clarify, JeffR who started the thread has a 1988 175 which is a big bore or 3.625. The #325638/9 heads are for this bore size only.

Jeff_S has a 1981 175 which is small bore or 3.5" and there are a few sets of similar heads with the shelf or squish area in the roof of the chamber (like the picture). There are also some that could be too tight if you got lucky and have CCC or RS race heads instead of 235 heads. If they are not the #323872, find out what they are before you bolt them on.

[JeffR]

Ordered my heads from racer and they arrived in two days with gasket set -- great service! Hopefully I'll have time to install them this weekend. My plan is to run pump premium gas, back timing down to 26 from 28 and use my stock (sea level) 61C jets as per racer's recommendation -- I'm at about 5000ft.

I'm the original owner of the 1988 175hp and up until about 3 years ago, all I ever ran was regular gas-- I didn't know any better! Regular in this area is 85, midgrade 87, and premium is 91. Guess I was lucky since I've never had a single problem with the engine. Still runs great and hopefully will run better.

Now I'm planning my next upgrade.

JeffR

[Jeff_S]

The numbers on my heads are 323457/8. does anyone know anything about these heads? I think they came off of an early eighties GT 150.

[Jeff_S]

I measured the bore on the heads with a micrometer and the heads will fit. The pitting isn't very bad, just several small dimples. I am gonna get some head gaskets tomorrow and bolt them up. I'll let ya'll know what the outcome is.