OMC. 115 Crossflow odd compression

**Fishbum** · 09-10-2020, 10:28 AM

Originally Posted by JoshKeller

I can tell you on my personal crossflows, the regular head will give 120psi and the bathtub style heads give 100 - 105.

You wouldn’t have a pict of the different heads? Anyway to tell by a number? Thanks

**JoshKeller** · 09-10-2020, 10:44 AM

Originally Posted by Fishbum

You wouldn’t have a pict of the different heads? Anyway to tell by a number? Thanks

What are the part numbers you have?

**Fishbum** · 09-10-2020, 12:39 PM

Originally Posted by JoshKeller

What are the part numbers you have?

The port is 329538. Starboard is 326505
the port is 100# and starboard is $120

**keefallan** · 09-10-2020, 01:24 PM

Ok. you should have 326504/505 for your year motor. The compression for them should be 120. The other head is is off of a 1988 110 crossflow. I dont know if thats a low compression head for that motor. The 88 and 90hp for that same year have a different head number. Now whether its a higher compression head than the 110, I dunno. Actually, I just checked again, the 88 and 90 use the same heads that your motor is supposed to have. Since it came off of a 110 and not a 115, it most likely is a low comp head and thats why it was rated at 110 hp and not 115. The 110 was a better fit back then when there was a 120 looper real close in power. So, they detuned the 115 with poor heads.....is my best guess.

**keefallan** · 09-10-2020, 01:27 PM

I just checked and found that the 1984 115 had the same heads that you do(the 504/505 heads). SO, it looks like they did in fact put on a low compression head for the 110..........I never knew that. I have been preaching that the v4's make 120 compression with tub heads(and they do), just not with the tub heads that 329538 part number. Swap out the head and your problem should be solved as to the compression mystery.

Powerabout, you ever seen a set of those 110 heads before? Is it a deeper head or more of a lip on it than the standard heads?

**LakeFever** · 09-10-2020, 01:31 PM

There it is, nice work keefallan

**keefallan** · 09-10-2020, 01:37 PM

I love talking about the crossflows Lakefever...........and I like learning about them just as much.

**LakeFever** · 09-10-2020, 01:42 PM

I’m going to run 504/505 heads on my 79 140. Same heads my 83 115 had and that motor ran strong and hard just over 6000RPM and ran there every time out for years and years on whatever marina gas I happened to be near and on any tcw3 oil I could get at the cheapest price I could find. Walmart brand etc. Never had a blip of trouble.

going for new reeds, square up the ports a bit and stuff it on my vandal. Should be a lot of fun

**keefallan** · 09-10-2020, 01:45 PM

Originally Posted by FMP

Tear it down, measure and deck if needed and bore it , stick four new Wisecos in it, degree all the ports remove pistons and light work them equal, measure and equal the heads to 130 , do the cages and reeds, set up the carbs , put new leads and plugs on it and coils and the rest if needed, use only minimum no alcohol 91and good oil and have fun. Because

Funny stuff!!! I missed this post earlier. I love your wiseco comments...........lots of haters of wisecos round here....me personally....no opinion. I've used them and seen higher compression on them versus a stock cast piston. Never checked into the why tho.

**keefallan** · 09-10-2020, 02:17 PM

Originally Posted by LakeFever

I’m going to run 504/505 heads on my 79 140. Same heads my 83 115 had and that motor ran strong and hard just over 6000RPM and ran there every time out for years and years on whatever marina gas I happened to be near and on any tcw3 oil I could get at the cheapest price I could find. Walmart brand etc. Never had a blip of trouble.

going for new reeds, square up the ports a bit and stuff it on my vandal. Should be a lot of fun

I have no doubt.

**powerabout** · 09-10-2020, 06:52 PM

the 110 head is a low comp version

**Fishbum** · 09-10-2020, 06:56 PM

Originally Posted by powerabout

the 110 head is a low comp version

Good to here!! Thanks everyone

**perfmarine1** · 09-18-2020, 09:44 AM

Originally Posted by keefallan

I have always wondered if there were different thickness head gaskets for the crossflows. But no one ever gave me an answer when I asked it years ago. I was hoping to know that brand x was this thick, and brand y was this thick.....etc. And I completely agree with you, crossflows are tough motors. Very few give them the props they deserve for that. A crossflow will outlast...........the energizer bunny of motors....thats bad, I know.

When they switched fuel to unleaded or was it ethanol,too old to remember, they sent out a bulletin saying you could run premium fuel or switch to the new thicker head gskt and reduce timing and keep running regular fuel

**FMP** · 09-18-2020, 10:55 AM

Originally Posted by keefallan

Funny stuff!!! I missed this post earlier. I love your wiseco comments...........lots of haters of wisecos round here....me personally....no opinion. I've used them and seen higher compression on them versus a stock cast piston. Never checked into the why tho.

The only one Wisecos

**keefallan** · 09-18-2020, 01:29 PM

Originally Posted by FMP

The only one Wisecos

Fmp, why are there so many haters of wisecos? Is it because of the amount of movement of the forged piston itself? I remember purchasing a 150 crossflow powerhead, and it had .30 wisecos in it. I threw on a set of 872/873 heads and did a compression check to just see what the tight heads would for me. I got excited. So, when I built a new powerhead with cast pistons and those tight heads, I was disappointed. I saw 5 or 10 less. I have another story with that 115 I keep talking about. It was messed up by the machinist. I bought it with a bad hole. The piston kissed the wall and left a bunch of aluminum on the side. But, it all cleaned up, minus a little tiny catch with a fingernail. I knew it would clean up with a .010 boring. The others were great after honing(before too, but I was installing rings anyways). When I got the block back, he bored the opposite caddycorner hole out, realized it, and resleeved it, and then punched out the needed hole to .064. So, I see 145 in the cast piston holes(90 in the broken ring hole), and 160 in the wiseco hole!!

I didnt know if it was from the amount of air being moved by the huge piston, or the forged design of the wiseco. But compression went way up. I didnt have anything I could do about it at the time, and I got 7 years out of it. I ran it all day yesterday without a hitch. Cant wait to build the new p-head. I have only seen good things from wisecos. I just havent bought a set yet, because my kits never had them in it.

When I tear this bad p-head down, I will compare the piston tops to decide what I am gonna do for my next build.....especially if compression goes up too. But I cant 100 percent confirm it. But my 2 experiences with wisecos have had bigger compression numbers.