The OMC Cross Flow Thread

Ok my White Motor Brothers, I want to discuss anything Cross Flow related.
Such as

.Top speeds
.Set ups
.Tuning
.Trouble shooting
.Performance tips
.Parts finding, sharing or trading
.Experiments whether successful or not
.Racing history
.Post pictures

I'll start with a question and a secret.
Question.
How fast would a modern high performance hull like an Allison or an STV go with a relatively stock 235 (just the usual bolt-ons)?

Now the secret.
This is my second year running my 235 with no top ring in a piston. The lip above the top ring broke off of a high ring piston and the ring broke off when it went by the port, so I moved the piston so the ring was in the exhaust port and fished the rest of it out. Now I only have a bottom ring on that piston. The good part is I still have 110lbs compression in that hole and I still see upper 80's w/ my Viking!

This is not the first motor I have done this with and I plan on fixing it this winter with a low ring piston.

I always wanted to take one of those second effort mod-vp stage 1 2 3 or something like that and resleeve it to the same size as a 3 liter looper OMC. Pistons would have to be made but i can`t help but wonder how it would perform. I drove an Allison XR2002 around 1987 or so with one of these motors at 2.6 liters (stock) and it was very impressive for the day.

DB

I couldn't remember if Land and Sea offered a big bore conversion for cross flows. This is from the 1995 Land & Sea catalog. Some usefull information, hope nobody minds.

http://i35.tinypic.com/2bwryt.jpg

Please tell us your prop pitch and rpm. to reach upper 80, s thanks.

Quote:

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Originally Posted by terry taylor

Please tell us your prop pitch and rpm. to reach upper 80, s thanks.

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Top speed so far is 87.6mph/gps @ 6500rpms. Thats with a 30p inline chopper that I recently aquired. My old top speed with another 30p inline chopper that I got with my boat in 1997 was 85.7mph/gps @ 62-6300rpms and that was in optimum conditions. I ran 87.6 in poor conditions, warm temps, sticky water, and 30-40lbs of gear in my boat, so I think 90mph may be within reach :rolleyes:.

I took a close look at both props, they both have the same part numbers. My old one has the line cutters, and the cup runs from the trailing edge of the blades, all the way around the tip, almost to the leading edge of the blade. My new prop has much thinner blades and the cup is only on the trailing edge of the blade, it stops right where the blade starts to turn round.

One thing I noticed while driving the boat whith the old prop is when at or near top speed the boat would continuously climb then touch down, like a very slow porposing
motion. The new prop seems to carry the boat well and is more predictable.

1990 XB 2002 CompPro (cut down lip), 10" set back, 2.6 GT bone stock less Boyesen reeds, solid mounts, Bob's cone and torque tab (even still has the complete air box) with a unworked 29" SRX. 94.9 GPS at 6800.

2001 SS 2000 Excell (cut lip), 10" set back, 80 235 light porting, V stacks, gold fly wheel, Boyesen reeds, solid mounts, ??? cone, weld on tab unworked SRX 94.2 GPS at 6800.

:cool:

The cross flows are known for snagging rings on the port windows. As a mater of fact I am fixing a 90hp for a friend of mine that snagged a ring last week. The key is to bevel the port windows when you rebuild it. They last a lot longer.

Quote:

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Originally Posted by Bartyparty69

The cross flows are known for snagging rings on the port windows. As a mater of fact I am fixing a 90hp for a friend of mine that snagged a ring last week. The key is to bevel the port windows when you rebuild it. They last a lot longer.

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Really? I say bull****. Never happened to me and I have run Xflows since I crawled in a boat… Had a few blow… never a locating pin that would cause a loose ring. ;)

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Any one? :eek:

Quote:

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Originally Posted by Forkin' Crazy

1990 XB 2002 CompPro (cut down lip), 10" set back, 2.6 GT bone stock less Boyesen reeds, solid mounts, Bob's cone and torque tab (even still has the complete air box) with a unworked 29" SRX. 94.9 GPS at 6800.

2001 SS 2000 Excell (cut lip), 10" set back, 80 235 light porting, V stacks, gold fly wheel, Boyesen reeds, solid mounts, ??? cone, weld on tab unworked SRX 94.2 GPS at 6800.

:cool:

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Thanks Forkin, been wondering that for a long time. :thumbsup:

Quote:

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Originally Posted by Forkin' Crazy

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Any one? :eek:

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The coolest sound in the world!

From this morning.

http://i37.tinypic.com/2uoqgd0.jpg

I want to be in the 90mph club really bad.

Quote:

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Originally Posted by Forkin' Crazy

Really? I say bull****. Never happened to me and I have run Xflows since I crawled in a boat… Had a few blow… never a locating pin that would cause a loose ring. ;)

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I keep looking over my post and I still don't see where I posted locating pin causing any problems. Maybe your seeing something I don't. I personally have seen a couple go down when the ring gets caught on the sharp edge of the port window in the sleeve. As for a known problem. Im just taking the word of a certified omc tech who had a brand new 235 that went down with the same problem after less then ten hours. But I suppose what the f*** would he know. Ill ask him if there was a bulletin sent out by omc on it. I also grew up on cross flows. Literally. My dad worked at OMC.

Quote:

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Originally Posted by Bartyparty69

I keep looking over my post and I still don't see where I posted locating pin causing any problems. Maybe your seeing something I don't. I personally have seen a couple go down when the ring gets caught on the sharp edge of the port window in the sleeve. As for a known problem. Im just taking the word of a certified omc tech who had a brand new 235 that went down with the same problem after less then ten hours. But I suppose what the f*** would he know. Ill ask him if there was a bulletin sent out by omc on it. I also grew up on cross flows. Literally. My dad worked at OMC.

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I agree! I worked at OMC Engineering in the late 60's and 70's when they came out with that d*** ring. Run them high, run them low, they are a port grabber. They will run longer if you raduis the port edges. Just my .03 worth.

Your right, I'm wrong. Happy now? Oh and I never said that you said anything about a lost locater pin, but that is the only way I can see to hang a ring in a stock port. Or if your rings got caught in the port (could happen on any motor but not as likely on a crossflow), sounds like the machinist didn't champher the port when he bored it. I use to work at an OMC dealership in the early 80's for what that is worth. Well good for your dad working for OMC. How that proves your case is beyond me. I have literally hundreds of hours on OMC Xflows, but that realy doesn't mean **** either I guess. Have a nice day. ;)

Quote:

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Originally Posted by Bartyparty69

I keep looking over my post and I still don't see where I posted locating pin causing any problems. Maybe your seeing something I don't. I personally have seen a couple go down when the ring gets caught on the sharp edge of the port window in the sleeve. As for a known problem. Im just taking the word of a certified omc tech who had a brand new 235 that went down with the same problem after less then ten hours. But I suppose what the f*** would he know. Ill ask him if there was a bulletin sent out by omc on it. I also grew up on cross flows. Literally. My dad worked at OMC.

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Quote:

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Originally Posted by Forkin' Crazy

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Very cool! For a 30 yr old John Deer motor ;) That's a bit better than when you were down here.

Quote:

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Originally Posted by 194268

I agree! I worked at OMC Engineering in the late 60's and 70's when they came out with that d*** ring. Run them high, run them low, they are a port grabber. They will run longer if you raduis the port edges. Just my .03 worth.

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I have to agree with Forkin on this, if it was a problem it seems that it was a QC problem.

Also, have you seen the port shape in the 9 pages of performance (modifications to omc 235 - v6 engine)

I tried to search for the 9 pages, no luck. Can someone post a link?

Quote:

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Originally Posted by John J 80`viking

Also, have you seen the port shape in the 9 pages of performance (modifications to omc 235 - v6 engine)

I tried to search for the 9 pages, no luck. Can someone post a link?

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Send me your email addy. Have it on a PDF. :)

Man, I've been waiting on this thread to come around. I got a 79 Viking with a '83 2.6L XP......been GPS 79 MPH with a 26" through hub turbo out of the box. Want to find a suitable SRX to get it well into the 80's. Was told when I bought the boat it had been 90+ with a 30" cleaver, but most dont run a cleaver on a V-pad 'stream.

Anyone got any good info on the 2.6L XP's?

Quote:

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Originally Posted by coupe

but most don't run a cleaver on a V-pad 'stream.

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30 cleaver is my favourite prop on the Viper.

I know a bunch of us could ramble on for a while about your motor, but the most important things for keeping it from blowing up are always use fresh high octain fuel, correct timing, and never over prop your motor. Do a cross flow search in the tech forum and feel free to ask if you can't find what you need.

You can do way better than that turbo prop. An SRX, chopper, Mazco, or any other over hub high perf prop in the 27-30" range should easily get you into the 80mph range.

That 2.6 xp will eat up Merc 2.4's all day long.:)

Forkin...Check PMs. Thanks.

It was in a gif not a pdf, but sent any way. ;)

Quote:

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Originally Posted by John J 80`viking

but the most important things for keeping it from blowing up are always use fresh high octain fuel, correct timing, and never over prop your motor.

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:iagree: :iagree: :iagree:

A 1983 XP 2.6 in 1986 w/a 26" Raker @ 6300 (8% slip) and 77 MPH's (indicated)
<a href="http://s290.photobucket.com/albums/ll255/Instigatorspixs/?action=view&current=conquestatspeed.jpg" target="_blank"><img src="http://i290.photobucket.com/albums/ll255/Instigatorspixs/conquestatspeed.jpg" border="0" alt="Photobucket"></a>

Same boat w/a looper.
<a href="http://s290.photobucket.com/albums/ll255/Instigatorspixs/?action=view&current=conquest.jpg" target="_blank"><img src="http://i290.photobucket.com/albums/ll255/Instigatorspixs/conquest.jpg" border="0" alt="Photobucket"></a>

Not a flow but a cleaver on a Stream.
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Here are the 9 pages (thanks Forkin). This isn't the first time this has been on S&F. I couldn't find it, probably because of the new format. Some great info!:thumbsup:

Credit for this work goes to Alan Stoker.

http://i38.tinypic.com/28lc0ea.jpg
http://i38.tinypic.com/ibe2ps.gif
http://i38.tinypic.com/34pgqjo.gif
http://i37.tinypic.com/fyocar.gif
http://i33.tinypic.com/2i95thk.gif
http://i36.tinypic.com/jud1ye.gif
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http://i38.tinypic.com/nboy01.gif
http://i38.tinypic.com/33dz9ll.gif

Correct me if I'm wrong (and I probably am), but I was under the impression that when you modify the 235 according to the 9 pages above it basically tuns it into a race only type of engine. Is this correct or if one is built like this it can have good longevity aswell?

I am no Guru, but IMO other than the added stress from the tighter heads and the actual power increase I don't see anything in the 9 pages that would turn a 235 into a time bomb.

The biggest thing I think you could do for reliability is to use low ring pistons.

They recomend retarding the timing back to 26 or 28*, and recomend 62-6800 rpms which is conservative for a race motor.

Does cutting the piston skirt cause more piston slap or any longevity problems? I asked one outboard guru about this and he said it causes no problems and offered a pretty good explanation but I still wonder.

Never had any problems. The XP/GT motors came with the piston skirts cut from the factory.

The 9 pages is too much for an every day engine, the bigger ports with smaller radius mean less ring support and more chance of bridge movement. A 5/8 or 3/4 cutter would be better. Any time you add power from porting, compression etc something has to suffer and that is generally longevity. The 9 pages was meant for race engines, I cant take full credit but had a LOT to do with them. They were also done early on before even fire cranks etc at the end we ran a lot more rpm than mentioned in those pages and not for short drag type burst.

I also dont agree these engine are port grabbers, if they do its because of any one of a number of reasons.

Quote:

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Originally Posted by racer

The 9 pages is too much for an every day engine, the bigger ports with smaller radius mean less ring support and more chance of bridge movement. A 5/8 or 3/4 cutter would be better. Any time you add power from porting, compression etc something has to suffer and that is generally longevity. The 9 pages was meant for race engines, I cant take full credit but had a LOT to do with them. They were also done early on before even fire cranks etc at the end we ran a lot more rpm than mentioned in those pages and not for short drag type burst.


I also dont agree these engine are port grabbers, if they do its because of any one of a number of reasons.

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About what RPM did these motors modified to the specs in the 9 pages make the most horsepower at ?

Mid to High 6k range later on in the low 7k range but they had more done to them

Last saturday at the NEODA end of season cookout.

http://i54.tinypic.com/2a4vi45.jpg

Quote:

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Originally Posted by racer

The 9 pages is too much for an every day engine, the bigger ports with smaller radius mean less ring support and more chance of bridge movement. A 5/8 or 3/4 cutter would be better. Any time you add power from porting, compression etc something has to suffer and that is generally longevity. The 9 pages was meant for race engines, I cant take full credit but had a LOT to do with them. They were also done early on before even fire cranks etc at the end we ran a lot more rpm than mentioned in those pages and not for short drag type burst.

I also dont agree these engine are port grabbers, if they do its because of any one of a number of reasons.

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So are you saying that with an everyday performance engine you should leave the ports a little more round than mentioned?

so where is the porting on a CCC compared to these?

I know I have seen pictures of the ccc ports here somewhere. They were a lot wilder. I think Chris Carson posted them if I remember correctly.

Yes for lake use they should have larger radius in the corners. Ports are similar but different than a ccc as it is a larger bore than a ccc and meant to push more weight so the ports are a little lower and less compression. Ports are as wide as the block/bore will allow.

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Scribed also.... missed this one! Gary