OMC Cross Flow Gurus Needed

[Bob T]

I have an 1979 175 Johnny on a 19' J Craft.It runs~65mph.The motor has Boysen reeds,relieved and "dry stacked" exhaust, and modified air box.My mechanic was cleaning his shop and found a set of 235 heads and carbs which he gave me :thumbsup:Can I just bolt these on and go? What kind of HP and MPH increase might I see? Any potential issues? Its the end of the season here and I'm going to do the swap over the winter.Thanks, BT

[Riverratt]

What year 235 are the heads and carbs off of? Post the part numbers. If the heads are from a 2.6 they will not help. The carbs may not be much different than what you have either. Do they have choke plates or did the 235 carbs he gave you use the enrichener?

[rockman69]

hey,
i did this same exact thing to my '80 150!! do it! :thumbsup:
firts things first, just as ralph said, figure theseout and go from there.
iput on 872-873 heads (small bore), 1 3/8 carbs from a 235 (had the nipples on top i just put caps on), ghet your self some intake stuffers too. i did all this and it really woke it up! keep us updated!
Dr. D

[EMDSAPMGR]

The 81 and later 235's (and later 175's/2.6) were big bore blocks their heads were different. Stick with the small bore 235 heads Rockman mentioned and you'll notice the difference. Probably gain 10# compression over the stock 456/457 heads. Those intake stuffers from the 200/235's are a worthwhile and easy addition. With these mods, I'd make sure you are running a pair of unlimited packs. If you use the 235 1 3/8" carbs, they are probably jetted to flow too much fuel for your low-port engine. Count on spending some time on the water to rejet downward.

[Forkin' Crazy]

Big bore started in 1980, not 1981.

I think the best small bore heads are from a 76 or so 200.

[wideglide55]

I'd leave total timing at about 26degrees and make sure to use fresh 93 fuel.

[rockman69]

Big bore started in 1980, not 1981.

I think the best small bore heads are from a 76 or so 200.

actually, Al (Stoker) mentioned that the 78-79 235 heads were better for upping comp. over the 76 200 (cuz i inquired) had a chanc e to get both.
give up the no.s on the heads, let us know whatu yo got.

[Bob T]

Sorry I haven't replied earlier.Daughter's having an engagement party tonight and I've been busy 'washing floors'..The carb numbers are 334 329 and have a 1 5/16 bore. I believe this is bigger than my current carbs.They also have 'pull over jets' that my current carbs do not.The head numbers are 328 324 and 328 326.The parts came from a newer 'bubble back' 175,which I believe is a detuned prop shaft rated 235.The powerhead was replaced in 1990 and I'm not sure if it's a 149 or a160 cube block.Is there a quick way to tell?.Thanks for taking the time to clue me in!!! BT

[Forkin' Crazy]

actually, Al (Stoker) mentioned that the 78-79 235 heads were better for upping comp. over the 76 200 (cuz i inquired) had a chanc e to get both.
give up the no.s on the heads, let us know whatu yo got.

I got 'em both. ;)

[Bob T]

Thanks for the replies! River Ratt-The carbs have no choke plates and are plumbed for the 'enricher" FYI,I converted the original carbs to to that system i.e,enrichers.Rockman ,I'm confused about the ''intake stuffers". Do you mean the exhaust stuffer blocks? Please enlighten me!! BT

[Riverratt]

The heads are off a 160 and you have a 149 block

[Bob T]

River... Hate to be the dummy, but.how can you tell that it's a 149 block?

[Riverratt]

River... Hate to be the dummy, but.how can you tell that it's a 149 block?
The 2.6 did not start until 1980 so the 79 235 was a small bore. The 80-85 235 was bigbore and the 86 and up 175 was the bigbore. The bore of the 149 is 3 1/2" and the 160 was 3 5/8"

[EMDSAPMGR]

The flatback engines were all smallbore 149 blocks. The 1 5/16 carbs should work fine. I'd run them jetted the way they are till you make all your mods-then get into the jetting issue. Likely they may still be slightly rich on top end. They'll be an improvement over the 175 carbs.

[Forkin' Crazy]

Thanks for the replies! River Ratt-The carbs have no choke plates and are plumbed for the 'enricher" FYI,I converted the original carbs to to that system i.e,enrichers.Rockman ,I'm confused about the ''intake stuffers". Do you mean the exhaust stuffer blocks? Please enlighten me!! BT


The intake stuffers are rubber blocks that go in the intake next to the reeds blocks. They increase the crankcase compression.

[Bob T]

Thanks guys, for all the info.BT

[rockman69]

I got 'em both. ;)

Oh sure...Rub it in! :D

[Bob T]

Hey Rockman.What kind of performance increases did you see?What kind of boat is your "150" on? BT

[B.Leonard]

I have a set... $50 shipped

-BL

[rockman69]

Hey Rockman.What kind of performance increases did you see?What kind of boat is your "150" on? BT

Well, kinda hard to give specific no.s since didnt really keep track b4 the add-ons. but what i did notice is more torque, better throttle response, (although i rebuilt the carbs too so im sure that played aroll.) more mid range grunt and even some on top end (boat is old, heavy, and prabably wet since it stayed in the water all season for 37 years!) Boat is a '71 and the brochure states dry weight without motor is 1650lbs. boat, motor, fuel, rigging, lifejackets, anchor, me (215), a buddy (180) and a can of chew i would guesstimate at close to 25-2600lbs, topped out @ 51 gps. 14.25 x 21+ @ 5500. prop calc. figures 13-17% slip, depending on 21 or 22 pitch (states add 1" for cupped props)
any way, just picked up a '78 vking that will host the motor next year. im sure ill pick up a few mph considering the vking to be about a HALF TON lighter than the "Banana" (yellow trihull)
hope this helps, i had fun doing these ad-ons, im a "body mechanic" (Chiropractor) and it was nice to get my hands dirty! :reddevil::D

If your Dr. keeps Gojo hand cleaner next to the luffa in the master bath...you might be a... nevermind
Dr. D