V4 Crossflow Question

[71V153]

Any truth that leaving the exhaust filler blocks outa a bubble back will gain a couple hundred rpm top end?

Guy on another site swears it's true ...?

[olboatman]

Scribed. Gary;)

[evilrude 1]

I would think leaving the filler blocks out would hurt exhaust flow and slow it down.

[EMDSAPMGR]

I would think that the engineers at OMC would have discovered that truth long ago and would have reduced the cost of those bubble back engines-if it were true.

[6Killer]

I would think that the engineers at OMC would have discovered that truth long ago and would have reduced the cost of those bubble back engines-if it were true.

Dude, don't ruin this!

[wired247]

I tried it both ways on the last 115 turned into a 140 on my boat. I had a bubble back and installed it during the rebuild and it took me a while to find a good set of stuffers. Without the stuffers I was able to run 62 MPH with a 23 pitch prop . The mid range sucked and off idle was terrible. With the stuffers it ran 60 MPH and pulled hard on the mid range and off idle. It had the stuffers in it when I sold the motor and the buyer was very happy with it.

Had to cut the lower section out of the divider to turn it into a 140 spec motor. Be careful if you ever do that. Nicked the water jacket and had to weld it up. D shaped the ports . Wish I kept that motor.

https://imagizer.imageshack.us/v2/1084x814q90/109/aidu.jpg

https://imagizer.imageshack.us/v2/1084x814q90/833/141zy.jpg



Had a string of V4 Johnson crossflows on that boat over the years and I always thought they were good motors. The original 90 from 1981 looked like new when I broke it open after nearly 30 years. They really like increased compression.

[powerabout]

Lots of exhaust stuff on various omc's is there to make an all round fish engine and not a kilo engine

[71V153]

I tried it both ways on the last 115 turned into a 140 on my boat. I had a bubble back and installed it during the rebuild and it took me a while to find a good set of stuffers. Without the stuffers I was able to run 62 MPH with a 23 pitch prop . The mid range sucked and off idle was terrible.Thanks 247, that's kinda what I envisioned. Didn't think it'd do much for mid range. But if I can pick up 2 mph top end it's worth a try.

Boat is 15' Baja SS. With a stock 140 & 13 3/4 x 24 SRX chopper it comes outa the hole like a freakin rocket & once hooked up pulls very strong all the way to the top. (Just under 63 mph.) I know a lotta guys with faster boats but not many with one that's quicker. I might be willing to sacrifice a lil hole shot'n mid range for 2mph on top?

Regardless. New project motor is a '92 88 special block. Divider is cut, scalloping the block'n pistons, porting, etc. Ultrafast is sawing on it so I trust it's in good hands, says he might have it done by the end of the week. Mebbe a pipe dream but I'm thinkin the mods might offset any ill effects from running without the stuffers?

Any thoughts on lightening up the flywheel? I got like half a dozen of em so's if'n it don't help I can stick a stock one back on.

Thanks for the input y'all. Yeah, don't be a party-pooper emd ... Heh heh heh

[wired247]

At least with the 88 block you'll have plenty of port side wall. D porting the 115/140's is an exercise in holding your breath and hoping for the best although come to think of it a '92 88 is going to have early 115 ports anyway . It getss awful thin in those bridges.

[71V153]

At least with the 88 block you'll have plenty of port side wall. D porting the 115/140's is an exercise in holding your breath and hoping for the best although come to think of it a '92 88 is going to have early 115 ports anyway . It getss awful thin in those bridges.Hear that, best to stay away from them. Yes the '92 88 block has the same (stock) porting as the 115 & 140.

[dompie99]

Hi great job.. I had one of those 140hp 199ishhh and I had one of those Glastron copy ( Sunray SS480 )) the engine was jacked 2'' and with a 25'' big ear chopper prop (Quicksilver) it ran 65-66 mph at 5800 rpm If i remember properly. But a LOTTT of chine walking OMG.

PS: with a lot of engine noise too, neighbour were P.O.....

[dompie99]

hummmmmmmmmm great beer add..lolllllllllll

[wired247]

Yeah, Thats what kept from going any faster with mine. The chine walk was unbearable before I finally installed the hydro steering. That and the lack of good 13 spline props although the V6 lower will swap in. Those 140's are good strong mid range motors. Great for small ish ski boats. They weigh close to nothing and are really good on the gas. Might have to build another and swap my current 2.5 onto something different.


I drink more than my share of that Torpedo.

[71V153]

Forgot to mention the Baja can get nearly uncontrollable at 63. Bobs true tracker does help. But the chine walk comes on hard'n fast sometimes. Ain't no steerin or powering through it in this case.

[wired247]

My boat was an uncontrollable mess over 60 MPH. There was no seat time BS that was going to straighten it out and I had 30 years of seat time behind the wheel of that thing. It was a disaster. I put big HP motors like a 225 and a 260 on it and it would power through to 75 or so but that would be with the trim down all the way and the bow of the boat inches off the water. Any trim and it would be all over the place. Now it scoots well into the 80's and its like driving it 55 used to be.

1. Solid motor mounts.
2. Hydraulic steering . Biggest change by far.
3. Prop centerline over the pad.
4. LWPU
5. Torque tab.
6. Prop selection. Most neutral steering props I've run were the SRX's but I get best speed out of choppers.

The old 90 would top out at 54 MPH which is respectable for a 90 and the 140 would top at 62 but thats only because I flat couldnt drive it safely any faster. It was all over the place. The checkmate guys dont like to adnmit it but there isnt much difference between a mate and a baja. Get that steering in order and "chine walk" will be a memory.

[olboatman]

Speaking of OMC 140s -- I have a 1984--- I was thinking of changing the reeds -- any suggestions for makers and does it already have intake stuffers? Thanks in advanced. Gary

[wired247]

Speaking of OMC 140s -- I have a 1984--- I was thinking of changing the reeds -- any suggestions for makers and does it already have intake stuffers? Thanks in advanced. Gary

It "should " have intake stuffers. If it doesnt they can be found in early 80's 90 HP motors too as well as some of the V6's. 140's should all have them but stuff gets taken out and motors that should have things dont sometimes.

I ran Boyesens and chris carson reeds in mine. I like the idle of the Carson reeds better and they were easier to get to lay flat plus the fact I like to support real people who will talk to you on the phone about their own products. .

[olboatman]

Thanks 247 I also like the way Chris is always very helpful here on S&F. Gary

[71V153]

Get that steering in order and "chine walk" will be a memory.Perhaps but I dunno, it really ain't all that sloppy?

Interesting that you acheived the same kinda speeds. My best with the 90 was 54.8, 62.9 with a 140.

[wired247]

The Checkmate guys wont admit to it but the Bajas and Checkmates ...at least the smaller ones... are close cousins. Ive heard Baja even got their first hull molds from Checkmate. Same town in Ohio. Its sloppier than you think. Like I said. Been there.

[71V153]

The Checkmate guys wont admit to it but the Bajas and Checkmates ...at least the smaller ones... are close cousins. Ive heard Baja even got their first hull molds from Checkmate. Same town in OhioBucyrus, OH to be exact. Yes the cousins lived right down the road from each other. Lil incest is understandable ...