V4 crossflow differences

[EdwardNigma]

This is mostly idle curiosity, but I'm wondering what, if any, are the major differences between the crossflow V-4s. I've seen a lot of suggestion here that there isn't a significant difference. I currently have a 1974 115hp and a 1977 140hp and other than the bubble back I can't see much difference.

 

[Dhadley]

Re: V4 crossflow differences

Port timing is the major difference in the powerheads. Obviously with better port timing you use bigger carbs. The combustion chambers are slightly different also.

 

[EdwardNigma]

Re: V4 crossflow differences

So there really is a power difference between them and not just some dynamo tricks and a badge?

 

[Dhadley]

Re: V4 crossflow differences

Technically yes, there is a difference. But both have the same bore & stroke, same intake, same ignition, same prop family and same gear ratio so if both were set up at 54-5500 or so on an average boat I doubt you'd see much of a difference. Once you get close to 6000 the difference will start to show.

 

[emdsapmgr]

Re: V4 crossflow differences

Though the crank/rods and pistons are generally all the same, there are other differences in the engines. The 140 block is ported higher, has larger throat carbs, tighter heads, intake manifold filler blocks, a different exhaust tuner in the midsection, in additional to the bubble exhaust. Most of these differences are not apparent until you start to take the engine apart.

 

[EdwardNigma]

Re: V4 crossflow differences

*snip*<br />", intake manifold filler blocks,"<br />*snip*<br /><br />I've seen those mentioned a few times. What are they / what do they do? Is it one of those things that can be removed or adjusted for performance gains?

 

[Dhadley]

Re: V4 crossflow differences

The intake filler blocks are rubber pieces that fit behind the reeds. The theory is that they fill "dead" space and force more fuel mix into the by-pass area and therefore thru the ports. At the rpm we're talikng about (the range the stock reeds work at) they really don't do much. In fact OMC quit using them. Once you get into the rpm range that stock reeds start to give up (flutter) that space becomes more critical.<br /><br />Your 140 will have a different tuner because the 1977 140 was when they started using the "new style" adaptor plate and center section. If you look at 135 adaptors and tuners (like in 1974) you'll see they are the same for an 85 or 115 or 135. Again, at the rpm we're talking about it really won't matter.

 

[EdwardNigma]

Re: V4 crossflow differences

So what would it take to get 6000 - 6200 rpm out of the 140? Would it be worth it for a boat used for water skiing / cruising?

 

[Dhadley]

Re: V4 crossflow differences

A bubble back V4 crossflow set up at that rpm on a ski boat will produce many hours of good, solid, reliable fun. I've had many ski boats set up like that over the years and folks were always amazed at how good I could pull doubles with a V4. Set up is the "secret".

 

[EdwardNigma]

Re: V4 crossflow differences

That begs the question "How do you set up a V-4 for those revs?" Is it just prop and elevation on the transom or is there engine modification involved? Yes, I'm fishing for details.

 

[Dhadley]

Re: V4 crossflow differences

I'd do it with set up, just like you mentioned, with prop and X dimension. I'm not big on modifying a ski or fishing motor. That's always seemed better suited for the motor on the race boat. Besides 87 octane is expensive enough.

 

[EdwardNigma]

Re: V4 crossflow differences

Ugh, I hear that about gas prices. I'm lucky enough to live in a state with some of the highest gas taxes in the nation. I'll get to work on that setup when I get the boat back from the shop and assuming it stops raining anytime soon. I've got a thread started over in props for this boat and I'm looking forward to having more info to contribute to it. Thanks for all your comments Dhadley and emdsapmgr.

 

[Chinewalker]

Re: V4 crossflow differences

As Dhadley pointed out, set-up is where it's at. I see folks all the time who want to "hop up" their motor with bigger carbs and opening up the exhaust when in fact they're swinging a dinged up prop that's also the wrong size, the motor is flat on the transom and the hull is a mess. There's more easy speed available in most rigs than people realize. I spent two hours on a friend's 15-foot, 36mph runabout and picked up 4 mph with about $100 invested in a used stainless prop from eBay, jacking the motor up two notches on the transom and some time spent cleaning the bottom and filling in some dings in the strakes. That was a more than 10% increase in speed without even taking the cowling off the motor, or spending a month's worth of paychecks...<br />- Scott

 

[Dhadley]

Re: V4 crossflow differences

Amen Scott.

 

[EdwardNigma]

Re: V4 crossflow differences

This boat is in need of that kind of TLC. I just bought it through a guy that buys out liquidated marine businesses. Apparently it had been sitting in a storage building in Texas for over 20 years based on the expiration date of the hull registration and the amount of dust on it.<br /><br /> I was able to run it once last week for a short time and the motor was definitely in need of help. It started fine, but idled a little rough. I had it up to 29mph @ 4900 rpm for a few minutes before the motor seemed to lose power. At that point I could never get it past 2500 rpm. It ran smoothly at that speed, but just wouldn't wind up any further. It has a slightly dinged up 12.75" x 21" aluminum prop on it right now and it's mounted at the top hole in the transom bracket which I suspect accounts for most of the 4900 rpm issue.<br /><br /> As for the power loss, I'm hoping that's just a dirty carb problem. I replaced the original plugs with Champion L77JC4's gapped at .040" and checked the water pump output which seemed to be plenty. It went into the local OMC dealer this morning for a tuneup / carb rebuild so hopefully I get it back in good shape for prop/engine mounting testing.

 

[Dhadley]

Re: V4 crossflow differences

Don't run it anymore until you get both carbs clean. And that means soaking them in cleaner, not gas. Running it with clogged carbs is just asking for trouble. If a cylinder isn't getting gas, it isn't getting oil. Pistons are about 100.00 a piece.<br /><br />Lets get a compression reading before you go any further.

 

[87Aggie]

Re: V4 crossflow differences

You mentioned two motors above, which one are we talking about in the last few posts? Reason I ask, if it's the '77 140, is he using the correct plugs? I have a '77 140, and mine uses UL77V (I think that the right number) but they're surface gap plugs - no gap adjustment.

 

[EdwardNigma]

Re: V4 crossflow differences

We're talking about the '77 140. The store I usually buy plugs at was out of the surface gap plugs so I went to one of the alternate plugs. The seller ran a compression test at my request before I bought it and he reported around 115 - 120 psi per cylinder. My local OMC dealer has the boat right now for a tune-up / carb rebuild so they should take care of the cleaning and sanity checks on the motor for me. We'll see what it's like when I get it back tonight or tomorrow assuming that the skies don't open up again. Today is the first day since this past Saturday that it hasn't rained.

 

[87Aggie]

Re: V4 crossflow differences

Is it alright to use the L77JC4's? If so, what's the difference - performance wise?

 

[87Aggie]

Re: V4 crossflow differences

Anybody got an answer for my question about the plugs? I'm just wondering cuz I always put the surface gap plugs in mine because that's what it calls for.