1979 140 heads

[monte100727]

i have 1979 140 without heads that I plane on rebuilding, I also have heads off a 1978 85 that i would like to use, the 85 was a 3.375 bore with 80 cc combustion chamber heads, i know these heads will bolt on to the 140 but the compression ratio may be to high, i can port the chambers to required cc if they are to small if any one knows what they should be to run on pump gas,thanks

 

[emdsapmgr]

Re: 1979 140 heads

An interesting question. Not so sure the 85 hp heads will fit properly on your 140. The 85 hp engine is a 92 cubic inch block (small bore.) The 140 is a 99.6 cubic inch block, (large bore.) Not sure the sealing ring face of the head will match the head gasket surface on the 140 gasket. Or (conversely) that the 140 cylinder lip will match the ring seal face on an 85 hp head gasket. Also, you may find the dome on the 140 pistons may hit the underside of the smaller (narrower) 85 heads. You need to do a trial fit without any head gasket-bolt the heads on lightly, but snug and hand turn the flywheel-check for binding. When warmed up to normal operating temps, the piston will grow .030 inches in height. When the final head gaskets are installed, this will resolve (compensate for) the .030 clearance issue. Let us know what you find.

 

[monte100727]

Re: 1979 140 heads

well thanks but yes the heads will bolt on as the gasket suface is the same the 1978 85 had the same 3.500 haed gasket as the 140, the 140 pistons had a taller compression hight of 0.20 , 0.10 on the dome and 0.10 in the cylinder, as the 85 pistons were short in their cylinder 0.10, so the 140 piston will come to the top of the cylinder plus 0.10 in dome hight, so clearencing aside the real concern is compression ratio as i have checked fitment in every other way and they will bolt on, but will it run on pump gas I dont wont worry about detination or adding octane booster but that may be an option to.

 

[emdsapmgr]

Re: 1979 140 heads

If clearance is not the issue, the next thing to do is to try the heads and see what the compression is. My stock 79 85 hp ran 120 to 125 compression after it was overhauled and broken in. The 140's ran quite a bit higher in stock form-as much as 135+. Bolt a head on one side and check the cranking compression. The 77 140's were designed to run 86 octane leaded or lead-free at 28 degrees [no mention of ethanol blends.] My preference on this older high compression engine like a 140 crossflow, is to run 92 octane- since most fuel today is 10% ethanol. You could back off the timing 3-4 degrees if you wanted to run 87.

 

[Dhadley]

Re: 1979 140 heads

The pistons will hit the small heads. You can make them work by cutting inside the combustion pocket. Your theory is correct, it will increase the compression and you'll have to use at least 93 octane. Rejetting will be required too. However, simply doing that alone to gain performance may backfire. Depends on what you're looking for and what else you're planning to do while you have the motor apart.

 

[monte100727]

Re: 1979 140 heads

thanks Dhadly sounds as you know your old johnsons well, as i already know this areas on both sides of the dome need minor clearencing on the heads as the opening between the humps is smaller do to the larger humps, I have two different sets of carb and 4 different jets 54, 56, 64, 67 1 set of 1 5/16 carb and a set i ported to 1 1/4, i am going to do a little clean-up on some intake and exhuast passages but not much you can do, what about raising the intake or exhuast ports in the cyclinders,this could change the power band but dont want to do it as i might go the wrong way any suggestions here would looked at, also i have intake fillers, exhuast tuners and hump back exhuast,timing will probably be set at stock 140 for starters.thanks and I read 135 psi before and would come in around 9.1 compresssion ratio based on the 14.7 into psi equation but I dont know this to be true and a 2 stroke will increase compression with rpm if i am correct.

 

[tashasdaddy]

Re: 1979 140 heads

Dhadley is an expert on racing engines. he does know his stuff.

 

[emdsapmgr]

Re: 1979 140 heads

Any crossflow will develop much more compression when running. That's why you take the compression at cranking speeds. I'd run the largest carbs you have, the 1 5/16", as they will flow the most air/fuel. You can start out with the .064 high speed jets, then start reading your plugs to see how they look. Then make changes up/down depending on how those jets run.

 

[Dhadley]

Re: 1979 140 heads

If you're using the 85 block I'd simply open the ports to the stock 140 sizes. A stock 140 (newer 115 style) is capable of 6900 with Boyesen reeds. A lot of where you're going depends on where you're at now (performance-wise). If your hull isn't capable of responding to very minor torque increases then I'd just simply make the 85 a 140 and use the 1 1/4" carbs.

Clearancing the heads will be a little more involved than you may think. You need to clearance them so they don't hit without a head gasket.

 

[monte100727]

Re: 1979 140 heads

yes i am using 85 block do you know the diameter of 140 port or suggest a size,and yes boyesen reed are going in, the boat is a 1985 mastercraft cajun 16'6'' shallow, stepped hull very nice for the year, it responds very good to changes, motor hight, prop pitch, and tunning on last motor,i just wont to get the most out of this motor why im going thru it,i have built and tuned several highend car motors so i feel i can do any saggested mods with professional result, porting ,epoxy filler, aluminum welding,stand alone fuel injection with mega-squirt computer will be future project if anyone is interested im in ft. myers fl. to assist on doing efi conversion on older cross flow motor this would be fuel only or fuel timming very cool and simple design.

 

[Dhadley]

Re: 1979 140 heads

I'd just look at a 140 style block (any V4 crossflow block with the tuned exhaust) and get the diameter of the intake and exhaust. Can't remember the sizes but it's a common cutter size. The blocks all used the same centerline so it's a very simple matter of opening the existing holes.

One thing to keep in mind if you're looking for rpm in excess of 6000 or so - the 1978 motors used a small center main on the crank. Not really sure I'd go after a lot of rpm with that crank.

The fuel injection stuff has been done to death. Whatever you do just keep in mind that when it's all said and done you'll still have a 1978 crossflow which is 1950 technology at best. No matter what you do it'll not likely make the torque of either style of V4 looper.