[Pitdad]

MerCruiser offered several inline 4 cyl engines for stern drive use. Most of MerCruiser's inboard powerplants were/are Chevy/GM based. All were/are identified by their horsepower rating, not their cubic inch displacement.

The 120 hp was for all intents and purposes a 1962-1967 Chevy II, 153 cubic inch, 4 cylinder, 3 7/8" bore x 3 1/4" stroke (same as the anemic 307 CID Chevy V-8). A cast iron head with "siamese" intake port design identical to the Chevy 194/230/250 6 cylinder head, lots of them were raced, but if you wanted to really make the horsepower, you needed to "de-siamese" the port and have individual runners for each cylinder. Later, the 120 hp engine would be the short lived 151 4 cylinder used in '77-'78 Chevy Monzas. It had a 4" bore x 3" stroke (same as 302 CID Chevy V-8) and used a factory "de-siamese" port design. Still cast iron. Rare. And very prone to crack. This engine was NOT the 1979 and later Iron Duke 151 CID (2.5L) 4 cyl as the Iron Duke was a cross flow cast iron head. Pontiac's Super Duty engines, which were popular for a spell as midget, Daytona Dash, and mini-stock engines were based on the Iron Duke.

The 140 hp Mercruiser also found it's way into midgets, provided the club's rules allowed a 3.0L engine. It was a purpose built boat/industrial power unit with a 4" bore x 3.6" stroke. It was never offered by GM in any street vehicle and does NOT mirror any Chevy street car engine because of the 3.6" stroke. This engine also has the better cylinder head design, but again, is heavy cast iron.

The 170 hp Mercruiser is the 3.7L engine originally asked about in this thread. It is a purpose built, cast aluminum block with iron cylinder liners that uses a cast iron 460 Ford V-8 head. At approximately 230 CID, I think this engine falls out of the rules for a lot of midget clubs and sanctioning bodies, but I have no doubt that some found their way into midgets (everything else did, outboard boats, motorcycles, tractors, etc.) I don't think you will find wide spread use of the 170 hp engine in automotive applications or racing applications as they were never that plentiful and the iron head on the aluminum block, along with some other design challenges, prevented them from being an effective alternative.

What I'm inferring from your request for information is that you are building a 3.7L engine and want to know what speed equipment might have existed in the marketplace. I don't think you'll find much, and obviously when you mention "MerCruiser" and "Midget Engine" together, the assumptions people make are that you're talking about the cast iron Chevy-based engines. If you are pursuing the build on a 3.7L, I suggest, if you haven't already, looking at a couple of old posts in other message boards regarding the engine. The first is from HAMB where a LENGTHY discussion that occurred 14 years ago https://www.jalopyjournal.com/forum/...banger.256713/ I couldn't even get through the whole discussion at the time. The second is a much more manageable discussion on hotrodders.com https://www.hotrodders.com/threads/3...ruiser.197289/

I hope this helps.

[opnwhlmnd]

I had a midget with a Chevy II/Mercruiser engine back in the day like middle 80s I believe. It had a Duggen Aries aluminum cylinder head that made the Chevy II a cross flow head instead of the stock cast iron intake & exhaust same side style. The Mercruiser cast iron head flowed better than the stock Chevy head and was preferred for those running Chevy II all cast iron midget engines. I think the Mercruiser block was also stronger in the crankshaft webs than the Chevy II. If I'm mot mistaken Fontana bought the blueprints to the Duggen Aries head.

I believe the first Mercruiser 170 HP engines seen in midget racing were a 460 Ford block cut in the middle using only the left bank of four cylinders. The cylinders were re-sleeved for smaller diameter pistons and the crank stoke was shortened to lower the CI to be legal for midget racing. Don Kirn of Kirn Racing Engines in St Louis did one for me. I never raced it as I switched to sprint cars before we could test it. Later on as Pitdad said above there were specialty aluminum blocks built which is the engine in your picture. SESCO did the same thing with using half of a V-8 Chevy. Think Dan Boorse's dad had a lot to do developing the SESCO.

To answer the OP questions on finding parts for his Mercruiser. All internal engine part specs except the crankshaft should be the same as the 460 V-8 Ford.