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1987pachanga22 08-15-2011 11:31 PM

Street 350 engine
Ok I know this is going to get more then one opinion but here I go. I have an 89 Chevy truck that runs great but transmission is gone along with the rest of truck so the question is what do I need to do to reliably use that 350 in ma 89 Mirage 21 Intruder?

From what I understand its the cam and valves that need replaced? I have marine 305 that wasn't winterized correctly, can any of this engine be used with the truck engine to get me going?

cliff_m_b 08-16-2011 01:18 AM

freeze plugs should be replaced with brass ones and head gasket to stainless, not so bad for fresh water but still needs to be considered.

1BIGJIM 08-16-2011 06:24 AM

The tolerances in marine engines are different than auto because they are always under a load. IMO its just not worth it unless you enjoy turning wrenches every weekend when things do not work out.

1987pachanga22 08-16-2011 08:58 AM

I have heard about the tolerances being different but I can’t get any hard facts about it. I talked to others that say that unless you are running big power beyond stock that it is not recommended.

I don’t know! To me it’s all opinion.

1987pachanga22 08-16-2011 09:00 AM

Does anyone actually have experiance with using a street engine without doing a complete rebuild?

apollard 08-16-2011 10:43 AM

There are a lot of differences as mentioned before - gaskets, cams and maybe valves. However, for a *stock* Merc engine, clearances are the same as the ones in the Chevy 454 tech manuals for trucks/cars. For example, piston clearance is listed as .0025-.0035 in both. And, I'm pretty sure I read that Merc 7.4s and 454 MAGs used the same valves as the stock Chevy engines (but can't find the refrence now).

Iggy 08-16-2011 11:09 AM

Cams and core plugs. Those are the biggst change.
I don't think a stock street cam has the HP and Torque in the right RPM range. If the overlap or lobe seperation (can't recall which) isn't right water can be sucked back through the manifolds and into the cylinders at idle.

Best bet is find a copy of Dennis Moore's book on small block Chevy marine engines.

stevesxm 08-16-2011 11:16 AM

Originally Posted by 1987pachanga22 (Post 3480266)
I have heard about the tolerances being different but I canít get any hard facts about it. I talked to others that say that unless you are running big power beyond stock that it is not recommended.

I donít know! To me itís all opinion.

it's a myth. if you look in the merc factory manual, the numbers , tolerances and clearences are the same as GM. that motor will be cammed wrong but will work fine.

Dennis Moore 08-16-2011 11:18 AM

The biggest difference is in the truck heads. The the 1988-1995 TBI truck engines head is very unique and was never installed on any other engine.

They are made with a very restricted intake port that is completely blocked off on one side of the valve stem. This port was designed to give the intake charge a swirl at low speeds.

They are extremely restrictive to air flow above 3500 rpm and will be useless on a marine engine.

Install any 1987-1995 marine head (same head that was used on the 1987-1995 350 Camaro and Firebird)

The engine block crank, rods and pistons will work perfectly for a marine engine. Engine clearances are exactly the same between a truck engine and a marine engine.
Purchase the hi performance 383 Truck (crate engine) roller camshaft from a Chevrolet dealer (GM Performance catalog) and re-use the stock truck roller lifters that came with your engine (the 383 truck camshaft is actually the GM marine camshaft used in all marine engines with a roller camshaft and it is a bargain when purchased from a Chevy dealer).

Install a 1987 and newer Edelbrock Performer EPS intake manifold and 750 Edelbrock marine carb along with your stock truck ignition distributor and you will be happy. The new style permanent magnet truck starter is the same as the marine starter.
You will have 260-265 horsepower at 4800 rpm.
Dennis Moore

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