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HybridZ

350 or 400?


Guest Anonymous

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Guest Anonymous

Thanks for all the response to my other meessage, its realy a great help to me. My question now is if a 400 installs just as easy as a 350, being that their basicaly the same on the outside. Reason being that a guy i work with has a late 70's El Camino with a 400 V8 and a 700R4 transmission, and he just wants to get rid of it because the body is in terrable shape. It has 60,000 and runs great. Shuld i take it and use it in my Z?

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Nick, if the car has 60000 original miles, I'd think even if you wanted to rebuild it and it NEEDED a bore (doubtful) then the cylinder walls will be plenty thick.

 

A larger engine (400 vs 350) allows you to build it mild and have the same horsepower (peak) with more torque across the rpm band - especially the important 1500-5500 range. The only difficulty with the 400 is the external balance (dampner and flywheel/flexplate). But if you're getting the package, all that is there anyway.

 

Look at it this way: for the same package size and weight, you'll have 50 more cubic inches (that's 1/3 the displacement of the L24 that's in the 240Z) than a 350 has. The increase in torque for a similar build will be 1 to 1.2 times that 50 cubic inches, assuming a similar "performance" build level. Or a bit less for a milder build, which would be more streetable than a hot 350 buildup.

 

The 400 is reputed by some to have an overheating problem. That came about when people put different (350 or 327) cylinder heads on the 400 and didn't put the steam holes in the head. That's a very important step. With the steam holes, there is no great increase in cooling needs between a 350 and a 400, especially in a street "performance" build. The increase in displacement does add to cooling needs a bit, but nothing a good Griffin radiator can't handle - same radiator you'd use on a 350.

 

Sure, you can't rev a 383 or 400 as much, due to the stroke making the average piston speed higher than a 350 at a particular rpm, but 6400 rpm is about 4000 fps average piston speed. You won't need to spin it that high even at a 475 peak hp build.

 

If it's a street car, I think a milder 400 is better than a rumpy 350 of the same hp.

 

JMO,

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Pete is absolutely right, but it can still come down to a preference on how the motor delivers how much power.

 

The 400 is also the only siamesed cylinder production SBC, this is what forces the steam holes. Also, they tend to distort the bores depending on how hot they run. A minor problem in a street car, but ring sealing can be affected negatively in a max output motor. Even with torque plate honing. The larger bore reduces the amount of valve shrouding for more flow, but it also requires more ignition advance because of the larger area the flame has to travel for complete combustion.

 

The bottom line for me is always the bottom line! With that said, you just can't go wrong building a 350. Dollar per dollar the cheapest motor to build anywhere. Cheaper to buy and cheaper to get parts for. Money saved on the short block can be spent on better cylinder heads. This can be the great equalizer if the almight dollar is the determining factor.

 

The 383 can nearly equal the torque output of the 400, but because it uses a cheaper 350 block can be another option. There are advantages to the longer strokes faster piston speed filling the cylinder better.

 

Because of the Zs inherent tire limits, I would be inclined to shift the torque up in the RPM range, and the 350 is better suited to that than the 400. But in the end, it will be your decision to make, most likely on how much money you want to spend.

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Mike has good points on the cost to do a 400 vs a 350. But if you are buying the engine, it's in good condition, and not planning a rebuild, then the 400 will be a good way to go. With the right intake, headers, carb, and maybe a cam (if it's still stock), you can have a nice performer.

 

Any idea if this is a stock engine, or modified?

Any aftermarket stuff in/on it? (intake, cam, etc.)

Compression ratio? Even the cranking pressure and cam specs would help you determine the range of compression ratio you have in it.

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