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Expert
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Location: San Antonio TX | So looking online, it seems all you really need to do to turn a 354 poly into a hemi is to get hemi heads, pistons, and crankshaft and swap them out. Am I missing something or is it really that easy to do? |
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Expert
Posts: 1740
Location: Alaska | You don't need to change the crankshaft, just heads ,pistons, pushrods, exhaust manifolds. You should have the rotating assembly balanced, a good idea on any rebuild. |
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Expert 5K+
Posts: 9900
 
Location: Lower Mainland BC | 58coupe - 2017-11-16 10:57 AM
You don't need to change the crankshaft, just heads ,pistons, pushrods, exhaust manifolds. You should have the rotating assembly balanced, a good idea on any rebuild.
I only see one listing for Chrysler V8 connecting rods for 55-56, i.e. 1323 338, so rods are the same (?) |
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Expert 5K+
Posts: 9650
Location: So. Cal | Yes, rods are the same for 331 and 354, and they use the same crank as long as it is from a '54-'58 car. For the conversion, don't forget the valve covers, rocker arm assemblies, spark plug tubes, tube covers & washers. Poly blocks may need to have the pushrod holes elongated so be sure to check that before you get it all together. |
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Expert
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Location: San Antonio TX | Cool. And all this can probably be done without pulling the engine too right? I guess I just have to find the parts now... |
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Expert 5K+
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Location: So. Cal | Except for the pistons. That's the kicker. And if you don't change them, you end up with really low compression. |
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Expert
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Location: San Antonio TX | Powerflite - 2017-11-16 9:21 PM
Except for the pistons. That's the kicker. And if you don't change them, you end up with really low compression.
Darn, I was hoping I could do all the work without pulling the engine! I may still do the conversion, but if I do, I don't want to half-ass it and keep the poly pistons. |
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Elite Veteran
Posts: 888
Location: Peoples Republic of Oregon | What is 'wrong' with the Spitfire engine? OK, it dosen't look cool....
If you are just looking at performance then keep the engine as-is. It easily keeps up with the Hemi with basic hot-rod parts on each.
Upper level builds will require some port work but still an excellent engine. |
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Expert 5K+
Posts: 9650
Location: So. Cal | Agreed. My 354 spitfire is a very strong running motor and the benefit of swapping heads is minimal on a mostly stock motor. Improving the exhaust system and converting to a 4bbl carb is probably the best bang for the buck you can make - beyond basic improvements like electronic ignition running with a good timing curve. Second would probably be the camshaft & lifters, but you can only take it so far without affecting your torque converter in a negative way. |
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Expert
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Location: San Antonio TX | wayfarer - 2017-11-17 10:11 AM
What is 'wrong' with the Spitfire engine? OK, it dosen't look cool....
If you are just looking at performance then keep the engine as-is. It easily keeps up with the Hemi with basic hot-rod parts on each.
Upper level builds will require some port work but still an excellent engine.
You basically nailed it; I just like the hemi aesthetics. I'm still not 100% sure about it. Something tells me finding all the parts to make it a hemi might be more work and money than just buying a hemi and dropping it in.
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Elite Veteran
Posts: 888
Location: Peoples Republic of Oregon | ....just buying a hemi and dropping it in.
Good luck finding a good running engine for less than the cost of rebuilding one...I would expect $4000 or more depending on your luck. Remember that a rebuildable 392 core will sell for $2500 or more, 354 are less money but still can run $1k for a complete package. In my shop basic rebuilds run around $5k these days.
I would not buy an old, un-rebuilt, engine and spend the effort to install it, Not worth the time/cost imho.
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354 Poly to Hemi conversion question.
