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Expert 5K+
Posts: 9647
    
Location: So. Cal | I was talking with someone from Hot Heads to get a new intermediate shaft to convert my 354 poly motor to run a 360 electronic distributor. He told me that the '57 poly motor needed to use the 392 intermediate shaft because of the difference in oil pumps that occurred from '56 to '57. But I asked him how that would work since the 392 distributor is longer so it wouldn't mate up properly at the top. He said that it would work without explaining why. To make things more confusing, I have been running a 354 hemi intermediate shaft in my other 354 poly motor for quite a while now and it seems to work fine with good oil pressure. Do I need to tear it apart and put in a 392 version instead? I might be able to dig up the original shaft to compare it, but it has been so long now that I am not sure which is which. |
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Expert
Posts: 3031
Location: N.W. Fla. | There have been reports of 3 or 4 different distances depending on year & application (car/truck) on 354s. LA dizzys shafts are shorter than OEM 354 |
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Expert 5K+
Posts: 9647
Location: So. Cal | I got to the bottom of this and found out that HotHeads was partially right, and partially wrong. I measured my original shaft and the distance required to mate up to the pump. The '57-'58 354 poly motors indeed use a 392 style oil pump that requires a longer 392 type of intermediate shaft. In fact, the 354 poly intermediate shafts are exactly the same as the 392 version.
However, when you convert it to use a 318 distributor, you cannot use the 392 conversion shaft because it will stick up too far at the top side. So you need a stock 392 shaft at the bottom end, and a 354 style conversion at the top end. Nothing that HotHeads sells will work here. I was able to get away with using the 354 conversion shaft on it with good oil pressure because it was making contact with only .07" touching. Pretty scary. So learn from my mistake and don't do that. I am in the process of making a custom conversion shaft instead now. |
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Elite Veteran
Posts: 888
Location: Peoples Republic of Oregon | ...4140 and induction harden the ends to Rc 55-65.....
The 'problem' that you have discovered is that some of the 354 engines used a much thicker main cap, presumably intended for the truck/industrial applications, but toward the end of the EarlyHemi run MaMopar simply used up whatever parts were in the bins. |
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Expert 5K+
Posts: 9647
Location: So. Cal | Thanks for the material & hardening tip! |
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Elite Veteran
Posts: 888
Location: Peoples Republic of Oregon | Happy to help. BTW, you can use the 392-LA assembly but you would then need to make a small spacer to raise the distributor to compensate. |
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Intermediate Shaft Difference 354 Poly vs Hemi
