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I have a 73 converible, it has the correct heads and intake. The block has been replaced with a 1969 passenger 427, 290 horse or so, and a 69 corvette carb. If I find a correct dated block I may go that route. If not would I be better to find 427 heads or a 454 block. Tuff question any ideas will help.
thanks
cal
Basically, 427 and 454 blocks are the same. If the 1969 block that you have is a GM casting #3963512 block, that block is exactly the same as a 454 block and it was used for 454 applications for 1970-71. All you need do is change the crankshaft and pistons to convert it to a 454. If you have an earlier 427 block, some can be converted to 454 by grinding reliefs in the bottom end of the engine for crankshaft/rod clearance. However, in that case, you'd be better off lokking for a block originally designed and clearanced for a 4.0 inch stroke (454).
As far as the heads go, if you have open chamber 1969 427 heads, those are the same as those used on 1970 454s. If your heads are GM casting #3964290, then you have what you need. If you have GM #3931063 heads, then those are closed chamber heads. I wouldn't use those for a 454 but they can be so-used.
Wether it is a 454 or not the casting number are not the same. From my understanding if you go get it judged you will basicaly loose those points. I would think your 427 would be worth some $$ and you could use that to fund a purchase of a correct casting numbered 454. I have a '72 BB car. Someone thought a '73 light truck 454 would get the job done, so now I have that in the car. However I found a 454 correct casting number engine dated in '73 that I bought. This didn't cost me much and now I will turn around and sell my engine, which runs great, to someone and use the $$ to fund the new engine.
Anyway, I would think that your 427 would give you good seed money and you could probably find a good 454 perhaps rebuilt ready to go for your needs. Less hassle.
The 454 crank rotating assembly is externally balanced and also requires a 454 externally balanced harmonic balancer and externally counterweighted flywheel or flexplate.
Yes, basically all that has to be changed to convert a 427 to a 454 is to change the crank, flywheel, balancer, and pistons. As I mentioned earlier, though, not all 427 blocks are clearanced for the longer stroke 454 crank. The 3964290, which was used for BOTH 427 and 454 engines, is one of the ones that is, however.
One of the big problems is, as clem mentioned earlier, 454 steel cranks are a lot more expensive and harder to find than 427 steel cranks. So, while the conversion can be done, it can't necessarily be done cheaply.
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