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ron37
270 hemi pistons


I have a 270 Dodge hemi and a set of .030 NOS 315 hemi car pistons that I picked up years ago at a swap meet. So when I get the 270 bored, if I use the 315 pistons, will it raise original 270 compression ratio from 7.6 to 1 to the 315 ratio of 8.25 to 1? The one book lists the pistons as 8.5 to 1. My Tex Smith hemi book says 8.25 to 1. Any ideas?
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on: Mon 03 of May, 2021 [18:38 UTC] reads: 1726

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George
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Re: 270 hemi pistons
on: Sat 14 of Aug, 2021 [15:38 UTC] score: 0.00
depending on year the 270 was advertised @ 7.6 or 8:1, the 315 is advertised @ 8:1. Advertised is sometimes optimistic, especially on the low decks. Keep in mind the 315 is 8:1 with a longer stroke. You'd need to get down to serious measuring and calculating with the formulas to figure it out

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30redram
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Re: 270 hemi pistons
on: Wed 26 of May, 2021 [04:00 UTC] score: 0.00
> I have a 270 Dodge hemi and a set of .030 NOS 315 hemi car pistons that I picked up years ago at a swap meet. So when I get the 270 bored, if I use the 315 pistons, will it raise original 270 compression ratio from 7.6 to 1 to the 315 ratio of 8.25 to 1? The one book lists the pistons as 8.5 to 1. My Tex Smith hemi book says 8.25 to 1. Any ideas?

After checking with my 1959 MOTORS manual, it appears the 270 and 315 have different wrist pin diameters. The 270 is .8592 and the 315 is .9216. Unless the small end of the rods can be re-sized to the 315 wrist pin diameter, it does not appear the 315 pistons can be used with stock 270 rods.

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30redram
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Re: 270 hemi pistons
on: Wed 19 of May, 2021 [03:06 UTC] score: 0.00
> I have a 270 Dodge hemi and a set of .030 NOS 315 hemi car pistons that I picked up years ago at a swap meet. So when I get the 270 bored, if I use the 315 pistons, will it raise original 270 compression ratio from 7.6 to 1 to the 315 ratio of 8.25 to 1? The one book lists the pistons as 8.5 to 1. My Tex Smith hemi book says 8.25 to 1. Any ideas?

I have no hands-on experience with the 315, but I'll offer an idea on some checking you might consider. Take one of the 270 pistons and one of the 315 pistons, remove the wrist pin from one, slide the other piston's wrist pin half way out, then slide the first piston onto the second's wrist pin. Look at the piston tops and see if the 315 top is higher then the 270. If they are the same, there will be no change in the compression ratio. If the 315 is higher, there will be an increase in compression ratio. If it is higher, and you carefully measure the difference with a depth micrometer, plus use some careful math calculations, you can calculate the increase.


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