MG Sports Cars

engine swaps and other performance upgrades, plus "factory" and Costello V8s

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Jim Evans

(6 posts)

01/08/2016 01:50PM

Main British Car:

Buick 300 heads on a 215?
Posted by: jim4mgs
Date: February 13, 2016 02:04PM

Hi! I'm new to the list but not to the hobby. I put a 215 into a 1978 MGB some years ago and am now redoing the whole project...picked up a set of of 64 Buick 300 heads years ago and am now wondering about bolting them onto the 215 block. I am aware that the larger combustion chamber size in the 300 heads will lead to a lessened CR but some seat-of-the-pants calculations indicate that using stock 215ci 10.25:1 pistons with these 300 heads would result in a final CR of about 9:1. Does anyone know if that is an accurate guess-timate? Has anyone out there done this? Those 300 ports are much bigger the the 215 ports as are the valves...a very tempting substitution at first glance.

Jim Nichols
(2057 posts)

02/29/2008 08:29PM

Main British Car:
1973 MGB roadster 260 Ford V8

Re: Buick 300 heads on a 215?
Posted by: mgb260
Date: February 13, 2016 02:56PM

I used 300 heads years ago on a 215. I used the hi compression pistons, and 8.5 to 9 to 1 is about right. You could use a compression calculator and figure 39 cc for 215 chamber vs 54 cc for the 300. .020 for steel shim vs .040 for composition head gasket. I would deck the block .030 and skim the heads to make sure they are flat to regain some compression. Here is a compression calculator:


Edited 1 time(s). Last edit at 02/13/2016 03:03PM by mgb260.

Carl Floyd
Kingsport, TN
(3957 posts)

10/23/2007 11:32PM

Main British Car:
1979 MGB, Buick 215

authors avatar
Re: Buick 300 heads on a 215?
Posted by: MGBV8
Date: February 14, 2016 05:50PM

The valves would be much less shrouded by using the bigger bore of the 3.9L.

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