65GS.com - Buick Gran Sport Enthusiasts!
General Discussion => Q & A => Topic started by: kcombs on May 29, 2017, 11:12:24 PM
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I am thinking about bidding on the 65 convertible on Ebay with a factory four barrel 300. Wondering if it will run on high octane pump gas or need additive every time I fill the tank. Anyone have experience with a "355"? If I buy it I will be selling a lot of 1965 401 GS parts.......
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No personal experience, but an owner of one told me that it still pings on high octane. Looks like a nice car.
Dan
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I drove one for many years and JMOS has it now and has driven it even more. You have to retard the timing to get it to run on 93 Octane (initial timing at 0), and you have to have a really good radiator that will keep it cool (count on having to put a new radiator in it). The other thing I did that made a huge difference was blocking off the exhaust crossover in the intake, but it was my daily driver at the time and that caused the carburetor to ice up in the winter time. If you are going to drive it just in the fair weather months, then it is not a problem. Lots of potential in that engine and it will run really strong with some slight modifications (bigger exhaust and a performance camshaft).
The other solution is to rebuild the engine and put a set of the 9:1 pistons for a 2 barrel engine in it. That completely cures any detonation issues with only a moderate loss in power.
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Or put a bigger cam in it to reduce the Dynamic compression ratio!
Water injection can reduce detonation too. Had a system on my Turbo Regal that allowed me to run higher boost on the street.
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Replacing the head gaskets is another way to reduce compression.
The advertised 10.25:1 compression ration is likely closer to 9.75:1 on a production build.
Replacing the 0.015" original steel shim head gaskets with new composition 0.045" thick gaskets should lower compression into the low 9's.
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Dear Walt and mid-60 Buick caregivers of original cars,
Thanks Walt for the good idea!
Replacing the head gaskets is another way to reduce compression.
The advertised 10.25:1 compression ration is likely closer to 9.75:1 on a production build.
Replacing the 0.015" original steel shim head gaskets with new composition 0.045" thick gaskets should lower compression into the low 9's.
That's a really good idea to lower the compression ratio with the minimum of work and changes to the engine. I don't know how many unmolested engines from before the mid-70s are still around, but if you have one, this is a way to continue to run them on pump gas without making any other changes.
Cheers, Edouard