GT6 GT6 engine questions...

question one, i have a 1972 gt6 that i believe, from all sorts of reading material, has a compression ration of 8.5:1. would there be any real benifit to increase this since i have the engine in the shop?

question two, with the above engine, what octane of gas would i need for 8.5:1, and how would that change with a higher compression?

question three, what do valve seals look like and would a stock engine benifit from it?

well, that's it for me today, maybe i'll come up with some more questions tomorrow.

In the 60's and early 70's my '67 ran much better on premium than it did on regular. I have no idea what the octane rating was and remember it was leaded gas.

I did burn a valve and felt it was from the regular that one station I frequented was putting in without my realizing it. That was the days when an attendant pumped the gas.

I think it was because I tuned the car with the higher octane gas in the first place. And then again it may have had nothing to do with it. I did not leave much time for the fuel to enter, ignite, and leave the cylinders if you know what I mean.

heh, attendants still pump gas where i live...i hate it.

67's did have a higher compression ration too, 9.5 or something.

What's the engine serial number? If it ends in "UE," then it is -- assuming it's unmodified -- a relatively low-compression (8.0:1), 79hp, US-spec. engine, and it should be pretty happy with "regular" gas.

i do have the UE suffix engine, which leaves me with a lower compression ratio then even i thought, at 8.0:1.

the subtle differences in reported compression ratios might actually come from the domed or flat top pistons, mine having flat tops at the moment, regardless of what it should have.

Higher compression will give the engine a litle more "snot"...years ago the local asphalt stock car racers were forced to go to a 9 to 1 engine rule to TRY to keep the "high dollar" engines (and the high costs) out of the cars.

The track officials used a "whistler" device that was screwed into the spark plug hole and, when the engine was cranked, would "whistle" if the engine was much over 9 to 1 compression.

You could stand in the corners at most tracks and pretty much hear who had the illegal "high compression" engines...they were usually louder and pulled harder off of the turns. The "compression police" would usually spot these pretty easy...

Flinkly said:

question one, i have a 1972 gt6 that i believe, from all sorts of reading material, has a compression ration of 8.5:1. would there be any real benifit to increase this since i have the engine in the shop?

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Yes, you will get more horsepower from higher compression, & you will want it if you don't get it. Mill the head for 9.5:1 compression (the pre-emissions spec), & use premium gas.

<div class="ubbcode-block"><div class="ubbcode-header">Quote:]question two, with the above engine, what octane of gas would i need for 8.5:1, and how would that change with a higher compression?[/QUOTE]

You should be able to run an 8.5:1 engine on mid-grade, considering that you'll be aiming for maximum spark advance which will sort of put the lowest-octane gas out of the picture.

If you experience pinging, you'll have to either pull spark or go to higher octane gas. Pulling spark will result in less acceleration, & you'll not like that.

9.5:1 with decent spark advance will require running premium gas. The average octane rating for premium varies around the country, 91 to 93-ish, depending on altitude.

The GT6 tank holds about 10 gallons, premium costs 10 cents more than regular, that will add about one dollar to the price of a fill-up. Whoop-tee-doo for a dollar more for the GT6! If you fill up once a week, that will mean you have bought 5 or so very welcome hp for $50 that year.

The later GT6 head flows better than the original head, so it's really nice when the compression gets back up to something realistic.

You really don't want to go more than 9.5:1, or you will have problems with detonation which will shorten the life of the engine. Higher octane gas doesn't add more hp, it just means it can be used in cars that produce more power via higher compression & more spark advance.

<div class="ubbcode-block"><div class="ubbcode-header">Quote:]question three, what do valve seals look like and would a stock engine benifit from it?[/QUOTE]

Little boogers that go on the valve stems, you don't need them if you put in new valve guides & your valves are OK.