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Old 05-09-2002, 08:59 PM
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Post What ever happened to high compression?

I seldom see in ANY of the engine build-ups mentioned by anyone, even the magazines, the use of High-Compression pistons any more. No matter whether you are using cast, hypereutectic or forged, the prices are all real close (within the type of pistons you choose) for a set of 8 1/2 or 9 to 1 pistons, as the price for a set of 10 1/2 to one pistons. And, dollar for dollar, again may simply be the CHEAPEST power upgrade you could do if you are putting new pistons in anyhow. What's the price difference going to be between low comp units and their high compression brothers? Check your Jeg's, Summit, etc. catalogs and you will probably see the price difference for a set of maybe $50 or so. For my money, this is almost FREE horsepower, and is ignored by the horsepower gurus these days. I honestly see NO point in putting a couple thousand dollars in some upgrades, and letting the easy and cheap horsepower get forgotten. That's kind of like putting on a blower with a two-barrel carb, why do it? You should still be able to use 91 Octane pump gas. What do you all think?

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Old 05-09-2002, 09:08 PM
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I agree. A few years ago, Hot Rod did an article about an engine with longer connecting rods, bumped the compression to 11:1 and flogged it on 87 octane. I am still planning to build this engine someday...

Everybody talks about "pump gas" but noone is exploring the rod ratio concept and how to run high comp with cheap gas. There are jut too many know-it-alls out there who "know it won't work" I guess. Screw those guys, I am all about hot rodding and to me, that means doing it better, cheaper and getting more out of less!

Red
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Old 05-09-2002, 09:08 PM
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Octane Requirements for High Compression Engines are Gone Forever. In the Old Days, say 70-71 Octane was still there in all forms of Gasoline.

Lets say 100-106 Octane Ratings, with the E.P.A. in Control since 71-on, Octane Ratings have Plummeted. Now all We have is 92 Octane available in Premium Unleaded.

About the Most Compression We can Run Now, [and still be safe from Detonation] is 9.5-1, a little more if You Run Aluminum Heads, Aluminum Dissapates more Heat.

Lower Octane in Fuel results in Lower Compression Ratios.
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Old 05-10-2002, 12:10 PM
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Not that I would ever break any EPA rules or anything. But if someone was to go to your local general aviation airport fuel depot, with a couple of 5 gallon cans, The nice folks there would likely sell you leaded 101 octane AvGas, for your airboat. (powered by a lycoming aircraft engine.)
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Old 05-10-2002, 12:22 PM
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i've got 11.5 - 1 pistons in my tbucket, it won't run on 92 octane with out pinging. got to add octane booster, and have learned the hard way which ones work and the boosters that don't. it's ok when you're not racking up a bunch of miles, but if i rebuilt this engine i would drop the compression.
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Old 05-10-2002, 02:20 PM
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Well, Besides the head ache of low octane fuel, higher compression leads to higher cylinder pressures. If you have to smog the thing, you will fail due to unusally high nox emmisions.
on the other hand, sometimes you can run a little higher comp ratio ,10.5:1, if you have a lot of durration and overlap. Then you get rough idle and hard starting and poor driveablilty. if you really want a lot of power cheap...I'd get a blower. it's a lot less trouble and if you start pinging you can allways turn it down a little.
Not so easy with high comp pistons.
Sam
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Old 05-10-2002, 05:16 PM
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hey dinger,I would like to know just what octane boost works the best.as I might need to use this stuff myself.
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Old 05-10-2002, 08:12 PM
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Obviously octane ratings have dropped over the years and we got rid of the lead. But in Jersey we also use what they call oxygenated gas in the winters. Even stock engines seem to run worse on this stuff, don't know about high compression. Hey Chuck what do you think about oxygenated gas, do they use it were you live, and do you think that it would even further cripple a high compression engine? Are you out there?
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Old 05-10-2002, 08:50 PM
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Yea DM, oxygenated fuel sucks. It leans the mixture and was designed more for older vehicles so they would pollute less since they run richer mixtures. So what that means is your new computer controlled vehicle injects more fuel to make up for the excess oxygen in the exhaust gas. The conversion of the chemical in the fuel to oxygen in the chamber eats up the BTU content so less heat is generated and hence less emissions. So you end up burning more fuel and getting less performance, what a great idea! I think some tree hugger/oil company executive came up with that idea!

Up here it sold as well as sandals in January and was discontinued, it was replaced with a 10% alchohol/gasoline mixture. At least a higher octane fuel but with no performance enhancement due to the need to rejet the carb to take advantage of the alchohol content. If you did this you would get poorer mileage as well. I seem to remember that they had a problem with the oxygen additive separating out at low (-40C) temps.
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Old 05-10-2002, 11:05 PM
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im curious to what the best octane boosters are?

when you experience "ping" in your high compression/blown engine, cant the timing be retarded (or is it advanced?) so you can run the high compression with pump gas to a certain extent?

how high of compression can i "push" without experinecing pinging?
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Old 05-11-2002, 12:35 AM
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i bought my tbucket, been sitting for 15 years, was built in 73 when gas was still gas. pinged like a deisel. changed the dual point, no vacuum advance distributor (after messing with timing, draining tank,new carb, messing with the carb,adding the additives,no luck) to an electronic distributor, still pinged but not nearly as bad. ran that gas out, bought more 92 octane, added some nos (brand name) gas additive pinged a lot less but still pinged a little. got madder than hell after test driving, adjusting timing, carb,etc., stuck it in low and drilled it, ping disappeared about 4000rpm, and it ran like a scalded cat. it may have been carboned up some, the harder i drive it the better it's been running. i've got it tore apart now, getting ready to paint. the nos stuff worked well, the bottle with earnhardt jr. and the 104 octane booster brand didn't seem to make any difference at all. a note on the oxygenated fuel, it's been in ca. for quite a while, it raises the cost, and now they're finding it in the water system, a carcinogen, just what we need is something else to give us cancer. another bright ca. idea that some dips@#@ politician jumped on. (i love this state but dislike politicians)another thought:how can you burn more gas, less mpg, and pollute less? it sure messes with my mind, been trying to figure that one out since 1973 when the big 3 had to start all this epa standard and mileage plummeted. if you're burning more fuel to get the same results, ???????
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Old 05-11-2002, 05:07 PM
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all this talk about detonation in high compression motors !y'all have me scared to death!! i've built my latest with more than i've ever done[10.1:1]my thinking[if you could call it that!] was that i would run it with around 36 or so degrees of timing on the street then go to about 38/40 at the dirt drags. of course these figures are just ballpark,the story cant be known till i install it.my heads are'nt alum.,have i really screwed up?the cam is 226/234@.500 and .480/.498 lift.also the ignition is crane hi-6 . see ya! jimm
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Old 05-14-2002, 09:04 PM
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I'm not sure bout anywhere else, but here in the mid-west we can still grt 104 octane automotive fuel at different gas stations. just dont get caught pumpin it in a vehicle sittin on the ground. we also have 85% ethanol blended fuels (E-85) we also have 93 octane for street use.
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Old 05-14-2002, 10:41 PM
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[quote]Originally posted by Biggarmike:
<strong>Not that I would ever break any EPA rules or anything. But if someone was to go to your local general aviation airport fuel depot, with a couple of 5 gallon cans, The nice folks there would likely sell you leaded 101 octane AvGas, for your airboat. (powered by a lycoming aircraft engine.)</strong><hr></blockquote>


Hey, someone who knows what an airboat is!
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Old 05-15-2002, 06:17 AM
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The only problem with buying Esso 101 for your "airboat" is that you forget to mark the cans and end up using the fuel in your high compression lead requiring car. That frequently happened to me. (an honest mistake) But it sure made a big difference. If you are doing the "buy it in a can" trick, ie: Cam2, the airport is a viable option. At last check Cam2 $4.79 gal, Esso 101 leaded: $2.79 gal.
Also, Real tetraethyl lead is available to mix your own. If you have tailpipe emissions testing you could have problems.

[ May 15, 2002: Message edited by: Biggarmike ]</p>
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