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TRW Pistons |
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PROSTOCKTOM
Supporter of TheAMCForum Joined: Jun/20/2010 Location: Indiana Status: Offline Points: 2427 |
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You can use those pistons with the Edelbrock heads and probably be alright, but a newer designed piston will allow you to run a tighter piston to wall clearance. Those older TRW piston need a lot of clearance (.008") do to expansion. That set would be fine for a race engine, but not the most ideal for a street ride.
Tom
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Molnar Technologies Full Service Dealer - Crankshafts & Connecting Rods
1969 AMC Rambler Rouge Race Car 1974 AMC Hornet Hatchback, Wally Booth Outlaw Nostalgic Pro Stock Race Car Project |
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68-73 amx
AMC Addicted Joined: Jun/14/2012 Location: Pa. Status: Offline Points: 533 |
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I have these pistons in my 68 390 , almost a race motor, have to use half race gas / 93 Sunoco to keep it from pinging , It's a beast of a motor on all race gas. ( built in the 80's , wouldn't do it today )
Edited by 68-73 amx - Oct/22/2021 at 6:12pm |
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Ken_Parkman
AMC Addicted Joined: Jun/04/2009 Location: Ontario Status: Offline Points: 1815 |
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There are a million factors so a single answer in not possible. Some factors are spark plug location, quench, combustion chamber shape, engine temp, volumetric efficiency, bore size, barometric pressure, underhood temp, air-fuel mixture, and maybe even the phase of the moon.
What is true is a point of compression is worth ~2% all other things equal. Now there are cases where all other things are not equal, and a lot of race applications would pay a body part or more for 2%. But in a typical street performance application there is about 8 hp in a point of compression. There is far more than that in an electric fan or an air filter. It just blows my mind when I see a guy run the risk of 10.5 or 11 compression, then stick an eggbeater mechanical fan on the engine. Does not make any logic whatsoever. So I am not a believer in pushing compression - until you need to. I too generally recommend about 9.5 compression max for an iron head car that you are going to drive around and could get stuck in a traffic jam on a hot day. I've found on a properly tuned and good running engine that makes some decent cylinder pressure and power much more than 9.5 in a 401 can be a problem. If there is something in the engine to screw up the cylinder pressure you might get away with more. You will also always find someone who has run more and says it worked well for them. While the AMC iron head is very good, particularly for the time, things have moved on. You can run a bit more compression with the Edelbrock head. It has a better spark plug location. For reference I ran an engine way back in 2004 in the PHR EMC. It was 11.7 compression, required to run on pump gas, and was somewhat designed for the competion site, which was Long Island in October where I knew the air would be good. You can definitely run more squeeze on a dyno engine, it does not have to worry about hot underhood air. The engine ran well, made 613 hp, and outscored a whole lot of higher compression small block chevy competition. It did rattle a bit with the extremely low 2500 rpm starting point of the pull, but not horrific. Some of the other engines detonated viciously even far up the rpm band once the induction system came "in tune" and the engines developed some cylinder pressure. Those high compression engines did not score well. Of course the real geniuses like John Kasse were able to make high compression work under those conditions, and that is an art form. There are very few engine builders that smart. This of course is why I don't believe in the "dynamic compression" theory.
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68-73 amx
AMC Addicted Joined: Jun/14/2012 Location: Pa. Status: Offline Points: 533 |
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How much more do you figure the motor ( 613 hp ) would make on 100 or 110 race fuel ?
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Ken_Parkman
AMC Addicted Joined: Jun/04/2009 Location: Ontario Status: Offline Points: 1815 |
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I did run it on leaded race gas in testing, and it made less power. The high test unleaded, even though lower octane, tended to make more power with the MMT back in the day, but I'm not current on the fuel composition today. For sure my old bracket car was slower on leaded race gas, but it was only 10 to 1.
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DragRacingSpirit
AMC Addicted Joined: May/27/2009 Location: Mo Status: Offline Points: 903 |
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How about E85 ? I ran those pistons in my 70 AMX around on the street all the time but I mixed 110 race gas with premium unleaded.....a little expensive but alot of fun. Of course Turbo Blue 110 back in those days was pretty cheap by the barrel. And like the previous posted commented they have to be run very loose and they are bad about scuffing cylinders.
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Best 1/4 mile 8.99, 1/8 mile 5.71, 60 foot 1.27, no power adders
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amxron
AMC Nut Joined: Nov/18/2011 Status: Offline Points: 295 |
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I think Jeff Lee got those pistons approved. Probably because they were the only off the shelf forged ones available at the time and very few AMC cars were racing in stock class then anyway so NHRA let them in.
BTW; All 70 AMC 390/325 have been rerated to 315 hp. by NHRA. Ron.
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AMXron
Fleet/Jeep Mgr. Orbit AMC/Jeep 50-1787 |
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Kbmwm3
AMC Apprentice Joined: Feb/12/2020 Location: Tampa Status: Offline Points: 47 |
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Love all the info and discussion.
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