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1970 390 piston choices |
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401MATCOUPE
AMC Addicted Joined: May/20/2010 Location: Salisbury, MD Status: Offline Points: 5370 |
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Posted: Mar/19/2012 at 4:07pm |
The Chief Piston Designer at Keith Black is a fellow Studebaker Enthusiast, he has 40 plus years of internal combustion engine experience and Custom Build Pistons for the Studebaker folks all in Hyperutectic Design. He has told me that the biggest failure issue is wrong ring gap for application. The old .004" of end gap per inch of bore size does work on all applications. Alot of Studebakers are factory supercharged and high output (10 psi plus), using these pistons but with a larger end gap. If you go to the Keith Black Catalog there is a great deal of info there that can be used on our AMC Performance Engines. If you want to build a performance engine using a supercharger, turbo or nitrous, KB can give some great advise.....give John Erb a call, he is an unbelievable mountain of information. He has been involved in 304 CID Studebakers at the Salt Flats going 200+ MPH and holding the record. Sorry for the Brand X Orphan Car references, but if they can make that kind of power so can a "Modern AMC V-8's".
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Ross K. Peterson
68X,GoPac,343,AT,52A(1stCar) 68X,GoPac,390,4sp,52A 69X,GoPac,390,4sp,64A 70X,GoPac,390,4sp,87A,8 70X,GoPac,390,4sp,BBO,8 70 Jav SST,390,AT,BSO 74MatX,401,AT,Prototype 74MatX,401,AT |
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smills61074
AMC Nut Joined: Feb/05/2011 Location: savanna, il Status: Offline Points: 270 |
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It appears everyone seems to recommend forged. I guess I will have to wait until I get my block checked out at the machine shop, Then I will know what size I will need.
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440sixpack
AMC Nut Joined: Feb/23/2012 Location: Oregon Status: Offline Points: 481 |
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Dan is correct don't have it in the hole that's a sure prescription for trouble, Bulltear will take your specs and make sure you are flat .
You didn't say if you have a standard bore or not, if you're headed to a .60 over like I have to go you better have your shop sonic the block before you go any deeper. I guess AMC can have a little core shift too.
There are lots of good pistons out there but when you can just make a phone call and get a set of american made customs to fit your needs for $600 it's a no brainer for me.
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amx39068
Supporter of TheAMCForum Joined: Feb/21/2008 Location: Arizona Status: Offline Points: 11576 |
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Custom pistons are just that, custom. You can have them made to fit your specfic engine's deck, bore and valve relief to have whatever compression you want.
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Dan Curtis-Owner and CEO AZ AMC Restorations; Facebook: https://www.facebook.com/amcmusclecars/ & Curtis Real Estate Development
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74Bubblefender
AMC Addicted Charter Member Joined: Jun/29/2007 Location: The AMC form Status: Offline Points: 2589 |
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China...heck no. Zero deck is what you want with a nice shaped D-dish
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We are just about to forge new AMC V8 crankshafts.. please check here
http://www.bulltear.com/forums/showthread.php?19564 |
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smills61074
AMC Nut Joined: Feb/05/2011 Location: savanna, il Status: Offline Points: 270 |
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Are the bulltears made in chna? If I go with a 401 crank, will my pistons still be down in the hole? I am taking my block to the machine shop this week. Once it is boiled and magnifluxed, I will know if I have to go oversize with the pistons. Everyone, thanks for your help.
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440sixpack
AMC Nut Joined: Feb/23/2012 Location: Oregon Status: Offline Points: 481 |
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If your detonation is bad enough to take out a piston you need to do something about it . no piston will take it forever, granted forged will last the longest. This pretty much covers it.
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17tamx
AMC Addicted Joined: Dec/23/2008 Location: Peoria, AZ Status: Offline Points: 1170 |
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401 pistons in a 70 390 block will be .060" down the hole and you will have pinging problems if not addressed.
I decked my 70 390 block .060" to get to zero deck height. I am using the Speed-pro forged 401 pistons with the .170" dish. I took .024" off of my 291C heads to get me to 10.71:1 and I run standard 91 octane pump gas here in Phoenix without any detonation. It took 312 grams of mallory metal to switch from external to internal balance. If I had used the lighter more expensive forged pistons the pistons would not have been $333.00 from summit but I would have saved money on the balance work. If I was doing it again in (2000) I would have bought the lighter forged pistons (Ross or J&E at $600+) rather than the Speed-Pro (TRW $333) from Summit. Now that we have the perfect AMC piston design from BullTear the $635 seems like a great deal and the best way to go IMHO.
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Kirk P. Fletcher
70 AMX BBG w/Shadow 390 4sp 71 SC360 Wild Plum Ram Air 4sp 67 Rogue Convert 343 4sp 66 Rogue Hardtop 290 Auto 66 440 Convert 232 Auto |
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SC397
AMC Addicted Joined: Apr/30/2009 Location: Michigan Status: Offline Points: 5428 |
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I will never use Hyperutect pistons again. They can't handle any detonation.
I use the cast high compression '71 401 pistons in the '70 390's. I will have to go through the numbers but I think it lowers the compression ratio down to like 9.5:1 which of coarse makes it less sensitive to detonation. |
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440sixpack
AMC Nut Joined: Feb/23/2012 Location: Oregon Status: Offline Points: 481 |
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I'm not sure the KB hyperutectics will be in the compression range you want but if they are and you want to run them by all means do they're great pistons .
Most guys problems with hyperutectics is they think they pour the nitrous to them or they don't file the top ring gap to specs. I've run them in my mopar big blocks for years turning 7500 rpm and HP that would tie an AMC V8 in knots and NEVER a problem one. I know many others with the same experience, hypers have gotten a bad rap for all the wrong reasons.
I'm going with Bulltear I think because I want about 10.0 and I'm using 58cc heads so the KB's don't quite get me there. if I was going to use my original 51cc heads then I'm a little too high so I'd have to cut the KB's and there again it's just easier to give Bulltear a call and get exactly what I want fron the start.
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