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Jeff Lee
AMC Apprentice Joined: May/14/2023 Location: Anthem AZ Status: Offline Points: 158 |
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Posted: May/29/2023 at 12:22am |
Had a few comments about my NHRA Class ’70 SS/G AMX. I thought any updates or discussion would fit better here in the Drag Race Section. If you wish to look at 9+ pages of the full build, see here at Yellowbullet.com
https://www.yellowbullet.com/threads/moving-from-cell-block-1-to-cell-block-2-in-chassis-prison.2650415/page-9#post-74054629 - https://www.yellowbullet.com/threads/moving-from-cell-block-1-to-cell-block-2-in-chassis-prison.2650415/page-9#post-74054629
I’ll keep brief as this isn’t a build section. Took it out to every event in AZ from January 1st to April NHRA Divisional. First 12 runs or so couldn’t figure out why it was so slow, 7.20’s in 1/8 mile. Figured it should have been 6.20-6.40 or so. After about a dozen runs, finally did a leak-down. 84% leak on #3 and took head off to find hole in piston as shop that balanced it (famous NASCAR engine builder, no names given) decided that #3 piston alone needed a ball mill to the bottom of the intake valve pocket (from the bottom of the piston; it was the only piston that was touched by the shop). So thin it blew a hole there. Welded piston and machined as necessary, went back racing. Shortly after fixing that, I did my burnout after being directed deep into the dry pavement. Fried the clutch. I mean, really fried it. Wanting to make the upcoming NHRA double header, I just cranked a bunch of base pressure into it. That will slow it down .400+ but will get you down the track. 4300 Autolite issues were plaguing me so I just threw a 780 Holley on it (not legal for my class). This allowed me to get things like chassis and shocks adjusted. Car drives like a dream, feels like a 12 second car. Launching at 6800-7200 RPM, shifting at 8,000 RPM, thru the lights at 8,000 RPM at 3,000’ track in Tucson, AZ. Finally ran a 10.15 @ 134 1/4 mile @ 3,000’ track with Holley. So I thought that showed the engine was okay. Made it to the NHRA race with 4300 Autolite in place. Couldn’t run any better than a 10.92 on my 10.45 index. Pulled valve covers and found a broken valve spring. Put it back on the trailer. Pulled engine apart and found a rock in #5 cylinder. The rock (about the size of the top of your thumb) bent the intake valve and obviously beat the crap out of the piston. Now engine at a different shop; using a profilometer found out the cylinder bores were horribly honed by NASCAR shop (way to slick), but also tapered at the bottom of the bores. So diamond hone is now done with proper profile on profilometer. And no taper. Ordered new pistons the other day and changing the ring combo. Going with stiffer valve springs and Milidon cam gear-drive also. Bearings all look new. 10 weeks on piston order. Have rings. Should be running again late August. |
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POS #1
AMC Addicted Joined: Jan/28/2014 Location: Ohio Status: Offline Points: 500 |
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WOW Jeff, That stinks... I have a guess the shop you used from before. i was going to run the mildon gear drive at one time also, Untill i mentioned that to Adkins... his reply.... Heck no, don't do it he told me... so rollmaster set it was... Best of luck,, look forward to updates. Mike
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Jeff Lee
AMC Apprentice Joined: May/14/2023 Location: Anthem AZ Status: Offline Points: 158 |
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It was a short lived shop here in Phoenix. A three-way ownership did not survive the honeymoon period and “poof” they closed the doors.
Adkins is not on board with my gear drive but I’m doing it anyway.
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amx600rr
Supporter of TheAMCForum Joined: Jan/26/2014 Location: Florida Status: Offline Points: 420 |
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Jeff, does “changing the ring combo” mean you went to the new steel race rings like .500 mm or .700 mm compression rings?
Thanks, Jerry |
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Jeff Lee
AMC Apprentice Joined: May/14/2023 Location: Anthem AZ Status: Offline Points: 158 |
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Old:
Top = .9mm steel flat face .125” radial 2nd =.9mm napier moly .125” radial 3rd = 3mm 12# New: Top = .043” barrel face moly .170” radial 2nd = .043” napier moly .160” radial 3rd = 3mm 9# New radials are akin to what I ran in Sock Eliminator and chambers / ports were almost always dry. This SS engine, always wet. Although, in defense of the old rings, the cylinder bore hone was WAY too smooth in peaks and valleys not near deep enough. That was the real problem. Maybe one day I’ll revisit the old rings but I need to go with what I am more familiar with; something I am 100% certain with. Using a Profilometer, here is before / after RVK = 36/55 RK = 33/59 RA = 14.8/20 RPK = 1/16 And there was .003” taper at lower end of the bores. Work just completed w/ Diamond stones and CNC boring. Took out about .003” so I’m at 4.243” bore. 4.245” is NHRA +.080” maximum. Milidon gear drive is installed. Now just need pistons, balance and (1) intake valve then assemble. It will all come together probably late August. Here’s the gear drive. Timing cover is getting modified for that bolt 7 o’clock position to the idler gear. Here’s an interior view: Rear (lower wheelie bar is off) |
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amx600rr
Supporter of TheAMCForum Joined: Jan/26/2014 Location: Florida Status: Offline Points: 420 |
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Thank You for the pictures. That is a beautiful piece. First class
All the steps you mention, diamond hone, profilometer, RK, RVK, RPK, thin ring pack, true cylindrical honing are exactly what is discussed on the Engine Performance Expo videos on YouTube They are discussed multiple times on videos hosted by Lake Speed Jr (from TotalSeal) and Ed Keebler (from Rottler Mfg). Apparently the piston ring materials have evolved radically in the past 5 years. Lake preaches that the moly coating is not the way to go. Too brittle and doesn’t last as long as the steel coated rings can perform. They say the NASCAR teams can get 1500 race miles now verse 400/500 on old ring materials. I’m no expert, just repeating what they are preaching.
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Jeff Lee
AMC Apprentice Joined: May/14/2023 Location: Anthem AZ Status: Offline Points: 158 |
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All good points. But what they never seem to talk about is reduced radial thickness of the ring (distance from face of the ring to backside of the ring). I was using .125”.
Reduced radial will give less pressure on the cylinder wall. You’ll probably find that a ring starts out around .200” radial. Reduction is ring tension is a good thing; to a point. The less the radial, the less the life. Also, .043” is only .004” thicker than a 1mm ring (.043” is .008” thicker than the .9mm ring). So in that department, really kind of splitting hairs. I’ve learned from this venture. Coincidentally, I spoke to somebody last night that was at the now defunct NASCAR shop that handled the hone. I told this guy I think they F’d up and he agreed. He confirmed I got the super whiz go fast hone and he agreed it’s something your good to make 20-40 runs on and then you need to tear down and re-hone. Regarding the radial width I had on the rings, same story; while you’re at the hone, get new rings. I’ll take the blame on the rings because I told Total Seal I wanted to be the fastest in the class, set records, blah-blah-blah. Well I was all that in Stock Eliminator and I was using rings like I’m going to use now (although thicker per rules; that rule doesn’t apply to SS). I know they worked so that’s what I’m going to. I’m getting good advice and I have learned many things about going down that new "trick of the week path" with lots of hoopla, and many come back to what always seem to work. New engine work will have 200# more open valve spring pressure at 1000#. Milling heads closer to minimum mandated chamber volume (legal minimum is 49.1cc, I have -993 head), pistons / rings / hone as discussed, and gear drive. Going from 2.93 1st gear to 3.02 (would like to change to steeper 1-3 gears but not in the budget right now), lower engine oil pressure and chassis work with firewall forward cage bars to tie in the mid-plate and motor plate. |
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Jeff Lee
AMC Apprentice Joined: May/14/2023 Location: Anthem AZ Status: Offline Points: 158 |
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Also...Moly rings have been around on race cars what, 50 years? I’ve never broke one. Maybe because I run proper fuel. Will try the fancy stuff later. I need to find 150 HP 1st! LOL
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WesternRed
AMC Addicted Joined: Aug/03/2010 Location: Australia Status: Offline Points: 5798 |
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I broke one moly ring and that was installing it, guess what, that motor got a regular cast ring in one cylinder and I haven’t looked back.
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I've finally given up drinking for good...........now I only drink for evil.
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Class Guy
AMC Addicted Joined: Jul/02/2007 Location: Arkansas Status: Offline Points: 969 |
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There is also a big difference between a moly-filled cast ring and a moly-sprayed ductile iron ring.
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Addicted to acceleration.
Owner and Admin for www.classracerinfo.com |
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