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Alternative to slotting intake holes |
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ccowx 
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Joined: Nov/03/2010 Location: Yukon Status: Offline Points: 3510 |
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 Topic: Alternative to slotting intake holesPosted: Jan/14/2020 at 7:11pm |
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70 390 with 291-C heads tapped to fit early intakes. I have used both an R4B and a Cross ram with no issues at all for 30 years and 20,000 miles.
Chris
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bwamx
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Joined: Mar/27/2012 Location: CT Status: Offline Points: 143 |
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Posted: Jan/14/2020 at 3:49pm |
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I have drilled & tapped my 70 block & 70 291C heads with 5/16-18 tapped holes plenty of room . I run a early crossram and you cant slot the holes as 1 hole on each side is about 5" long through the intake.
I run 2 gaskets on 1 side, and RTV on the ends, and have no problems . I do not run the valley pan. Going on 10 yrs this build.
Edited by bwamx - Jan/14/2020 at 3:51pm |
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73 Jav-AMX " The Black Widow"
358cu/in Crossram T-10 9" Rear |
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AMXFSTBK390
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Joined: Oct/22/2013 Location: SF Bay Area Status: Offline Points: 3489 |
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Posted: Jan/13/2020 at 4:57pm |
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I installed dog-leg heads on my 68 AMX390 with a AirGap intake. Had to slot the holes figure 8. Used billet fender washer to cover the original inline holes not used. Wee bit of bling. See pix
 
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Trader
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Joined: May/15/2018 Location: Ontario Status: Offline Points: 6913 |
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Posted: Jan/13/2020 at 4:38pm |
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Glad some one else went first. I've had little issues going back and forth. Nothing, thicker or thinner head gaskets, adding intake gaskets. Not a huge problem.
RTV for the valley seal that I prefer anyhow. As for the bolt offset, fill with JB Weld and drill new holes in the intake, never an issue. I use RTV and washers on other's that have leaking slots - usually on Eddy slotted intakes. Just my experiences - street motors. I believe there is a huge difference once you cross to the 500+ HP build.
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Greyhounds_AMX
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Joined: Nov/14/2009 Location: Kansas City Status: Offline Points: 1268 |
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Posted: Jan/13/2020 at 4:32pm |
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I've got late model heads on my 68 AMX 390 that I drilled and tapped so I could use the 68-69 intake. They are one size smaller than the rest of the bolts.
20 years and 10,000 miles, no problems.
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1968 AMX 390 w/T5
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WesternRed
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Posted: Jan/13/2020 at 4:29pm |
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I have some 291C heads, they certainly have enough metal in the casting to accommodate the extra holes. Hadn't looked at other heads in the lineup. At the moment I'm thinking R4B for the 343 if I can find one although I currently have a short deck air-gap that may have to go back on instead, but is not the period correct look I'm after.
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I've finally given up drinking for good...........now I only drink for evil.
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BassBoat
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Posted: Jan/13/2020 at 4:24pm |
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Sealed up just fine but did you check the alignment of the ports?
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matty 401
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Posted: Jan/13/2020 at 4:13pm |
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i slotted a 343 intake to put on my 304 sealed up just fine
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72 matador 401 the beast
79 concord 2 door 72 matador 304 grasshopper 68 Rogue 406 93 Cherokee 4.0 5 speed |
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BassBoat
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Posted: Jan/13/2020 at 3:40pm |
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Just throwing this out, I found the speed of assembly comment interesting. Whether intentional or not, it certainly is easier. I had always assumed the move was to "Murphy Proof" so you couldn't mix intakes for tall engines and for short engines. Note to Newbies... There is more than bolt location difference between the early and late manifolds. They are different in width for different deck height blocks.
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PHAT69AMX
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Joined: Jul/07/2007 Location: West Virginia Status: Offline Points: 5926 |
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Posted: Jan/13/2020 at 3:33pm |
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Only from looking, not from doing, '70 & Up look to have the material.
Have seen where folks have done it. It's just a 'cleaner' approach imho to tap the extra holes. It 'hides' the modification / mis-match. BUT most would probably want to add the '70& Up Holes to '69 & earlier heads AND the early heads do NOT appear to have material to add the 70 & Up holes... Again, only from looking, they may have moved them since early ones are somewhat 'inline perpendicular' with a vertical early 7/16" head bolt clearance hole in the head. '70 & Up heads went to 1/2" head bolts which needed a larger head bolt clearance hole so those 2 center intake mounting tap locations were moved to get them off from over top of the underlying vertical cylinder head bolt clearance holes in the heads ?  |
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