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Max cubic inch out of a 401 |
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jpnjim 
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Joined: Nov/25/2007 Location: New England Status: Offline Points: 2752 |
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 Posted: Nov/26/2021 at 4:48pm |
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Big inches & Service Block talk made me think about the 3.87" billet crank & Molnar rod order jcisworthy put together a few years back: What's the better match for a billet 3.87" crank? 401 block, and make the extra stroke worthwhile: Std bore 401 = 422 +.020" 401 = 426 +.030" 401 = 428 Or a Service Block, where you don't get all the extra cubes, but the block strength is closer to that of the cranks: STD 4.08x3.87" = 405 +.020" 4.1"x3.87" = 409 +.030" 4.11"x3.87 = 411 +.040" 4.12"x3.87 = 413 +.045" 4.125"x3.87 = 414 (^would make nice forced induction builds  )I wonder how many of the 3.87" stroke engines got built so far, and what blocks they all went into(?) Anyone? |
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71 P-code 4spd Javelin/AMX
some Jeeps and some Fords |
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DragRacingSpirit
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Joined: May/27/2009 Location: Mo Status: Offline Points: 903 |
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Posted: Nov/26/2021 at 10:38pm |
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When I think of this post "max cubic inches" of the original poster, that leaves thinking of a stock AMC iron block. The fact of the matter is that an AMC has a 4.75" bore spacing. Why the factory did that with smallish cubic inches is beyond me ! Were they looking ahead in the late 60's and thinking more cubes ? They laid the foundation for it but never followed through with it ?? The only way to get the potential of of the AMC design is with an aftermarket block and the head design to go along with it. What a shame....AMC had an engine design that could have offered an easy 500 cubic inches....albeit with a taller deck.....but used it for a measly 400 inches ?
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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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PHAT69AMX
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Joined: Jul/07/2007 Location: West Virginia Status: Offline Points: 5919 |
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Posted: Nov/26/2021 at 11:09pm |
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DragRacingSpirit - The 4.75" AMC Gen-2 Bore Spacing was a machinery and tooling carry-over from the previous Gen-1.
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DragRacingSpirit
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Posted: Nov/26/2021 at 11:46pm |
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You are suggesting that AMC was just being cheap and went with what they already had........I wish I didn't believe that you are most likely correct ! Cheap to the end ??????????
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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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BBO UK
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Joined: Feb/17/2020 Location: UK Status: Offline Points: 288 |
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Posted: Nov/27/2021 at 7:15am |
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If only they`d had time for a Gen 3, taller deck block, but along came the "fuel crisis"
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Ken_Parkman
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Joined: Jun/04/2009 Location: Ontario Status: Offline Points: 1814 |
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Posted: Nov/27/2021 at 11:28am |
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Dunno, AMC deck height is probably 30 years ahead of its time. You could get over 500 with that bore centre.
Interesting that the modern pushrod V8's (mopar gen 3 hemi, LS) copied the AMC 9.2 deck. And the race pro stocks have pushed the big block deck down to just below the AMC. Fore sure the 4.75" bore centre deserves more bore in a perfect world. 4.500 or 4.550 would fit with a siamese, maybe 520 cubic inches in a "small block".
Pretty perfect. |
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DragRacingSpirit
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Posted: Nov/27/2021 at 4:55pm |
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I don't even pretend to know what you do about engine design! A large, longer stroke, short deck engine with a low rod length to stroke ratio and large bore seems to be all the craze in pro stock these days. But for an engine to be long lasting in a situation where you want to put 150,000 miles on it (factory mass produced) and have 500 cubic inches, in the same basic platform, the taller deck is a must have for the lifespan of the engine. I'm not referring to strictly the drag racing angle but a high torque large cubic in engine that will last a long time. As an example, I have a 2003 GMC one ton van with a 496 factory cubic inch engine in it. It has 496 inches and 225,000 miles on it. If it was a short deck engine with the same bore and stroke, i suspect the engine longevity would not be there because of the thrust loads and thus bore integrity over the long haul. This is all hypothetical as in AMC wanted to have a reliable 500 inch engine in 1971 ????? That didn't happen unfortunately but they did have a base platform to work with.....with some modification. Either taller deck or siamese bore...or both.Edited by DragRacingSpirit - Nov/27/2021 at 5:15pm |
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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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DragRacingSpirit
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Posted: Nov/27/2021 at 5:27pm |
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Beings we are talking stroke and deck height. I am building a new Indy block. I am inclined to go with the 4.15" stoke for 499 cubic inches. That is what I have ordered from Moldex. But...The later versions of the complete engine that they were offering actually had a 4.25" moldex billet crank. When I look at the compression height/rod length I think that the 4.25" stroke is just to much in a 9.4 deck height engine. What are your thoughts about this ? Of course the constraint on cubic inches is what their 300cc port size versions of the heads will flow.
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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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Ken_Parkman
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Posted: Nov/27/2021 at 9:38pm |
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A smart engine guy once said a good guideline is the rods should be 2" longer than the stroke and don't worry about rod ratio or side loading. And that's pretty much what the production LS7 is. But that does make for a really short AMC piston of about 1.025" with the 4.25/9.4 and zero deck.
You could talk to your piston guy and see what he says about a 4.375" bore and 1.025" CH. Another way could be cam machine the crank counterweights and use a little shorter rod. Or push the piston up into the gasket (see Kasse EMC Ford from some years back). Some have been down those roads. But no question 4.25 in a 9.4 is getting tight! What do you want to spin it too? I have some data on the Indy's and I can run a velocity/rpm calc.
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DragRacingSpirit
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Posted: Nov/28/2021 at 1:06am |
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I actually have a crank in the works from Moldex for a 4.15" stroke but wanted to hear your thoughts on it. I just thought that 4.25" was to tight. But I would still love to see some of your calculations I am planning on spinning it to 8-8500 and N/A If I have the flow I need to make horsepower at that rpm level. Indy block, moldex billet crank and GRP 6.2"rods is the bottom end that I have in the works along with the 300cc version of the -1 heads.
Edited by DragRacingSpirit - Nov/28/2021 at 1:15am |
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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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