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Old 01-02-2020, 06:30 PM   #1
Pvmt-Pndr
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Big Block Build

For right now well call this a hypothetical build... It will be in a 4500 pound mud truck. That will be it's only job. I'd like a torque curve that is pretty flat mid range. No real set horsepower number but a minimum of 500 would be nice. It will spend most of its time at a redline bolted to a th400.

It's a 72 427 tall deck. Now I know everyone will tell me to ditch it for a 454... forget it. I've got it, it's mine and it will be built.

I'm no engine builder by any means at all but since my 427 in my C60 is running like a champ I have the old block still that needs overhauled. I'm not going to do this tomorrow or next week but I need help making a solid plan for when it does happen. Bellow is what I know aside from that I'm going to need some help.

What I know I want to do is drop a 4.25 crank with 6.535 rods. Something around .100 over that would give me a 505 (condition of the block dependant). I want to run it on E85 so I should be able to run fairly high compression. I would like to spin it around 6000 rpm. I've priced out the bottom end and it looks reasonable to me. I want to build the bottom end stout because I can always swap the top end and upgrade that while the engine is in the truck down the road.
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Old 01-02-2020, 06:36 PM   #2
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Re: Big Block Build

6k rpm with a tall deck block? get out the check book. It can be done, but it's going to be pricey getting that much mass and long rods spun up and hold together
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Old 01-02-2020, 06:44 PM   #3
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Re: Big Block Build

6k rpm is not set in stone at all. That cam easily be moved down to a lower rpm. I figured a forged bottom end should hold together pretty well. I'm willing to spend the money so I don't need to get into the bottom again.
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Old 01-02-2020, 10:44 PM   #4
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Re: Big Block Build

It be easy. What’s the difference between a standard deck long rod 427 and a tall deck long 427?? Piston pin height. All decks have forged crank so don’t need to spend money there. Only real cost would be the longer rods. Use standard deck 427 pistons.
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Old 01-02-2020, 10:53 PM   #5
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Re: Big Block Build

A 427 will be more apt to turn 6000, but it will not produce the torque that a 496+ engine will. The 496 will produce more torque at a lower rpm.
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Old 01-02-2020, 10:55 PM   #6
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Re: Big Block Build

If your going to run E85 you should be at 12-1 compression minimum, and if you can get a tight quench area. You can go as high as 14-1 with pump E85.

Other then that it should add alot across the whole rpm band, and have a wide range of tuning.
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Old 01-03-2020, 04:31 AM   #7
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Re: Big Block Build

The difference in deck height is .400" between standard and a tall deck. The tall deck crank, rods and pistons are useless in this situation. They're good for a low reving engine to run at 3200 all day long but 4000-4500 rpm is the hard limits for the bottom end. I don't recall what size the crank is off the top of my head but it's small. Since I'm committing to it I'm going to drop a bigger crank in anyways.

I had 13:1 compression in mind but most of my knowledge is from reading a lot.

Anyone have suggestions on heads? I'll get a single plane intake and narrow that down once I know I have a solid plan for everything below it.
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Old 01-03-2020, 06:37 AM   #8
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Re: Big Block Build

A 427 is a 454 block with a 396 crank, or a 4" bore with a 3.76" stroke. What heads are on it now? Also, it would help to know what pistons were in it, domed, flat, or dished? And, do you plan on using the old pistons or buying new? Heres what I did when my L34 396 threw a rod out the side of the block. I bought a gen 1 454 truck block for $100 and bored it out .060" over to 4.310". Installed my 396 crank with the factory 454 rods and a set of brand new JE forged domes to fit the .060" over bores. That combo took the 396ci displacement .060" past 427ci to 439ci. Now keep in mind stroke is torque and rpm is horsepower. A shorter stroked big bore motor will deliver both if that rotating assembly is balanced to within a gram of fly weight. (gnats ass) And add a quality solid lifter cam and EDM lifters (EDM's is self oiling lifter, Electronic Discharge Machining with a hole laser cut in the face of the lifter) and you have an internally balanced Big Block Chevy motor that will spin up 8000 rpm and live to do it time and again! Now, your kinda stuck with that truck tall deck block. You got a couple of options, Mark IV engines saw extensive application in Chevrolet and GMC medium duty trucks, as well as in Blue Bird Corporation's All American and TC/2000 transit buses (the latter up until 1995, using a 427 with purpose-built carburetor). In addition to the 427, a 366 cu in (6.0 L) version was produced for the commercial market. Both the 366 and 427 commercial versions were built with a raised-deck, four-bolt main bearing cap cylinder to accommodate an extra oil control ring on the pistons. Unfortunately, the raised deck design complicated the use of the block in racing applications, as standard intake manifolds required spacers for proper fit. Distributors with adjustable collars that allowed adjustments to the length of the distributor shaft also had to be used with 366 and 427 truck blocks. You can either reach deep in your pockets and use that block but you'll pay dearly matching pistons and an intake to justify building the power it's capable of making. Or, set it back and find a cheap 454 block to throw that 427 crank in. That crank is most likely a forged steel crank and should also be an internally balanced version. You don't need that 4-bolt main block if you balance the rotating assembly, a must in any build! And you don't have the heads bought yet? Post some numbers off those heads you have, they may very well be some old school closed chamber heavy hitting heads like I had on my 396. That motor I'm building right now will have the 1969 3964290 heads with 101cc chambers. Them with 37cc domed pistons will end up at around 13.5:1 compression demanding 110 octane fuel. But that motor will live at 7500+ rpm beating up LS motors at the drag strip. Sometimes I wonder what it would do in a mud pit...
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Old 01-03-2020, 07:11 AM   #9
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Re: Big Block Build

The specs are 4.25" bore and 3.76" stroke on the tall deck, same as the short deck and the bore is the same as a stock 454.

Current heads are stock medium duty heads 330865 or 343772 I don't recall off the top of my head which set I put on my C60. Both if I recall correctly are open chamber heads and have the same valve specs. I figured aluminum heads would be the best bang for my buck, I understand I'll have a couple/few grand into them alone. The pistons have small notches in them I assume for valve clearances. I plan to buy new pistons because the tall decks uses 4 ring pistons. You're correct the stock crank is forged.

The tall deck intake any more shouldn't be a problem as I understand that most single plans intakes come to accommodate the longer distributor needed for the tall decks. Basically the hole is drilled down lower in the intake to accept the standard distributor.

Running E85 I will be able to run a much higher than usual compression ratio. I'll just go through a lot more of it than I would 110 octane. It should run cooler and have potential to make more power. I'm no expert, no dummy either but not quite knowledgeable enough to dive in without some guidance.

I don't have a set hp goal. I'm not going to say I want an engine that makes 900 hp. The way the truck is set up I feel a strong mid range torque build with a pretty flat curve would do best. Wherever the horse power lands is where it lands. Torque is the only thing measured, horsepower is figured.
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Old 01-03-2020, 08:12 AM   #10
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Re: Big Block Build

Hello from Michigan! your best bet for big block info is to go to the Chevelle website. They are real big block fanatics. there are a lot of really good vendors that hang out there as well. The big block bottom end is pretty robust. Any of the many aftermarket stroker kits available will turn those RPM with no problem. The weakness in the big block in in the valve train area. It cost a fair amount of money to get a reliable valve train. I would recommend Chris Straub (Straub technologies) to help you set up a great combo for whatever you are planning. getting it right the first time is a money saver.
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Old 01-03-2020, 10:55 AM   #11
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Re: Big Block Build

The 366/427 tall deck cranks are prolly the strongest factory crank. Might even be the same as a 396/427 steel crank in the late 60s. The block is a 4 bolt, it's strong. Local machinist has on in his rail drag car. Last I knew it made over 800 horse. Any body that says can't make a tall deck 427 work doesn't know how to build a motor. Yes it requires some special parts, but for what it cost to buy one verses a 454 4 bolt, ahead already.
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Old 01-03-2020, 11:30 AM   #12
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Re: Big Block Build

Thanks TTurbo. I have gathered a bit of my knowledge on that site reading through old threads.

I also happen to have a 366 too... I have no plans for it. Since the 427 in my C60 needed an over haul and I managed to find another 427TD for dirt cheap. I now have the original 427TD that I pulled out of my C60 laying around.

I want to bore and stroke it, at this point I have $0 into this engine and can't sell it for enough to recoup any substantial difference in cost to build this block vs a 454. What I have gathered is the 427TD is one of if not the strongest production blocks Chevy made, that's piece of mind to me. It will be able to handle more than my wallet will be capable of throwing at it with some prep.

I only plan to use the block. I understand it's an all or nothing engine to build. If I did cheap out to save myself some money and keep it a 427 then I'm still buying longer rods and different pistons due to boring the block. Since I'll be that far into it anyways I don't see why I wouldn't swap the crank to at least a 4" crank. Knowing a 4.25" crank will fit with minimal grinding if any (some blocks don't require any grinding some do. Depends on rods and casting).

So let's stick with me saying I'm building a 505. 4.25" crank, 6.535" rods and bore to 4.325", roughly 13:1 compression with the only intent to run E85 and a power band with a very strong mid range torque curve. What parts would you use to achieve that?
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Old 01-03-2020, 12:15 PM   #13
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Re: Big Block Build

I can't make the standard "kit" parts fit that combo. You get close with 454 pistons on a 4.25 stroke with 6.535(wrong 6.385) rod, but the piston ends up .040 down in the hole. you could deck the block .020 and run .020 thick head gaskets. 13:1 pistons are a dime a dozen for 454. The Scat or Eagle kits are pretty good. this is the cheapest way, and checks all of your boxes for the bottom end. Add the cost of custom pistons on top, and you are covering the cost difference between the 10.2 inch deck and the 9.8 inch blocks. Used 10.2 inch block intake manifolds are pretty available. The key to what power you make will be in the heads. aluminum heads are nice, but they are expensive. A set of properly prepped 781 heads will get you the flat torque curve you are looking for. Spend your money on one of Straubs custom cams and a set of Crower sportsman rockers and you will have a combo that will run for years.

scratch those numbers. I need to use the proper calculator for pin height.

you will need 6.385 rods with decking the block .020.

Last edited by TTurbo565; 01-03-2020 at 12:37 PM. Reason: wrong calculations
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Old 01-03-2020, 12:40 PM   #14
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Re: Big Block Build

you will find that most 496 stroker kits come with a 6.385 rod.
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Old 01-03-2020, 05:01 PM   #15
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Re: Big Block Build

That was unexpected until I spent half the day digging into what you posted. Everything I've read leading up to making this thread said 6.535" rods with standard 454 pistons would be good to go. Since standard rod length is 6.135" and by simply adding the .400". I've only come across one person saying they had to deck the surface around .025" also to bring the piston to the top. So thank you for that info! Much appreciated.

What I've gathered about these tall decks they were never very straight even when new.

I believe I'm at the point with some confidence in what I'm talking about now to call a builder and tall over my plan with them. With any luck my block will be in good shape. Thanks guys.
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Old 01-03-2020, 06:33 PM   #16
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Re: Big Block Build

use the Wallace compression distance tool. If you put in the dimensions for a 454 standard deck (4.0 X 6.135 on a 9.8 deck and 0.020 in the hole) you come up with a pin distance of 1.65". Then take the stroker dimensions (4.25 X 6.385 on a 10.180" deck and 0.020" in the hole) you come up with the same compression height for the piston 1.65". there are a few thousandths here or there, but it gets you in the ball park. Next you need to decide on heads. there are various combustion chamber shapes that will dictate what Piston to use. If you go with aftermarket heads they come in varying valve angles and positions. there is even a large variation in combustion chamber volume. You might want to keep it simple and stick with a conventional head with around 118-120 CC chambers. then you need to calculate what your compression will be based on the cubic inches of the cylinder and the combustion cylinder CCs. a 13:1 454 piston with 47CC dome will give 13.8:1 on your 505. I didn't have time earlier, work gets in the way, but there is also a combo that uses 496 short deck pistons that uses a 6.8 inch rod. fairly common rod and piston set up. it will put the piston about 0.010 in the hole. I personally don't like the wrist pin that far up and only do it when necessary.
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Old 01-04-2020, 09:01 AM   #17
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Re: Big Block Build

Didn't say the tall deck block wasn't buildable, just better have deep pockets to make one capable of spinning up 6K+ rpm...That entails pistons, rods, crank, (to utilize the stroke) heads, and a tall deck 10.2 intake. That's roughly $3.5K before machining, bolts/studs, gaskets, cam & lifters, carburetor, oil pump, high torque starter, distributor & wires, timing set, pan & covers, etc. etc...I'm by no means saying don't do it because that alcohol burning BBC would literally be a blast! I imagine you could empty a mud pit in 4 seconds with that thing! I say go for it!
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Old 01-04-2020, 10:55 AM   #18
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Re: Big Block Build

Building a tall deck isn't really any different than a standard deck. Machining is the same, stroker crank, rods, pistons, cam, the same, most parts are the same. Only thing I can think of that is different is the intake and distributor. Even the dizzy is the same if you use the intake for the tall deck and not run spacers.
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Old 01-04-2020, 11:00 AM   #19
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Re: Big Block Build

Push rods too. A distributor with a slip collar or some machining. I have access to machining tools and know how to use them. Nothing engine specific.

I expect to have somewhere around $10k into this motor and if it's more then it's more. I'm not after a cheap build, I'm after a solid build.
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Old 01-07-2020, 11:44 AM   #20
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Re: Big Block Build

For heads, best bang for the buck are late model Vortec heads. Best exhaust port that Chevy ever produced on an iron head and a very efficient chamber. Hint - lots of boat guys pull these in favor of bigger heads so you can find them on Ebay cheap.
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Old 01-07-2020, 08:08 PM   #21
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Re: Big Block Build

After weighing some options and looking at a lot of crate motors I'm debating if I would be better off buying this motor instead, any thoughts on it? The compression lands about perfect for E85 also

https://www.shafiroff.com/chevy-drag...-drag-race.php
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Old 01-08-2020, 12:42 AM   #22
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Re: Big Block Build

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Originally Posted by DieselSJ View Post
For heads, best bang for the buck are late model Vortec heads. Best exhaust port that Chevy ever produced on an iron head and a very efficient chamber. Hint - lots of boat guys pull these in favor of bigger heads so you can find them on Ebay cheap.
Those heads can't get much past 4,500 rpm. That is likely the reason the boat guys pull them.

The D shaped exhausts are nice but the ski jump in the intake port kills the flow and you will find water if you try and make it go away. The heads with a good cam will allow torque to come on like a freight train til that 4,100 - 4,500 but not much after. The non adjustable rockers are kinda lame too.

I think that there are plenty of better heads out there that would out do the big block version of the vortec heads. Don't get me wrong, they're decent heads but think that if I didn't have a set to begin with, Id have run something else.

That said, they work real well IMO for towing. If I was to spend more time bouncing it off the rev limiter, Id try and find some good large ovals, a set of squares or maybe some AM heads.
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Old 01-08-2020, 12:40 PM   #23
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Re: Big Block Build

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Those heads can't get much past 4,500 rpm. That is likely the reason the boat guys pull them.

The D shaped exhausts are nice but the ski jump in the intake port kills the flow and you will find water if you try and make it go away. The heads with a good cam will allow torque to come on like a freight train til that 4,100 - 4,500 but not much after. The non adjustable rockers are kinda lame too.

I think that there are plenty of better heads out there that would out do the big block version of the vortec heads. Don't get me wrong, they're decent heads but think that if I didn't have a set to begin with, Id have run something else.

That said, they work real well IMO for towing. If I was to spend more time bouncing it off the rev limiter, Id try and find some good large ovals, a set of squares or maybe some AM heads.
I read your L29 build thread a few times when I was looking at doing the head swap onto my 87 block. Do you remember the duration of your cam? I saw the lobe center post but didn't see the duration. Clay Smith came to the same conclusion about not needing a split duration with those heads. Mine is 214/214 at .050 and about .510 lift. Just curious as to how close he was to the Straub recommendation. I'm running stock TBI on a factory adapter on a Weiand intake. Been considering swapping to the Vortec intake (have it laying in the garage) and later ECU.
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Old 01-09-2020, 08:43 AM   #24
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Re: Big Block Build

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Originally Posted by Pvmt-Pndr View Post
After weighing some options and looking at a lot of crate motors I'm debating if I would be better off buying this motor instead, any thoughts on it? The compression lands about perfect for E85 also

https://www.shafiroff.com/chevy-drag...-drag-race.php
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