502 Block with 3.76" Crank - Chevelle Tech
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post #1 of 20 (permalink) Old Oct 12th, 03, 9:27 AM Thread Starter
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Wanted to start a new thread. Just finished reading the nephew on a 427 versus a 454. I have a 502 GM block that I am planning a future build project. I am thinking about using the 427 crank in this motor which gives 472 cubic inches with a 4.47 bore. Tell me what is good and bad about this combination and how would you build it up!
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post #2 of 20 (permalink) Old Oct 12th, 03, 4:05 PM
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hope you like to spin motors pretty high cause thats what you will get

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post #3 of 20 (permalink) Old Oct 12th, 03, 4:49 PM
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That could be a very interesting motor if you go with solid flat tappets to allow for 6500 + RPM shifting. The torque wouldn't blow off the tires on a street car and with the high RPM efficiency it would be a very eqasy 600+ HP motor in street trim.

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post #4 of 20 (permalink) Old Oct 12th, 03, 7:19 PM
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the SAM school put a destroked 502 into their 78 (or something) Malibu. Running heavily ported ZZ502 heads, a big solid roller, lots of compression, etc. According to SAM, the car made 660 rwhp, and 700 rwtq on the chassis dyno. And also spins to 8100 rpm. The torque numbers are funny, but RWTQ compared to engine tq is different than RWHP compared to BHP.

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post #5 of 20 (permalink) Old Oct 12th, 03, 11:37 PM
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How do you adapt an older crank designed for a 2 piece seal to a Gen VI block that uses a one piece rear seal?


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post #6 of 20 (permalink) Old Oct 13th, 03, 12:27 AM
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you would have a motor that would allow the car to hook easier and pull like a bitch on top end, i say go for it, be our high dollar test mule [img]graemlins/thumbsup.gif[/img]
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post #7 of 20 (permalink) Old Oct 13th, 03, 1:11 AM
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Just buy the rear seal kit that is being sold for this and do the drilling and the older crank will fit right in it!!

And consider boring her out to like .090" or so to turn her ito a 491!!

Drop some Pro-Stock parts into her to be able to withstand the 9,000 rpm redlines and have at her!!!

Wow, what a motor!!


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post #8 of 20 (permalink) Old Oct 13th, 03, 1:17 AM
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I say go for it [img]graemlins/thumbsup.gif[/img]


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post #9 of 20 (permalink) Old Oct 13th, 03, 7:06 AM
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Well, for one thing, the larger bore unshrouds the valves...which is good for airflow.

The down sides I see...

502 has no provisions for a mechanical fuel pump

502 requires an adapter & machining to run a two piece seal crankshaft...more $$$ to convert

502 has an oddball timing cover which means your stuck with a stock style timing chain, or special machining to accept a mkIV double roller chain cover

Personally, my ideal street/strip engine would be a 509 which is a 4" stroke with a 4.500" bore...kinda like a big bore 454.

The short stroke is entirely up to you and is dependant on your intended usage. There are many ways to skin a cat...each has their pros & cons.

- What weight vehicle will this be used in?
- What rpm range (redline) are you looking to stick to?
- How will the car be used, and what percentage of each assuming street/strip?
- how much compression & cam?
- what trans?
- what converter?
- what rear gear?
- what tire size & type?
- any specific race class, or just for pleasure/T&T use?
- will power adders be used?

Many, many things need to be taken into consideration to make a balanced package. A matched combination is much more important than one part such as crank stroke, rod length, cam choice, or head choice. None of these matter a hill of beans if the combination is mismatched.
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post #10 of 20 (permalink) Old Oct 13th, 03, 10:14 PM
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you had me thinking there too for a minute, but i think i'll stick with my stock 502 build and use a single plane intake to take away some of the lower-end torque...

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post #11 of 20 (permalink) Old Oct 14th, 03, 12:41 PM
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I have 2 combinations that I run in my car. A 509 4.500 X 4.00 stroke and a 4.500 X 3.76 stroke. Both are nitrous combos in a 3400lb car. Yes, I do spin the short stroke motor a little higher than the 509, which I feel is probably not the best tradeoff. It seems if you are going to spray an engine, the faster you spin it the less time to fill the cylinders. I have gone just as fast with the 509 as the 477 but I do it with less RPM on the 509. Now I am talking 7700 on the 509 and 8600 on the 477. I have spun the 509 to 8700 with little if any gains.This is a little tire car-9X30 slick- that as far as traction is concerned, the best money I have spent is the digital7 unit. WIth this setup you can build as big an engine as you please and be able to move the car down track. And dollar for dollar, what I have in the 477 I could have built a 632. I say build as big as you can afford and tune the ignition and suspension around the engine combo.
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post #12 of 20 (permalink) Old Oct 14th, 03, 6:55 PM Thread Starter
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It appears that there is some very good discussion. From my reading and discussions from the pro stock ranks, the 3.75 or so crank is what is now almost the standard. It allows the piston speed to to keep from ring flutter, etc. The down side is much higher RPM which is great in some circles when extracting every last bit of horsepower, but is very hard on the valve train. But the combination with the right heads probably would be a blast to drive. Still haven't decided, but the next step which is probably selecting the heads, pistons for a target compression ratio, then the camshaft. Not to worried about adapting to a two piece oil seal for the crank or working the front timing cover to adapt the "good" timing chain. The car (my '70 chevelle) is targeted to weight between 3400 and 3600 pounds (Heavy). But that is what I am planning on starting with. The question is how would you set it up?
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post #13 of 20 (permalink) Old Oct 14th, 03, 7:16 PM
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My comments on the block prep were to alert you of expected expenses. With the cost of a new 502 block and the needed mods/machine work, it's probably not but a couple hundred dollars more and you can have a Dart Big M block which doesn't requires such mods and is a much stronger block and can handle a much larger bore 4.600"+.

One member here Thor (he built a 540) brought this to my attention...if it were me and I wanted the cubes, I'd go with an aftermarket block.
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post #14 of 20 (permalink) Old Oct 15th, 03, 2:25 AM
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You can get a forged 3.76 crank from GM with a one piece seal.
post #15 of 20 (permalink) Old Oct 15th, 03, 4:14 AM
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GM's best 3.76" stroke crank, p/n 3967811, which only came in 1968-69 L88/ZL1 engines (and later L88 crate engines) was discontinued several years ago. It was the only 3.76" crank which was factory counter-weighted for the larger/heavier 7/16" bolt rods. Early Mk IV 396/427 steel tuftrided (nitrided) cranks with cross-drilled mains have also been discontinued. I have seen a lot of NOS GM Mk IV 3.76" truck cranks on eBay in the $300.00 range but theese are not the same as the Hi Perf passenger car units though they are the same forging number. They do not have cross-drilled mains nor are they tuftrided. A good Crower or similar quality crank will run you $1500.00!

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