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Longest stroke non-tall deck?
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journeyman
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PostPosted: Wed Aug 26, 2009 9:23 am    Post subject: Longest stroke non-tall deck? Reply with quote

I know I can fit a 4.25 stroke in the 454, but will the 4.375 fit?

How much modification (relief) would be required for this and is this something to be undertaken only by someone who has experience with relieving blocks for longer strokes?
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Blown65
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PostPosted: Wed Aug 26, 2009 11:32 am    Post subject: Stroke Reply with quote

If you are grinding to fit a big crank in a stock block, the biggest problem you will find is breaking into water. Unless you fill the bottom up with hardblock.


Corey

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journeyman
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PostPosted: Wed Aug 26, 2009 12:40 pm    Post subject: Reply with quote

So is ANY grinding (relieving, etc.) required for a 4.25" crank?

I thought (possibly incorrectly) that a 4.25 crank and rotating assy could be installed in a stock block with no relieving whatsoever.

If that were indeed the case (and it may not be), it seams odd that adding 1/16" to the crank's radius to achieve the extra 1/8" stroke would make that much difference in clearance.
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Blown65
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PostPosted: Wed Aug 26, 2009 1:00 pm    Post subject: Block Grinding Reply with quote

I cannot say with certainty that you will need to grind the block with a 4.25 stroke, but I would say that to get the .060-.080" that you need, you will have to grind a bit. Usually you won't hit water with a 4.25 stroke. Putting a crank in a block that is 1/16" larger will eat up the .060 clearance you ground out. 1/16=.062" If you went to .080" you now have only .018" left. You will now be getting thin on the bottom if you clearance the block again. This is why the aftermarket blocks start looking better and better when building stroker motors.



Hope this helps
Corey

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journeyman
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PostPosted: Wed Aug 26, 2009 1:23 pm    Post subject: Reply with quote

My assumption all along was that going to a tall deck block in a street vehicle would be complicated as fit becomes an issue with bolt on stuff (including exhaust)

Is that assumption correct?
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Blown65
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PostPosted: Wed Aug 26, 2009 2:48 pm    Post subject: Blocks Reply with quote

For a straight bolt in, the exhaust will not fit because the head will be .400 higher than before, but any muffler shop should be able to make the minor change to bolt up again. Moving the head out farther may cause it to hit your brake booster or other underhood obstructions.The intake manifold requires spacers or a tall deck version ( better choice in my opinion). You will need a distributor with a slip collar to accomodate the taller deck. Everything else will work externally. I guess it up to you to decide if the extra work is worth the effort.

Corey Smile

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PostPosted: Wed Aug 26, 2009 2:59 pm    Post subject: Reply with quote

Starting to think that 3/8" ain't so necessary afterall.
1/4" seems a lot more practical.
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Blown65
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PostPosted: Wed Aug 26, 2009 3:12 pm    Post subject: Blocks Reply with quote

On a basic 427 build with a .060 overbore the difference in cubic inches is only 15. 496 for the 4.25 stroke and 511 for the 4.375. If you can notice that on a street engine with all else being the same you are a better man than me Very Happy

If you stick to a 9.8 short deck block things get even easier and you can still build a 496. Smile


Corey

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PostPosted: Wed Aug 26, 2009 3:52 pm    Post subject: Reply with quote

The longest safe stroke for a Mark IV two piece rear main seal standard deck block is 4.375" as there is both oil and water running down the pan rail. If you have a Gen V or Gen VI block the oil is above the cam tunnel so you can run a 4.5" inch stroke with a standard deck block (once again you still risk striking water if you get carried away with a grinder.

You will get more torque out of the longer stroke motor which is more important than horsepower. You should be able to feel the difference in the seat of your pants as the difference in power is akin to turning off the A/C in your wife's econo box car that additional six or seven horse power not driving the A/C compressor will be noticable. You will get more than a difference of seven horse power with the bigger motor.

Big Dave
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PostPosted: Wed Aug 26, 2009 3:58 pm    Post subject: Reply with quote

So what exactly do I need to do to install a 4.25 rotating assy? Is there any interference with everything else being factory?

Will there be clearance problems?

FWIW:
App is a slow turning torque motor.
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PostPosted: Wed Aug 26, 2009 4:06 pm    Post subject: Reply with quote

As with any stroker you are going to have clearance issues. The reason the standard deck Mark IV has a 4.500" stroke limit is the cam is in the way so you are talking a reduced base circle cam and H-beam rods to reduce a rod bolt nut from hitting anything. You have to have 0.060" clearance (I use a zip tie to check as I grind if it hits; it is not metal on metal and the plastic absorbs any contact stress) all the way around the entire throw of the crank (cam tunnel, bottom of the cylinder bore, pistons skirts, block pan rails).

Big Dave
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PostPosted: Wed Aug 26, 2009 4:40 pm    Post subject: Reply with quote

Wait... You mean 4.250", right?
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PostPosted: Wed Aug 26, 2009 4:57 pm    Post subject: Reply with quote

OK, so I am wondering what 454 do I really have?

It is a 1993 16,000 Lb truck chassis (engine probably built in 1992). I found a little help on Ebay (of all places) with this:

Quote:
Mark IV: The engine that most people think of as the "big block Chevy". Released partway into the 1965 model year as a 396, superseding the older 409. It is a development of the Mark II and using similar but not identical canted valve (semi-hemi/porcupine) cylinder heads. It was later expanded to 402 (often still labeled as a 396, or even a 400,) a 427, a 454, and a few "special" engines were produced in the late '60's for offshore boat racing as a 482. There was a 366 and a 427 version that each had a .400 taller deck height to accommodate .400 taller pistons using four rings instead of the more usual three rings. These tall-deck engines were used only in medium-duty trucks (NOT in pickup trucks--think in terms of big farm trucks, garbage trucks, dump trucks, school busses, etc.) The tall-deck blocks all had 4-bolt main caps, forged crankshafts, and the strongest of the 3/8 bolt connecting rods. All-out performance engines used 7/16 bolt connecting rods, along with other changes. This engine family was discontinued in 1990, with the Gen 5 appearing in 1991.

Gen 5: General Motors made substantial revisions to the Mark IV engine, and the result was christened "Gen 5" when it was released for the 1991 model year as a 454. There were 502 cu. in. versions, but never installed in a production vehicle, the 502s were over-the-parts-counter only. Changes to the Gen 5 as compared to the Mk IV included, but are not limited to: rear main seal (and therefore the crankshaft and block) were changed to accept a one-piece seal, oiling passages were moved, the mechanical fuel pump provisions were removed from the block casting, the machined boss for a clutch bracket was eliminated, the cylinder heads lost the ability to adjust the valve lash, and the coolant passages at the top of the cylinder block were revised. The changes to the coolant passage openings meant that installing Mk IV cylinder heads on a Gen 5 block could result in coolant seepage into the lifter valley. Frankly, the changes (except for the one-piece rear main seal) were all easily recognized as cost-cutting measures which also removed some quality and/or utility. All told, the Gen 5 engine was not well regarded by the Chevy enthusiasts because of the changes to the coolant passages and the lack of an adjustable valvetrain. As always, the aftermarket has provided reasonable fixes for the problems. The Gen 5 lasted only until 1995.

Gen 6: GM recognized that it did not make any friends when it designed the Gen 5, and so they chose to revise the coolant passages again when designing the Gen 6, allowing the older heads to be used without coolant seepage problems. The boss for the clutch bracket returned, but was generally not drilled and tapped. The non-adjustable valvetrain remained, as did the one-piece rear main seal. Some but not all Gen 6 454 (and not 502) blocks regained a mechanical fuel pump provision. Production engines installed in pickup trucks got a high-efficiency cylinder head, still canted-valve, but with a modern heart-shaped combustion chamber of about 100cc. The intake port has a "ski jump" cast into it to promote swirling of the intake air flow. All production vehicles with a Gen 6 used a 454 version, but over-the-counter 502s are available. The Gen 6 is sometimes referred to as the "Gen Fix" because it fixed a number of issues that disappointed enthusiasts when the Gen 5 was released. As an added bonus, most if not all Gen 6 engines use hydraulic roller lifters.


So from this should I assume I have a Gen 5?
Or were the truck versions different?
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PostPosted: Wed Aug 26, 2009 5:57 pm    Post subject: Reply with quote

If it has a one piece rear main seal or built after 1991 (date code on the block) then you have a Gen V or a Gen VI block. You can check out the casting number on the block at Mortec.com to be sure of what you have. All Gen V and Gen VI blocks are four bolt main one piece rear seals with the Gen VI having roller tappets instead of flat tappets.

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PostPosted: Wed Aug 26, 2009 10:50 pm    Post subject: Reply with quote

Big Dave wrote:

You will get more torque out of the longer stroke motor which is more important than horsepower.
Big Dave


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