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Old 11-24-2018, 09:22 AM
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Big Block Quandry

I love big block chevys. My first experience has been with a 402 bored to a 408. Even with stock heads this thing is a real kick in the pants in my G-body. Here's the deal: I bought a 427 from a friend of mine and I'm not sure what to do with it. I know there's no replacement for displacement but do I really need a 496 in a G-body? The car weighs about 3900 pounds with me in it and it has a 3:42 gear. Even with the "little" 408 it goes from 3 to 6 grand in a hurry in drive. I've debated leaving it a 427 because they can really wind but I'm also a big fan of torque. Having never owned a 496 I worry about the thing totally over powering the tires every time I mat the gas. I don't want to tub the car and a 10 inch tire seems to fit the best in the wheel wells. I'm asking for advise from other big block owners who know what these engines are capable of. Don't get me wrong, I love the "too much is just enough" theory but I like to drive what I build and want a pleasant and powerful experience. My fear is dropping down a gear to pass someone and the rear end breaking loose. Any thoughts?

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Old 11-24-2018, 09:34 AM
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All I can say is that my 454 with 9" street tires and about 80lbs more than your can breaks them loose at 35mph and sometimes at 40mph going WOT. And it's not like it's that radical of a build either.
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Old 11-24-2018, 10:04 AM
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thank you. That kind of info helps.
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Old 11-24-2018, 02:31 PM
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With a forged crank and decent aftermarket rods, a 496 revs just as fast as the 427, actually even faster when its in gear and moving the car rather than just being free revved in neutral.....reason is the more power you make, the faster the car accelerates and thusly the faster the engine gains rpm.

that old wives tail about 302 and 327 SBC, and 427 BBC being "quick revver's" stems from the fact that in the days when those were the new technology engines, comparing them to Y-block Fords, Flatheads, Chrysler PolyHead, Ford 390 FE's and other typical passenger car designs made the Chevy's seem like quick revvers. But in truth RPM gain depends entirely on how fast you can move the mass of the vehicle.
how it free-revs in neutral means about as much as how fast you can pedal your bike with the back tire off the ground

As far as blowing the tires off on the road....you've got a brain connected to your foot....just use it.
When you've got real power you don't need to mash it clear to the floor just to get around somebody.

As far as that G-body goes....I hope you have more than a stock 7.5" 10-bolt in there, because real power will tear it up right quick if it hooks up at all....plain street tires usually won't hook well enough to break it, but stickier street/strip or autocross tires will.

Either the 427 or a 496 will be a several levels of magnitude improvement over the small BBC you have now, a real eye opener about cubic inches and how bore diameter impacts head flow for you.
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Old 11-24-2018, 06:13 PM
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WOW 8.1 + G Body =

Sounds like a good time
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Old 11-25-2018, 08:29 AM
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You make quite a few valid points. As far as my brain and right foot, sometimes there's a disconnect lol! The rear end is still a 7.5 but it has a custom made auburn posi and 31 spline axles with Richmond 3:42 gears. With the 408 I blew apart two factory posi units and twisted three sets of stock axles. I've been to the drag strip with the new setup and even with hard launches and 13.5 quarter miles with only the primaries opening on the carb (not a misprint, wrong spring in the secondaries) the rear end has held up. sounds like the Stroker McGurk theory screams 496 lol.
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Old 11-25-2018, 01:49 PM
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Yeah, the factory posi's are weak, the side and spider gear teeth are real fragile.
Care to share how you got 31 spline axles into a 7.5"?? No one makes them, or a posi or spool to fit them, and that size axle won't even fit through the carrier bearings on each end of the differential for that matter.

Biggest axles that will fit through the bearing are 28 spline, up from the factory original in your G-body of just 26 spline....but even then, with 28 spline axles the axles aren't the problem....you get this down into the high 12's at the strip and it's going to start peeling ring and pinion teeth off(pinion stem flexes due to small size and gear mesh goes all to crap and crunch ), and there ain't no heavy duty fix for that except an entire rear end swap to something that will handle the power....12-bolt, 8.5" 10-bolt, Ford 9", custom Dana 60.

There's a reason GM put the 8.5" in turbo Buick G-body's, looks like you're about to find out why with the new engine
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Old 11-25-2018, 04:52 PM
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Quote:
Originally Posted by ericnova72 View Post
Yeah, the factory posi's are weak, the side and spider gear teeth are real fragile.
Care to share how you got 31 spline axles into a 7.5"?? No one makes them, or a posi or spool to fit them, and that size axle won't even fit through the carrier bearings on each end of the differential for that matter.

Biggest axles that will fit through the bearing are 28 spline, up from the factory original in your G-body of just 26 spline....but even then, with 28 spline axles the axles aren't the problem....you get this down into the high 12's at the strip and it's going to start peeling ring and pinion teeth off(pinion stem flexes due to small size and gear mesh goes all to crap and crunch ), and there ain't no heavy duty fix for that except an entire rear end swap to something that will handle the power....12-bolt, 8.5" 10-bolt, Ford 9", custom Dana 60.

There's a reason GM put the 8.5" in turbo Buick G-body's, looks like you're about to find out why with the new engine
The axles are from superior. I bought them back in 2003. They were supposed to be a direct replacement for a 7.5 26 spline rear. However when I got them they either had 31 or 33 teeth on them. When I ordered the posi from auburn I asked if I could get gears to fit those axles and they said no problem I put it all together with new bearings & seals and everything fit like a glove. I don't know if you can even get those axles anymore. Another thing I did was use a 3:08 and lower carior? and put 3:42 gears on it. It has a thicker ring gear that way. I have also heard that this rear will not hold up to 12's & lower. Thinking about a strange with the new engine.
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Old 06-23-2019, 08:45 PM
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I would like to make a correction about the axles. They are 30-spline, not 31 or 33. They were an option for the 8.5" 10-bolt. You can get 30-spline side gears for the 8.5" carrior which are also the side gears in my 7.5" custom Auburn posi. Everything fits like a glove. BTW moser makes these axles too.
Anyway, getting back to the topic at hand, If I do go with the 496 build what are the clearance issues that might arise?
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Old 06-23-2019, 11:35 PM
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If you are talking about rotating assembly clearances, then the connecting rod nuts(if thru-bolt) or bolt head(capscrew type rod) may have clearance problems with the oil pan rail area of the block.....easy to fix, slight 1/16-1/8" groove ground to clear the rod in the oil pan rail, and the stroker oil pan with clearance flats stamped in the pan rail.
you will also have to put similar notches at the bottoms of the cylinder barrels, near the can tunnel, depending on which connecting rods are used.

You'll need to do a trial assembly, one cylinder at a time. to find all the locations to grind. SBC strokers have to go through the same process.

This pan image will give you a good idea what this is, block needs to look something like that at the oil pan rail.


Block images:
https://www.bing.com/images/search?v...=0&eim=0,1,2,6



Hot Rod mag article that will help you a lot.
https://www.hotrod.com/articles/how-...stroker-crank/
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Old 06-24-2019, 07:35 AM
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A 496 assembly from Scat or Eagle will not require any block clearancing, at least not in a production block.
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Old 06-24-2019, 07:18 PM
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Thank you. Those images helped. My next question is and Imsport brought it up, which is better, Scat or Eagle for a rotating assembly? I guess my concern is Eagle being made off shore. How are their tolerances and how well do they hold up? Next up is the heads. I plan on buying a set of AFR 290 ovals. I also want about 10.25:1 compression and run pump gas. I believe that requires a domed piston. does anybody have experience with these heads and a particular piston fitting the chamber? Building this engine is a little out of my comfort zone so any info to help me along would be greatly appreciated.
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Old 06-24-2019, 08:15 PM
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If you're not gonna rev it to the moon, either should be fine. If you are, forged crank just to be safe, they aren't too terrible more expensive.

My 496 has 20cc dome pistons on zero deck, the heads have 119cc chambers, comes out around 10.3:1 iirc. Mine is in a 445 casting block and did not require any clearancing.

Are those heads"raised exhaust port" heads? If so, don't be surprised if you have to smash a header tube or two. I have race rite ovals, and darn glad they are stock exhaust port location heads, driver side header barely clears everything, passenger side looks to have way more room for stuff. This is in a mid 60's a body though, not much room for anything.
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Old 06-24-2019, 08:48 PM
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Quote:
Originally Posted by Dfish1247 View Post
If you're not gonna rev it to the moon, either should be fine. If you are, forged crank just to be safe, they aren't too terrible more expensive.

My 496 has 20cc dome pistons on zero deck, the heads have 119cc chambers, comes out around 10.3:1 iirc. Mine is in a 445 casting block and did not require any clearancing.

Are those heads"raised exhaust port" heads? If so, don't be surprised if you have to smash a header tube or two. I have race rite ovals, and darn glad they are stock exhaust port location heads, driver side header barely clears everything, passenger side looks to have way more room for stuff. This is in a mid 60's a body though, not much room for anything.
The heads have raised exhaust ports. The chambers are 112cc and everything is cnc machined. This engine will be in a 1984 G-body. Space is at a premium in one of these too. I don't plan to rev it to the moon. I'm looking at a custom street grind cam where I'll be shifting at about 5500 rpms. I would think a cast steel crank will be fine for my application. High rpm horsepower isn't my goal. I like my peak torque to hit by 4 grand and a lot of it. For me that's the fun stuff for a street vehicle with a occasional pass down the 1320.
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Old 06-24-2019, 09:54 PM
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SCAT is also Chinese sourced forgings and castings, but SCAT does finish machining here in the US whereas Eagle doesn't.

Most all you crankshaft companies entry level stuff is cast or forged in Asia..Callies CompStar, Molnar, Ohio Crankshaft, along with SCAT and Eagle.
The better companies just do the final machining here in the US, so they can control finish quality.

I like SCAT over Eagle....but Eagle has improved from their earlier problems with sizing and finish and don't appear to have the same problems and poorer reputation they once had.

Stay away from CAT though(Cal Auto Transpeed), very poor quality and finish on the cranks I've seen.
Current unknown on exactly how good the quality is happens to be SpeedMaster(ProComp)...some of it is Ok, some is poor, but it is steadily improving in most cases.
I don't personally know anyone who has used their cranks or pistons....but their connecting rods or decent. You can get the rods fairly cheap, but with questionable Chinese bolts in them...by the time you add replacement ARP bolts and pay for a roundness check on the bores after adding the better bolts you are getting close to SCAT or Eagle price territory.

For your plans, the SCAT or Eagle cast crank would work out fine. I recommend forged pistons to everyone who askes about a stroker, I just think it is good insurance as strokers are never driven by a grandma, they are driven fairly hard and forged pistons give you a wider tuning window along with room to grow down the road(nitrous, bigger cam, more rpm) as hot rod stuff often evolves as we change our minds on what we want or get greedy about power.

This is the best deal on stroker kits I've found as it includes harmonic damper and flexplate and has a special forged piston...you can find cheaper but they typically leave pieces out or use lower grade components or hypereutectic pistons to get that lower price point.
https://www.ebay.com/itm/BBC-CHEVY-4...UAAOSwo3pWgk44
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