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Old 12-09-2010, 06:20:38 AM   #1
z28rod
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How much can sbc 400 stock rods and crank handle?

My best friend is building a stock bottom end sbc 400, bored .30 over to 406, stock gm crank cut 10/10 , 5.565" stock rods shot penned and resized with arp rod bolts, the rotating assembly will be balanced with speed pro hyper. flat top 4 eye brow pistons. we are discussing the max hp this stockish bottom end could handle on 93 oct. gas no nos. he says 450 hp , i say 500 plus some as long as its street ran 90% and raced 10% of its life and not reved over 6500rpm..... he plans on using alum heads with 70-76 cc chambers, wants about 10.5-1 comp. and a flat tappet cam of under .500 lift..... oh headers 1 5/8" duals and hei with 750 holley d/p, 4 peed with 3.73 eaton posi 10 bolt. He has a 80 malibu wagon, he is running my 350 out of my z28 right now, its a flat top rebuild with mild cam and home ported heads, maybe 300 hp... but now he loves my 406 so he wants one for his wagon. I am trying to talk him into getting at least a nodular stl. crank from scat. Any ideas to help us end our arguement.
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1981 z28: 406 Sbc with Scat bottom end,ARP bolts thru-out eng. balanced/blueprinted , 10 bolt posi 3.73 gears, Th350 dynamic street/strip 2200 conv., SR Torquer heads ported, runs high 12's on street 60's...

Last edited by z28rod : 12-09-2010 at 06:30:13 AM.
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Old 12-09-2010, 06:33:03 AM   #2
frankz
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The best way to end that argument is to agree on 475HP!!! j/k
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Old 12-09-2010, 06:51:00 AM   #3
z28rod
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Ha to funny, but was looking for a more technical explanation haaaa was funny though.
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1981 z28: 406 Sbc with Scat bottom end,ARP bolts thru-out eng. balanced/blueprinted , 10 bolt posi 3.73 gears, Th350 dynamic street/strip 2200 conv., SR Torquer heads ported, runs high 12's on street 60's...
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Old 12-09-2010, 07:37:00 AM   #4
MyBoTy
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Stock rods are his weak points, he'd do a lot better with some 5.7's. GM had to remove some beef for clearance, it came right off of the shoulder of the rod.
That crank is nodular, they'll generally outlast the block, 500hp is fairly common out of 'em.
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Old 12-09-2010, 09:01:22 AM   #5
79RedZ
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I would think the rpm that he is planning on spinning it too would be a bigger factor. Keep it under 6000 would probably be best for the stock crank and rods, actually 5500 would be a better number. If he is going to turn it over 6000 I don't think I would trust that. just my 2 cents worth.
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Old 12-09-2010, 11:43:14 AM   #6
high impact
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The crank isn't the short coming - the rods are. Put some aftermarket rods in that bugger and let her rip.

I ran a 13.5 to 1 compression solid roller cam 406 with a gm cast steel crank, aftermarket rods (eagle, oops), forged pistons producing close to 600 hp for many seasons and it was fine. It had a 4500 9 inch converter, transbrake and 10 inch slicks, I ran it on the street and strip - this thing screamed to 6500 rpm too many times to count. I was really happy with this engine other than its deep thirst for race fuel.
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Old 12-09-2010, 01:37:57 PM   #7
middleagecrisis
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More than a few years ago I ran a completely stock bottom ended 400 SBC that began life with me at the 90K mark. I slapped some double hump heads on it, a TM-1 intake and a Comp Cam 280 Magnum cam. That motor was a daily driver and saw 6K RPM shift points on a regular basis. I ran that motor for another 30K miles. I rebuilt it and added TRW forged pistons, ARP rod-bolts (stock rods), balanced it, added a .550 lift solid cam and improved the oil system. I ran that motor to 6500 RPM and higher on a few occasions. The next owner of my Camaro suppodesly blew up the motor I never could. If you keep below 6000 RPM and keep the motor naturally aspirated (no nitrous), my personal experience is you'll be fine. My .02 worth.
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Old 12-09-2010, 05:21:04 PM   #8
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I always recommend using 5.7" rods. The 400 rods will be the weakest link in your engine. You must check camshaft lobe to rod clearance when you do this on cylinders 1,2,5 and 6. I have failed the 400 rods in a 450 HP engine.
I believe that the throttle response, or acceleration rate is the key factor, not the peak HP. If you use stock heads, maybe not an issue.
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Old 12-09-2010, 07:10:58 PM   #9
NYH1
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HERE are some Scat forged 5.7" stroker "I" beam rods with cap screw bolts. Not to expensive, and good insurance.
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Old 12-09-2010, 07:17:53 PM   #10
wild84
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Um..... mabey I'm skeptical, but I dont see 450 hp, let alone 500 out of a hydrolic flat tappit with less than .500, and only 1 5/8 headers. Better be some really good flowing heads. Anyways, good luck.
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Old 12-09-2010, 08:49:15 PM   #11
z28rod
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Quote:
Um..... mabey I'm skeptical, but I dont see 450 hp, let alone 500 out of a hydrolic flat tappit with less than .500, and only 1 5/8 headers. Better be some really good flowing heads. Anyways, good luck.
afr 195's will be what he wants to use.
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1981 z28: 406 Sbc with Scat bottom end,ARP bolts thru-out eng. balanced/blueprinted , 10 bolt posi 3.73 gears, Th350 dynamic street/strip 2200 conv., SR Torquer heads ported, runs high 12's on street 60's...
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Old 12-09-2010, 09:01:03 PM   #12
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Mine is surviving me driving it and I am not easy on it. AFR 195's 65 cc chamber, zero deck 4 bolt block with ARP studs, dished pistons, stock rods resized with ARP bolts, manual trans shifting between 5500 and 6000. Have a Lunati flat tappet cam 489 intake 504 exhaust, Performer manifold and a reworked Quadrajet.
Engine runs strong and pulls hard. Last trip was 1300 miles in 3 days and averaged over 19 mpg with the AC on.
Don't know how much horsepower it has, but enough to make me happy and pucker the ass of my brother in law.
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Old 12-09-2010, 10:58:08 PM   #13
z28rod
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I think he and i have discussed this with the input from here, he has decided to use his 2 bolt main block bored 30 over , all arp studs and bolts thru-out engine with the speedpro 4 eye brow pistons to get around 10.5-1 compression. he is going with 5.7 scat rods sfi balanvcer and a good street balance on the shortblock. he is go to use the lunanti Voodoo Hyd Cam Valve Lift (Int/Exh): .489/.504 and get the afr 195 heads, use stainless steel roller rockers , a edelbrock air gap intake, holley 750d/p carb. we are hoping for 450 hp and 500 ft lbs.tq.
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1981 z28: 406 Sbc with Scat bottom end,ARP bolts thru-out eng. balanced/blueprinted , 10 bolt posi 3.73 gears, Th350 dynamic street/strip 2200 conv., SR Torquer heads ported, runs high 12's on street 60's...
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Old 12-10-2010, 09:59:52 AM   #14
Rich Schmidt
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We have ran a few stock crank,rod 400's in race cars with no issues. The 400 rods are as strong or stronger then any stock 350 rod out there. I dont know hwere anybody came up with the idea that 350 rods are stronger. We ran a 7200rpm nitrous'ed 406 with a stock crank and stock rods for well over 200 runs. Eventually it failed because we did nothing to the engine but beat on it and shoot it with as much nitrous as the head gaskets could handle. Probably in the 750rpm range total. It had ported to the max Dart 2 heads,a .680" lift solid roller,12.5:1 compression with cheap TRW pistons that were fly cut to death,and a big shot plate system. It ran 10.0's in a 3500# car on nitrous and 11.20's on motor.

My personal experiance with many 400's over the years is that you run into a head gasket retaining problem before the crank or rods fail as long as you arent going over about 7500rpm and the pictos arent extremly heavy.
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Old 12-10-2010, 01:41:52 PM   #15
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Quote:
Originally Posted by Rich Schmidt
We have ran a few stock crank,rod 400's in race cars with no issues. The 400 rods are as strong or stronger then any stock 350 rod out there. I dont know hwere anybody came up with the idea that 350 rods are stronger. We ran a 7200rpm nitrous'ed 406 with a stock crank and stock rods for well over 200 runs.......................................
My personal experiance with many 400's over the years is that you run into a head gasket retaining problem before the crank or rods fail as long as you arent going over about 7500rpm and the pictos arent extremly heavy.



I have always wondered myself why the stock 400's internals get such bad rep - and I wonder if its because most expect it live in conditions where the 400 may not be ideal in stock form

I understand that revving it to the moon perhaps is not a good thing - and I personally think it has something to do with the whole external balance setup-- unlike say a good hot stock internal 355ci which you can flog and rev all day

I am working on finishing off a 406 with stock rod/crank (cut 20/20) and decent TRW pistons - picked up at a swap meet with damper/flexplate included for $300

I am using my original solid crower compupro cam 244/250 .503/.518 106* from my 355ci and milled Sportsman II 60cc

and I expect to run it under 6000 rpm and use more of its natural torque in a street to strip heavy car

Frankly I expect it to live with the approach I am taking
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