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Old 03-09-2013, 02:42 PM
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400 sbc advice

I have a old 400 sbc in a gmc motorhome and it's been sitting for years and just had a thought about building one and just need to know if it would worth it or should I just get a 350 IM wanting to make 425 to 450 hp at the crank thanks

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Old 03-09-2013, 02:49 PM
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400

You can do alot with a 400 sbc. Thats the engine I'd stick with. Bore it out to a 406 (.030) and you can build a monster on a budget. What kind of budget are you working with? Great engines to build.
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Old 03-09-2013, 03:57 PM
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Right now IM not sure what budget. What heads would be best I have found some double hump or vortec and what could I do with the head I have it's a 76 model so I know it has some emission controls on it. Should I bore it I know it could be a 406 but if my cyl are ok should I and it's froze up it wouldnt turn over I don't know if it froze up or locked up. It's still in the motorhome I have started pulling it so I know more when I get in it how would 5.7 rods would be thanks
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Old 03-09-2013, 04:13 PM
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Rebuild the 400 you have. It will make more horsepower and most important, it will make more torque over a 350. You can also use less cam and have better street manners with a 400 and it will pull hard. You may want to consider modern cylinder heads as they flow much better than the heads that you have that are from the 1970's. By the time you recondition those old heads you can purchase a decent set of newer heads that flow much better. Good luck
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Old 03-09-2013, 06:22 PM
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rebuild the 400. your working with a larger engine with more displacement should be cheaper and more easy to hit that hp mark that you are seeking as well. with a few exta bucks thrown at it you can build a monster. Plus you dont have to go out and buy a 350. (Money Saved)
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Old 03-09-2013, 07:24 PM
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I will play devils advocate

400 is the weakest structure of the Chevy small blocks.
Decks are subject to cracks at steam holes to head bolt holes and to cylinders. Decks also tend to be wavy and not parallel to the crank. Tend to pull head bolt threads.
Cylinders are the weakest of the sbc series.
Main bearing saddles are the weakest of sbc engines
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Old 03-09-2013, 09:15 PM
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400

You can get a decent set of used aftermarket heads for a few hundred bucks that will boost that compression. some 64cc or 68cc heads, a set of flat top pistons and a good cam ( Comp Cam 284 ) and you'll be at the mark you want with a set of headers and a good carb.
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Old 03-09-2013, 09:46 PM
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Quote:
Originally Posted by BOBCRMAN@aol.com View Post
I will play devils advocate

400 is the weakest structure of the Chevy small blocks.
Decks are subject to cracks at steam holes to head bolt holes and to cylinders. Decks also tend to be wavy and not parallel to the crank. Tend to pull head bolt threads.
Cylinders are the weakest of the sbc series.
Main bearing saddles are the weakest of sbc engines
I've built 7 or 8 400's in the last 10 years. A couple of them were warmed up pretty good.

I've yet to see any of those problems you speak of.
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Old 03-09-2013, 09:55 PM
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I found a set of double hump for 25 a set or I know I could find a set of vortec
I am not sure on what lifters to use thought about going to a solid lifters and maybe roller cam and rocker I don't know anything about rollers I am thinking about 5.7rods. What about stroking to a 421 is it worth it and would the block be any different with it being in a motorhome then a car or truck if I helps my casting number are 330817 I know it's a 1976 gmc mitas RV it had a 4 barrel carb on it. Would it be a 2 bolt main or 4 bolt thanks
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Old 03-09-2013, 10:09 PM
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There are several variations of the "double hump head." Some have 2.02 valves while some have 1.94. Also the runners are too small for your 400. As stated you can get a decent set of modern heads that flow much better than a double hump.

I would use a roller cam and lifters. IMO thats the only way to go. they make more power, and there is no worries about wiping a lobe or trying to find an oil with the right wear additives.

I personally would not stroke it. As BOBCRMAN stated, the blocks are weaker than say a 350. A stroker crank would put even more stress on it. 2 bolt 400 blocks are actually stronger than a 4 bolt. Either way you will be fine.

If I was building it on a budget I would use the stock reconditioned rods, but if you are going with a different piston, then Id use the 5.7. There are advantages and disadvantages to both.

Im sure it would clean up at .030 over. Then rings are probabaly siezed to the bore, no big deal if you are rebuilding it.

Do your homework before buying parts. Make your combo match.. intake, cam, heads, etc. You will be very happy in the end with a very "torquey" 406

Chevyguy13
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Old 03-09-2013, 10:40 PM
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How is destroking vs stroking and would it be better on a block then stroking one? Right now IM just thinking I hope to get the engine out soon and I could take a better look I know I could get a set of 5.7 easy probably on a trade but would 5.7 rods give more hp then the stock rods. I was thinking of flat top piston but a guy at a local engine said that I might not be able to run pump gas. What size carb should I use and are any of the efi worth the price I thought maybe later on putting one on it
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Old 03-09-2013, 11:00 PM
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would 5.7 rods give more hp then the stock rods?

On a street 400 the longer rod just gives less rod angle and is easier on the cylinder walls. Watch for rod/camshaft clearance.

Destroking is defeating the purpose of using the 400 block.
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Old 03-09-2013, 11:13 PM
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Quote:
Originally Posted by jrbaker View Post
How is destroking vs stroking and would it be better on a block then stroking one? Right now IM just thinking I hope to get the engine out soon and I could take a better look I know I could get a set of 5.7 easy probably on a trade but would 5.7 rods give more hp then the stock rods. I was thinking of flat top piston but a guy at a local engine said that I might not be able to run pump gas. What size carb should I use and are any of the efi worth the price I thought maybe later on putting one on it
5.7" rods are not for power, they're for reducing side loading of the cylinders caused by the short stock length rods.

Use the factory crank. No stroke/destroke necessary to make all the power the tires can handle on a street machine.

Fuelie/Vortec heads are 64cc nominal. You need to look into a D-shaped dished piston in the 22cc dish volume range to reduce the CR to a pump gas friendly level (9.5:1 area) to use 64cc heads.

Fuelie heads are OK if you want a low rpm torque engine, cam it to match. But to make good hp will require a larger intake port volume and an all around better design head.
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Old 03-09-2013, 11:34 PM
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I agree... You may could use a flat top piston, but you would need a 72-76 cc combustion chamber head. Or as Cobolt327 said us a D shaped dish piston with a 64cc head.

Rod length will not change HP. As stated above it will change the rod angle, there for changing the load on the cylinders. It will also change how long the piston "stays at the top" what I call Dwell positon. Depending on the rod length, and type of rod you could have clearence issues with the cam shaft. Manufacutres now offer a small base circle cam, just for this issue.

I would use your stock rods and crankshaft. The crank is probably in great condition and with a regrind or a little polishing it will be good to go. It is a 3.75" stroke crankshaft. I would not change the stroke at all. Destroking will just make less torque, and you will have to turn a lot more RPMs to get to the same power as with the bigger stroke. More stroke will make more torque at a lower RPM, but will put more stress on block and bottom end as well as create more clearance issues. I would have the rods checked and reconditioned.

I built a 406 last year with a 3.75" stroke Lunati crank and 5.7 rods. I had my machinest drill the steam holes in the heads just for extra precaution. I put a set of RHS heads on it. Also put a roller cam in it. I believe it was a Comp Xtreme energy 286 hydraulic roller (I may be off a little on the number, its been a while) ... Any way the motor is now in a friends truck and makes great low end torque with plenty of power to 6,000. Its a tire melter!

Using your stock bottom end, a nice cam and heads, you will make great power for the street!
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Old 03-09-2013, 11:58 PM
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I wasn't planning on stroking it at all but I did have a thought about it but I really didn't want to get into it at all. Really I ain't decided on what car I want to put it in now thought abt a 3 gen Camaro or firebird thanks
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