MAX RPM stock chevy 400

[blue88]

Ok... This may have been asked before.. but I could not find in archives. Here is what I am looking for.

Stock 400 sbc motor..standard bore.. stock pistons, 5.565 rods.. with good rod bolts installed. It has ported fuelie heads, high rise gm intake and open headers.... Running in very thick mud. How many rpms can this be safely turned? I am thinking 5500. Anyone with any experience in this area?

[Wolfplace]

Ok... This may have been asked before.. but I could not find in archives. Here is what I am looking for.

Stock 400 sbc motor..standard bore.. stock pistons, 5.565 rods.. with good rod bolts installed. It has ported fuelie heads, high rise gm intake and open headers.... Running in very thick mud. How many rpms can this be safely turned? I am thinking 5500. Anyone with any experience in this area?

Get two
Test the first one
Lower the RPM a few hundred in the second,,,,,

Sorry,, just couldn't help myself,,,

[levisnteeshirt]

i helped my brother build a 383 about 15 years ago , he didn't want to spend alot ,,, had a cracked 400 block , so we used the 400 rods and crank,( balanced ) he turned it 6700 many times , no problems , engine is running today , dern thing got 19 mpg with a 4 speed, 230 @ .050 cam 109 lsa , 323 gear , 69 camaro ,,, 6700 for short bursts in a street car , it does fine , mudd bogging with alot of gear , it will do ok until it doesn't , if you want a serious effort , its almost cheaper now to get the longer rods instead of trying to save a few $ with the short rods

[ZIGGY]

Running in very thick mud

I don't know much about mud bogging or whatever but lugging an engine on a heavy dirt track is one of the best ways I know to break a crank. I'd be way more worried about that than the top rpm limit.

[rally]

blue88 i would only spin your 400 6,000 Rpms, thats it. They are a torque engine first and foremost. What i dont understand is why do people want to spin the living daylights out of engines. It doesnt mean nothing and if you over rev you are losing power. My guess is 6,000 Rpms are plenty for that stock bottom end and good rod bolts, dont press your luck.

[rustbucket79]

5500 peak with the odd 6000 RPM "whoops" is fine. Going over 6000 can result in main bearing damage and cap walk/fretting.

[jason snyder]

The question should be HOW long will it last above 6k !! my buddy has a stock short block ( looks like it probably has 100,000 MILES ON IT ! simply bolted on a set of 210 heads ,and a flat tappet cam 256-264 @.050 and .550 lift ,on a 105lsa .. nova runs 7.6 in the 1/8 with lots of passes,shifts 7k ! BUT its only a matter of time ,before the block goes boom .

[rfoll]

I think I would be more concerned about the stock pistons if you still have them. I have a friend that builds race motors for a living. Has a dyno in his shop. Personally he races mostly SCCA stuff. He ran various configurations of 400 blocks over the years and clued me in on the problems I would encounter when I started building them for myself. The fretting in the main caps will show up eventually if you don't use splayed caps or an internal balance crank. The stock crank will fail before the rods. The external balance will fatigue the crank to failure after sustained high rpm usage and it will break near the front. That said, I have only used stock cranks in my bracket car and have yet to break a crankshaft. Hundreds of passes, always shifting over 6300 rpm. One of my fellow racers had over 400 passes on his 406.

[Cogburn]

I had a stock 400 in my '70 Camaro for a while and managed to crack 5 pistons after buzzing it a little over 6ooo rpm. It never did blow but it did blow by. A few of the pistons literally were ready to fall apart when I took that motor apart.

5500 rpm is probably a good place to stop. Running it against a rev limiter hard will kill it too.

[ZIGGY]

FWIW, my circle track experience w/400's is that the cranks are stronger than the 350 stock cranks. Splaying the mains is less benefit than 350. Block is weaker all around. They will split webs, cyl. walls, etc. more readily. However I have run many 400's with stock rods & crank, dbl. hump/EQ/vortec heads, comp.11to1 plus, cast pistons, turning them to the low 6's, sometimes much more, and had relatively few failures. That's with good tune and good drivers. I'd throw the crank & rods away at the end of each season. The stock pistons would scare me. And as I said before, don't let it lug. JMO.

[blue88]

Thanks for all the input.

I can always go the built motor route.. but this one is sitting on floor in garage and cost is .. well right. I guess if/when she goes boom.... I will have to build the second one.. the correct way.

I was thinking 5500 rpm max.. just don't quite no how to achieve that in mud... spinning tires can cause some rpm hikes.. I am sure of that.

[levisnteeshirt]

had a friend with a 400 rod 383 , he ran it in a circle track car a few years , then drag racing a good while , they took it apart after 5 years and it looked great inside , Bowtie0069 on the Nova site has a 400 crank still in tack he took over 7500 many times , the deal is , how far do you want to push your luck ? I think thats why immediatly a pro engine builder will tell you to stay away from the 400 stuff , i've never saw a 400 rod break , but have saw a crank or 2 bite the dust ,

whats your long term expectations is another consideration , how long do you want this mud bogger to last ? those 4130 cranks are not that expensive considering what they'll protect from happening comparring to a stock cast crank failing , think about it like that ,,,, i've been lucky with the factory stuff keeping the rpms below 6500 when its what i had , good prep and machine work goes a long way for anything to last , a bad builder can blow up a lawnmower ,

find a 1182 factory forged 350 crank and make a 377 with 350 rods and main spacers not made from a bearing , , they'll stand alot of abuse ,

[CNC BLOCKS]

400 blocks can be a horror show to say the least!!!

http://www.stevesnovasite.com/forums/sh ... p?t=185248

[levisnteeshirt]

^^^^ so true ,, its a roll of the dice if you have a good one , some people have great luck with them ( and its luck ) , best one i've seen has 10 years use in circle tracking , left a 2 bolt main and had straps put on the caps , his philosophy was , if its limber , don't make a stress point with splayed caps , which in this case , seems to be working ,, its not a high rpm engine , they turn this one 6200

[CNC BLOCKS]

^^^^ so true ,, its a roll of the dice if you have a good one , some people have great luck with them ( and its luck ) , best one i've seen has 10 years use in circle tracking , left a 2 bolt main and had straps put on the caps , his philosophy was , if its limber , don't make a stress point with splayed caps , which in this case , seems to be working ,, its not a high rpm engine , they turn this one 6200

don't make a stress point with splayed caps Could please explain where the streess point is.

I think splayed caps are the way to go as they tie the pan rails in with the webbing which makes for a much stronger lower end.

I wish I could base all my info on one block that went for 10 years LOL