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big block rpm?

17K views 45 replies 16 participants last post by  OldGuy 71Acadian 
#1 ·
my car has a 1970 396 (402) not sure if its a 4 bolt main or 2. My question is how many rpm can a stock 2 blot main big block handle. The guy who built the engine said the cam should make power to 6500 rpm. I shift at 5300 cause im not sure if the bottom end will handle 6500. I cant remember if he said it was a 4 bolt or two. I know its a cast crank. Also I have a steel crank from a 427. can I make this work in the 396? Thanks guys!
 
#2 · (Edited)
396/427 strokes are the same. I have a "STOCK" 2 bolt block (454) that I have no problem twisting to 7200. There are many more important parts giving the ability to get there. A steel crank is a good idea. You may never need to wind it up to the redline, but the dyno will tell no lies (well, sometimes). That would be a good place to start anyway.
In short, yes it will go there. Many folks get the wrong idea about 4 bolts vs 2 bolts. If I happen to get a deal on one, great. If not, great. Machine work quality is key. What type of cam is it? I'm assuming it is hydraulic.
oh yeah, I'm pretty sure its not a fourbolt. That's not too common..
 
#3 ·
for a stock bbc 5,400 rpm would be the max I would go...if you want more ya gonna have to pay more...:yes: Crank, rods, push rods, etc... I would be glad to help but together a nice "Rat" !! Depends on your budget! but its soo easy to get power out of a BBC!!!:yes:
 
#5 ·
If you have just stock but good condition parts and proper assembly, 6500 should be no problem at all. Valve springs would be my only reservation and if they are correct for the cam, you should be good to go.
I have done many, many BBCs and even 496 with stock two bolt mains have gone 7000+ with never any main or block issues. Not even mild supercharged.
 
#7 ·
a 396, 427 ,,, 7500 used to be the standard rpm for 'em ,,lol ,,, a 2 bolt with a 4 speed i'd kinda worry about ,,, many many old write ups of tests with BBC's with 2 bolts going to 7500

one i remember the most was a stock 396 PHR mag built ,, they went stock everything , then they put a Lunati 268 @ .050 solid cam in it , a scorpion intake and a 850 and made 501 hp ,,, then they put a 125 NO2 kit on it ,, 2 bolt main ,, then they put a tunnel ram and 2 750 DPs on it ,,, winding it to 7500 ,, 538 gear in a Vega with 14 x 32 slicks ,, old school :)
 
#17 ·
Not quite, his credentials speak for themselves on both sides of the boarder and he was also employed through GM. He passed away a few years ago, but as I mentioned, all his accomplishments still stand, this is not my opinion of him, it's actually who he was, a well respected engine builder up here in Southern Ontario. Any one who is affiliated with drag racing up here, is well aware of who he is.

Since his passing, I am now the only person, who can prove a true 69 SS Nova without paper work, so it's not another "I know someone story" just because he didn't make the big headlines. He as well known up here as Grumpy is down there!
 
#18 ·
Since his passing, I am now the only person, who can prove a true 69 SS Nova without paper work, so it's not another "I know someone story" just because he didn't make the big headlines.
Assuming what you say about his accoplishments is true (which i question because you dont reveal this master engine builders name), you are not him. Therfore, not being a machinist, you can not accurately answer the question.
If you truely follow the creed "Nova People Helping Nova People", you will let this poor guy seek advice from those whom have first hand (not second hand) knowledge of the subject.
 
#21 ·
Exactly how many big blocks is that? And how many drag strip passes did you make? Im assuming you raced in a super stock or stock eliminator class?
And if he in fact was the greatest engine builder who ever lived; him being deceased means he can no longer build an engine for the poor guy that you're telling to shift his motor at 7500rpm.
So that being said, lets participate in that "creed", and let him check with a reputable engine builder for advice :), as opposed to someone he doesnt know who has bunches of big blocks built by a guy that no longer is above ground.
 
#22 · (Edited)
When did I post he was the greatest and where is it posted, that I told anyone to shift at 7500rpm?:confused:

I posted I twist my 402 2 bolt, cast crank to 7500 rpm! you're implying something else.

Reread the original question before you start bashing my response, that is nothing what you are implying.
 
#25 ·
Well I know im just a shade tree mechanic and have alot to learn but im sure even if it will hold at 7500rpm, its not making power any longer. Thats ok though, im only looking for 6000 to 6500 frequently. thats really why i asked about the steel crank. I really need to get to the dyno and see for myself what she is pullin instead of taking the builders word for it. that way i can see if she even will make power at 6500 like he claims. If i short shift at 3500 she really blows the tires off which makes me think 3500is where my torque peak is, and if my torque peak is at 3500 im kinda thinkin max hp is somewhere in the neighborhood of 5500 give or take. Am i thinking right? really wish i knew what cam was in it. i really appreciate the input guys please keep em coming!
 
#32 ·
Until you go threw that motor yourself and know whats in it!! I would advise staying away from those high revs...the motor has to be built to handle high rpms safely..Besides bbc's or "RATS" make plenty of street power in the lower rpms any way! RIGHT!! Imagine you shifting a built BBC at 8,000 rpm on the street!! YOU will go to jail and lose your car....hopefully thats all...:yes:

Good luck man!!!
 
#26 ·
FOR ME IT'S WHAT YOU WANNA DO WITH IT, IF YOU WANNABE THAT SLUGRUNNIN' AROUND TOWN WITHA BIG MOTOR WITH NO GUTS, DO SO, I'LL SEE YOU SOON, :yes:
BUT IF YOU'RE REAL WITH IT, DO THE FULL WORK ON IT.
 
#28 ·
I've run 396/402/427's for over 30 years and one of the best engines I've raced was a cast crank, 2-bolt, 402 with 12 1/2-1 compression. That engine ran 72-7500 every pass and I NEVER had a crank problem. Yes I run a steel crank now, but that what was more available back then. Engines will naturally live longer at a lower rpm if it's built for it. But something else to consider in his combo is, what heads and cam is he running? If it's a hydraulic cam and oval port heads, he'll be limited to around 6500rpms. Not saying it can't go higher, but that's about it for making power. I've never driven over a cast or steel crank in a two bolt block. And if I remember correctly, red line on a SS396 car with a 325/350hp combo with hydraulic cam was around 6000 from the factory. The 375 horse engine was higher with a solid cam. Dave
 
#30 ·
i would like to see the parts list and builders assurance and dino results before i ran my BB at 7500. forums give out a lot of great info dont get me wrong but like mentioned earlier it is the net and everythings true on the net isnt it?:rolleyes:.rember......theres alotta over reved BBs used as boat anchors.
jmo.
 
#31 ·
Great point, you need to know your builder, my father grew up with my builder, so I've known him my whole life and spent plenty of time at the track with him. I was lucky, because he was a person family friend. I don't think I would walk into any builder and request this build with no background information.:no:
 
#33 ·
We ran a 427 with a stock crank and rods (balanced though). We launched at 5500 rpm, shifted at 7000 and went through the lights at about 7200. It was raced every weekend for several years until it eventually blew up :D

Chris.
 
#35 ·
i think the nah sayers in this thread have read too many magazine articles , with hyd cams on a 114 LSA :: gag :: ,, and EFI :: PUKE :: ,,, and 496's that only wind to 6000 :sleep: ,,,, a 396 or 427 used to be built to wind around 8500 ,, with the right stuff of course ,, but they will wind and they can last ,,,

with a 2 bolt i'd get main studs , and maybe gets straps for the center 3 mains ,, a BBC will stand way more than most will think
 
#37 ·
back in the 70's ,, a 427 bbc gear was a 557 with a 32 in tire ,, they'll wind ,,, they really pull hard at those high RPM's with the right cam ,, thats where the square port heads shine on a 427 ,, they're evil ,,, my neighbors 435 tripower vette was amazing ,, the tach would sweep past 7000 like a rocket ,,, it had been balanced and had hooker side pipes on it ,, and had the vacume linkage took off the front and back 2 barrels and a mechanical linkage installed ,,, roar just isn't the word when all three were wide open ,,, i still find it hard to believe they released these cars to the general public ,,lol,,,
 
#38 ·
A friend of mine drag raced a two bolt 468 with a cast crank and 3/8" truck rods for quite a few years shifted at 7K and it never did break, it was replaced with a 540 and is collecting dust in the shop awaiting street duty now. I think the 2 bolt blocks and cast BB cranks are underrated by many.
 
#41 ·
Im asking for advise from you guys. I am very conservative with what i do to my engine. kind of a poor boy here so i cant afford to tear a big block up. thats why I asked what would be safe for the stock bottom end. I wouldnt blame what ever happens to my engine on anyone but me. You wont hear me whining because of advise i asked for. Thanks for your input anyway.
 
#40 ·
Let's keep the "bench racing" civil, guys.

My only comment is one person's anecdotal evidence isn't proof that everyone's results will be the same. Excessive rpm can ruin an engine. I would never assume that all 402's can rev to 8,000 with no ill effects.
 
#42 · (Edited)
@Shauns BB70

Will I hope somewhere along the comments you got a little more info on rpms on a stock BBC!!! you definately got a pretty good BBC in your Nova.. Don't blow your motor up!! You have to know whats in it before you even go to a machine shop..Fact! they, he are going to ask. what crank, rods, etc..what the motor has in it.. but I would just Shift at a safe rpm or get it dynoed.. Then when you decide you wanna hold that pedal down and shift a little later. Tear the motor down and build it stronger....:yes: Rember you got a "RAT" and the power and torque come in at the lower rpms.. :yes:
 
#43 ·
@Shauns BB70

Will I hope somewhere along the comments you got a little more info on rpms on a stock BBC!!! you definitely got a pretty good BBC in your Nova.. Don't blow your motor up!! You have to know whats in it before you even go to a machine shop..Fact! they, he are going to ask. what crank, rods, etc..what the motor has in it.. but I would just Shift at a safe rpm or get it dynoed.. Then when you decide you wanna hold that pedal down and shift a little later. Tear the motor down and build it stronger....:yes: Rember you got a "RAT" and the power and torque come in at the lower rpms.. :yes:
Thanks man, that's probably what I'm gonna do. Might just build a different BB while still running the 396. If I can find a good block for a decent price that is.
 
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