I'm no builder but I'd say valvetrain then rod bolts are gonna factor, provided the other systems like fuel and ignition will support the rpm.

 

Experience and you're trust in the parts. Generally, no need to turn faster than it'll make power.
Boot77 pretty much has it down. There not a relaible mathematical calculation or anything.

 

Well, when a rod is sticking out of the pan, that's usually a good indicator that you found the upper limit!

There are some calculators online that can give you a number, although I think they are a little conservative. Rod ratio can play a big part and of course when the engine simply runs out of air that can be another indicator. Take a mid-60's small block chevy and normally people would say 6500 was the upper limit but a bunch of us used to turn those puppies to 7300-7500 pass after pass and that was with stock rods and bolts.

 

I have seen some bone stock small block chevy builds from the 70's with nothing more then old factory rods with factory bolts and were resized and cast cranks that were grounded under size and just stock cast hyper pistons and they were ran upwards to 6500 rpm on a regular basis with hydraulic flat tappet cams back in the 90's in dirt track racing with just junk yard car bodies while they were still available in my area. I don't know if that is what is called circle track racing or not but it was a dirt road circle track and just stock cars with nothing fancy and were beaters but it was fun watching when it was something that could be done with the common folks who used to like doing that.

I don't know if it still exists anywhere else in the U.S. but here were I am in Ohio I have not seen anything like that for over twenty plus years. The motors were nothing fancy and a lot of them was the same for Ford with a lot of 302 and 351 builds and the old Mopar 360 small block. They seemed to hold up pretty well. I can't say for how long but my Dad used to race them all the time and I never saw a failure on one ran for a whole season.

 

Shifted my 355 stock crank & rods with cheap Northern rebuild kit flat tops at 6000 mostly but 6500 many times when racing because I thought it had ARP rod bolts(young and didn't check the shops work). Cam went but otherwise I still got it and I'd run it with new bearings, a quick ball hone and some diff heads, fresh cam of course LOL

 

So.....it's basically use your best judgement? And, it's more a function of valvetrain than bottom end rotating assembly (crank,rods,pistons)?

Although, i'm generally more of a fan of longer(long as possible) stroke, which also tends to limit rpm?

 

from an engineering point, piston speed can be a factor. The manufacturer can tell you their limits. With rocker shafts and new spring technology 9k is not crazy. Nascar engines run 9+ for 500 miles. Formula 1 engines have run to 20k. Motorcycle engines have run up close to 20k. Thats probably close to the limit as there isnt enough time to fill the cylinders with air and fuel.

 

Good assembly and proper machining of the parts and good judgement with experienced eyes and hands can go a long way on a basic build. I have had several budget builds done back in the day and my Dad would always take my old 86s10 I used to own out and just romp the heck out of the thing and about threw me through the window into the bed lol as it would just take off so quick at just hitting it to 6500 rpm with no issue with tires a blazing all over the place.

It was just a bone stock bottom end with flat tops and a set of world product sportsman 2's with an old comp cam magnum 292h flat tappet cam and it held together the whole time I had that engine and it still exists today but not in a vehicle but still held together for many years after I sold it.

I also once had my one and only stroker build and was a 377 cubic inch aka 383 but it had a standard bore as the block was new and the rotating assembly was a used 400 small block crankshaft that was grounded under and the rods were the poorly made 5.565 factory rods that looked anorexic to a factory 5.7 rod in my opinion or it was just because it was that much shorter and I had TRW forged pistons on that rotating assembly and I had it up to 6000 rpm plenty of times with an old Crane flat tappet cam that was pretty wicked at 246/246@50 with 500/500 lift and a 106 lsa and it had a ton of torque.

That engine held up pretty well but I can't remember what happened to it as I have changed things one to many times in my life.

 

Good assembly and proper machining of the parts and good judgement with experienced eyes and hands can go a long way on a basic build. I have had several budget builds done back in the day and my Dad would always take my old 86s10 I used to own out and just romp the heck out of the thing and about threw me through the window into the bed lol as it would just take off so quick at just hitting it to 6500 rpm with no issue with tires a blazing all over the place.

It was just a bone stock bottom end with flat tops and a set of world product sportsman 2's with an old comp cam magnum 292h flat tappet cam and it held together the whole time I had that engine and it still exists today but not in a vehicle but still held together for many years after I sold it.

I also once had my one and only stroker build and was a 377 cubic inch aka 383 but it had a standard bore as the block was new and the rotating assembly was a used 400 small block crankshaft that was grounded under and the rods were the poorly made 5.565 factory rods that looked anorexic to a factory 5.7 rod in my opinion or it was just because it was that much shorter and I had TRW forged pistons on that rotating assembly and I had it up to 6000 rpm plenty of times with an old Crane flat tappet cam that was pretty wicked at 246/246@50 with 500/500 lift and a 106 lsa and it had a ton of torque.

That engine held up pretty well but I can't remember what happened to it as I have changed things one to many times in my life.

A 377 is a 400 cid ( 4.125 bore) with a 350 cid ( 3.48 stroke , while a 383 is a 350( .030 over) 4.030 bore block with a 400 cid stroke (3.75) . different block , bore ,& crank .

 

Valve train:
Weight.....Lifters, push rods, rockers, keepers and retainers all weigh something.
Pistons:
Weight.....Pistons, rings, pins, bearings, all weigh something too. Then you have to find those parts that will stay together while changing directions every 2 to 4 inches. The momentum is what pulls the pins out of the pistons, pulls the caps off the rods, breaks the crank and breaks the main caps.
You can add weight to add strenght but the added weight reduces the maximum speed so what your paying for is someone who can figure out how to make things lightweight AND strong. It's not an easy feat and all the R@D costs money and time.
There isn't a straight answer to give you.

My 2.1cc single cylinder 2 stroke RC car engine turns 30,000 rpm and makes 1.1hp
It'll move a 6lb car up to about 45mph.

Generally speaking, Shorter strokes and smaller bore means more RPM capability.

 

Two things, where the motor stops making power. Once the HP curve starts dropping, then there is no reason to continue trying to push it harder. When a crate motor ad lists that max rpm is 5000 rpms, then I'd safely assume that the cam and heads are all done by that point - quite typical for a 250ish HP crate motor.

Second, the limit of the parts. As mentioned, rods, rod bolts, valve train stability, heads, intake, exhaust, etc. I'm not familiar with any SBC that won't withstand 6500rpms occasionally and 6000rpms regularly.


Are you planning a build or already have a motor put together?

 

When an engine says 5000 rpm redline, it's not necessarily because things will explode at 5500. It means that the cam, valvesprings, compression, and airflow are matched to make power in a certain RPM range, and revving it past 5000 is pointless and makes the car slower. No reason to risk the extra wear/fatigue on parts for less power.

Most stock SBCs will take 5500-6000 without falling apart. I had a Detroit 60-series that "redlined" at 2200, but it would be mechanically fine at twice that RPM without damaging anything.

where you get into trouble is if you choose components that move the powerband up to something above what is safe for the moving parts. If you put a cam and heads that would work well shifting at 6500 with cast pistons and rods, then you get things exploding

 

You can blow up engines at any rpm , depends on how hard you try !

 

Lots of reasons why they may suggest 5k rpm Generally that low, it's not the bottom end for a SBC(other engines it may be)

I like to call the SBC a leaky dam VS the stock LS that is well built, plug all the holes and the SBC will perform(course the LS has a few holes as do most stock engines).

TPI intake is a good example, people have constantly said it's done by 5k or w/e. It may be peaked but it's not done if you plug the common SBC leaks. Then the power doesn't drop, it flat-lines and why would you want to shift at 5k n have less average power? I hate to bring it up because I know people will debate and of course the TPI intake is the limit and others will out perform it. But just because there is a limiting factor doesn't mean you can't shift higher IF the engine will hold, just look at Stock Eliminator.

edit: Corrected for the wrong type of racing.

 

Boo77? what are you saying? Sounds like non sense (re tpi flat lining). If you rev the tpi to 7k while it remains at 220 hp your torque will fall off the graph so, YOU ARE LOSING POWER! Torque and HP are just numbers we use for discussion.

Super stock engines use tunnel ram intakes allowing (or forcing) more air into the engine. Lots of science in building a SS engine.

 

I never said 7k, the stock bottom end wouldn't hold. Stand by what I said if supporting parts are good power may stop climbing.

Meant Stock Eliminator racing, I'm not talking tunnel rams.

 

Sorry , neglected to note the .030 overbore of the 400 block , my bad

 

TPI

 

It comes down to weight and balance.

4500 for a big block and 5000 to 5500 for a small block. Is a good safe bet.

Most engines see these rpm breifly. I have held 3800 to 4400rpm for over a hour on several sbc without issue on several occasions. If you build the engine/cooling/drivetrain to run these rpm and dont mind the additional wear then you can run most engines at 4500 without much concern.

Now when you start going above 5000 most heads will run out of air. Then you have the oiling and cooling systems being pushed. Dont forget that alternatior that may be spinning faster then it was designed for.
This is all assuming your running a manual transmission in which a majority of the lubrication is splash based. A automatic may get hot fast holding 4000 rpm.

But all the above being "fixed" the real issue is weight. At those rpm that piston still needs to do a 180 at the top and bottom of the bore. The oil pump is already working overtime and the potential for those rings to run a bit dry and dig into the cylinder walls is there.

Of course lighter (forged) parts can help eliminate this slap. But for prolonged periods of more then 20 minutes 4500 is as high as I would push a sbc.

You may get away with 6000 for a few seconds before you shift. But if you want to go above 5500 there are several better engines out then a sbc to run above 5500 rpm and still make similar power in a more controlled manner. Some of these engines have sprayers to lubricate the bottoms of the cylinders and even other areas such as the cam(s) making sure these critical areas maintain lubrication at higher rpm. A oil coolier is usually used which also increases capacity. Several modern engines come with forged internals stock allowing for you to run 6500 without concern.

But for a sbc there is not much need to hold more then 5000 or shift above 5500.

 

I've shifted multiple SBC 350's stock bottom end shortblock 6000 many times. 4 bolt and 2 bolt usually racing or testing. The original 2 bolt in my 77 Corvette idk how many passes it's seen 6k both shifts. I pulled the pan and bearings looked Not great, ran em for a few more years and finally put some new bearings in it.

 

Essentially there’s a red line for the valve train and another for structural failure or the chamber goes into detonation.

Your more likely to experience valve train red line more often in your building career than structural. Both of these things relate to component strength.

For valve train the engine generally just lays down at some RPM. This can be structurally destructive if under the loads for example a valve is still open because it is bouncing off the seat or a lifter adjusted low is pumped up when the piston gets there. The ensuing collision usually busts something being the valve and or piston, rocker arm or it’s stud, or bends the push rod. Any of these can be in a and/or condition.

At high loading and or high RPM on the bottom end the most likely failure is the connecting rod. This most frequently starts at the big end with the bolts allowing enough distortion where the cap mates to the shank such that the bearing crush is lost, the bearing distorts into the crank journal wiping the oil off, everything gets very hot and the the bearing spins. At some point things come apart. There are other bottom end failure points but this is more typical.

Detonation and preignition, at high loading and high RPM combustion chamber temps are at the extreme and highly sensitive to cam and ignition timing in a tune sense, specific cooling like the SBC runs the adjacent exhaust valves on the middle cylinders really hot so if coolant flow is inadequate these often blow the head gasket and go into detonation. Detonation is also affected by mixture ratio to where the carb might fall lean up on the top end or the chosen manifold distributes mixture ratio inconsistently. Detonation/preignition destroys pistons quickly and frequently pounds out the rod bearing leading to loss of the rod.

With the right racing parts the SBC can sustain 9000 RPM, but here we’re talking 20 to 30 thousand dollars right more for a Late Model Dirt engine in parts and precision machining and assembly. A mid competition build at 7000 maybe 8000 RPM your looking at a 15-20 thousand dollar investment. A low level build say for Stock Street your looking at 10-15 thousand dollars for a red line in the range of 6 to 7 thousand RPM. A good on the street performance engine red lining at 6 to 7 about 7 to 10 thousand in parts and labor. A decent home build or crate motor red lining at 6 to 6.5 RPM the cost is about 5 to 7 grand. A stock replacement motor good for 5 to 6 thousand RPM is about 2.5 to 5 thousand dollars.

The old adage that “speed costs money, how fast can you afford to go” holds true for establishing redline. So I guess you need to tell us your budget and we can tell you your expected redline.

Bogie

 

chas, richard johnson used what I believed to be a tunnel ram. It was a dual WCFB system but many years ago

 

More about SBC max rpm I'd look at the restricted class type circle track racing that had to use stock stuff, idk if they could upgrade rod bolts for some?

 

Max rpm,,,

 

Peek-a-boo!

 

Back when I was a young man my commanding officer had an Oldsmobile and a teenage son. The kid is out driving the old mans Olds one day, we’re in his office for a meeting when he gets a call from the kid, ‘hi dad I’m on the side of the road and the car needs some oil‘. Meeting finishes up, dad leaves the base to take some oil to the son. Next day the story goes that dad arrives and adds oil pulls the dipstick to see no gain, then looks down to realize the oil he just poured in is running over his boots. Dad looks closer at the engine and realizes he can see through the pan to the oil puddle on the street below. At the minimum I’m sure the kid looses driving privileges, but I don’t remember if the ’ol man shared his discipline plan. But it was evident that he was so mad he didn’t appear to be mad.

Bogie