Revving your big block

[fastd]

Wondering what you rev you big block to?

And where you comfort zone is - what rpm range.

I recently heard at a car show that the Chevy 396 has a small block stroke that can rev all the way to 7k rpm.

My 351w have a rev limiter at 6200 and is comfortable all the way to the limiter. My pontiac big block revs to 5k or so but really is comfortable to 4500 rpm.

[Tom Wells]

fast,

I limit my 521 and 557 to 5800 on the street. Each has a Crane hydraulic roller setup. For the track I use 6000.

Tom

[4pipes]

482 rev limited at 5800 rpm.

[patrickt]

My FE with the SCAT 4.125" crank, Erson rollers, solid flat tappet cam, Wiseco pistons, and aluminum flywheel, goes straight to the 6500 rev limiter, and I bounce off it maybe once every year or two. Not because the peak of the curve holds up at that point, but because the sound just takes you away and you're there before you know it.

[olddog]

That's kind of like asking how much does women turn you on. Well if your gay and the answer is not at all, then I suppose the question isn't difficult. However for the rest of us the obvious question is what type of women? Old, young, blond, fat, skinny, big tits, ugly, are all variables that matter.

A 383 & 400 cid Mopar has a shorter stroke than a 350 Chevy, but what does that prove?

There are two main areas of concern. Where does the rotating assembly fail? Where does the valves loose control - (typically before they float)?

If the valves float before the rotating assemblies failure point, you will break a valve spring before the bottom end grenades, assuming the rest of the valve train holds together.

The third area is a decent oil system. If the oil flow is too slow or not enough cooling, the oil will break down and metal to metal contact will take the engine out. If the oil pumps up to the top of the engine faster than it can drain back down, you will run out of oil at sustained high rpms.

A stroked out big block can be built to turn high rpm, for enough money. It's not all that ridiculously hard to get to 7000. but it is a whole lot cheaper to stay under 6000. What bore and stroke, and what valves sizes can sway these numbers a 1000 rpm either way.

Personally I prefer to keep my small block under 6000 rpm. Don't really see any reason to limit a big block any lower. They just tend to live longer and fail less catastrophically at lower rpm.

[blykins]

You have to qualify this into two categories.....what the rotating assembly can handle and what the engine as a whole can handle.

For example, a rotating assembly could potentially turn 7000 rpm without issue because of the rod design, piston design, etc. However, due to the cylinder head, compression, and camshaft, it may only make peak hp at 5000 rpm.

Looking at the opposite, you may see someone put a big set of cylinder heads and a huge cam into an engine with factory rods, cast pistons, etc. In that scenario, the bottom end may be able to handle 6000 rpm, but the heads and the camshaft want 7000.

As an aside, one of the BIGGEST fallacies hopping around the internet engine forums is that a long stroke engine can't turn high rpms. I get very tired of hearing that big blocks with long stroke crankshafts are slow revvers, or can't turn higher rpms, but a small block is very zippy and can spin to the moon if necessary.

There are so many variables involved, that a blanket statement like such simply can not be made.

[mdross1]

Don't be afraid, rev it till the pistons start swaping holes.
As you have read it all depends on what's inside the engine block that you need to know.

[Ron61]

The horsepower on my 428 SCJ peaks at 6,300 RPM and I have the rev limiter set to 6,000 RPM. It has gone past the 6,300 a couple of times but the engine is old and I keep it at or below 6,000 now.

Ron

[DanEC]

Originally Posted by blykins

As an aside, one of the BIGGEST fallacies hopping around the internet engine forums is that a long stroke engine can't turn high rpms. I get very tired of hearing that big blocks with long stroke crankshafts are slow revvers, or can't turn higher rpms, but a small block is very zippy and can spin to the moon if necessary.

There are so many variables involved, that a blanket statement like such simply can not be made.

I used to subscribe to this idea that long strokes killed revs, but I started to have doubts when I bought my 2003 Lightning with the 5.4 modular motor that is about as undersquare as you can get. Then I bought a Coyote engine Mustang GT, which again is undersquare and zings towards it's 7000 rpm redline like no body's business. That pretty much killed the myth for me. Also, my 4.25 stroke FE seems to rev just as strong as my 3.75 stroke Chev 427 - well, at least up to a point.

[blykins]

Horsepower/torque is one of the biggest factors there.

Most of your Mountain Motor and some of your Pro Stock engines use extremely long strokes.....like 5.5-5.75". They will zing to 8000-9000 as quick as you can get on the loud pedal.

[moore_rb]

Originally Posted by fastd

I recently heard at a car show that the Chevy 396 has a small block stroke that can rev all the way to 7k rpm.

Well, if you heard it at a car show, then it must be true....

The reality is just like everyone here suggests - Compression ratio, valve train rebound rates, cam profile, crankshaft balance - All play a part in how high any engine will comfortably rev.

Regarding car show 396 Chevies being able to rev to 7 grand... Well, that also really depends on whether the engine has chrome valve covers, a polished intake manifold, and polished Billet accessory brackets....

[scottj]

Originally Posted by blykins

Horsepower/torque is one of the biggest factors there.

Most of your Mountain Motor and some of your Pro Stock engines use extremely long strokes.....like 5.5-5.75". They will zing to 8000-9000 as quick as you can get on the loud pedal.

Long stroke Pro Stock engines? I don't think anyone uses a bore smaller than 4.70" with stroke in the 3.50"-3.60" range. I think they are also using an 8.90" deck height to keep the compression height to a minimum while utilizing a shorter, lighter rod and to keep the push rods shorter. Regarding rods, I believe they are running Honda rods. They're basically BB's built to ultra-light SB specs except for the bore... so they'll rev...

[blykins]

Depends on the class...

EXTREME PRO STOCK 932 CU. IN. 2140 HP RACING ENGINE - Sonny's Racing Engines - Sonny's Racing Engines

Google some of Pat Musi's stuff and take a look at some of the mountain motor classes.

Obviously the parts are light but I'm using this as an example when people say a big block won't rev....or a long stroke won't pull rpms...

[scottj]

Originally Posted by blykins

Depends on the class...

EXTREME PRO STOCK 932 CU. IN. 2140 HP RACING ENGINE - Sonny's Racing Engines - Sonny's Racing Engines

Google some of Pat Musi's stuff and take a look at some of the mountain motor classes.

Obviously the parts are light but I'm using this as an example when people say a big block won't rev....or a long stroke won't pull rpms...

Got it... when you said "Pro Stock" I assumed you were referring to NHRA Pro Stock a.k.a. Pro Stock...

I understand your references and your point... I agree. A more accurate generality would be that lighter revs higher and accelerates quicker (engine accel) than heavier, all else being equal. Of course, when comparing SB to BB nothing else is equal... but they sure do go to extremes with the Pro Stock stuff to copy a small block rotating assembly, huh?

[blykins]

Lighter parts are certainly easier on the system. I can't imagine the piston speed of a 5.750" stroke setup at 8000 rpm.

You'd be surprised at how quick a 12.5:1, 720 hp Ford FE will rev though with a 4.250" crank....that's not really anything exotic, and the crank weighs about 70 lbs.

[Tom Wells]

https://youtu.be/pYIkzqBjdHo

[olddog]

Well Ford was putting 429 engines in dump trucks with heads and cam that gave them stump pulling torque at low rpm. Totally out of breath long before 4000 rpm.

At about the same time, they were dropping 428 engines into Mustangs as high performance machines.

428 FE ------ bore 4.130 x stroke of 3.98
429 385 series bore 4.360 x stroke of 3.590

That always bugged me back in my puppy days. Why was the short stroke engine that is supposed to be ideal for high rpm, in the dump truck, and the long stroke engine that is supposed to be ideal for low end torque, in the Mustang?

Well the answer is because Power output of a given cubic inch displacement, at a given volumetric efficiency (same amount of fuel and air), is the same regardless what bore and stroke combination got you to that CID. In the old days, with crappy head designs, the big bore allowed bigger valves, making it easier to pump more air. Today with good flowing heads and the fact that smaller bores make meeting emission standards easier, engines tend to be long stroke and small bores.

The power output is irrelevant. Power is just a question of how much air can you pump.

As for spinning a rotating assemble fast. If you can get a rod bolt strong enough to not stretch, when the forces required to stop the pistons at the top of the bore and reverse its direction occurs, then you do not have to worry about spinning a bearing. As long as the rod and wrist pin can take those same forces, then your good to go. Well assuming the crankshaft doesn't flex too much and crack, and you were smart enough to balance it. These are just physics calculations that any good engineer can do. Huge engines can be designed to spin very fast, but the materials required gets expensive.