High Revving engines... How and why?

HP= TQ x RPM / 5252.

Because RPM is a factor of HP, the more RPM we add, the more HP potential exists.

This being said, I'm not a fan of high rpm street engines. Why? Because I've built plenty of high rpm track-only engines, and they beat the crap out of themselves.

The stresses past 7,000 rpm multiply exponentially, not in a linear fashion.

The tradeoff in stress is rarely worth the power gained unless the power is an absolute necessity, as in a race-only situation where the engine only has to last 500 miles or whatever. You know it's fresh when it goes in, and it'll come right back out for a rebuild after the race.

The street is a whole 'nother animal. You want it to last and be reliable for a long time. You want it to run on shitty cheap gas. And, of course, you want to be able to spin it to 8,000-plus whenever you feel like it.

It's a death sentence for at least one important part inside your engine...and you won't even know what part it is until it fails.

I design and build really good engines for the street. They are first and foremost durable and reliable. They will last a long time. They also make really good power on really shitty gasoline. And, they're usually done by 6,500 rpm.

I choose bigger cubes over higher rpm.

I choose high velocity air over massive quantities of air.

I choose efficiency over rpm.

Of course, you have to compromise because you only have one camshaft profile. Where the cam is designed to run best is where the engine will run best. For my engines, that 'sweet spot' is usually 3,500-5,500 rpm. The idle may be choppy, and don't expect to make a bunch of vacuum...and don't spin it past 6,500 either...but, in that sweet spot, your stomach will pinch up.

Evolution has led me to this philosophy toward street engines. Sure, you can build an 8,000-plus rpm engine for the street, but I promise it won't last too long. If you love building and rebuilding engines, you might be okay with that.

But, as much as I love building engines, maintaining a solid roller lifter engine with a Demon carb and a progressive nitrous setup ahead of a stick trans is plenty for me to do. Keeping a good engine in a perfect state of tune is more fun than picking busted piston rings out of your oil pan.

If you want to build a race-only engine, have a ball with high rpm. If you want a reliable-but-serious street engine, up the cubes and cam it to run below 6,500.

If you'd like any advice on building any engine for any purpose, I'll gladly offer up what little I know.

If you'd like to know what I built for my own street car, here's the link:
http://www.compcams.com/Community/Articles/Details.asp?ID=1945664039

If you need more than 545 horses on 87-octane, add a bottle for another 150and you'll have near 700. Not bad for a small-block.

If you need more than that, build a 600 incher.

~Scotch~

 

Scotch knows his stuff, FWIW - if it's not already obvious.

Back when I did some streetracin', I'd seek out the guys with really big cam motors that wound to high heaven; they were beatable on the street as long as they didn't line lock and stutter box with cheaters; it's difficult to leave the hole hard on the street - and that was the only way a winding motor would prevail over a 'lesser' motor.

Today's newer port configs do allow motors to spin faster than they did back in the day; if I was building a motor 20-25 years ago, I'd have built it to spin to 6K; now 7K is common - so it's relative. A far cry from the 4400 RPM peak of an 80's SBC, tho.

I'm with ya on the light car setup; power/weight is where its at. Not a fan of monster cubes - it's fun to make a little winding motor to whomp on a big one!

 

Scotch rules the most... That's fer-sher...

I was hoping he'd shime in. One of the most knowledgeable engine builders on the HAMB.

Thanks for input Scott, I'll be in contact with you when I get a little closer to makeing something of this.

Thanks for your input (both of you).

The DOHC Ferd is really intriguing.... I checked the web site though and it ain't cheap. But I guess if I went all-in on a hi-rpm SBC, I'd be into it for more.

 

So can you build a 283 or a 327 or even a 302 sbc to handle 7000 or 8000 without problem? Is 7000 around the cut off point before you have to get to exotic on parts and coatings? With stress levels becomming a factor?

 

I didn't read any reply's in this thread cause I'm tired and ready for bed, but I was talking the the driver of the drag car sponsored by my dad's restaurant (400ci sb '57 chevy that runs low 9's) and he was telling my about a '57 chevy he saw at a track somewhere that had the original 283 with a lot of head work, the biggest cam he could fit in the block without any machine work and somewhere around 7:1 or 8:1 rockers (I remember him mentioning over .700 lift) with a tunnel ram/duel carb set up that ran low 10's leaving the line at 6k rpms and reved to over 10k rpms.

 

I recently sold the most fun to drive car I have ever owned. Powered by a 283 SBC the channelled coupe had a close ratio 4 speed and a 3.50 nine inch ford. The sensation of running this motor hard through first gear then grabbing the next and feeling it pull till time to shift again is about as good as it can get in a moving car. With a 270 hp solid lifter cam the small motor sounded right but it wouldn't burn down the tires or get you going so fast that you couldn't stay in it. RPM? Turned it tight enough to straighten out the fins on the generator!

 

High rpm's create annoying high frequency vibrations and resonances. They cause more stress on an engine too. Having driven many low and high rpm vehicles on the street I am of the opinion that even a hot street engine really doesn't need to rev over 5500-6000 rpm.

If it's gonna be raced, well then that's a different story.