Flow vs hp

[Steve.k]

Is it possible to make 1100hp with fow numbers under 400cfm? No power adders.

[ptuomov]

How many cylinders and what displacement per cylinder?

[andyf]

Sure. I don't see any reason why someone couldn't make 1100 hp with heads that flow 399 cfm on the flow bench. Everything else would have to be well sorted out.

I have a 514 BB Mopar that makes more than 900 hp with heads that flow in the 350 range. There are always tricks that can be pulled to make more power. Different fuel, lots of pan vacuum, lots of valve lift, tuned exhaust, etc.

[mag2555]

It's all about VE!

[Frankshaft]

Sure. I know I cam make over 1000hp with 380 cfm, like 1020, and its not a basic build. To find 80hp, it would be tough, but not without more head work. Like Andy said, a lot more to making horsepower than flow numbers. The other thing, people get funny when I bring this up, but there ABSOLUTELY are happy dyno's out there, period, end of story, I don't care what anyone says. I know shops f%ck with the numbers, lots of stories. The engine above, take it off the dyno I use, that performance more than matches the numbers, take it 40 miles to the east, just across the border, and it would absolutely be an 1100hp engine. On average, the 10-12 examples, that have been run at both shops that I know of, make a bit over 10% more everytime. So which is it, 1000hp or 1100hp? Its on a sheet of paper after all.

[Steve.k]

So does rpm skew the cfm therory? For example if you have a350 cfm head that good for roughly 800-900 hp at7-8000 and you wick it up to 9500-10,000 does this actually amplify head flow somewhat? Or is flow at valve as good as it gets period?

[Newold1]

One must only widen their knowledge horizons to see that there are a lot of racing engines through out the world that make 1100HP or more without power adders and cylinder heads that flow less than 400cfm per cylinder! If you are looking for a more specific engine family and application then please identify that application for good discussion.

[Rick360]

1100hp from 400cfm is 2.75 hp/cfm. That is a lot more than most N/A engines.

When the head is sized for the engine correctly and it is well built it isn't uncommon to get 2.2-2.5 hp/cfm.
Lots of things affect the hp/cfm. Things like compression, rotating friction, fuel, port shape, chamber shape and head/port size vs cid. When a port is shaped right you get more HP than the cfm would normally indicate. Take a great head for a 400ci engine and put it on a 450ci engine and it will make more power than the 400ci so the hp/cfm goes up but the hp/ci goes down.

The question I have is why would you try to make 1100hp with less than 400 cfm? it'd be a lot easier to do it with 450-500cfm.

Rick

[ptuomov]

Suppose we have a V8 here so the number of cylinders is known. You need to make 140hp per cylinder thru a cylinder head that flows 400 CFM on the flow bench. The key is that this flow is at 28" test pressure. If you have less vacuum at the cylinder, it'll flow less. If you have more vacuum at the cylinder, it will flow more. How do you make the vacuum larger? You increase the displacement and rpm. A large displacement engine at high rpm can absolutely pull enough vacuum in the cylinder to trap enough air mass to make 140hp per cylinder thru a 400 CFM head. Small displacement engine at low rpm absolutely cannot. So you can't answer this question without knowing the peak power rpm and the engine displacement.

[PackardV8]

The question I have is why would you try to make 1100hp with less than 400 cfm?

Could be, it's just a bench racing question; as suggested earlier, the OP will have to clarify.

I always think the question should be, "How much horsepower-per-dollar can you make?" Many of the engines mentioned as pushing the limits of horsepower-per-CFM are built on unlimited budgets. If the cost was as available as the horsepower, most would look at it differently.

Just because potential customers always ask early on, "Whaddalit make?" I usually say, "A good typical affordable Gen I SBC build makes 2HP-per-CFM. The budget, the end use and the compromises accepted can push beyond that. Define your goal and then we can talk budget." And they always come back with some You-Tube internet BS with much higher numbers, taken out of context, and say as much, "You must not be a very good engine builder if you can't do better than that." At this point, try to ease them on down the road, because if they're having to ask those questions and taking what they see on the internet as how the world works, some other shop would suit them better.

[Steve.k]

Well heres the deal. As most of you notice im a huge fan of the iron cleveland. Im also going to receive soon a cgi version of the Trackboss block. Ive been wanting to put together a heavy hiiter iron motor. I've got a set of early prostock heads from Paul JENKINS of florida. I flowed the early heads and on our bench they were in 350cfm range. Since then I've done work on another set and have them sitting in the 368 range. Some guys claim to hit over 400 but I've never seen the sheets so who knows. Anyhow whats it going to take or is it possible. We would be able to hit close to 450 cubes.

[PackardV8]

That's 2.44 HP/CU.IN., which happens.

Just asking, why is 1100 the magic number?

The other factor is does the intake manifold have to be aftermarket or can it be custom? Any height limitations? If anyone's been noticing, we're getting back to the 1960s Ramcharger days; many of the highest-scoring intakes in EMC are TALL and probably would be taller if the aftermarket offered them for dyno racing..

[Rick360]

Yes, 2.44 hp/ci happens, but it won't happen in a long stroke engine that is trying to get 2.75 hp/cfm from the heads.

Are the heads raised port? What's the avg csa of the intake ports?

Rick

[user-23911]

Is it possible to make 1100hp with fow numbers under 400cfm? No power adders.

But 400 CFM is just an imaginary number which flows when there's a constant pressure of 28 inches water across it.


Increase the pressure and the flow goes up.


Flow goes up with a bigger cylinder and more revs.
It goes down with a smaller one and less revs.

[Frankshaft]

2hp/cube would be a great number with that combo. 2.44/cube, ain't happening. Not to burst your bubble, but it's just not. It's hard enough with the very best heads available, and that's close to the limit at those cubes.