Supercharged v NA
 

I will go ahead a say this might be a stupid question but if I don't know well....

If you have two motors that are both 800hp. One is supercharged (any style) vs a naturally aspirated motor. Does it boil down to torque to determine which is stronger or a more powerful motor?

I believe the SC motor will have more longevity and make the power easier than NA. TQ should also be higher

Blower motor_ torque curve is flatter, lower RPMs (unless you are comparing a blown 454 vs a 732 NA)

Really depends how your asking because this can get quite intricate. And beware, even when get down to the nit picky, many will disagree with each other. Read on and you'll see why.

1st, torque is measured by the dyno. Torque is the force, and again, that's what the dyno can measure. But it does not involve time, Since we need to find out how much work the force can do, we need to involve time. So, rpm is figured in. And the term for work done, is Horsepower. Why ? BAck in the day, we used horses to get work done. Yup...believe it.

Now.....we can have two motors, one with a lot more torque than the other, but the other has more horsepower. So, which is stronger ? IMHO, it depends to me what it's going to be put in. One will be 'stronger', actually 'better', for one application while the other will be better for another application.

682Gold, maybe, if you mention an application maybe we can discuss that.

Not really an application in mind. I was on the Corretti racing engines site and he has a monster 700 ci motor producing 900hp at 5800 rpm's. Also has a blower motor 565i making 850 hp . I know the cu is smaller in the blower and the hp is not the same but for this lesson lets say they are both 875 hp which will push the same boat faster?

Probably be damn close. We would need dyno graphs to see what may have the edge.

How about a blown 502 making 750 horse at 5200 vs a NA 350 Nascar making the same at 9500. Even though they make the same power, the 502 could turn say a 28 pitch prop and the 350 a 16 pitch.

The 502 cruises at 3k, the 350 at 6k.

if boat A makes 850 hp at 5800 and can spin a 30" prop and boat B makes 850 hp at 5800 and can spin a 34" prop, then shouldn't boat B be faster? If it is then boat B is making more torque near 5800 than boat A?

If it's making more torque at 5800 then it is making more horsepower at 5800.
Hp=torque x rpm /5250

You can take that to the bank. Something none of us will disagree on because it's fact.

how dare you bring fact,s into the mix,LOL.

I didn't, it was Mr Maine, But that's a fact. So now I did. LOL.

Your right, I forgot about that

Now I'm going to bring physics into the discussion. (learning about intergrals in Calc class) The engine with the most area under the curve is the stronger engine.

Now I had it explained to me this way many years ago by an older retired navy man. Horse power is waking up with a big raging one , and torque is having your feet fly out from under you when you push it down to take a pee..

And that is now where we get into application.

Some lighter, and faster hull boats ...this doesn't necessarily ring true.

If we lose overall in the curve to get more power at WOT, then speed can be higher.

If heavier, slower hulls - than yesm this is predominantly true.

I'm talking speed, not necessarily acceleration, above.

I might lose some traction when I push it down but I'm pretty sure the days of having my feet fly out from under me are a thing of the past. I've used it nearly every time I had the chance so I'm good with losing a little traction.

I can totally relate to that.:cartman:

Yes sir, I had a feeling you could because IIRC we're pretty close to the same age.

I learned early, on my own, it's easier and safer just to lean and put your forehead against the wall. Better aim and it hurts less. Ha !

You always seem to catch on quicker than most Steve.

And hey Sam, You're right there with us bud.

And you would be correct . lol

Twin Turbos

Unless you can make same hp at same rpm the na motor will never compare to a sc motor. A local guy (todd kramer) had a 27 foot fountain, someone who supposedly worked for Sterling at somepoint built him a NA 540. Had a solid roller cam, dynosheet showed something like 745hp at 7300 or so from what I remember. He previuosly had a 502 and a 26 pitch prop, he bought a 30 pitch BEFORE ever running the motor, absolutely wouldnt pull it, wouldnt pull the 26 either. He ended up with a 23 pitch to break 78 mph but oil temp was sky high, cruise rpms sucked. My Baja at that time had a blown 502 that made about same hp but at much lower rpm, had much more useable midrange torque and beat the fountain every time we ran. Now sure, you could compare a blown 454 to a na 572 then the tq would be similar depending on boost, cyl heads etc, fwiw, Smitty

Well of course a 7300 rpm motor is going to suck in a boat.
Let's keep this conversation to real world experience that most people can afford, like 650hp for the NA and blower motor, and the blower motor has a top rpm of 5300 and the NA motor spins up a bit higher, say 5700 rpm. Now that's a real world comparison and let's say it is in a 32' deep vee.
I think that comparison is more useful to most people making engine build decisions here

Opinions on both have value.... However the question that should be asked is what engine package will twist the drive the fastest. Unless you have SSM. Even then 700CI NA is going to make a big torque number.

My point was based on a real experience, thats why I brought it up, Todd told his engine builder he wanted 750 hp and didnt want a blower, he got close to it but had no torque where it could move the boat so his 750 ish hp motor was about useless.
Now comparing blown motors to NA, you build a 500 cu inch 500 hp base engine, boost it 14.7 psi, the hp /tq increases 100% theoretically minus parasitic losses from generating the boost, 7.5 psi= 50% increase. Now of course base motor will make less hp NA if built blower specific. a good NA motor should last 400 hours if camming isnt stupid nutz, IN MY OPINION a blower motor RAN HARD should be rebuilt every 100 hours (thats what I do with mine) so a larger NA motor should be much less maintenance and less work. You can make up a thousand different scenarios, dice it up 50 ways from Sunday, everyones got a opinion , compare a low compression blown 502 to a big NA motor, argue till the cows come home, whatever.
IF a guy was starting from scratch, build biggest motor you can, even if boosted, run less boost and make good power, aftermarket blocks and cranks are all the same price regardless of stroke. Im running my current boat NA, probabaly will stay that way too, not sure how big I will make the engines when I do them, its a fast hull to start with so I dont really feel the need for 1000 hp motors

Did you ever meet Todd, he lives on 15 between richville and Vassar?

I'd say pretty darn close as well but it also depends on the hull it's going into. Like SB said, there's so many factors.

I also think the 565 would be much more affordable and you could get parts off the shelf to fix it if you ever had a problem. I would imagine the cost to build and rebuild the 700 would be much higher. You'd also be beholden to the manufacturer where the 565 most any reputable marine engine builder could work on it. I know that's not the original question but when I hear questions like this, these are the thoughts that immediately go through my mind. :-)

But you know what they say about opinions. :-)

Do blower motors run cooler oil temps simply because you're not banging the crap out of them to get the same power?

No. Blower motors have to make more power (burn more fuel/air) to make the same power at the crank. Power = BTU's. An engine burns fuel to push the pistons down and make power. It has to take in an appropriate amt of air to support the fuel so it can burn right.

Thinking further, if you greatly increase the NA's rpm to make same hp as the blower motor, than the engine fricition, especially the valvetrain (think springs) could add more heat. So...this may trump what I said above.

I believe a 700HP blower motor will outperform a built 700HP NA motor in all aspects everyday of the week maybe twice on Sunday. If they are relatively close in cu/in. I've seen the difference when someone went from 700+ blown vs 700+ NA I believe he lost 4mph, 102mph to 98mph.
But now the drives last 2-3 years vs 2-3/yr.

It seems to me with a blower you can run a much smaller cam, with less lift and lighter springs. How does the benefit of a smaller cam and manifold style exhaust compare to the maintenance of a blower?

I don't think I know Todd, but I am terrible with names. It just seems like this builder knew nothing about marine motors, cuz high rpm and stern drives rarely end well.

I do like hearing the experiences of those like yourself who have owned both and which they prefer

Tell 14 Apache his boat is 4mph too slow. It's only one of the fastest apaches around :D

their is no replacement for displacement,except BOOST.

Boost IS displacement. ;)

cubic inch displacement.the big cu in n/a guys like to say [no replacement for displacement]surly you have heard that through the years.