How would the two compare?

Lets say you are building a 6.4 hemi, and you have the choice to set it up like a Hellcat or go N/A and get the same amount of steam from it.

Will one engine be more fun to drive? Will the both be nuts?

If the make the same power, what would you choose and why.

68, B-body, street/ w/ little strip

If they both make the same power, I would take the one that made the most torque at the given torque/HP curve I desired.

700 blown, can be done with a very mild engine that would live longer, and yes, it will have much more torque, so you can run a taller gear.

I'd take the blown one, it would be MUCH more street friendly.Dave

My head says the blown motor will have more torque, a milder idle and properly tuned, be more street friendly. My heart says nothing sounds as good as a high compression engine with a lopey idle, and that anything else sounds boring.

I agree, while I like the blown or turbo better power wise, nothing sounds like a nasty motor with a big lopey lope cam. But a blower motor with extreme blower surge at idle is pure sex also

On paper they should be equally as quick, but realistically the blower motor would get there easier and would be a lot more fun to drive. I also think the blower motor would be quicker with a not so ideal set up (who ever has a perfectly dialed in set up). I'd go forced induction

Thank you guys for the help, believe it or not this is a high school shop class project, you might have read about it in Chrysler Power. We have a chance to build a supercharged engine and it will be a first for us.

Picture this: 6.4 " Hellcat esque" blown motor, caged, General Lee fresh off the rotisserie.

Think Galen would certify that as a 1 of 1 lol.

I'd wager the blower would be faster, but i'd go N/A personally. A 700HP Hemi is just a stock pull-out these days (ever thought you'd hear anyone say that?). What fun is that? Build a 700HP N/A hemi and they'll hear you coming. Yeah man... ragged...

The blower motor should have a flatter torque curve and hold more torque longer so it would have an performance advantage in the real world. Is budget an issue? The blower stuff will take more coin than the N/A.

Wow, sounds like more fun than the high school shop project we did.We got to put a shortblock in a Vega .Times sure have changed.

I agree cos we've all seen too many slower than they should be blower motors and a FEW fast n/a cars.........

I would think of how much added strain driving the blower makes on the motor, compressing air driven off the crankshaft takes HP and adds strain on every part of the motor, before making the final decesion. As far as turbos I've been told that( by racers who use them) they do add additional concerns off the back side of the motor so I guess there are no free lunches. Adding boost into a motor definetily makes more power easier per C.I. than N/A motor do.

Boosted will be milder for sure at the same power... but there is something to be said about the nasty intimidating sound of a 700hp motor.

My Dad's NSS A/FX car (9.25) isn't that much faster then mine at 9.88. But his 572" 14:1 motor scares the hell out of me just to start up in the car. My turbo motor is so lame sounding compared to it... lol

Lopey?
https://www.youtube.com/watch?v=ojnNWlEgJfM

And as we all know, that rilly kewl sound is why we build motors...

It can take 100+ extra horsepower to drive a supercharger even on a mild 600-700hp street engine, so the entire rotating assembly is going to see additional stress from the cylinder pressures over an n/a motor. However, for the same displacement the n/a motor would have to spin at higher rpm, which requires more expensive valvetrain components.

Both are cool. I like torque so I prefer big blocks, or supercharged/turbocharged smaller displacement engines.

Chevy i know... but anytime we get into YT dyno wars i always come back to this one... Pretty close to 700HP N/A too, at the crank anyways. 562RWHP.

You want LOPE...???


https://www.youtube.com/watch?v=WNnSs_oN704&spfreload=10

That wasn't a Shivvy, that was a Ram with a 420" Gen III Hemi.

Cranks see maximum stress near TDC. Because boosted motors run less timing, the cranks actually see a lot less stress vs. a N/A motor.

Right now we have a new 6.4 short block, we want to change at least the rods and pistons to forged. I understand the crank is a nice piece from the factory.

Fully ported eagle heads, flow 340ish

Got a chance to use a magnuson supercharger- if we can afford it that is!


Anyone see a problem yet?

Let see, the boosted motor has forced a lot more air and fuel into the cylinders and that ignites and makes a lot more power than a N/A combination would so how can that posiibly make less stress? BTW, I have made motor with Roots super charger that made peak HP (496 C.I.street hemi on pump gas 927HP) at 7300 on pump gas and N/A motors on race gas that made peak 730 HP( 471 C.I. wedge) at 7300 RPM. Same RPM for peak HP, which one has the most stress on the rotating components in your mind? Insert whistling Emotioncon here with smiley face after it. On your deal with the turbo where it does not drive the turbo off of the crank and it does not gain boost directly proportionally to RPM, depending on the throttle and gear it is in, it will not have the same stress per RPM as a supercharge motor will with all other things being the same. HP makes stress, less is less.

Cab we're talking 700hp NA to 700hp boosted right? Not 927hp boosted, vs. 730hp N/A. I think it's fairly obvious that more power means more stress, but you're trying to compare apples and oranges to make a point.

What about 730hp N/A vs. 730hp Boosted both at 7300rpm. Which one has less rotating assy stress? I bet the N/A motor has 35 degree's of timing in it, and I bet the boosted motor has 25 degree's in it.

Less peak pressure but holding it over a longer period of rotation will make more power with less stress on the parts.

If I shove a bunch more air/fuel in the cylinder, and light it off late (low timing), it can keep burning nice and long at low pressure to keep pushing on the crank as it rotates. N/A has to light off what little air/fuel it has early (lots of timing), and that tries to push the crank out the bottom of the block from the pressure spike.

Same reason in principal why parts get damaged when the motor detonates. That early pressure spike near TDC is HARD on parts.

Below is a really good graph. The red line is a 11:1 4 banger motor at 45 degree's of timing which made 156 ft/lbs. The blue line is the same motor with 15 PSI of boost, and only 25 degree's of timing but it made 213ft/lbs. Notice that the peak pressure is the same on both. (Meaning in this particular case they would have similar crank stress). This is a good example of what I was talking about above... that the boosted motors can hold the pressure on the crank longer/later to make power. No additional peak pressures (stress) at TDC... but picked up 35% in torque.

However if we were just looking to make the same 156ft/lbs you can imagine with lower timing how low the peak would be on the boosted motor to make the same power. This is what I'm talking about why boosted motors are less stressful on parts then they're NA counterparts at the same power level.

BTW... the link below is a good read if anyone wants to dive into the topic further.

Ottoboost_2 by wright2305, on Flickr


https://www.physicsforums.com/threads/high-compression-turbocharged-engines.646362/

Doesn't the cylinder pressure required to make the power equal the same in the end? Kinda a wash IMO? Difference is one crank has more leverage on the crank snout,blower pulley, than the other. I like turboes more betta...

The blower motor can make the power at a lower engine speed which is the key here. To make the 700hp N/A will usually take more RPM. Stress/load goes up much faster with increased RPM than it does with increased HP. So the stress/load may be the same at the same HP and RPM between the 2, but additional RPM adds additional stress and load.

boosted would give you a drivable/usable car, whereas 700N/A would give you a super high compression, big bumpy cam not streetable car that would require high octane, expensive high stall and most likely need steep gears to work.

Let me try to set this up so it does not come off as arguing for argument sakes, I'm of the opinion that any time you use a power adder of any sort your adding stress into the motor by artifiscially (SP?) inducing more power than the motor will make normally. As far as HP per C.I. you can make a very small C.I. motor make a lot of power with enough compression and RPM, you can make a much larger C.I. motor make the same HP at a much lower RPM with a lot less strees on the components due to the lower RPM. As far as adding boost and reducing timing your reducing the timing the stay out of detonation, the inside combustion chamber temps. are much higher with the added pressure of the boost and will detonate a lot sooner than having the pressures less, hence you retard the timing to stop detonation. The blown Hemi mtor I referrenced like 33 degrees total timing with 7 lbs of boost at 12 % underdriven on CA pump swill, I had tried 28 to 35 degrees and it like 33. We switched the fuel to C16 and reverse the pulleys so the motor would overdrive the blower 13%, I reset the timing to 25 degrees and made a pull. The motor made peak HP (1027 HP) at 6500 RPM with that timing and 12lbs of boost, but is was on the edge of detonation and stop gaining power at 6500 I reset the timing up 2 derees to 27 and the motor started into detonation at 6200 RPM so we stop the pulls at that time. Maximum effeincy can be tuned for any combination, large C.I. and slow RPM will make a lot more torque than a smaller motor making the same HP at a higher RPM, especially with boost Is that chart you link to for a small europen deisel motor, Otto cycle? If so you and I both know that diesel motors that self ignite have to have stronger cranks, rods, pistons and blocks to make them live at the same power levels as a gas motor makes, correct? If it isn't for a deisel motor forgive me for seeing and thinking of Dr. Otto Deisel, or Dr. Deisel Otto (which ever his name was ) the inventor of diesel motors and theory. My last pump gas street stroker motor in my Duster made 727 HP at 6700 RPM and 540 ft. lbs at 3500 RPM and had 735 FT lbs at 4500 RPM. It was a blast to drive and did require some maintenance on the valve springs do to using a moderate solid roller cam on the street, if I had added a blower to a smaller C.I. motor to make the same HP I'm sure it would have required more maintenance and better parts to live at that power level Lots of ways out there to have fun

Rudolf Diesel (who invented the diesel) worked at Deutz as did Nikolaus Otto (who gets the credit for the current 4 stroke engines).

Thanks for clearing that up Seems like there are a lot of German inventors in the automobile and internal combustion motor designing and history

Nah, 12.1.1 comp.,5000 plus vert, .680-.660 solid roller and 4.11 gears here and it drives like a kitten till you stab the happy pedal then it`s a tiger. Great torque off idle and pulls past 7 grand with ease and I drive it more than just to car shows. N/A all the way for me till something changes between my ears and eyes.

haha you are not going to take a 700hp on a 150 mile road trip you can however do it w/ a 700hp boosted motor. It is what it is.

NEVER ASSume anything and I have driven it that far for a local movie shoot in the middle of bfe..........

I believe the naturally aspirated 700HP will vary more as weather conditions change and the blown 700HP would be a better power plant on the street.

One downside the blown combo will have is the increased weight on the front end. I'd still choose the blown engine if its a street driven car.

my old big block made over 700 and drove 400 miles a day at Drag Week without a single problem and it was like 5 years old at that point

and my current Hemi is around 600+ and it very mild and I already did Drag Week with it also

If forced induction was that hard on parts, the OE's wouldn't have been doping it since the 30's.

You think Gm is going to put out a 650 supercharged cadillac if they think it will be hard on parts and come back for warranty work?

The OEM's put in the correct parts to survive supercharged applications. An LS9 chevy has forged pistons, while the n/a LS7, with a 600 rpm higher rev limit, has cast pistons in it instead. Cylinder pressures are highest at lower engine speeds, and this problem is exacerbated by adding a supercharger. Dizduster brings up a good point regarding timing but that is only one piece of the puzzle.

Blower looks kewler!!

Not if they're slow..............looks funny in that case, kinda like a wing on a honda.

Both are cool, N/A or supercharged. What I take from this is 700 forced induction HP will be easier to live with, better on fuel etc. Not saying that 700 N/A HP can't drive long distances or on the street regularly (ThumperDart and sixpackgut both proved it), but again a forced induction engine will do it a lot better, likely less maintenance and likely be faster with a compromised (streetable) set up. Look at Dizusters Savoy, 9 sec whip that idles like it's almost stock! No crazy gears of convertor needed

It sounds like a very cool project, but what happens when it's done?

Call me crazy or over-protective, but being a parent that managed to get a couple of kids grown up without major damage has left me with some opinions....

Does having a bunch of high-school kids build and drive something with an honest 700hp sound like a good idea to everybody else? I see hundreds of labor hours turning into a pile of rubble and possibly some damaged kids thrown in as well. I sure hope I'm wrong!