alright, you advanced tech nerds!!
what is the BIGGEST limitation of a normally aspirated 350? reason i ask is because 350's keep getting stronger and stronger, but what is the limitation that will one day inhibit further increase in horsepower? there has to be a "terminal horsepower"....how close are we to reaching it? please, expound on this anyway you wish, i'm curious as to what everybody thinks.


--shokor--

 

LOL, that sounds like the drag racers back in the day saying there was a 1/4 mile hp limit due to tire traction.

Basically the limits now are rules.

Technology is what gets us there.

Head flow, Coatings, Cam Lobes, Octane, combustion chambers, piston speed yadda yadda limit what is going on now.

If you can have a 350cfm LT1 head and a 220 deg cam with .450 lift at the lobe, a chamber that produces max power @ 25 degs of timing, coatings that keep all the heat in, along with piston speed of 6000ft/min then you can have alot more power! Basically this is stuff that the Yates/Sb2.s heads do today in NASCAR (except the flow is much better, 390-420cfm!) There are no cam lobes out there for a small block that do that either.

Basically a LS1 is what you are looking at! Bigger cam journal size to allow more lift per deg. 15 deg heads that can flow 350cfm, nice chambers that burn the mixture faster........ Things like that!

Everyone says that NASCAR doesn't have any advanced technology. B.S! the LS1 or Gen III heads are based upon things GM has learned from the Winston Cup boys.


Bret

 

<smartass>
Biggest limitation to HP would be not getting enough oxygen in the combustion chamber.
</smartass>

Everything comes down to feeding as much o2 into the combustion chamber as possible. Stroked and bored? Larger cylinders will have more volume w/ more 02. Forced induction? More 02. Nitrous? More 02 added. Higher rpms? More air per second. Tuned runner length, plenum sizes, etc...

The next limitation would be the strength of the parts. More o2 + fuel per cycle = larger combustion event, higher cylinder pressures, for more stress on the parts, so parts have to be stronger. Higher rpms also add more stress, so then you have to decide which way to go - more cylinder pressure (nitrous, forced induction) or more rpms (same cylinder pressure, just more often, for more power). There's no such thing as terminal HP, just what you can achieve with what you have. If you want numbers, you can say a stock crank can't take more than x lbs of force on the journal, or a rod will break at y lbs force, or the main caps will distort too much at Z, or block cracks at X psi or Y rpms, etc... What are you looking for? The max HP a 350 cubic inch internal combustion engine can make? I suppose you could machine a super thick casting block that wouldn't distort, run a real big bore and short stroke, spin large rpms with nitrous and forced induction, and be well over 2000 hp. Think F1 engine, but with nitrous/forced induction, a heavy steel block, and 350 cubic inches. Maybe have ceramic metal matrix pistons, heads, and cylinder liners invented so you can run nearly infinite combustion temperatures w/o giving HP away through a cooling system.

Or was your question - what is the most my stock LG4 350 can make?

Andris

 

this is at least interesting: those 3.0 liter f1 engines make 800hp NA..... and they have plenty of rules from restricting them from the thing's they'd like to put in their engines

 

hehe

but, actually, i'm just trying to understand if there's a point beyond which, there is diminishing returns. I guess i'm trying to see if there's a HP number that marks that point. I remember watching a commercial where a guy is surfing the net, and all of a sudden, the computer says, "you have reached the end of the internet, please go back." I wanna know if there's such a thing for a motor.

i know that bigger cam, bigger bore, thicker walls, higher compression...blah, blah, blah...all make more power, but is there nothing to surpasses all of that? molecules...


Is the only true limitation to power the molecular stability of the parts that are used? Because (assuming normal aspiration), the slope of the HP graph doesn't go down until molecular bonds start breaking up from all the stress.

 

ok i think i'll take a jab here and say the most volumetric efficiency you can get is maybe 110% MAYBE 120% on a specially tuned engine....... so lets say you are getting 110% VE and that gives you a certain torque..... then how fast do you wanna spin it?

lets say 8k, maybe that gives 1000hp for a 350 engine if you reduce carious friction and thermal losses with good drivetrain and thermal coated compenents..... something along those lines


or you could go F1 style and spin 15k rpm and get some really good VE like they do and make the same hp/liter and get 1500hp.....


those are some thrown out numbers but maybe you can see where i'm going, you wont make 2000hp from a small block at 4k rpm

 

It's over 850 now, according to the best sources I read.

Interestingly enough, other than displacement (3.0L) and fuel (a form of gasoline submitted to and approved by the FIA), and some exotic metals (like beryllium), as defined by strength/weight ratio, there are very FEW engine rules. No supercharging, of course.

Things like number of cylinders, bore stroke, v-angles, number of valves, camshafts or direct acting valve mechanisms, fuel injection, timing, computer controls, etc. etc. are open. They get to try almost anything they want. They get maybe 285 hp/liter. Winston Cup engines at about half the size get half the hp/l, and nearly the same hp at half the rpm. Pro Stockers (500 cubes) get about 160 hp/l around 10k.

Engine speed is basically limited by piston speed (which is proportional to stroke). F1 engines run twice as fast as Winston Cup engines with half the stroke.

Now look at torque/liter @ power peak. 85 to 90 lb-ft per liter is just about the current limit for all top end NA engines. Pro Stockers get about the best because they only need to run for a few seconds at power before changing valve springs. (1 inch of lift at 10k will do that).

Volumetric efficiency generally determines how much torque is produced at any given rpm. VE is determined by how efficient the engine is as an air pump. IMO, state of the art limiting factor is VE @ power peak or torque/litre @ power peak.

To answer the initial question, look to Winston Cup for 350 small block limits, as SStroker Ace said, at least for engines designed to run for a period of time.

"Is the only true limitation to power the molecular stability of the parts that are used? Because (assuming normal aspiration), the slope of the HP graph doesn't go down until molecular bonds start breaking up from all the stress." (rage366)

Say what? Breaking molecular bonds in solids with force probably isn't where we should be looking for limits, IMO. Leave that to the particle physicists (or some cam designers...). Pumping air quickly is the limit.

My $.02

 

from what ive learned hp is not everything esspecialy for drag racing torque is king of road thats for shure and if you are building a 350 you wont go for 8000 rpms for a street engine due to idle aroud 1500 and negitive mpg #. For me turbos with efi are the answers to all problems mpg is almost as good as N/A. You dont have to spend more time on tweaking the the engine so you can use it for what its built for racing . all the coating and other mods will help out what i feel is the limiting factor for street detonation . I dont think its cool to build an engine that will be used on the street and have to mix race fuel in to prevent knock or have to run full race gas. A well designed street 350 with turbos can make ~850 hp @6700rpm and thats on 93 octane with no boster, a good idle, and decent vacume to run power brakes. To acopmlish this with a N/A engine would be almost impossible, and cost big $ to harness and support air for 8000+ rpms. acording to desktop dyno i pluged in some big N/A parts and came up with 650 hp at 8000 adn torque peak at 6000!

 

that would be jim lab's engine......
he does make 400ftlbs from 2000-7000 though or something like that

 

Nope, coatings hold heat in the chamber to convert it into TQ rather than let it escape. Energy is not created it just changes into different forms. Coatings will let you change the potential energy of air/fuel into heat and TQ, the more you can change into TQ the better power you make. The engine is a horrible at thermal effiecency (sp?) coatings just help that.

Coatings DO NOT ALLOW THE USE OF MORE COMPRESSION RATIO, AS LONG AS THEY DO NOT ALLOW THE USE OF MORE BOOST FOR A CERTAIN OCTANE! they will protect pistons from melting holes in them because of the high heat.

Since they hold more heat in they might actually require a lower maximum compression ratio for the engine than without.

To each his own on the turbo point. I'm not a fan of turbos, they do a good job at making more power per L, but they usually are not a durable and smooth in power delivery, evne though they can be.

Bret

 

i'm not a big fan of turbos either, bret. turbos/blowers/NAWWWS make cars fast, but to me, that's half the fun. The other half is making a motor run as efficiently as possible. Putting a turbo on a car doesnt make it more efficient...all it does is increase two factors (air and fuel). when i think of efficiency, i think of using less fuel to create more power. Once the turbo kicks in, the gas gauge drops.
I like doing one thing at a time, and right now, i dont think we've reached the limits of normal aspirated engines, to just strap on a turbo (although it's a much easier way of getting power)...but i digress.
I guess maybe i should stop trying to understand the limits of a 350, and instead, try to find a way to shove on a nuclear reactor in my engine bay...

--shokor--

 

Yes i agree turbos arent perfect and they may have lag but, shouldnt if tuned right. but we are taling about terminal hp and for me this would be for street if i was building a race car 100% strip you wont build a 350 you'd make a 383 406 454 502 ect... but in the real street world the terminal hp is non existant its terminal stretablity.

The best and most efficient way of adding streetable hp is turbo (well nos dosent count cuz you dont always have it when you want it) superchargers are second because they are paricitic. example: supercharged engines bottom end may be taking a beeting of 800 hp just like the turbo engine but the sc engine only 725 hp is getting to the flywheel due to the drive for the compressor. While turbos there is the backpressure but the loss is less than the sc loss to drive. and N/A engins just arent streetable if built for hp.

 

well, i used a 350 just as an example...i just used a 350 because it's a very common engine size...the terminal horsepower question can be directed toward any engine size, because the question is asking what the underlying limitation of a normally aspirated motor is. and i didnt mention anything about street use, i know that there are quite a few limits for street performance. my question is based on theoretical limits.

i'm not bashing on turbos, i just wanna get the most out of normal aspiration before i move on to forced induction.
hehe, dont wanna get the turbo/blower/NAWWWS ppl mad at me.

--shokor--

 

I think another of the biggest limits is what kind of fuel you use. Just by switching to a different fuel, you can pick up power or lose power. If you build the engine for a different type of fuel, then you can use a much higher compression ratio (static and dynamic) safely.

I don't see why that would be impossible. It would only take 2626ft/lbs of torque Just a rough guess here, but I bet a small bore, long stroke, high boost twin-turbo intercooled 350cid diesel on propane could get close Put a powerglide and a 1:1 gear ratio behind that and it would haul!

 

"I bet a small bore, long stroke, high boost twin-turbo intercooled 350cid diesel on propane could get close Put a powerglide and a 1:1 gear ratio behind that and it would haul! "

adioss, stop cheating, no turbos allowed, let alone twin turbos!

--shokor--