I'm not sure what sub-forum to put this question in, but I had a thought yesterday...which is harder on an engine at similar power levels?

Let's say we have a B20VTEC, 14:1, forged internals big cams, stroked, ported, etc. It puts down 280 hp all motor at 8500 RPM.

Compared to another B20VTEC, but low compression forged internals, stock stroke, turbo, putting down 280 hp at 8500 RPM.

Common sense tells me that the N/A engine, built to within an inch of its life to make that kind of power, is less reliable than the turbo engine which isn't even close to its limits of power, i.e. isn't "working as hard".

Then I started thinking maybe it all depends on the cylinder pressures, the turbo just has more POTENTIAL. Maybe they would both have the same reliability at the same power level? Or is the N/A engine going to be inherently "sketchy" at its N/A limits?

 

Generally speaking boost is, not N/A.

 

At the levels a lot of these engines are running at it takes equal maintenance to keep either one running

 

Thinking about it, I was coming to this same conclusion.

I would think the forces and pressures would be about equal for the same power levels turbo and no. Which in turn would mean the same level of wear overall.

The one aspect that I think separates the builds is the turbo has more components so more components to maintain. So really between the two, the NA motor should be a touch cheaper to maintain over the long haul.

 

[QUOTE=DumpdEJ6;51122596]Common sense tells me that the N/A engine, built to within an inch of its life to make that kind of power, is less reliable than the turbo engine which isn't even close to its limits of power, i.e. isn't "working as hard".

Your common sense is right.

If this is going to be a race/track car or you are planning on spinning it at 8500 rpm everywhere you go neither will have any longevity, both will be running at high compression i.e. high rpms = high turbo boost = high compression.

For a daily driver, the low compression engine w/ turbo will be more reliable than the 14:1 compression. With the 14:1 the engine it is always running at high compression which can cause problems like Detonation, whereas a turbo is not always running at full boost, even at normal driving rpm you're not getting much boost if any.

Detonation is influenced by chamber design (shape, size, geometry, plug location), compression ratio, engine timing, mixture temperature, cylinder pressure and fuel octane rating. and... When people see broken ring lands they mistakenly blame it on pre-ignition and overlook the hammering from detonation that caused the problem. Good read about detonation and pre-ignition... Engine Basics: Detonation and Pre-Ignition by Allen W. Cline

This is not to say it can't happen in a turbo engine, just more likely in a n/a high compression engine.

In variable output systems such as automobile engines, exhaust gas pressure at idle, low engine speeds, or low throttle is usually insufficient to drive the turbine. Only when the engine reaches sufficient speed does the turbine section start to spool up, or spin fast enough to produce intake pressure above atmospheric pressure. Quoted from Wiki (This also why you get turbo lag)

...turbos are efficient when cruising ‘off boost’ (ie when the turbo isn’t really working) but very inefficient when ‘on boost’. - See more at: https://www.carwow.co.uk/guides/glos....N4F06wly.dpuf

Hope this helps

 

Not always true. My friends turbo b series has held together for over 3 years running multiple low 9 second passes. Same motor, same turbo setup. Same fuel system. It's a pretty simple setup making around 800 on c16. He's only recently started trying new parts in an attempt to break into the 8s. Whereas my NA K series on methanol will more than likely require a tear down and inspection after every season.

 

What do you end up replacing each season in your K series?

 

Mine hasn't fired up yet but I'm already planning ahead. Biggest wear items would be bearings and rings. Headgaskets and seals and guides. Even checking rod lengths to make sure they haven't stretched beyond what's safe since they're aluminum. Methanol is nasty stuff and takes it's toll on everything, even with routinely flushing it from the system.

 

Would you attribute the bearing wear to high compression (I'm assuming since you're running methanol) and rings due to bore wash from running rich AFRs?

 

Thanks for your thoughts, everyone. I was worried that this would be a "stupid question", but from the variety of responses it seems valid. I asked because I was reading about a few NSX builds and day-dreaming about building my own that I'll get one day. The "sweet spot" as far as HP seems to be around 400-450whp, exciting enough to drive without losing the "feel" of the NSX. The usual way to get there is forced induction, but if there are 300whp 4-cylinder B- and H-Series engines, it stands to reason one could conceivably get 400 or so, N/A, out of a 6-cylinder. I like to fantasize and build my perfect NSX in my head all the time, lol. So it got me thinking about which would be the better route to take. Obviously if you can reach the same power goal with both NA and boost, NA will be the better option as far as linear power delivery, but at what cost to reliability?

 

You got it. The bearings are going to take a beating from 10k rpm shifts and just normal wear and tear.

 

I think Judgegauge hit the key portion that throws a monkey wrench into my who thought pattern I posted. And it conforms to what you are saying about your friends turbo going strong still after 3 years of use.

That detail totally slipped my mind but makes total sense. The turbo isn't always running near top end forces on the parts. The NA is always pushing near the limits of forces being applied on the parts.

Makes total sense the NA motor will need major maintenance more often than a turbo motor in most cases. The exception is a dedicated track car being they are always pushed to their limits at all times. But for a street/strip car.... The turbo will fair better.

 

280whp boosted will be MUCH easier and cheaper than 280whp NA. Period. Stock blocks w/ ebay kits will do that all day long on pump gas without issues. 280whp NA will **** all over a boosted car with the same power though...BAD. My B20V @ 253whp pulled the first 1/8 then ran door to door with a 420whp LSV in a lighter hatch. He caught me at the big end and pulled ahead by about a car length. I ran a 12.1 @ 114 and he was something like 11.7-8 @ 120

High comp all motor cars do take quite a bit of maintenance, especially when you run anything besides pump gas like ethanol or methanol. I change my oil after about 15 passes and the oil is diluted with some ethanol.

 

280whp turbo will win over a 280whp n/a car all day just compare the torque curves it's really no contest
If you want to compare 250whp na vs 400whp turbo you are getting into turbo sizing territory, gearing and traction at launch we are still talking torque but we are also talking where that torque is peaking.

Most issues come on the NA side and turbo side when you are pushing limits. Running 8500+ rpm to build N/A power is very stressful over a long enough period of time. Cramming big boost into a 4cyl is also stressful over a long enough period of time. Figure out how much power you reasonably want to make and then build to that. Low stress turbo and power peaking lower in the RPM range for N/A will insure a long lasting build. But, realistically, don't plan on doubling or tripling your stock crank hp without there being some downside.

 

Show me a 280whp turbo B outrunning a 280whp NA car.

I have beat 300whp GSR turbos from a dig, on the freeway, you name it. NA power > turbo power number for number. Otherwise the all motor cars running mid 9's with 450whp vs turbo cars needing 600+ is just a fluke.

It goes the same way in the domestic world. 600whp V8's will run with 800+HP turbo cars all day long. It's a give and take thing. Are there some exceptions? Yes. But generally that is how it works.

 

Which do you think is faster?
Turbo 5.5 vs NA 6.2 AMG

 

Poor example but the S63 will be faster. Even at its lowest power point it makes more power than the SLS. A graph between those 2 motors doesn't reflect the graph of a 280whp NA vs 280whp turbo 1.8L motor I put in my statement above. Thats comparing apples to broccoli at this point.

I'm not trying to bench race or start a pissing match, I am simply stating 280whp NA WILL BE FASTER than 280whp turbo in comparable sized motors. Are there exceptions? Yes. But the basic logic has been proven for years and years. I would gladly line up against any 253whp turbo B to prove it over and over again. Hell, I'd give them a 50whp handicap to make is more fun. Turbo lag is a real thing, and unless you pair your turbo to have zero lag like the dyno above (impossible if you want to make power on a small cube motors) it's not a 1:1 comparison. Turbo will always be playing catch up and it requires more power to do so.

HP is just a number, its what's under the curve that tells the true story.

 

I was beating 300hp turbo b cars on the street in my 3000lb 260hp NA rsx. At the track our times were very similar.