Compression Ratio?

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toocrazy2yoo

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I know I've seen this before, or maybe asked way way back, but why would my 92 Hyundai 1.6 4 banger have an 8.5:1 compression ratio, and my 2005 Hyundai 1.6 4 banger have a 10.5:1 compression ratio?

What are they going for with the higher compression ratio in this thing? Isn't that harder on the head gaskets and whatnot (whatever whatnot would include)?
dunno.gif
 
engine compression ratio has no direct correlations to headgaskets(thinking of potential failure due to high compression?). In fact, any diesel engines running in excess for higher than 15:1 compression and the head gasket still holds for many millions of miles.

For the most part, gasoline engine's compression ratio has a direct correlation to how the engine is designed and it's intended output and usage. It is not uncommon to see that N/A engines can run close to 11:1 ratio with pump gas these days due to advancement in engine electronic control.
 
I assume they're doing it for better thermal efficiency which would equal higher MPG figures, and to ________ with durability. If it'll last til the warranty runs out then all's well from the manufacturer's point of view. That's just my opinion.
 
Better engine tuning, cooling, along with knock sensors, allow higher CRs. Higher CR leads to more MPG and power.

How much HP does the '92 have compared to the 05?
How more technically advanced is the '05 compared to that '92?
 
Hey, Dummz..

The 92 advertised 110 HP at 6000rpm.
This one, 105@ 5800. I would imagine the 2005 is QUITE technologically advanced way beyond the 92. Show me a motor that isn't. The emissions, the materials, the oil recommendations are WAY different. But the compression ratio is way different.

Didn't understand why. I know it's their way these days of getting to the HP figure they wanted, but 10.5:1 vs. 8.5:1 seems pretty high for a plain old engine.
 
i think it has more to do with squish than anything. you can setup an engine to ping on 8:1 and 93 octane if the combustion chamber sucks. on the other hand, 13:1 is possible with 93. actually the toyota prius has 13:1 and runs on 87!
i think the problem is proper squish involves more costly engine assembly procedures compared to just slapping any old head on and checking the compression ratio. so more often than not automotive engines dont use squish to its fullest extent. racing on the other hand, oh yes they very much use squish heads and pistons.
look at an old small block chevy, or really any old american iron engine from the 60's-70's-80's with original iron heads. combustion chamber design and exhaust porting were less than optimal to say the least. it appears to me they didnt know about, or didnt care about squish back then.
 
2Crazy2U: The horsepower may be close, but what are the torque ratings?
Giving the consumer the CR spec is really just marketing tech filler and keeping up with the Joneses. Did it affect your buying decision?
 
Quote:

Hey, Dummz..

The 92 advertised 110 HP at 6000rpm.
This one, 105@ 5800. I would imagine the 2005 is QUITE technologically advanced way beyond the 92. Show me a motor that isn't. The emissions, the materials, the oil recommendations are WAY different. But the compression ratio is way different.

Didn't understand why. I know it's their way these days of getting to the HP figure they wanted, but 10.5:1 vs. 8.5:1 seems pretty high for a plain old engine.

Click to expand...


The SAE changed the way horsepower was to be tested in 2005. Some larger engines got a "boost" in horsepower, while it seems that the smaller ones took a hit (that's just my general observation). Therefore, the difference in testing metrics could be much of the cause.

Just to compare, what are the torque readings for the 2 motors?
 
I've seen the torque numbers, they're not huge, maybe 155 foot/lbs tops, but the old butt-dyno tells me it makes the maximum torque this thing is capable of very much lower, RPM-wise, than the 92 Elantra. This thing lives between 1000, and 4000 Rpm, which in 5th is a shade over 85. It's plenty.

Above that, there's just no point, it's just making noise, and while this Accent has a pretty stout GT handling package, I have a LITTLE respect for the speed limit, my license, and the law in general, so 85-ish is the cap. It gets up real handily from idle through 4000 rpm, but the good pull is done by 4000. At 4000, it starts getting buzzy, which was a nice surprise, this thing is really smooth and quiet, refined, even, compared to the 92.

I got the Deja Vu all over again when you mentioned the torque, I know now I asked about this once. Sorry to trouble you guys. But, once again, lo these many months later, the high compression ratio made me wonder.

Some revelation, eh? This is the dog here..

Thanks, yall!
cheers.gif

48.jpg
 
Here I allways thought higher CR was a GOOD thing! more power,throtle response, better fuel efficiency. If it's properly engineered no reason it shouldn't stay together.

I'll (as a generalization) take 150-200 thousand miles of performance and fuel economy over a 250-300K mile dog's arse any time!

UUH Chris, what's the touque output on you're jeep's engine?

Bob
 
Yeah, yeah, Chris..
Quote:

My Jeeps lugnuts take more tq than that engine puts out.

Click to expand...
laugh.gif


I saw a quote with funny little script attached that said the same about someone's Honda.
cheers.gif


Now, is this higher compression ratio synonymous with lesser durabilty? My 8.5:1 Elantra (the aforementioned 92) had 269K on the bottom end (heads, cams and valves were re-worked because the first owner was unaware of the concept of a timing belt). It burned no oil, cleared emissions with flying colors, and made no noises, ticks or knocks. Throughout its life, any misfires were cured with new plugs and wires. The day I traded it, it was fresh off the 80MPH Boston-Washington run, never missed a beat.

Does high compression exclude durability/longevity?
dunno.gif
 
It is very possible that the cranking compression of the 8.5/1 engine is HIGHER than the 10.5/1 engine.
It is directly related to the camshaft, specifically the intake cam. A long duration late closing intake cam will make the effective compression less than with a milder cam.
The higher compression is a good thing for efficiency, by itself.
The newer engine is designed for more power/ci.
 
Mechtech is on to something, the "rated" compression ratio has other factors like cam overlap that "poison" the high compression to make it run on cheap gas. EGR systems help too.
 
A properly set-up and designed engine is more important than the CR as far as reliability is concerned. The old Shovelhead Harley engines of 30 years ago had low, low CR's yet would need 3-4 top-end overhauls in the same number of miles that newer models (1985-1999) would need just one overhaul. The newer ones went up in CR, performance, economy, with lower emissions. Now the new models 1999+ have made another step with higher CR's and better reliability. They still don't have 10.5:1 yet but my motor does and I doubt if there will be any affect on wear due to the CR. Also, an aluminum head can support a lot more CR than an iron one because of improved heat exchange. A general rule of thumb is at least 1 point higher. I don't know if the 92 is iron but it might be. I would consider the higher CR as a benefit-better MPG, power and emissions. Also, the 10.5:1 is only the static compression, the "real" compression is affected by cam timing, intake and exhaust flow and head design.
 
Like Mechtech said, it is the "dynamic" compression that matters. As the valve opening/closing get tuned differently, you can have a very different "dynamic" compression than the static compression in different rpm.

My corolla has 10:1 compression and get 100hp out of 1.6L, my integra has 8.2:1 compression and get 140hp out of 1.8L, both are well known as reliable engine. How is that possible? it is all about ignition timing, AFR, and power band tuning (via valve timing).

Engine with "drive by wire" (controlling the ignition and throttle body based on gas pedal, rather than just controlling the throttle body and let the ignition controlled by O2 sensor) can run safely up to 11 CR, by removing the safety margin of a sudden, wide range throttle change. Those changes cause pings and need extra safety margins, if you remove them you can run closer to the design's edge, safely.
 
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