And that's exactly what we were saying. Since the RSX-S has a higher compression ratio than the Si, it needs higher octane gas. Try reading and comprehending what we are telling you.

 

That's asking a whole helluva lot without saying which two things you're comparing.

 

i may be mistaken, but isnt the i-vtec in the si and base rsx similar to the sohc vtec found in civics? and when i say similar, i mean the vtec function is more of a fuel economy and good emissions version of vtec. rsx-s has the low and high performance lobes on the cams,=(high output vtec).

 

First of all read the link I posted a few posts up and that should explain the differences.

If not, then basically the difference in the systems used on the Si/RSX and the RSX-S is that the RSX-S switches the cam profiles on both its intake and exhaust cams while the RSX/Si switches only its intake cam profile. So in a sense, yes, it is kind of like the difference between SOHC VTEC and DOHC VTEC in terms of its functionality, but it is still a DOHC motor either way.

 

the compression ratios...which is better in performance? i was talking to my dad about this, and he said he didnt know that they were still making an 11:1 compression ratio...he remembers when they had them in the muscle car era, but i'm not so sure that they make that kind of compression anymore...do they? unless the engine is really super duper.

 

Obviously they are still making 11:1 compression ratios, because that is the stock compression ratio of the RSX-S. If you take 2 identical motors, and give one higher compression, it will make more power. Race cars use compression ratios sometimes in excess of 17:1, and I have a friend running 13:1 compression in a daily driven ITR. Higher compression means you need more fuel or higher octane fuel to overcome detonation.

 

The compression ratio is pretty much what it sounds like--how much the motor compresses the air/fuel mixture before it burns it up (by igniting it with the spark plug). The thing is, the more you compress an air/fuel mixture the more it's going to want to explode without adding a spark to it. When this happens it's called detonation, knock, ping, etc. They're all the same thing. This is bad and can mess up your motor. Higher octane gas has a higher resistance to detonation, which is why you need the higher octane gas in a car that runs a higher compression ratio. This is obviously only one factor though and there's tons of other things which determine what octane your car needs.

 

Hmm, this is gonna piss everyone off but..

So i-VTEC is kinda like BMW's Double VANOS? At least the continuously variable valve timing and cam lifting part versus the old school VTEC "switch point" at a certain RPM.

 

Read the thread I linked to. Double VANOS is a cam-phasing system that adjusts the timing of both the intake and exhaust cams. It has no effect on lift since it does not change the cam profile.