Installshield

You will usually be able to get the proper octane rating in your area for a decently turbocharged engine. In higher elevation areas, premium fuel can be at 91 octane (Denver from what I remember)

I am not positve about this however. Something to think about if you head to a higher elevation area on a vacation or something you might need to talk to some people that know more about this. A turbo will still cram the same amount of air into the engine at higher elevation, the boost is set at a limit and the wastegate won't vent until that psi is met. But you won't be able to get the same octane gasoline, which could pose a problem. It wouldn't be a problem with an N/A car because the engine won't pull in as much O2, and the reaction(s) will not be the same... Somebody clear this up if they can...

gcs118

My car is going to be NA, so a lot of that shouldn't be too serious of a problem. I am just wondering if I can take the C/R up to 12.5:1 or something like 13:1 even. I haven't seen anyone else do this, highest I've seen was 11.9:1. Just curious how high I can go without damaging my engine or other systems.

Scarmiglio

Not exactly. The following is taken from howstuffworks.com:

"The octane rating of gasoline tells you how much the fuel can be compressed before it spontaneously ignites. When gas ignites by compression rather than because of the spark from the spark plug, it causes knocking in the engine. Knocking can damage an engine, so it is not something you want to have happening. Lower-octane gas (like "regular" 87-octane gasoline) can handle the least amount of compression before igniting."

Check out this link for a good explanation:http://science.howstuffworks.com/gasoline3.htm

Installshield

I have seen some 13:1(modified, not stock) Honda engines, and heard of even higher for purpose built race engines. With proper tuning and engine timing I think you would not be able to meet the fuel requirements before your pison actually taps the cylinder head and valves..So meaning the higher compression you go, the higher octane fuel you need. It would not be very productive to drive around with $20+/gallon 105+ octane racing fuel...

gcs118

Good point. I didn't think of the octane required if I took it to the max. Thanks for pointing that out. Any ideas how high I can go with 93 octane? I'd definitely like to go higher than the 10.7:1 FS-ZE pistons.

SedanMan

Why wouldn't you go turbo? You have seen what TheMan has achieved with his many NA mods. I dont think there is much to be gained going that route.

Installshield

There is plenty to be gained just not without a lot of time and money...

I like Ed's method for "pre-turbo" tuning. And I also agree with Jesse in that 150whp N/A would be great, nice and smooth. Personally I am looking into a slow custom process with a small lightweight turbo (a lot of guys hate t-28's, but that is what I am eyeballing). Maybe a spoolin manifold with a t-28, and just around 4 to 5psi I just want a quicker car that is still 100% streetable. I don't want the turbo to be known to everyone that looks or hears the car, just a subtle addition.

I would love to remain N/A and start ripping the car apart to rebuild the engine, but I need it almost all the time and don't have time for a complete engine rebuild. Maybe if I get really good with engine management software, or find someone that is I can raise the Compression Ratio closer to 10:1 and keep about the same amount of boost -1 or 2psi. That would not make a FWD that will just roast the tires in every gear from 3k up. I don't need or want 200whp or more, just enough to keep the car competitive with most sport compact car's acceleration and then worry mostly about the suspension...

SedanMan

I would like an elaboration on that. How could someone possibly get 150whp going NA with our engine? I haven't seen a single person succeed in even getting 140whp NA. How would more money and time make 15whp appear.

I agree that it would be great to be at 150whp, it's exactly what I want at the moment. But I just don't see how that can be done by going NA. That's why I've given up on buying CAI and exhaust upgrade. If ever I make my little car fast, it will be with a turbo since its the most cost effective,easiest and most streetable way of getting more power to the wheels in my opinion.

Installshield

ok...assuming we are talking about 2.0L FS's...

A FS-ZE is N/A with a claimed 170bhp, and with our 15% or so powertrain loss that is right around 140whp. That is in the j-spec familia Sport 20 so to get that across the pond you would need a new or modified ECU ($$$) Then bringing in the obvious slue of bolt ons (I/H/E) you would bring that up marginally. possibly up to 150whp. And then some headwork (valve cuts, porting/polishing) you could bring it up even more. Then you could bore the cylinders a litte, bringing the strokey FS to oversquare (I would think this would be one of the best cures for our terrible high rpm breathing problems) and raise the compression (160whp + maybe??)....I could go on...custom cams and stiffer valve springs, engine blueprint/balancing...

I tried to keep that on a pessimistic side, the gains could be considerably higher...

It would not be cheap and you are absolutely correct that a turbo will get you more power for much less cash...

Installshield

Toyota's Celica GT-S 180bhp 1.8L engine run around 11.1:1 compression. I am sure B18C5 Honda engines (Type R hand built power plant) will probably be around that if not more, don't know off hand. But both of these engines do fine with premium gasoline...By the way that modified 2.0L Honda engine ran on premium gas too...So you may be able to go considerably higher than the Mazdaspeed pistons...

gcs118

Do you think up at my dealer they would have an FS motor expert to talk to, or is my only chance to find my answer through my own research?

carguycw

Yeah, but keep in mind that the GT-S and Type-R engines both have variable valve timing and lift, so they use very aggressive cam profiles during high rpm, WOT operation. Most engines will tolerate a higher c/r with longer duration cams because the cam overlap bleeds off cylinder pressure at TDC of the intake stroke. However, the FS obviously does not have variable valve timing or lift, so you are stuck with one cam profile all the time. Using cams with enough duration to allow a higher c/r will probably have a negative effect on low-rpm torque, drivability, idle quality and a VERY negative effect on emissions.

Keep in mind that determining the maximum possible c/r on pump gas of a given engine is a very complex topic; it's dependent on a variety of factors, including cylider head, intake manifold and cam design. However, the upper limit on modern 4-valve engines with relatively conservative cams and WITHOUT variable valve timing is *usually* about 11:1. An FS MIGHT tolerate ~12.5:1 with really aggressive cams, but it's really hard to say. However, I would not start out any higher than the 10.7:1 FS-ZE pistons; I seem to recall some FS-ZE swap owners on this forum complaining about mild detonation during high-load, mid-throttle driving, although I could be mistaken.

Installshield

Very true, I only mentioned these becuase he asked about engines with higher compression...

Also a FS-ZE has a stock compression ratio of 10.4:1. You can purchase the 2.0L Mazdaspeed high compression pistons (10.7:1) but they are not stock in the engine...So if guys are having trouble with a knocking FS-ZE, it is most likely with a compression ratio of 10.4:1(unless they installed the other set), which means it would probably be worse with the higher set. I remember hearing the same thing as well, but can't remember how they handled the ECU. I know of a few guys that were not getting the ZE's full power because they just spliced the harness's or something together, and did not have the j-spec ECU. Without a stand alone, or some sort of upgrade you will notice little power with higher compression pistons, and potential pinging problems...

gcs118

How much more power could I pull from the high compression pistons (10.7 or 11.1) if I did have a stand alone? Enough to make it worth the extra money?

carguycw

Well, consider that an FS-ZE has a claimed horsepower rating of 170 hp; you can start there. However, if you're looking for an *ultimate* power figure, it's really hard to determine because it's dependent on a lot of other things such as the cams and the cylinder head, and also the amount of rpm the engine will tolerate, which is extremely important on a N/A motor. The FS has an open-deck block, a fairly long stroke, and a pretty lousy rod ratio, which does not bode well for the engine's ability to hold together above 8000 rpm.

I'm guessing that you're probably looking at 180 reliable, streetable hp. ~210 hp on pump gas should be possible but drivability will probably suffer and I don't know how long the engine will survive.