Paperboy7777

I'm about to swap a JDM F20C motor into my AP1, but I just heard that it was designed to use 93 octane, is this true?

I live in California, our highest available commercial grade gasoline is 91 octane, can the JDM motor safely operate on that gas?
Or should I just stick to swapping a USDM motor...

this whole sourcing an engine for the S2000 is so frustrating....

Chance S2K

That's actually a good question.

USDM F20C have 11:1 compression ratio, JDM F20C has 11.7:1 if I remember correctly.

I'm not sure if those 2 points are enough to make a difference. Curious to find out, I'm sure someone here knows. Worst case scenario you could probably dial back your timing a little with tuning but that's probably more hassle than it's worth.

Paperboy7777

I tried to find the info on the forum, but didn't find much pertaining to the matter.

I might just jump the gun, install the JDM motor, pump Chevron 91 and hope for the best.
I guess I'm hoping to see people validate the reliability of a JDM motor swap running below 93 octane gas.

cdelena

Octane ratings are confusing because tests can be RON. MON, or here in the US the rating is AKI which is and average of the two. As I understand it premium fuel in Japan is 100 RON and probably equivalent to about 94 AKI. So a bit higher than here in the US although I have seen that rating on a few higher priced pumps in Canada.

Chance S2K

I have no idea if this is just heresay, but apparently Shell stations are one of the better stations to go to for consistency with their quality of high octane gas.

If you decide to install it I'd just give it a couple weeks of monitoring and make sure you're not getting any detonation. Test out all RPM ranges and throttle loads, include some uphill pulls too. If needed you could dial the timing back, but like I said that would require tuning which would increase cost/complexity somewhat.

I'd still recommend waiting a bit though as I guarantee there's some US owners here with JDM F20C engines that can chime in.

Slowcrash_101

The only difference is a thinner head gasket, the car will pull timing if it knocks too much and you'll notice that the car falls flat on its face when you accelerate.That said, I doubt it'll do any real harm, or that you'll notice.

1SIKAP1

I had a jdm motor dropped in about 14 mo ago, I use chevron 91 because I heard somewhere that it's more like 93, who knows if it's true, but my car does run better with chevron compared to shell. I believe it does retard just a tad, seems to like low elevation also, I live in the high desert. idk if this is all relevant these are the thing I've noticed with this engine, doesn't burn a single drop of oil, had a bit of misfire on idle but I believe it's my map sensor, I give it a whack and it's back to normal, I would love to put in higher octane but I'm in Cali, just checked my spark plugs after 28k miles and there a bit white "lean?", I'm not a mechanic and don't know if all these relate but just giving my input, also I run an 02 ecu in my 00

Slowcrash_101

White grey tannish plugs = normal, unless it's crusty.

B serious

Lol yes...I'm sure the motor will run fine with 91 octane. The ECU will adjust timing if it sees knock.

I have had to run my USDM motor on 87 octane...in mid summer because this gas station in middle of nowhere Iowa had a choice of either 85 or 87 octane.

The USDM owners manual strongly SUGGESTS 93 octane for S2000's. It doesn't REQUIRE it. 87 is the minimum.

So I'm sure a JDM motor with a tiny bit more compression will be fine with 91 octane.

Chuck S

I can't answer the JDM question but octane for USDM cars isn't all that critical as long as it's greater than 87.

Direct quote from my 2006 AP2 owners manual doesn't mention 93 octane let alone suggest it:
From the 2002 AP1 owners manual (no mention of damage with octane below 87 but I've never seen octane below 87):
(Emphasis added.)

-- Chuck