The '97 Miata appears to have about as good a tune as it needs from the factory. To get more power without going FI is a challenge.
It appears that E-85 is an option that keeps me class legal in CSP. I can get 460cc RX-7 injectors for cheap. At that point I assume I'll have to Megasquirt it to get things going correctly. What else, and how to get there? Shave the head for another compression point?
Is e-85 worth it? Do I need to start chasing new lines and fuel pump, etc if I go that way?
here's the canonical Miata.net thread about naturally aspirated builds. Be warned that while the numbers quoted in that thread do appear to be real numbers, they aren't necessarily as easy to get as just bolting parts on, there's a lot of subtleties.
A friend of mine had a Rebello-built NB motor (the NB head has significantly better port geometry than your '97) running E85 with a megasquirt, high-compression pistons, cams, EU intake manifold, fancy header, etc and I think it made about 160 at the wheels, maybe a tad more. (This was a DP car, so there was a lot more to play with than CSP, but it wasn't built to the limit of the DP rules in the motor).
As for E85, I'm pretty sure you'll need a new pump, but I think the stock lines are probably OK for NA use. It's probably safer to replace the rubber parts with something E85-compatible.
Can you shave the head? I know you are looking more at the O2 that Ethanol brings, but if you can take advantage of it's knock benefit, hey....
I looked the rule up once before- and it wasn't really clear if that was an option for CSP- it's allowed to factory min thickness specs, but without that, there's an allowance (IIRC).
Worth it? Sure.
Shaving the head might help a little but I think at that point you are well into the diminishing returns on that engine and you might as well just move to the 01+ engine that will give you even more power. But E-85/megasquirt even on your 97 would be a little bump in power and easy enough to swap over to an 01+ engine later.
Can you get yellow RX-8 injectors cheap? They should be a little better than the old style RX-7 injectors.
I haven't thought of E85 in NA performance builds. I know it has been big for FI for close to 10 years for it's knock resistance, around 120 octane equivalent. Good luck, I'll be watching.
Brian wrote: I haven't thought of E85 in NA performance builds. I know it has been big for FI for close to 10 years for it's knock resistance, around 120 octane equivalent. Good luck, I'll be watching.
Very popular in the BRZ community. Typically worth around 15whp on bone stock vehicle.
BRZ is running considerably higher compression than a 1.8 NA, though. I think for getting the full benefit you'd need more than the head shaved a little, most likely high compression pistons (IIRC someone makes either 10.0 or 11.0 pistons) and some other supporting parts.
BoxheadTim wrote: BRZ is running considerably higher compression than a 1.8 NA, though. I think for getting the full benefit you'd need more than the head shaved a little, most likely high compression pistons (IIRC someone makes either 10.0 or 11.0 pistons) and some other supporting parts.
Except for Street Prepared, that's not allowed in the rules. Just the head shave is.
The engine part starts on page 98 of the whole book, but only page 12 of that specific subset.
You can overbore, but no increase in compression or lightening of pistons. Head can be shaved 0.010" if not specified. You can port match withing 1" of the manifold interface (both intake and exhaust). Intake is free, exhaust is pretty free (some restrictions). And adjustable cam ends can be used with the stock cams.
On the last part- I'd very much check the actual stock cams that they are within spec- for an engine that old, they can be pretty worn.
If I did my math right, a 0.01" decrease in the head will bump the 9:1 compression to almost 9.2:1.
The legal thing to do is go to a 99 engine with 9.5:1 compression which ups to 9.72:1.
Or a +2001- which starts at 10:1 and ups to 10.25:1. With VVT. The E85 will take care of any VVT induced knock pretty effectively.
alfadriver wrote: The legal thing to do is go to a 99 engine with 9.5:1 compression which ups to 9.72:1. Or a +2001- which starts at 10:1 and ups to 10.25:1. With VVT. The E85 will take care of any VVT induced knock pretty effectively.
If you're going to build a serious CSP car, go straight to an NB2 motor. 10:1 compression, better-flowing head, and it drops right in, it's a no brainer. Always upgrade to the best starting point before you start spending money on things that won't transfer like head work. Give it a megasquirt, an EU intake manifold, and a nice header and you could be out the door for around $2-2.5K.
E85 is worth something like 15% on a turbo car, half of it comes from the increased octane, the other half comes from the fact that it's got a higher hydrogen to carbon ratio. The limit on power is how much oxygen you can pump through the engine, the oxygen gets reacted with the H and C in the fuel to release power, and for the same amount of oxygen you get more energy by burning H than you do for C. Ethanol is 5:2, octane is 18:10.
For the E85 smell alone its worth the switch, never mind that it burns cooler, cleaner, cheaper and makes more power. GRM did a test of different fuels on a CSP miata, if I recall E85 made 8hp over 93 E10, I just switched to E85 on my challenge tercel which is built to the letter of street prepared rules (FSP), I didnt need a new pump or lines I just installed 50% bigger injectors filled up with E85 and tuned it. Im also not running a fuel sensor its not needed if your always going to run E85.
If only there were a magazine which conducted tests of different types of fuels and their affect power in a Miata! Maybe even in a car intended for CSP.
https://grassrootsmotorsports.com/articles/fuel-truth/
Okay it's a 1.6L instead of a 1.8L, but I'd assume you could draw some similar conclusions.
Snrub wrote: If only there were a magazine which conducted tests of different types of fuels and their affect power in a Miata! Maybe even in a car intended for CSP. https://grassrootsmotorsports.com/articles/fuel-truth/ Okay it's a 1.6L instead of a 1.8L, but I'd assume you could draw some similar conclusions.
Actually it is an 01+ engine in that article.
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