High compression E-85 Miata?

I have a worn out 1.8 Miata engine. I have been considering rebuilding as a naturally aspirated high compression E-85 engine. I have read about turbocharged engines set up for E-85 but very little about naturally aspirated engines optimized for it. How much compression could it run? Would it make much of a difference in power compared to a stock gasoline engine? Am I crazy for thinking this is a good idea?

The head doesn't flow as well as most other "famous" all motor engines.

That said, not many people have tried it, so i'd do it just for something new.

It's not like you'll make LESS power than stock, right?

I see a lot of people on various forums get discouraged with their all motor builds, become disappointed that it isn't making much power. But then again, i also wonder at what point that 10.5:1 compression was considered "high."

My Fiesta has 11:1 and runs on 87. One thing people forget with E-85, you have to be able to flow a lot more.

I am thinking 13 or 14 to 1 compression and some head work. Also big injectors and an upgraded ECU or Webers.

pilotbraden wrote: I am thinking 13 or 14 to 1 compression and some head work. Also big injectors and an upgraded ECU or Webers.

14 might be pushing it with the head design. I think last time i looked into it, i was thinking 12.5:1 or 13:1, some big cams, ITBs (why not?), and a Hydra Nemisis.

Yeah, I can't imagine going to the effort of setting up an engine for E85 and NOT going forced induction. Well really the fuel system I guess.

It's not like it's a huge amount of effort. Drain gas, put in E85, swap injectors if need be (not always), and tune for E85. A LOT easier than building a turbo system.

^What he said. Not including EMS, because you'd need that either way, it MIGHT cost you like.. $300 to "convert," and that's including your first tank of E85.

Dave, We're talking about an N/A NA, so unlike your build, we can't just turn up the wick after dumping in the corn squeezin's.

I've been looking into this as well for a long term Prepared build. I'm thinking that E85 will be the way to go since you don't have to flow as much air to get it stoch, it burns cooler, should make more power, and it's cheap compared to race gas.

tpwalsh wrote: Dave, We're talking about an N/A NA, so unlike your build, we can't just turn up the wick after dumping in the corn squeezin's. I've been looking into this as well for a long term Prepared build. I'm thinking that E85 will be the way to go since you don't have to flow as much air to get it stoch, it burns cooler, should make more power, and it's cheap compared to race gas.

You still can, in terms of timing.

A REAL N/A build doesn't really see much benefit after a point on 92-93 octane pump gas. There's big gains to be had properly tuning for E85.

I don't see running 14:1 compression on pump gas on a BP. I do see it (assuming you don't have nasty positive deck height) happening on E85.

92CelicaHalfTrac wrote:

tpwalsh wrote: Dave, We're talking about an N/A NA, so unlike your build, we can't just turn up the wick after dumping in the corn squeezin's. I've been looking into this as well for a long term Prepared build. I'm thinking that E85 will be the way to go since you don't have to flow as much air to get it stoch, it burns cooler, should make more power, and it's cheap compared to race gas.

You still can, in terms of timing. A REAL N/A build doesn't really see much benefit after a point on 92-93 octane pump gas. There's big gains to be had properly tuning for E85. I don't see running 14:1 compression on pump gas on a BP. I do see it (assuming you don't have nasty positive deck height) happening on E85.

To find the compression you can run you really need to decide on a few things first. How much cam are you going to run? If stock, what you can do is measure your dynamic compression ration, which will be lower than your static geometric compression ratio. There are tables which can approximate the RON (I think) with the dynamic compression ratio. Bigger cam means you can run more compression generally, so you may want to go through the trouble of measuring the dynamic compression with the big cam as a halfway point of the build with stock pistons.

I'd expect near 13:1 static, but it's a shot in the dark.

DILYSI Dave wrote: It's not like it's a huge amount of effort. Drain gas, put in E85, swap injectors if need be (not always), and tune for E85. A LOT easier than building a turbo system.

Yeah, I was thinking of my own build. The HP level we could attain with the bottom end and proper tuning might even necessitate larger supply lines.

Still not THAT big of a deal, just another hassle.

92CelicaHalfTrac wrote: I see a lot of people on various forums get discouraged with their all motor builds, become disappointed that it isn't making much power. But then again, i also wonder at what point that 10.5:1 compression was considered "high."

I'm making over 50% more power than stock, on 10.75 to 1

tuna55 wrote: To find the compression you can run you really need to decide on a few things first. How much cam are you going to run? If stock, what you can do is measure your dynamic compression ration, which will be lower than your static geometric compression ratio. There are tables which can approximate the RON (I think) with the dynamic compression ratio. Bigger cam means you can run more compression generally, so you may want to go through the trouble of measuring the dynamic compression with the big cam as a halfway point of the build with stock pistons.

plus 10

oldeskewltoy wrote:

92CelicaHalfTrac wrote: I see a lot of people on various forums get discouraged with their all motor builds, become disappointed that it isn't making much power. But then again, i also wonder at what point that 10.5:1 compression was considered "high."

I'm making over 50% more power than stock, on 10.75 to 1

tuna55 wrote: To find the compression you can run you really need to decide on a few things first. How much cam are you going to run? If stock, what you can do is measure your dynamic compression ration, which will be lower than your static geometric compression ratio. There are tables which can approximate the RON (I think) with the dynamic compression ratio. Bigger cam means you can run more compression generally, so you may want to go through the trouble of measuring the dynamic compression with the big cam as a halfway point of the build with stock pistons.

plus 10

I meant the BP in particular... i know a couple of the older toyota motors were quite different... 4age, 18rgeu, and 3tc in particular.

And of course, it's not all in the compression, but it just bugs me when i see people saying "i'm going to do a high compression build!" and then get disappointed when their 10.5:1 compression BP only makes 130whp or so.

There are a few CSP folk who have converted- to gain the extra 5-6 hp in the fuel. They were not really allowed to crank the CR up- just to shave the head to min spec.

One note- which should not be an issue at all on a Miata- not all fuel lines are happy with alcohol. Easy to check- get some E85 from a pump, and see if any parts desolve.

Fuel requirement is a big change, stoich goes from 14.3:1 on E10 to 10.something on E85. Having done it before, if you can make a gross change in fuel flow out the injectors all at once, it will be pretty close right off the bat. You will need more fuel to start the car, though.

Other than that- tuning with the right tools is the same regarless of the fuel.

Have fun- I totally encourage this job.

(oh, I'm suprised nobody has brought it up- make sure with the higher CR- the valves don't run into the pistons. Thinner head = changed cam timing. So double check if you can.)

alfadriver wrote: (oh, I'm suprised nobody has brought it up- make sure with the higher CR- the valves don't run into the pistons. Thinner head = changed cam timing. So double check if you can.)

I just assumed that the builder would know to cut reliefs in the pistons.

What would be the easiest way to raise the compression, milling the block, the head or new pistons? Or a combination of these? I am wanting to do this as inexpensively as possible.

Easiest = thinner head gasket.
Next = milled head.
Next = domed pistons.
Next = decked block.

I prefer to get where I want to be with as little machine work as possible though, so I prefer to use pistons and headgasket thickness to get what I need if possible.

E85 won't "give" you more power. The engine needs to be modified to take advantge of the higher octane.

If you run it in cold weather, you might want to carry a squirt can of gasoline for starting.

What will you do when the gov't stops the subsidies for corn based fuels? I would think a bunch of companies would stop selling that stuff.