E85 and boost, what compression ratio could I run?
 

I've run 38 PSI boost on my 9:1 motor without any detonation on E85.

My previous motor was 10.5:1 compression, and had a lot more low end, and I swear even more top end at a given boost level. Admittedly, I never ran that motor past 22-23 PSI though.

Just wondering, I have a spare motor and was curious how much higher I could go on compression with E85 and the same high boost? 11:1? 12:1? more?

Hahah, you are NUTS dude. Nuts.

9:1 static at 38psi is 32.27:1

11:1 static at 38psi is 39.44:1

12:1 static at 38psi is 43.02I was trying to find information on the flash point and other info on E85 to help you further, but I suck. I could only find anecdotal evidence for static compression ratios used succesfully on E85.

12.5 or more if you can find the pistons

There was a guy selling some 13:1 pistons here a while ago. Idk if they ever sold.

Ive got 2 builds at just under 12:1 at over 25psi.

Both are awesome and not even close to knock.

Dann

I could even share timing tables if anyone wanted.

Dann

Off the shelf 11:1 pistons plus a couple of quarters per cylinder should get you 14:1.

--Ian

Yes please share. I've been trying to find a timing map of a high comp turbo e85 setup to see if I'm running anywhere near what someone else is running. I know no two engines are the same but it would still be nice to see what others are running. I'm only running 10.5 wisecos and I think I still have plenty of room to go on timing.

10:1 and 25psi is 20 degrees safe as houses.

Could you post a screen shot of your timing table

When I get to work.

Ok thank you sir

I'd love seeing some spark tables you guys are running. I had no idea you could get away with those kind of compression ratios with that much boost on E85.

corn loves compression. and there's rarely any knock, if ever. and you can run astronomical boost and timing.

but

you really have to keep in mind that despite not being det limited, there is such a thing as too much timing, and that you are putting crazy stress on your engine when you're well past MBT.

But yeah, this might be a good place to discuss/share spark maps on e85

I feel sad that I am sitting here with an 8.6:1 motor with dreams of e85/flex

Not to mention making less power. You really need a dyno to tune it.

--Ian

Ok here is my map currently. This is by no means a good or great map, it is not dyno tuned and it needs work in several places and needs smoothing out I'm sure. I am not a tuning expert but trying my best to learn. It's what I've come up with based on other e85 maps and also driving around with electronic det cans and monitoring knock via MS3. I have not seen or heard any knock at all and I think that this timing map is still somewhat conservative and has plenty of room for improvement, thus why I'd like to see what others are running with high compression, high boost and e85. I'll get it to a dyno someday. But for now I'd just like to see if I'm somewhat close to what others are running. Any help and feedback is welcome. This is with 84mm 10.5:1 wiseco pistons, diy ported and polished 99 bp4w head and a relatively big turbo that hits late.

https://cimg0.ibsrv.net/gimg/www.mia...366c844589.png

Can't speek on the boosted cells, but that is less agressive in the 100KPa and under cells than I am running on my 1.6 with 87 octane....

Yeah, you can run way more.

19kpa cruise should be 40*
taper to
100kpa should be at least 27-30*
taper to
230kpa 16* is ok but should not be dropping, should be ramping up to redline, to at least 20*

Assuming built engine, competent setup, and at least e70 actual in tank, preferably 80+

Thanks. I was thinking around 12:1 or so if I make the switch.

Dann, how much over 25psi? 26, 30, more?

Added some timing and smoothed it out a little more. Only briefly ran this map being cautious looking for any signs of knock but I didn't hear any and the logs dont show any more noise than the first map. Definitely pulled much harder and actually got rid of my little stumble/misfire at higher rpm and high boost. I have been trying to figure out what was causing that and couldn't come up with anything. I couldn't imagine 14 degrees or so of timing up top would be to retarded for it to pull cleanly but maybe so. 18psi does this table look a little better for a 10.5:1 high boost e85 engine? Yes its built with supporting mods and at least e70 in the tank. EGT also appeared to drop 100-150 degrees or so in cruise but need to drive around more to be 100% sure

https://cimg1.ibsrv.net/gimg/www.mia...b7c32f415b.png

Much better.

Yeah 26-27

I didnt get to the tuning laptop today also guys

Bummer. I'm curious to see your map. You said you run 20 degrees at 25psi? So your map still must be considerably higher than my second one

Maybe, Im just picking numbers by memory.

Ill show you the exact map.

Dann

Yep better, and make sure your AFR's aren't dipping below 11.8 or you might get misfires from that too. You've still room for more advance too, this is on the conservative side

Really? Damn e85 must really be some magical unicorn gizz. It only takes 11.8 to be rich enough to misfire? I figured it was closer to 11. Because it's definitely dropping below 11.8 at some points. It's already pulling much cleaner and harder so I'll keep playing with it. I'd still like to see what other people are running

nah it's probably fine at 11.8, but once you start dippin lower by too much, you'll start losing spark. you're pumping ~30% more of the stuff into your cylinders, it overwhelms the spark

Even while running boss d585 coils and a reasonable spark plug gap?

with those you're likely fine, but I'd still run 12:1 on the dot cause it should be a wee bit faster and waste less fuel.
On Ryan's built 1.6 we could only go up to 21-22psi due to weak spark, but we still ran 20* midrange tapering up to 30* up top. that car put down 360whp on a 1.6 and a log manifold and a chinacharger. we've done BP4W's similarly and it was over 400whp.

the stuff is pretty nuts

Pat I think you're capable enough that I can remind you to disregard static, and focus on dynamic compression ratio. If you fuck up and end up with too much static, so you have to pull so much spark it makes less power fix it is just a cam timing adjustment away.

I was just wondering what everyone thought would be doable. Not a lot of high comp, high boost builds in miataland. I haven't looked, but I'm sure there's some folks in other 4cylinder platforms doing it, probably evos and STIs if I had to guess.

I run 17* @ 38 PSI with no knock. Not going higher till I get it on a dyno.

Year long bump. I searched the forum to see if anyone is running high compression + boost, and found my own thread discussing this...

Getting bored, thinking of putting together a new shortblock to experiment with some things. One being high compression. Current thought is to try AT LEAST 12:1 with E85/Boost. Actually thinking about going to 13:1 or even 14:1 and see what happens. Would have to get custom pistons made to do this, looking into that now.

:eek3:

YES!! do it for science.

Although a local buddy of mine is running 12:1 already on a miata that traps 132mph currently.

So you gotta go higher to blaze new trails :likecat:

12:1 BP? What fuel? How many passes has it made and not blown up?

I am tempted to go higher.

Yes, Yes, cornjuice of course. It's been at least a year and I wann say a couple dozen passes? I'll ask him to chime in or at least fwd me the details. but he beats on it like a redheaded stepchild very very often. this is by no means a garage queen

Thanks, yeah would be great to hear from him.

I run 11:1 with 9psi with a Rotrex on E85. The cams have shorter seat timing than stock further bumping static compression, Not extreme but it is a track car that gets flogged hard!

I suggest you start from the top and work your way backwards. Determine whatever you plan to run (15-20-25psi) to meet your HP goals and then fill in the compression that keeps your dynamic numbers sane. Somewhere around 18:1 is what I shoot for. I have another marque I build using the same formula. Been running 10+ years strong on the street with some track days sprinkled in.

This is a pretty good tool to help you play with some numbers. Wallace Racing: Dynamic Compression Ratio Calculator

The extra compression buys you more HP per PSI of boost. The motor tends to be much more lively in transient phases and just rips WOT. Good Luck Pat!

Using your calculator, my current setup with 84mm bore, 85mm stroke, 5.233" rods, 9:1 compression, 50* ABDC inlet valve timing, and 40 PSI boost, I get
7.96 dynamic compression ratio
29.62 effective boost compression ratio.

That is already significantly over your 18:1 sane numbers.


If I ran 12:1 and 35 PSI boost:
10.57:1 dynamic compression ratio
35.74:1 effective boost compression ratio.

run 15:1 and 30psi. For science

I genuinely wonder how high you can go on a dinky BP head before you run into serious issues

Try these and let us know

Attachment 231740

What serious issues would you run into? Lift the head? crack the head?

LOL on the rods!

e85 does knock/detonate with enough craziness thrown at it, so there's that.
and then there are the physical load limits you mentioned

That's beyond where I would be comfortable. Kudos for boosting "All of it".

At 20 psi you're at 18.77 dynamic with the same above info. Again just my target on race gas or E85 in a highly stressed environment. YMMV. In for results.

Yeah, I think I have octane to spare right now. At least for how I use the car, which is street and drag.


My spring pressure for wastegate is 30 psi.

So if you consider 18:1 safe for track, and I have gotten away with 29.62:1 effective compression ratio, that is quite a difference. Do you think you could run more boost, or more compression on your setup?

I know this thread is about high comp and e85 but there is also some good info about high(er) boost levels and e85. I want to add some timing to my map but a lot of timing tables that Ive found are all for lower boost numbers.
I hit 22psi at ~4700rpm and it tapers up to 25-26psi by 7250. E85, stock 9.5:1 pistons, stock rings, stock head.
My current WOT, full boost timing numbers are highlighted in the picture. Could I safely add 4-5 degrees in all the cells?

https://cimg5.ibsrv.net/gimg/www.mia...daeb1fac9a.png

no such thing as a definitive answer to that. assuming you don't start knocking, and don't stop picking up significant power per degree of timing, you might. I have on several cars in the past