So we have to get back into the bottom end again - don't ask

After taking some advice and going with 8.5:1 pistons, now that we'll be in there again, we're second guessing that decision and thinking about going to 9:1. Head is slightly milled.

So what are the opinions with e85 and 18-20 lbs of boost?

Anyone can guess. Looking for experience to lead your comments.

 

full time e85? go 10.5-11.0
Id say even higher, but you start to get into nasty things like interference past that

 

Full time e85. Don't want to give up all the timing. Definitely don't want interference . Originally were planning those type of numbers but the machinist got out some chart and did I some figuring and thought we'd be sorry even on e85. He recommended 9:1, but with the slightly milled head ordered the 8.5s.

 

I definitely would have gone higher.

 

That's silly.

Anything lower than 10:1 on e85 is just a waste. Normally I don't care but if you're building the engine and have a choice, there really is no reason not to at least to 10. Oh well.

 

Not to doubt, cuz I did ask for the advice, but what are you guys basing this opinion on?

 

10:1 motors not being detonation limited on E85.

 

Im doing 12:1 on the white car from the shitfight thread in the next couple of weeks. I'll post results.

Everyone on the planet recommends under 10:1 and I'm like, "Sorry, is is 1994?".

**** it, Im doing it.

 

So is it theory or proven? Saying it's not detonation limited doesn't make sense. At some level of boost, it will detonate. I understand that combustion chamber design and other factors do come into play, but an octane calculator says 9:1 and 20psi requires 110 and 10:1 with 20psi requires 116. I also understand that ethanol has some cooling properties to it, but it's also only roughly 105 octane.

Who has actually run 10:1 or higher successfully on a BP?

 

Information and testing results posted by dozens of engine builders and tuners from many different engine platforms, including the miata.

You can even search and find it yourself actually.

I'm curious what "chart" your silly mechanic referenced to suggest 8.5:1 on e85. Id love to hear that reasoning.me. and dozens of people much smarter and better than me

Most recently I ran something like 22psi and 30* of timing on Ryans car and it took it and asked for more.

ran 22* and 14-16-18 on my old '00 (though that was 9:1)

and ran 25+psi on 11:1 on another local guys car



*edit: again, I'm not saying you're gonna have a terrible engine or not make power, but you're just throwing away a ton of response for no reason whatsoever.

 

That's the kind of info I'm looking for. Thanks. And although I usually try to search this stuff on here, sometimes lack of patience gets the better of me. And let's face it, some things are easier to search than others.

 

My heavy boost experience is in EVO's, but in my last EVO I was running 30 psi of boost on E85 on the stock 8.8:1 pistons. Saying you need 8.5:1 on E85 in the low 20's boost pressure is just silly. Most EVO guys who do a build go at least 9.5:1 on gasoline and higher than that if they plane on E85.

Keith

 

I ran 3deg past MBT on an 8.6:1 motor on E85 at 17psi/350whp and never saw detonation. I had a conversation with eliminator77 years ago where he talked about his E85-specific bottom end, and IIRC he said it was 9.5:1 and he regretted not going higher. If I were building a dedicated E85 bottom end, it would be 10 or even 10.5:1.

 

Motor and car are here, 12:1 turbo thread here.

12:1 E85 turbo build - Miata Turbo Forum - Turbo Kitten is watching you test compression.

Dann

 

It looks like SuperTech only offers 9:1 , 9.5:1 or 11:1 pistons for the 1.8L. Is there a 10:1 or 10.5:1 option that would be available for this application? This relates to a thread that I started recently, but also got varying responses.

 

What's wrong with 11:1? For full time e85 it should be fine.

 

Gonna do the Wisecos at 10.5
*edit - actually Wiseco lists them as 10.03:1. Not sure why 949 lists them as 10.5. Either way, it's better than the 8.5s in there now and it should land somewhere in between with the milled head.

 

I am running 11:1 CR with 11psi of Rotrex boost. With a turbo that comes on harder/sooner I might opt to run less.

The whole CR/boost relationship comes down to being able to run ideal timing to get MBT. Having to back off boost or timing because of detonation means you went to far.

In other words:
Choose HP goals and back into boost/CR numbers.
Choose CR and run as much boost as possible to maintain ideal timing and settle for whatever that HP number turns out to be.

I have played with boosted applications on many cars. I have done low CR high boost and high compression low boost builds. I am currently leaning towards the high CR low boost builds. While not quite the excitement of a big boost rush they have an eagerness that can't be matched. Done right they feel like a big high compression NA motor.

 

What power are you making?

Dann

 

Close to 300WHP on a dynapac. Once I fix the fueling problems I expect it to be a bit higher. I think around 315-325whp at 8k