Trevor

I've read 11.0 to 11.5:1 while searching. I usually found these references in random posts with no extra information behind them. So what should I tune to on 91 octane? Is the slight power loss at 11.0:1 worth the extra safety?

I know most turbo piston motors take a pretty decent power hit when going from 11.5 to 11.0:1 (and can even start breaking up a little and stuttering) but it seems the rotaries I've played with keep things together pretty well at 11.0. Yeah...its not the most power but it's a little safer.

This isn't really something easily proven so just a simple blurb about what you believe and have had success with will be great. Thanks guys!

cewrx7r1

iTrader: (2)

It is not that simple with a rotory which requires a richer AFR for reliability.
We require richer AFRs than piston engines. Timing also has an affect on required AFRs. And do not forget porting also affect this requirement.

I had been running 12 AFR at 10PSI boost, 11.8 at 12PSI, and 11.3 at 14PSI with stock ports and non-seq. Did this for over 4 years until I went single turbo. Made 350RWHP with the twins at 15PSI boost, stock ports.

Now I am running 11.7, 11.5, 11.2 with only the turbo being different than before. The biggest change was in timing especially at 10 and 12PSI where more timing had to be removed than at 14PSI. The single has so little back pressure compared to the stock an also spools like seq-twins. I am talking about a GT35R.

Trevor

Eh...crap. I had a decent post but I lost it.

Sounds like you have me confused with somebody that hasn't been around the block a few times. Funny how people instantly assume you know nothing because they don't see you post 10 times a day.

Yes timing advance affects optimum AFR's. If I was stuck with a map with hardly any advance of course I would lean it out as the knock overhead would be higher. The thing is you would make more power on 91 by advacing the timing, throwing more fuel at the motor, and possibly even bringing back the boost and letting the timing do he work if you have a small turbo/IC setup that's out of its efficiency range. As I'm sure you know they all intertwine. I know this and I will make the required changes. I'm just looking for some clarification on some things. There seems to be a lack of consitency while serching the board for target pump gas AFR's and I'd like to get some more info on the subject. Everyone says that a rotary needs to be drowned but yet some of you are tuning for 11.5:1 on 91. That's more the norm for piston motors.

And to throw some more info in I'm asking about a stock port motor specifically.

So you run no richer than 11.2-11.3. Good info. Thanks for chiming in!

Trevor

Soooo...only one person has info to pass on?

I should have guessed that this thread would be dead. Seems most FD owners pay others to do their tuning and the tuners keep their cards to their chest to keep the cash rolling in.

rizzxx7

iTrader: (4)

so what timing were you running?

rynberg

Maybe I'm reading that wrong, but that seems like a pretty dickish attitude to give someone who tried to help you. I didn't see anything in Chuck's post that was the least bit condescending....

Most people are tuning for an A/F ratio between 11:1 and 11.5:1, although most of those examples are running 93. Most of the tuner sheets I've seen for 91 octane were low 11s:1.

And what the hell is wrong with that? I think it's funny that you seem to be insulting people for not knowing the same thing that you are asking for information on...

Maybe I'm reading your comments wrong, and you're not being a bit of a dick. After all, people misread my posts frequently....

Trevor

Chuck's first four sentences were well known information to anyone that has done their homework. I was informing him that I have a decent foundation of knowledge to work with....the only thing I'm looking for here is rotary specific experiences and to clear up the inconsitencies in the posts about optimal AFR on the board.

I'm sorry if it was hard to interpret my tone...if you read my post again hopefully you'll notice I thanked him for his contribution.

My statement about most FD owners not doing their own tuning was just that...a statement of what I've noticed...I wasn't trying to insult anyone. If you don't have time or want to learn how to tune your own vehicle thats your choice. It seems to be the norm around here and since we don't have a decent sized group of people sharing their experiences that makes it difficult to get quality information.

So you've seen alot of low 11's floating around for 91 octane tunes...thanks for the tidbit.

rynberg

The A/F ratio you want to run really depends on your safety factor....there are several members running near or at 12:1 to get the most power output. Their knock levels are still ok but they are running too close to the edge for MY comfort level. The stock ecu runs at 10:1 or so (or even richer!) with pretty conservative timing as well. Low 11s:1 is a pretty good compromise zone for reliability and power output. Below 11:1 at higher power levels seems to lead to the inability to completely combust the mixture, so again, low 11s:1 seems a pretty good ratio and most tuners seem to be tuning to that A/F range for most customers.

You may already know all this and if you do, then your question is answered. Chuck knows a hell of a lot about timing too, he has MANY good posts about a/f ratios and timing in the PFC section -- some are from years back so a search is required.