I think you have it backwards, my friend. The car is purely a MAP system.

 

Rich, those are Rojas I picked up used from a certain 20b owner named David Hayes

 

yeah I think it's fine, but I typically run 11.2 in summer...the lower charge temps decrease the risk of detonation, at least to my way of thinking, I could be wrong

 

Isn't it the other way around? I don't know a lot about diff charge temps but I read somewhere on this forum one time that it increases detonation. Let me know if I'm wrong so I can have the right info.

 

detonation risk goes up with higher charge temps, otherwise why run an intercooler?

 

^^^ to a point, you're correct. Higher temps lead to pre-ignition.

Low temps = more dense air charge = more oxygen and a lean fuel mix

If your car's running on the ragged edge of what's safe, and you push it with really cold intake temps, you're really playing russian roulette.

 

the increased risk comes from more air making it's way into the engine with possibly the same amount of fuel.

(stock) ecu's tend to undercompensate for air temp changes and adjust fueling mostly based on coolant temperature. Which is where the risk comes from and why turbo cars tend to blow up when the weather changes.

I'm sure you've got a wideband marky, just keep an eye on it, it's probably fine.

 

It is lean for me if it isn't for you then so be it, 11.2 is alright. Maybe I just like to have more margin for error than you do, I like to assume the worst when it comes to equipment so assuming error in the wideband readings not being perfect.

 

Are we really having this conversation?

 

oh. so if he posted that he was running 11.3:1 (read: one tenth of an AFR point leaner than you like) would you say that's too lean?

i was just trying to show to the other people in this thread, most of which have probably never tuned a car --though most may not care-- that an engine isn't going to start pre-igniting and blow up because it's running 11.5:1 AFR. one probably shouldn't tune to any leaner than 11.5:1 on a rotary running 15psi on pumpgas, but to say "11.5 is too lean," would be incorrect.

 

if it was gonna pop at 11.5, it would have done it by now, I've had it tuned (BDC) the same way for almost two years

 

Also, Supras use a MAF and a MAP sensor. There are a couple ways of converting it to a speed-density system (MAP), which is how mine was. RX-7s are MAP only, and MAFs are supposed to be much better in terms of ECUs relearning based on altitude/temp, etc.. I wonder if this is related to FD reliability issues and tuning unfamiliarity...

 

Subsitute my lean for "too lean for my liking" like I said and boom end of story. Are we not allowed to different opinions? According to what you are saying 11.5 is the leanest you would go, so even by your very definition he is on a knife edge? I am not trying to start a cat fight if you would like to discuss please PM me

 

There are MAF conversions, if you want to spend upwards of $1500. I saw one on rhdjapan IIRC.

 

"knife edge" at 11.5 and 15 psi? aren't there people on this forum running 17 psi at that AFR?

 

The afr's are going to be dependent on other factors to determine if its safe, or on the edge. For instance someone running their turbo way out of their efficiency range. creating more heat then boost on an undersized intercooler then 11.5 @ 15 psi is definitely on the edge and will probably blow up at some point. Or if someone is running extremely high ignition advance, then their motor will be closer to the edge as well. If the engine is already on the edge due to its existing setup then running higher afr's is just going to put it that much closer to.. and over the edge.

It should also be noted that running your engine on the edge means you are trusting that every premium tank of gas you buy is exactly what it says at the pump.

Personally I consider 11.5 @ 15 psi at the edge of reliable on a correctly setup car, and would prefer to tune a bit richer. I'm sure it will run fine for many people, and may cause no issue for them, but i cant afford to what "might" happen. I will gladly give up 5 HP for that extra insurance. I also consider 15 degrees advance @ 15 psi on the edge of reliable. So I would rather run 13 degrees advance for that extra bit of safety. While I personally like the extra safety i wouldn't frown on someone pushing farther then i do, which may in fact be perfectly safe for them and their situation.

 

I run 18 PSi with 11.5 AFR with 13-14 leading with a 10 split...

thewird

 

^^ what grade fuel? You had an apex seal go running 12:1 afr right?

 

Sunoco 94. Yes, I blew a motor at 12 AFR, the timing was a little more advanced as well.

thewird

 

I still think that's too far ahead Marco and that ya ought to turn the wick down a bit. That's really pushing it even though you've got the two slight advantages of very good grade pump gas (Sunoco 94) as well as Canadian cool weather. When it mysteriously yet randomly blows up, don't say I didn't tell you.

B

 

Yeah that is a bit better fuel then most people are able to get on this forum. And that should to be taken into consideration when comparing what AFR's people are running at certain boost levels.

I do agree with BDC here that its pushing the limits @ 18 psi. With 94 octane i would feel 11.5 @ 15 psi is about as far as i would go. then probably taper to 11.1-11.2 @ 18 psi. But i don't know the details of thewird's setup. With lower compression rotors for instance you could run higher AFR's at a given boost level.

On the other hand some people manage to live on the edge for years without anything going wrong. While other people can go through several motors while being extra careful.

Brent

 

I guess I should mention the 18 PSi tune is only for short bursts of power like on the highway. On the track for example I only plan to run 16 PSi with the same 11.5 AFR which I know is fine cause I ran it this year all summer on the track. Also, now that I've gone single turbo my engine bay temperatures are gonna be much lower. Even though my manifolds and downpipe are ceramic coated, I'm going to put a turbo blanket and heat wrap the downpipe for additional cooling. I also have an aluminum heat shield protecting the lower intake manifold. Guess I should have said all this from the start.

thewird

 

So just out of curiosity, I bought a '94 RX7 from RickRX7 in Washington last month (28K miles and steve kan tuned, this car is mint!) and the tune that steve put into the PFC is targeting a 10.9 - 11.0 AFR. The Dyno slip is showing that the AFR goes as high as 11.1-11.2 at 7K RPMS and I am pushing 13psi on the stock turbos Is this considered rich or just conservative? I have read a number of posts (and discussed this with the folks at kantuning) and it seems to be solid, with the idea that I should back off the bost to about 12.5 to ehance the life of the stock turbos.

BTW, I drove it on thanksgiving as well in the cool Chicago air, and it pulled like an SOB, but the boost also spike to 13.5. Needless to say the car is parked now that snow is on the ground, but should I be concerned?

 

13psi should be fine. I would say 14+ psi is when turbos really start to get over-worked. Since you were tuned for 13psi at 11.0afr, spiking 13.5 should also be ok. That why tuners tune conservative.

 

thats considered conservative. Just how conservative depends on what the rest of your setup is and the grade of fuel you have available to you.

That boost level is fine for the stock turbo's, unless you're still running the stock intercooler then you should keep a close eye on air temps because it does a bad job of removing heat especially above stock boost levels.

If you're running a good intercooler and 93+ octane you could safely run a little bit higher AFR's, but where its at now will help protect your engine more.
If your AFR's were in the 10's I would say your fuel maps should be leaned out. But 11.1 -11.2 is good for a conservative, safe, tune.

*If you were just tuned while it was cold out then it will probably be a little richer come summer time due to the air being less dense.