theory

iTrader: (5)

I'm just looking for some NA tuning advice. I'm heading to the dyno in a week for a baseline, and then I want to begin making changes.

I've got a S4 rebuilt motor(stock ports), headers with high flow catback, "short ram" intake, 6pi runs off RTek.
I've installed my RTek and hooked up my Wideband to log.

I've attached 2 jpeg's. They are the AFR's I logged and recently plotted in a spreadsheet. First chart is from 1st gear, the second chart is from 2nd gear.

The MAP is reading 0.1-3.7(in-hg) in first gear, in 2nd my MAP is reading 0.1-3.7 as well. When looking at the graph on my PDA, the MAP is very "peaky". It has a very consistent up and down motion on the graph (i.e. ^^^^^^^), I'm not sure if this is normal at WOT?

From what I've read, it looks like for peak power in NA I'm going to be looking for ~13.5 AFR's on WOT. As you can see in my charts I have to go up a full point or more to reach that.

The point of this thread was for guidance and confirmation on the AFR's you guys aim for, as well as if you guys think my MAP readings are normal.

I'm not up on timing yet, I still have a bunch of reading and understanding to do for timing. I just want to begin learning how to slowly/safely tune my NA with fuel only for now... timing to come later.

pp13bnos

iTrader: (1)

Its been a couple years...but when I had my N/A s5, ( it made peak hp at 14.25-1 a/f ratio. 14.25 was the magic number for me. Anything richer and it would lose power, and anything leaner, and it would lose power too. It lasted 50k miles on that tune, before I traded it in on a Rx-8. It was still running great.

If you want to learn about my setup, search with my name (pp13bnos) in the 2nd gen forum. CJ

j9fd3s

iTrader: (3)

ive found with the SAFC, most of the power gain is going from the stock 11:1 to high 12's. going leaner than that, you still make more power, but diminishing returns...

timing seems to be best around 26BTDC, but start low and work your way up.

fidelity101

iTrader: (11)

really? stoich is 14.7:1 on gasoline that sounds a bit tooo lean for WOT

C. Ludwig

iTrader: (27)

That's normal. The pressure in the manifold oscillates.


That's been my experience.


Before you begin tuning you should at least confirm the timing is synched with what you have programmed. Don't just assume that it's correct. Best timing on a stock port engine will fall around 25-27* leading. You can tighten the split up but despite what the common theory is I've never found much power in it. I know the S5 2.0 has a nearly ideal ignition curve pre-programmed. Never worked with the S4 unit.


You need to log in 3rd or 4th gear. 1st gear is useless. You rip through it so quickly that the measurements are invalidated. See how different the two charts are? Since topping out 4th gear is too fast for the street this work is best done on a dyno. You'll get better results, more quickly, and in a safer environment.

arghx

iTrader: (3)

engines generally speaking are not supposed to run at stoich under heavy load. 14.7:1 is the "ideal" AFR because it has the best average emissions output -- leaner is more NOX emissions (less HCO) while richer is more HCO emissions (less NOX). Diesels and direct injected motors run superlean and that's why they have disproportionately higher NOX emissions compared to regular port injected gas engines.

fidelity101

iTrader: (11)

13.1:1 is richer than 14.1:1


doesn't mean anything because that is a short pull, the most accurate dyno (basically your simulating a dyno but doing street pulls) readings are your slowest increment.

peejay

14.7 is "ideal" because it is stoichiometric... equal parts oxygen to combustibles.

Actually, the stuff normally on the market is about 14.2 thanks to the alcohol content...

Best power is typically richer than stoich because the fuel never fully atomizes, so more fuel means there's a better chance for the oxygen to combine with fuel. That's all. The better your atomization the leaner you can run for best power.

theory

iTrader: (5)

I'm hitting the dyno for the first time tonight for a baseline. I'll see what she makes as it sits now and hopefully see if I can get a print-out of the afr's in 4th.

I will check my RTek and see what the timing is at now.

I'll post back with results. Thanks for the help.

theory

iTrader: (5)

As promised: (don't mind my 3800 hesitation, I've tried almsot everything to fix that damn thing)

fidelity101

iTrader: (11)

^^ locate, clean, re-crimp on all the ground points and wires. Mine didn't go all away until I did it to all the ones in the engine bay, and a spot behind the gauge cluster.

theory

iTrader: (5)

I've re-grounded the appropriate wires at the ecu, and grounded the tranny to firewall, motor to firewall, cleaned up all the grounds I could in the engine bay. The ONLY ground I haven't fixed yet is the one under the manifolds. Im waiting until I do my S5 intake swap to fix that one.

Those pulls were done in 4th gear, about a half hour between pulls, car is un-tuned still.

The guy at the shop said something about how the afr's are going to read leaner then what the actual afr is because I'm still running my air pump(to control 5/6 ports with the RTek). I'm going to look into this as I'm not running the stock exhaust so I'm not sure where the air would come from.

fidelity101

iTrader: (11)

the one under the manifold is a common one, don't forget the one behind the coils and under the airbox, if one is bad it could cause it. its not a vacuum problem of the ports opening its an electrical problem of poor grounds, IE your injectors are electrical and are taking the fall for poor grounds.

peejay

If the air pump is dumping into the exhaust upstream of the O2/wideband, it will read leaner than actual.

j9fd3s

iTrader: (3)

that ground under the manifold is the important one! you can get to it with a swivel socket and the right (long) extension

rotarygod

iTrader: (1)

You are the first person I've seen that actually gets it! I keep seeing false information going around that says decreasing split increases power. As with everything else this too has limits. It can but it can't. There can be times where decreasing split decreases power. On stock n/a engines I've never found a power increase from decreasing split below 10* at full throttle. The key to making good power on a rotary is a balance between total advance AND split. Not having trailing plugs or having too much of a split and you lose power. In some instances having no split hurts power. In other instances having no split makes the most power. Factors such as port timing/overlap, compression ratio, rpm, and load all play into this. I know everyone here probably thinks that the 3 plug per chamber R26B had no timing split but this isn't true! There was a split. The trailing and far trailing plugs fired at the same time as each other though but not the same as the leading.

rotarygod

iTrader: (1)

As far as a/f ratios are concerned, there is no one magic number. As with split, other factors are involved. What may be the best a/f ratio for full power at one load and rpm point may not be the same a/f ratio that makes the best power at another load and rpm point on the same engine. You actually have a range and it's pretty wide. This is why you'll see some people say 14:1 worked better for them and others will say that 11:1 worked best for them. It all depends. There is no one right answer.

When I tune an n/a I start shooting for 13:1 across the whole rpm and load range. That's my base default. I also have a generic timing map and split as well. Then I go back and start tweaking from there, one variable at a time until it works itself out. I may not always go for max power at every load or rpm though. At part throttle and low rpm settings I shoot for efficiency which means I try to get the car as lean as I can within reason for economy reasons. If I want more power, step on the throttle more. The higher the load, the more aggessive I tune. Aiming for 14.7:1 does not mean you'll make the most power. Stoich is merely the rpm at which you are cleanest. Seldomly does it ever correspond to making max power. A/f ratio may not even hold steady across an entire rpm range of a full throttle run. It may fluctuate a bit but this isn't necessarily bad.

theory

iTrader: (5)

Is there a way to keep air pump running but block the port air that it dumps into the exhaust without adversely affecting the way anything else runs?

I want to have accurate AFR's before I start tuning.

j9fd3s

iTrader: (3)

yep. you'll have to look at the FSM/vacuum diagram for specifics, but the Air Control Valve is controlled by 2 solenoids, and 2 vacuum lines.

over 2500rpms it dumps into the bumper anyways....

theory

iTrader: (5)

Looks like if i disconnect the port air solenoid and the split air solenoid I should be ok to run without any adverse affects?

j9fd3s

iTrader: (3)

yep, easy enough to check too. big hose on the side of the acv, is the vent

actually you'll be able to see it on the WB too, it'll be rich at idle

Judge Ito

when I made 338 rwhp back in 2005 my a/r was at 13.9 14.0 way to lean... I added fuel across the map and a/r went down to 12.9 and power average was 315rwhp. I left it there since this was my a/r goal...

theory

iTrader: (5)

That's the second time I've heard that number (well really close). I saw somewhere else that the owner aimed for a 12.8 and it worked great.

rotarygod

iTrader: (1)

I'm not quite sure I follow you.

There are 2 trains of thought in regards to advance and split. One is to use zero split and then just vary total timing as necessary. This would of course mean that you can't run as much max leading advance in spots as you could with a wider split. The other train of though is to try to run as much total leading advance as possible and then to vary split according to detonation limits. This would mean you can run more advance but would have to have a timing split to accomplish this. Obviously types of fuel and even which rotors and compression ratio you run will change this a bit.

I have seen people from each camp swear up and down that their way makes more power than the other and in truth it's hard to definitively say that one always works better than the other. There are things that can affect the results. I personally prefer to run more advance with a split. However I also subscribe to the negative split camp and have a very simple way of thinking about it. Negative pressure (vacuum)/ negative split. Positive pressure (boost)/ positive split. This is a generalization though and doesn't apply at every load level. Depending on compression ratio and porting, max negative split can be anywhere from -35 degrees all the way to -75 degrees!!! I can't explain it easily though.

Back on topic. Generally at the torque peak you should have to back off timing and/or increase split to avoid detonation. After this point you can readvance timing and/or decrease split again. I've seen many people tune to a max timing point and then leave it there, even after the torque peak is passed. This leaves some power on the table though that isn't being realized.

I'm not quite sure what you were seeing but each car is different. What works for you may or may not be the best method. I subscribe to one as a generalization but am an extremist in some other ways. Try different things.