CorvetteC5Norway

LS1 stock with a Novi 1500 kit. I've understood that afr 11.5 at wot is perfect, but at what afr do it start to get too lean at wot?

silver408z

Probably get a better response in the tuning section.

itsslow98

Anything higher than 11.8 would concern me.

0MVP @ TheRaceEngineShop

BLOWNBLUEZ06@RKT Performance

This is a subject that I've studied for some 35 years. What I've learned is that it's all relative.

Relative to what fuel you're running, your engine parameters, elevation, spark advance, barometric pressure, humidity and so many other things.

If you learn to PROPERLY read plugs, you'll learn how to determine what your engine wants. For my entire life, I've heard "Run 11.5", "Run 11.8", "Run this", "Run that".
If I find the time, I'll post up a story that I don't currently have the time to.



Bret

CorvetteC5Norway

The reason I ask is this; my car was fitted and tuned with a NOVI 1500 kit last summer. As expected, the MAF ran out at approx 5500 rpm. My tuner tried to compensate for this the way you are supposed to (rape PE table?), but not being familiar with LS tuning, he did not go so far as needed. The result is that it's still leaning a little after 5500 rpm. The tuner says the tune now is completely safe (rev limiter set back to 6000 rpm from 3-6 gear). As you all say, this must be seen in relation with timing etc. My tuner did numerous pulls and never got a knock warning either. But, since I have fitted an AEM x series wideband lambda to monitor this my self, I wondered if there where some limits I should/could look for. My tuner is very experienced, developing superchargerkits for different cars (was developing a kit for Lamborghini Huracan when my car was inn), but it could be that what he considers safe actually is not on a LS...


And yes, I will retune the car, but right now I just want to drive it and enjoy it....btw the car will just be used for spirited road driving this year....

BLOWNBLUEZ06@RKT Performance

If any tuner doesn't know the smart play by taking measures to guarantee your engine remains safe throughout the tuning process, whether or not their hands belong on your car is questionable. It makes no difference if they've developed supercharger kits for Huracans or any other "super car". It only matters that your car is treated according to its needs. The safe methods for properly tuning an engine are the same. How your engine is built determines how conservatively your tune should be set so that it can survive long term.

CorvetteC5Norway

In relations to this question, I took some time to study dyno charts for boosted Corvettes with afr logging online just to see where it goes. One thing I notice is that there is a dotted line in the chart on almost all of them at afr:13. Why is that?

BLOWNBLUEZ06@RKT Performance

Here are a couple of considerations for you.
First, there is usually a significant time delay between actual AFR changes and logged changes because of the way that most get their readings. They typically run a line up inside the tail pipe. There is a long air line that draws exhaust through the tube and eventually across the sensor element.
Second reading from the tail pipe yields leaner results than what you get when sticking a sensor in the exhaust pipes, up front.


Bret

stevieturbo

You will almost never see a boosted engine living happily at 13:1 AFR.

You maybe perhaps see a dual graph and that could also be a boost trace ? 13psi.

Obviously what AFR numbers...depends on what load, rpm, conditions, fuel etc. But you could say there is quite a range of AFR's that will be perfectly safe.....Timing on the other hand would be more critical.
So fuel mixtures cannot be the only consideration.

11.5 could be considered very rich for a low boost build...or perhaps not enough for an all out build on pump fuel.

For race fuels you could easily run 12:1 and all would be well ( and I've done this on 4cyl cars with 40psi boost )

But as long as everything else is ok...11.5 under load would not concern me at all.

BLOWNBLUEZ06@RKT Performance

A few years back, I was on the trailer with a boosted Camaro in a particular race class, running 36psi boost and race gas. He was running low 8's. After he made a pass, I looked at his plugs and asked him if he was going to lean it out. He said "no, it's at 11.8:1, I'm not touching it". I showed him the plug and explained that it was rich and that until the plugs read right, he should continue working on the fuel. He agreed to lean it out to 12.0. He went faster than he ever had gone before and was still showing rich. I told him to work on it until the plugs look right. He ended up leaning it out to mid 12's and being the first in his class into the 7's.
I've seen people run 12.8:1 before their plugs look right and race with that target for years without issue. Properly tuning an engine is about giving the engine what it wants. It's about gathering data, interpreting that data and making calculated moves to get the car to perform as well as it ever can or will.

If a tune gets over cooked in any way, you're probably going to see damage occur. Too much timing or too lean. If you want to change the fuel to more lean, you should consider backing off the timing first since leaning out a motor at a certain point affects how much timing it will take. You might make the exact same power at 12.2:1 with 15° timing as you do with 11.5:1 fueling and 21° timing. It's called a hook test, something RoadRebel (aka Phil Hoefler) shared with us many years back.

The one thing you can do to best guarantee you don't hurt the motor is to go slowly. Creep up on it while you continue to make moves that get you gains on the dyno or at the track. Once you find the max on the dyno, back it down. Chances are that if you max the tune out on a dyno and then go out on the street and beat on the car that it will result in engine failure. If you max a car out in the 1/8mi and then try to race on that tune up in the 1/4, chances are you're going to hurt the motor. Tune the car for what you're doing and never take to the edge unless it's done deliberately.

Bret

NSFW

Is there a reason to prefer one over the other?

stevieturbo

Generally, if you can make best power with least timing....that is a good thing. It means the burn is faster and more efficient.

Assuming of course it also doesnt have a negative effect on EGT's

Rkreigh

thus spake truth here! I was reading about how to do hook tests. combustion and piston design have a big impact on how much cyl pressure the engine will tolerate and how much timing

on the old LT5, the engine runs 12-1 compression, and because of the dished pistons and pent roof combustion chamber the car ran just as strong at 28 as it did at 31 so you know you have arrived.

Giving the engine "what it wants" is spot on. Kenny D. is one of my tuning heroes and watching what he does with George Poteet has been very educational.

Brent thanks for all the solid info! u da man.

CorvetteC5Norway

Thanks all for the educating posts! I will probably never tune the car myself, but as explained I've got the wideband AFR and would like to learn more. I've now bought a open serial port and serial-to-usb cable with the intention to be able to log the afr. I actually thought that you needed HP tuners (or the likes) to log, but I watched a video last night that showed that you could log directly on your laptop from the AEM with the 0-5V output. Can anyone recomend a good, simple software for the logging on a laptop?


Another thing, it's a possibility that Mike from Vengeance Racing will visit Norway through a businesspartner that they have here to perform tuning. I sent them en email with some questions, and Mike answered quickly that he could be of assistance. As I've read, Mike is one of the best, so hopefully that will happen :-)

CorvetteC5Norway

I have now driven my car on the Autobahn and been able to visually log the AFR from my AEM X series. If I can trust the AEM, my car is actually running rich. I made several 4'th gear (M6) passes right up to rev limiter set at 6000 rpm and it showed AFR's in the 10,5 - 10,8 range. I don't think I ever saw it creep over 11.0.


Couple of questions; do I leave much HP on the table at those AFR numbers? Are we here in the rich territory where I need to worry about cylinder wash? The car runs strong and was giving my friend with a stock C6Z06 a run for his money, so if this just leaves a little hp on the table and is safe, I will probably just leave it for now....

stevieturbo

It's perfectly fine.

BLOWNBLUEZ06@RKT Performance