I did a long post on this a week ago or so and had determined I'm getting true knock (even on a dyno tune). I determined it's true knock because I only have the knock retard when my timing retard is set at zero. It was tuned with it set at zero so in theory it shouldn't knock but motors see different loads and temps/humidity when on the road. There was no knock on the scans from the dyno runs but that was at W.O.Throttle. I'm seeing the knock at about 4,500 RPM in third gear at about 85% throttle after I've already been through 1st and 2nd at the same throttle position though 5000 RPM. It won't do it in 1st or 2nd gear at that throttle position ....my theory is the higher IAT by the time I get up to 3rd gear is the cause of the knock. I will get some retard as well from a roll in 2nd gear at WOT ...but the tuner thinks that is burst retard due to the sudden airflow change. I've noticed my timing will drift as high as 47 degrees when at the lowest loads and wonder if that could be the cause of the knock I get from a roll in 2nd gear. It would have to see load first before it takes the timing down from 47 degrees so there's a possibility it's getting a quick spike of true knock at the moment when you mash the gas at such high timing. I'm generally seeing about 4.5 ~ 6.0 degrees of knock retard and it looks real because the decay rate is very slow.

Now for my questions; Can the computer adjust spark for different loads above 100 KPA or is it just like fuel ....blind above 100 KPA and reliant on MAF and other tables? The reason I ask is it almost seems like I get more knock retard at 65 ~ 85% throttle than I do at WOT. Perhaps that is from the computer leaving more timing in at 65 ~ 85% than at WOT? ....or ....does the computer only adjust timing via RPM once you're above 100 KPA?

If it adjusts the timing by BOTH ... RPM and boost I think I'd be interested in having some timing reductions done at the loads slightly below WOT. This way my peak power from the dyno tuning will be unaffected and I'll be in a safer zone for the middle to high (but not highest) loads.

If that is not the case and the computer only adjusts timing via RPM once you're into the boost, I think I'm just going to get some Xylene and start mixing a little bit in with the 93 pump gas we have around here. I wouldn't want to remove timing if it's going to have to affect my max power output simply because I wouldn't know how much power I'd lose and wouldn't have honest dyno numbers in my sig anymore.

See if you think this timing could be a little too aggresive to be well on the safe side based on your experience with timing on boosted stock LT1's please. This is from the scan of my max power WOT dyno run:

Spark output:

Dead on 35 degrees from 2,200 RPM to 3,500 RPM (shouldn't it change some within that range? boost goes from 1.5 PSI to 3.2 in that RPM range), ..... then from 3,600 to 4,800 it gradually lowers from 35 to 30 degrees (in this range the boost changes from 3.2 to 5.5) ......then from 4,800 ro 5,800 it goes very gradually from 30 to 27, with a boost change of 5.5 to 7.8.

My A/F (wideband checked) is fairly safe being 12.2 thoughout most of the run ...only about .5 leaner when it goes to 12.7 or so above 5250 RPM. Tuner says it's normal and safe to go slightly leaner above the torque=hp point because the load isn't as high.

Summary= Do you think I need some timing removed at WOT just to be safe? Can I have some timing removed above 100 KPA without removing WOT timing? (somewhere in between 100 KPA and the max boost you can make at various RPM's)

 

Maybe I missed it in your writeup, but do you have a 2bar MAP sensor? Can I assume you are running the stock PCM? If you are running a 2bar sensor, how did you adress the interface with the stock PCM, which is expecting a 1bar signal? If you still have a 1bar sensor, how could it measure boost?

Obviously, I'm not "up" on S/C tuning with the stock PCM, but curious about how you handled the sensor issue.

 

You have hit the majical problem I warn ALL SC guys of. the only true way to get "GREAT" drivabilty out of one is to add a Fast or other after market controler. There is no true way to get a stock PCM to understand the differance from 100KPA and boost.

I have tuned many cars with blowers and can tell you for sure no matter how good you get it there is always some thing missing. The problem is what you are talking about. There always needs to be a way for the car to use a BOOST sensitive fuel system.

Every Person who has tried and swore they could do it have buckled in the end and added an after market system

Good luck man!

 

Yep, someone in the forced induction forum just explained to me that above 100 KPA the timing is RPM dependant. Therefore I'd lose my WOT tuning and valid dyno #'s if I alter it above 100 KPA.
Injuneer, I forget about the bar stuff but from what I understand you compensate for the computer's lack of ability to see above 100 KPA two ways on my 94 OBDI .....in the PE vs RPM table you add some extra fuel to be safe. Also, the MAF is telling your PCM to add extra fuel (kind of the same thing I guess). Problem with that is it still doesn't address boost variations at all....just airflow.
I have accepted the fact that I will have to run timing retard on pump gas. At least I still have the timing retard even though it wasn't tuned with it .....so I still have something that's actually boost sensitive. When I go to the track and run zero retard I am going to be adding a decent bit of Xylene.
I've spent enough money on this car until I don't want to fool with a FAST system but I kind of wish that's what I had done to begin with after all the money I coughed up for dyno tuning ($3,000 believe it or not ....lots and lots of little problems including weak valvesprings and bad ignition system).
I guess the FMU/BTM setup has some validity.....it's funny how soooo many people told me to trash both of them before tuning because they are extra variables which could fail that are always a step behind and inconsistent anyway. If I had to choose between which one to keep again I would definitely make the same decision again, keep the BTM and lose the FMU.
Time to find some Xylene, pull a little timing on the BTM, and wash my hands of this staring at the scanner crap and enjoy my car.

 

I would say that if you were tuned at 12.2-12.7 to one on a dynojet that you are way too lean on the street.


I tuned my car at 12-1 A/F on the dyno and I was running lean in 3rd and 4th (due to the higher load).

I retuned it to 11-1 A/F on the dyno and I've brought it up through 5th gear at WOT no problems.

If I tuned my car at 12.7-1 on the dyno my pistons would be melted by 4th gear on the street.


You need to do an ultra safe tune on the stock PCM and boost because it's running blind. It has no boost reference and the MAF sensor is usually maxed out. I am switching to the FAST system in the near future so I don't have to worry about the possibility of my car going lean.

 

I agree with Intimid8. I also tune rich on the dyno. one the street you will be leaner.

I also run into people all the time who say to tune it and trash the BTM and FMU. The may both be crutches but with the PCM we have to work with they have there place

you know what they say! Live and learn I enjoy my car much more now that it is simple and Blower free again

Helllo MY name is Ellis and I have been blower free for four years

 

It's very common to have these cars tuned at 12.0 ~ 12.8 with low boost like mine. I don't think fuel is a problem....as removing timing with the retard **** gets rid of the knock. However, I guess that could be remedying the fuel. Anyway, it's more like 12.0 ~ 12.3 for most of the dyno runs.....only above 5250 RPM it goes a little leaner because there is less load above the HP=Torque point. If anything I would think you would tend to run richer by the time you hit 3rd due to more load. More load = less airflow per given RPM so you would run richer if I'm not mistaken. Are you sure there isn't something wrong with your fuel system? Remember, you are running a lot more boost than me so you would probably want to be in the high 11 range on the dyno.
I would believe however that you may lean out on the street some due to the air getting to the filter at higher speeds and/or lower humidity on certain days. My fuel readings seem really consistent so I doubt that's a problem for me. I think by the time you hit the higher gears it's the increased IAT's and load that cause detonation.

 

Injuneer, I forgot to mention another way that fuel is addressed is by the stock regulator. The stock regulator is sort of like an FMU ....it works on a 1:1 ratio. For every one PSI of boost I get one extra pound of fuel pressure from the stock regulator.

The more I think about it, a Speedpro or FAST system would be overkill for a low boost blower. A high boost turbo is a whole other animal though. Basically fuel is addressed in my situation via the MAF, PE vs RPM table, and the stock regulator adding some boost referenced pressure. The timing isn't as well addressed due to the computer being blind above 100 KPA and no other means of adjustment other than RPM at that point. The way I look at it, if it's safe timing at WOT/full boost then it should be safe anywhere in between 100 KPA and full boost. Timing shouldn't be a huge issue below 100 KPA since you're not making any boost anyway....only moving additional air and making less vacuum. So if the timing's set up just a couple degrees or so less than stock below 100 KPA and gradualy transitioning to more like 7 ~ 8 degrees less than stock at full boost (7 ~ 8 PSI in my case) .....then as far as I can see I should be OK with no FMU, no BTM, and no Speedpro or FAST setup either. The only problem is mine apparently just wasn't set up quite safe enough but very close. I'm pretty much "on the edge" when the timing retard is zeroed out but pretty safe as long as I'm dialing in one degree per pound or so. I guess I'm going to leave it alone. I'll add Xylene and zero out the BTM when I go to the track

 

I thought that:
1) the dyno jet weighs 4000 lbs. and you are tunning a 3500# and that my AFR is measured at my exhaust rear and not at the headers. sothe tune would be a bit leaner than it really is... Other than that I tune to 12.4:1 and I run ok on the street... for now... I think...

 

A little richer will give you more torque. A little richer might get rid of the detonation problem as well. Also, you can adjust timing per map%. You could take out 2 degrees from 4500 to 5000 at 85%. This will of course be taken out in all gears but you'll be faster without the knock.

I think to get a better more true dyno tune you'll want to exagerate the car weight (4200?). I think that slows the drum more which puts more of a load on your engine.

Hal

 

Hit the LT1 Edit list, and ask for LJ and how he got his car in the 9s on a stock PCM/MAF.

 

That is a brake dyno if you put 4200 when the drums only weigh 4000? Right?

How could I bring the air fuel completely down without altering the "curve" since I already have a straight line at 12.5?