James Montigny

iTrader: (13)

While dyno tuning last week, we found that the car made the most power when running extremely rich.
I found that I little odd and wanted to see if might be a symptom of some other issue.
The car drives around just fine at 14.6:1 and feels strong at WOT.
Both left and right header-mounted wideband sensors agree with the tailpipe-mounted sensor we used to tune.



The engine is a 383 LT1 block with an 01 LS1 Camaro PCM (EFI Connection 24x conversion).
55psi fuel pressure
42# racetronix injectors (flow-matched and recently cleaned/verified by Racetronix)
211cc Dart heads
2.055, 1.65 valves
234/240 107 cam
ATI 4000 Stall
4" GM MAF

Old Geezer

iTrader: (3)

42# injs at what pressure?? 3 bar? 4 bar?
Did you data log the runs?

James Montigny

iTrader: (13)

3

I did not have my laptop with me to datalog
I do have the Dynojet file though (the viewer is free from DJ)

Old Geezer

iTrader: (3)

@ 55psi, those 42 # injs are rated at 47.22PPH. Is the program corrected to reflect this difference? [IFR table].
How is the fuel system set up?? [W/ a vac referenced regulator, return line, or???]

James Montigny

iTrader: (13)

Yes, the tune is set up for the correct flow rate and pressure.
We input all of those values before starting the dyno tune.
Injectors are assigned to the appropriate banks and fire sequentially.

The fuel system is a 255lph walbro pump running stock lines (including return).
I used an AFPR in the stock location with the vac line.

BLK02WS6

iTrader: (2)

The fuel system would have nothing to do with the engine liking a rich mixture... If it was lean and you couldn't get it rich, then I'd look at the fuel system.

What is the compression? Pump gas I assume? High(er) compression would make it want a rich mixture to make the most power - but richer than 11:1 is quite a bit...

You really need to log the pulls - do you have any idea what timing you were at? Were you able to vary the timing to see what it wanted? Doesn't sound like it if you didn't have your laptop... You need to watch the knock too... If it was knocking at leaner mixtures and you didn't know it, richening it up could be cooling the burn and making more power - but that is not the way to do it... you would need to pull the timing back and then lean it back out.

There is a reason, but you don't have enough data to know what it is...

James Montigny

iTrader: (13)

11.44:1 Static Compression
I run 91 octane pump gas (which is typical for premium in this part of the country)

The engine seemed happiest at 36* up to 5500RPM
We saw an increase in performance by boosting that to 38* above 5500.

My block is 1/2 filled with hardbloc, so my knock sensor is useless.
Any knock would have to be detectable with the human ear.
I can datalog a WOT run on the street if that will help any.

I'm going to put a fresh set of plugs in this week and run a leak-down test while I am at it.
I also want to re-adjust the rockers to make sure that they are ok. I don't expect miracles from either,
but it's better to check the simple/cheap stuff first.

BLK02WS6

iTrader: (2)

So you did start low on the timing and work your way up on the dyno - that's good. Compression is a bit on the high side for an LT1 on pump gas - could explain it to some degree... Is your gas 10% ethynol in your area?

Was your cam degreed in or installed straight up?

gregrob

iTrader: (8)

No its not, not even close...

gregrob

iTrader: (8)

Read the plugs...

James Montigny

iTrader: (13)

Gasoline in the area contains no more than 10% Ethanol.
11.44 shouldn't be an issue, I've been running similar compression in cars on pump gas here for 10 years.

The cam was installed with a 0* bushing, but I am beginning to wonder if I shouldn't go back and double-check the alignment.
I wanted to eliminate other possibilities before I go tearing my timing cover off.
The fact that this is impacting both sides of the engine evenly and that power numbers are
well below expectations, the cam is looking more and more suspect.

I'll post pics when I pull them out.
I'm going to pick up a new set today and my new leak-down tester is due here tomorrow.
I don't think it's a head gasket or bent valve, but I'd might as well check while I am under there.

James Montigny

iTrader: (13)

2,4,6 and 8


1, 3, 5 and 7


Here are the plugs I removed today.
They were gapped at .024" (IE: unchanged - out of the box)
I installed fresh ones at .060" per the manufacturer's recommendation.
The car feels about the same, maybe a little smoother at idle.

I also changed the oil and filter since I had the car on the lift anyhow.
No real surprises; the oil came out pretty clean and with no signs of water/coolant.

James Montigny

iTrader: (13)

Ok, now I am even more confused.
I went back and looked at the runfiles from the dyno session and found one where we put down 385 at 13:1.
That was before we started messing with the timing.
I wonder if we didn't have it at 36* the whole time.

Based on what BLK02WS6 was saying, that is backwards.
We should have been using a more conservative value.

This doesn't explain why I am so low on power, but it does make the rich condition
seem like is is a symptom of poor tuning decisions rather than a mechanical condition.

gregrob

iTrader: (8)

Those plugs are terrible. Some part of the tune is WAY off.... Unfortunately if they have been in there a while, they wont tell us very much about the WOT portion of the tune.

The idle could be way rich, and color the plugs.

What you need to do is put in fresh plugs on a warm engine, do a couple on each side at least.

Then do a 1-3 WOT pull, and immediately shut down the engine, and pull the plugs.

Then cut off the threads, and post pictures...

MY GUESS about what is happening, is you have way too much timing, and the rich mixture retards the combustion process, and lets the engine have back the power it was losing on the verge of detonation.

I would start with a much more conservative timing number.

Get the fuel right, slightly on the rich side.

Then feed the timing back in and see what happens.

You do this by reading the plugs, the fuel ring on the porcelain and the timing mark on the ground strap.

Dont worry about what the dyno says, give the engine what it wants. The only way to know what it wants is to interrogate the only eye witness to the combustion process: the spark plug.

gregrob

iTrader: (8)

Another thing you need to be sure of is that your actually receiving the amount of timing advance that you are commanding.

DO NOT TRUST THE SCANNER!

Put a timing light on it and verify...

If the cam / crank signals get out of phase the timing can shift drastically at any point in the RPM range, and you'll never know it unless you're watching it with a timing light.

James Montigny

iTrader: (13)

I appreciate the advice; the dyno I tuned at is 3 hours away.
I'll see if I can find someone locally who will help me out.
Otherwise, I'll be renting dyno time and learning to tune on my own.

gregrob

iTrader: (8)

Honestly, you dont need a dyno to do any of this...

I would get your issues squared away, and read the plugs like I said. Then when its running strong on the street, you could revisit the dyno.

My car rarely if ever see the dyno. Dyno numbers do not make you faster. Hell I find the tune changes a lot between the dyno and street / track anyway, especially on an inertia dyno.

LT4T56Monte

Ur truely wasting ur time if not data logging. Recently pulled a lot of hair because while I thought the tune was calling for big numbers @ WOT, a scan showed timing pulled all the way back to 4 or 5 degrees! Would not have figured it out if I was depending on the ECM to provide the timing I asked for. Like all computers, it was doing what I told it....I just did not know what I was telling it. GMs settings and algorithms are VERY consertavtive. If Ur actual timing is not what you expected, check: Burst Knock settings (ECM anticipates knock even if your sensor is inop), Knock Retard Limits, Smoothing OFF, and ECT/IAT tables/modifiers. Also set all Torque Limiting settings to max values. My problem was Torque Limiting and ECT modifiers. Finally, the ECM ANTICIPATES where spark is going (just like it learns fuel trim numbers). So you have to look to the extreme edges of your High Octane Spark MAP 'cause the ECM will average spark settings from several cells away. The ECM does not like maps with steep slopes on the curve.

LS1x2

iTrader: (11)

I agree that you probably have too much timing for that octane and compression to lean it out how it should be.

T/A KID

iTrader: (12)

Post your tune, (may have to email it) and I can look at it for you