Hey guys,

I can't figure this thing out, I've got a eaton supercharged LT1 and I can't keep the thing from screwing up at 4000rpm or a little after.

A little run down on the car

Roots supercharged 7psi
Autolight 103 plugs gapped at .032
Crane HI-6S/91 box/coil with retard
new wires
new optispark (As of yesterday)
4:1 FMU


WHat happens is the car runs totally awesome till about 4200-4400rpm stops maybe falls down a few 100 rpm then takes back off. I can't figure this dead spot out to save my life!

The AFR is a little richer than i would like but its staying consistant during this time. (its about 11.5~11.8)

What I am noticeing is that i'm geting burst of knock retard. Its only .9 degrees but where i got programmed 34 degrees the scan tool is saying 21 degrees. No matter if i got the retard set on 1degree per PSI or 3 degrees per psi that spark retard is there.

WHAT IS THE DEAL??

Attached is a datamaster dyno graph perfectly depicting what i'm feeling

 

Have you tried some 110 Octane???

 

You know what? I think we had a similar problem with yours right?

Help me my memory is old, what did i do to fix it?

 

Actually I had a bad Jacobs Ignition.

I returned it for a new computer, but decided to sell the new one on EBay and went with all MSD components.

Recall that when I added the Xylene the problem went away.

Maybe you have an ignition issue???

But also try the higher octane since you are seeing knock.

I am adding an SMC Alky kit since I will be pushing 5 more pounds of boost once I change the blower pulley.

Quick check, go with higher octane. See what happens.

 

I had some similar problems with my Crane Hi6s also, the revlimiter was screwing up once and awhile. I had it set for 3500 for takeoffs, and once and awhile it decided to activate on its own, and bounce around on me. Something to think about anyway.

 

The only time Ive ever had a problem likek that, i had my rev limiter set to low LOL

Sorry, Ive never been down that road. Id suggest trying what some of thees guys have mentioned.

Good luck

 

Yeah, I guess everyone is dead set on ignition problems.. SO i'll get rid of that brand new box for a MSD BTM.. A shame really. Anyone have any better suggestions? It sure is a ton of money

I dont see how it can be spark knocking i've had it as low as 3 degrees per psi with 30 degrees of advance THATS like only 9 degrees! how could it possibly knock!

 

I know a guy with a syclone that had the exact same problem, first we replaced the plugs and it went away, but then it came back and it was also picking up knock on 10#s with 110 octane.

it turned out to be tha accel ECU he was using, we put the stock ECU back in and it's problem free.

You might want to check all your engine grounds because I have heard of that causing the same problem, I don't know if it would be the same on an lt1 but it's worth a shot!

 

Just try a .025 plug ga[ and see if that clears it up.
The Optispark set up has a HUGE air gap between the cap and rotor. While the HI-6 might be generating enough voltage, it might not have enough current behind it, to maintain a good spark.

Plus as mentioned check the grounds.

 

you say it takes off well, falls down in the middle, and then takes off again?like there is somethin that is messing it up in the midrange? try some high octane fuel to rule out massive detonation in the midrange. Im not talking about some pump crap with octane booster added either. Im talking about some unleaded race gas from a pump at a track or from a barrel.

 

I agree.

If you are still falling flat with 110 octane, the problem is not knock.

 

Ahhhhh!!! My car occasionally does the same thing. Better richen up the fmu.

 

Just installed a MSD 6 BTM

Problem is still there. It seems to not do it as much with the boost retard set low than high. For example its definately there at 3 degrees per psi and not as aparant at 1 degree per psi.

I've got a crazy hunch that my WB and NB o2 sensors are reading wrong during this period. I'm going to try to richen that area up


Does anyone have any octane directions with Xylene?

 

Hey Rooster!

Remember I used this when you tuned my 91' TA.

Xylene is 115 Octane.

So if you mix at a 1 Gal Xylene to 2 Gal. 93 Octane Gas ratio you get 100.33 Octane fuel.

Please be advised that prolonged use will swell your O-Rings.

Good Luck!

 

Yeah, i've been waiting since last week to bleed out all this gas.

Right now with that formula i would need like 4 gallons of the stuff..

$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$

i won't fill up again without trying it

 

Yes Sir!!!!

 

Well i put the MSD 6BTM on the car today. Still no help.

My 02's have been in the 950's and the wide band has been in the low 12's. But I had a hunch that my something was off.

I decided to throw in a freaking stuiped amount of fuel in the car and the car responded very very well. This time the WB showed a 14.0 and the narrows around 1000mvs. Well kept tuning it and now the thing is a monster. It seems like it so far off from the start that the WB and NB sensors just lead me further astray.


Now if you get on it in second gear at 2000rpm's it runs like crazy until about 4500rpm then starts spinning its a$$ off (like in the 40-55mph zone) I think thats truely impressive seeing how its a 3.23 car with a automatic. It realy is a monster.

Here is a datamaster dyno picture. HP falls off hard if the car reports any knock. ON this run at the RPM it falls at it reported 0.9 degrees. TOUCHY eh?

BTW... look at the thin lines (RAW DATA) its more accurate i think.

 

Looks like you got it solved!!!

Nice numbers. So you did this on pump gas?

Track time!

 

Yep,

Believe it or not but the car is averageing like 30 more miles to a tank with the new blower

I tell you, I'm ******* the crap out of it too.

I built a new cold air intake for it today.

 

Amazing !!!

Great job Rooster.

 

Thanks,

that intake really woke up the blower.. Its alot louder too

 

Gotta love that sound!!!

So is it done now???

 

cool...

keep tabs on what you're doin..... because once i get my long block together, im saving up for multiport EFI..... and once i have that, im going to fabup a low profile intake for a M112...........


atleast thats the current plan....

 

it will never be done!

Honestly i can't tune the 5000+ range now because it breaks the tires loose in 2nd and if i was that high in third i would be well over 100mph.