Cobra4B

iTrader: (9)

Update - Dyno'd again today. The plenum milling fixed the air/fuel imbalance. Car was only 0.3 air/fuel different bank to bank.

Car made 323/351 hp/tq with 13:0 AFR and only 22 degrees timing. Couldn't get the car to fatten up any. Upped the jets in the secondaries from 79 to 82 to 86 and air fuel only fattened up to 13 which is way less that it should have. Turns out the air bleeds had all been drilled out haphazardly and we only had four blanks. Going to have Pro-systems send a fresh set and try yet again. Trying to get air/fuel in the mid 12s before advancing timing. Car has a good bit more power/torque left in this stock LS1.

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6K pull, 22 degrees timing, 309 rwhp, 357 rwtq (stock 2004 GTO LS1 crate engine). Left bank going lean in mid-14s per tailpipe wideband vs. mid-12s on right bank verified by onboard wideband and tailpipe sniffer.

A fellow LS1 swapped Panoz owner told me he had the same issue and had to cut the center divider out of the manifold.

Has anyone else had this issue? Most cars have an H-pipe or X-pipe blending the exhaust which would potentially mask this. I'm going to weld a bung in the driver's side pipe to verify the lean reading seen on the sniffer.

wildcamaro

iTrader: (15)

If carbed why would you cut divider in manifold when you can adjust fuel on either side...I know you can on Holley for sure...just a thought

Cobra4B

iTrader: (9)

It's a dual plane manifold, each side of the carb feeds two cylinders on each bank. Something about the design seems to be leaning out the left cylinders. Trying to see if anyone else has had issue with this manifold.

ZONES89RS

iTrader: (25)

Very interesting. Keep us updated. I have never heard of this.

Cobra4B

iTrader: (9)

Here's a picture of the manifold for reference. The supposed fix is to cut this center wall out.

Cobra4B

iTrader: (9)

Edelbrock's tech said:

1. They didn't see anything like this in testing. 1/2 point AFR variation bank-to-bank max.

2. Some of the Performer RPM manifolds come with the center "wall" cut down already. Suggested doing it, but not more than 1/2". Said it'd lose some low end torque, but not material for my application in a 2500 lb car.

Here's the Performer RPM off the 347 SBF we had in the car before.


Generic picture of a SBC manifold w/ the same "cutout"


3. Said they never trust tailpipe sniffers.

89gmcs15

iTrader: (7)

Just throwing this out there but couldn't you jet your one side alittle fatter than the other? I'm only suggesting this if your plugs egt's and widebands are all showing a lean mixture across all holes on one bank vs the other. Call me stupid but it seems as if you should set the engine to work how it wants to, not make te engine work how you want it to. Like tuning a itb or multi carb (ie. 8 singles) vs one "main" setting across the board?

snook

iTrader: (1)

Ive thought about doin that to mine. Saw it in this video before, skip to 6 minutes if you don't wanna watch it all

Cobra4B

iTrader: (9)

Guys it's a dual plane manifold... not single. Each side feeds two cylinders on each bank.

89gmcs15

iTrader: (7)

Yes, run the carb with the lean side on both the primary and secondary part of the carb. say your left side is leaner, so jet up the left side accordingly.

Cobra4B

iTrader: (9)

How's that going to work when the left side feeds two cylinders on the left bank and two on the right bank? Jetting up the left side of the carb will add fuel to two cylinders on each bank. Might get the lift side reading in the correct range while making the right bank run rich.

Ls_Notch

none of the holes for mounting the ignition box are all the way through are they? I think I saw one somewhere that the hole was open to the intake and cause some problems.

89gmcs15

iTrader: (7)

I see what you mean now. I assumed the left side controlled the left and the right controlled the whole right. Another idea is the bolt holes that need to be plugged on the victor jr as stated. If not I'd say look into milling that channel so it's combined better? There's gotta be a way to tune the 2 cylinders on one bank. At wot is where it will show staggered jet changes I'd think you could put more fuel to one side of the manifold an it would show at wot?

Cobra4B

iTrader: (9)

One of them is, but I put a bolt in there with thread sealant per the instructions. We tested for air leaks with brake cleaner on the dyno and found none. Going to put the bung in the driver's side bank and mill the center divider. The folks at Pro-Systems said they've had similar issues using the dual planes and do the same thing. They prefer the dual planes for road racing vs. the single plane.

Prorac1

iTrader: (4)

With a tailpipe sniffer, a small exhaust leak, and I mean SMALL, could cause a false reading. Something to check. Eric L

Cobra4B

iTrader: (9)

Noted. However, the exhaust is all new (I built it) and fully tig welded. I'm going to put a bung in the driver's side to verify the lean condition just aft of the manifold.

Pop N Wood

iTrader: (1)

+1

I assume you have tried swapping the 02 sensor left to right to see if it is the wideband? Also what brand of wideband?

Cobra4B

iTrader: (9)

I can't swap it to the left until I weld in a bung. I didn't bother putting a bung in the driver's side when I built the exhaust. The onboard wideband is an AEM UEGO which is the one I have in my Z06 as well. I have no idea which brand sniffer the shop was using.



EDIT - If you meant the sniffer, then yes. Putting the sniffer in the passenger side where my onboard wideband is resulted in them both reading mid-12s. Sniffer in the driver side pipe resulted in mid 14s. I'm going to put a bung in the driver side pipe and mill the plenum divider some.

newschool72

iTrader: (12)

Do the rules in your class prohibit spacers? Why not throw a 1/2 " open spacer on there and see if that fixes the condition. If it does, you are on the right track. If not start checking the checking equipment.

Cobra4B

iTrader: (9)

Don't have room under the hood or it. Switched from a 1.5" dropped base air cleaner to a 1.75" after putting the LS1 in there. It's taller than the SBF.