Too rich or too lean with longtubes??

[GT500Droptop]

I have a 2007 GT500 with Stage II, that is JLT CAI, pulley and tune. At the time I purchased this setup the tune was a box tune by Evolution. This year I put Dynatech 1 7/8 longtubes and high-flow cats. The axle backs were FR sgt's but I'm sure that doesn't matter. I melted the high flow cats at the track and gutted them. Dynatech told me I was probably running too rich and the unburned fuel burned off in the cats and melted them. They sent me new ones free of charge and told me to have my car re-tuned. Talking to some friends that various Mustangs GT500's and Boss 302's etc. feel that the reason the cats melted was due to being too lean not too rich.

 

Before the longtubes I noticed that my tailpipes were a medium gray color after running on the track (road course) all day, which I believe would indicate a perfect fuel /air. Now with the longtubes and gutted cats the color of the tail pipes are charcoal/black. To me that would indicate a rich condition. I guess I just don't understand how headers would make that difference.

 

I asked the vendor of the headers whether I needed a re-tune and he said it wasn't necessary.

 

Need some advise from the experts on the forum.

 

Thanks

[07SGT2899]

if you had cats on the car previously you can't tell about afr from the color of the tailpipes.

 

the cats are altering the amount of unburned fuel comomig out the pipes thus altering the color of the deposits left in the pipes.

 

generally when exhaust gets red hot and melts cats its because of unburned fuel leaving the combustion chamber and burning in the exhaust system, thus super heating the pipes and melting the converter substrate.

 

the long tubes have increased the exhaust scavaging effect of your exhaust system. it actually creates a mild supercharging effect by aiding to pull out more air and fuel than the actual displacement of an individual cylinder.

 

your car was probably too rich before the long tubes, but now with the longtubes pulling harder on the cylinder you getting enough unburned fuel in the pipes to do damage.

 

all in all you need a retune to get thing back to normal.

 

for what it worth, on my old 2k gt, after the longtubes were installed i needed to add about 10% more fuel to make up for the leaning out/scavaging effect the headers had.

 

so your car was probably super rich before, the long tubes have leaned it out some, but its still so rich that the unburned fuel is entering the pipes and melting the cats

 

sorry i got kinda wordy, but thats what i think is going on with your car

[07SGT2899]

ps. don't let any one fool you. ANYTHING that alters how much air an engine can ingest or expel will ALWAYS require a retune for optimum performance

[2010KonaBlueGT]

Talking to some friends that various Mustangs GT500's and Boss 302's etc. feel that the reason the cats melted was due to being too lean not too rich.

 

 

Nope.

 

Think about it for a second.

 

Cat's don't melt from too little heat (i.e. fuel), they melt from too much heat.

 

If you have a camp fire and you add wood, does it burn hotter or cooler? If you remove wood, does it burn hotter or colder? NOTE: Wood is fuel and the answer is obvious.

 

When you use a WOT box that cuts out ignition pulses when staging, it burns out the CATs because of the EXCESS fuel being dumped into the CAT's, not from the lack of fuel.

 

Make sense?

 

 

Phill

[GT500Droptop]

Thanks for the responses. I agreed with the techs from Dynatech, not my friends, so I agree with all that are saying too rich. I just couldn't wrap my head around the reason But the more scavaging explains it. It seems that the longtubes are pulling the fuel air mixture out faster than it can be burned by the current tune. Almost like the unburned fuel is igniting in the cats like a torch. I live in central NJ can anyone point me to a reputable tuner? I think it's time for a custom tune.

[mgmustang1]

Hit up Lundracing

[2010KonaBlueGT]

I live in central NJ can anyone point me to a reputable tuner? I think it's time for a custom tune.

 

 

Are you near Tasca Ford in RI? I know that Dennis Gomes, from Tasca tunes them "right" (as Ford recommends).

 

 

Phill

[GT500Droptop]

Since some of you took the time to try and help with information I thought I should keep you all updated on what I learned when I contacted Jon Lund at Lund Racing. Here is what he said;

 

"Unfortunely in 2007 the tunes you have from a Stage II JLT

Evolution kit were not mine. I did not start doing Evolutions full-time

tuning unitl May 2009. So what you have is an old Pre-Lund Evolution file

that would have done by Fred Cook.

 

Also not the CATs burned out due to not having the Cat

Overtemp Cooling (COT Logic) on. With this logic off Fuel is actually

not being dumped to cool the cats and they overheat and fail.

 

You don't have an overly rich condition you have a tune

that is designed for offroad no cats".

 

Thanks

 

Jon Lund

 

 

 

I certaining did not know that the tune was supposed to dump fuel to cool the cats!!

 

I'm purchasing an updated tune from Jon since I do want to put cats back on my car.

 

Jim

 

PS this is what my cats looked like after running them with my current tune. My axle back tips were also blued from the excessive heat.

[07SGT2899]

holy shit! blue tips! i've never seen that! crazy!! i've read about the cot logic and from your description i'd swear you were rich, but it just goes to show you, you can diagnose anything from behind a conputer!