Fuel evap/emissions questions for K5 5.3 swap

[93FatBottom]

I did a search and found nothing concrete about this, so if anyone has the answers, please post!

In doing the research for my swap, my truck is a 1979 K5, and the new tank is a 31 gallon TBI tank. The donor vehicle was a 2003 Suburban, also with a 31 gallon tank. After a disagreement, I ended up not getting that engine, but I have a line on a new donor, a 5.3 from a 2004 Tahoe, with a 26 gallon tank. My K5 still has the 31 gallon tank. I came across whispers about the fuel evap for these swaps, people saying that the donor vehicles fuel capacity (stored in the PCM) has to match the vehicle getting the swap, or pressures won't be read correctly and that will trip and DTC, and can cause trouble with how the engine runs all together. My question is, does this theory hold any water? It seems to me that it does, but I don't know enough about fuel evap systems to have a definite confident opinion. If I can avoid an issue, I will. I know of a place to get a 2003 Suburban 5.3, though with higher miles for slightly less money. I chose the one from the Tahoe because it was considerably less miles, closer, and only slightly more $$. Has anyone had an issues with this in the past, or should I play it safe and find one with matching fuel capacities? If no one has the answer, I'll play it safe and take the other engine.

My other emissions question is about the cats. I saw some guys on here and LS1 talking about the cats needing to be the same distance from the exhaust manifolds. I know they sell cats and crossover as one unit, but I'm using 2002 F body exhaust manifolds, so I will need to get my cat/cross over pipe modded to fit. Is there any truth to the cats needing to be the same length from the exhaust manifolds down the pipe? I believe someone said it was just to pass the visual with the smog ref, though, I can't imagine them actually using a tape measure to check as long as I have 2 carb legal cats and 4 O2 sensors hooked up and operating.

If anyone has any info about this, please enlighten me and anyone else who might come across this seeking the same info

Thanks!

Stephen

[chebyshortbox65]

No it dose t matter on the fuel tank size. It is not that easy to just hook up the evap and go you have to jump through some hoops to get the readiness test to set. Also there is no way to make the stock exhaust fit so you will have to modify the cats I would make them close as possible to the stock specs they will check. It all depends on the referee I have got a few Ls swaps through just depends on how clean you work is and getting everything in and working

[mattcrp1]

I am in the middle of a 4.8l swap in a '76 swb my self and have had questions in regards to this as well.

Chebyshortbox65 - do you have any pics of the evap set up on your truck? Did the referee actually run the evap test or just check the monitors?

Thanks