3400 LIM gasket with 3500 head upgrade

[kprower]

I have the classic LIM leak with oil in the coolant at 112k on my 2004. What started out as a repair has turned into a 3400 with 3500 top end upgrade. I have a few questions though:
1. Since the heads/manifolds are going to be off I am considering headers. Will they work with the stock exhaust? Would it be worth it to do since it will be torn down or will the stock exhaust rob any power gains?
2. Do I need to reprogram my PCM with 3500 heads? Where to/how to do this/cost? (Been a pre-60’s car guy for years so minimal PCM/OBD experience.)
3. Below is what I am looking at for parts, does it look like I missing anything?
Coolant temp sensor G6 (AC Delco)
Temp extender (WOT)
Fender well CAI
65mm TB (?WOT?)
3400 block
3400 head gasket (Fel-Pro)
3500 heads (WOT)
New head bolts (Fel-Pro)
3500 LIM gasket (Fel-Pro)
3500 LIM ported (WOT)
3400 UIM gasket (Fel-pro)
3400 UIM ported (WOT)
Exhaust Manifold Gaskets (Fel-pro)
Exhaust manifold bolts (Fel-Pro)
Thermostat w/ new thermostat o-ring (Stant SuperStat)
Radiator/Heater/TB hoses (Gates)
Waterpump (Cardine severe duty)
12 fuel injector o-rings (Fel-Pro)
Thread Sealant
RTV sealant
EGR gaskets
?3400 Valve cover gaskets? (Fel-Pro)
New hose clamps to replace the old ones
6 liters of Dexcool antifreeze
5 liters oil
Vertical oil filter adapter (GM 12578893)

[MidnightriderZ24]

headers will be the best choice, but the factory exhaust might choke it. the pcm will need programming to get the most out of the new heads and intakes and headers if you do them. it will run, but not to its potential without some adjustments to the pcm. 3400 valve cover gaskets will work. as for your list it looks complete, but once again injectors might be too small, so the o-rings might not be needed. make sure to replace the water pump bypass tube o-ring, and the coolant inlet pipe o-ring that runs from the heater core. distributor shaft o-ring is a good idea as well. wouldnt hurt to pop the timing cover gasket off and inspect the timing chain (theyre known to stretch) for wear.

[prophiseer]

If you're looking at headers - S&S setup is superb. I had to do a little "tweaking" to clear the thermostat housing and line the crossover tube to the back header - but aside, install went smooth. They fit great. Price is very respectable, too - especially compared to some other designs. Only other curve ball I was hit with was having to turn the flange to properly bolt to the rear of the exh system. Was simply a matter of cutting the flange off and turning it 6*, then welding it back up.

As to the fuel injectors - if you're re-using the factory units, they might be a little thin. If you're keeping the block at the OE bore spec (or even up to .020-.030 over) ,I'd recommend 19# units minimal, 21# preferred. You can probably go with 24# - but you'll defi need the PCM retuned . . . it'll run, but the stock PCM tuning wil be trying to starve them out.

You probably won't have to retune the PCM with 3500 heads . . . but, PCM tuning is highly recommended to get the most out of it - unless you do some extensive porting. If you're having mild port work done to the runners (pretty much smoothing out the transitions and the runners themselves), it shouldn't throw things out too much. I'd defi recommend either having someone experienced with port work (especially on more modern motors) do the work . . . unless you have the capability, in which case, I'd recommend doing some extensive research into the best methods for newer fuel injected compact motors. Although theory and implimentation have remained the same, newer motors don't always respond to the same techniques that older motors did, and the 60* is already fairly efficient from the factory. If you're going to have the runners hogged out, then you'll defi need the PCM tuned. IMHO, aside from hogging things out and/or smoothing transitions, the only real area that needs addressing are the combustion chambers on the OE heads.

[AaronGTR]

He got an '04 gagt.... already comes with 22.5lb/hr injectors and those will be plenty for just swapping to a 3500 top end.

[3400-95-Modified]

One thing not mentioned... the stock 3400's use a 3 pin temp sensor... the 3500 has a 2 pin one in the head. The threads are not the same so you need to re-thread the head to fit the three pin one, OR have the three pin sensor milled down and re threaded to fit the hole in the head. The first option is better if you have the heads off, I was already together before I realized I forgot that so I had a three pin sensor modified to fit. There is no spot on the LIM to put the sensor where it used to be.