I have an LS3 with cathedral heads. Plan on putting it in a 2003 Z71 Tahoe. Looking for complete list of things that will need to be addressed and who supplies the parts. Would like to use as much off of the Tahoe as possible including the intake.
LS3 Swap 2003 Z71 Tahoe
- Thread starter reath1
- Start date
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iamdub
Full Access Member
I don't know about a "complete list", as you're looking for, but I'll list off what comes to my mind:
First off- what cathedral port heads do you have?
For the nitty gritty: It's a gen4 motor and your Tahoe is set up for gen3 controls. The camshaft position sensor and knock sensors are in different locations, but this can easily be resolved with some simple wire lengthening, rerouting and addition of the correct connectors. I believe you need to tweak the knock tables in the tune, but you should have a full custom tune performed anyway. The big hurdle is that the gen4 uses a 52x trigger wheel on the crank whereas the gen3 uses a 24x. You can either remove the crank and swap the trigger wheel or get the TRG-002 converter module from Lingenfelter. This module will make the combo work, but it causes longer cranking when starting (about 2 seconds) since it has to determine the crank and cam positions first before it is synced. A starter that can spin the motor faster will reduce the starting time. All accessories from your original motor will bolt up to the LS3. I'm not sure, but the exhaust manifolds may be larger for a 6.2. So, either see how stock 6.2 manifolds compare to your 5.3 manifolds or just get headers. For the intake manifold and throttle body, '03 is a midyear change. Earlier ones still had the drive-by-cable (DBC) TB and the later ones got the electronically actuated, drive-by-wire (DBW) TB. Also, the TB inlet for the LS3 is 90mm and the 5.3 (I assume your Tahoe has the LM7) inlet is only 78mm. You'll lose lots of top-end power which is where the LS3 really pulls. You could change the LS3 cam to trade off some of that top-end power to make it a low-end torque monster, which is much more befitting of a Z71. If you must use your stock IM, then you can just slap it on and go, as-is. You'll certainly need the tuning to be on point since you'll basically have a winded gorilla trying to breath through a straw. If you want a bigger IM to better compliment the additional cubes, you can get a F.A.S.T. 90 or larger with the appropriate TB. If your Tahoe is DBC and you get a larger IM, then your easiest solution is to get a 90mm DBC TB such as the Edelbrock ACC-1033. If it's DBW, then you can use the LS3 TB. Depending on whichever combo you end up with, you can get an adapter to bolt the LS3 4-bolt TB pattern to the earlier 3-bolt IM inlet as well as a harness adapter to convert the LS3's DBW plug and pinouts to the LM7's. You may need to swap some wires around on the TAC module if the TB operates in reverse.
Off the top of my head, I believe that's about the bulk of it.
Ok, that is a pretty good perspective on it.
On the sensors, I'll order the pigtail extensions. So, good there.
Not solid on whether to change the 58x reluctor or go with the box. Still kicking that one around.
I haven't gotten as far as the exhaust manifolds yet. The motor has PRC heads. I know nothing about them but they look pretty expensive...lol.
My intake is DBW, would really like to use it. Trying not to sink more money into this than needed. I'm in pretty deep on the motor and heads now.
One concern I have is that I know nothing about cams and this motor has a Mast Motorsports 230/237 112+4 . Any clue where that will pull? Up high? Mid? Down low? Stall needed?
Will my flex plate and starter work or do I need to swap those to...what?
Many thanks for the tips above and please keep suggestions coming.
ivin74
05 NBS Nali
Reath,
You can get most of the info you are looking for at performance trucks.net forum. Those guys do those kind of swaps all the time.
You can get most of the info you are looking for at performance trucks.net forum. Those guys do those kind of swaps all the time.
mikeyss
Full Access Member
Then there's the 4L60 that will not be pleased about the added power, and the 8.6" rear may give up the ghost after a few good hard launches. You may need to beef the trans up, replace it with a 4L80 which has bad gear ratios for a screaming LS3, or maybe a 6L80 swap could be done if you're gonna run the 52x crank. That opens up another can of worms through, lol
stagrlee
TYF Newbie
I put a Texas Speed 408cid (6.7L) stroked iron block in my ‘04 Z71. Stock heads with STI valves and a mild Texas Speed cam. Texas Speed suggests the LS6 PCV engine valley cover and an external oil vapor recovery system so I put that in. I used the Elite Engineering catch can. Everything else is stock. I change the tranny, xfer, and diff lubes every 40k miles. Tows my 25’ Airstream like a boss.
Going from 5.3L to 6.7L required a visit to Texas Performance. They had to program the ECU to keep some throttle open at idle and give the the engine more air and air it up throughout the RPM range. Otherwise it stalls about 2 mins after startup on the stock ECU code. Also had to detune the misfire detection as the cam puts a bit of a lope to the idle.
This was all triggered by Castech heads getting coolant in my oil and destroying the original engine. Fun truck but requires 93 octane now.
Going from 5.3L to 6.7L required a visit to Texas Performance. They had to program the ECU to keep some throttle open at idle and give the the engine more air and air it up throughout the RPM range. Otherwise it stalls about 2 mins after startup on the stock ECU code. Also had to detune the misfire detection as the cam puts a bit of a lope to the idle.
This was all triggered by Castech heads getting coolant in my oil and destroying the original engine. Fun truck but requires 93 octane now.
Thank you sir. This is the stuff I need to see. Which balancer did you use and did your accessories from the 5.3 line up? I'll try to get a look at the oil vapor system you used. Please feel free to post up any other details you can think of.
