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LS Swap- Stock LM7 Gen 3 Intake Upgrade - Looking for Recommendations..

PWagon

PWagon

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Hey guys, I hope everyone is healthy with this Corona virus going around. I'm cooped up in the house and have been thinking about my next upgrade on my 2003 LS 5.3 (Gen 3) that came out of a Tahoe (I stuck it in my 86 K5 Blazer).. I still have the ugly-as-sin factory stock intake manifold. From what I see online, there are not too many options for replacing it unless I want to do a car height intake (low & completes for real estate with accessories/pulleys/water pump etc) or a fancy cathedral style intake. Now I'm not rich, but I would like to find a compromise between price vs performance in an intake upgrade. Here's what I need recommendations on:

1.) What would you guys recommend I replace my stock intake with to gain a bit of performance & improve the engine appearance?
2.) What size throttle body would you guys recommend going up to (92 or 102mm, or keep it stock)?
3.) Let's say for argument sake that I upgrade the throttle body size, does that necessarily mean I must re-tune the ECM?
4.) Does an upgraded intake manifold & throttle body require me upgrading my injectors (I have stock ones now)?

I'm just trying to get an idea of a parts list before I make a decision on my next steps. I appreciate any help you guys can send my way. Thank again!

-Mark
 
centexk5 said:
I'd recommend leaving it alone.
Click to expand...

He's got a solid point. Granted truck LS intakes are ugly as sin for sure, but they are there to build torque down low with the long runners. The Vette/Camaro intake looks a 1000 times better, but don't have as long of runners so what little low end torque the 5.3 builds is going to move up the RPM band. Plus as you mentioned the car intake puts the throttle opening right in the path of the truck serpentine setup.

I'd throw another idea out at you. De-ugly the stock intake. Many have shaved all the fins, casting lines and other ugly off of the runners and then paint to match or accent. You don't see it done much around here, but the 2wd crowd over on the 67-72 chevy truck forum has many done that way. Looks pretty cool.
 
I would agree about leaving it alone, especially if the engine is still stock. Unless you've added forced induction, nitrous, or (maybe) a stroker kit with aftermarket heads you likely won't use the extra airflow from an intake upgrade. I wouldn't bother with a bored throttle body yet either.

For bang for the buck power upgrade on an LSx based motor, I'd throw a decent cam in it and have a professional tune done (unless you can tune yourself). In a 5.3L engine, it should be relatively easy to pull an added 60 to 70hp out without losing low end. Also, if you don't need a huge jump in injector size you can look for GM flex fuel injectors from an L59 engine. They typically flow about 33 lb/hr (vs ~25 lb/hr for a non-FFV LM7) and can be sourced from most u-pull type junkyards.
 
As far as factory intakes go, the truck intake isn't that bad performance wise. The only other factory intake worth upgrading to would be the TBSS one, which is another truck intake. Beyond that, an aftermarket one is going to be the best performance/looks wise.

If it's the looks that bother you mainly, then shaving it down isn't that hard and with a little body work they can look pretty good. Or pick up one of the different types of engine covers and run that.
 
toomany said:
As far as factory intakes go, the truck intake isn't that bad performance wise. The only other factory intake worth upgrading to would be the TBSS one, which is another truck intake. Beyond that, an aftermarket one is going to be the best performance/looks wise.

If it's the looks that bother you mainly, then shaving it down isn't that hard and with a little body work they can look pretty good. Or pick up one of the different types of engine covers and run that.
Click to expand...
LM7 is running the cathedral port heads the TBSS intake is for the later gen IV LS engine with the big rectangular ports. The TBSS intake won't fit on the older heads.
 
There is a TBSS intake version that is running on an LS2 which still has cathedral port heads (243 or 799 castings). They do run 4 bolt throttle bodies and a returnless fuel system.
 
The only GenIV engines that got the larger square port heads are the 6.0L and 6.2L in all it's forms (except the TBSS L76 and the Vortex Maxx Silverados.)
Gen IV 5.3s still had cathedral ports and their intakes will bolt in place of your Gen 3 and the swap is usually good for about 20+ HP. However, the injectors and fuel rails are different as well as being an 87mm 4 bolt throttle body. You can get conversion connectors for both or you can swap the connectors.

Any changes to the throttle, intake, or injectors will require a custom tune to run properly.

Is your current setup tuned now? Or is the only thing disabled is VATS?
 
PWagon said:
Hey guys, I hope everyone is healthy with this Corona virus going around. I'm cooped up in the house and have been thinking about my next upgrade on my 2003 LS 5.3 (Gen 3) that came out of a Tahoe (I stuck it in my 86 K5 Blazer).. I still have the ugly-as-sin factory stock intake manifold. From what I see online, there are not too many options for replacing it unless I want to do a car height intake (low & completes for real estate with accessories/pulleys/water pump etc) or a fancy cathedral style intake. Now I'm not rich, but I would like to find a compromise between price vs performance in an intake upgrade. Here's what I need recommendations on:

1.) What would you guys recommend I replace my stock intake with to gain a bit of performance & improve the engine appearance?
2.) What size throttle body would you guys recommend going up to (92 or 102mm, or keep it stock)?
3.) Let's say for argument sake that I upgrade the throttle body size, does that necessarily mean I must re-tune the ECM?
4.) Does an upgraded intake manifold & throttle body require me upgrading my injectors (I have stock ones now)?

I'm just trying to get an idea of a parts list before I make a decision on my next steps. I appreciate any help you guys can send my way. Thank again!

-Mark
Click to expand...
There isn’t really an upgrade intake that will flow better than the stock one will on a stock 5.3. Whatever you come up with will be for looks only...Summit Racing has done many builds proving there is no performance advantage without other modifications like cam swaps
 
I vote lsa supercharger and intake adapters

but seriously the stock intake isn’t too bad other than looks. Holley makes a couple styles that aren’t priced too bad. I have no first hand experience with them, but I wouldn’t worry about tuning with just changing an intake.

but if you went to a bigger throttle body I think you would probably need to update the tune. I would say go to a 92mm throttle body
 
gonefishin said:
I vote lsa supercharger and intake adapters

but seriously the stock intake isn’t too bad other than looks. Holley makes a couple styles that aren’t priced too bad. I have no first hand experience with them, but I wouldn’t worry about tuning with just changing an intake.

but if you went to a bigger throttle body I think you would probably need to update the tune. I would say go to a 92mm throttle body
Click to expand...
I agree however, even feeding more gas won’t help much if at all. In the LS world outside of smog, the first performance upgrade should be a cam...for a better look, just go with a F body intake...even with a cam you couldn’t go wrong.
The stock LM7 can easily see 400 HP with a cam before needing anything more
 
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