# LS1 vs LS3



## Ross61 (Jan 27, 2014)

Soooo,

Had a better clutch installed into the GTO and in the process noticed the oil level warning (see my other post). The shop I took it to for the clutch (cause I don't have the time to mess with it right now) is a very well known Corvette Shop in San Diego (total cost was less than $2K with the better clutch, pressure plate, and slave cylinder included) but I digress...

In the process of discussing the above and explaining my consideration of installing a Maggie, mild cam, JBAs, some 243 heads, and freshening up the engine's guts, the owner of the shop mentioned how his son wanted my motor (or any other 2004 GTO motor) and *HINTED* I could have a new LS3 installed where the cost of the parts would *PROBABLY* be less than parts of the LS3 install.

LOTS of *HINTS* and *PROBABLES* in there, I know.

So here's a question posed to the collective (WRP, Doric, HRJ, and others with similar reputation, please - your input is HIGHLY regarded here), *IF* I can trade my LS1 motor for an installed (and new) LS3 motor with the intention of doing a Maggie (6 psi) and headers, would I be looking at an equitable trade?

The installed motor would be required to pass CA smog of course.

+++++++++++++++++++++

BTW - this is an honest guy and the motor will be put into his son's Miata. As California's CARB rules work, putting an LS3 into the GTO is considered a replacement motor. Hence, for smog laws, the new motor would only need the same smog related items installed as the OEM motor.

When the LS1 motor from a GTO is installed into the Miata, the LS1 motor is required to have the same smog related items installed as the motor was configured from the factory. What this means:

If car X and car Y are the same manufactured years and both came stock with the LS1 where car X came with an air pump but car Y did not (same motor and same internals) when the motor from car X is installed into the Miata it MUST have the air pump to pass smog REGARDLESS of how clean it burns when tested (gotta love it when democrats are in charge, huh?)
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## EN3DVED (Oct 14, 2010)

Ross,

A couple of things to consider if it is a fair trade is the baseline of the engines. I know you had talked about wanting to do the maggie, heads, cam and all of that to your ls1 but from a baseline ls1 motor to a baseline ls3 motor it would be a good trade. 

One of the big things between the two is the displacement. Going from a LS1 to a LS3 is a pick up of .5 liters or 35 cubic inches, 347 vs 378. From flywheel specs this is a little less than a hundred horsepower difference from a stock LS1 to stock LS3 hp output. The heads on the LS3 are also better than LS1 heads in terms of flow given the larger bore of the LS3 which equates to larger valves in the LS3 heads. Now you can get aftermarket heads for both engines and some will outflow others in either case but a straight stock to stock evaluation the LS3 is a better motor. 

With all of that being said, stock compression ratios for both motors is low enough that you could run 6 psi of boost safely. So you would have the benefit of being able to do those mods later on down the road to an LS3 if you wanted as well but you will be ahead of the game because of the displacement your gaining by doing the swap if you decided that. 

In regards to emissions stuff I couldn't really tell you? I am in California but military with out of state plates and emission requirements. I do know that of all things given the cam and headers are really going to mess with the emissions guys and will most likely trigger a fail. Don't take my word on that but any kind of fueling mod with adjustments in air flow from a cam will alter the readings and make it difficult to pass. I would personally go to a few shops and talk to their customers and employees to see how they do with cars passing smog with work done to them. Hope this helps some.

Ed


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