I read somewhere that some Camaros were equipped with a two catalytic converter setup paired with a high flow air filter that had a 13% increase in power or something alone those lines over the single setup.

If the single cat setup i have now is that restrictive over the other, THEORETICALLY if i took the cat out would this give me such an increase in power for my LO3 305 TBI motor? Or to be more politically correct would a high flow cat really give me a boost paired with an upgraded air filter unit?

 

The FACTORY 2-cat setup gave a minor power increase over the FACTORY single-cat setup, IN CERTAIN CARS THAT ALREADY WERE ABLE TO TAKE ADVANTAGE OF IT.

However, an AFTERMARKET high-flow cat, with an AFTERMARKET high-flow exhaust, gives a corresponding power increase to those 2-cat setups, because the cats aren't the bottleneck; the rest of the system is.

Just slapping 2 cats on a L03 won't magically increase the HP by 13%, because the cats themselves aren't the bottleneck there either.

A set of headers, chassis-specific to these cars BUT NOT FOR L03, plus a good cat and cat-back, is the way to go. Get GOOD QUALITY headers for something like a 88 350 TPI (not just the cheeeeeeeeepest thing you can find that the FTC will allow the word "headers" to be printed on the box without criminal penalties) and have them ceramic coated, a 3" cat, and a 3" cat-back of your choice.

 

Okay so your saying my bottleneck is the motor not the cat in this particular setup. However if i put MY setup on say a HO 305 or 350 theoretically, at that point upgrading would make a significant difference.

 

No, that's not quite it, yet.

The bottlenecks in the L03 are the size of the Y-pipe inlets and outlet. The outlet size is is also the size of the cat in and out, and the I-pipe.

Since the Y-pipe inlets are the same size as the manifold outlets, that means the manifolds are part of the restriction in the L03, compared to the performance oriented engines, as well as all those other parts. (yes they are different)

So let's inventory the pieces of the L03 system that are comparatively restrictive, that want to be thrown in the trash:

That's the manifolds, Y-pipe, cat, I-pipe, and the muffler/tailpipe welded assembly. Basically, every piece from the heads to the back bumper. All the rest of the exhaust is perfectly fine. All you have to replace to un-bottleneck the exhaust, is just those few pieces. You can leave all the rest in place.

Which is exactly, 3 hangers.

Reason you DO NOT want to use ANYTHING that will fit L03, is because ANY OTHER PIECE that will bolt to ANY PIECE of the L03 crap, will PRESERVE THE BOTTLENECK in the exhaust.

The motor is a whole other matter. There, the heads are the primary bottleneck; the stoooopid "swirl" feature in the intake port is a MASSIVE obstruction. Thank you "old GM"; a total NEGATIVE feature, just to fake your way through the CAFE requirements of the day. (much like your gears) FIRST UPGRADE to the motor proper, would be to put better heads on it. The heads to get are the ones off of a 87 LG4 or a 87-up LB9; casting # 081.

But don't worry about that just yet. If you're working on the exhaust, concentrate on the exhaust.

 

Good info thank you very much for you time!

If i do anything at all itll just be the exhaust and maybe an air breather unit. This is my daily and no time for big projects with the job I have currently.

Im very happy and proud of my still running smooth 25 year old stock car

 

[quote=sofakingdom;5797480The heads to get are the ones off of a 87 LG4 or a 87-up LB9; casting # 081.[/quote]

sofakingdom,

I have to ask, s a fellow L03 owner...I read much about the restrictive exhaust. So nothing new there. But this is the first time I recall reading this head recommendation. (Admittedly, I've only had my car and been reading these sorts of threads for a short time).

Are you saying the LG4 and LB9 use the same casting, #081? As reviled as the L03 is to some, it still makes more power than the LG4. If the heads on the L03 are the biggest offender, it's hard to imagine the LG4 heads as an upgrade.

Not saying they aren't....you obviously know more about this than I do....but would love to hear a little more history / detail on this. Thanks.

 

Yes the LG4 & LB9 use the same head casting.

In the years of the L69, the LG4 also shared the heads with that motor.

The reasons why one motor makes more power than another vary widely. Even more, the reason why one motor is "rated" higher or lower by the factory, which may have NOTHING WHATSOEVER to do with actual power output, vary widely.

In the later years of the LG4, it was "rated" at 165 HP. The L03 was "rated" at 170 HP. Is that REALLY so different? Or is it just marketing-speak sleight-of-hand, like the "375 HP 327" of the 60s, that if you build that IDENTICAL motor today, part # for part #, MIGHT MAYBE put out 275 HP on a good day? Or, might various individual LG4 cars ACTUALLY vary between say 160 and 180 HP, but the L03 cars have more consistency, like all of them between 165 and 176 HP? I don't know.

Or to ask the same question in another way, if you lined up a dozen LG4 cars and a dozen otherwise identical L03 cars (both auto or stick, same gears, same weight, etc.) which one(s) would win? I haven't a clue about that, myself; I'd actually expect it to be pretty close. The L03 would probably be ahead at 330' but the LG4 would probably drive around it at 1000', but I don't know that.

However all that may be, all you have to do is look at the flow #s of the heads (187 vs 081) and it won't be too hard to figure out why you'd prefer the one over the other... once the other bottlenecks have been cleared..

Remember, the way to make a CAR go fast, is not to unbolt and re-bolt big shiny cool-looking things that sit up on top of the ENGINE out in the open where everybody can see them (carb, air cleaner, valve covers); nor is it, to install whatever "all the fast cars at the strip" have; the only way that makes a CAR faster, is by weight reduction, with all weight savings concentrated at the driver's wallet. Rather, the way to make a CAR faster, is to identify the ONE THING producing the greatest effect toward keeping THE CAR slow, which may very well not be THE ENGINE at all, and FIX THAT ONE THING, in a manner consistent with the owner's goals and the rest of the car. Then once that ONE THING is no longer the bottleneck, some other thing will be exposed as the ONE THING keeping the car slow, which you would then fix, which will expose yet another ONE THING, and so forth.

In the case of L03 cars, the first ONE THING is the exhaust. The 2nd ONE THING is the rear gears. The 3rd ONE THING is the heads. The 4th will be the air cleaner. The 5th will be the cam. The 6th will be the torque converter, in auto cars. Of course at each stage, TUNING will be required, as the engine's operating conditions will have changed rather drastically. TUNING is often overlooked in EFI setups, but is just as important in those, as dialing in a carb was in the old days.