79Rod

I have 2.5" true duals, borla S type, no cats and I like it. Just wonder how will it sound with an X pipe

krackenvette

I am sure there are videos of sound clips out there. But, you will probably not notice the difference with an X pipe.. You may notice more drone though.. L98? LT1? 50 Hp between the two is allot of extra air going through the exhaust too.

84 4+3

probably next to nothing unless its a pretty high hp mill...

79Rod

I have a create 383 with sniper efi

CharlieNC

Gutted my cats, sounds just like I wanted!

Tom400CFI

In the Kart, (mostly stock L98 with dual 2.5", and two straight through, perforated tube bullet style muffs), I added an H pipe (that's about 1" long or less) and it made a big difference in the way it sounds. It went from deep/burble, "Mustang-ish", to more rippy, like a C6^ w/exhaust.
Not the direction or sound that I had hoped for, that's for sure, but it also mellowed the volume quite a bit, and that part was appreciated.

yakmastermax

I am still curious just how much HP is being sacrificed various muffler options vs a system with no cats, no mufflers at all. In both cases long tube headers.

I would prefer to keep my exhaust sound relatively tame but I also want to open up flow as much as possible.

Also I wonder if Borla might sell the 92-96 square tip mufflers as an axle back as opposed to cat back configuration. Alternatively I wonder how the 92-96 Borla square tip setup might be made to fit on an 1989 with long tubes.

Tom400CFI

I depends. Watch the Engine Master's coverage of this very topic.

Fabrication.

krackenvette

Virtually no HP gain in reality. Its a sound thing.. A C4 LT4 has the best chance of gaining minimal HP gains. Maybe 5 to 10 hp..
You have to remember, its an air pump. Air in Air out. If you have OEM cats, factory exhaust manifolds, on an L98/even LT1 a cat back is virtually worthless. Return of investment is not worth it. Sound is subjective too.

Tom400CFI

Have you tested this?

IDK about an LT1, but I believe that exhaust would/could produce meaningful gains on an L98.

krackenvette

Tom. I have tested my LT1 when it was slightly modified. 2500rpm GM Converter, 3.73 1.6 LT4 RRs, KN and Flowmaster cat back, Hypertech chip, 160 stat.
20rwhp SAE Huge, huh.
Now, take a L98 with a whopping 255 hp, put a cat back on it. How much do you think it will gain. 5hp on a cold day?
And cat backs on L98 and LT1s have been beat to death since late 90s on this forum.
Negligible gain till you retune, add headers and cam etc etc.
I believe Corvette Fever did a cat back test and gained 15rwhp on an LT4. Its been years, and I may be off on the numbers.
I stand by cat backs really are a waste till you add some more air through them via modifying engine.

84 4+3

I won't argue that a cat back is worth nothing more than sound mostly. But i would bet a LT1 setup installed on an l98 would in fact be worth some power. Those crimp bends off the manifolds aren't exactly the best but going to a better stock full exhaust would do something. Otherwise it's sound. I do not disagree. Is it a ton of power? No. But you'd be able to measure it for sure I'd think.

The other nice thing about cat backs (aside from sound) is they can be light. But the stock LT exhaust works really really well.

Tom400CFI

Well IDK. You got 20 RWHP from a cat-back on a (mild) LT1? I'd say that's pretty significant. But to extrapolate that over to an L98 and claim "5hp on a cold day"....that don't work. First, different exhaust. The L98 is a single exhaust...it's not nearly as good as the LT1 system.


Sooo, I built a dual exhaust for my 'Kart ('89) and dyno'd it. UNFORTUNATELY, I didn't do it bone stock -couldn't have, since it came to me, missing the whole "Cat back" portion of the exhaust anyway. My "base line" was a stock engine, the dual exhaust I made, and "free mods" was 240RWHP. Now, we know from history that most L98's do about 210 RWHP, box-stock, so I got ~30 hp from timing and dual exhaust. Where do you think the majority of that 30 came from?

krackenvette

Yep, we can play the game all day..
My "mild" HP was loosened up via a torque converter and gearing. Converters are lighter and "free" hp up all day.. 3.73 gears help engine spin up too. Hypertech chip did timing and fuel adjustments. So, if this all mild.
But, I digress.
My OEM LT1 exhaust behind my headers put down 400RWHP. With Flowmaster cat back it was 425. This is with same driveline with exception of 396LT1 and Long Tubes making 515 fwhp ( on dyno, no accessories other than water pump. Thats an engine with almost twice the power. Lot more air being pushed through the exhaust. Dont say its restrictive, as there was no cats with long tubes and OEM cat back.
Your 30whp, was it SAE? Or just another dyno day. That makes a difference.
And bumping up timing can add a little power, as we all know.
Apples to Oranges. Put a cat back on a stock vehicle. See what happens. Lets search threads on here. SAE changes...

Tom400CFI

I'm curious about this b/c I've read on here a bunch of times that "LT1 exhaust is good" or "there are no gains from exhaust on an LT1". Did you gain 20hp with all ^those^ mods combined? Or did you get 20 from the exhaust? I'm asking b/c to ME, 20 is pretty substantial and meaningful. *I* would do an exhaust for 20, that's for sure!



SAE corrected. Not a Dyno day. I paid for dyno time for that specific baseline.
Yep on timing; we know that it adds power...hence my question; Where do you think the majority of that timing came from.

krackenvette

The 20rwhp was all mods combined.
On my 396LT1 engine set up, I lost 25rwhp with just the Flowmaster cat back being exchanged to LT1 OEM cat back.
Not sure what you are asking as far as "Where do you think the majority of that timing came from?" L98s dont do all of timing well. My L98 was limited to 6 to 8 BTDC, after that it was pinging. But, it was a stock coil and such and in a Camaro Z28 IROC.

Tom400CFI

O.K. Got it. Thanks!
I don't doubt for a second that you lost 25 on a 500+hp engine. I think that the general consensus on here is that on a stock or stockish LT1, the stock exhaust is better than good enough. Meaning, as you say, "no gains" from a cat back. No meaningful gains, anyway.


I think the L98 is a different story, however.....
IDK HOW the hell that word ("timing") got in there. That SHOULD have said, as it did in the original question, "Where do you think the majority of that 30 came from?" Meaning, the ~30hp I saw over typical stock L98 RWHP numbers? As you stated, many TPI can't take a lot of additional timing. I'd give 10 hp to timing. The rest of the gains I saw? I credit the exhaust.

krackenvette

L98s benefit from Different manifold, and of course heads. But the manifold, with a redline of 5000 maybe, is a choker.
Torque was never an L98s issue though.. 330? pretty decent.
I like the fact an L98 is a distributor car.. You can modify the crap out of that engine relatively easy.. Parts for it are far cheaper than LT1, and our Achilles tendon, that damn Opti.

coupeguy2001

Nothing i will say is relevant since you have an LT-1.
But:
i have an 86. 383, 14 cc dished forged kieth Black pistons, and i used 87 corvette heads. I ground down the square block under the spark plug in a curve to mimic slightly the heart shaped chamber on vortec heads.
unshrouded the valves. On exhaust, i used an 89 rh exh manifold, and 87 exh manifold on the left.
if you look at the welds for each tube at head flange. The weld protrudes into the tubes. I ground that excess away, opening up maybe 10% more tube.
using a stock 89 corvette prom, i eliminated the 9th injector, 58mm edelbrock throttle body,
cam is a Crane compucam with 1.6 rockers on the exhaust, 1.5 on intakes. Harland Sharps.
i used aluminized 2.5 exh tubes with a 6” H pipe, no precats, no cats, and 91. Vert mufflers.
the mufflers are the last year of L98, so i figured they had to be the final refined L98 muffler.
absolutely no drone. The car gets it done.
trans is a 700R4 out of a 91 Firebird so it doesn’t jump into gear. Rear is a 3.07 out of a 96.
using the 96 dogbones and half shafts too.
the car used yo vibrate the interior screws out of their holes with the original engine and exhaust.
Not now.
i think the front Y pipe is responsible for the drone.
if one of the front tubes on the Y were at least 6inches longer than the other, it would have had no drone.
happy with what i have, it cruises at 100 effortlessly and pleasing note and level from the exhaust with no drone. Gets 25 on the highway and 16 around town.
given what these cars are selling for , i have
tried to be as economical as i can with the idea that if i had to sell it, i could recover at least 3/4 of money spent.
but no drone.

GREGGPENN

On an LTx, removed the stock mufflers (aka muffler delete). Most will like the sound...better move IMO than gutting the cats. Much better. Very cheap to do. sawzall before mufflers, shop bends/welds in replacement. Cheap tips to dress up.

If still not happy, post why the change isn't satisfactory.