mcm95403

Today I cut off the tips from a set of OE LT-1 muffler for my planned cat-back project. I have to say I was quite surprised to see that they are only 2" I.D. I thought they were 2 1/4, but I was wrong - definitely 2".

No wonder the LTx cars respond so well to exhaust changes!

I still have the mufflers and may cut them open as well just to see what they look like inside. Looking in from the ends doesn't look good.....

eatmydst1234

I hate to tell you this, but LTx cars don't respond well to exhaust because the factory exhaust is a very free flowing 2.5" system.

The L98 cars do respond to exhaust pretty well. What year car do you have?

mcm95403

My signature describes my car. The engine is basically a LTR LT-4, or a 385 hp crate motor, however you want to look at it.

That 2.5" system still goes through a big resonator and restrictive mufflers. Pipe size alone doesn't determine how well a system flows.

eatmydst1234

I'm on mobile so I can't see your sig. If it is so restrictive why is it a popular upgrade for the pre-ltx cars to upgrade? The mufflers aren't that restrictive just too quiet. The res also isn't that restrictive, unless you are running a lot more power than stock, and it sounds like you have a fairly stout engine.

JackDidley

My L98 car goes through a single cat and back out through 2 mufflers. Now thats restricted.

powerpigz-51

I read a mag article where they put a 1300.00 Stainless exhaust system on a stock LT Vette, long tubes and everything. A gain of 6 HP was the result. I would post it, but it has been a few years. I would say the stock one was pretty good. I suppose there could have been a tune issue, but still.

ch@0s

I suspect the difference in HP was the LT headers.

How the hell .. I'm confused how does adding fastburn heads and a small LT4 cam make an L98 an LT motor. And you are still arguing that the LT1 exhaust is restrictive..why? where is the proof?

mcm95403

The cam is a duplicate of the LT-4 cam, the heads use the LT-4 exhaust ports and an improved Vortec port which is based on the LT-4 port. The only difference at that point (to me) is the intake manifold, half a point of compression, and the computer. Granted I have to go through a single cat, but if we're talking engines they're basically the same thing.

I realize I don't have the reverse flow cooling and optispark, but neither of those are power-producing items. The reverse flow cooling was supposed to be to allow for higher compression ratios but that being done with better chambers instead now.

Am I missing something?

ch@0s

Yes you are missing an LT engine for one and 2 proof the LT1 exhaust system is restrictive.

mcm95403

OK, so what you're saying is: If I had a 96 LT-4 car and rebuilt the engine using aftermarket:

crank
rods
cam
heads
rockers
intake
timing set
oil pump
Canton pan

that I'd no longer have an LT-4 - or does the block still make it an LT-4 after all the other parts have been changed out?

And of those parts, which made a power difference aside from the heads, cam and intake - and possibly the rockers?

Tell you what - if I ever hit the Powerball or anything like that just for everyone to finally have real answers I'll buy a few different cars, lots of parts and spend a bunch of time dyno'ing all the different combos so that the whole world will have dyno sheets to back up what does what.

ch@0s

Look, I get you are proud of your car and I kinda get your reasoning but an LT cam and Vortec heads on a SBC do not an LT4 make. If that is the case then there is no such thing as an LT4 because according to your reasoning its just like a L98 ..right? Or did I miss something and you have a LT block?

aboatguy

The reverse cooling and OPTISPARK..... are the two things that make a LT1/4 (GEN II) different than a GEN I Small block chevy.





MIke

PLRX

NO

You have a modified "L-98" engine.

aboatguy

In this scenario you'd have a modified LT4

MIke

QCVette

I was surprised to see them that small. When I put some different mufflers on my '94 I remember the pipe size was 2 3/4". I didn't realize it necked down to 2" at the tips. I have also heard that the LT exhausts were pretty good, but it sounds like they can be improved.

As for whether people call it an LT1/4 or L98, if it has a similar cam, similar ports, similar intake, and similar exhaust, shouldn't the power be similar too? Actually, I like that an L98 can be upgraded with parts similar to an LT1/4. It seems like a good reliable way to go.

cv67

They may be good for the 300 rating. If hes truly making 80 more with his 350 bet he could pick it up some; not a bunch btu some meaning it wouldnt be a wash a 3" collector header would really help
Take the tips to a muffler guy see if it will fit in his expander. Have a set here and wondered the same thing or do some cutting/welding and make them work.

I wont call your 350 any names I dont think it cares.

wingnut96lt4

Just my 2 cents My L T 4 has 3" exhaust. I cut the mufflers off and put muffler eliminators on. The pipes I got were 3" all the way back. If you read an artical in this site you can see where stock L T 4s were tested and the H P ran anywhere between 245 to 280 STOCK so this engine according to tune can be all over the block. But an LT4 IS an LT4. You may have a clone [close]

mcm95403

My plan at this point is to run 2.5" into them but instead of expanding them (which I think would just split the steel or the welds) I want to run the tube directly into the "upper" part of the taper above the 2" opening. I'll use the bottom of the 2" as the starting point, then open it up from there. It's kind of hard to describe, but when the time comes to start fabbing it up I'll post pics and that will make a lot more sense.