A Chart for those changing exhaust

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Feb 6, 2006 | 05:08 PM

#21

GREGGPENN

Thread Starter

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From: Overland Park Kansas

2020 Corvette of the Year Finalist (appearance mods)

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Quote:

Originally Posted by LT4POWR

Lighten up, Francis…just didn’t want everyone jumping on the L98's should be using 2.25" duals (factory size) and LT1's should be using 2.5" duals (factory size is 2.75") bandwagon. I also didn’t see anything about mufflers when talking about the exhaust system.

You say you don't want every jumping on a bandwagon (above) but no reason is given. Do you sell exhaust? The chart I referenced is on a manufacturer's site THAT MAKES MUFFERS. If that was important, don't you think they would have referenced it?

Besides providing a link to a chart that MIGHT be useful, I was curious if real-world experiences supported the numbers provided. Based on all the owners who think modifying (and increasing) exhaust size is such a good improvement, the whole topic seems worth debating. By posting this link, a debate is what I hoped to start.

If you don't have evidence to dispute the chart, that's fine. Even if you say something funnier than your "kicked in the nuts" comment, I'll laugh. Directly translated, you're joke implys that early C4 owners should be ashamed if they consider their stock L98 a "performance car". In a Corvette only forum, how well do you expect that to be received, Eleanor?

Feb 7, 2006 | 02:35 PM

#22

stearnman

Instructor

Joined: Mar 2005

Posts: 178

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From: Thornton CO

I know in my recent quest to better understand my LT1 stock exhaust and it's restrictions another poster/member at CAC put in this link: http://www.zr1specialist.com/HAT%20W...ckpressure.htm

Granted, it's based on a ZR-1, but the overall message in the link was taking about back-pressure losses at different point in the entire exhaust system (well, starting at the exist of the exhaust manifolds).

The article showed 5PSI (all measured @ 7000 RPM for an LT5) before the cats, 4PSI before the resonator, 4PSI before the muffler, and 0PSI after the muffler.

Biggest restriction being the muffler area (4PSI loss. Could be the tappering down of the pipe to enter the muffler?). Next being the cats at 1PSI loss.
;shrug

Feb 7, 2006 | 03:46 PM

#23

mikey whipreck

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Joined: Jun 2004

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Quote:

Originally Posted by GREGGPENN

Is it any more of a stretch to call a dual system with a Xpipe or Hpipe true dual? In all three setups (Xpipe/Hpipe/Ypipe), the separate exhaust sides are merged/joined in order to stabilize/match engine bank pressure.

Seems worthwhile to look past the hype and figure out whats real.

Have you ever actually seen an L98 exhaust?

And for what it's worth, the factory piping on an LT1/4 engine does slim down to a dual 2.5" pipe through the resonator. I dont' think anyone with a stock engine has ever complained about their stock LT exhaust anyway... other then maybe the sound.

Feb 7, 2006 | 06:12 PM

#24

GREGGPENN

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From: Overland Park Kansas

2020 Corvette of the Year Finalist (appearance mods)

C4 of Year Winner (appearance mods) 2019

Quote:

Originally Posted by mikey whipreck

Have you ever actually seen an L98 exhaust?

Absolutely. In fact, here is a recent pic of the LT1 and L98 side-by-side.

I can understand why you say the L98 is not a true dual system. From my viewpoint, neither is a system with an Xpipe, though. Semantics.

Feb 7, 2006 | 06:26 PM

#25

GREGGPENN

Thread Starter

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Posts: 12,221

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From: Overland Park Kansas

2020 Corvette of the Year Finalist (appearance mods)

C4 of Year Winner (appearance mods) 2019

Quote:

Originally Posted by stearnman

Thanks for the link! That's exactly what I would have guessed. And, that's exactly what I replaced several years ago.

Now, I'm trying to decide what other changes are worth pursuing in the exhaust system and that's how I came across the chart initially posted.

The question in my mind is whether larger pipes and/or headers significantly increase an L98's performance vs. merely shifting it. That is to say -- shifting the power band to a higher RPM.

It also seems unclear (or at least explained) how backpressure actually HELPS a motor. If backpressure helped open/close valves, I could understand it. Does it? If so, does it influence air/fuel "throughput"? Descriptions like scavenging and pressure balancing don't really capture what's going on. At least not for me.

Please know, I was all for increasing my L98's pipe size and making my system true dual (w/o any friggin x/y/z pipe)! Then I started reading. And, we all know how bad that is!

Feb 7, 2006 | 09:41 PM

#26

CentralCoaster

Team Owner

Joined: May 2002

Posts: 24,337

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From: San Diego , CA Double Yellow DirtBags 1985..Z51..6-speed

John Lingenfelter and David Vizard both say exhaust backpressure is a bad thing.

Here's some good reading:

http://www.geocities.com/MotorCity/T...92/vizard.html

Last edited by CentralCoaster; Feb 7, 2006 at 09:52 PM.