dbs1vette

I had this 416 in my 02 camaro prior to it catching fire at the track. It had a 3" free flowing exhaust with no cats, 1 7/8" tsp headers and a dyno max stock style muffler on it. Changing out to 2 bullet style mufflers raised rwhp from 510 to 525 with 3.73 gears.

When I put the same 416 in the 04 Z it showed 515rwhp using ARH 1 7/8" catted headers with x pipe to the stock TI catback setup and the stock 3.42 gears.

Although the Z is lighter it did not seem to pull on the same cars like the camaro did going down the straight. Same tires for the road course and the gearing in the Z trans should get me similar zip as the gears in the camaro, so I had it on the dyno today just to test the diff with the current setup vs unbolting the catback to see if I would gain anything with cutouts.

Dyno showed an 11 hp gain with just that change and shop felt they could pick up another 6-8rwhp with more timing and less restrictive muffs, which if like the camaro I would feel on the top end.

I'll be leaving the stock TI there for now, but at least I now know what the gains would be with cutouts. Thought I'd pass it on. Thanks!

ajrothm

Interesting...Thanks for posting..

So basically you made a pull on the dyno, then immediately dropped the TIs at the flanges and made another pull right then?

Or different pulls on different days?

I just built cut outs into my XS Power cat back, basically bypassing 75-80% of the muffler when the cut out is open. I haven't tested it yet to see what the gains are but...I'm hoping for something.. My cat back is 3" into the muffs, where it necks down to 2", has a 180* bend inside, then a 2.5" outlet... so hardly a true 3" system.


If you gained 11hp on a 500 rwhp car, would it be safe to say one would gain 20-30hp on a 900hp car? I'll track test mine this winter with the cutouts open vs closed and see what the verdict is...

I'd take 20 rwhp all day long though.

Sigforty

You may have something similar to what I have going on. It appears the exhaust pulse with your new setup does not like the exit length of the stock Ti exhaust. I resolved mine by adding cutouts. While it does not make a big impact on peak HP, it does however make one on midrange torque. Below is a dyno graph of my cutouts open vs closed. If you look at the torque curve between 3500 - 4500 rpm you will see the change of about 30-40 rwtq.

95wht6spd

Exit length, are you speaking of just the length of the tips on mufflers?

dbs1vette

Yes, pulls were within an hour of each other. Dyno'd, dropped stock catback, dyno'd again.

I'm interested in cutouts, but with the problems with elec versions, and only really wanting to open them at the track where I typically have a jack and jackstands anyway, I may just install some manual ones far enough away from the composite spring to not do any damage.

At least that is what I'm currently thinking.

And I'm guessing the higher hp car you have, the more benefit one would see from bypassing the stock TI exhaust.

Sigforty

The exit length is the length of the entire exhaust system. There are optimal lengths for the best power given your engine, headers, cam, valve sizes. If you do not have the right length you will see a reduction in midrange TQ like I have shown.

There are not too many issues with the electric cutouts. I have had the DMH cutouts on my car for almost 6 years now. I had to replace one right at the 4 year mark because the motor fell off. I am not sure if that was the cutouts fault or my dad who drove my car that day it was lost.

I think the main reason you see the issue is not because of the Ti exhaust, but because of pipe sizing. On most aftermarket header systems like LG, you get the headers and 3" pipes back to the stock mufflers. The stock mufflers and almost all aftermarket mufflers only have 2.5" pipes. That reduction in pipe size is what I think causes the exhaust pulse issue that we see as a power drop. I have not been able to prove my theory, because I have not bought a LG big 3 exhaust. I think if someone would do a direct swap from a stock Ti exhaust to say the LG big 3 we could truly see how the 2.5" pipe restriction is impacted.

dbs1vette

With the expereince on my 02 camaro using this same engine, I think you are correct on all 3 accounts-

1. TI mufflers are restrictive.
2. 3" piping all the way out is more conducive to higher hp/tq.
3. Optimal length is indeed part of the equation.

My camaro was about a 80% track car so I could live with the loud exhaust and bullet style mufflers in the quest for the most power. This Z is about a 80% street car so the quieter stock exhaust is more inline with its use.
On the last road race that the camaro was in prior to its burning up session I was side by side with a 2010 ACR viper that I normally would slightly pull down the straight up to 150ish. On that day he pulled me and I was not sure what the deal was. It was not until several weeks later when I was parting out the car that I discovered the shop had reinstalled the "street" exhaust back on the car with the more restive stock style muffler and more bends, as well as necking down to 2.5". On the dyno it gave up almost 30hp at the top end for the trade off in power (and still was not quiet enough to meet the sound restrictions at one of the tracks).

I remember thinking I had a plug wire off or something and could actually feel the power diff in the butt meter as well as seeing it with that viper pulling me by 2 car lengths. Those 3 items indeed make a diff.

I'm planning on giving the Tx mile a try in Oct. Not sure how I'm going to try to access that additional 10-15hp as I'm planning on driving there from AZ, but the manual cutouts seem to make the most sense right now.

ajrothm

Here is a thread I started on the subject and the mods that I did to try to improve... I have not track or dyno tested yet to verify gains but... I will be during the winter months when it cools off..

I'm HOPING to gain 20-30 rwhp with what I did....But it wouldn't surprise me if I didn't gain anything...

http://forums.corvetteforum.com/c5-f...t-testing.html

Breze84

You notice the difference no doubt when it comes to exhaust flow. With a H/C 427 in my C5Z I picked up 35whp without a tune from going from 1 3/4 x 2.5" with cats to a 1 7/8 x 3" no cats... I want to throw some cutouts on and see If I can pick up a couple tenths...

PeteZ06

Hmmm.. This makes me want to drop my cats!!

dbgoodwin

Interesting. I wouldn't think 10rwhp would make that big of a difference. Personally I would think the gears were more the issue. Looking forward to more info!

dbs1vette

Just a report back...I was hoping to put some cutouts on before running the TX mile at the end of Oct but my tuner/shop owner was concerned that without a different tune for the cutouts the car would not run properly and with driving it all the way down (800miles/15 hours) I opted to not do the cutout thing.

Besides being 90 degrees when it's typically 65 the car just did not pull well at the higher rpms. It's interesting that without being able to run the car this long at wot ever I hadn't realized how bad the power drops off at wot.

It's very noticeable and having been able to push the former car with the same engine at a track with a 2.5 inch exhaust and transfers muffler (02 camaro) vs running it down same track with straight 3" exhaust and low restriction bullet style mufflers I'm sure this stock TI exhaust is most of the issue.

It would have been nice to been able to switch from one tune to the other with cutouts. I'm guessing I left 2-4mph out there even in hot weather as I did on the camaro down a 3/8 mile track. Bummer!!!