Dynamometer Results & Comparisons - Cut out comparision

OK, lets try posting here. and i will try to summarize the point

So Im thinknig 3 inch cutouts dupped after the headers before running my 2.5 inch true duals and crush bent overaxel set up.

Mr Luos made a great point by saying he didnt care what power he made with the cutouts capped because at the strip he would run them open

so i believe he made a great point because the cut outs will eliminate back pressure causing more hi end power at the strip and with them closed i will gain back pressure and low end power (that will suffer a bit from the crush bent overaxel piping

however, some are saying i will ultimately loose power thruought the curve because of the cut outs being open....

right now im bolt on but this will someday soon be a 500-600wrhp FI car...

thoughts? dyno comparisions? track time comparisions? anything>?

My old car gained 21rwhp on back to back pulls with the dual cutouts open versus closed. It gained throughout the whole pull and never lost anything anywhere.

what was your exhaust and how big were your cut outs?

My best mph at our local 1/8th mile was 92.4 before the cutout, through the stock catback with a dynomax muffler. 94.2 mph after the cutout with it open. I have LPP 1 3/4" headers and the cutout is located where the stock catback would have met the header y pipe neckdown.

how consistant were these and what tires were you on? was it at the same track? same tires? ...same year even?

Dual 3" cutouts right after the headers and an original loudmouth1 catback.

Dual 3" cutouts right after the headers and an original loudmouth1 catback.

and that is a very low restriciting catback... i wonder what the gains would be over catbacks that ACTUALLY have something that resembles a muffler

I really wish I had gotten a graph. We did the back to back runs open and closed just to prove to a friend that the cutouts were worth alot more than just noise. Me and my tuner knew it would make a pretty big difference because when he tuned the car with them closed, opening them changed the A/F ratio almost a whole point leaner.

Well looks like ill have to show this comment to a guy i work with. He keeps saying theyre worthless

IMO, they are worthless, if you have a good flowing cat back.

I had a 412ci LS2, it made 519rwhp in 2005 with open Kooks 1 7/8" headers. We put the Magnaflo cat back on with the kooks 3" into 4" Y pipe and it made 512rwhp. Then put dual 3" QTPs and dual Randomtech metallic cats. Put it back on the dyno with the cutouts closed and it made 478rwhp. Open the cutouts behind the cats and it made 511rwhp.

So it still made 511rwhp through the cats for a loss of only 8 hp.

You can only have your tune correct in either open or closed, your pick. I prefer full hp when ever you want it.

BTW, had 5 cutouts fail in one season, 2 different brands. Driving home 40 miles with one failed open. That has to be bad for the motor.

Thats why im buying manual cutouts. Im 19. I dont
Mind climbing under there haha

You have true duals, you are wasting money if you run a straight through muffler

IMO, they are worthless, if you have a good flowing cat back.

I had a 412ci LS2, it made 519rwhp in 2005 with open Kooks 1 7/8" headers. We put the Magnaflo cat back on with the kooks 3" into 4" Y pipe and it made 512rwhp. Then put dual 3" QTPs and dual Randomtech metallic cats. Put it back on the dyno with the cutouts closed and it made 478rwhp. Open the cutouts behind the cats and it made 511rwhp.

So it still made 511rwhp through the cats for a loss of only 8 hp.

You can only have your tune correct in either open or closed, your pick. I prefer full hp when ever you want it.

BTW, had 5 cutouts fail in one season, 2 different brands. Driving home 40 miles with one failed open. That has to be bad for the motor.

Your CATS cost you 34rwhp and your cutouts got you 33 of that back with the CATS on there...looks to me like they wasn't worthless at all! Wonder what you would have done with cutouts and no cats!

Dont plenty of people run duals thru muffler or "resonators"?

Dont plenty of people run duals thru muffler or "resonators"?

Thats what true duals are... x pipe with 2 mufflers (dual mufflers)...

Thats what true duals are... x pipe with 2 mufflers (dual mufflers)...

thats what i thought too but i dont know what blk98vert is talking about
:lurk:


You have true duals, you are wasting money if you run a straight through muffler

Your CATS cost you 34rwhp and your cutouts got you 33 of that back with the CATS on there...looks to me like they wasn't worthless at all! Wonder what you would have done with cutouts and no cats!

No, cats cost only 8hp. The turbulence of the closed dual cutouts caused a loss of 34hp.

No, cats cost only 8hp. The turbulence of the closed dual cutouts caused a loss of 34hp.

like i said. i wont care about performance with the cutouts closed.

and i dont need cats because we dont have emissions

like i said. i wont care about performance with the cutouts closed.

and i dont need cats because we dont have emissions

Understood, but what will you tune for, open or closed? One of them will have the potential of harming the motor. Rich can wash down the rings, lean can cause knock and damage the rings and pistons.

You seem to know what you want. I am just trying to tell you the pitfalls, I have tried a lot of them. 1 HC motor, 3 strokers motors and all the stuff that bolts on to them. I like well thought out engineered solutions over hack jobs. I had cutouts too, and tried to do it right, I just realized what a hazard and waste they were. Everyone talked about how great they were, they were not that great.

good point.

is there a way to have two tunes and be able to switch between the two?

i mean i know there is but how do i do that?

Rampant and I have talked about this in the past. It shouldn't be an issue with HP tuners switching to a "cutout" tune from a street tune. I'm have a single 4" manual cutout which comes off an 10" extension that is after my flow master merge.

Rampant and I have talked about this in the past. It shouldn't be an issue with HP tuners switching to a "cutout" tune from a street tune. I'm have a single 4" manual cutout which comes off an 10" extension that is after my flow master merge.

It does not stop me from trying to educate those, young and old of my hard learned mistakes. :cheers:

Did I just call you old? :-)

good point.

is there a way to have two tunes and be able to switch between the two?

i mean i know there is but how do i do that?

As Orange Juice said, if you do not mind switching with HP Tuners you can do that. I recall some one made a dual ECU deal that was switchable, but do not know if they built it or not, or if it worked.

Frost offers one. I might check into that and the hptuner

I dynoed the same with closed cutouts as I did with no cutouts...no turbulence problems there...Your CATS cost you more than 8rwhp...If they didnt, more people would run them and not care about the performance loss.

Mine gained 10 rwhp 10rwtq back to back. This was when my car had bolt-ons only with pacesetter headers, ORY, flowmaster muffler, and a 3.5" cut-out

I dynoed the same with closed cutouts as I did with no cutouts...no turbulence problems there...Your CATS cost you more than 8rwhp...If they didnt, more people would run them and not care about the performance loss.

Reread the posts, they did not!

It made 511 with them, 519 with out. It went 11.0@129 thru Cats. The 478 was thru cats cut outs closed, 511 was cutouts open thru cats. The 512 was thru the full Magnaflo no cats. All pulls 1 day apart same dyno and tuner.

As for the guy picking up over a Flowmaster, the are known to be terrible cat backs.



I have some real special ones on the car now. Hoping to see over 600 rwhp with cats and passing Canadian emissions. We will see how that goes in a week or two. They are OBDII certified too. Not cheap though.

3 1/2" inlet, 4 1/2" OD.

https://public.blu.livefilestore.com/y1pvJweiYkWxiUQMRy_wQwcn2-USnSTM1mxx9iVMPsI8W-lQIzYlq9DHDaKB-evtTiffmlepZURQA7EFQe566LO3w/IMG_7018.JPG

how consistant were these and what tires were you on? was it at the same track? same tires? ...same year even?

Same track, within the same week with about the same weather conditions 90 degrees and humid. They were both on 295/50R16 M/T ET Street DRs. 3 runs with each setup and they were all about the same mph with each setup.

btw, it's a manual cutout, I only use it at the track and I just take the cover off when I put my ET Streets on. I probably wouldn't have bothered with a cutout if I had a good high flow catback but it was easier to spend $32.99 on the cutout vs $400 on a magnaflow kit with tips I dont like. Plus it just sounds cool!!!

so some people it hurts... and other people prosper...

from what it looks like... its more of a tuning issue... and the bigger the power(bigger CI or FI or N02), the more benefitial the cutouts are...

is anyone else picking up on this pattern?

so some people it hurts... and other people prosper...

from what it looks like... its more of a tuning issue... and the bigger the power(bigger CI or FI or N02), the more benefitial the cutouts are...

is anyone else picking up on this pattern?

Where do you see that trend, I made 512rwhp through full exhaust, no cut outs and 519rwhp with open headers. Has anyone else that commented made more than 500rwhp? It was my 412ci LS2.

The 478 was purely turbulence from the cut outs. All the power came back when we opened them. No extra power though. Not sure where people are getting lost on this.

I see people with crappy Y pipes and cat back (especially restrictive mufflers, like a Flowmaster) are picking up more power and have little more than stock bolt on motors.

That said, I do think you can gain 10ish rwhp, I just prefer to always have it all on tap all the time. Maybe that is just me.

Where do you see that trend, I made 512rwhp through full exhaust, no cut outs and 519rwhp with open headers. Has anyone else that commented made more than 500rwhp? It was my 412ci LS2.

The 478 was purely turbulence from the cut outs. All the power came back when we opened them. No extra power though. Not sure where people are getting lost on this.

I see people with crappy Y pipes and cat back (especially restrictive mufflers, like a Flowmaster) are picking up more power and have little more than stock bolt on motors.

That said, I do think you can gain 10ish rwhp, I just prefer to always have it all on tap all the time. Maybe that is just me.

ive been searching throughout this forum, tuning forums, and ls1lt1 and that seems to be the trend

lol i get slammed for not searching and then i get slammed for searching... i just cant win! haha

12:1 396 LT1

Dual 3" open cutouts after the headers - 414 RWHP
Decent y pipe and a 3" dynomax ultraflow - 400 RWHP

torque curve beefed up, but that dynomax muffler was a good piece!

were they cutouts capped in the 400 pull or were they not even on the car then>?

Capped.

I also had a single 3" cutout setup with a magnaflow out back, different dyno, that was 410 RWHP single cutout open, 390 RWHP cutout closed through the muffler. No clue what my true duals made after that.

I think a dual exhaust or even a single 3.5 using a dynomax ultraflow or hooker maxflow would be the perfect system.

My car has duals (no crossover) with dual cutouts 12" behind the collectors.

Back when I had 2.25" exhaust over the axle the cutouts were worth 2 tenths and 1.5-2mph in the 1/8th mile.

Once I had 3" exhaust from cutouts to mufflers with 2.25" tails they still gained a tenth and 1 mph.

Once I had 3" from cutouts to mufflers (except a shitty joint right at the collector which was still 2.25" and entered the 3" pipe at a 45* angle) with 3" dumps after the muffler they gained little to nothing.


Since then I have corrected the joint in front of the cutouts. My exhaust guy couldn't make a tight 3" bend so I was stuck handicapping it with a 3" to 2.25" reducer welded at an angle into some 3" pipe at the collectors. This meant the exhaust left the header into an extreme bend necked down to 2.25" for a length of 2" then into 3" to a cutout to 3".

I'm curious to go back and see if I gained anything losing the 2.25" and if the cutout might start helping again since now the mufflers are a bigger restriction than the shitty joint at the collector. I know for a fact it drives a lot different in the low-mid range with a proper 3" setup all the way back.

It obviously depends on the setup as every car is different. I could care less about dyno numbers, the proof is in the pudding with track results, I gained almost 2 mph in the 1/8th because my stock cat back piping and dynomax muffler are restrictive. If you have a better flowing exhaust the less the gains will be:cheers:

My car gained a total of 20RWHP and 19RWTQ on back to back dynos with the cutout closed then open, I had the car tuned with the cutout open. I am sure alot of my loss comes from the single 3 inch catback after the 4 inch cutout and y pipe. my motor makes way to much power and to big of cubes for a single 3 inch to not lose anything. im sure if I had a good tru duel setup the loss would not of been as great but for now i noticed a difference in how it runs with it open vs closed. I also dont see how anything could be damaged by a exhaust that is a bit restrivie or un restrictive, after all how many people actually get tunes after going to a different exhaust with no cats and a catback?

OP my point is that unless you are running a big muffler with multiple chambers or a turbo muffler there is no point to adding cutouts on a true dual setup. With a muffler like an XR1 or a Magnaflow they are straightthrough mufflers, so you are bypassing something that has no more restriction than an open section of pipe. I can understand running a quiet muffler like a full size Borla or Magnaflow and using the cutouts to make it loud when you want to but there would be nothing to be gained by running them. Does that make sense?

Yeah i understand. But if (and when) i go to d1sc or even f1a, its best to get the exhaust out asap because the procharger so throwing so much air down its throat.

It seems like anything with big power needs a good air intake and a good exhaust out take.. And what with dual 3" cutouts after the headers, you cant get much better flow than that haha.

But troy said a few posts above.. I looks like it does depend on the setup.
Cutouts may be overkill right now, but for future expansion, it looks like they would benefit me.

What I am trying to say is that it wont matter, you would be bypassing a straight section of pipe. If you want it for sound do it but it wont gain, as stated you have nothing to bypass unless you are running a full size chambered muffler

Well the magnaflows I am looking at are pretty large and will not flow as much as resonators or bullet mufflers

All magnaflows that I know of that have a single inlet and outlet are straightthrough, so again there would be no restriction to bypass

What about the crush bends?

i still vote for the dynomax ultraflows if you can fit them. Maybe you can even run a dual in dual out in the back of the car. my high comp motor made about 5 more RWHP with that muffler then a magnaflow.

see this is why i am going to use cut outs...
if i want sound... closed

if i want performance... open

ill tune it for open becuase it will only be a few off and not enought to hurt the engine (people run new exhaust without tunes all the time)

IMO, they are worthless, if you have a good flowing cat back.

I had a 412ci LS2, it made 519rwhp in 2005 with open Kooks 1 7/8" headers. We put the Magnaflo cat back on with the kooks 3" into 4" Y pipe and it made 512rwhp. Then put dual 3" QTPs and dual Randomtech metallic cats. Put it back on the dyno with the cutouts closed and it made 478rwhp. Open the cutouts behind the cats and it made 511rwhp.

So it still made 511rwhp through the cats for a loss of only 8 hp.

You can only have your tune correct in either open or closed, your pick. I prefer full hp when ever you want it.

BTW, had 5 cutouts fail in one season, 2 different brands. Driving home 40 miles with one failed open. That has to be bad for the motor.

You are making misleading statements/observations.

You made:

-519 open headers
-512 trough a Magnaflow exhaust (loss of 7hp)
-478 after adding cats and cut-outs(loss 34hp)****
-511 with cut outs open (gain of 33hp)


****I believe the majority of this loss was due to adding cats as opposed to the claimed "turbulence." If you had added cats only (no cut-out) the loss would have been similar.

You can't say the loss was ONLY attributed to the cut-out since you made two modifications(added cats and cut-out) on that dyno pull.

Am I right or missing something?

You are making misleading statements/observations.

You made:

-519 open headers
-512 trough a Magnaflow exhaust (loss of 7hp)
-478 after adding cats and cut-outs(loss 34hp)****
-511 with cut outs open (gain of 33hp)


****I believe the majority of this loss was due to adding cats as opposed to the claimed "turbulence." If you had added cats only (no cut-out) the loss would have been similar.

You can't say the loss was ONLY attributed to the cut-out since you made two modifications(added cats and cut-out) on that dyno pull.

Am I right or missing something?

When the cutouts were open, it was after the cats. How can they be leading to the majority of the loss. It is at most 8hp. With no cats and the same exhaust it lost 7hp. With cats and cutouts it lost 8hp, no more, no less. I have spent the last 25 years in mechanical engineering, I kind of understand this stuff and math. With cats, full exhaust and no cats it might have lost 15rwhp(7+8) on a 519 rwhp set up. It went 10s through the cats at full weight. If you go back and do a search on Randomtech cats back in the mid 2000s, nothing flowed close to them, they also cost a fortune. My new ones will out flow the Randomtechs.

You can believe what you want, but your current assumption, is 100% wrong, I was there and have the dyno sheets to prove it somewhere here. It was quite interesting doing all the back to back stuff, and it cost me for all the extra tuning and dyno time, but that is how I do things. I want to truly learn from the experience and gain first hand knowledge. Not internet hearsay.

Same as all the flow bench time to experiment with things on my Harrop intake, and gained 45cfm through it, and know what each individual change resulted in to get that total. Not all my experiments resulted in gains though.

Sorry to the OP, this is a little off base,

I personally am more interested in a refined sound, smooth idle, pass emissions, and make lots of NA torque and power with no road side hassles or interest from the local constables.

i just like em for sound. the neighbors really love mine!

What about the crush bends?

Crush bends? In what the muffler?

no i ment if i had cut outs... it would be to bipass the crush bends overaxel

If your mufflers are before the axle its still a waste of money as long as the bends arent drastically tight.

they wont be before axle

here is where my mufflers will be
http://i1271.photobucket.com/albums/jj631/jadedbird/tech%20posts/exaust2.jpg

crushed bends over axle

summit x pipe
with extra piping crush bent to get it where it needs to be

still debating between 2.5 and 3 inch

This is how mine is setup if it helps, cheap, easy and it works!


http://ls1tech.com/forums/picture.php?albumid=24496&pictureid=91449

no bad. i wish it wasnt a federal law that muffler shops cant work on cars without cats

why is it easier to buy drugs than it is to get a damn exhaust welded

Cutout location in my old 1998 Z28...look closely to see them both before the ypipe...
http://i9.photobucket.com/albums/a73/moez28/My%20old%2098%20Z28/034.jpg

See thats about where mine will be as well.