Gains/Losses w/SRT exhaust on WK 3.7?

[TimmyB]

I've had the SRT exhaust set-up on my 3.7 Laredo for a few weeks now and for some reason to me it seems to "lag" from stopped to giving it gas, like it hesitates. I deleted the muffler and added a Y pipe going back to the srt dual pipes over the axle to the two srt resinators out the rear. It does seem quicker on the highway when passing though compaired to my previous Magnaflow cat back exhaust. I've been searching online and have heard now that i have no muffler and two larger pipes there is now less backpressure and that "might" be bad for the exhaust valves and my performance might be down now. I did come across this post on a BMW site that kinda made sence.

Myth.

Modern BMWs don't have to worry about the effects of reduced backpressure, because the DME (car's computer) that controls the engine will detect that the engine is burning leaner than before, and will adjust fuel injection to compensate. So, in effect, reducing backpressure really does two good things: The engine can use work otherwise spent pushing exhaust gas (http://forums.bimmerforums.com/forum/showthread.php?t=1208398#) out the tailpipe to propel the car (http://forums.bimmerforums.com/forum/showthread.php?t=1208398#) forward, and the engine breathes better. Of course, the DME's ability to adjust fuel injection is limited by the physical parameters of the injection system (such as injector maximum flow rate (http://forums.bimmerforums.com/forum/showthread.php?t=1208398#) and fuel system pressure), but with exhaust backpressure reduction, these limits won't be reached.

Older cars (http://forums.bimmerforums.com/forum/showthread.php?t=1208398#) with carburators, could run lean due to reduced backpressure, and without adjustment, could lead to bruned valves in some cases, but outside of that, the slightly reduced backpressure of removing resonators or mufflers from an otherwise full length exhaust does NOT reduce torque, even a little bit. IN fact, it can often INCREASE power and torque, due to less restriction and better exhaust flow. If reducing backpressure reduced torque, then no reputable engine builder
http://kona.kontera.com/javascript/lib/imgs/grey_loader.gif
(http://forums.bimmerforums.com/forum/showthread.php?t=1208398#)would build or install free flowing cat-back exhaust systems or higher flow exhuast headers.


One thing I havent done is dissconnect my battery, thinking that might make the cars computer reconfigure itself for the new exhaust. Im lazy and dont want to reset all my stereo settings, but would it be a good idea to dissconnect the battery or would my cars computer already have reconfigured itself by now with the new exhaust?

[TimmyB]

Also, would making a true dual exhaust, meaning after the headers and cats weld on pipes that go back to an X pipe to the srt dual exhaust, deleting the single pipe I have in there after the cats have a better effect?

[DJ BoNiOmArIo]

great find and it all makes sense :)

[TimmyB]

hmm,

[DJ BoNiOmArIo]

ok ur second post didn't make sense ... but resetting ur jeep ... I heard from a mechanic that after 40 resets of ur vehicle meaning turning it on and off ur car will automatically adjust and reset to itself to any new thing added ...

[TimmyB]

ok ur second post didn't make sense ... but resetting ur jeep ... I heard from a mechanic that after 40 resets of ur vehicle meaning turning it on and off ur car will automatically adjust and reset to itself to any new thing added ...


My second post where I wrote about making it a true dual exhaust? If so, I meant instead of how the headers on each side of the motor go to one pipe I cut that off and have a single pipe coming off each header, just like the SRT exhaust. It shouldnt be that expensive to have done im thinking, and if it would free up more exhaust flow it might be worth looking into.

[DJ BoNiOmArIo]

sounds like a really good idea, and of course would free it up and make it better for the engine to breathe.

If you can do it on your own I would say that's the way to go.

I was thinking about doing the same thing to once I bolt on a turbo to my 3.7 setup.

My mechanic friend did a job like that once where he split the header exit pipes to make it into dual exhaust, it took him half a day to it with the right parts.

fyi a lot of people might say it's not worth it but I am firm believer in doing what you think is right for your car :)

[TimmyB]

I would want the pipes welded on after the headers so its not something i can do myself. I'd get all stainless steel, so I never have to worry about going under there changing out rusted pipes ever. I was just under there yestarday and think there is enough room to install the two pipes, as its done the same way on an SRT basically.

[FlyinRyan]

I told you about the true duals, you did not listen...

the burnt valves is BS, that comes from a lean AFR....

[TimmyB]

I told you about the true duals, you did not listen...

the burnt valves is BS, that comes from a lean AFR....


You told me?? Lol. Whats an AFR? And I was really not worried about the burnt valves myth with my WK because of the computer being able to reset itself. Just wanted extra extra advice on it thats all. You know how the net is, some people say this some people say that, was just trying to get the real deal info so i could fully understand it and why.

Sleepy4.7 I have read many of your posts on other threads and seems you def have alot of great info and have picked up a few things from you. thanks.

[FlyinRyan]

You told me?? Lol. Whats an AFR? And I was really not worried about the burnt valves myth with my WK because of the computer being able to reset itself. Just wanted extra extra advice on it thats all. You know how the net is, some people say this some people say that, was just trying to get the real deal info so i could fully understand it and why.

Sleepy4.7 I have read many of your posts on other threads and seems you def have alot of great info and have picked up a few things from you. thanks.

The computer has a very limited ability to reset/adjust it's parameters. It's for this reason that people need aftermarket fuel/spark controllers aka "tunes" to modify those parameters to achieve peak performance, especially when they add modified heads, aggressive cam profiles, etc.

The "real deal" is that you should have utilized a dual exhaust into the SRT catback, rather than throwing in multiple Y's , etc. There should also be a crossover pipe, such as an H or X pipe. Which you want to use is based on preference.

Backpressure is a myth. A motor needs as little backpressure as possible for peak performance, all the while maintaining air velocity.

AFR= air to fuel ratio.

[DJ BoNiOmArIo]

Ryan very impressive ... I am amazed on how much you know ...

Great to have you on here :)

[B.P.O.D]

good info ryan!

[Scottina06]

LOL...you are fine bro. Absolutely no need for the true duals unless you have major power adders going on the 3.7 in the future

[FlyinRyan]

LOL...you are fine bro. Absolutely no need for the true duals unless you have major power adders going on the 3.7 in the future

The point is that it's far more ideal to run a true dual setup. Theres alot of surface area for the exhaust gases to cover without a merge to help scavenging (expelling gases out faster) . running a exhaust setup that optimizes scavenging has similiar effects to adding displacement.

[Scottina06]

this is true...but on a truck that as he has said "I plan no more perfromance mods for" I was just saying its not really worth it unless he plans heavy perfomance mods. maybe he has changed his mind?

[05wkguy]

Less backpressure is better,yes,but it can cause some other problems at low rpm. Rough idle for one and some vehicle computers have a problem with transition throttle response,going lean during quick throttle adjustments. Sounds alot like what TimmyB is experiencing. Not dangerous but annoying.

Max power is definately acheived with minimum backpressure but it's the part throttle driveability that suffers.

[TimmyB]

I dont plan on doing any more engine mods to my little 3.7. But looking at it i dont see it being hard or expensive to cut off the stock Y pipe after the cats and have two straight pipes welded on back to the srt dual pipes at the axle. I took a picture of the exhaust layout page from my WK manual on disk, for some reason it wont let me cut and past the diagram.

http://i276.photobucket.com/albums/kk37/tdiglar78/DSC03138.jpg

Right now I have a single straight pipe on where the muffler should be. Right after where the muffler is shown in the pic is where my dual srt pipes start and i have a Y pipe there.

http://i276.photobucket.com/albums/kk37/tdiglar78/021.jpg

Here's my idea, install two pipes I drew in red in place of the single pipe i have on there now going to the dual srt pipes in there now shown in blue.

Right now I just think its odd how I have almost a "true dual exhaust" except for the Y and single pipe where the muffler goes. Im trying to research and understand if it will be beneficial to do what im thinking. Or would it make no difference.

[TimmyB]

this is true...but on a truck that as he has said "I plan no more perfromance mods for" I was just saying its not really worth it unless he plans heavy perfomance mods. maybe he has changed his mind?


Nope, you are correct. Im all about visual mods, and only did the srt set-up for the dual tips out the middle of the bumper. But since its on right now i'd be willing to go the extra step and add two pipes in place of the single pipe if it will be "better" for the motor and it might add a little HP.

Would a PCM flash help, though I really dont know what that is or does but I heard its a mod people do. Lol.

[05wkguy]

IMHO, it wouldn't make a sniff of difference. May however, change the exhaust note. True duals on a v-6 could be interesting to hear.....

[FlyinRyan]

Less backpressure is better,yes,but it can cause some other problems at low rpm. Rough idle for one and some vehicle computers have a problem with transition throttle response,going lean during quick throttle adjustments. Sounds alot like what TimmyB is experiencing. Not dangerous but annoying.

Max power is definately acheived with minimum backpressure but it's the part throttle driveability that suffers.

Not arguing but I have NEVER seen an issue with idle quality at low rpm relating to backpressure. The part throttle transition is a bit more plausible. I am not of the belief, however, that these are the problems Timmy here is seeing.

Before I started learning/studying EFI and the JTEC/NGC PCM through my own tuning and also in porting TBs for others, I was very into carb tuning for atvs/dirtbikes, motorcycles etc. A change in vacuum/backpressure would affect both areas that you describe, but it was because the carb was no longer jetted properly.

I am tempted to say that the above scenario sounds like a MAF-based system issue? Not MAP like the Jeeps.

From what I have seen the NGC PCM's do not as much of a capacity to adapt. They appear to be more fixed in their WOT fuel tables (i.e. you add a modification, the PCM will often not adapt much if at all to the newfound airflow, meaning a leaner WOT AFR) . The JTEC/JTEC+ seems to behave much differently in that regard.

[TimmyB]

IMHO, it wouldn't make a sniff of difference. May however, change the exhaust note. True duals on a v-6 could be interesting to hear.....


To be honest I would like to hear what it sounds like back there, im always driving it so never had a chance to have someone else take it for a spin and hear it. I added alot of soundproofing to my doors, cargo floor, and cargo door so its pretty quiet in the cabin.

Thats all I was looking for:

A- Am I ruining my motor having the srt set-up on?

B- Would I benifit from making it a full dual exhaust like I drew in the pic?

[TimmyB]

Not arguing but I have NEVER seen an issue with idle quality at low rpm relating to backpressure. The part throttle transition is a bit more plausible. I am not of the belief, however, that these are the problems Timmy here is seeing.

Before I started learning/studying EFI and the JTEC/NGC PCM through my own tuning and also in porting TBs for others, I was very into carb tuning for atvs/dirtbikes, motorcycles etc. A change in vacuum/backpressure would affect both areas that you describe, but it was because the carb was no longer jetted properly.

I am tempted to say that the above scenario sounds like a MAF-based system issue? Not MAP like the Jeeps.

From what I have seen the NGC PCM's do not as much of a capacity to adapt. They appear to be more fixed in their WOT fuel tables (i.e. you add a modification, the PCM will often not adapt much if at all to the newfound airflow, meaning a leaner WOT AFR) . The JTEC/JTEC+ seems to behave much differently in that regard.


I understood most things you said, not sure what NGC and JETC/JETC+ is though. Basically what I think you are saying is my cars PCM does not have the ablity to adapt that much from stock settings?? And if so would a flash help, or anything else for that matter? Like I said before, I dont plan on doing anything else to the motor but want what I have done to it working in "perfect" order if possible. This is the first vehicle I have ever done mods to, and have always had great luck with my previous cars running great and lasting long with just the basic oil changes and minor repairs.

[B.P.O.D]

timmy - sitting in the back seat is very different!!! i just tried it and i was like HOLY CHIT its LOUD back here lololol... needless to say i'll be doing some work in the rear cargo in the spring

[TimmyB]

timmy - sitting in the back seat is very different!!! i just tried it and i was like HOLY CHIT its LOUD back here lololol... needless to say i'll be doing some work in the rear cargo in the spring

I went crazy with soudproofing, and still not done all i want to do. I completely filled the cargo door frame with spray foam, covered the cargo floor pan with several layers of peel n stick membrane, spray foamed the framing behind the bumper, and shoved mineral wool insulation behind the plastic interior fender panels back there. I still want to undercoat the car, pull the seats and install peel n stick membrane on the floor boards under the carpet, and undercoat the wheel wells. I have a huge roll of lead I was thinking of laying under the front and rear seats too. I have access to waterproofing peel n stick membrane free from construction sites I have visited for work, so I have stock piles and it acts the same as Dynamat.

I have a full roll of it I can send you for just shipping cost if you want, goes for about $80 cost. Can do your whole cargo and floor area with a few layers of it with the amount thats on it. Its an asphalt based membrane so its not ideal for vertical applications like doors because it does get soft in high temps, but perfect for horizontal applications like floors.

[B.P.O.D]

timmy that would be sick bro!!! call me and we can discuss this more in depth... i def need to insulate!!!

[TimmyB]

Here's a cut sheet on the membrane.

http://www.chasephipps.com/documents/Carlisle%20Coatings/CCW-705%20TWF/CCW-705%20TWF%20Data.pdf

Its a 12"x 50' roll I believe or 100'. Its been in my basement for awhile now, and I have so much more other rolls I was just going to throw it out since im moving soon. I've used this over my cargo floor, used 3M spray glue to make it stick down really good.

http://i276.photobucket.com/albums/kk37/tdiglar78/DSC03170.jpg

http://i276.photobucket.com/albums/kk37/tdiglar78/DSC01129.jpg

[B.P.O.D]

that stuff looks good bro!!! i'll def take that from you!!!

[05wkguy]

I'm definately not trying to argue but i do speak from personal experience and have had a few mechanic friends confirm the idle issues. Nothing major mind you but just a rougness to the idle that wasn't there before. I do agree that it sounds like a maf issue but obviously can't be-but what we do know is that a MAP (aka:speed density) system is less tolerant of mods and combined with the down right anal-retentive computer systems on these jeeps, could contribute to an issue.

Oh, and Timmy,to answer your questions:

A) No
B) No

[FlyinRyan]

I'm definately not trying to argue but i do speak from personal experience and have had a few mechanic friends confirm the idle issues. Nothing major mind you but just a rougness to the idle that wasn't there before. I do agree that it sounds like a maf issue but obviously can't be-but what we do know is that a MAP (aka:speed density) system is less tolerant of mods and combined with the down right anal-retentive computer systems on these jeeps, could contribute to an issue.

Oh, and Timmy,to answer your questions:

A) No
B) No


I wasn't implying that you were trying to argue- I don't know if I came off that way, but if I did it wasn't intended. I think this is a great discussion so far.

Most of my experience has dealt with speed density systems in general so I can't confirm this detail, but I have heard that MAF systems are much more dependent on custom tuning. Since a MAP system is dependent on reading pressure, it typically has some "wiggle room" , because pressure in most cases does not change a great deal. Airflow (read by a MAF system) is a different story, it would seem.

The way I see it, the greatest concern with MAP systems the idle/low speed areas of the tune. For example with a big cam the vacuum drops greatly and MAP voltage fluctuates due to overlap/reversion etc.

The computers themselves are not really the problem. You see, GM and Ford tend to share their programming language with the aftermarket. DCX on the other hand does not, which means that any company looking to market a DCX tuning product, they literally have to basically "translate" tons and tons of code. It's reverse engineering to the nth degree. Because of the various revisions of the PCM over time (JTEC has 16 revisions alone) it's an enormous task. This is why we do not have full tuning capability.

[FlyinRyan]

I understood most things you said, not sure what NGC and JETC/JETC+ is though. Basically what I think you are saying is my cars PCM does not have the ablity to adapt that much from stock settings?? And if so would a flash help, or anything else for that matter? Like I said before, I dont plan on doing anything else to the motor but want what I have done to it working in "perfect" order if possible. This is the first vehicle I have ever done mods to, and have always had great luck with my previous cars running great and lasting long with just the basic oil changes and minor repairs.

NGC/JTEC are the "languages" of the PCMs since 1996. Well, technically they are two different types of controllers.

What you think I am saying is correct, the PCM has a limited ability to adapt to any kind of modification. It can adapt to weather changes, but anything beyond that it only has a partial understanding of whats going on.

A PCM flash/tune is set to a specific set of mods. If anything it's configured to adapt LESS than a stock calibration (to minimize torque management, performance loss due to heat soak, etc).

[TimmyB]

Thats odd, I was googleing something just yestarday and I came across an article on heat soak, but I just started to read it then had to leave.

And I will be 100% honest in that now I do experience a slight rough idle from time to time, I notice this when im sitting in my car with it running during lunch break for awhile, but doesnt last and its very minimal. Seems like the rpm's get low. Its nothing major, and maybe it even happened before and I just never noticed it. Im going to really start paying attention when im driving so I can tell in detail exactly what its doing, but it seems the low end isnt as good now but the highend is better.

[Scottina06]

jeep sare notoroius for rough idles in the lower rpm's while idling. My 4.7 did it from the time it had 7 miles and no mods

[DJ BoNiOmArIo]

^ mine has been doing it lately ... thought I was going crazy good to know I'm not the only crazy one :)

[FlyinRyan]

There are several reasons as why you may have a rough idle...in some cases it is part of the PCM calibration (low idle saves gas), in others it is due to a clogged/gunked up IAC valve.

[TimmyB]

Whats an IAV valve? When I start my WK the rpm's are high, around the 1k mark. Then after just sitting there on lunch break it goes down to about 500rpm and stays, idle seems to be fine but once in awhile it will drop below that and appear rough for a minute or two then go up again. Im not concerned really and prob think its normal, but if there's something I can clean to help it i'd do it. I do have the K&N CAI and people have told me the oiled filters can screw up the intake parts from the oil being sucked in, but im very careful to only add enough oil on the filter during cleaning so its not sloppy soaked with the oil, if anything I dont put enough on.

I have a can of Gumout air intake and throttle body cleaner, would it be good to remove the intake tube and spray some into the TB?

[FlyinRyan]

Whats an IAV valve? When I start my WK the rpm's are high, around the 1k mark. Then after just sitting there on lunch break it goes down to about 500rpm and stays, idle seems to be fine but once in awhile it will drop below that and appear rough for a minute or two then go up again. Im not concerned really and prob think its normal, but if there's something I can clean to help it i'd do it. I do have the K&N CAI and people have told me the oiled filters can screw up the intake parts from the oil being sucked in, but im very careful to only add enough oil on the filter during cleaning so its not sloppy soaked with the oil, if anything I dont put enough on.

I have a can of Gumout air intake and throttle body cleaner, would it be good to remove the intake tube and spray some into the TB?

Idle Air Control valve. it's plugged into your TB, should be the right hand side. It tends to get gunked up with oil and so on, so it should be cleaned, and in the long run replaced over time.

the K&N thing applies mostly to MAF systems, in other words, that's a non-issue for you.

TB cleaning is a good idea to do occasionally but you have to remove the IAC from the TB to clean it.

[TimmyB]

I have about 70k miles on my 05 WK right now, bought one year ago and have no idea what the previous owners ever did to it. I was thinking spark plugs cleaning the TB and now that IAC valve.

For the valves and injectors do those bottles of cleaners actually work? On my previous 94 GC it had over 200K miles on it and would start to run like crap so i would put a bottle of the high mileage injector/complete fuel system cleaner in the gas tank and it did seem to run better for awhile.