Question about UnitedMotorsport tune

Hi everyone, I got a question about the UnitedMotorsport tune for the 2.5L.

I got my car tuned a few month ago and the dealer told me he flashed UM Stage 2 on my car.

I'm happy with the tune, but I noticed something, since my car has been tuned, every time I release the gas pedal, my car make some "back-fire" sound, like some gas would not be burned and it would go through the exhaust.

Is this normal ? I asked myself this question this day, but I always liked that sound and thought it's normal, but it's probably not normal since I can't find similar case on the web.

Also, I don't find anything about Stage 2. UM seems to offer 3 versions: octane 91, octane 91/93 and SRI version.

Does someone know why my car is making back-fire sound when I release the gas pedal ?

Thanks for reading,
Kind regards.

FlowMK6 said:

Hi everyone, I got a question about the UnitedMotorsport tune for the 2.5L.

I got my car tuned a few month ago and the dealer told me he flashed UM Stage 2 on my car.

I'm happy with the tune, but I noticed something, since my car has been tuned, every time I release the gas pedal, my car make some "back-fire" sound, like some gas would not be burned and it would go through the exhaust.

Is this normal ? I asked myself this question this day, but I always liked that sound and thought it's normal, but it's probably not normal since I can't find similar case on the web.

Also, I don't find anything about Stage 2. UM seems to offer 3 versions: octane 91, octane 91/93 and SRI version.

Does someone know why my car is making back-fire sound when I release the gas pedal ?

Thanks for reading,
Kind regards.

Click to expand...

Two things, it's tuned for a bit of extra fuel availability for the extra power and the fact that you no longer have the original mid muffler installed which keeps everything quieter.

MLue1 said:

Two things, it's tuned for a bit of extra fuel availability for the extra power and the fact that you no longer have the original mid muffler installed which keeps everything quieter.

Click to expand...

Is that sound normal:

https://youtu.be/GFx3pP2kkXc

Could it be possible that it makes that sound because the dealer could have accidentally flashed the SRI version ? Because of the extra fuel, the stock manifold compared to the UM / C2 / IE manifold would stock less air and would not be able to supply enough air (since the intake valve close once you release gas pedal) for combustion and the unburned gas would burn into the catalytic converter thus resulting in back-fire sound without seeing fire ?

I have been driving with my USP catted downpipe for a week and never hear that sound and right after my car have been tuned it started to makes that sound.

Thanks again for your reply, it's fun to see that the 2.5 community is active

Is there any advantage of changing the fuel injectors for 550cc ? I have seen on the UM website, that they offer F/I tune. I think it's an option from the 2.5L performance upgrade of the rabbit, because when you select the rabbit, it shows the same page that the golf mk6 2.5. Maybe they don't offer fuel injector tune for the golf 2.5.

One thing at a time get your Exhaust legal then see what up then.

FlowMK6 said:

Is this normal ? I asked myself this question this day, but I always liked that sound and thought it's normal, but it's probably not normal since I can't find similar case on the web.

Click to expand...

Back in the day it was a feature for the Neon SRT:

MLue1 said:

One thing at a time get your Exhaust legal then see what up then.

Click to expand...

Finally I decided to keep my current setup, I'm shifting earlier and I try to be the more quiet I can on the city and I also stopped downshifting. I can't find cheap parts for the exhaust and it would cost arround 700$CAD to get a legal setup. Also it would be hard to find a buyer for my cat-back and even if I could sell it, I would lose so much money, I prefer to take the chance of getting new ticket for my exhaust, it is better to lose money on a long period than losing a lot of money on a short period, I know I'm not clear, english is not my main language and I can't figure out how to express myself correctly, I mean I prefer this : 169$ + 169$ + 169$ + 169$ + 169$ than 845$. Plus springtime is comming, so summer cars will be back on the road and the attention will no longer be on me.

red_stapler said:

Back in the day it was a feature for the Neon SRT:

Click to expand...

Yea, my car makes similar sounds. So this would not be an issue, but just a feature from the tune ? I should find some other people with UM Stage 2, just to know if they have the same sound.

I also noticed that on cold start, it doesn't make the sound and once the catalytic converter gets hot, the sound come back, so it's probably unburned gas, why there is some much gas being released ?

The UM tune greatly reduces rev-hang, which is the slow closing of the throttle plate (which controls the amount of air entering the engine) when you let up. As a result, after you have been hard on the gas pedal and suddenly let up, the throttle plate snaps shot, causing the mixture to favor fuel (rich) for a brief moment. And that unburnt fuel causes the backfire.

The UM tune actually makes the car run slightly leaner compared to stock tune. The stock tune is designed to run slightly rich to reduce engine temperature and therefore be slightly safer.

As far as 550cc injectors on a non turbo car, you'd have to get it custom tuned. I don't think there has been any N/A cars needing enough fuel to require upgraded injectors, and therefore no off-the-shelf tune available for it.


Peter

and how much the srt-4 pops on decel is quite annoying..... as if it's trying too hard to get people's attention....

gugu1981 said:

The UM tune greatly reduces rev-hang, which is the slow closing of the throttle plate (which controls the amount of air entering the engine) when you let up. As a result, after you have been hard on the gas pedal and suddenly let up, the throttle plate snaps shot, causing the mixture to favor fuel (rich) for a brief moment. And that unburnt fuel causes the backfire.

The UM tune actually makes the car run slightly leaner compared to stock tune. The stock tune is designed to run slightly rich to reduce engine temperature and therefore be slightly safer.

As far as 550cc injectors on a non turbo car, you'd have to get it custom tuned. I don't think there has been any N/A cars needing enough fuel to require upgraded injectors, and therefore no off-the-shelf tune available for it.


Peter

Click to expand...

Is it bad for the engine or it more hurts the internals of my catalytic converter ? I received an answer from UM, they told me that it's common for car with high flow exhaust, I don't know why car with high flow exhaust would make pop sounds when car with stock exhaust won't, is it because the air leave the chamber more faster ?

FlowMK6 said:

Is it bad for the engine or it more hurts the internals of my catalytic converter ? I received an answer from UM, they told me that it's common for car with high flow exhaust, I don't know why car with high flow exhaust would make pop sounds when car with stock exhaust won't, is it because the air leave the chamber more faster ?

Click to expand...

As a said earlier in the thread, if you install the original mid muffler, you won't hear the backfires with it in place.

MLue1 said:

As a said earlier in the thread, if you install the original mid muffler, you won't hear the backfires with it in place.

Click to expand...

I put back the stock cat-back and it is way more quiet. I did forget that a golf is that quiet... I'm already missing my Borla

Back-fire reduced but it still there, we don't hear it from the outside but sometime I can hear it like if it would be under my feet, sometime before the catalytic, sometime between the catalytic and the resonator.

I also noticed that I have more torque at low rpm, probably because the diameter of the piping is smaller, so the flow velocity is higher, high enough to evacuate the gas. But at higher rpm it seems that there is less gains, from 200 - 210 it's slower than before, maybe because the volume is smaller.

FlowMK6 said:

I put back the stock cat-back and it is way more quiet. I did forget that a golf is that quiet... I'm already missing my Borla

Back-fire reduced but it still there, we don't hear it from the outside but sometime I can hear it like if it would be under my feet, sometime before the catalytic, sometime between the catalytic and the resonator.

I also noticed that I have more torque at low rpm, probably because the diameter of the piping is smaller, so the flow velocity is higher, high enough to evacuate the gas. But at higher rpm it seems that there is less gains, from 200 - 210 it's slower than before, maybe because the volume is smaller.

Click to expand...

I think you are right in your assumption. The pipe size is correct I honestly believe the CAT is really restrictive as it has a very dense core so at high RPM, high exhaust gas volume it chokes.

gugu1981 said:

The UM tune greatly reduces rev-hang, which is the slow closing of the throttle plate (which controls the amount of air entering the engine) when you let up. As a result, after you have been hard on the gas pedal and suddenly let up, the throttle plate snaps shot, causing the mixture to favor fuel (rich) for a brief moment. And that unburnt fuel causes the backfire.

The UM tune actually makes the car run slightly leaner compared to stock tune. The stock tune is designed to run slightly rich to reduce engine temperature and therefore be slightly safer.

Click to expand...

Hi Peter, very interesting, this is something I'm going to investigate and tinker with.

Cheers !

I contacted UM asking them some informations about their Stage 2, like dyno chart or some numbers. I got an answer, they asked me where I got my ecu flashed, this doesn't seems like a good news. I have been trying to find the UM Stage 2 and I find nothing, it's like it would not exist and the dealer would have flashed something else like the SRI version, because I paid arround 720$ CAD for the tune which is the price for their SRI version and from what I can read on their website, there is only N/A version, SRI version, F/I version (for turbo car) and custom. No stage 2...

The fact that the dealer might have flashed the SRI tune on a car with the stock manifold could explain the back-fire sound, could it be bad for the car ? I drove against my friend with his 2010 Lancer, I did pass him but not that much and he missed a gear when I didn't and I was not able to lost him, I meant he always have the same distance with me even if I kept pressing the gas pedal. I also met a stock golf 2.5 ( not sure if he was stock because the car exudes a lot of smoke) but anyway, he did pass me pretty easily. I'm starting to think that he flashed the SRI version or a F/I tune and it does affect the performances + making that back-firing sound, which I can also hear with the stock exhaust system... Maybe I'm wrong and my engine's compression is bad, but I doesn't find anyone on this forum with a UM stage 2 on a 2.5. I have found one person on an other forum with the um stage 2, but he went to the same dealer that me.

Hi Flow, chances the dealer installed the UM Tune you paid for, the Canadian to US US exchange is really high.

I'm currently at my place in SC, there is a guy here with the UM 91/93 Tune and his 2.5 gurgles alot when he backs off, there is nothing wrong just unburnt fuel meeting air in an unmuffled system. You young guys get off on the sounds of open exhaust but as Guru quite accurately pointed out our normally aspirated engines require some back pressure to make power. The stock exhaust on the 2.5 was derived from the MK5 Rabbits and there are guys doing 14 second quarter mile tickets t the track, using the stock 55mm catback exhaust system and 15 inch steel wheels. That's one of the reasons I kept my stock mid muffler and only installed the GTI axle back muffler.

VW shafted us when they installed long 1st and 2nd gears in the 5 speed, that one of the reasons why the 2.5 doesn't accelerate like the GTI even with the the UM tune.