vikingdiesel

My car felt very fast, with my current mods of ec pulley, ec mids headers with primary cat delete, intercooler with Johnson pump, tcu, tune and k&n filters. I had a complete 3" exhaust put on today with no resonator, secondary cat delete, x-pipe and also a belt wrap kit. Got it retuned and it sounds fast but for some reason feels slower, I saw 9psi on my boost gauge. Is it the tune or did the exhaust really slow me down? Also when cruising my afr gauge shows between 13ish to 15ish with being in the 14 majority but when I'm slowing down and letting off the gas it'll get to a brief 16-17 and then show nothing until I give it gas again, is this normal? The prior tune/setup would immediately show no reading when I let of the gas and never would I see 16-17 even though it's literally less than a second. Is this all normal?

TheTherapist

You should be way higher than 9psi - with your mods I would think 13 or 14 psi? I'm no expert in these matters but I'd be checking for a vacuum leak and/or checking to make sure your tune is optimised for your exhaust and other mods.

Hulk

Measure boost in 3rd gear to redline and what is the boost?
If you have the EC sc pulley then he is not at 13-14psi. Probably more like 11 or so

TheTherapist

Oh do an adaptive trans reset also just so you know that's performing optimally.

cnterline

That's a lot of stuff done ,you had TCU tune AND a new engine tune ? Also lower boost after the belt wrap kit ,I'd check the tension on the belt ,they may have given you the wrong belt ,

HeissRod

He would have gained boost with the EC pulley, but then lost boost with the headers and full exhaust. However, I would think that 9psi is a little low.

TheTherapist

Yeah you're right of course, I was a little overly optimistic but regardless with the belt wrap also he ought to be on 12psi I would have thought?

HeissRod

BWK doesn't add boost. It only keeps you from losing the boost you are making due to belt slip.

cnterline

If by accident they gave you the wrong size supercharger belt with that belt wrap kit and it's too big that wouldn't help boost that's for sure ,I would check that first then go from there ,typically I see high boost numbers when I go into 3rd and higher numbers going into 4th ,then they start coming down.

MJ50

retune is #1 suspect IMO...

Hammer Down

A number of factors: wrong belt size which would cause belt slippage, new tune, loss of primary & secondary cats....... You guys have to remember that supercharged engines like some back pressure. I have to believe there is a reason why AMG chose the pipe size for our cars. I still have the factory h pipe, secondary cats, resonator and stock modified (for sound) mufflers

kponti

Supercharged engines do not require backpressure, in fact there is hardly any efi engines that requires backpressure for torque

SICAMG

Correct. Problem is that smaller pipes will flow at a faster velocity. Larger pipes will not. Pipe diameter has to be right on the money to flow enough volume and move the air as fast as possible.Exhaust "pulse" also plays a big role as to when and how fast the air is moving out. We do not want the pulse's to collide with each other or they will slow down and effect exhaust flow. Heat plays a big role to. Keeping the heat in the pipes will increase the velocity as well.

vikingdiesel

I'll check the belt and tune on Monday, thanks guys

sircl55amg

the exhaust mod you did will not slow you down for sure,must be someting else

vikingdiesel

How about my afr numbers when I'm letting off?

Hammer Down

In relation to boost it does. If you remove the cats and add larger diameter pipes your sc will run more efficient but it will produce less boost due to the less restrictive exhaust.

sircl55amg

dont worry about afr went you let off .. it's when you WOT you need to monitor most.. what is your afr at WOT ?

vikingdiesel

High 11s, low 12s at wot

Hulk

Is that a 3rd gear pull to 6k rpm

mobhouse

I literally have the same mods and my car definitely feels faster after I did the exhaust work. I can try and check what my boost levels are

sircl55amg

usually we see a bit ritcher ( 10.8 to 11.5 ) but its ok ,over 12.5 its risky

so it looks to be belt slip

vikingdiesel

I'm seeing like 7-9 psi and I saw 11 spike otherwise I'm seeing 7-9psi in 3rd gear

Hulk

It's not belt slip
If it was it would be spiking up and down

vikingdiesel

So tune then?