Little about the car before I get into the issue I am currently having. '03 Evo,


Engine:

Brand new fully built engine,:
Manley rods
Wiesco pistons
Head is fully ported and polished including the combustion chamber
Kelford 272's
BC springs and ti retainers
Supertech valves
New valve guides

Turbo:

Buscher Racing 20G
Full Buscher 3" exhaust
3" Elbow
JM Fab FMIC
ETC 2.5" IC
Tial BOV
MAC EBC

Tuned - 427 WHP 369 lb-Ft 26 PSI

Alright so, I do not normally really use fifth except for cruising. I was in fifth today just to see how well she would pull and @ 19-20~PSI I feel a lack in power and the car is making a "wom, wom" sound. A/F is still at a nice rich 12.5, boost will not really go up, it just kind of creeped up a tiny bit but basically would rise much. I was able to continually hear the noise and lack of power was very noticeable. Car runs beautiful in 1-2-3-4, peaks at 26 PSI~ car pulls hard. The compressor surge (that is what I believe it is, does not happen until about 19-20~ PSI, so it won't happen at WOT or partial throttle under 19-20~ PSI.

Any thoughts? Anyone have this happen before, any preventive measures I can take? The only two things I can think of is, don't use 5th gear at lower rpms, or have the boost controller mapped to 5th gear to gradually allow boost as respective RPMS.


Thanks! and Cheers.

 

Your first problem is thinking 12.5 AFR is "nice and rich"

It does sound like you are experiencing surge. What RPM are you at when doing this in 5th?

 

I wouldnt mind be a little educated on 12.5 not being too, rich, when I think of 12.5 I feel it's not drowning my cylinders, so maybe I said the wrong wordage sorry - I first tried it at about 4K RPM and when 20 PSI hit the issue began. I then wanted to see if I could replicate it, I placed the car in 5th at 50 MPH and began to begin boost, once it hit 19-20 ~PSI same issue, I am not sure of the speed at the time. I was checking A/F and Boost. I would like to figure out what to do next.

 

The lower the Air Fuel ratio the richer the mixture , higher number means leaner.

On a turbo car the richer fuel keeps combustion chamber slightly cooler EGT’s. Too rich is also not good.

Whats considered good A/F ratio ? Well that depends on an individuals car setup, but for general purposes mid low 11’s is considered good A/F . Factory tune has something like low 10’s for either safety margin or something in that nature reasons.

Also it depends on what RPM’s your in, really low rpm range will be slightly leaner but your shouldnt be pulling WOT that low anyways unless its 1st gear.

Unless your running some sort of alternative fuel that burns “cooler” or meth/water injection etc.. The 12.5 is actually very lean for a turbo setup, unless something has changed as of recent about cars and tuning that Im not aware of.

 

Surge is caused by insufficient airflow for the boost that it's making.
If it's going to surge then it's going to show up in top gear.
When the air consumption increases, the surge will stop.
It'll be surging in all gears but because the revs pick up quickly in lower gears, you go through it and don't notice.

The cause is that the turbo isn't matched properly to the engine.
If you still had a stock BOV you wouldn't notice because they're designed to leak and in doing so the airflow increases.
An anti surge housing does the same thing only it's not anti surge, just less surge.


Making the AFR overly rich.......that'll reduce the power, spin the turbo slower, get you out of the surge region.

Easy fix........don't use 5th at low RPM.

 

It's been fixed this way before: if you have wgdc=100% under x rpm on, disable it and lower the duty cycle. This really depends on wastegate spring, preload of available etc. You will stop forcing shaft speed during surge remedying the situation by slowing the rotating assembly down some.

disregard too much turbo for the engine, that just sounds negative!!

 

Yeah its previously been said but that is NOT RICH, 12.5 is lean AF for these cars, you also shouldnt be going WOT in 5th gear, never boost that much with such load.

 

Using 5th gear at low RPM'S and flooring it is extremely hard on the motor. It really serves no purpose when another more appropriate gear can be uses.

 

Easiest remedy, Don't use 5th gear at high load, low RPM, I was just making sure it was compressor surge. The car will be getting a different turbo in time, I just wanted to make sure I was on the same page. Also I looked, under full boost, my AFR is actually 11.2-11.5 - I must have looked a the AFR at a different moment.

Thank you all for the help.