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Stopping Overboost With Iw

Finny

By Finny,
in Engines & Forced Induction

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Finny Community Regular

Finny

Posted
Posted (edited)

Hi all,

I am having big over boost issues with my KKR 480.

If I disconnect my actuator so the waste gate is fully open the car still hits about 25psi at 5000rpm :S...

The turbo is fairly new and the wastegate isn't getting stuck closed.

It makes no sence... you shouldn't really see any boost when the wastegate is fully open.

I had this same turbo on my VS commodore and that didn't over boost.

First time I boosted it with the KKR480 in it I saw my AutoMeter boost gauge hit the stopper so about 35-40psi and it blew one of my silicone joiners inside out when I ripped my foot off the accelerator and this is running with the actuator hocked up with no boost controller.

Edited by Finny
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-==L=a=N=c=E==- Rising Star

-==L=a=N=c=E==-

Posted
Posted

either the internal wastegate is too small, or your exhaust is too free flowing.

perhaps try a restrictor in your exhaust first, and if that fails, look at an external wastegate setup.

Finny Community Regular

Finny

Posted
  • Author
Posted

Yes my exhaust is very free flowing, Also jeff please read the tread before replying.

Problem is I want a low mount manifold because I just got my dump pipe and intercooler piping fabricated to suit the low mount but I am pritty sure there is no low mount external gate manifolds about.

PM-R33 Grand Master

PM-R33

Posted
Posted

I had the same problem as you man, turned out the dump pipe i had on my stock turbo wasn't the right size for the new turbo and the wastegate flap would hit the inside of the dump pipe when it opened and blocked it off. This ment that it would overboost something crazy just like you said. I ended up getting the wastegate pipe enlarged so the flap could fully open.

Disconnect your actuator and then open the flap and listen if it hits the dump pipe before it is all the way open.

PM-R33 Grand Master

PM-R33

Posted
Posted

Actually scratch what i just said above!

My car is still doing it!!! Went for a spin then with the actuator disconnected and still hits around 20psi!!

I had the dump pipe fixed the other day and the wastegate doesn't hit on it anymore so i thought it was sweet but after going for a test then its still doing it.

Looks like im still in the same boat as you buddy. So does anyone know what F***ing causes this??

Is it that the split dump pipe can't flow enough gases through the 1.5" wastegate pipe or what?

Finny Community Regular

Finny

Posted
  • Author
Posted

Dude KKR480s have a dump molded into the turbo so that its just got a V clamp back end. It is impossible to modify.

I got my waste gate bored out about 5mm all the way around so from about 20mm to 30mm and it made no difference, still boost spiking like crazy with the waste gate fully open.

PM-R33 Grand Master

PM-R33

Posted
Posted

Hmmm well i guess in your situation the dump pipe isn't the cause of it. I reckon in my case its the turbulance in the split dump in the place where it joins is that its not flowing into it and causing back pressure through the wastegate. This means that the exhaust gases go the path of least resistance through the turbine housing.

I might try to get an all in one dump pipe with no split, or just make mine into a screamer, which i dont really want to do....

PM-R33 Grand Master

PM-R33

Posted
Posted
I had this problem when i started tuning my ecu.

With the stock ignition map, the ignition is so retarded that boost is uncontrollable.

I fixed my ignition map and it was sweet.

Could it make it overboost that high from just the standard map :)

Finny Community Regular

Finny

Posted
  • Author
Posted

I have done some pritty mad tuning with my SAFC II so that this thing spools at 3000rpm I might disable my changes and see how it goes.

I also have maximum timing and a strait through 3" exhaust with a cannon, no mufflers.

I bored the wastegate out my self... but because I didn't replace the flap I bored it out about 1-0.5mm less than the size of the flap which is still a huge difference. I will bore it out further and change the flap and see how I go but I dont think its going to make any difference because the V clamp dump is too restrictive for a larger wastegate hole.

I really don't know why people say that the KKR 480 is a laggy turbo, my car is pritty much stock and it spools it before 3000rpm.

Haines Rising Star

Haines

Posted
Posted

so can having a car running too rich and retarded make it overboost

Ive never heard of this before

It may be the answer to my problem

mine doesnt overboost by too much i can still rev to around 6000 rpm before it boost cuts

PM-R33 Grand Master

PM-R33

Posted
Posted

Yeah i've never heard of it either Pedro, doesn't really make sense how a car running on a rich and retarded map would somehow cause the exhaust gases to go through the turbine instead of going through the wastegate. At the end of the day exhaust gases are just basic fluid mechanics, go through the path of least resistance, usually being the wastegate when it's open. So to me, any major overboost problem is caused by the wastegate pipe no longer being the path of least resistance, wether it's caused by turbulance or something else?

Has anyone had a major overboost problem, not talking about 1-2psi and found a way to fix it??

srf Rookie

srf

Posted
Posted

This is from http://www.sdsefi.com/

"In severe cases of retarded timing, the mixture is still burning when the exhaust valve opens. Because turbochargers are driven by the energy in the exhaust stream, high EGTs caused by retarded timing produce so much energy at the turbine that even a fully open wastegate cannot control the boost pressure. All in all, retarded timing is counterproductive to producing an efficient, durable, powerful engine."

So at the retarded map with a very free exhaust the wastegate cant flow enough. I had 20psi with stock maps and went down to 7psi with a advanced ignition map. nothing else was changed

If you did have a larger wastegate that would solve the overboost problem as would having more exhaust back pressure.

icemm Apprentice

icemm

Posted
Posted
I had this problem when i started tuning my ecu.

With the stock ignition map, the ignition is so retarded that boost is uncontrollable.

I fixed my ignition map and it was sweet.

how did you do it? (ignition map) manuali? or i can fix it by AFC NEO ?? ( i have afc neo) an if by afc neo what settings you did?

srf Rookie

srf

Posted
Posted (edited)

Na factory ecu tuning. the last load pont of the rb25det map for ignition is super retarded. If your hitting that point it would cause problems. I was hitting it on the rb25det ecu with a straight pipe and a intercooler.

Its just R and R which everyone goes on about.

Dont have a clue how to tune an afc.

If you bring down the afm voltage you could read of a lower load point i surpose?

Edited by srf

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