Thread: Turbo Isuzu Questions

I think my turbo is too small. I'm running a T25/T28. The turbo starts to spool at like 1000 rpm and by 4000 rpm it sounds like its going to fly right off.

Even at 100km/hr in fifth gear the turbo sounds like its being worked hard.

I think i need to upgrade to a large turbo. Whats a more practical turbo i.e perhaps one that comes on later in the rev range?

Also, aircleaner noise has increased 10 fold since installing the turbo which is contradictory to what others have posted. I'd have to say 60% of the noise emanates from the aircleaner- really pulsey sound

Cheers

Originally Posted by 110Landy86

I think my turbo is too small. I'm running a T25/T28. The turbo starts to spool at like 1000 rpm and by 4000 rpm it sounds like its going to fly right off.

Even at 100km/hr in fifth gear the turbo sounds like its being worked hard.

I think i need to upgrade to a large turbo. Whats a more practical turbo i.e perhaps one that comes on later in the rev range?

Also, aircleaner noise has increased 10 fold since installing the turbo which is contradictory to what others have posted. I'd have to say 60% of the noise emanates from the aircleaner- really pulsey sound

Cheers

Your tach is wayyyy out, 4BD1 is governed to 3200rpm. Have you checked and rechecked all the hose clamps on the pressure pipes from the turbo to manifold etc as they can squeal etc if pressure is escaping under boost. I coul've sworn my turbo had developed a problem until I discovered 90% of my silicon hoses were leaking past the clamps...

JC

Originally Posted by 110Landy86

I think my turbo is too small. I'm running a T25/T28. The turbo starts to spool at like 1000 rpm and by 4000 rpm it sounds like its going to fly right off.

Even at 100km/hr in fifth gear the turbo sounds like its being worked hard.

I think i need to upgrade to a large turbo. Whats a more practical turbo i.e perhaps one that comes on later in the rev range?

Also, aircleaner noise has increased 10 fold since installing the turbo which is contradictory to what others have posted. I'd have to say 60% of the noise emanates from the aircleaner- really pulsey sound

Cheers

T25/T28 is ideal size for a 4BD1 running 15psi or less. What rpm are you pulling in 5th at 100km/h? Real calculated RPM, not what that dodgey tacho is reading. That size turbo would normally run somewhere from 5-9psi at cruise depending on your rpm and your turbine housing size.
Or have you really wound the rev limiter screw out to 4000?

I had major aircleaner noise problems for a while, the cause was small air-gaps around the lid which howled under the extra suck of the turbo. Sealing up those gaps quietened it down nicely.

At 100kph in 5th gear the dodgy tacho reads about 2400rpm. Based on what others have stated engine rpm should be around 2000 under these conditions. I acknowledge the tacho is probably out by ~300-400rpm. I also have wound the governor out a tad so assuming the tacho is out its probably more like 3700rpm.

The sound that I refer to from the aircleaner isn't turbo whine (sucking) it's more like super prounced pulsey intake sound. Probably the best way to describe it is that it sounds like it did with no turbo except 10 fold louder such that my mates think it's running sick (but I know it isn't).

Also to my surprise increasing the fueling by about 1/4 turn (position when n/a - not factory setting) is about the most I can run without blowing out smoke. For instance during my tune-by-drive 1 full turn would result in epic black smoke- not sustainable. This is contradictory to what others with the same turbo are experiencing.

I'm thinking this is related to the abnormally loud aircleaner sound.

I will also look at tightening up all the silcone fittings (2no) for boost escaping.

Also could someone please confirm if turbo whine is crudely indicative of boost pressures?

To try and summarize the symptoms...

1) prounced pulsey aircleaner sound- sounds abnormally loud (60% source)

2) small adjustment in fuel screw over n/a position results in abundant black smoke (possibly starved turbo??)

3) power increase is rather timid (compared to what others have said- i.e time to reach 100kph is marginally quicker than when n/a- with ****load of black smoke)

Def not having a bitch (nor disappointed) just real keen to tap into some of the engines potential. Will happily post some pics when I'm back home.

Cheers

4)

P.s I'm running a 3in dump pipe into the existing tailpipe (joins near front left floor well) however I intend on running 3in (or 2.5in depending on loudness)

Fit an EGT and boost guage ASAP. It is impossible to tune the engine properly without them.

Some turbos whine/whistle, some don't. Offender90s whined much more than mine ever has, even though he was running low boost and NA fuelling at the time.

Are you using the stock air cleaner???

I have a boost gauge which I need to fit. Need to pick up an Egt gauge. The aircleaner is original but I've reversed it and shut off the original intake outlet (originally connected to snorkel). I wouldn't mind getting hold of a proper 4bd1t aircleaner or perhaps a new Donaldson filter

Originally Posted by 110Landy86

I have a boost gauge which I need to fit. Need to pick up an Egt gauge. The aircleaner is original but I've reversed it and shut off the original intake outlet (originally connected to snorkel). I wouldn't mind getting hold of a proper 4bd1t aircleaner or perhaps a new Donaldson filter

Remove the metal side cover on the filter housing (the filter will still work). If the noise stays the same, you have a leak between the turbo and the inlet manifold.