Compressor surge at 10psi steady

[STP]

Ok, buildup is as follows...274" production headed offcenter, front mount, JC-45 .82 housing (i know it's small), 83's, FAST, stainless headers, etc....Just put the FAST on it and decided to take it out to tune on it a little on the interstate. With copilot I did a 0psi pull, 5psi pull, and a 10psi pull just to see where the A/F was at. While holding it steady at about 7psi the compressor wheel starts to surge. Anyone have any experience with this? New one on me...Wide open it's fine, just needs more turb on it. Could this turbo be flowing more air than the engine needs at 10psi? Or vice-versa, engine flowing more air at 10psi than the turbo can provide at same psi? Blow off valve needed? Thx Scott

[qwknuf6 jr]

Scott
It is common for the 45 turbo to surge between 7-10 psi boost ,steady load ,at least on stock mtrs ,and since you have stock heads ?

[STP]

Well, I'm going to remedy the head problem here shortly. It didn't surge before I put the FAST and the headers on it. Strange...When it surges it ralphs a little blue smoke out of the tailpipe. Probably oil seeping by the piston ring in the turbocharger.....Really just curious as to why it's doing this.

[bruce]

Originally posted by STP
With copilot I did a 0psi pull, 5psi pull, and a 10psi pull just to see where the A/F was at. While holding it steady at about 7psi the compressor wheel starts to surge. Anyone have any experience with this?

Try pulling a lil timing out, and or adding a smigeon of fuel in that area of the map when it's doing that.

[Eric Stage I]

That big inch motor is spooling that 45 very fast. Your right, its supplying too much volume of air for that particular throttle angle. It should help when you go to a bigger turbo. I had a PT51 on my 4.1 motor for a while and it surged horribly. I changed to a PT70 and it stopped with no other changes.

Eric

[odell4o8]

scott, your valve spring is on its way. by us mail. i picked up a new 2500 hd truck with 6 liter motor it is a dog compaired to my 1500 4/4 i havent tied the 8000 lbs trailer to it yet,, you should get your spring by friday.

[TurboTR]

If you're doing this at part throttle, which it sounds like you are, then it'll surge like that all day. Assuming you don't have some tuning issue making it misfire. The problem is that you've built pressure, but since the throttle is ~ closed the airflow is too low. This moves the operating point in the compressor map to the far left, past the compressor surge line and presto, off it goes. We all just learn to drive around the surge issues with bigger compressors. In the end it's not a big deal really for most of us. You just won't be able to hold a low boost setting by closing the throttle.

TurboTR

[Reggie West]

If you have the FAST unit you need to datalog the runs and then go have a look at them.

Check to see if the VE table is way off. You can overlay the WB02 readings to the VE table and it can tell you where you are rich or lean in any given cell.

The surging could also be because there is a big variance in between cells too.

You should be able to smooth out the surge in the fuel map. I really doubt that the compressor is what is causing that.

If it is not the FAST then the surge is being caused by too much backpressure. In other words, you need a bigger wastegate. A 274 inch motor likes to breathe and that means more exhaust gases sooner than a stock motor.

[STP]

OC- Thx again..I'll be looking for it. I doubt that 6.0liter will be a dog with that enclosed behind it.

Thx for the responses guys. As far as lowering the timing, I took 4 degrees out it across the board. Still surged. The wastegate is a 46mm Tial unit with 1 3/4 tubing. Surely that will suffice?? When I got back to the garage I looked at the VE table...For some reason or another there was one block around 7psi that was 199!! Doesn't the FAST "average" 4 blocks for reasons such as this? Dunno how this got changed to 199, this is a borrowed program. Haven't run the car since I fixed that...Could one block cause it to do that if the FAST averages 4 blocks? The other three blocks on the VE read 58, 62, and 72. The 45 is small, plan is to put it on my driver and upgrade to a ~76 when the heads go on...Thx

[Reggie West]

Yeah that 199 is definitely the problem.

The highest value in the VE map should be 100 as in 100%. That value should be at max torque on the table.

The wastegate you have is big enough so that should control it.

I would recommend you keep the boost at 5 psi, datalog the runs make two for comparison, get the map trimmed up and proceed from there.

[STP]

That figures...Found a 199 in the a/f table as well...Driveability is fine. Gotta get her to the dyno for some tunin. Thx again