Atr43G3 Lag Monster After Rebuild

[Daza33]

Hi guys, so I am just after a bit of advice about this problem of mine. Last year I did a forged rebuild on my rb25 after burning out exhaust valves and scoring the bore. Since the rebuild my atr43g3 is 1000rpm laggier than before the build.

I get 19psi at 5000rpm, whereas I used to get that at 4000 before the build. I am thinking it may have to do with my cam timing since I had the head skimmed and the block decked. I dropped the standard cams back in, lined up the marks but didn't adjust my exhaust cam gear so it is currently set to 0 degrees. The car sits at 18mmhg at idle when it used to be at 22-24mmhg before the build as well.

Other than the turbo lag the car runs smooth, makes 301rwkw but only sees 220rwkw at 5000rpm, making it a nugget off boost.

I am thinking of retarding the exhaust 2 degrees tomorrow, but thought I'd get your opinions before I do.

[rondofj]

Check timing with a timing light? Easy to do

[Daza33]

Ignition timing is all good, 15 deg at idle. Vehicle has been tuned but the tuner didn't play with the exhaust cam gear.

[Ben C34]

Skimming the head and block would retard the cam timing, but only very slightly.

Regarding the exhaust cam will mean you will pull even less vacuum.

I would consider advancing both cams and seeing what happens.

Is vct functioning correctly?

[hypergear]

As mentioned above. Check VCT, and Actuator preload.

[scotty nm35]

Last year I did a forged rebuild on my rb25 after burning out exhaust valves and scoring the bore. Since the rebuild my atr43g3 is 1000rpm laggier than before the build.

If all is mechanically ok, there is a chance the high exhaust temps from the failed valves have warped the rear housing on the Hypergear, and now the wastegate puck won't seal fully. I have seen this before, it's not hard to check if the back of the turbo is flat still.

[jay-rod]

Scotty has seen it personally on mine

Same turbo, though my lag wasnt as bad.

[Daza33]

Well 2 months ago I fried my power fc when the Vct solenoid died. Got it repaired and put a new solenoid in, I can see it switching through the hand controller. Guess I'll disconnect it and take for a drive.

As for the wastegate, I've got close to 5mm of preload on it and have fabbed up a screamer for the internal gate, doesnt creep open it just snaps open and makes a shitload of noise.

One last thing, if I were to adjust the cam timing is it going to throw out my tune at all?

[scotty nm35]

It doesn't matter how much preload you put on the puck, if the back of the turbo is only a little warped, it will never make a seal.

Cam timing would need to be out a fair bit... Yes it will affect the tune.

[hypergear]

The wastegate flapper has a smaller tolerance of play that is to compensate for any changes might be during heat expansion and contraction of the turbine housing. beside Jay, your rear housing was cut and welded to suit an external gate.

This particular car has an external screamer. For 1000RPMs difference, The take would be half of the 38mm gate. It will be making a very noticeable sound. OP have replied on an earlier post as the screamer does not make any noises till the gate opens. Plus this behavior was not present after the new engine was assembled. In my opinion The waste gate assembly on this turbocharger is unrelated.

I'm not sure how bad the older engine was damaged. If bit of failed engine ended up in the turbine housing, then it might be accounted for a damaged turbine wheel. It could rise the lag issue also, how ever on the same time it is not capable of making any power.

I have experienced similar issues in the past when my VCT was dis-engaged, since it has been previously burnt, functionality of the part might be questionable. Simply unplug the solenoid and feel for the changes in drive ability. No differences usually means malfunction in the VCT assembly.

The adjustable exhaust gear makes pretty much no differences working with stock cams, It was the first thing I've tried improving boost response and that was a waste of dyno time.

[jay-rod]

Yeh i meant before mine was welded, and was internal setup.

But 1000rpm difference is alot, so something defiantly not right, whether it be the turbo damaged or engine doing something strange.

[methz]

I put my money on vct, when mines turned off its around 1000rpm laggier. check it!

[Daza33]

Ok thanks for the responses guys, I'll unplug the Vct and go for a drive this afternoon

[Daza33]

So vct definitely works, so I can rule that out.

Only other thing I can think of, and will check tomorrow, is that I changed the exhaust after the rebuild. It now has a nismo kit from cat back and now has a mid muffler and oval rear opposed to the cannon that it had before.

[R31 POWER]

What the compression ratio now with forged pistons?

[Daza33]

8.5:1 although I did get then cometic mls head gasket which may have dropped it a bit. Doing a standard compression test shows 170psi across all 6

[CEF33Y]

What boost controller are you running? EBC? same settings as before?

[Daza33]

got a turbosmart bleed, same as before, holds boost perfectly. Ball and spring design

[scotty nm35]

To lose 1000 rpm of response you would need a pretty restrictive exhaust, think 1 inch...