Aww.. Pls Help Me.. Turbo Surging Under Load.

[R32-PSH77]

Hey guys, i really need a hand trying to get my car not to surge under load..

I recently installed a larger turbo to my car of a T3/T4 nature.. using an Rb25 exhaust housing bored out and steel wheels with a t4 compressor wheel 60mm blade. This setup is running on my Rb20 currently not runing a After market Ecu as im still shopping for one. it has the supporting mods. However my problem lies with Labouring/Load of the engine.

For Example. High way Driving 5th gear around 100km/h depress accelerator and slowly makes around 5psi before it start to splutter boost needle rapidly going back and forth. You can tell its suffering. its not coils.. and i hardly doubt boost cut when it happens at only just 5psi..

the same affect can be done from climbing hills in 4th.. under load.

I REALLY REALLY want to enter the QLD dyno day thats happening on the 24th of this month thats only days away.. but..

If the car is driven under load in 4th gear like they will do at a dyno im afriad it will just surge.. and not make any power.. and the car will have to be pulled of the dyno.

I guess i could miss this dyno if its not logical to try it.. or ther is no fix for this problem..

Any help would be greatly appreciated

Regards, Adam

[BHDave]

Whether you fix it or not, put it on the dyno and identify the problem.

Did you really expect it to run properly with no tuning though?

[Beer Baron]

i would say it's the fuel cut. there is no such thing as 'boost cut'. it doesn't cut fuel based on boost, it does it based on airflow. so a larger turbo could be flowing the same amount of air at 5psi as a small one is at 14psi. so my solution is get a new ecu, or have the stock one re-mapped with the fuel cut removed.

[blind_elk]

It's compressor surge - the engine simply can't ingest the increased fuel / air charge being supplied by the larger turbo.

You had better find that aftermarket ECU pretty quick if you want to impress on the dyno.

[discopotato03]

Usual "high flow" issues , the "turbo" sounds like it was put together by someone with no idea . Doing it with factory engine management was not a good idea because the std system only knows how to deal with standardish states of emmision tune .

Slide knows plain bearing Hi flows so talk to him , a good price for a known quantity . If you show him your turbo he can explain why its giving you grief .

Cheers .

[Dale FZ1]

It's compressor surge - the engine simply can't ingest the increased fuel / air charge being supplied by the larger turbo.

You had better find that aftermarket ECU pretty quick if you want to impress on the dyno.

I agree on the point of it most likely being compressor surge.

But not with you on the new ECU.

The surge is related to the physical capacities of the engine vs compressor. Changing an ECU won't cure surge. But obviously it will give him the freedom to tune decent AFR + ignition once the surge issue is corrected.

[R32-PSH77]

I never thought it would run Any good with the standard ecu. im currently in the market for an aftermarket ecu.. still weighing up my options. i was just hoping it to actually just make a reading so i can compare it to the dyno tuning when i finally get my aftermarket setup. i can have the turbo on as low as 7 psi.

obviously though as i thought its a Rb20 " beinge to small" to push the turbo problem.. something thats not really gonna be easy to fix. oh wells.. i'll just sit and watch.. Maybe next time i can enter.

Thanks for your help anyways guys.

Cheers, Adam

[Dale FZ1]

obviously though as i thought its a Rb20 " beinge to small" to push the turbo problem.. something thats not really gonna be easy to fix.

Adam just as a point of reference, check this page: http://www.turbobygarrett.com/turbobygarre...bo_tech103.html

which gives a bit of technical info on what causes surge.

Basically, it's not the case that the engine is too small to push the turbo, rather it is too small to ingest the turbo's output once the turbo is allowed to crank up to a certain pressure ratio (ie. boost level).

And yes, once diagnosed it's not easy to fix without some $$. Ported shroud housings and BOVs can/do mask the event, but you do need to be in the ballpark first off. Sometimes not too easy when you're dealing with high flows either.

Best thing is there are some very knowledgeable traders out there with a wealth of proven high flow specs so you're not out on a limb.

From previous posts you should be able to tootle around with a lower boost level without coming up against the surge issue. Let us know how it works out for you.

cheers

Dale

[benl1981]

Where you able to tune this out mate?