I have an H22 with an OEM RB25 turbo; full boost by 2700rpm, and response at higher RPMs is near instantaneous. As such, my wastegate cant seem to keep up with the turbo. It will spike to boost cut if I go full throttle in 3rd gear or higher, unless I roll into the throttle gradually.

The boost reference line is tapped into the charge piping ~1ft from the compressor and uses less than a foot of vacuum line. Converted from internal wastegate to an external Tial 38mm.

Stock MAP sensor so I cant raise the boost cut any higher. I asked my tuner about rescaling my map for a 2.5bar sensor but he didnt feel comfortable "e-tuning" it without datalog info (neptune without an RTP board, so I cant datalog)

Ideas?

 

bump! need suggestions! Would vacuum line inner diameter play much part in this? I just looked at the Tial specs and they specify 6mm I.D hose...thats freaking huge!

 

This is one of those instances where your wastegate placement is above and beyond much more important than anything else. Pics of your manifold?

If I had to take a guess from the info provided, I would guess that your main issue is that your manifold gives priority to your turbo and not your wastegate, and when you get on it and get that instant spool up you're initially getting very little air (comparatively) through the wastegate. Instead, you're forcing the manifold to build back pressure which in turn makes the wastegate the priority (it becomes the low pressure system in the exhaust flow and exhaust will take that way out first).

Bigger line may help with response time of the wastegate, but I'm unsure if that will actually help your problem.

As far as doing the rescale, I don't forsee there being any issues. The rescale shouldn't change your tune that already exists whatsoever. I've done it quite a few times with no issues.

 

my revhard manifold used to spike in low gears as well and the wg placement was pretty decent on that manifold. do you have a pic of the current setup?

also what size line are you using? 6mm = 1/4" which is the standard for all vacuum lines on a turbo setup. your line may be too small

 

isn't this turbo internally gated? if so i'm in for this..i spike too

 

I believe it is, good call.

 

 

he converted to external

 

I have a "DRAG" manifold. Really terrible wastegate placement unfortunately... but its what I had to work with to make this turbo fit with the internal setup I ran previously

 

Uh, the Revhard manifold has an awful wastegate placement. 90* placement off of a single runner is not "decent."

OP, "drag" manifold is the same thing. I don't think you'll ever actually cure the issue, the turbo just responds too quickly for the wastage to catch it. If it was still internally gated I doubt you'd have any issues at all.

So... probably best to get that new MAP sensor on there and tune for the spike. Shouldn't be a big deal.

 

Yeah, this was never an issue with the internal wastegate. Guess I'll further look into getting the map re-scaled. Thanks for everyone's help!

 

damn you hit me with a crooked face...that hurts. i said decent becuase at least the revhard design was slightly better than drag's design. closer to the collector and pulled from the #2 runner some. every inch (or half inch) counts right?

 

OP, as mentioned above, poor manifold design and a small turbo are the cause of your issue. The turbo spools so quick it takes a second of the wg to catch up. Have you double checked your line size?

 

Sorry to bring that old topic up again, but i have the same issue, never the less use a much better WG/Manifold design then the Drag/Revhard manifold.

Was there anything which helped?

 

What helps is a properly designed manifold or dual wastegates.