So I wanted to start a new thread to get feedback on boost spikes. I've spoken to a few people and it sounds more common than people think, but it's hidden by the very slow resolution of the boost gauge.

I'm tuning alpha 2873s with an 84mm anti surge cover. I've been battling boost spike for a while now. First with the new greddy EBC - 1.4bar spike that settled to 1.2 bar. Just went back to N75 and I'm seeing about a .2 to .3 bar spike. It's worse in the lower gears especially 2nd and 3rd.

What I would like to hear is if anyone else is seeing similar. What did you do to get rid of it? I've looked at 3 a28 cars logs this week, and all of them had it. It go as far as saying that I think most of us with small frame turbos, pushing 1.25+ bar actually have this problem, but it's hidden. Our tuners have us do a pull in 4th gear from 2k, but this doesn't reflect how we really drive...

 

FYI - Im using the new oled greddy profec - which charts boost real time. You can see how quickly it ramps and if it peaks, drops or keeps climbing. This is the only reason I found the boost spike.

 

Just curious but what are you running for wastegates? The stock style? Aftermarket gate? Do those turbs utilize the factory exhaust housing? If it's a common thing for these setups, is it possible that the gate can't bleed off exhaust gas fast enough? I've heard similar issues for particular turbochargers that require bigger gates to avoid boost spikes like this. Just thinking out loud.

 

Bingo! 2873 (same compressor wheel as a 3073) has too much back psi.. If you could open up the turbine A/R that would help (not on a Alpha) or maybe even have the clearances between the turbine and housing increased to allow some psi to escape.

 

I'm running billet actuators with 1bar springs.


I dont think the wastegate is the issue - because just on wastegate it goes straight to actuator pressure and hold spot on to redline. If the wastewater was to small I would see boost creep. To me it feels like wastewater response - the long lines coupled with the pickup and twin turbo setup. I had been throwing around the idea of running dual port actuators and picking pressure up of the turbo

 

Tim - back psi is something I have been considering. It also has an effect on the wastewater. I really like the 2873 setup, spool is about 200rpm slower the 2868 but boost and temps upto are fantastic.


Do billet 16s 24/18s or any other small frame turbo experience this. Clearly a28s hit pretty hard down low, and have been associated to bent rods (the other thread made me ask this question) - but my research is convincing me that they are prone to boost spike, which can be pretty excessive and very fast. I think the spike could have a lot to do with this.


Thoughts

 

It could be the small internal volume of the wastegate. I use nos jets to slow the boost controller down, with full port size (-4) it may be fighting itself. the factory n75 control is just a duty % value.

 

Can you explain a little more??


Audi guys with similar turbos and n75 have been running a mbc in parrellel for years to control boost spikes on that platform

 

The air volume of the 1bar wastegate actuators is less the the stock actuators. The lack of the volume makes the response time much quicker and the ebc is can not respond quick enough, I would put a NOS jet in the outlet of the ebc solenoid to mechanically slow the response time. Or you can get wastegate actuators that have larger heads with more volume. Just my .02c

 

Hmmmm - interesting. I would have thought that it would be the opposite. This will be in an interesting test. Response is the issue. Only one way to find out. thanks tim