mx5-kiwi

Since fitting the new GT2860rs my MS tuner/dyno guy says the car pulls like crazy but has boost surge issues under 2800 rpm.

I have spent the past few days trying to find a thread I am sure I read here somewhere a year or two ago about how all the MT guns offered solutions and methods to resolve a common boost surge issue with this turbo.


Am I on the right track or have i imagined this in a previous life...?

Something about porting around the wastegate....if anyone can point me in the right direction or offer advice i'd appreciate it.

aidandj

iTrader: (5)

What BOV?

codrus

Anti reversion housing?

Wastegate porting is for boost creep near redline, not surge.

--Ian

mx5-kiwi

Thanks codrus. That'll be why my searching hasn't found it..

Aidandj - It is a mid level Turbosmart unit. The cars out of town at the tuners so I cant check what model but I think its a vee port from their web site...

codrus

AIUI, surge usually means you're using too big a turbo on too small a motor. Anti reversion compressor housings help. I'm a bit surprised a 2860 would do that on a 1.6 though.

--Ian

mx5-kiwi

Well it is a biggish turbo for a 1600 to my understanding.

I suspect we may have exaggerated the problem by using a log/extreme short runner manifold as well.

Previous turbo was a journal bearing T28 with downsized compressor housing. Didn't have the problems then but turbo was on its way out anyway (we since found out..).

Full_Tilt_Boogie

iTrader: (1)

Interesting issue.

Do you perhaps have very restrictive charge pipes and/or intercooler? Being that it is a dynamic compressor, I am not sure that this would matter, but it is worth a thought.

Plenty of people have run the ol' Potato on the B6 and the spool being too fast is not a common issue as far as I know.

18psi

iTrader: (76)

This doesnt sound right. You'll need to post boost plots to convince us it's actually surge, because I've tuned 6th gear pulls (that's right, from 2k all the way to 7k or 155mph) on a 30R and 1.6 and we had no surge. I can't see a disco potato doing this

The one miata where I've seen this was a 1.8 bp with a 35r at 25+psi on e85 and doing pulls in 5th on the freeway (because he's crazy, that's why)

aidandj

iTrader: (5)

I don't think your exhaust manifold choice would do this.

Compressor surge happens when you are too far to the "left" of a compressor map, high pressure ratio but very low airflow. The compressor is essentially chopping nonmoving air.

See surge line here



Though I guess technically you could try and target less boost to get rid of the surge though.

18psi

iTrader: (76)

A 3port bcs will sometimes create "flutter" that sounds kinda like faint surge when it activates in interrupt mode.
Have said tuner disable bcs and run wastegate. if it still "surges" then it aint surge

aidandj

iTrader: (5)

Well disabling bcs would build boost slower and not surge. So wire the wastegate shut too when disabling ebc

18psi

iTrader: (76)

He needs to rule out if it's the preload on the wga or the bcs

mx5-kiwi

Actually we did put slight preload on the Wastegate......picking car up tomorrow will see.

Do you think we will see any change buy uprating the IC piping from 2" to 2.5"?

18psi

iTrader: (76)

if anything, a restrictive ic should be helping you not have boost surge

Savington

iTrader: (31)

I've seen similar issues on a 56-trim 2871R without the anti-surge housing, but it only happened on the dyno because you're able to hang the motor at very low RPM and let boost slowly build to the surge line. On the road, the RPMs rise fast enough that it's never an issue. If you aren't seeing real-world surge, I wouldn't be awfully concerned about it.