Any one ever encountered SURGE under WOT ?

[turbo96max]

So I tested the stock Garrett .63 housing machined for the P wheel . I wanted to test for better boost response.

I had my wastegate venting back into the downpipe. Never really ran over 15 psi in the past but I had the car ready for more boost now and cranked it up. I found that as soon as the boost got above 15-16 psi the turbo would intermittently surge or give a quick short sneeze under wot. the boost gauge also would dance around +- 4 - 5 psi.

I tried a harder spring, same thing just changed a bit depending on the spring, tried a soft spring with boost to the top of the wg, same thing. I figured the wastegate could be causing more back pressure and decided to dump it to atmosphere. The surge got better but still would get an irratic boost gauge and slight surge here and there.

I ended up putting the garrett 82 housing back in and the gauge holds 25-26 psi true without any turbo surge.

Is it likely that too much back pressure causes these symptoms?
Would a open downpipe help?
What do the turbo gurus think about the .63 housings? Will I have this issue when I get my new turbo 6266 with the precision .63 housing? Is there something else I need to look at ?

Chime in if you can, appreciate the help

pt 70 h
casv front mount
small 206 cam
1 in intake spacer
Tial 44 wastegate
TH dp
ATR dual 2.5 exhaust
sd chip 120s e85


old wastegate routing initial controller rjc


dump tube w knob controller

 

[Lil Truck]

Everything you describe sounds like a back pressure problem. I would not expect the 6266 to give you any problem as the wheels are a better match. I will be interested to see if Bison gives a comment on this combo.

 

[delcowizzid]

big compressor small turbine housing making the turbo hit the surge line on the compressor map

 

[Mr.Spool]

I have never had a problem with the .63 ex housings on the p trim turbine even with the big compressor.testing for backpressure take the guessing out

 

[bison]

Usually the converter will keep the turbo out of surge. If the throttle is not open all the way you can get surge with the small housing and the converter holding the engine rpm down. There's no way there's backpressure unless the quarter mph is in the mid 130's. That's over 750hp. You won't hit backpressure till 78-80lbs/min with that turbo. Well I the 9's. A Garrett .63 housing will choke it a little but not enough to cause a backpressure problem Under 70lbs/min

 

[WarWagon]

I used to have this problem with my first turbo (T04b H trim compressor with stock '86-'87 turbine wheel in a Garrett .63 housing) it was just a miss match of wheels and would surge at 19 psi and anything over that. Swapped that turbo out for a PT53 and no other changes surge was gone and was able to finally turn the boost up over 20psi.

 

[turbo96max]

Hmm are those numbers expected through the mufflers or with the downpipe dump open? The car is definitely not at those numbers probably making 400-450 range. I did notice the turbine wheel and the opening on the th dp dont line up perfectly and the dp opening is smaller that the turbine wheel opening. Should I be investigating the throttle plate not opening fully?

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[bison]

Hmm are those numbers expected through the mufflers or with the downpipe dump open? The car is definitely not at those numbers probably making 400-450 range. I did notice the turbine wheel and the opening on the th dp dont line up perfectly and the dp opening is smaller that the turbine wheel opening. Should I be investigating the throttle plate not opening fully?

Posted from the TurboBuick.Com mobile app

Here's the t70 map. You're likely above the surge line if attempting to use the t70 compressor at 45lbs/min. It definitely not happy that close to the surge line. You would pick up power and spool and eliminate any surge issues with a smaller compressor and turbine. Likely pick up power across the board. Either go down in compressor/turbine or increase the mass flow potential of the engine mechanically. Better heads and more cam. I would eliminate any overlap at the outlet but I doubt it will have any effect at your current level. Just a set of heads would move you to the right quite a bit and throw you right in that tall high efficiency island for a wide range of mass flow at the pressures most run.

 

[bison]

Here's the t70 map. You're likely above the surge line if attempting to use the t70 compressor at 45lbs/min. It definitely not happy that close to the surge line. You would pick up power and spool and eliminate any surge issues with a smaller compressor and turbine. Likely pick up power across the board. Either go down in compressor/turbine or increase the mass flow potential of the engine mechanically. Better heads and more cam. I would eliminate any overlap at the outlet but I doubt it will have any effect at your current level.

 

[Ed Valvo]

Are you sure your BOV is working properly?

 

[turbo96max]

Bov was tested off, 20 inc vac spring and 15 inch vac spring. Didnt make a diff.

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[turbo96max]

Thanks for the map Bison. So essentially right now the engine isnt flowing enough through that turbo. Did I read the map correctly?

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[WarWagon]

Also I forgot to mention when I was working on keeping the boost consistent on my target which was over 20 psi, I had to move the boost reference source from the compressor housing to the intake manifold. Doing that really made the boost settle on target.

 

[bison]

Thanks for the map Bison. So essentially right now the engine isnt flowing enough through that turbo. Did I read the map correctly?

Posted from the TurboBuick.Com mobile app

Yes. The turbo doesn't determine the mass flow potential unless you're running it all out. The engine is the limiting factor. If you figure about 1lb/min per 10hp you are above the surge line. Keep in mind the pressure at the cover outlet is the pressure compressor is generating and should be used when plotting where you are on the map. Any inlet restriction will further raise you above the surge line. Like your engine is swallowing 45lbs/min but the inlet pressure drop is 1psi With a stock MAF the pressure drop at 50+lbs/min is pretty severe. (14.7+16)/(14.7-1)=2.24:1 PR. Now look at your 45lbs/min and 2.24:1. That's with no pressure drop from compressor to intake. If the pressure at the compressor outlet is 19psi your PR is 2.46:1 but the mass flow is still 45lbs/min. Then youre definitely in the surge area