p7100 4bt surge

S

stothew

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got my bronco running with the new p pump 4k gsk and injectors. sdx 7x10 sticks and bw s256 with a .62 turbine housing. on the top end around 35 to 40 psi i am experiencing some surge. smoke is cleared all up long before this point of surge. i know this is a small combo from what you're used to dealing with, but anybody know if i should be chasing cause due to not enough fuel or too much air? even though its a 4 cylinder. thanks

scott
 
thanks forrest. so much for my quick spooling .62. but i suppose with a larger housing it will drive harder giving me more overall power?
 
check your drive pressure now, i bet its 50% more than boost.

that will definately cause surge. a wastegate will help alleviate drive pressure and power will rise significantly due to less exh restriction. or a bigger turbine, will alow more exh to flow through it and possibly control boost and keep drive pressures lower, but if you add nitrous or turn pump up any more you might experience the same thing again.

if you dont want to add a wastegate, you could swap on a holset he341 (from 03-04 cummins) its comparable in size, spools close to the same and has an internal gate. and costs less to put it on than an external gate.


are you measuring egts before or after the turbo?
 
crackerman said:
check your drive pressure now, i bet its 50% more than boost.

that will definately cause surge. a wastegate will help alleviate drive pressure and power will rise significantly due to less exh restriction. or a bigger turbine, will alow more exh to flow through it and possibly control boost and keep drive pressures lower, but if you add nitrous or turn pump up any more you might experience the same thing again.

if you dont want to add a wastegate, you could swap on a holset he341 (from 03-04 cummins) its comparable in size, spools close to the same and has an internal gate. and costs less to put it on than an external gate.


are you measuring egts before or after the turbo?
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The problem isn't excessive drive pressure. The problem is he is running in the surge line on the compressor map. He's running the same PR that we are, but 2/3rds the flow. He needs a turbo capable of that pressure at the mass flow he is using (ie, smaller turbo).
 
measuring egt before turbo.

i dont know what my fuel pressure is. i have a new cummins lift pump in and new ofv. guess i should check that out as well. so those symptoms can come from low fuel pressure as well?
 
Lreiff, you dont think it is turbo related? surge can come from not enough fuel as well? thought the lift pump would be adequate being its feeding two less cylinders. but guess not. I know you mess with these baby 4bt's often.
 
LReiff said:
Ditch the cummins lift pump, go electric...problem solved.
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I disagree. factory mechanical lift pump has made me 550rwhp on a 5.9... I don't see why it couldn't do the same on a 3.9. This issue is turbo related IMO.

my 06 would flutter like that at WOT with the Turbonetics 66 I had on it. Changed the turbo, and the problem went away. NOT fuel related.
 
stothew said:
Lreiff, you dont think it is turbo related? surge can come from not enough fuel as well? thought the lift pump would be adequate being its feeding two less cylinders. but guess not. I know you mess with these baby 4bt's often.
Click to expand...

The lift pump that Cummins puts on the 4bt is lower volume than a 5.9 lift pump.
On any B-series Cummins piston type lift pump, if the spring in the lift pump is weak the plunger will float.
 
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I would put a 6B pump on it then. I'm unaware of the differences, but I see no need to introduce another electrical failure point. I prefer mechanical pumps when given the option.
 
I've made around 830hp with a stock 12v fuel pump. Don't get sidetracked, it isn't the fuel pump.
 
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