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+--- Thread: Om617a max safe boost on 30 year old head gasket (/showthread.php?tid=7404)
Om617a max safe boost on 30 year old head gasket - Evenglass - 09-09-2016
What be a max safe boost level?
RE: Om617a max safe boost on 30 year old head gasket - R-3350 - 09-10-2016
i am currently running around 16-17 peak on a maxed stock pump. 15-16 is enough for all the fuel the stock pump can deliver. however if you get a new pump i would try to stay below 25 lbs. i have heard that 2 bar is the redline for bending rods. however that was with the fuel to match the 2bar of boost. the HG is not the weak point on these engines its the rods and cracking the head from the heat.
RE: Om617a max safe boost on 30 year old head gasket - NZScott - 09-10-2016
Was talking with a guy recently who says he has 396hp with 2.2bar.
Agree with the above, 2 bar is a never-can-go-wrong level. People have run 2 bar with NA engines with the weaker rods so up to you.
Boost doesn't kill an engine, heat does. Better to have fuel burning properly with high boost than smoking at low. That's my theory anyway
RE: Om617a max safe boost on 30 year old head gasket - kestreltom - 09-11-2016
(09-10-2016, 12:32 AM)R-3350 ...HG is not the weak point on these engines its the rods and cracking the head from the heat.
I also agree on these points. You should be worried about a cracked head instead of a blown hg.
I am also running a maxed out OE pump, plus I am using a gt2256v with an electronic controller, and an a/w intercooler. it is very easy to achieve 21+ lbs of boost by 2100 rpm with this setup. This at least keeps the cyl head temps in check.
I have noticed that the stock coolant sensor shows a marked drop in temps every time I turn on the cabin heat, which leads me to believe that the stock coolant flow through the head is not adequate for highly modified engines. I am thinking of adding a pump/coolant loop by teeing into the heater loop just above the oil filter and returning it by teeing into the output of the electric coolant pump.
RE: Om617a max safe boost on 30 year old head gasket - Evenglass - 09-15-2016
Thank you all for the replies. I am currently running a dieselmeken M pump with a Holset Hx30w turbo and small intercooler. My wastegate starts to open at about 20psi and is fully open by 22psi. Sounds like I can boost to 25-28psi no problem. If I stay on the fuel hard and long it smokes and the EGT's start to raise pretty quick. Do the egt's go up because of the unburned fuel or the 21psi of boost?
RE: Om617a max safe boost on 30 year old head gasket - NZScott - 09-15-2016
Diesels are the opposite of petrol jobs - high EGT is caused by excess fuel to air ratios, so either back your fuel down or bring your boost up a touch or a combination of both.
How's your HX30 going for you? I have one but not road legal yet so barely driven it.
RE: Om617a max safe boost on 30 year old head gasket - Evenglass - 09-16-2016
(09-15-2016, 10:39 PM)NZScott Diesels are the opposite of petrol jobs - high EGT is caused by excess fuel to air ratios, so either back your fuel down or bring your boost up a touch or a combination of both.
How's your HX30 going for you? I have one but not road legal yet so barely driven it.
The HX30W is fantastic! Lowered egt's by 100*f alone. It boosts as fast as the stock Garrett mybe faster, the boost riserises extremely quickly. One of the best sounding turbos out there and industrial rated.
RE: Om617a max safe boost on 30 year old head gasket - kestreltom - 09-17-2016
(09-15-2016, 10:01 PM)Evenglass ... Do the egt's go up because of the unburned fuel or the 21psi of boost?
it's the unburned fuel. You can run more boost, but will the piston rings hold it? Keep an eye on your crankcase vent pressure. It wouldn't hurt to run a 50/50 water/meth injector into the intake after the intercooler... or a bigger intercooler... or both
How is your transmission holding up to the full throttle runs?
RE: Om617a max safe boost on 30 year old head gasket - baldur - 09-17-2016
The EGTs go up due to late combustion of the last bits of fuel when the oxygen is mostly depleted, as well as the fact that maximum flame temperature comes when you've combusted all of the oxygen and thus combusted the maximum fraction of the charge air. When you add boost pressure to reduce EGT without being at the smoke limit, what you're doing is adding more inert gas (nitrogen) and uncombusted oxygen to serve as thermodynamic working fluid (fluid that gets heated and expanded to extract mechanical energy from the heat). With more mass of working fluid inside the cylinder but the same amount of combustion energy, there's a lower temperature increase.
By the nature of things, unburned fuel doesn't contribute to increased temperature as such, but a late combustion of fuel that doesn't immediately find oxygen to attach to when injected but manages to react with oxygen later in the cycle does contribute to higher exhaust temperature without increasing peak combustion temperature and without contributing to making power (it needs to burn while the piston is near TDC and heat the air before expansion starts to make power)
The real danger when overfuelling a diesel is pre ignition. Normally a diesel doesn't experience pre ignition as there is in normal operation no fuel present in the cylinder until the injector opens, but a diesel that's being grossly overfuelled with a massive amount of black smoke pouring out is leaving unburned fuel inside the cylinders after the exhaust stroke. When enough of that fuel builds up it can start to ignite before the injection happens and you've got a melted piston on your hands.
RE: Om617a max safe boost on 30 year old head gasket - kestreltom - 09-17-2016
(09-17-2016, 04:47 AM)baldur .... With more mass of working fluid inside the cylinder but the same amount of combustion energy, there's a lower temperature increase.
Wow - nice explanation Baldur !
I just remembered that my boost spiked to 24-25 psi a few times while I was sorting out the software in the controller for my gt2256v. No bent rod / blown head gasket happened. I replaced the crankcase vent system with a 1/2" ID hose that runs down and back a bit. The hose leaves one drip on the floor each night, which I catch with a peice of cardboard.
RE: Om617a max safe boost on 30 year old head gasket - Evenglass - 09-17-2016
(09-17-2016, 01:13 AM)kestreltomIt's a buibuilt chevy 700r4, holding up fine. Temps stay about 200F after the torque converter.(09-15-2016, 10:01 PM)Evenglass ... Do the egt's go up because of the unburned fuel or the 21psi of boost?
it's the unburned fuel. You can run more boost, but will the piston rings hold it? Keep an eye on your crankcase vent pressure. It wouldn't hurt to run a 50/50 water/meth injector into the intake after the intercooler... or a bigger intercooler... or both
How is your transmission holding up to the full throttle runs?
RE: Om617a max safe boost on 30 year old head gasket - NZScott - 09-17-2016
(09-16-2016, 09:50 PM)Evenglass The HX30W is fantastic! Lowered egt's by 100*f alone. It boosts as fast as the stock Garrett mybe faster, the boost riserises extremely quickly. One of the best sounding turbos out there and industrial rated.
Awesome. They do sound really good
(09-17-2016, 01:13 AM)kestreltom(09-15-2016, 10:01 PM)Evenglass ... Do the egt's go up because of the unburned fuel or the 21psi of boost?
it's the unburned fuel. You can run more boost, but will the piston rings hold it?
Not sure if rings are a worry - they've held up on the dyno with one chap running 50 odd psi
RE: Om617a max safe boost on 30 year old head gasket - Evenglass - 09-17-2016
(09-17-2016, 04:47 AM)baldur The EGTs go up due to late combustion of the last bits of fuel when the oxygen is mostly depleted, as well as the fact that maximum flame temperature comes when you've combusted all of the oxygen and thus combusted the maximum fraction of the charge air. When you add boost pressure to reduce EGT without being at the smoke limit, what you're doing is adding more inert gas (nitrogen) and uncombusted oxygen to serve as ...........Good info. So can timing adjustment help with this also?
RE: Om617a max safe boost on 30 year old head gasket - baldur - 09-17-2016
(09-17-2016, 05:15 PM)Evenglass(09-17-2016, 04:47 AM)baldur The EGTs go up due to late combustion of the last bits of fuel when the oxygen is mostly depleted, as well as the fact that maximum flame temperature comes when you've combusted all of the oxygen and thus combusted the maximum fraction of the charge air. When you add boost pressure to reduce EGT without being at the smoke limit, what you're doing is adding more inert gas (nitrogen) and uncombusted oxygen to serve as ...........Good info. So can timing adjustment help with this also?
Yes, advancing the timing will reduce EGT, but whether that's a good thing or not can only be told by measuring the power output. If you advance the timing too far EGT will continue to fall but power will not increase, instead that heat which would've been blowing out the exhaust remains inside of the engine to be carried away by the cooling system.
Too little timing advance will give you low power and high EGT, but the drop in power output is rather gradual once you've advanced past optimal timing. Instead what happens is you increase the mechanical stress and thermal stress on your engine by too much timing advance. When I was finding the best timing setting on my engine on a dynamometer I advanced it until power stopped climbing, then retarded back to the minimum advance required to reach full power output.