back Pressure advise
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Joined: Jul 2008
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From: Dalton,Ga
back Pressure advise
First of all, here is how I am feeling about my truck right now
Hope it plays.....
now to the issue...I went to Jodys (DP Tuners) for some fine tuning a couple of weeks ago, rough idle, cold hesitation(resolved), while there it was decided to go through the tunes and check them out...all is well until we got to the 100 perf and @WOT,52 lbs of boost, eather the head gasket blew or it lifted the head...
..blew antifreeze out of the degas bottle..
I was using Cometic gaskets (75ths thick) due to heads and block being decked...I have learned and some advise when approching high boost, STAY away from them...
I am also using a .91 exhaust housing on the turbo (S468) instead of the 1.10...While tuning Jody remarked that my exhaust back pressure is off the chart (factory) @ wot....Now I believe the factory gauge is only good to 40-50 psi (may stand corrected)..
I really like how the truck runs with the .91 housing,but if I need to use the 1.10 I will...
Now given the information above, keep in mind I rarely push the truck..
I need to understand the effects of EBP...Please advise
Hope it plays.....
now to the issue...I went to Jodys (DP Tuners) for some fine tuning a couple of weeks ago, rough idle, cold hesitation(resolved), while there it was decided to go through the tunes and check them out...all is well until we got to the 100 perf and @WOT,52 lbs of boost, eather the head gasket blew or it lifted the head...
..blew antifreeze out of the degas bottle..I was using Cometic gaskets (75ths thick) due to heads and block being decked...I have learned and some advise when approching high boost, STAY away from them...
I am also using a .91 exhaust housing on the turbo (S468) instead of the 1.10...While tuning Jody remarked that my exhaust back pressure is off the chart (factory) @ wot....Now I believe the factory gauge is only good to 40-50 psi (may stand corrected)..
I really like how the truck runs with the .91 housing,but if I need to use the 1.10 I will...
Now given the information above, keep in mind I rarely push the truck..
I need to understand the effects of EBP...Please advise
Hotshot
Joined: Jan 2011
Posts: 18,849
Likes: 179
From: Puget Sound
Awww crap. 52PSI? What's our compression ratio... 19:1? Almost 1000 PSI before you add fuel... and the Start Of Combustion will come so early. It takes a late SOI to compensate for the quick SOC... let alone the head hardware you need to hold that compression and backpressure in (including stronger valve springs to prevent an exhaust valve from opening into a rising piston in the next cylinder).
If you're real lucky and you've been a good boy all year, it's just a head gasket or an injector cup. Dragons are known to blow exhaust out the degas bottle.
I had a scare with the 80e, and I think I'll keep it safe with no more than 60 HP boost on my stage II injectors.
If you're real lucky and you've been a good boy all year, it's just a head gasket or an injector cup. Dragons are known to blow exhaust out the degas bottle.
I had a scare with the 80e, and I think I'll keep it safe with no more than 60 HP boost on my stage II injectors.
Post Fiend
Joined: May 2009
Posts: 5,470
Likes: 3
From: Pea Ridge, AR
Sucks to hear Joey, how many miles on this build? Had you done some retorqueing on the studs after a few thousand miles?
I always assumed 52psi on the factory sensor, but as to your further questions I have no absolute answers only speculations and theories.
I always assumed 52psi on the factory sensor, but as to your further questions I have no absolute answers only speculations and theories.
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Posting Guru
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From: Dalton,Ga
Awww crap. 52PSI? What's our compression ratio... 19:1? Almost 1000 PSI before you add fuel... and the Start Of Combustion will come so early. It takes a late SOI to compensate for the quick SOC... let alone the head hardware you need to hold that compression and backpressure in (including stronger valve springs to prevent an exhaust valve from opening into a rising piston in the next cylinder).
If you're real lucky and you've been a good boy all year, it's just a head gasket or an injector cup. There be dragons in exhaust escaping the degas bottle.
If you're real lucky and you've been a good boy all year, it's just a head gasket or an injector cup. There be dragons in exhaust escaping the degas bottle.
what I am looking for is what roll does (if any) EPB play in cylinder pressure?? Also the ill effects of EPB, I know it may lift a valve but I dont have that issue..
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From: Dalton,Ga
Alan, 3500 on this one...Thing is, it has seen 50psi boost on more than once (what a ride)..At 52 the gasket let loose..I know of a few people that are seeing 60 psi of boost with stock head gaskets and ARP studs with no problems and after researching the Cometic gaskets,(they are 4 gaskets to make 1)..they just cant handle the pressure..
current plan is to shave 10ths off the valves and use stock(factory)head gaskets and new ARP studs...
I am just undecided on what to do with the 2 turbo exhaust housings..
Cargo Master
Joined: Jan 2002
Posts: 2,079
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From: LA and CO
Were the heads and block machined properly for the Cometics? Those are real good gaskets but there is a very specific finish the heads and block needs for them to seal properly. They typically won't seal good if the machine shop just machines them how they would for a typical stock type gasket.
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Posting Guru
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From: Dalton,Ga
Were the heads and block machined properly for the Cometics? Those are real good gaskets but there is a very specific finish the heads and block needs for them to seal properly. They typically won't seal good if the machine shop just machines them how they would for a typical stock type gasket.
I don't know that answer...and probally never will..The 1st builder installed them and his motor trashed @4000 miles..His answer "your problem not mine"
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Cargo Master
Joined: Jan 2002
Posts: 2,079
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From: LA and CO
Gotcha. From what I recall they need a real fine finish on the head and deck. If not the head and deck will "grab" the gasket during the contraction and expansion process tearing the gasket leading to failure.
Junior User
Joined: Oct 2009
Posts: 84
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From: Woodlawn TN
Just to throw it out there, even though its been said...
Boost and back pressure never ever blow head gaskets by themselves.
Cylinder pressure is oh so much higher then boost/BP it's not comparable.
If you've blown a head gasket and you're studded and you've driven easy for the first 5-10k that it takes for head gaskets to "season," then you need to do fire rings or back the tune down.
The only thing high back pressure tears up is turbos.
High boost/BP are not a direct indicator that you're experiencing high cylinder pressures.
Boost and back pressure never ever blow head gaskets by themselves.
Cylinder pressure is oh so much higher then boost/BP it's not comparable.
If you've blown a head gasket and you're studded and you've driven easy for the first 5-10k that it takes for head gaskets to "season," then you need to do fire rings or back the tune down.
The only thing high back pressure tears up is turbos.
High boost/BP are not a direct indicator that you're experiencing high cylinder pressures.
Junior User
Joined: Oct 2009
Posts: 84
Likes: 0
From: Woodlawn TN
Also... I don know if I've seen a single high hp 7.3 get put together in the last couple years that didn't do stock gaskets and fire rings. Unfortunately, that's about the only way to be sure you won't pop a gasket.
Lead Driver
Joined: Sep 2005
Posts: 9,399
Likes: 188
From: Norco,CA
I would say the same thing, to install o-rings. I would of also shaved the pistons not the valves if you think cleance between the two are to close. This sucks! But I would think you could reuse your ARP heads studs without changing them. Call if not sure. If you had a builder put this together again he should of measured the cleance and reworked the pistons. And thats before you had them coated if you did. I use to build a lot of gas engines to race around in the 60's and we always checked piston heights etc..
Chet
Chet
Cargo Master
Joined: Jan 2002
Posts: 2,079
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From: LA and CO
Work the pistons to get you piston to valve clearance not the valves. But that's only if the piston crown is thick enough to allow removal. How much do you have to remove? Never cut valves for clearance. Do that and you'll end up dropping one.
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Posting Guru
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From: Dalton,Ga
Just to throw it out there, even though its been said...
Boost and back pressure never ever blow head gaskets by themselves.
Cylinder pressure is oh so much higher then boost/BP it's not comparable.
If you've blown a head gasket and you're studded and you've driven easy for the first 5-10k that it takes for head gaskets to "season," then you need to do fire rings or back the tune down.
The only thing high back pressure tears up is turbos.
High boost/BP are not a direct indicator that you're experiencing high cylinder pressures.
Boost and back pressure never ever blow head gaskets by themselves.
Cylinder pressure is oh so much higher then boost/BP it's not comparable.
If you've blown a head gasket and you're studded and you've driven easy for the first 5-10k that it takes for head gaskets to "season," then you need to do fire rings or back the tune down.
The only thing high back pressure tears up is turbos.
High boost/BP are not a direct indicator that you're experiencing high cylinder pressures.
this is the information I am looking for.....thank-you
I would say the same thing, to install o-rings. I would of also shaved the pistons not the valves if you think cleance between the two are to close. This sucks! But I would think you could reuse your ARP heads studs without changing them. Call if not sure. If you had a builder put this together again he should of measured the cleance and reworked the pistons. And thats before you had them coated if you did. I use to build a lot of gas engines to race around in the 60's and we always checked piston heights etc..
Chet
Chet