Been reading around that 12-15psi is the "red zone" or "do not pass" zone. Is there any actual proof of this? Any experiments (long and short term). Any data? Any facts? Or has this just been passed down by word of mouth from the old timers? Within my searching I've found members (on various forums) hitting higher numbers than 12psi without any adverse side affects. Obviously I know studs are different, I'm talking for head bolts. Does any body know a definitive answer and/or a legitimate source stating that 12 -15 psi is infact, the danger zone. Thanks for any info you can provide.
"Safe" boost?
- Thread starter Blsford
- Start date
idiabuse
Full Access Member
heat limits boost. after 12 psi air gets hot so water injection/intercooler needs to keep temps down in the 100/200 degree range.
GenLightening
Yeah, it's a CHEVY!
You also need to tell us if you're talking 6.9 or 7.3 as they have different limits in stock form.
idiabuse
Full Access Member
in theory they do, but some qban will prove the theory just that...
Javier
Javier
icanfixall
Official GMM hand model
Lets look at the stock 7.3 engine. The head bolt when new will have a breaking psi of 153,000 lbs. They are known to work very well. Now add a turbo and boost to 12 lbs. thats generally felt the safe limit of boost for two reasons. The stock head bolts are being stressed at that pressure. Plus any more boost is so hot from the turbo compressing the air that its a waste to go higher. About 300 degrees is the temp of the air going into the engine when boost reaches much above 12 lbs. Yes, we have seen members boost to 20 lbs and stay together too. Its really not doing any benifit to run that much boost unless you have an intercooler or water injection to cool down the air charge. If you looking at installing a Moose pump the directions clearly tell you an intercooler is needed and highly recommended. Can you run without one safely... Yes. Most do just that. I sure do but I need to install my hypermax intercooler too. Just kinda lazy about doing it. BTW a set of ARP head studs will allow an easy 20lbs plus boost and the heads will not lift. Running that boost without an intercooler will be like racing with a heavy triler in tow.
PwrSmoke
Full Access Member
There is a reason the aftermarket kit makers set their kits up to run at around 10 PSI. Those reasons were outlined above...intake heat and blown head gaskets. The head studs address the head gasket issue but more insanely hot air is not much better than less cooler air from a performance or durability standpoint, making the intercooler necessary for high boost. High boost and fuel to match is not so bad in short spurts but try it with a trailer going up the Rockies... EGTs will be stupid high and you'll have to slow down just to keep from having to watch molten pistons come drooling out the tailpipe, which itself would be glowing red. Lower boost/fuel rate at a level the engine can tolerate long term is better for a workin' engine. If you want one to make impressive numbers on a dyno or on a drag strip, I suppose it's not as critical because you only need 15-20 seconds worth of endurance. I could make a bedroom analogy here....
I think you'll find that most of the old timers here speak from experience.
WhiskeyBottle2
Full Access Member
Not to be a "snit", but I wouldn't worry about the boost numbers...I would kinda use them as a guide, but I would pay a lot more attention to the EGT's...Why? Well we know our pistons are aluminum...and it is a fact that aluminum will begin to soften around 1100 degrees and will start melting to a liquid state around 1200 degrees...
Some will have boost at 13 psi and have egt's at 800, some at 900, etc...so I think egt's are more important than boost...but that's just me...
I'm probably the oldest one, and I ain't sayin nuttin.
WhiskeyBottle2
Full Access Member
EGT's
There you go...see so many things are tied to each other. Yes you can have high boost, but like I said...Those egt's are very important and that's what I look at most in the long run...Boost is good...but again it is egt's that will tell you if you are "In The Danger Zone"
Good Luck....
There you go...see so many things are tied to each other. Yes you can have high boost, but like I said...Those egt's are very important and that's what I look at most in the long run...Boost is good...but again it is egt's that will tell you if you are "In The Danger Zone"
Good Luck....
FordGuy100
Registered User
I've pegged out my gauge more times than I can count. I do have head studs though....
One day I'm hoping to run around 20-23psi with a stock bottom end, more with a better cam.
One day I'm hoping to run around 20-23psi with a stock bottom end, more with a better cam.
A Safe boost level is just prior to one's back side inhaling the seat!
JM2CW
JM2CW
88 Ford
Full Access Member
Another way to address the issue of higher egts at higher boost levels is a more efficient turbo. It can definitely be stated that the 3 turbos made for these engines start to heat air up at higher boost but if you have a turbo that is still in its efficiency range, you really don't have to worry about IATs as much. With that said, it is easier to hit 20+psi and still be safe as long as you have head studs. Another thing you get with less heat is less cylinder pressure which can also save a gasket as well...
Has anyone actually had a air temp guage after the compressor?
