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What really is the safe limit?

R

Ratchetnator

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I have heard so many different opinions on what is a safe boost pressure for the 6.5. I have also heard that its not the boost that blows your motor but the heat that goes along with it. This sounds pretty believable but then Kojo tells me that anything over 12psi is dangerous. First I will say I do not tow so I see the highest boost on hills with the tc locked wot. If I keep my egts low what is a reasonable boost peak? I had mine set so on hills it would top out at 17psi. I read that this was too much so I turned it down to peaking boost at 15psi. After hearing that 12 was the maximum safe boost level. I turned mine down to hold 11 psi and peak at 12 but I must say I definitely feel a loss of power at this boost setting. Were the higher boost pressures just a placebo effecT? Let me know your opinion
 
12psi is about the max you want to run the gm if you want your motor to last. Its not only the high intake temps but also the high drive pressure on the motor. If your still looking for a bump up in power, you might want to consider a larger turbo. There are many good choices out there. The most suggested turbo I always here about is the a team turbo, must be good if people are always praising it.
 
Safe boost is what the Head gaskets, head bolts, bottom end, and turbo can take.

With ARP head studs I sustain 23 PSI all day long with a HX40II Turbo with the higher 6.2 compression. (21 peak and 18 PSI sustained with an A Team Turbo. Just because I am out of fuel at 18 PSI.)

The factory turbo overspeeds and becomes a air intake heater over 14 PSI. Heath Diesel TM install says keep it under 14. The turbo is seriously worthless over 2200 RPM, but, that is another discussion. Drive pressure is also a consideration to keeping the engine together and the factory turbo makes high drive pressure.

So safe boost is limited by the factory turbo running out of it's efficiency range.
 
Seems to me that the general rule of thumb with this motor is if you have a stock motor and turbo, keep the boost under 15psi. If running headstuds and a bigger turbo/more effiecient setup/less backpressure (and a tune to supply the fuel lol) to keep sustained boosting under 25psi. That is just what I have gathered from others.
Im with WarWagon on headstuds and the hx40ii sustaining 20psi all day long.
 
Im going to stick with my current setup. It doesnt hit 15 unless im on a steep hill od locked. I dont beat on it often or tow. I just wanted piece of mind till I can go with an hx40II. Thanks
 
You do know that boost alone doesn't make power. You have to get the exhaust out as well. A small gm turbo makes boost and heats the air. Doesn't get the exhaust out as efficiently as it should. And as boost raise so does air intake temps, high intake air temps lower the benefit of any turbo.
 
So, if running a larger more efficient turbo that is creating less backpressure, what would be a safe boost pressure to run without having headstuds on a basically stock motor?
 
GM-X turbo I like 12 psi as max sustained boost and ECT under 215F as a good combo for longevity.

No pat answer though because it does depend on set up : turbo, cooling, tune etc. You are right heat kills the engine. IMO its how hot the combustions event gets which depends on heat balance determined by: cooling system, turbo effeciency, timing/tune and more. So it does heavily depends on overall set up of truck and can vary a good bit.
 
How hot the combustion event gets and when the peak temperature and pressure are reached I mean. I am not talking about just how high is the EGT. Its a bit of inference from all indicators IAT, ECT, EGT, timing, and oil Temp mainly. Each can be a little discussion on thier own.
 
STEVE53 said:
So, if running a larger more efficient turbo that is creating less backpressure, what would be a safe boost pressure to run without having headstuds on a basically stock motor?
Click to expand...

I wouldn't go far above 20 Imo. I think it's still a gamble at that point but the chances of lasting are better with a good turbo than with the factory butt plug in place.
 
I sustained 20psi+ through my ATT for about 30 seconds and it held up just fine. Not saying it will be the same for everybody but I wouldn't worry greatly if it spikes above 15psi. I'd start to worry around 18psi personally.
 
I don't plan on doing studs on my 93 K3500 until it pops so we will see. I'm going to try to stay around 20psi and while towing it could be there for awhile at times.
 
Just a bit off teh subject but I hear about the ATT and the HX40II as the predominant aftermarket turbos for 6.5. Can I get some info on the two? opinions on which is better? I know ATT bolts in how about HX40II? Pros and cons of each? Any input on each?
 
Cali6.5 said:
Just a bit off teh subject but I hear about the ATT and the HX40II as the predominant aftermarket turbos for 6.5. Can I get some info on the two? opinions on which is better? I know ATT bolts in how about HX40II? Pros and cons of each? Any input on each?
Click to expand...

Try the search function here on the site. Lots of info on both more so for the ATT
 
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