how much boost is to much

[motown]

i got air intake 5in exhaust im thinking about a manuel wastegate controler i seen a few guys on here saying 22 and others say 12 or 15 is one for towing

[6.5 Detroit Diesel]

the safe number is set at 12 psi. if you go higher, you take a risk of melting stuff or blowing things out. But, I have yet to do any damage to the engine and have towed some very heavy loads. Today I kept the boost at around 24 PSI for a few minutes well towing a big hill. Again, it is at your own risk when you go beyond 12 psi on an unmodded engine

[lfytsmith]

I have wondered the same question. My boost guage only goes to 15, when climbing a hill while pulling I will peg the meter. As long as my EGT is less that 1000F preturbo it shouldn't hurt anything, should it? I guess my question is, Is it high boost or high EGT that fries the engine?

[6.5 Detroit Diesel]

high egt's is what will melt things. boost that is to high can do damage to gaskets and apparently heads as well

[DennisG01]

Does your exhaust system include a good downpipe? Stick to that 10 - 12 number. If you get an IC, you could push up to 15 or 16. But, even that - while not really dangerous with an IC - is getting inefficient. The exhaust side of the GM-X turbos become more and more inefficient as you get over 10psi. Pushing the boost higher only makes the EGT's rise faster - doesn't really give you any more power. It don't much matter how much air you cram in if you can't get it out fast enough. :D

[6.5 Detroit Diesel]

One of the members on here, I think it was 67C-10, had made up a custom dump off the turbo that was nice and smooth.
Don't know if I totally agree with the inefficient boost. I do know that it makes a huge difference when pulling to have the boost that much higher as opposed to 12 psi max. :D Course, I am still waiting to rig up my intake directly through the fender wall and get myself into a WAI setup.
Melt down happens past 1250 F preturbo.

[suburbanK-2500HD]

One of the members on here, I think it was 67C-10, had made up a custom dump off the turbo that was nice and smooth.
Don't know if I totally agree with the inefficient boost. I do know that it makes a huge difference when pulling to have the boost that much higher as opposed to 12 psi max. :D Course, I am still waiting to rig up my intake directly through the fender wall and get myself into a WAI setup.
Melt down happens past 1250 F preturbo.

Hi, do you plan to get the air from a hole in the fender ??
ore through the inner fender.?
I have been thinking about the same idea for a while, i seems like i good idea if we can supply the engine with more, and cooler air..

Also thinking of making a small air outlet scoop on the hood above the turbo area.

[DennisG01]

Don't know if I totally agree with the inefficient boost.

I'm certainly by no means an expert on the subject and I'm not discounting your input - but there are generally thought of safe limits that have become an excellent rule-of-thumb. I completely agree with your other comments regarding blowing things up and melting things down - all excellent points that the OP should be aware of.

Just some clarification on why I mentioned the "inefficiency" -- I'm basing what I said on a number of things, most importantly what I've learned here over the years. When I did timed-hill pulls (recording data such as E.T., Max Boost, Max EGT, etc) using the exact same weight behind me under nearly exact conditions (close enough for it not to matter), I found absolutely no improvements in the amount of time it took through the 1.1 mile hill course when I adjusted the boost higher. The only thing that happened was the EGT's crept up faster and then I had to back off throttle - actually causing a slower time. The article on Turbos talks about the inefficiency of the GM-X turbo, as well. The inefficiency of the back-end of the turbo has also been talked about quite a lot on another site, along with the use of a different turbo.

All that being said, I applaud you for having the guts to push your engine to those extremes, because I certainly don't have it! (I say that with sincerity - I don't want anyone reading that wrong and thinking I was being sarcastic).

[JohnC]

There are two reasons to push air through the engine. One is to burn the fuel. The second is to cool the engine. Any more than that is a waste.

Given a particular turbo and a set fuel rate, increasing boost requires closing the wastegate. Closing the wastegate increases the back pressure in the exhaust, increases the heat held in the engine, and decreases the volumetric efficiency. Increasing the boost level also increases the intake air temp and consequently the EGT. Without an intercooler I would stay below 12 PSI and limit the fuel to what can be burned cleanly at that boost level. Any more and you're asking for trouble. 20 PSI without an intercooler is a prescription for trouble and likely not netting you any performance gain anyhow. Do you have an EGT gauge? I'm guessing your EGTs are way too high.

The stock turbo is a compromise between low speed response and high power efficiency. Pushing it to 20 psi is way beyond its comfort range. If you really want to do that, consider a different turbo and plan on giving up some low speed response.

[6.5 Detroit Diesel]

Dennis- No I didn't think you were sarcastic :D The nice thing is, I usually drop a gear into 4th if needed and keep the boost up high well keeping the temps lower. So far so good, but I think I am lucky with this 6.5. Yea the GM turbos could be better, but I am using what I have on hand at the moment. :)
John- I have an EGT and have been monitoring it. High boost well pulling up big hills and I can keep it under 1000F preturbo. I can make a video if needed. I don't think that I am deadpanning on the power line. I am going by seat of the pants feel and watching the speedo, but I have experimented with different spring tensions and this setting seems to give back the most power and boost. The pump is turned up, and if anything, pulling through switch backs on slippery roads that force you to slow right down arond corners is where my EGT's can climb if I don't drop gears fast enough.
It has handled the +20 boost so far and I have messaged with a few people here who agreed that it would. I don't intend to give up the low end power either. If anything, work out a TT system that will give me low through high rpm response. :D

Suburban- I am going to come right through the fender wall and onto a cone filter in front of the turbo. The stock intake is way to small for me. I guess putting a scoop in the hood is another way to do it.

[DaveBr]

Is there anyway to lower backpressure in the turbo? 6.5DD You are really pushing way past the comfort zone. Not bad for a truck with as many K's as yours has. How many K's have you been running like this?

Dave

[6.5 Detroit Diesel]

I am going to say by opening up the exhaust elbow. Would probably be the best I can think of.
I have been running the truck this hot now for close to 10K. Probably close to half of that have been towing anywhere from 4-10,000 lbs around our area and to the coast, so plenty of decent hauling going on. :D
I kinda realized today, that I can probably get away with pushing the envelope a little for a few reasons. First, I am young and single, and don't have to worry about a lot of headache getting to work if my engine blows up. (Being an owner instead of a worker has it's benifits!) Also wouldn't have to explain to the wife why I pushed it so far.
Second is, I have a second block to build if this one cooks. So I take a little comfort from that.
Let me be clear, I in now way disregard advice given on here from all you guys. I have done some forum shopping and TDP has the most information and the friendliest enviroment out there. :)

[JohnC]

Opening the elbow can't hurt, but the real problem is the scroll on the turbine. You simply can't have a tight scroll that gives good low speed response and expect to pass huge amounts of gas at high power levels.

[6.5 Detroit Diesel]

So what we would need is different turbos? :D Like I was thinking, how about two smaller turbo's that had different sized turbines? Something set up that would provide constant 20+ psi? From what I have read, running each manifold to it's own GM turbo won't provide enough exhaust to spin the wheel fast enough.

[DaveBr]

Has anybody out there ever tried to open up the exhaust elbow? I'd like to know how much difference it makes.