How much boost?

Adrenaline73

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I’ve been searching and reading for days on this subject but I figured I would ask here to get clarification. How much boost can these motors hold? I have a 1994 turbo in mine with 500 miles on the rebuild. It does have arp head studs but what I’m after is at what boost is the bottom end going to give up I’m at 15psi empty. After reading some back post on here makes me wonder a little bit about it. Also is there anything else I should be considering that could go wrong? I’m going to intercooler it here soon and bigger pump and bigger turbo.
 

The_Josh_Bear

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If you have a 7.3 with ARP studs then you have a lot of overhead yet. Not many studded 7.3's have bent rods or blown out the bottom end that we know about. The ones that do:
1. Weren't intercooled and boosted over 30psi
2. Were a test mule for R&D or Wes and again 30psi+ and nitro and abused in the efforts of science and fun.

I'm certain there are more I can't think of, and some of the boys around here with a better memory or knowledge can come by and set it straight.

Some main points for building your setup:
1. Run the biggest/most efficient charge air cooler you possibly can, so that your boost numbers stay *down* and your air density stays *up*.
2. Don't hammer the throttle at low RPMs. Big power is much safer at midrange or higher RPMs rather than down low. The rods can't take it. These aren't big rig engines!
 

CBRF3

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If you have a 7.3 with ARP studs then you have a lot of overhead yet. Not many studded 7.3's have bent rods or blown out the bottom end that we know about. The ones that do:
1. Weren't intercooled and boosted over 30psi
2. Were a test mule for R&D or Wes and again 30psi+ and nitro and abused in the efforts of science and fun.

I'm certain there are more I can't think of, and some of the boys around here with a better memory or knowledge can come by and set it straight.

Some main points for building your setup:
1. Run the biggest/most efficient charge air cooler you possibly can, so that your boost numbers stay *down* and your air density stays *up*.
2. Don't hammer the throttle at low RPMs. Big power is much safer at midrange or higher RPMs rather than down low. The rods can't take it. These aren't big rig engines!


There is more to it than just head studs to allow for above 15psi boost even with intercooling unless you decompress our motors above 15PSI is risky yeah you may be able to do 20psi but when you get brave and hold it there and your pistons swell in the bore and essentially try to seize pinching the rings and shattering them or making a inner rod become a outer rod well lets put it this way that is our weakest link the piston / rings in our motors and our compression ratio. The way around this is if you get the pistons that have the wrist pin 10 thousands farther up and shave 5-10 thousands off the piston top you would have equivalent of 20 thousands less squish which means around a 2-3 point compression reduction our motors are 21.5:1 factory so that would put you in the 18.5-19.5:1 area making for around 20-25 psi max boost if you have the valve springs and valves to handle it. I want to point out as you add heavier valve springs you add alot more wear on the valve train / cam so be aware doing so really reduces reliability longterm.

I sacrificed 15+ of our motors testing theyre limits and have pushed them in alot of different ways to theyre breaking point and i got a barn full of destroyed engines and another full of my successfull setups I did propane / nitrous / water **** injection / and well good old boost and I thrashed them hard and worked them hard.

I got 13 of our trucks with our motors and many other well how should i say it custom designed vehicles with our motors in them and around 20 or so still good loose motors setting around in running order some beefed up some stock none for sale i buy every motor i find of these engines 6.9 or 7.3 idi that are reasonable local to me wherever i am.
 
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IDIoit

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i have a factory N/A block, that had previously dropped a few glow plug tips into the pistons before i got it.
3 of them looked like this.

i slapped new geadgaskets on, oki lapped the valves, all guides were decent, and they wernt cracked.
threw some comp 910 springs on them, and BOLTED it back together.

now all of my IDI "career" ive heard 15 psi max.

its like they all work for the dealer :kick::joker:
this engine got put aside for a rainy day, incase i needed it.

i decided to run this engine in the offroad truck i built about 4 years back,

now i dont tow with this, but it is a on/off road vehicle.

and i am not nice to any of my vehicles :)
i push 25 psi, intercooled, twin t04e's i dont even have my pyro hooked up because im only on a R&D 110
i push this on long roads with the pedal to the metal.
until i just about shard myself.
4 years of this abuse.
63 ranchero - YouTube
 

Laine D

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There is more to it than just head studs to allow for above 15psi boost even with intercooling unless you decompress our motors above 15PSI is risky yeah you may be able to do 20psi but when you get brave and hold it there and your pistons swell in the bore and essentially try to seize pinching the rings and shattering them or making a inner rod become a outer rod well lets put it this way that is our weakest link the piston / rings in our motors and our compression ratio. The way around this is if you get the pistons that have the wrist pin 10 thousands farther up and shave 5-10 thousands off the piston top you would have equivalent of 20 thousands less squish which means around a 2-3 point compression reduction our motors are 21.5:1 factory so that would put you in the 18.5-19.5:1 area making for around 20-25 psi max boost if you have the valve springs and valves to handle it. I want to point out as you add heavier valve springs you add alot more wear on the valve train / cam so be aware doing so really reduces reliability longterm.

I sacrificed 15+ of our motors testing theyre limits and have pushed them in alot of different ways to theyre breaking point and i got a barn full of destroyed engines and another full of my successfull setups I did propane / nitrous / water **** injection / and well good old boost and I thrashed them hard and worked them hard.

I got 13 of our trucks with our motors and many other well how should i say it custom designed vehicles with our motors in them and around 20 or so still good loose motors setting around in running order some beefed up some stock none for sale i buy every motor i find of these engines 6.9 or 7.3 idi that are reasonable local to me wherever i am.
I kinda just skimmed through this but are you aware that there are a lot of guys running well over 20 psi with just studs. Some without studs.
 

Farmer Rock

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I kinda just skimmed through this but are you aware that there are a lot of guys running well over 20 psi with just studs. Some without studs.
I remember reading a while back on FTE, a member was running 35 psi. I don't know how long it lasted though



Rock
 

CBRF3

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i have a factory N/A block, that had previously dropped a few glow plug tips into the pistons before i got it.
3 of them looked like this.

i slapped new geadgaskets on, oki lapped the valves, all guides were decent, and they wernt cracked.
threw some comp 910 springs on them, and BOLTED it back together.

now all of my IDI "career" ive heard 15 psi max.

its like they all work for the dealer :kick::joker:
this engine got put aside for a rainy day, incase i needed it.

i decided to run this engine in the offroad truck i built about 4 years back,

now i dont tow with this, but it is a on/off road vehicle.

and i am not nice to any of my vehicles :)
i push 25 psi, intercooled, twin t04e's i dont even have my pyro hooked up because im only on a R&D 110
i push this on long roads with the pedal to the metal.
until i just about shard myself.
4 years of this abuse.
63 ranchero - YouTube



I kinda just skimmed through this but are you aware that there are a lot of guys running well over 20 psi with just studs. Some without studs.


I remember reading a while back on FTE, a member was running 35 psi. I don't know how long it lasted though



Rock


The point is I wouldn't trust anything over 20psi with just studs not for the headgasket but for the pistons / rings themselfs the compression is still to high the force on the ring lands is way to high and will quickly make the ring lands sloppy / loose causing alot of blowby / oil seapage unless you decompress I wouldn't run over 20psi simple as that and anything above 10psi you want to intercool or your negating even pushing boost above the 10psi range due to charge heat aka hot intake air negating density making the added boost useless.

This is not even taking into account the issue with valve springs and valves themselfs unless you have the inconel valves your playing with disaster there is alot more to our motors than just boost to get our motors to run reliably at boost lvls above 15psi alot of factors to make them do it reliably and safely.

I pushed 35psi before and yes it held and nothing bad happened yet on a cold day running 30psi I blew a motor to pieces so would I trust that daily no for me after decompressing 20-25 psi is the safe point for driving it /towing or whatever in any climate / temp / elevation again this is my findings PSI is not everything your air density and charge temp is much more important 25psi at sea lvl vs 25psi at 5000feet above sea lvl are very different air density this has to be factored in. So just throwwing out a high number to someone unfamiliar is like telling them its okay to shoot a 150 shot of nitrous into our engines ( I did this on a NA motor and it survived but had a tick / knock for rest of its life ) its a gamble and much more needs to be factored in so saying 25psi+ with just studs is okay is not a wise idea.


I want to point this out also ambient temp and humidity play a huge factor in whats a safe amount of boost cooler air is more dense meaning 20psi of cold air vs 30 psi of warm air the 20psi of cold has more energy potential. Then you got again humidity to factor in not including elevation. The point is in hotter higher elevations you can run more boost than you can in lower / cooler elevations before things go pop. So throwing a blanket high PSI number out there is not a good idea factor in a safety margin not just I run 25+psi with just studs people need more info like elevation and ambient air temp and humidity.

I also want to put this out there if your sucking in engine air into the turbo your literally throwing all the numbers out window engine bay temp vs ambient air temp is way off if your sucking air in from engine bay your air density will be much lower so you in theory could run more boost pressure than if you had a proper cold air intake system again all because of density.
 
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03wr250f

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To op as a general rule 12-15 psi non studded for a 7.3
Studded as much as you want.
Your question about the bottom end, na bottom ends start breaking with a 150cc
I also saw justin peg a 60 psi gauge with a rering craigslist idi that was studded and had a 150

I have seen 19 psi intercooled on water **** without studs and drove that way for a test and a half.

How you get into the throttle plays a big difference, rolling in at mid to high rpms creates far less cylinder pressure rather than matting the pedal from idle..


To answer your question past about 15 psi you are going to be hot charging the air and not being efficient making much more boost than that with any of the stock turbo setups( banks ats etc)



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cozinsky

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How much is safe on stock valve springs? I have studs but decided against 910s because I don't plan on running this thing like a race car and I don't care for the added stress and wear on the valvetrain components so I shimmed my original stock springs back to factory specs.
 

CBRF3

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To op as a general rule 12-15 psi non studded for a 7.3
Studded as much as you want.
Your question about the bottom end, na bottom ends start breaking with a 150cc
I also saw justin peg a 60 psi gauge with a rering craigslist idi that was studded and had a 150

I have seen 19 psi intercooled on water **** without studs and drove that way for a test and a half.

How you get into the throttle plays a big difference, rolling in at mid to high rpms creates far less cylinder pressure rather than matting the pedal from idle..


To answer your question past about 15 psi you are going to be hot charging the air and not being efficient making much more boost than that with any of the stock turbo setups( banks ats etc)



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The issue is I believe the OP is after a daily driver so going crazy and saying there is no limit to amount of boost with studs is just asking to give him a sour taste in his mouth and future hatred for our motors and from other people following your said advice ( Studded as much as you want ) which is insanity and very bad advice because they will think they can treat them like a power stroke / cummins / duramax and pile on the boost not understanding there is a difference ( indirect injected vs direct injected ) we have a limit with indirect injected you forget a key thing our motors when you go crazy on boost / fuel the pre cups crack over a short period of time and cause all kinds of problems PLZ use a little caution before throwing such claims of numbers like 60psi and such those are not daily driveable numbers theyre set to kill numbers and is literally telling him to have his engine commit suicide. A reasonable advice would be 20-25 psi is a safe number with studs / intercooler and daily driveable if decompress you can push 25-30 psi safely with studs / intercooler but decompressing brings other issues like hard to start and well cold nature issues and cylinder washing / glazing.

This is not even getting into other issues like valve springs and such above 25psi the stock valve springs float if springs are in good shape at higher rpm and this can make a piston and valve kiss making for a nasty outcome if your valve springs are worn and unknown I advise not to run above 20psi.
 
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03wr250f

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The issue is I believe the OP is after a daily driver so going crazy and saying there is no limit to amount of boost with studs is just asking to give him a sour taste in his mouth and future hatred for our motors and from other people following your said advice ( Studded as much as you want ) which is insanity and very bad advice because they will think they can treat them like a power stroke / cummins / duramax and pile on the boost not understanding there is a difference ( indirect injected vs direct injected ) we have a limit with indirect injected you forget a key thing our motors when you go crazy on boost / fuel the pre cups crack over a short period of time and cause all kinds of problems PLZ use a little caution before throwing such claims of numbers like 60psi and such those are not daily driveable numbers theyre set to kill numbers and is literally telling him to have his engine commit suicide. A reasonable advice would be 20-25 psi is a safe number with studs / intercooler and daily driveable if decompress you can push 25-30 psi safely with studs / intercooler but decompressing brings other issues like hard to start and well cold nature issues and cylinder washing / glazing.

This is not even getting into other issues like valve springs and such above 25psi the stock valve springs float if springs are in good shape at higher rpm and this can make a piston and valve kiss making for a nasty outcome if your valve springs are worn and unknown I advise not to run above 20psi.
I will agree that it is always recommended to run stiffer valve springs, and have the guides replaced when you stud(have the heads entirely gone through)
But I disagree with most of what you have said especially with factory fueling.
As well as the decompressing statements.
My decompressed truck starts just as good as any stock truck.

This is Provided coolant temps and egts aren't out of control I see no reason running as much boost as you can push.
At a certain point yes you do start overspeeding the turbo, but that depends on the turbo, an intercooler is recommended for lowering intake temps and not hot charging the air, but with a factory turbo cal ip I had no problem running 23psi boost. Which is about as much as i could make.
You have to have a 150 or better to be making 60 psi so 99% of your average idiers aren't going to ever make that much.
My point is if you have the supporting mods (studs, valve springs, gauges and a intercooler) I would run it. I understand he doesnt have stiffer valve springs so i would keep it under 20 psi, but even so that is going to be at the upper limit of what a mostly stock truck will make.

To op run it. I reccomend intercooling to get the most out of it, and a turbo upgrade would be awesome, but I understand not everyone will do that.. watch your gauges and try to keep it under 20 but it isnt the end of the world if you dont.
That being said if you drive it like you care about it the engine will last a long time. But even a n/a engine driven like it owes you money won't live long

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CBRF3

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I will agree that it is always recommended to run stiffer valve springs, and have the guides replaced when you stud(have the heads entirely gone through)
But I disagree with most of what you have said especially with factory fueling.
As well as the decompressing statements.
My decompressed truck starts just as good as any stock truck.

This is Provided coolant temps and egts aren't out of control I see no reason running as much boost as you can push.
At a certain point yes you do start overspeeding the turbo, but that depends on the turbo, an intercooler is recommended for lowering intake temps and not hot charging the air, but with a factory turbo cal ip I had no problem running 23psi boost. Which is about as much as i could make.
You have to have a 150 or better to be making 60 psi so 99% of your average idiers aren't going to ever make that much.
My point is if you have the supporting mods (studs, valve springs, gauges and a intercooler) I would run it. I understand he doesnt have stiffer valve springs so i would keep it under 20 psi, but even so that is going to be at the upper limit of what a mostly stock truck will make.

To op run it. I reccomend intercooling to get the most out of it, and a turbo upgrade would be awesome, but I understand not everyone will do that.. watch your gauges and try to keep it under 20 but it isnt the end of the world if you dont.
That being said if you drive it like you care about it the engine will last a long time. But even a n/a engine driven like it owes you money won't live long

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The question is how decompressed are you its a very fine line on what makes our motors hard to start been there and done this many times and well you need to do your research some stock pumps maxed out pump a substantial amount of fuel and can spike a turbo quick over driving it and well also over fueling equaling the perfect recipe for chaos my marine pumps I use pump a crazy amount of fuel.

https://www.stanadyne.com/dealerportal/ssi/english/Parts Bulletin/159.pdf DB2831-5090 1993-1994 Marine 260BHP injection pump that is like 264hp if remember correctly so again you need to be carefull and that pump can be turned up even further if remember correctly is a DB2 DB4 hybrid and can do like 120cc-130cc of fuel before turning them up. I have 5 of these injection pumps and only got the one left still working and haven't been able to find anyone able to rebuild these injection pumps supposedly a special custom injection pump.
 
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