Engine/Transmission (1994 - 1998) Safe PSI limit on stock engine?

[QWaller]

I have a 10 plate not full forward and my afc is not either. Clutch easily slips. In it too long and my heat gets 1350 ish. However, it is easy to run 34 psi and I have seen 40 on a hill with load if I dog it. I did disconect the wastegate line. I am thinking that these pressures are too much. What say the informed public? Will my temps get even higher if I limit to say 30 PSI?

 

[R.ebel]

For a short term fix reconnect you wastegate line and get a "boost elbow" The stock HX35 goes out of it's map at around 35 psi, any more than 35 psi and you are just making a lot of hot air contributing to your high egt's. It's time to start looking for a larger turbo. Welcome to the slippery slope know as bombing :-laf



Edit: The stock head gasket is good for 40-45 psi if the engine is warmed up properly.

 

[arthr31]

if it's the stock clutch, that's not surprising it's slipping... you are about 100HP over the rated power it can handle.



What's your timing? That contributes to the overall pressure being put upon the engine. I'd say keep it below 34 psi boost and you should be OK. Also, south of 1200 degrees and you should be fine too...



I have to really get on it to see 1200 and by that point the clutch is totally sufferring. .

 

[QWaller]

Timing is stock. All I have is a BHAF and the plate. Average mpg 17, 18. 5 interstate, with a beefy flatbed. I am not complaining. Paid for and has great power IMO for the little that has been done to it. Next will be a four inch exhaust. I am hoping that this will cut the egts 100 or so?

 

[wildmanben]

Yeah it should.

 

[CumminsPower98]

I personally have my timing at 16 and finally blew the gasket while towing in sub-zero temps at about 247k (334k now). My boost accidentally (was trying to keep it lower) got up to about 38 psi a few times and I think this is what did it. To be safe I installed a boost elbow and adjusted it to 30 psi. I do have studs now but I'm paranoid and much more then 30 really doesn't do much for me anyway with the stock turbo. So I would also say to keep it under 35. You just never know, some hold a lot more then others.

 

[arthr31]

So, to follow up on this, does anyone know what's the max psi that a stock head (with stock studs) can take? I'm thinking of installing the 12mm arp head studs but might reconsider not doing it if I'm still safe at 35psi - my timing is 18* btw...

I personally have my timing at 16 and finally blew the gasket while towing in sub-zero temps at about 247k (334k now). My boost accidentally (was trying to keep it lower) got up to about 38 psi a few times and I think this is what did it. To be safe I installed a boost elbow and adjusted it to 30 psi. I do have studs now but I'm paranoid and much more then 30 really doesn't do much for me anyway with the stock turbo. So I would also say to keep it under 35. You just never know, some hold a lot more then others.

 

[dpuckett]

I frequently saw the 40psi gauge pegged on my old 91. Wasnt making the power yours is, as it wasnt intercooled, but it held just fine after the marine head gasket went in.



Daniel

 

[MAleksandrowicz]

I was hitting 50 psi with the stock turbo and gasket. :-laf As you can see in my signature it didn't last too long.

 

[JAyers]

Ive been hitting 45-50psi for the last year and a half. Just lil 3-5sec bursts. Prolly just jixed my self. Although it is seepin above the timing case and around the thermostat.

 

[CToney]

I'd keep her under 35psi and under 15. 5 degrees of timing. I don't mind doing a little wrenching but changing headgaskets gets old after a couple times. I tow so maybe that has something to do with it.

 

[bmoeller]

Next will be a four inch exhaust. I am hoping that this will cut the egts 100 or so?

I only saw a 50* drop with a 5" straight-piped exhaust. Bumping the timing to 15. 5/16* should lower the EGTs about 100-150*. All numbers pre-turbo.

 

[Voodoo Trucker]

My truck is a 94 2500 with 230,000 miles on the clock. It still has the original head gasket and head bolts. I run 24 degrees of timing with pump putting out 780 cc's of fuel and running 60+psi of boost (HTT sled puller 66). Why have I not blown my gasket so far? The first thing I did before I ever turned it up was retorque the head. When I checked my bolts they where at 65-70 lbs. ft. , way under spec. The first thing I do for all my customers before I turn up there truck is re-torque the head. And to date I have yet to see a truck that the head bolts where to spec. Head retorque should be right up there with the KDP fix. And as far as timing goes if you look at cummins marine timing spec (370 marine 5. 9) they are at 21-22 degrees timing from factory.

 

[CumminsPower98]

What is your method for re-torquing the stock bolts? Do you pull them out one by one, lube the threads and torque to spec or what? What about if the threads in the block are not fully clean?

My truck is a 94 2500 with 230,000 miles on the clock. It still has the original head gasket and head bolts. I run 24 degrees of timing with pump putting out 780 cc's of fuel and running 60+psi of boost (HTT sled puller 66). Why have I not blown my gasket so far? The first thing I did before I ever turned it up was retorque the head. When I checked my bolts they where at 65-70 lbs. ft. , way under spec. The first thing I do for all my customers before I turn up there truck is re-torque the head. And to date I have yet to see a truck that the head bolts where to spec. Head retorque should be right up there with the KDP fix. And as far as timing goes if you look at cummins marine timing spec (370 marine 5. 9) they are at 21-22 degrees timing from factory.

 

[Voodoo Trucker]

What is your method for re-torquing the stock bolts? Do you pull them out one by one, lube the threads and torque to spec or what? What about if the threads in the block are not fully clean?

First I find out where the bolts are at torque wise with a torque wrench I start at 70- 75 lbs ft. (center bolt #1) and turn the torque wrench up in 5 lbs ft inqraments until I notice movement. Then I follow the torque sequence in the book and check all bolts. I know the longer bolts end up with more torque then then the shorter ones. You may want to take the bolts with the lower torque to the highest final torque wrench setting step that is right before the final 90 degree torque turn method listed in the book. Most bolts will turn some may not, move on to the next one in sequence. I keep increasing the torque and feel for the bolt stretching. If you have been wrenching for awhile you get the feel for when you have exceeded the yield limit of a bolt. You get this feel by breaking plenty of bolts over time :{ . The torque to yield bolt is like a rubber band and you are trying to get as much stretch out of it as you can to gain clamping force with out over stretching it and loosing clamping force. I end up around 100-115 lbs ft. final torque.

 

[Voodoo Trucker]

One other method that would work that I have not tried would be to pull one bolt at time clean the bolt up, clean out the bolt hole with brake clean and air nozzle making sure there is no oil left in the hole. lube up the bolt and retorque the bolt to the highest "TORQUE WRENCH IN LBS. FT. " setting listed in the book. Do this one bolt at a time in the torque sequence shown in manual (from the center of the head out). Retorque the heads again to this final torque until all head bolts are torqued to the final torque listed for that bolt. Then the final torque for all bolts, 90 degrees torque turn method. Then adjust the valves to spec.

 

[CToney]

Increasing the timing raises cylinder pressure on the Piers website they recommend only one degree over stock timing. Also advanced timing moves the power band up higher at the expense of low rpm grunt. Advanced timing improves cold start, reduces egts, increases NOx emissions and lessens white smoke w/ a cold engine. Everything is a trade off and we each have to make an educated decision for our own situation. A marine engine probably has more radical timing because it runs at 2500 rpm all day long and the timing is more beneficial then.



What Voodoo trucker says about retourquing the head bolts makes alot of sense. It doesn't cost anything and is a good maintenance check.

 

[arthr31]

I have a question about this re-torquing... What if the HG is already compressed to its theoretical max (whatever that is). Wouldn't retorquing just introduce new compression values to something that is already (theoretically) spent therefore introducing the potential for either a leak or blow out?



This is so timely for me it's incredible. In a week and a half I have a conOFE installed, and I'll install new 191DVs and slide the 10 plate full forward. . I can already push over 35lbs boost so obviously I'm concerned...



I don't have the cash to do head studs now, but i certainly don't have the cash to do a full head rebuild like 5k from now either...



And, i guess, it also depends on wear-tear of the system and it's daily use, right? I'm 118k in and drive it every day, some days are a lot harder than others, but generally pretty moderate...



Okay, more than one question, I'll go back and get a beer now. .

Thanks for any input folks...

 

[Voodoo Trucker]

Increasing the timing raises cylinder pressure on the Piers website they recommend only one degree over stock timing. Also advanced timing moves the power band up higher at the expense of low rpm grunt. Advanced timing improves cold start, reduces egts, increases NOx emissions and lessens white smoke w/ a cold engine. Everything is a trade off and we each have to make an educated decision for our own situation. A marine engine probably has more radical timing because it runs at 2500 rpm all day long and the timing is more beneficial then.



You hear people on this site and others like it all the time talking about fuel plates, bumping the timing, bigger injectors,turbo, etc. You hear about people retorquing studs which are superior to the stock bolts all the time, some people due it once a month. You never hear people retorquing or even checking the stock bolts. If the engine is left stock running stock boost (18-20 psi) stock timing etc. you will most likly never have a issue. Now you bomb it and double the power and expect it to hold ? The only thing you hear about is blown head gaskets. Don't take my word for it, go get a torque wrench and see where you bolts are at. It takes far less time to check then to do a head gasket.

As far as timing goes its set where it is for emissions more than anything else. I own a 83 International S900 service truck with a DT360 (360 c. i. )and inline Bosch A pump, timing is set from factory at 18 degrees. There are other Int. trucks out there running more timing then that.

 

[Voodoo Trucker]

I have a question about this re-torquing... What if the HG is already compressed to its theoretical max (whatever that is). Wouldn't retorquing just introduce new compression values to something that is already (theoretically) spent therefore introducing the potential for either a leak or blow out?



This is so timely for me it's incredible. In a week and a half I have a conOFE installed, and I'll install new 191DVs and slide the 10 plate full forward. . I can already push over 35lbs boost so obviously I'm concerned...



I don't have the cash to do head studs now, but i certainly don't have the cash to do a full head rebuild like 5k from now either...



And, i guess, it also depends on wear-tear of the system and it's daily use, right? I'm 118k in and drive it every day, some days are a lot harder than others, but generally pretty moderate...



Okay, more than one question, I'll go back and get a beer now. .

Thanks for any input folks...

It has more to do with the stock torque to yield bolts. Like a rubber band they loose there memory over time and stretch out which in turn reduces the clamping force on the head and head gasket. Remember metal is very elastic. The other thing people rely on and never think about is that it was torqued correctly from factory :-laf, I have seen rods go through the side of the blocks on 5. 9's because one of the cap bolts was under torqued from factory. A engine is only as good as the people and machines putting it together and will only stay together accordingly. This applies to head gasket also. They only have to be with in industrial tolerances + or - 5% and that tolerance does not apply on mondays or fridays.