Who Tows and hits over 30 psi on stock headbolts - headgasket ?

[cajflynn]

I thought 40lbs was the over under for head gasket damage.

[98whitelightnin]

I have hit 42 psi on stock gasket and bolts but usually dont run the edge up that high and on 2x5 it will only hit 38psi. I dont do much pulling but have been over 30psi while doing it.

[JOHNFAK]

I thought 40lbs was the over under for head gasket damage.

ID say thay sounds right from what I have read. Problem is a lot of guys cant hit 40 with the factory wastegate and even if adjusted with factory or low injectors. So 30 seemed more appropriate So I think looking at the results - you dont need aftermarket studs towing on a mainly stock truck (HY35/HX35).

[Mopar1973Man]

Well I got back from a camping trip and hauling the trailer around. Yes I can tag 35 PSI without thinking but do I really want to hold it? Naw... I typically go over at 20-25 PSI in 4th Gear holding 53-55 MPH... Not a problem!

[JOHNFAK]

Same for me just did a move to outer banks .... Hit 42 psi a couple times ... But generally between 15-25I have studs tho do kinda doesn't count ....

[AH64ID]

Cylinder pressure is what blow's HG's, not boost. Generally more boost means more cylinder pressure, but not always. Boost is just a measurement of restriction. Stock a 04.5-07 will hit about 32 psi peak, and settle down to 28-30 empty and 28-32 with a trailer. I added a Smarty Jr to my truck, all hard parts were stock, and could hit about 33-35 normally, up to 37 twice. No issues. Smarty Jr adds timing, up goes cylinder pressure. I then did a couple of intake mods (GDP horn, Airaid MIT, HD CAI) and my boost dropped didn't change, but IAT's went down.. cylinder pressure goes up. I then installed a Colt Cams Stage 1 cam. Boost dropped a psi or two at certain power and went up a psi or tow at others. I was now peaking at about 32-35 on SW1, and 34-35 on SW2. Les restriction, more air and more cylinder pressure. I then installed a Garrett Stage 2 turbo and now I have to WORK it to get 32 psi on SW3. I run cooler EGT's and more power with less boost than I ever did on SW1 or stock. Why... it goes back to restriction. The intake mods dropped the temp of the air, so more 02 and thus better combustion. The cam left the intake/exhaust valves open longer and has a better LSA. Restriction goes down, boost goes down, airflow and cylinder pressure goes up. The turbo eliminated my exhaust restrictions. The stock turbo could easily pull 30 psi of boost and 50 psi of drive towing up a grade. The Stage 2 does the same work at 26 psi of boost and 20 psi of drive, with same/lower EGT's. The boost makes it look like less air, but the EGT's indicate that the same or more air is moving, more air means more cylinder pressure. The airflow is increased from the turbo my running the drive pressure lower than boost, and a more efficient comp wheel runs the lower IAT's per psi of boost. When I did the turbo I also installed studs, even thou I only have hit a peak of 32 psi with my current setup and stock head bolts are supposed to be good to 40 on a HPCR, I am running a LOT more cylinder pressure than a stock motor at 32 psi. How much more I don't know, but I didn't want to mess with it!So, long story short is you have to consider all of your mods, not just the boost gauge.

[JOHNFAK]

more air means more cylinder pressure.

I guess thats the point. Obviously differs under so many variables noone here could ever really know. Only way to kinda guage it is the DP guage from the exhaust side. Since most people run a HX35 and stock bolts - this side of thing is pretty much same - not many people run a cam or twins (thats why I didnt pay much attention to catjflyn or myself results). The thread was actually started because a number of comments were made that if you tow and hit high PSI then you better have studs or risk a headgasket. This thread was an attempt to show 2 things (based on most common configurations outside of injectors/programmers). 1) Towing has little/no effect - as it doesn't increase cylinder pressure anymore than romping on it down the street - probably proven based on the results above already. 2) 30 PSI is pretty safe - street or otherwise on a hx35.

[MnTom]

I am the one that had to replace my head gasket. The reason I did was to fix a water leak by the water pump. Then I did have a gasket blow between #5 & #6, but that was a fault of the gasket I used. I can hit 36 PSI and higher if I turn up the propane..........