Engine/Transmission (1998.5 - 2002) difference between a 24 valve so head and a 24 valve ho head

[JPoindexter]

have been checking into parts and have found that there are different part numbers for the 24 valve so and ho heads for years 2001 and 2002. the so requires one p/n and the ho requires a different p/n. anyone know of the differences?. thanks

 

[Yooper1]

I think the difference between the two motors was how much compression and different injectors. With this little information I am guessing it is the "mill" hight on the head. . Block is most likely the same, only a lower hight on the head??? Sounds good.

 

[JPoindexter]

Yooper1. cummins said they control compression ratio with the heads. so you might be onto something. i have heard that the valves come very close to the pistons. this is why i am wondering if you can run a so head on a ho engine. i do not think the valves or seats are different however there must be a physical difference or it is all just marketing and they want to charge you more for the ho head.

 

[jwilliams3]

The pistons had a higher compression ratio on the HO engines.

IIRC the head differences HO had inserted valve seats and maybe better valve stem seals.



Someone correct me here!



For a High Horsepower application I would rather have the SO head that is not inserted (no worries of losing a seat into the engine).

 

[JPoindexter]

jwilliams3. the higher compression ratio of the ho engine is why i am wondering about using a so head on a ho engine. i do not want to ding the pistons with the valves ect. the so head has been decked 0. 011 and o-ringed. i want to run a 0. 010 over modified 12 valve headgasket and head studs. but do not want to run into clearance problems. i figure it is better to ask questions before. thanks

 

[Yooper1]

I don't think you would have any problems with that. I have a new rv head on my 01 and it's o'ringed with a . 010 over gasket. The person I would ask would be Olee Poole at www.powerbypoole.com. He put twins on my truck and know a lot of information of what to do and what not to do. Plus he's a good guy.

 

[JPoindexter]

Yooper1. i will give Olee Poole a call. thanks for the help.

 

[Mundgyver]

I believe that you will also find that not only the heads on an HO are different, but the pistons are different too. Probably has to do with the valve clearance. I know that the book warns about mixing and matching. They call is piston grading and pistons for one will not go straight into the other. I can't remember exactly, but I do remember a Cummins mechanic telling me you can bugger up a good engin real quick if your not carefull.

 

[JPoindexter]

Mundgyver. you are correct on the piston grading. they are graded by measuring the distance from the piston at tdc to the top of the block. even though the so should have greater clearances, if the pistons on the ho engine are at the min dimension and i substitute a so head from a engine that had the max dimensions for grading, could the valves from the so engine hit the pistons in the ho engine????. also i would think the compression on the headgasket should be greater with the head studs. i realize i am talking about very small tolerance changes but i believe the tolerances are very close on the engines as they come from cummins. i hope Olee Poole can answer these questions. yes i am trying to be careful. thanks for the info

 

[Bob Wagner]

Yooper1. i will give Olee Poole a call. thanks for the help.

Olee will take very good care of you. nice? yep :-laf

 

[JPoindexter]

Bob Wagner . i hear the same thing over and over about Olee Poole. from your "yep" reply it sounds like you might have a little more info on this subject. do you?. thanks

 

[Jetpilot]

SO and HO heads will have the smae compression ration, the difference in CR is the piston..... The HO heads have hardened valveseats which really help with the cracking issue our heads have. Personally I prefer the HO heads over the SO heads for this reason.



Doug

 

[JPoindexter]

Jetpilot. the whole deal with this is depending on who you call you will get several different answers. i called cummins and they say compression ratios are controled by the cyl head end of story. everyone else says its the pistons. my loyality with cummins is fading fast. it is one song and dance after another just like daimler chrysler. both cummins and daimler chrysler are willing to sell you parts at highly exaggerated prices because they are trying to limit the part availability. i do not know where all this will end up but one thing is for sure (daimler chrysler has lost a future customer as far as i am concerned). thanks for the information about the so/ho cylinder head. if you ever do need a cylinder head for a 2001/2002 ho engine cummins quoted me approx 2340. 00 and that is U. S. currency.

 

[Partyat33]

Cummins quoted a complete head for ~ $1200. $2340 seems unbelievable.

 

[JPoindexter]

Partyat33. do not know where you got the 1200. 00 from. the 2340. 00 was for a new complete/loaded ho head from cummins. perhaps the 1200. 00 was for a overhauled head. i agree with you on the 2340. 00 price. i have heard that the new heads from cummins are often not straight, meaning they often require a trip to the machine shop to get a straight surface. you would think for the price they would be perfect.

 

[Partyat33]

I am pretty sure of that price. If you want I will call cummins and check again. I just checked a couple of days ago. That is for a complete new head !

 

[justinp20012500]

The pistons had a higher compression ratio on the HO engines.

IIRC the head differences HO had inserted valve seats and maybe better valve stem seals.



Someone correct me here!



For a High Horsepower application I would rather have the SO head that is not inserted (no worries of losing a seat into the engine).

You are right.



I have a SO motor and have been running a HO head for 15K. No problems.



If my truck were seeing 1600*+ everyday I would rather have the SO head.



My SO head had 20 or so cracks in it and so have a few other SO trucks I have seen.





Justin