compression versus port velocity on a DD truck

kawi600

kawi600

got Coal for Christmas
Joined
Jun 9, 2008
Messages
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Im in a bit of a pickle with this truck. I put a cam in it awhile back and it ran real nice. Problem is it ran so nice I went and popped the head gasket in no time flat. :kick:
So I had the head gasket done. Shop milled off .015 and installed a .020 head gasket on it. way up on top in the rev range it runs great. But I spend like .001% of my driving time in that part of the revs. Most of the time Im driving at part load, low revs.
With the head gasket swap the economy went down to 8mpg. Haze never goes away. I tried a pile of stuff because everyone insists a tiny change in compression just doesnt do this sort of thing.
So now after trying everything else here I am. I have one more question to think on before I decide between a hamilton 12v head and zach's idea of decking the head a little more and effectively placing the valves further in the cyl (with a clay check of course)
Either one of these ideas would restore or add extra compression. The hamilton head might have consequences for a DD truck on the low end with reduced velocity. when you open up the intake ports on a motor, you lower velocity. When you port or cam a gasser, usually they recommend you put in high compression pistons to help offset the loss in low end power (im assuming).
Would it follow that raising compression on a diesel could be a substitute for port velocity to help boost part-load power?
This truck is driving me nuts. If I dont get this sorted Im going to drive it off a cliff somewhere. :bang
 
sounds like a timing/ injector issue

what injector shims are you using? sounds like you could be out of the bowl


i dont think that hamilton head would run worth a crap under low load
 
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Its not injectors or timing. Ive tried settings from 15 - 22*. Ive tried 4 different sets of injectors, most recent sets from weston. running .6mm shims have even tried with 145* nozzles.
Re-did the transmission after the TCC lunched itself.. benched the injector pump. compression reads 380psi across the board Im told. Checked the valve lash. no boost leaks, etc. I mean seriously, whats left?? Gotta be the deck height. process of elimination.
I think you might be right with the hamilton head. its an awesome setup, but for what I do its probably not the right one. Zach even pointed me in the direction of modding the head thats on there now
since Ive had this low end power / haze / economy problem going on.
Id buy it in a heartbeat if I can compensate for that loss in velocity with compression, but I dunno if it works that way on a diesel.
 
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Maybe a bad valve job? I know of a 24 valve that is doing exactly as yours and this happened after a local shop resurfaced the head and did a valve job.
 
when they resurfaced the head did they sink the valves or deck the head and add a thicker gasket? I have the thicker gasket, it kills compression and low end. Economy is awful too.
For a drag truck lower compression might be good news, for a DD toy hauler not so good.
 
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this is why i went with cummins industrial pistons that started with 17.5 before reliefs and will run a standard thickness head gasket.. until someone starts making a relieved piston that has higher comp and big bowls we are all sol.. kindof silly really.
 
Whats the compression on the stockers that came with the 160hp auto motor back in 95?
Thought all the non-marine ones were the same 94-01? If theyre off a specific motor, I wonder what else is different about the setup.. different cam or injectors? Lots of variables. The more I mess with this stuff the more appreciation I have for these engines and cummins R&D.
 
all 12 valves from 94 to 98 we the same in light duty trucks.. at 17.1 to 1.. 98.5 to 01 was a 24 valve.
commercial pistons have a bigger bowl and thicker upper crown and distance to the first ring.. 10.8 mm vs 8mm.. along with this piston also has a slightly higher cr at 17.5 to 1..
im with you on keeping as high or as close to stock cr as possible for dd for all things mentioned.. haze, spoolup and low end responce, efficiency... i see no real reason to loose compression.. but just my opinion for what thats worth.
 
do you have a hamilton head on that truck? just reading your sig
 
i just got it to the door today.. im building the motor right now after the last one cracked the block. i run higher timing so i also had 2 of the stock pistons start to crack(only one 1/8 crack in two different pistons) so it was a complete rebuild.. that and after first welding the crack when it finally let go a couple months later it lost all the water so cracked the stock head bad and ended up breaking one of the cylinders.. so this is another complete rebuild. should be a good one thow..
 
You talking to dezlfrek or me? dezle just got his. I have one on my truck as well though and like it a ton so far.
 
So did they deck the head or block? If the decked the head and you put a .020 hg on it you dropped your cr quite a bit probably in the 14.5 to 15 range. I would sink the valves, shim the springs and run a normal gasket
 
yeah, just curious what you had on the truck before the head and then after.. and what the truck drives/ drove like around town.
Im getting a lot of conflicting info about whether port velocity (and swirl) is needed on diesels. Dont think the hamilton head does much of either till further up in the rev range.

Lostnwalmart said:
You talking to dezlfrek or me? dezle just got his. I have one on my truck as well though and like it a ton so far.
Click to expand...
 
kawi600 said:
yeah, just curious what you had on the truck before the head and then after.. and what the truck drives/ drove like around town.
Im getting a lot of conflicting info about whether port velocity (and swirl) is needed on diesels. Dont think the hamilton head does much of either till further up in the rev range.
Click to expand...

Zach did a lot of port work to my head to increase my low lift and swirl. I changed way to many things at once to do a comparison but the truck spools my 75mm turbo like nothing.
 
Lost, I just got off the phone with him Im going to do the same route. Even if the low end is a little less than stock its better than what I got now. Truck is lazy and smokey.
Plus I want to put twins on there and keep the head gasket, so this sounds like the way to go.
Do you recall if he needed piston protrusion before he machined the head? He didnt say if decking the head and lowering the valves into the cyl was part of the plan or not. Im assuming it is.
 
I don't belive he machined mine other than for orings because I told him I wanted to run the 188 with out fly cuts.
 
It will be interesting to see what Zachs head does with a 13mm pump. Hopefully someone will try it soon.
 
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