economy problems, compression and head porting

kawi600

kawi600

got Coal for Christmas
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Jun 9, 2008
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Ive got a truck that does hauling and DD duties. Ever since the cam went in and the head gasket failed soon after Ive had major issues with fuel economy and dirty oil. I mean like 10mpg and oil black like paint in 100mi.
My current theory is that when I decked the head .015 and added a .020 gasket I lost enough compression that at low loads the motor doesnt push enough exhaust to put the turbo in the sweet spot.
So I have two questions.. Whats the best way to get some of that compression back? Or heck even adding another point or so over stock to optimize for response and spool times. I dont expect to want to go over 650hp in this, I think I can hold the head on with studs and orings at those pressures.
I know I need a new head since I have to account for valve protrusion. The gasket is where Im losing compression. If I replace the head, Im guessing its worth having it ported first but I dont want to lose low rpm flow. In that case would a hamilton 12v head or a ported stocker be better?
 
I would have the valves sunk .015" to compensate for the cut and run a standard gasket...

and if the Hamilton head is in your realm of affordability, I would be all over it
 
Looks like hamiltons 12v head flows better than stock. I dont want to do anything that upsets low rpm power obviously. Think porting that head even further would help out? Or would that hurt low-end? Not sure if that is gasser thinking there and if diesels are different with flow.
 
what model cam and did you degree it in?

A 0.020" over headgasket is only a 1 point drop in compression. I don't think you would see those symptoms from just a 1 pt drop in compression.

How did the headgasket fail? Did you end up with coolant in your oil?
 
I had a shop do the install so Im assuming they set it up according to Zach's spec. Its a mild street 181/210 cam, cast.
The head gasket failed with the extra power, it was totally a self-inflicted wound, lol. When it failed it was coolant leaking only over #6.. not oil / coolant mix.
Well, put it this way.. the symptoms began right after the new head gasket. It used to get 13mpg city if I beat the snot out of it. Now I get 10mpg mixed city / highway driving it easy.
I already had the pump reworked.. and my trans is built up with a decent converter. So I think compression might be the key to low end efficiency. And it cant hurt my take-offs.. which are awful now. all smoke and it goes nowhere fast unless I brake / boost launch it.
compression reads at 360psi hot. Seems a bit low.
 
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kawi600 said:
I had a shop do the install so Im assuming they set it up according to Zach's spec. Its a mild street 181/210 cam, cast.
The head gasket failed with the extra power, it was totally a self-inflicted wound, lol. When it failed it was coolant leaking only over #6.. not oil / coolant mix.
Well, put it this way.. the symptoms began right after the new head gasket. It used to get 13mpg city if I beat the snot out of it. Now I get 10mpg mixed city / highway driving it easy.
I already had the pump reworked.. and my trans is built up with a decent converter. So I think compression might be the key to low end efficiency. And it cant hurt my take-offs.. which are awful now. all smoke and it goes nowhere fast unless I brake / boost launch it.
compression reads at 360psi hot. Seems a bit low.
Click to expand...

wish mine had that much 130 all i get
 
I think the pump shop put it in the ballpark with my #10 plate on there and the shop dialed it a little. I have experimented with the AFC star wheel cranked down to limit on-boost fueling a little more but it doesnt help the haze or fuel economy much. Right now it doesnt smoke much, it just hazes at idle and on take-off.
Honestly this all seems to point to a compression issue. No one else gets this with lower CR from a thicker head gasket? Does 360psi sound okay? I think Ive lost about 100psi over stock.
130psi would make a good race truck Id guess, but as a DD id imagine youd probably need ether to start it and your exhaust would be set on 'mosquito control' no matter how much pedal you gave it. ;p
 
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I did a compression check on my 12v a couple months back, it was 400 psi across the board. Thats stock gasket. A friends 12v was 390ish, stock gasket. So 360 for dropped compression sounds about right.

Have you tried swapping injectors at all? Might have gotten damaged during the head overhaul.
 
Just throwing this out there, but have you checked for boost leaks, and checked to make sure your pump timing hasn't slipped?
 
yeah Ive seen 425psi posted elsewhere for a stock setup so Im guessing the 360psi is about right for a point of compression.
I had the shop check for boost leaks when they replaced a damaged cam and pushrods (not enough ZDDP in the oil apparently). I had them set the pump to 15 degrees in the hopes of getting some low end power back.
I tried it at 19 degrees for awhile but the economy was unchanged. Maybe a little cooler when I was really hard on the throttle.
Truck is going back to the shop in 100mi to make sure the new valvetrain parts are holding up. Maybe do an oil analysis.
Id have them do a leakdown test but Im not sure that will be really useful.

Another thought I had was maybe the torque converter Im using is just really lossy at low revs. But I dont get much improvement on the highway, maybe 14mpg if theres no city driving mixed in. Pretty sure the TCC is locked up during those trips.
 
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iam having nearly the same issues regarding fuel economy/haze at idle and take off..

ive done several pump adjustments with starwheel possion/stock vs> cut fuel pin and fuel screw.......it helps but not substantialy

i have my head gasket weaping outside #1 and a retourqe to 120 stoped it for now while i gather parts.. iam getting 11mpg with the VE :doh:

i just put the new convertor in and only have a couple hundred miles on but my thoughts are.

my converter is too tight and my he351 is struggling to spool it....wierd thing is it feals as if its getting worse too....:nail:

the injection pump is weak
or my injectors are the issue..pop pressure out or....?


ill be following this thread cause the .10 over head gasket port job and new injectors going in have me worried my milage will get worse if even possible

:pop::pop::pop::pop:
 
Theres a lot of things that play into fuel economy. Like gearing (4.10 is probably bad) city driving, tire size, etc.
I know what Ive tried so far that didnt net me an improvement so Im going to try the head and head gasket since I want to get a ported one on there anyhow.
 
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