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Modified 6.2 turbo diesel

Definitely right. It's cylinder pressure at the right time, that makes power. For smaller degrees of compression lowering, like my 19:1, I think a little additional boost can compensate & there's still reasonable mixing going on in the pre-cup. Otherwise, I'm not certain I can explain why it will get 19+ mpg on the highway.

Seems logical that the lower the compression goes, the lower % of the overall cylinder fill goes thru the pre-cup & gets the benefit of of all that induced turbulence to help the fuel/air interaction - given our relatively low psi squirt injectors.

Beyond concern for longterm durability, the concerns/issues you're seeing w/ modified inj pumps is why I expect to be happy when I've maxed what I can get out of an off-the-shelf DS4 reliably for 100 k miles.

Still, I'm quite interested in what you're doing/what's working/what's not etc.
 
Must be why Bill Heath said stock compression is fine,you might get more power with a given amount of fuel,guess he must control cyl pressure more with timing,I still think lower is better, to a certain point, for longevity. Reliability is not a major concern with this motor,its more like a test mule, once I think I have it figured out I'll build one the right way for a tahoe or burb with reliability in mind,so the wife can drive it. It wont hurt so bad when blow up a motor I got for free compared to one with lots of money in the block,I focused mostly on the injection and turbo,they can be reused if the motor blows,and start all over again,lots of money for pistons and block machine work could be lost if I would be experimenting with a fresh rebuild.
 
My understanding (not that complete, but keep trying to expand it - 6.5-wise) is the potential longevity benefit in lowering comp a bit, relates to peak cylinder pressure/temp.

Can't really seeing it being lower average cyl pressure, as that's somewhat equal to power... & there have been some strong 18:1 performances.

Peninsular found the lower comp to eliminate some piston to cylinder scuffing/seizure problems they found when running stock comp ratio turbo 6.5's on the engine dyno at high constant loads for hours at a time.

The lower comp solved that problem for them. Another thing that Matt told me when I spoked to him about 18:1 while deciding what I wanted to do: he said they'd never had a head gasket failure warranty issue in all the marine 6.5's they'd sold.

Now the better coolant temp control a boat's seawater heat exchanger system allows could certainly contribute to improved head gasket survival.

Still, it was convincing enough that I decided to go lower comp on my project. Certainly not necessary, but it might enhance reliability. Who knows, guess I thought so.
 
Yeah, if you raise boost, then youre shoving more mass in there, so cylinder pressures still go up even at lower compression ratio. After seeing bk95td's album, confirms I'm going to cermic coat the pistons, valves, head surface and precups.
 
Some people told me my pistons will seize on the 6.2,especially since there not oil cooled,Ive had my pyrometer at 1600 degrees for short periods,that seemed to be hard on the head gasket ,but the pistons still look fine,my 6.5 had stock compression and exhaust temp was normally maxed around 1000 degrees 1300 if held flat for a long period, it cracked a piston,looked like it started at the wrist pin, probably from the compression being to high,I was running about 38 psi boost on that motor ,I guess it had no room for all that air. Lower compression should run cooler,mine dont because of other issues,any time you compress air it gets hot and the higher its compressed the hotter it will get.
 
I got my four plunger head and rotor today, its going to need a different cam ring or a custom made one, dont know if the cam ring that matches this head and rotor will have enough lift, looks like it will take a little work to figure it all out.
 
Ill try to get some pictures on here,my camera cord is bad,I bought a card reader but it didn't show up yet.There is definitely a issue with the shoes and cam ring,as it will bottom out the shoe in the rotor,Im guessing the db4 uses less lift,and definitely different shoes as I had to modify one for a test fit,If the db4 uses less plunger travel than the db2 this is good news for me,maybe I can mix and match for more travel,the only people that I know ,that made this pump work is the pump shop that builds them for peninsular.
 
Yeah, sorry forgot about your camera card reader issue. If the camera has a standard mini USB port and mini USB cable will work on it.

That may be why the DB2 and DS4 can keep up with the DB4? DB4 has less travel in the plungers. It may be more reliable then though. Work at higher rpm.
 
Would seem logical the DB4 might be more reliable running at consistently higher rpms & fuel flow. At least the one rated at 310 hp for marine use.
 
Got my card reader today,now Ill have to take some pictures,I talked the guy I got the head and rotor from he is looking into the cam and shoes for me,if no one can come up with any thing, it will all have to be custom machined. I want more than 310 hp of fuel but it might be a good place to start with.
 
Im still learning how to do pictures,didn't know about editor mode
 
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Worked on my pump most of today,only thing it needed was different shoes,I reused everything else. Should have it running monday.
 
Try this one, it brings up a big picture for me.
 

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Got my truck running last night , definetly runs better,the head gaskets are leaking already.
 
What gaskets are you running? How did you get down to 16-1 compression?

What you may find is that you reach a wall of diminished returns when boosting this high. It take fuel to make boost, and it takes power away to create more exhaust backpressure. So you might try only pushing say 30psi and see how it runs ;)
 
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