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Discussion Starter · #1 ·
Has any one ported and polished the head? How much difference did you notice? Is it worth it?
 

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Hi, I'm new to diesels, but I often wonder this also since lurking here and other diesel forums.

I have built several NA gas motor putting out well over 1.5 hp per CI at the wheels.
The secret has always been in the heads.
 

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Discussion Starter · #4 ·
So in other words its just know worth it so spent the money to get it done. But wouldn't create better air flow?
 

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So in other words its just know worth it so spent the money to get it done. But wouldn't create better air flow?
It might create better airflow. But nothing like a turbo can.:grinpimp:

But really, because the rpm and air speeds on a diesel are much lower, they won't get the improvements you can make in a high revving petrol engine.
Diesels also have big ports already because they don't need the extra turbulence that gas engines thrive on.
 

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THINK DIESEL NOT GAS......... leave it stock and it will live forever, soup it up and it wont last long. been there done that.... heat & pressure kills quickly.....
jmo
bob
 

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Just putting the head back on tonight, after gasket matching the exaust ports, and turbo flange. This is not a daily driver, and I wouldnt even mess with it if it was. You can see in the picture how much is inside the gasket on the left port. All I did was cut it almost to the gasket, and smoothe out the corners. You cant realy get to the intake side unless you cut it off like ZZ Fab does, and I didnt want to mess with going all the way in by the valves. Just was trying to clean things up, well see if was worth the 5 hours of eatin metal dust. :rasta:
 

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I agree for competition, port matching and then blending is about all that is usefull. A port polishing job will be of very little benefit especially with a daily driver.
 

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Most of the gain on the 2 valve cummins head can be made from removing material from around the intake valve, and impoving the shape. A pocket ported 12v dodge head will out flow a stock 24v head. I have done 3 heads on 4bt's. I don't remove any material from the runner. If you open up the exhaust port like that you end up with manifold sealing problems. I would say all things the same, you lower egt's by 150deg. This means more power at the same egt level. I just got my suburban project on the road. No ic yet. It make about the same power, and a lot more torque as the 454 it replaced. At full boost it has just a haze of smoke. It also has more power than my brothers 94 6.5 burb with intake, chip and open exhaust. It takes about 6hrs to do a head.

On a side note, Max rpm for 4bta is 3750, per cummins spec.
 

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THINK DIESEL NOT GAS......... leave it stock and it will live forever, soup it up and it wont last long. been there done that.... heat & pressure kills quickly.....
jmo
bob
wow, this makes no sense... head porting lowers boost and reduces EGT's.

production engine calibrations make many concessions to emissions and noise regs. those calibrations can be altered to yield more power and better fuel efficiency without compromising longevity
 

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It might create better airflow. But nothing like a turbo can.:grinpimp:
you can move the same mass of oxygen at a lower boost level... less stress on the turbo.

also, turbos are driven by exhaust energy. if the exhaust has a restriction-free path to the turbine, more of that exhaust energy is utilized by the turbo, thus increasing efficiency
 

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There are many wild and fantastic claims regarding engine work, including porting and polishing.
Often those claims are carried across from other applications which lose relevance, other times they are hyped up beyond anything of substance.

Port matching is usually worthwhile, but removing material from the head of a high compression and highly boosted diesel is more than a little risky.

Regarding application. In petrol engines more power is all about getting more air through at high engine speeds. Our diesels turn at much lower speeds, the air velocity through the ports is relatively constant, only the density and temperature is changed by the turbo boost.
As far as I'm aware noone has yet measured the volumetric efficiency of one of these engines, until they do then the proclaimed great benefits from head porting cannot be proven. As we are all aware, the universal butt-dyno is not an accurate device.
 

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wow, this makes no sense... head porting lowers boost and reduces EGT's.


Well actually it does.
Try blowing through a small straw, see how much back pressure you get in your mouth.
Now try blowing through a garden hose, see how little back pressure you get in your mouth.
But notice how much more air you blew through the garden hose, same principle....
:)
 

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THINK DIESEL NOT GAS......... leave it stock and it will live forever, soup it up and it wont last long. been there done that.... heat & pressure kills quickly.....
jmo
bob
Come on Bob quit being an old conservative and have some FUN!

Porting a head won't hurt. I doubt it would help a lot but if it's free it's free.

Save the money and do a compound turbo setup IMO.
 

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wow, this makes no sense... head porting lowers boost and reduces EGT's.


Well actually it does.
Try blowing through a small straw, see how much back pressure you get in your mouth.
Now try blowing through a garden hose, see how little back pressure you get in your mouth.
But notice how much more air you blew through the garden hose, same principle....
:)
Likening a straw and garden hose to an unmolested vs ported head is a long way off. You're going to be removing a few millimetres of material at the most.

Your exhaust manifold is far more important, your turbo selection vastly more so.
 

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disagree on the exhaust manifold... the biggest restriction in the entire intake and exhaust path is in the cylinder head in the intake and exhaust bowls and around the valve itself. Port matching won't net you ANYTHING unless you have a slight mismatch in your path. All opening up a port will do is slow down the charge. Your biggest gains are with bowl work and a nice valve job. That's with pretty much any engine, but these heads are especially restrictive.

I have run both stock and aftermarket and ported aftermarket manifolds on 12v trucks, and I honestly can't tell a performance difference between them.

I have also run unported and ported heads on 12v, and I noticed 200* EGT reduction and MUCH better turbo spool up with less smoke.

I have also run a compound setup and various singles, and I would prefer a nice Airwerks single turbo with a ported head and a camshaft over compounds and an unported head and stock cam.

the free breathing engine with a properly matched turbo will exhibit similar EGT's, far superior drivability, spool-up onset and needle-sweep time, and will probably make more power due to less exhaust restriction.

I went from an HX35-12w on top of an S400 with an unported head to a ported head with an sps62. didn't dyno with the twins, but the truck hit 40psi of boost about 300rpm SOONER with the single and ported head. the needle started moving 100rpm later (1600 instead of 1500), but it moved SO much faster. drive pressure was BELOW 1:1 at 55psi below 3000rpm. it was 1:1 at 48psi all the way to 4000rpm. I'd imagine drive pressure at 55psi from those twins breathing through an HX3512 would be in the 85+ range (hurting power)

I made 535rwhp with the single combo. Never had clutch problems w/ the twins because they didn't make a ton of boost below 2000rpm. when I went to the single, I would blow through the clutch in OD below 2000!

truck made 1196ftlbs to the wheels on the dyno taking it easy down low to not hurt the clutch.

EGT's were 200* higher w/ the single than the twins. A nice camshaft probably would have brought that closer in line and would have spooled the turbo even sooner than the twins!

from rotty: Well actually it does.
Try blowing through a small straw, see how much back pressure you get in your mouth.
Now try blowing through a garden hose, see how little back pressure you get in your mouth.
But notice how much more air you blew through the garden hose, same principle....
I was saying it made no sense to discount port work just because it's a turbo diesel and that the turbo had more of an effect than porting. I would certainly rather have a nice aftermarket turbo w/ a stock head than a ported head w/ a stock turbo, but if I was building a combo, I would CERTAINLY port the head (correctly)
 

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also, I sold that twin setup to a buddy. he's running a 14cm gated top housing, so it should breathe a little better. He has YET to be able to break 500rwhp with that combo. unported head, same injectors and pump that I was running... and then even BIGGER injectors than I was running.

high drive pressure = trapped horsepower
 

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I went from an HX35-12w on top of an S400 with an unported head to a ported head with an sps62. didn't dyno with the twins, but the truck hit 40psi of boost about 300rpm SOONER with the single and ported head. the needle started moving 100rpm later (1600 instead of 1500), but it moved SO much faster. drive pressure was BELOW 1:1 at 55psi below 3000rpm. it was 1:1 at 48psi all the way to 4000rpm. I'd imagine drive pressure at 55psi from those twins breathing through an HX3512 would be in the 85+ range (hurting power)
So you changed both the turbos and the head?
Did you get a chance to run ported vs stock head with the rest of the setup unmolested?
 

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well, I am running the same exact turbo (as in, I pulled it off the red truck before I sold it) on my current 98 12v. the truck is set up the same.

the turbo lights 100-150rpm later, the needle doesn't swing as hard up to 15-20psi (throttle response), the truck smokes more from 0-20psi part throttle and at WOT and EGT's climb faster.

with that said, I still prefer this turbo over the compounds... it hits 20psi at roughly the same RPM, but it'll still hit 40psi a good 200-250rpm sooner, and hits 50psi a good 300rpm sooner.

cruising down the highway with 15psi or so on the gauge, the boost needle acts like a throttle position sensor read out. 50psi is pretty much INSTANT. the twins were more like "1-mississippi, 2-mississippi, 50"

the diesel is an internal combustion engine... it requires air and fuel, that's all there is to it. you can put a bigger turbo on it and get more 'air', but a bigger turbo will spool up later and drivability can really suffer.

the turbine is driven off of exhaust energy... you cut the restrictions between the piston pushing that exhaust and the turbine wheel, and you're going to spool that turbo a lot sooner and quicker. cut the restrictions on the intake side, and the engine is going to be more responsive off-boost and the turbo won't have to work as hard to move the necessary air MASS... IE, you move the same amount of oxygen at a lower boost pressure... less pressure = less heat... less boost pressure = less exhaust energy required = less exhaust backpressure = freed up horsepower

long story short, port work is a good thing

true story
 
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