Porting and almost done.

Boost decreased, as well as EGTs on mine. But feels like I have more power before boost kicks in. I was told it has something to do with volocity and volume of exhust.
 
Restriction in the exhaust shows up as a restriction to intake flow and pressure backs up and builds then shows up at your boost gauge as increased boost pressure.
Remove the exhaust and intake flow restriction and the boost pressure is not longer building up as much...free flowing easy in/easy out.
That's why many say we should be looking at drive/exhaust pressure too.

Wow, looks like a vortex valve pocket. You can open an intake valve about 1/2 inch, give the intake port a straight shot of WD40 and watch it come out past the valve as a little vortex with a spin.
 
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Wow you lost me. So drive/exhaust pressure will be lower and thats a good thing rite?
 
yes, at a given pressure, flow will increase in a ported head.

just as at a given flow, the pressure will be lower.
 
DTanklage said:
you are not alone
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Think of things like this, pressure..ie. boost or drive pressure is simply a sign of restriction. The more a head can flow, the more air you get in and out of the cylinders and the lower your boost and drive pressures will be. Lowering the drive pressure or boost is not a bad thing. Given a specific rpm, engine load and boost reading, increasing the flow will result in lower boost and egt's. This happens because more of the air that the turbo is flowing is actually making it into the cylinders and there is less restriction or boost.

Super simple time. Take a 5 gallon bucket. Try to fill it with the hose, nothing on the end of it, just free flowing. Now cover the end of the hose with your thumb like you're going spray something. The free flowing example will fill the bucket faster with less pressure. Covering the hose and making it spray increases pressure and decreases the flow. You have created a restriction and pressure. Pressure is not always a good thing.
 
don, consider the case of the difference between fuel pressure regulators & pumps



flow @ pressure!
 
Ok. So I'm not wrong for feeling like I have more power with the same or a little less boost? Because I'm flowing more volume
 
12v porting

looks good guys! keep up the good work. it's tough and time consuming porting this cast stuff ain't it. i've done a couple 12v heads and i'm getting some good flow numbers on the flow bench from mainly working the bowls and valve angles. i'm no expert but as a rule of thumb when porting, your bowls should be around .200 smaller than your major dia valve size. all of your pics look great an are major improvements but your biggest gain with lees time and effort will be picked up in the bowls. if you have any questions i would be more than happy to help you out with the things ive gather so far on 12v porting.
 
Rodram2002 said:
Think of things like this, pressure..ie. boost or drive pressure is simply a sign of restriction. The more a head can flow, the more air you get in and out of the cylinders and the lower your boost and drive pressures will be. Lowering the drive pressure or boost is not a bad thing. Given a specific rpm, engine load and boost reading, increasing the flow will result in lower boost and egt's. This happens because more of the air that the turbo is flowing is actually making it into the cylinders and there is less restriction or boost.

Super simple time. Take a 5 gallon bucket. Try to fill it with the hose, nothing on the end of it, just free flowing. Now cover the end of the hose with your thumb like you're going spray something. The free flowing example will fill the bucket faster with less pressure. Covering the hose and making it spray increases pressure and decreases the flow. You have created a restriction and pressure. Pressure is not always a good thing.
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Drive pressure is almost 100 percent dependent on exhaust restriction from the turbine wheel, turbine housing, and anything down the line from there.

I can't fathom how drive pressure will be lower after a port job at the same gauge measured boost pressure at same RPM.

Someone want to explain why they believe exhaust drive pressure or turbine inlet pressure will be lower after a port job?
 
Big Blue24 said:
Drive pressure is almost 100 percent dependent on exhaust restriction from the turbine wheel, turbine housing, and anything down the line from there.

I can't fathom how drive pressure will be lower after a port job at the same gauge measured boost pressure at same RPM.

Someone want to explain why they believe exhaust drive pressure or turbine inlet pressure will be lower after a port job?
Click to expand...

I would guess since your boost will be lower at a given load and/or RPM due to the port job- the drive will be lower also. The drive won't be lower because of the port job, just lowered from lower boost needed. $.02
 
Looks to me that with the same turbo/EX housing that drive PSI would be up with a ported head... more volume through the head but the same restriction at the EX. housing... But i realy don't know...just a thought!
 
Well, I got the head and an H2 cam installed on the truck this weekend.

I think I might have gone a little further with the porting than I wanted. I might have worked the bowl too much and taken out some of the swirl pattern.

Here are the results.
Cruising around I see less boost and temps are up just a bit, maybe 50* EGTs. For the same amount of boost at any given rpm it requires much more temps and throttle input. But on the flip side, once the rpms are 2000 or more the temps drop and the boost picks up some. Kinda acts alot like a large single does.

WOT is another story, boost comes on faster and the truck wants to rev faster. Much more responsive. Boost is down about 3-4psi and EGT's are down 250*!

Like I said, not quite what I was expecting, but very pleased with the WOT results.

180 pump with 181 DV's, rack plug, gutted AFC, fuel plate full forward, 370's, and a stock hx-35 only making 1400* EGT's.
 
I could be thinking of this in the wrong way but it makes sense to me why drive pressure would be lower. Your flowing pretty much the same amount of air on the intake side just at a lower pressure. Drive pressure exists because it takes force to spin the turbine wheel and compress the air(which is naturally resisting being compressed).The higher boost you run the more force it takes. Drive pressure provides that force. When the boost is lower(less restriction) it takes less force(or less pressure) to turn the turbine wheel so it will spin faster allowing more exhaust gases out.

Sound coherent enough?

The other reason I could think of is by looking at JUST the exhaust port itself. It it were rougher and smaller it would flow less. The piston acts just like a positive displacement pump. So the air in the cylinder is either getting pushed out or its getting compressed(in this case its doing both). The air is getting compressed because the port can't flow as much as the piston is displacing.With a smaller port that would lead to more exhaust gases still being in the cylinder. So that would mean that there is still pressure in the cylinder(or less vacumn) when the intake opens so you would need more boost pressure to get the same intake charge as you would with a freer flowing head. However you wouldn't be able to measure that with a DP guage in the exhaust manifold.

Hows that? or am I overthinking this just a bit?
 
ok let me set a few things straight. drive pressure gauge is reading the the pressure in the exhaust manifold therefore the porting of the exhaust port has no direct relationship to it but there is a indirect relationship to the porting.
as said before boost is a measurement of the restriction of the exhaust and intake ports. if the exhaust port is restrictive and not allowing all the gases in the cylinder be pushed out then there is residual pressure left in the cylinder when the intake opens up to the point that the piston moves enough to adjust the volume and it there is more pressure in the cylinder than in the intake when the valve opens this is when you get exhaust blow back into the intake.
now in porting the intake and exhaust ports you are reducing the restriction in the head allowing for more volume to flow freely. the turbo is the most restrictive item in the exhaust and this is what is read by the drive pressure gauge. due to the fact that the exhaust wheel and compressor wheel are connected by a shaft if the compressor wheel does not need the tq to compress the air going into the engine than that tq is not having to be applied to the exhaust wheel by the exhaust. in order to create the tq on the exhaust wheel you must apply pressure to the fins on the wheel the more tq required the more pressure required. so again if you reduce the restriction in the head in affect reducing the pressure needed to feed the engine the less pressure required on the exhaust side.


hope i didn't send anyone in a tailspin with that one.
 
Hey look! Its Pete and Repeat! :poke:

Now who sounds more intelligent? :hehe:
 
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