port and polished heads, need some opinoins

[jvs8864]

hey everyone, im looking to get a little bit more out of my 2.9
i came across this port and polished tutorial. what do you guys think?
should i do it? anyone else try and it get any substansial power?
thanks alot!!
-James

 

[Wicked_Sludge]

a port and polish well help ANY production engine. theres just so much crap left over from quick and sloppy production techniques that can be removed and smoothed. a gasket match is a good idea while your at it.

 

[MAKG]

Perhaps it might help a LITTLE.

But substantial power from a tiny bit of grinding? No. Just no.

Frankly, if you aren't winding the piss out of it and hanging at WOT all the time, you won't see ANY benefit. If your throttle isn't completely open, it's BY FAR the largest restriction. By design; that's what throttles are supposed to do.

Wicked, be careful about giving that advice to just anyone, at least without some clue as to the actual request. Almost all posts in this board that want "more power" actually want more acceleration at 2000 RPM (or even lower). In which case porting is silly.

And the risk is ruining a head and/or intake manifold.

 

[Wicked_Sludge]

i tend to disagree, although not wholely.

power gains from just a P&P will be on the low-ish side. but when used in combination with a dozen or so other "little" improvements, it will add up.

the biggest gain from a P&P will be at WOT, where those opened-up runners will gulp down the air. but smoothing fords crappy castings over will smooth the airflow out under all conditions, increasing VE throughout the powerband.

just this observers $.02

 

[jvs8864]

k thanks everyone
i did a research, its exensiveeee

lol cheper to get a 5.0 cobra engin from a junk yard
thanks again all, i apprciate it!!

 

[krugford]

I find absolutely nothing wrong with smoothing out cast ports. A smoother port wall should decrease the pressure drop across the port in all cases.

I would recommend against modifying the stock port geometry (other than surface finish) unless you have a specific goal in mind. An increase in volumetric efficiency does always mean an increase in combustion efficiency. And a smoother straighter port does not always mean an increase in volumetric efficiency. The flow into the cylinder plays a large role in controlling the rate of pressure rise in the cylinder. If you want an increase in power throughtout the rpm range, then go with a larger engine.

There's no replacement for displacement.

 

[MAKG]

No, increased VE does not increase combustion efficiency. That is UNCHANGED.

If the engine were to get more air (somehow -- which is a silly assumption given that you don't even know if the throttle is open!), the fuel system will provide proportionally more fuel. Combustion efficiency is not affected by that.

Now, you may screw it up by eliminating flow shaping within the cylinder, in which case combustion efficiency goes DOWN. Efficiency likes turbulence. That mixes the fuel. But that's not likely to be an issue with removing a tiny bit of texture. Though you'll never know without a wet flow bench.

Efficiency and peak power are very different things. If you mix them up, you lose credibility.

 

[almostclueless]

I would argue it's good to remove the parting lines....but not the rough texture all over the ports.


Either way, no 2.9 is worth modding to the point that polishing would help appreciably.

 

[krugford]

No, increased VE does not increase combustion efficiency. That is UNCHANGED.

If the engine were to get more air (somehow -- which is a silly assumption given that you don't even know if the throttle is open!), the fuel system will provide proportionally more fuel. Combustion efficiency is not affected by that.

Now, you may screw it up by eliminating flow shaping within the cylinder, in which case combustion efficiency goes DOWN. Efficiency likes turbulence. That mixes the fuel. But that's not likely to be an issue with removing a tiny bit of texture. Though you'll never know without a wet flow bench.

Efficiency and peak power are very different things. If you mix them up, you lose credibility.

Sigh, I need to learn to slow down and type what I'm thinking.

What I meant to say was "An increase in volumetric efficiency does not always mean an increase in combustion efficiency."

Most of the "port and polish" jobs that people usually post pictures of are nothing more than gouging the hell out of the port to open it up as much as possible. If you've got a port specifically shaped to produce a high level of swirl in your cylinder and you remove that feature, then your VE is probably going to go up due to the decreased restriction (it takes power to create swirl) while your combustion efficiency will likely go down.

I still believe that a polish job can do nothing but help, regardless of how much, especially if you've got the time on your hands.

 

[MAKG]

Yup, that makes sense.

Though I'd argue that "help" that can't be detected doesn't exist.

There is SOME risk. Just removing and reinstalling the heads on a 2.9L can crack them (ask AllanD about that one), even if you never touch a die grinder.

 

[almostclueless]

http://en.wikipedia.org/wiki/Cylinder_head_porting#The_.22Porting_and_Polishing.22_Myth


"A rough surface on selected areas of the port may also alter flow by energizing the boundary layer, which can alter the flow path noticeably, possibly increasing flow."

 

[Wicked_Sludge]

you cant trust everything you read on wiki.

they are mostly correct on the physics of boundry layer until the end. claiming that a slightly rough surface will not slow the flow toward the middle of the port is incorrect. a boundry layer is just that...a layer. meaning it contours to whatever is under it. a rough runner will produce a rough, uneven boundry layer that the air toward the middle of the runner has to then flow over. in effect it sees the same bumps, dips, and twists as the boundry layer.

a smooth intake runner will produce a flat, smooth boundry layer...which will produce less drag on the air sliding past it. one could go on to say that the air velocity would then be increased, increasing the sheer action between the boundry layer and "other" air...making the intake runner more effective yet.

 

[MAKG]

Wicked, you guys are both doing approximations. His is different than yours. Yours isn't really a (thick) boundary layer approximation. It's more of a transmission line approximation. Both have their limitations. His is right for a straight tube with texture smaller than the boundary layer thickness. Yours is for a narrow tube.

This is neither. In effect, your argument about thickening the boundary layer for a tube that isn't so narrow ignores that the flow in the center speeds up to (largely) compensate; it's the old familiar venturi effect. And it can keep doing it until it runs out of Reynolds number.

 

[rusty ol ranger]

Dont be like that one guy on a honda forum that wanted to port and polish his head so he stuck a bag of abrasive sand over the intake and let it suck into his engine to figureing he would get the same effect.

If you want accleration regear to something lower. Chances are you got 3.45's, a set of 3.73's or 4.10's would do wonders, all though, you'll be whinding hard at 70 down the interstate.

later,
Dustin

 

[HndMeDnBroncoII]

Wicked, you guys are both doing approximations. His is different than yours. Yours isn't really a (thick) boundary layer approximation. It's more of a transmission line approximation. Both have their limitations. His is right for a straight tube with texture smaller than the boundary layer thickness. Yours is for a narrow tube.

This is neither. In effect, your argument about thickening the boundary layer for a tube that isn't so narrow ignores that the flow in the center speeds up to (largely) compensate; it's the old familiar venturi effect. And it can keep doing it until it runs out of Reynolds number.

okay so i have been working oncars all my life even in a few shops.
and to this day i stii cant get a proper tecnical answer (how about you guys)
with all the technology why cant we have intake headers one tube for each port just think inch and a half tube forced air it would look just like a reverse exhaust header

either way when you guys laugh at this idea just remember they laughed at eddison tooo
lol