Porting head: What to do about the "humps" in the exhaust port?

[dsm-onster]

What's under these humps at the bottem of the exhaust ports on the outside walls? water or oil passage? Do they serve some aerodynamic purpose? Has anyone done away with these? They look like they are just squeezing flow.

The valve side of the hump is flat and smooth right into the valve seat. The port literlly keeps going at this spot from the valve seat and rises above the rest of the port into a little mound. The other side, below pictured, shows how it falls back into the port wall.

 

[Freerevving]

you can shave them if you want... i round them out pretty good... not sure why they're there... probably has to do with aerodynamics but I remove a lot of aluminum on the exhaust side, and the hump won't help anything

 

[dsm-onster]

I don't see how it can. So you've seen no adverse effects by removing them, right? I'm really leary of changing the port shape. But this seams rather obvious. . .

 

[Freerevving]

no adverse affects

I notice a lot of features in the ports that look like they were put there for strength or to even the air path for other obstacles opposite of them... of course, the head bolts are between ports (no real strength issues), and I remove anything preventing an even taper. I never concentrate too hard on that hump (although I do work it over)... I concentrate much harder on the short side radius since, overall, porting can become very time consuming

I should add that that hump has little to do with port shape... the sharpness of the curves, from many different profiles, is what makes up the port shape. In specific areas (protrusions, longitudinal radii) the curves can be enlarged and deadened.... but in most areas they should be enlarged and exaggerated... it helps to look at it from an artistic point of view and make it "go with the flow"... without removing too much material.

 

[Freerevving]

I think I'm reading into your question more accurately... the simple answer is yes... remove the ridge... it's one of the very things that's in the way of having an even taper. The hump often extend toward the roof and I thought you were pointing toward the roof... you should definitely remove it from the side

 

[dsm-onster]

Thank you very much! Great info here.

 

[Defiant]

This is the sort of thing that makes professional porting so expensive, and so worth it. Any artifact in a passage will effect things, and finding out what direction and at what flow rate (rpm and load) takes hours and hours of flowbench and Devcon research. Sometimes taking out a "bump" can change output by ten horsepower at a given flow rate.

 

[Freerevving]

It's not that delicate of a procedure... most pros will tell you things like that to explain their pricing. It's expensive because it's not easy and it takes a lot of time. If you remove restriction (within reason), you'll get more power, but this doesn't mean it will always be perfect.

Flowbenching is useful if you are trying to change the overall shape of the port.... without flowbenching, if you do a terrible job of creating an even taper, or mute the lateral radii, or remove too much material in one area (or all areas), you could/will have adverse effects.

I've seen many non-flowbenched heads perform as well/better than flowbenched heads... I've also seen crappy ports that lost power/flow after porting... but it was very obvious (to me) by looking at those heads. Common sense plays a huge role in doing this.... and the f-ed up heads showed a serious lack of it.

Flowbenching is a method of making the ports even between cylinders... It can also show you if you're f-ing something up, but usually is the easiest way to show how much you've removed in each port. It cannot reflect how well your engine will perform at different rpm's. It only tells you how much better it flows compared to where you started. Better maximum flow almost always guarantees that it won't have as much power just before its previous maximum efficiency.

you need to be very careful porting the intake on these heads... there are only a few things to remove.

you should also be careful on the exhaust but remember that these exhaust ports are like a crimped tube... by opening up the exits on this head, it's like you're un-crimping a tube. Nothing but gains there. If you remove too much, you'll lose air velocity which is not something you want with a turbo.

 

[dsm-onster]

Yes. I've only so far blended in the seats to the bowl and taken the the hump out pictured above and port matching the exhaust mouth to the exhaust manifold. I then will polish. Bt that's it. I am no professional. So Guy's advice is well noted and "a word to the wise is sufficient".

Oh, one other thing I did was that I cleaned up the shortside radius in those exhaust ports. I did not change the shape of the port. But there were actual ripples rolling over the shortside rise from the bowl to the rest of the runner. So I smoothed that. No more material remove. No change in angle of the port. No widening the port more than blending in the port-match.

And with the intake I plan on ONLY blending the seat to the bowl, then polishing. The ports seam to match rather well to the intake manifold from what I'm seeing. I must agree with my minute experience, the intake ports look very nice for a mass produced head. The intake ports are already rediculously large. So taking out the seat lip and polishing should bemore than enough, correct?

 

[Freerevving]

yes. If you want to get crazy you can also grind away the material around the valve guides, any irregularities within the port, any irregularities between cylinders, sharpen the center divider (a little), and there is a small area on the short side radius that can be modified. These ports are cast almost perfect except for the narrow section around the valve guides. You'll see the most gains from removing the mass of material around the valve guides and blending it into a taper. This will take a lot of time if you're being careful. The rest of the port should only be resurfaced because, as you said, these ports are (abnormally) humongous.

 

[Freerevving]

Here's what you can do if you're feeling feisty... Even though the work performed in this photo is about a stage 2 or 3... the end result I would call stage IV

sorry about the crappy photo. It's easier to see what I'm talking about on the left side

 

[dsm-onster]

Thanx for the pic. This will be a good guide for me.

I'm always feeling feisty .

 

[mach4g63t]

When you say, "Shortside radius", could you explain to me what you mean? If you could point it out in a picture that would be extremely helpful too. I understand all that you're saying here, but I don't feel like I'm getting 100% of the knowledge because I don't understand that term! Thanks!

 

[dsm-onster]

In my first picture, the bottem; and in freerevving's picture, the top. The port floor as it turns into the valve seat.

 

[ApexVIII]

i dont have any pictures but i removed those humps also, and smoothed out the roof,,

i believe you are not suppose to touch the roof unless you have a flow bench, just smooth it

and the floor is where it would be better to remove any material if you want to.

 

[Freerevving]

When you say, "Shortside radius", could you explain to me what you mean? If you could point it out in a picture that would be extremely helpful too. I understand all that you're saying here, but I don't feel like I'm getting 100% of the knowledge because I don't understand that term! Thanks!

aka "short turn radius"... In my opinion, for a 16V head, the 4g63 intake ports are very nice and need very little work when it comes to the curve.

from wikipedia

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You don't need a flow bench... just a good way to measure and a little patience

btw the short side is technically the floor... typically the floor will already have little restriction... but with a good port and polish you should hit the roof before the curve and the floor at the curve

this essentially changes the angle of the airflow to something less restrictive

I could find a better picture than this one (lazy) but it should make the point if you think about it:
from wikipedia

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[all_motor_mike]

that sure is a shiny intake port.


mike

 

[Freerevving]

that sure is a shiny intake port.


mike

Bad lighting... It's still barely "rough to touch" even though I don't believe in it. I just did it so no one would cry "why didn't you leave it rough?" The rough surface was lightly cleaned with a polishing buff, then coated in oil, so it is a little on the shiny side.

 

[all_motor_mike]

Bad lighting... It's still barely "rough to touch" even though I don't believe in it. I just did it so no one would cry "why didn't you leave it rough?" The rough surface was lightly cleaned with a polishing buff, then coated in oil, so it is a little on the shiny side.

so basically your saying that u make your intake ports mirror smooth but wont post those pics because u dont want to get flamed? smooth intake ports are a no no.


mike

 

[ApexVIII]

so basically your saying that u make your intake ports mirror smooth but wont post those pics because u dont want to get flamed? smooth intake ports are a no no.


mike

This is true.... but only for Carb'd motors

it does not matter on Fuel injected motors, being that the carb motor does not atomize anywhere near as well as as EFI ones do, so there is no "puddling" as it would on a carb motor

 

[90laserRSfwd]

While I agree with "apexVIII" I also agree with "all_motor_mike". The thing is it's true that modern day efi engines don't "need" to have rough ports because they don't suffer from poor atomizing of fuel / air mixtures like carb'd engines. But when you add boost (above atmosphere pressure) the forced air would benefit from the "tumbling" effect that rough intake ports provide. Although we're talking about splitting hair's here, it's more a mind game... (If it makes you feel better knowing your intake ports are rough, keep them rough).

 

[mach4g63t]

In you're first diagram, it's okay to remove as much of the "guide boss" or "fairing" material as you can get to while making it smooth, right? Or is there a general amount you want to leave there?

 

[dsm-onster]

While I agree with "apexVIII" I also agree with "all_motor_mike". The thing is it's true that modern day efi engines don't "need" to have rough ports because they don't suffer from poor atomizing of fuel / air mixtures like carb'd engines. But when you add boost (above atmosphere pressure) the forced air would benefit from the "tumbling" effect that rough intake ports provide. Although we're talking about splitting hair's here, it's more a mind game... (If it makes you feel better knowing your intake ports are rough, keep them rough).

Freerevving correct me if I'm wrong. . . But, tumble into the cylinder is not the same. Scroll down to the tumble and swirl subheading:

A description of tumble is that the rotational motion of the incoming mixture is in a plane approximately perpendicular to the axis of the crankshaft as it enters the bore, coming down one side of the cylinder and rolling back up the other. A good example of this would be pouring wine into a goblet and having it run up the opposing side.​

Tumble doesn't actually occur until the air is in the cylinder. And port angle and stroke is king. 90laserRSfwd, you're talking about getting the air particles to spin ??? as they go through the port. This takes energy away from motion and slows the velocity. A boundry layer of slower moving particles are created and suddenly your effective port diameter has shrunk. What the air feels is more important .

A rough wall was purely for the sake of further atomization. A boosted motor has more turbulant air (which can vaporize fuel better) and hotter air (which can vaporize fuel better).

 

[Freerevving]

so basically your saying that u make your intake ports mirror smooth but wont post those pics because u dont want to get flamed?

no I'm saying I made those intake ports a little rough. I did it only for pictures to avoid confusion, but the camera sucks dick, and I still haven't purchased a new one. The intake ports were polished very smooth shortly after that photo, so any further documentation will have the added confusion of mindless sheep commenting on how the RA is a no no... Unless I get some time to buy a new camera, I'll have more crappy pics up soon

smooth intake ports are a no no.

mike

It's not a no-no.... not even on a carbed head. But if you make your ports extremely rough you will gain a little power on a carbed engine.

The general consensus is that intake ports should be rough for any engine. This is wrong and unproven. The only dyno charts I ever been able to come up with for fuel injection, that show any comparison between rough and mirrored, showed a small increase with polished ports... 2-4 hp (at just over 300whp) might be a variable in the tests, but the tests were in favor of polished ports on two different cars.

While I agree with "apexVIII" I also agree with "all_motor_mike". The thing is it's true that modern day efi engines don't "need" to have rough ports because they don't suffer from poor atomizing of fuel / air mixtures like carb'd engines. But when you add boost (above atmosphere pressure) the forced air would benefit from the "tumbling" effect that rough intake ports provide. Although we're talking about splitting hair's here, it's more a mind game... (If it makes you feel better knowing your intake ports are rough, keep them rough).

you make a good point... but the problem is that, without creating a large amount of air friction, you can't atomize the fuel much better than the injectors already do. A carbed engine uses airflow to atomize the fuel and the particles are quite large. Turbulence is effective for futher atomizing carbureted fuel. No amount of port turbulence is going to give you additional horsepower on a fuel injected engine. Injector technology is far beyond what your port surface is capable of.

This is true.... but only for Carb'd motors

it does not matter on Fuel injected motors, being that the carb motor does not atomize anywhere near as well as as EFI ones do, so there is no "puddling" as it would on a carb motor

Couldn't have said it better..... well, wait a second... as far as I know the "puddling" thing is an old wives tale... a rough surface only makes a thicker boundary layer which would trap more a/f mixture... but because of air pressure and velocity I have never seen or heard of it actually happening. It's like saying that if you line your ports with netting it's going to prevent pooling. However, an extremely rough port surface does create enough turbulence to affect the main channel of flow, enough to help atomize fuel on carbed engines.

btw I really like your link to cylinder head flow testing... very useful information... thanks

In you're first diagram, it's okay to remove as much of the "guide boss" or "fairing" material as you can get to while making it smooth, right? Or is there a general amount you want to leave there?

No, you should stay within reason. You can remove more on the exhaust side, because the aluminum from top to bottom of the valve guides is much thicker.

 

[mach4g63t]

you can't atomize the fuel much better than the injectors already do

This is pretty much what I would figure also. Have you ever had your fuel rail out and accidentally turned the CAS on our vehicles and cause the injectors to fire? You can initially see the puffs of fuel, but the instant it fires, it's gone. It might be different for larger sized injectors and the amount of fuel they spray, but from what I've seen (660cc and 1050cc injectors) the fuel comes out in such a fine mist that you can't really argue that much of anything else is going to cause that to atomize better.