Port match intake manifold?

[Lazeum]

I'm in process of rebuilding my engine. the whole intake is down so it's a good opportunity to perform some mods I should have done already (who said "while I'm at it?" - I've already redone the whole front/rear suspension, steering & brake system while the engine was down ).

 

My setup is 3 Webers 40DCOE with Cannon manifold. this combo goes on a F54 / flat tops with ported P79 head made by Braap with Rebello "street" cam.

 

There's a lot of material to play with on the manifold and I'm wondering what I should do. I mean intake ports are quite small vs. head ports. It would make sense to me to make them as large as the head to improve (or should I say "optimize") flow, at least to avoid steps on the way that could create vortex / turbulences.

 

it's obviously better to have a small (and fast!) flow going thru a big hole than a big flow trying to go thru a small hole and hitting walls but none of those situations seem to work good in my book. First one will slow down flow a lot when going into the large section, the other one would obstruct the flow.

 

I believe also some phenomenon could occur according to RPM making the engine hard to tune; such as rich spots at some RPM range.

 

By doing so I might have a large section becoming big (exit of carbs) then small (middle of the intake) then big again (head port). So pressure will follow the same path, it could create some pressure variation issue also.

 

And what about flow reversion? Is there anything to fear about? A small step could after all be beneficial...

 

By looking at my intake and the shape of the gasket, I might have a much as 3mm of material on one side to be removed around the port which is a lot. The only thing clear so far is to make sure I never get intake ports bigger than head ports.

 

So far, I've only performed the porting between the intake and the carbs.

 

 

 

 

For the record, here are links about the topic, it seems something could be done after all

 

http://www.cartuning...ching-an-engine

 

http://www.torquecar...g-polishing.php

 

 

 

 

I've searched as well HBZ with no luck, I'll be happy to find some talks about it on the board if any (the only threads found were about EFI intake and if it was possible to do; not about the effects...)

Edited August 11, 2011 by Lazeum

[z-ya]

At a minimum, I would just make the transition from the intake to the head as smooth as possible. Trim the gasket to match the head, and then use the gasket as a template for porting the intake. I would transition smoothly from the carb port diameter to the head port diameter. I've never done a comparison (with vs. without port matching), but all of the engines I have built have had this simple port matching, and they all make good power.

[madkaw]

There was a thread which i posed the same question-except it involved a Mikuni manifold. The general consensus was to leave it alone because there is a reason for the step-as you have stated. Unless your are building a race motor, I would leave the step there---IMHO

[Xnke]

I would cut the head side of the manifold to match the ports in the head. The head side of the manifold will have the smallest diameter, it should taper down from the carb through the intake, through the head, to the valve.

 

The long, smooth taper will actually increase velocity, while still allowing the large intake port. So, to recap:

 

Carb throat = carb side of manifold > head side of manifold = port opening

[Lazeum]

I'm more thinking about porting the intake than leaving it alone.

However, contradictory advices show my question is not so straight forward.

So, madkaw, I have looked for the thread you're talking about and there're a lot of good info in it.

 

If I summarize some of the comments made by Tony and Braap (please forgive me if the meaning has been lost without the full context), here is what I got.

 

I'm not saying Tony & Braap are always right (I have to admit they are most of the time ) but the comments below make sense to me.

 

 

 

 

The 'port matching' phenomenon has shown to be a red herring for the most part. What people are now realizing that having STEP from the intake manifold to the head (manifold SMALLER than the head by some margin) actually HELPS with low speed drivability by creating an anti-reversionary effect in the intake pulse.

 

I have mine unaltered, I was pleased with the results. Once you make it larger, it's hard as hell to bring it back to a size smaller! If anything, I'd not go any larger than 1mm diametrically at the extreme outside unless the head is being worked. The whole theory behind the Mikuini manifold was the ability to RAISE THE PORT ROOF to allow a better shot at the back of the valve. If anything, ADDING material at the bottom of the runner is what is required, in addition to welding in the floor of the stock intake port!

 

Actually, Cannon manifold runners are not round, they have a 'eye shape' hole, there's more material than could be 'removed' on the lower side of the runners which tend to go towards Tony's comment above.

 

IF the HEAD side is SMALLER than the Manifold Port, there will be an impeding of the airflow caused by the bump.

If the HEAD side is BIGGER than the Manifold Port, there is a 'check valve' action during overlap, and no real impedance to flow whatsoever.

If they are MATCHED in size, you have no overlap anti-reversionary step, making for worse ariflow, and chances are that the porting will not MAINTAIN a taper from throttle plate to valve. It will OPEN UP in the 'match ported' region, and then begin to taper again in the head. This is TERRIBLE for flow, because it kills velocity.

 

 

The key is unless the manifold continually tapers from the throttle plate to the back of the intake valve you are FAR BETTER OFF having a smaller intake manifold so you have the reversionary step than to make it the same size. If you are not willing to properly taper the manifold to match the port in the head, then LEAVE IT ALONE. Hogging out 2" of port for the sake of making them even is useless and a waste of your time. You will GAIN nothing, and likely will hurt reversionary tendencies of the setup, if not overall flow.

 

To get back to the links I've posted above regarding port matching on V8's, Tony made an interesting comment.

 

Port matching got a BIG NAME from DOMESTIC heads where the ports are misaligned and in some cases the gasket blocked half the port, or were off by hald the cross sectional area.

In an old Chevy, port matching is almost MANDATORY because of the piss poor casting alignment.

 

This ain't a Chevy. They don't need an overhaul at 100K. They don't need manifold port matching. They don't need ridge reaming.

Let the domestic myths die!

 

 

 

 

At the end, Braap also made a comment that goes towards the vortex creation t the step that could help mixing air & fuel together:

 

 

Tony,

I’m merely theorizing here, but after reading your input here, (good stuff by the way), I have inferred that for carbs or EFI being injected way upstream before the butterfly, that this as cast ridge/step at the manifold to head mating surface is aiding even further atomization beyond what is achieved at the venturi or injector nozzle due the drastic velocity/pressure change across that step, therefore realizing more efficiency, drivability, and power due to more thoroughly atomized fuel? (which would support injecting fuel at the port close to the valve means that step has less importance?)

 

Would that be accurate or am I chasing mythical creatures?

 

 

 

 

On this thread I can see TimZ made some comments saying porting the intake could be beneficial. Based on power made with his setup, it can't be wrong...

 

Should I conclude it would depend on the setup? high rpm/power monster (race applications) will benefit from this mod since flow reversion is minimal, intake shape optimized to keep the taper all the way along the runners? whereas street versions would benefit from keeping the intake as it is since flow reversion would be important at low rpm where the engine would be mostly used?

 

I start to be really confused. I might keep the intake the way it is for now since it is easy to get back on it later than adding material in the future if I do a bad move... I'm mostly in the 2500 / 6000 rpm range with my engine.

 

Anyhow, thanks all for your answers

[Tony D]

JeffP's engine has the step, and he's there with Tim in power numbers. But Jeff and Tim BOTH have ported heads AND manifolds.

 

You're not reaching any stated high flow regions, therefore the step would benefit you the most. The step helps with anti-reversion from big cams, low port velocity, etc.

 

On mild street engines, it's where it shines the most.

 

The problem here is inability to differentiate applications. Just because it's good in one application making 600HP with a turbocharger cramming in fuel and air does NOT necessarily make it applicable to a stock-rpm range N/A engine. In some cases it does, but it goes back to 'total package' thinking.

 

Additionally, as you yourself are now realizing: If you take it off NOW, it will be HELL putting it back on later!

 

Frankly most people are advocating leaving the step alone, I don't see where the confusion is on this matter. When you build a bottom end capable of withstanding 600 or 700 HP, THEN I'd start worrying about it. Below 450? I wouldn't waste my time.

[Lazeum]

Just to add on more item, here is a picture of the intake with the ports that go to the head. We can see the shape of the gasket and where some material could be potentially removed.

Whereas Mikuni manifold is having a some 'extra' material all around, my Cannon manifold is having some only on one side. Not sure what would be the reason: to tilt the flow, cheap design with no reasons?

 

 

 

 

 

 

I will leave alone my intake then

 

 

Edited August 11, 2011 by Lazeum

[Tony D]

What you experience is WHY on DOMESTIC PRODUCTION engines, "port matching" was so important. They used castings which weren't necessarily precision.

Cannon is USA manufactured, and is 'off a bit' while Mikuini is made in Japan and has a nice consistent material wall as they used a more precise casting/construction technique.

 

Gaskets are bigger than the holes they seal PRECISELY because of this phenomenon. If they were 'precision' then the ports would HAVE to match up exactly (racers index the manifolds to the head using dowels, not the bolt holes!)

 

On a production engine, the gaskets being larger than the holes allows for a mm or two of misalignment between the ports without the gasket becoming another potential point of restriction.

 

Just because the gasket is bigger, doesn't mean the hole in the head needs to be that size. FYI, the FIA Homogolated Dimension for the intake runners at the head surface is 35mm. If you can get 210+ CFM port flow on the intake side of the head with the hole being 35mm, exactly what are you looking for by making it LARGER? Less velocity? More flow? What?

 

BIGGER is NOT better when it comes to manifold runner size.

 

I don't know TimZ's port dimension, but Jeff is supporting 600+ HP on a 34.5 or 35mm maximum diameter head port hole size. He gives up 30CFM per runner off that 210+ CFM by using the stock EFI manifold which has an Extrude-Honed Runner Diameter of roughly 33mm.

 

What was that about you wanting bigger port runners again?

[Lazeum]

I've got your point

 

My intent was more about avoiding flow restriction because of the step (whatever the flow direction was) than improving flow. The goal was just to make sure I would run with optimal conditions with the head. No point of having a $$$$ cam/head if surrounding components are not able to keep up with it.

 

Here was my basic idea when I first asked the question (intake is obviously on the left, the right part is the head). Vortex would create flow restriction and would avoid to use efficiently the intake system.

 

 

 

The question then became: vortex presence < ? > anti reversion effect

 

...and based on comments, it tends to depend on the application.

 

in "street" mode: vortex presence < anti reversion effect

in "race" mode: vortex presence > anti reversion effect

Edited August 14, 2011 by Lazeum

[didier]

Tony D : racers index the manifolds to the head using dowels, not the bolt holes!

 

that's a good reason for making the best alignment you can !

[Tony D]

The anti-reversion effect is FAR more important than the little 'drop' in flow you 'might' see from the step.

 

Of course, if the HEAD hole is smaller than the intake manifold, then you should do something about it. But if the head hole is larger than the end hole on the intake manifold, I'd say 'leave it be'...

 

As to the comment about about alignment, ALIGNMENT is different than PORT MATCHING. And RACERS are not STREET CARS. Racers have ported both the intake manifold AND head to a consistent taper from one end to the other, and as a result any misalignment will result in a flow disruption. But as I have said in the other post: some racing head porters WILL LEAVE THIS STEP for an anti-reversion effect. So don't read or rationalize into this something that isn't there. Don't add non-relevant situations which will only confuse the issue. This is why the post was up there in the first place...there is a LOT of stuff out there, but the problem is people can't differentiate between PURE RACING and STREET applications, and what transfers and what does not.

 

Having an aligned port is one thing. But consensus is that the effects of 'port matching' (which means you take any misalignment and grind one of both of the pieces back 25mm or so to make a tapered blended transition with no step) doesn't have any appreciable BENEFIT, and in some instances because of the removal of that step where the intake is smaller than the head port compounds losses due to reversionary effects.

 

Again, that 'vortex' MAY 'lose' flow, but the anti-reversionary effects MORE than compensate with increased torque, consistent AFR's, etc...

[Lazeum]

I think it is clear in my mind, thanks Tony

It's good to have feedback and knowledge from people with experience

Edited August 16, 2011 by Lazeum

[ozconnection]

And, instead of the reversionary step being at the head/manifold interface, that reversionary pulse is allowed to reach the venturi in the carb which totally changes the way the fuel is metered through the carb. Can you say "rich mixtures" and "Standoff"

 

Thank god for WBO sensors!

[Noddle]

Again, that 'vortex' MAY 'lose' flow, but the anti-reversionary effects MORE than compensate with increased torque, consistent AFR's, etc...

 

I assume this is more relevant to a N/A engine than a Turbo engine?

 

Nigel

[Xnke]

It is; but it also applies to turbo motors when the turbo is not spooled up.

 

My engine has no anti-reversionary step, and I do run a moderately large cam. Lift is rather docile; but the duration and overlap are getting into the middle range. I did have a reversion problem when I first started running the motor with the ported intake manifold, as evidenced by dark coloured deposits from inexpensive gasoline (DAMN YOU local Jr. Food! you USED to sell non-ethanol fuel!) in not only the intake port, but about an inch upstream of the injector, indicating that the fuel air mix was indeed getting pushed back at least that far. Adjusting cam timing helped a LOT, but without the step I doubt I'll be able to remove the effect entirely.

 

Am I worried about it? Nah. The pull-stop-stop-stop-pull-stop-stop-stop-pull pattern does just as much detriment to flow as any kind of reversion does.

 

In summary:

 

I went with the long consistantly tapering port on my engine. Your milage WILL vary.

[Tony D]

"It is; but it also applies to turbo motors when the turbo is not spooled up. "

 

Like I said "especially at lower engine speeds"...

 

JeffP's engine had a marked reduction in the 'black runner' phenomenon Xnke speaks of with the step, versus when he had a 'properly done' matched port. The porting guru mentioned the smaller runner "won't appreciably hurt anything, and will likely help quite a bit with reversion'..." By "Porting Guru" it's one of the guys who "wrote the book" everybody is reading...

 

The problem is that theoreticians will spout and tout the matched port in all-out race engines because it made 3hp more on the dyno at the peak point. So 'matched ports are the best'...

 

Problem is, at 3000rpms, you're down on power because you're fogging out the carb throat like an old 2-Stroke Rotax when you go WOT because of the reversion (well, maybe an exaggeration, but you get the idea...)

 

The 'theoretical' points on the internet just blow my mind. There is PLENTY of stuff out there on DATSUN engines which shows match porting (not a tapered runner, but MATCH PORTING) doesn't do ANYTHING!

 

To get the best advantage, you need that tapered port, AND EVEN WITH THE TAPERED PORT, the 'down low, useable everyday rpm range' benefits MORE than outweigh what 'penalty' you have at Peak Power Production Point of 6500rpms (or higher) from that tapered runner.

 

Remember, there WAS a tapered runner on Jeff P's engine, it now has a distinct 1.0mm step at the manifold / head junction. This (as far as we can see) has resulted in absolutely NO penalty that we can discern on the engine dyno, but we CAN see there is far less reversion evidenced in the intake, and like mentioned above, even with a plenum-style manifold, there was a noticeable change in fueling requirements (especially around Peak Torque) once the 'step' was added to the intake runner.