Port matching inlet manifolds

I've been having a read through the exhaust manfiold thread, and it got me wondering about the inlet manifold on my G60. Having a couple of spare inlet manifolds laying around (as you do) I checked them up against a gasket and was stunned by how much extra metal there was on the manifold that came within the edges of the gasket.

In an effort to extract anything I can from mine, is it worth me porting one of these spare manifolds around where it attaches to the head? Are there any downsides to doing this? If the car is being remapped would it be likely to even make any difference?

Not sure how much difference it makes but mine has been port matched, its all smooth as in no steps etc like the exhaust thread.

Yes and no depending whether you do it properly. When done properly you are potentially going to see small hp gains but more importantly smoother power delivery.

The key to it is the following DO NOT match it to the gasket!

Some simple flow dynamics explained now - A tube irrespective of how long it is will flow equal throughout it's whole length assuming you can maintain the same pressure across it's length.

Making it wider will change the pressure across it and it can now potentially flow more or less depending on all the other characteristics of the engine and it's components.

when looking at a port you want ideally an identical cross sectional area along it's entirity only widening as you get to the bowl underneath the seat to help the air slow down to make the turn. If you slow the air down at any other point you will loose flow.

So when you match the intake and the port to the gasket 90% of the time you are taking cross sectional area x and making it bigger to match the gasket only to reduce it back down to the original cross sectional area x.
Which basically buggers up your flow creating a flat spot in the low to mid range.

So if you want to benefit from port matching and reduce turbulance make a template of the existing intake ports and then match the intake mani to that template.

I logic is sooo simple, but half the time you don't think about it....

I port matched the inlet manifold on my valver, but I matched it to the gasket. I'm not entirely sure if I ended up with the above problem, it didn't seem to have any flat spots, so maybe not, but so many people say to use the gasket as the template, I mean, that's what I was told.

I think it's more pronounced with standard length intake manifolds, where the long tubes speed up the intake flow. Any port bodges here can affect the air flow balance and speed VW painstakingly achieved at the factory. You should chop open a VR6 intake and look at the trouble they went to on that thing!

With short runners, where the air flow has a much shorter path to the intake valves, all that goes out the window it's not so important, particularly where boost is concerned.

Yeah, when I go back and read my opening thread now, it does seem very naive - I mean, why would I match it to the gasket, when the gasket isn't any indication of the sixe of the openings in the head. Thing is it does get talked about a lot, so a lot people will have done it and probably been shocked if it didn't do much.

So it looks as though if I am to do it, then I should match it to the inlet ports on the head rather than the gasket. Cheers

One thing you'll notice about all the "talk" of doing it on the forums is a lack of dyno evidence to back up the claims.

Not that I've ever searched especially hard for proof (got better things to do ), but I've only seen one thread where someone dynoed each and every change and it concerned a NA VR6 with 3 different types of intake manifold and flowed heads etc.

With exception of the schrick intake, the differences were so tiny it was barely worth anyone's time and money doing it. You're talking no more than 10hp and negligable torque gains, which when you've got 200 to start with, at say 5500rpm, another 10 at 6500 will barely even register on the butt dyno

As has been said on here before, flowing, matching etc should be done as part of a bigger package of changes so that one mod allows another to work as it should

it's worth making sure the gaskets don't obstruct the airflow at all, I've noticed this on both the upper and lower manifold sections on a 16v.
what about internally polishing an inlet manifold though, some have minor casting marks that look like a good idea to remove, the engine shop that did my head (port and polish) also internally polished the inlet manifold lower section, not like mirror finish or anything, but as with the inlet ports a nicely worked but rough polish.

so hows the 16v affected when the inlet is a 50mm as thats got to be bigger than the inlet ports?

Flusted wrote:so hows the 16v affected when the inlet is a 50mm as thats got to be bigger than the inlet ports?

I think it very much depends on the spec of the rest of the engine, IIRC when GVK fitted a 50mm inlet to his 2L block with KR cams he actually lost a couple of HP as the torque dropped but his rev range wasn't extended, I guess the result may have been a little different with more aggressive cams, I think that was with a ported and polished head though.
I also think the length of the runners also has some influence, they're slightly different from 42 to 50mm and the chamber from throttle to runners is a different size.

What you don't have with a 50mm is the diameter varying, it goes 50mm straight to the head, so you should have slightly lower gas speed when the air hits the intake port than the 42. Somewhere I might have a copy of GVK's torque plots for 42 and 50mm inlets.

Long narrow ports give good torque delivery which is why all the naturally aspirated VAG motors have quite long runners. Short fat ports give top end hp and loose torque.

A correctly configured engine with a 50mm setup will give good high end gains at the sacrifice of some low end tq.

Unfortunatelly the 16v engine/head is possibly the worst one to compare different setups on as there is various castings through the years (small and big port) and change in exhaust valve sizes too. On top of which the minute someone says it's been ported I can gaurantee that 80% of them will loose bottom end torque and feel gutless till the top end of the rev range where it suddenly springs alive making not a lot more power than standard.

The 16v head is a delicate design where the port make up is pretty good.
I did a 1.8 KR lump with a standard head within the rules and regulations of the gti racing series so no porting allowed, running standard KR cams, standard untouched intake and not even the best exhaust in the world. Got setup after 400 miles of running in and made 166hp and 130ft/lb, with a pretty flat tq curve. Which I believe are the sort of figures people are getting from most 16v ported heads out there without the flat torque curve.

It's all about knowing which casting number of the 16v heads flows the best and doing a pucker recon job. If you clean up the intake runners it wont give any more power but improve throttle response. In a normal day to day situation it's considered a waste of time, however on a track it could mean 0.25-0.5sec quicker laptimes as you have better response out of the corner. Meaning the difference between winning and loosing over a 20-30lap race.

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do you think the earliest 16v head casting was the "best" ?

If I remember correctly the part number is 027103373e but I'd have to double check when I get one in. They are the small port late KR ones cast in germany with a real smooth finish as standard.

early heads hand bigger inlet and smaller zorst ports 051?

051 are abf heads they got the better flowing intakes like the late KR's but have smaller exhaust valves. In standard form they are a smoother functioning head in ported form you can take advantage of the large exhaust valves of the KR