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Tech Forum : Porting

- BMW E21 Community
   - Tech Forum
      - Porting
Matt   Posted Tuesday, Jun 24th 3:08am [Edit] [Quote] [IMS] [View car]
Member
Post nr. 58
   
SF Bay Area
81 320i
Has anyone tried/succefully ported thier head? I am REALLY intimidated by combustion chamber work and valve jobs so I don't know if I will take a swing at that unless it proves to be fairly simple.

I am also wanting to port out that tiny TB and maybe the air flow sensor in/out. I also have my eyes on the TB port in the intake manifold, that thing looks pretty restrictive.

I will have a semi-knowledgable person by my side but I will be doing the actual work with a die grinder and a dremel. He has some honing stuff so we will use that for the polish.

I will try to take some pics for people that have never seen any of this stuff and I'll try to get some of the actual work done.

m10_power   Posted Wednesday, Jun 25th 5:45am [Edit] [Quote] [IMS] [View car]
Member
Post nr. 4


About 15-20hrs went into the 8 ports for this effect.



Aim for this

This was my first attempt at porting, mind you I had every porting tool you could imagine at my finger tips, and a guru steering me along.
It far easier to make the ports worst then it is to make them better, hogging isnt what your after.
Numb hands, and many hours picking alloy filings out of my skin, dress in coveralls and use duct tape on your gloves.

Matt   Posted Wednesday, Jun 25th 6:56am [Edit] [Quote] [IMS] [View car]
Member
Post nr. 63
   
SF Bay Area
81 320i
Is it just me, or is the exh port much more polished than the intake? Also, did you bore out any of the openings to match the gaskets?


m10_power   Posted Wednesday, Jun 25th 7:26pm [Edit] [Quote] [IMS] [View car]
Member
Post nr. 8


The exhaust port is fully polished, the intake is polished near the seat and gradually less polished out to the port entrance, by design. BMW heads are very nicely cast, the ports shouldnt require the port matching that say a chevy port would. Very minor amounts were needed to be removed for the gaskets I had, you want to avoid having a big 'ball' area at the port just to match them.

M42powered   Posted Wednesday, Jun 25th 7:46pm [Edit] [Quote] [IMS] [View car]
Staff
Post nr. 67
   
Arizona, USA
1981 BMW 320i
The intake is roughened as you near the valve for mixture's sake correct? turbulant flow allows for a better disspercement of fuel in the intake charge. The exhaust side is polished all the way so that the spent gases can be aborted much more rapidly and efficiently, this way there is less spent mixture in the combustion chamber.
-- Am I close Paul? Just wondering if I get the general idea --

m10_power   Posted Wednesday, Jun 25th 9:10pm [Edit] [Quote] [IMS] [View car]
Member
Post nr. 9


Ya Nic that is the gist of it, the exhaust polishing is also there to resist heat transfer.

M42powered   Posted Thursday, Jun 26th 1:27am [Edit] [Quote] [IMS] [View car]
Staff
Post nr. 70
   
Arizona, USA
1981 BMW 320i
Ah, right... the less surface area (ie. smooth not rough surface) the less contact a hot gas has. Never thought of that. Have you done anything to the intake manifold? Jake's old turbo 4 runner was extrune honed from TB to head I believe. Really well done and smooth as can be (so I hear, I didn't get to touch the inside of it at all). Of course there are two camps on the whole manifold polishing thing. Do you subscribe to one?
Great info Paul, thanks for sharing!!!!

Matt   Posted Thursday, Jun 26th 2:50am [Edit] [Quote] [IMS] [View car]
Member
Post nr. 69
   
SF Bay Area
81 320i
Wouldn't the full polish of the intake help to resist carbon build up? Does the extra 'mixing' time give a greater positive effect than the resistance to carbon build-up?


m10_power   Posted Thursday, Jun 26th 6:49am [Edit] [Quote] [IMS] [View car]
Member
Post nr. 10


Actually, extrude honing the manifold would be a good idea as long as they dont make it larger dia. at least as minimum as possible. I dont think it would be worth the money, also polishing the intake wouldn't matter much as the fuel is injected at the very end of it, so the port is more important for the surface prep.
I am a big believer in 'bang for the buck', so extrude hone isnt worth it to me. Sure the ball bearing turbo is better but in my application is it worth twice the price??? I didn't think so.

M42powered   Posted Thursday, Jun 26th 7:38am [Edit] [Quote] [IMS] [View car]
Staff
Post nr. 71
   
Arizona, USA
1981 BMW 320i
The roughness of the intake port after the injector is only to create turbulence for mixing. Pre-port there is not mixing to be had. Extrude honing is used so that the air travels more rapidly. This is true for objects moving through still air. The object will "slip" through a blanket of still air more rapidly and with less resistance if its surface is smooth and polished. Having the working fluid (air or water) moving through conduit (be it an intake runner) is a whole new ball of wax. The behavior of the fluid and its velocity is based more on the Reynold's number (a dimensionless constant). Depending on the Reynold's number (which is based on velocity, viscosity, temperature and density) a rough surface or a smooth surface can be more desirable for a higher velocity. There are boundary layers, no slip conditions, the list goes on and on. I love this fluid dynamics stuff. I love it even more when it applies to motors. The jury is still out on which is preferred for an M10.
And I'm spent *deep breath*

Yety   Posted Thursday, Jun 26th 6:38pm [Edit] [Quote] [IMS] [View car]
Member
Post nr. 15
   
Europe, Romania
320i/6
Question from a total ignorant of porting : if I'm using a carburettor, would porting make some significant change ? And if yes, exactly what should I do ?

Matt   Posted Friday, Jun 27th 12:29am [Edit] [Quote] [IMS] [View car]
Member
Post nr. 74
   
SF Bay Area
81 320i
Should I just polish the whole thing totally?
It's my labor and the head is a spare so there's no real time constraint.


M42powered   Posted Friday, Jun 27th 12:48am [Edit] [Quote] [IMS] [View car]
Staff
Post nr. 79
   
Arizona, USA
1981 BMW 320i
I think you're missing the point. The injectors don't spray into the combustion chamber. If they did (which they don't on any car that I know of) then you could polish the whole thing with out much trouble. The thing is that the injector is placed in the intake track, above the valve. The fuel is injected before the valve. Therefore mixing the fuel and air before it reaches the open valve is essential. It is true that even on a perfectly polished intake track the air entering the combustion chamber before the valve is not laminar (in that it is turbulant). But creating more turbulance at this point would further the mixing process. A better mix ensures a more complete and powerful burn. Thus HP.

Yety -- Your case is a little more simple I believe. Since the mixng process for your 320/6 occurs mostly at the carburator, I believe the polishing the intake might help you more than on an fuel injected motor. I'd do a search on google or something for polished intake manifolds on carburated cars, might help to shed some light on the subject.

RDAvena   Posted Friday, Jun 27th 1:12am [Edit] [Quote] [IMS] [View car]
Staff
Post nr. 62
   
SELECT * FROM users WHERE clue > 0
1981 323i, 1988 545is, 1997 528i
Yety,

Some have said the biggest benefit on a Naturally Aspirated engine would be in port matching rather than polishing. Someone threw out a line once that port matching will yeild the biggest benefit rather than trying to polish/resize the ports. If that was all that you could do to the head, that is. But, then I could be wrong.

I have the BMW 3.5l turbo motor (M106) and I put a bigger/better flowing intake manifold from a e34 on it, and matched the ports only to find out later that matching ports on a turbocharged engine is not important. So they say. There was not much to take off in order to match them just a little flash casting left and some ridges. But I would think if it was not as important why did Paul do it and get such good performance out of his motor?

You can tell on the exhaust side that the BMW builders did polish and smooth the ports out there. and had a slight dusting of carbon on the exhaust ports.The head is stamped "turbo" by the way. Hmmm, makes the mind think.

Nic is right on polishing NA motors for performance. If not why do so many big block domestics go this route when trying to pick up HP?


Standard Abrasives has a do it yourself guide on head porting pretty intuitive:

http://www.sa-motorsports.com/diyport.htm

Yety   Posted Friday, Jun 27th 11:15am [Edit] [Quote] [IMS] [View car]
Member
Post nr. 17
   
Europe, Romania
320i/6
Thank you very much, guys

Please correct me if I'm wrong : in my case, polishing the intake and the exhaust manifolds could add a little power to my "becoming engine".

I've already mentioned that I'm ignorant about this stuff, so please be tolerant if my next question will be too stoopid When using a carburettor, how much the length of each "tube" (from carburettor to head) influences performance ? I'm not very familiar with the technical terms used on this subject, so I'm gonna ask another thing : what exactly is a "port" and what do you mean by "port matching" ? In carburettor engines would it mean to provide the same length for each "tube" from carburettor to head ? I don't know how could I do that, as these "tubes" are united right under the carburettor. Maybe it's a bad idea, but I was thinking to use an intake manifold from an engine with injection and somehow fit the carburettor on it (fill the injector holes, replace air filter with custom cold air intake, cut the hood).

Instead of wasting your time answering to my "greenhorn" questions, I would be very happy if you could give me a link to a site where all this is explained for rookies like me I know I should be ashamed for my ignorance and for being so annoying, but I can't help it I wanna know everything that can help me

All my apologies and my thanks are presented in advance. I'd never even dreamed to find so much help for my projects

M42powered   Posted Friday, Jun 27th 7:29pm [Edit] [Quote] [IMS] [View car]
Staff
Post nr. 84
   
Arizona, USA
1981 BMW 320i
Yety -- Ports are the physical openings to the head. The port is the "tunnel" that the air and fuel go through to get to the valve and finally to the combustion chamber. Port matching is when you make the outlet of the intake manifold (the inlet being the carb side) and the inlet of the head the same shape and size. This way there is no portion of the head blocking the intake track. Of course you can't put your intake manifold on the head and trace the shape of the intake outlet on the head (you'd need a weird scribe and some long fingers). So the gasket is usually used as a guide.

The intake runners (the tubes to which you refer) are designed by BMW to provide, most likely, the best performance. Changing these usually don't help much unless there were fitment constraints that the BMW engineers could not overcome.

Yety   Posted Saturday, Jun 28th 7:55pm [Edit] [Quote] [IMS] [View car]
Member
Post nr. 20
   
Europe, Romania
320i/6
Thanx, Nic ! Now I finally know the signification of these technical terms

But now I have another question : providing the same length for each "tube" from the inlet to the outlet of the intake manifold would significantly improve engine performance ? Or is it better to use the original intake manifold designed for the Solex 4A1 ?

RDAvena   Posted Saturday, Jun 28th 9:39pm [Edit] [Quote] [IMS] [View car]
Staff
Post nr. 66
   
SELECT * FROM users WHERE clue > 0
1981 323i, 1988 545is, 1997 528i
Prob the port matching of the stock manifold might give you the best return.

This and changing the carb to an Edelbrock or a Holley carb will allow you to use a more modern carb design. More adjustability, easier to fix, and jet changes are allowed in these carbs as well. It may allow for the removal of a lot of vaccum hoses that are associated with the Solex.

Some have done this with removing a little bit of material off of the top of the stock mounting area of the manifold. This is so the new carb will seat flat. Slap in a 310 degree cam and watch the tires burn. 310 degrees is the highest I have heard of someone going on these carbs.

Of course you will have to tune it a little but it will be much easier with the aftermarket carb. It will still work a lot better than the one carb to a horn design though.

M42powered   Posted Saturday, Jun 28th 10:06pm [Edit] [Quote] [IMS] [View car]
Staff
Post nr. 88
   
Arizona, USA
1981 BMW 320i
Yeteee -- It is true that equal length runners on the intake improve performance, much like equal length primaries on the exhaust. What you have to do is look at it from a feesabilty (spelling) aspect. Creating your own manifold is not easy. Infact it is probably something not many of use would under take. You would need custom bent piping, a flange to fit the carb you want and one big chunck of time to engineer it properly. BMW probably did a great job on flow benching the setup you have for maximum performance. I'd take BMW's word on it and keep the stock manifold. Simple, cheap and much less of a headache. Ray hit the nail on the head. I'd got as far as port matching and no further. Maybe do a little port polishing if your interested. If you're interested in more performance and adjustability a newer carb might be the way to go. You could tune the car to match your driving style. With a cam and a nice free flowing exhaust you'll boost torque and horsepower.

Yety   Posted Sunday, Jun 29th 8:59pm [Edit] [Quote] [IMS] [View car]
Member
Post nr. 22
   
Europe, Romania
320i/6
All my gratitude goes again to you, guys

Getting an aftermarket carburettor is out of question due to my extremely low financial resources (I hate to admit it, but it's damn' real, so I have to think about what I can really afford myself to do )

So I'll take your advice and go for port matching and original manifolds polishing (DIY is my law ), but keeping the stock Solex A4, as I'm quite satisfied with it (more than 10k miles and absolutely no problems) and I received as a gift 3 more of these carburettors from one of my father's friends who knows that I'm addicted to working myself on my E21.

Being said that, "Yeteee" raises his hat again before you

JDBeyer   Posted Tuesday, Jul 1st 7:21am [Edit] [Quote] [IMS] [View car]
Member
Post nr. 22
   
N. Humboldt county Ca.
82 323i on steroids
I am curently fussing with the head on my new engine and Like Ray was saying about port to manifold matching this is important for NA I think. I am using the 2.5 intake and head and it is not very well matched, I was suprised.

Dorzas323i   Posted Friday, Jul 4th 7:15am [Edit] [Quote] [IMS] [View car]
Member
Post nr. 4
   
Victoria, Australia
euro 1982 323i
hey, i think i have to agree with nic. making a intake manifold would be a huge task, and you'd be surprised by how quick the cost would run up, special flange plates, gaskets, pipes, tig welding it all together (at least if your using aluminum). better using what you have and doing some port work. i would suggest saving some money, and buying a new carbie down the line, the basis for real tuning.

and i'll plug one question wile i'm here does anyone know if the s38 m5 enigne needs port work. cause i know it has six throttle bodies, and i'd assume it it would be pretty well built. -doran

M42powered   Posted Friday, Jul 4th 11:14pm [Edit] [Quote] [IMS] [View car]
Staff
Post nr. 111
   
Arizona, USA
1981 BMW 320i
Porting that motor would probably be a small waste of time. Jake has the S14 (basically an S38 with 2 cylinders lopped off). I'd suggest running it stock. Just syncronize the throttle bodies and set the linkage to open all throttle bodies at the same time. The S38 is a race motor (out of M1's), so I'd be surprised if porting would do that much. I could be wrong though.

Dorzas323i   Posted Sunday, Jul 6th 2:24pm [Edit] [Quote] [IMS] [View car]
Member
Post nr. 15
   
Victoria, Australia
euro 1982 323i
yeah nic, i assumed that much. i didn't think that those engines would need much, and for the money i'm gonna fork out for it, i don't want to spend too much on it.

ps: i love it when you say it comes out of a M1, makes me think that i have this huge 'M' motor in an e21, happy is me.

cyaz -Doran
pps: that's an M1 motor under my name innthe thumbnail.

JDBeyer   Posted Monday, Jul 7th 4:51am [Edit] [Quote] [IMS] [View car]
Member
Post nr. 31
   
N. Humboldt county Ca.
82 323i on steroids
I hope you can work out all the details,and I am sure there will be some to do this! It does seem do-able. Thought I might keep you motivated with these M1 engine shots from one we had apart a while back!



Dorzas323i   Posted Monday, Jul 7th 2:23pm [Edit] [Quote] [IMS] [View car]
Member
Post nr. 20
   
Victoria, Australia
euro 1982 323i
such beauty, (drool) thanks for the encouragement
-Doran


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