Boring and porting

[AceKing]

Well basically my dad owns a machine shop, and i want to increase hp in my bmw. so to take advantage of the fact my dad owns a machine shop how do u bore and port and engine. Is there a certain amount of metal i take off before i screw up the holes?

Another thing is if i do bore out the engine, should i get bigger pistons that fit the hole better. Is it better to just buy some, or make some?

Thanks for any help.

Adrian

[stevehuckss396]

The smart thing to do is to buy the pistons and fit them to the block. Bore about .007 smaller than the piston and hone out another .010 thou. Typical clearance is about 1 thou per inch of bore. Alot can affect that so you better do alot of reading and talk to a local engine builder for advice.

[RICHARD ZASTROW]

You might think twice about boring a Bimmer engine. Find out if the bores have a special coating like "Nikasil" or other. This requires extremely expensive equipment to replace the coating. Without the coating, the aluminum block will wear out in no time. There is the limited possibility of sleeving the bore with a cast iron liner. All above is for aluminum engine blocks.

[bowber]

You really need to consult someone who's tuned these motors before, you can make a mess of an engine unless you know what you are doing.

However if you want to do this yourself there are some very good books on tuning and most likely some on BMW's.

Steve

[racingguy2]

Which engine is it?
Most of the BMW engines have Alusil coated bores. It's not expensive to have recoated, but for the 1-2mm that you MIGHT be able to enlarge the bores, it's questionable if it's worth it. Adding iron bore sleeves, and using a turbo is the best option for most of the BMW engines.

If you DO enlarge the bores, the only realistic option for pistons is to buy new ones in a custom size. ($$$) High performance pistons are made on a special Piston Lathe that the tool occilates with rotation to make the piston an oval shape (about .003" out of round), which aides ring sealing. Most BMW pistons have asymetric dishes as well.

A friend of mine had a BMW V12 sleeved by a "BMW Race shop" and when he got it, the block was so warped it wasn't even usable, much less race worthy. He took on doing it himself, and after scraping a couple, has it down now. It's still not a cheap option though.

Cylinder head porting is generally not as much an issue in BMW heads. An average port flows about 220-230 cfm in stock form. I've only been able to increase this to 250 cfm with LOTS of time and tweaking.
For a fuel injected engine, it's kind of a side point, and only really worth it for all out race or forced induction.

The best options if you want a shop project, are to make custom titanium valves, and add a turbo.

Regards,
Eric

[NC Cams]

Caution: Do NOT use message board specs to bore and/or hone your block.

Why? Each piston maker has a preferred gage point and a preferred clearance that they want the piston-to-bore clearance set at. Some pistons are measured right below the lower oil ring groove. Some are measured at pin bore C/L on the major thrust face of the skirt. Some are measured at the skirt tails and some are measured half way between the bottom of the tail and the bottom of the strut where it meets the full skirt.

SOme pistons need 0.0015" clearance, and some need/want 0.0025". Yet others go in at 0.004" and some "california alloy" pistons need 0.012". I've seen any number of genius engine builders set any/all pistons at some "hot ticket" clearance that some "expert" claimed was correct. These same guys often had noise and/or skirt cracking problems because they didn't use the piston maker's skirt clearance checking and setting specs. Someone who claims to know everything there is to know about setting skirt-to-wall clearance usually doesn't know all that there is to know - especially when it comes to some of the aftermarket forged and some cast replacment pistons.

The same goes for bore honing. Hone the block to size using the wall finish and preparation method prescribed by your ring supplier. They know what the rings want, and the recommended method works 99% of the time with the least amount of grief. The use of some super trick, double throw down, ultra slick bore method should be reserved for the pro's who have the experience - trick ring finishes are NOT for beginners, especially those that involve "polished bores".

On porting: Anything other than a VERY MILD clean up of port's shart edges should be left to someone with a flow bench and porting knowledge. Period, Paragraph.

Why? Because some ports respond quite well to simple clean ups. Others can become quite lame if you get carried away with the porting tools and/or die gringders and make them too big or remove certain flow diverters/enhancers that are being used these days by some OEM's.

Leave any serious metal removal to the EXPERST with flow benches.

There was a real good article on home brew DIY porting in an issue of Popular Hot Rodding or Super Stock Drag Illustrated quite a few years ago. They showed how to take a stock Chevy 1.9" intake/ 1.5" exhaust ports and make it flow as well as 2.02"/1.600" "fuelie" heads with only a 3 anglve valve job and about 10 minutes work with a die grinder in each port.

Of greatest importance, they did NOT remove an appreciable amount of metal in the process of making the modifications.

Porting, like engine boring and honing, are NOT skills that are particularly suited for rank beginners. These efforts take proper equipment and experience to do them properly. Seek competent help before you try doing it yourself. You can't go putting metal back once you've hacked it away....

[Kipper]

Originally Posted by AceKing Well basically my dad owns a machine shop, and i want to increase hp in my bmw. so to take advantage of the fact my dad owns a machine shop how do u bore and port and engine. Is there a certain amount of metal i take off before i screw up the holes? Another thing is if i do bore out the engine, should i get bigger pistons that fit the hole better. Is it better to just buy some, or make some? Thanks for any help. Adrian

Ignore everyone and listen to me. Buy a faster car. I get 0-60MPH in 2 seconds






























Admittedly it's a motorcycle but hey catch me if you can









Hope you don't break your car

[NC Cams]

IF the questioning member's father REALLY owns a machine shop, the father should be able to at least explain what's involved in boring and honing as opposed to having to rely on a message board for the learning experience.

Although a general machine shop may not do automotive work, the basic premise of honing and boring are pretty much the same no matter what. Come to think if it, it is pretty sad when/if a father and son can't get together to share in the experience of teaching/learning how to do these basic operations.

Before the member starts trying to craft on a BMW (not the easiest nor most readily hot rodded vehicle), I'd almost be inclined to suggest that the member do something a bit simpler/easier, like maybe a small block Chevy or Ford. Parts are dirt cheap and readily available via mail order or the internet (IE: Jegg's, Summit, etc).

Once you get your feet wet doing a "belly button motor" (as in everyone in America has one), you can then take on the more challenging effort of building a hotted up European or Pacific Rim "fast and furious" ride. If/when you do, have lots of money ready as the Euro/Pacific stuff is horribly expensive as compared to American iron, especially when you start looking for trick parts.

[DRD]

I own and operate a high performance engine building and cylinder head machine shop. We have a flow bench and dyno at our shop.
You are better off sending your BMW engine to a shop that knows these engines. The phrase "machine shop" is very generic statement.

I get heads sent in all the time, people get in the ports and make a mess out of them, bigger is not allways better.

Good luck!
Darren Gurrola
DRD RACING HEADS

[AirChunk]

I am with NC CAMS , why didn't you ask DAD ?

[greg b]

I would have to go along with DRD and nc cams i to do alot of porting and boring and honing, every engine has its own clearance specifcations and needs as far as air flow goes.As the old saying goes you can always cut some of but its bloody hard to cut some on.Go get some imformation of people that have experiance with that engine.I have had so called machinist stuff cylinders up before especially,2 strokes with there sleeve fittings,and it is not easy to repair.Sure have a go but get the right imfo first good luck greg b