Techie views on porting and polishing m30B35 heads

[Turbo Ready]

Hi Guys,

I am rebuilding, more like refreshing an m30b35 engine with only 86,000 miles for my e30 335i engine swap project. The engine came out of a wrecked 90 735i
I will turbocharge this motor after I get it running well in my 325is.

I have been doing some research and have discovered that while porting is great for added performance, polishing might not be.
Experts are saying that the rough casting effect actually create eddy currents creating turbulence of the intake charge which helps with the flow. They also said that polishing the head to a mirror finish actually reflects the heat making it more prone to detonation.
I tend to agree with the above, any techie views with port and polishing and or turbocharged experience would be appreciated.

Thanks.

[Robin-535im]

Hi Guys,

I am rebuilding, more like refreshing an m30b35 engine with only 86,000 miles for my e30 335i engine swap project. The engine came out of a wrecked 90 735i
I will turbocharge this motor after I get it running well in my 325is.

I have been doing some research and have discovered that while porting is great for added performance, polishing might not be.
Experts are saying that the rough casting effect actually create eddy currents creating turbulence of the intake charge which helps with the flow. They also said that polishing the head to a mirror finish actually reflects the heat making it more prone to detonation.
I tend to agree with the above, any techie views with port and polishing and or turbocharged experience would be appreciated.

Thanks.
Very interested in this too... but IMHO the fluid dynamics involved are more complicated than laminar vs. turbulent... one could calculate the Reynolds number for air in a 45mm tube with 3000 RPM x 3.5L/6 litres per minute flow, I bet it is very turbulent no matter the surface drag... Properly set up CFD models or better yet controlled test data are likely the only trustworthy answer, and even then the difference is probably very small - in the noise for any but the most exact comparisons.

Despite that it would be interesting to hear people's experiences for sure.

[Blitzkrieg Bob]

Port the intake, leave it unpolished.

Port and polish the exhaust.

Match the manifolds

polish the piston crowns and CC and polish the heads.

If you can find a shop the does extruded hone you can save time and get a real nice job done.

[Turbo Ready]

Port the intake, leave it unpolished.

Port and polish the exhaust.

Match the manifolds

polish the piston crowns and CC and polish the heads.

If you can find a shop the does extruded hone you can save time and get a real nice job done.

Bob, all the info and advice seems to point in this direction. I might look at the roughness in the intake and might smooth it out without polishing it to a super mirror finish. Will just look at the possibility of removing hot spots from there.

Thanks so much for the input, it helped allot.

[Blitzkrieg Bob]

polish everything mirror smooth too.

[Turbo Ready]

polish everything mirror smooth too.

Thanks.:)

[632 Regal]

Bobs right on here. Although I wouldnt do an extrude hone as you need velocity too which plays a vital role in flow.

Dont ever open the area just below the valve seats as that will kill any performance gains you might have otherwise seen, just smooth them out (blend any sharp angles).

The intake ports should be finished after you smooth it out, finish with an 80 grit roll on a drill or similar slow speed tool to leave it rough.

With a turbo you might want to go with larger exhaust valves while you are in there but not absolutely necessary, with the larger valves you can open up the exhaust port side a bit but watch the area uner the valve seats so they are all exactly the same. Dont hog them out tho, you will lose all velocity.

Even might want to look into a turbo cam if money isnt much of an object.

[Turbo Ready]

Bobs right on here. Although I wouldnt do an extrude hone as you need velocity too which plays a vital role in flow.

Will not do extrude honing

Dont ever open the area just below the valve seats as that will kill any performance gains you might have otherwise seen, just smooth them out (blend any sharp angles).

Will follow that.

The intake ports should be finished after you smooth it out, finish with an 80 grit roll on a drill or similar slow speed tool to leave it rough.

With a turbo you might want to go with larger exhaust valves while you are in there but not absolutely necessary, with the larger valves you can open up the exhaust port side a bit but watch the area uner the valve seats so they are all exactly the same. Dont hog them out tho, you will lose all velocity.

Even might want to look into a turbo cam if money isnt much of an object.

The engine turbo charged develops over 350 BHP without changing the valves and on a stock cam.

I was thinking of getting Jeff from IE to grind me a turbo cam, but since this engine is going into an e30 which is over 1000 lbs lighter than the e34, the 350 BHP I think will be enough for now.

I would like manageable power and though I am rebuilding the car from the ground up including a GC/Koni suspension and a 5 lug swap to facilitate handling and traction, 350 BHP will still be fun to control.

Thanks for the input, I will let you guys know how things progress,

[rob101]

Very interested in this too... but IMHO the fluid dynamics involved are more complicated than laminar vs. turbulent... one could calculate the Reynolds number for air in a 45mm tube with 3000 RPM x 3.5L/6 litres per minute flow, I bet it is very turbulent no matter the surface drag... Properly set up CFD models or better yet controlled test data are likely the only trustworthy answer, and even then the difference is probably very small - in the noise for any but the most exact comparisons.

Despite that it would be interesting to hear people's experiences for sure.
I did a quick calc, the reynolds number is about 30 000. which is very turbulent. the air is going 11.83 m/s there is a calculator here (http://www.engineeringtoolbox.com/reynolds-number-d_237.html)
it is true that in venturis the best geometrys for do not produce laminar flow. some turbulence can be good.

[Turbo Ready]

I did a quick calc, the reynolds number is about 30 000. which is very turbulent. the air is going 11.83 m/s there is a calculator here (http://www.engineeringtoolbox.com/reynolds-number-d_237.html)
it is true that in venturis the best geometrys for do not produce laminar flow. some turbulence can be good.


Cool, nice find, thanks.

[fin]

Rough intake for turbulence.

Polished combustion chamber (head and piston) and exhaust to keep the heat out of the engine, putting it into the exhaust.

If you have knock sensors and running good gas, detonation shouldn't be a problem.

Cheers,

Fin

[Ross]

A polished surface in the intake is thought to cause the fuel to precipitate out of mixture. Polish on the exhaust side is good for flow but the path the gases follow is more important.

[Turbo Ready]

Thanks Vin and Ross for the tech advice.