Port and Polished???

[kennejp]

Hey my sixth cylinder is really low and I think I am going to have to rebuild my head. When I am doing it do you guys think it is worth the 4 or 500 more dollars to port and polish my head? Has anyone done it or anyone have any pros or cons???

[mount2010]

Gran Turismo 4 ftw?

[Truman325i]

some people talked about it before and it totally not being worth ti unless you go FI

[87esir]

when you say low do you mean compression? Why do you think its the head? Yea, the valves might not be seating good but it could be your rings/piston/cylinder. How many miles on it?

port and polish is generally not worth the money on cars like these unless you were to do it yourself and save the bucks.

[kennejp]

Well I did a compression test and leak down test and the 6th cylinder was really low on the tests

compression
1-210
2-215
3-212
4-215
5-215
6-165


Leak Down
1-10
2-10
3-12
4-10
5-12
6-45

The local shop said that I needed rebuild the head and put new valves and springs on it....

[DiScoTeknix]

Port and polish will improve airflow but not by much. If you are rebuilding your head, spend the money on a race/performance valvetrain and cams rather than extra machine work.

But as previous posters have mentioned, definatey check to see what is really the culprit. If you rebuild the head and find out your bottom end was the problem than that is a lot money wasted. Money that could have gone towards an S52 swap.

[pioneer416]

The local shop said that I needed rebuild the head and put new valves and springs on it....

is the local shop under the impression that they will be doing the work? if so they see $$$. as mentioned b4 usually low compression is cylinder related not head related

[TCarlisle]

More than likely, they determined they source of the leak during the leak down test. DUring the test, one can listen through the oil dipstick tube and if the sound of compressed air leaking is heard, it would indicate leakage through the piston/ring. Listening at the tailpipe will tell if the leak is through and exhaust valve, and listening at the intake will tell if the leak is through an intake valve. If none of these seem to be conclusive, then it is the HG.

Before tearing into the head, query the shop that did the test on how they determined it was a valve. If they are just guessing based on experience that it is usuually a head problem, then pass. I would expect that the shop validate their instinct through the listening tests.

[kennejp]

Ok thats great advice- They are a BMW racing shop that does tons of aftermarket racing stuff and I do not know how they came up with that conclusion but they said they were 95% sure it was the head and when they took of the head they would be able to see if the bottom was scored or anything....

[Mitch]

Ok thats great advice- They are a BMW racing shop that does tons of aftermarket racing stuff and I do not know how they came up with that conclusion but they said they were 95% sure it was the head and when they took of the head they would be able to see if the bottom was scored or anything....

Hey, what's the name of the shop?

[pioneer416]

More than likely, they determined they source of the leak during the leak down test. DUring the test, one can listen through the oil dipstick tube and if the sound of compressed air leaking is heard, it would indicate leakage through the piston/ring. Listening at the tailpipe will tell if the leak is through and exhaust valve, and listening at the intake will tell if the leak is through an intake valve. If none of these seem to be conclusive, then it is the HG.

Before tearing into the head, query the shop that did the test on how they determined it was a valve. If they are just guessing based on experience that it is usuually a head problem, then pass. I would expect that the shop validate their instinct through the listening tests.

damn thats some good advice, never heard of that b4...thanks

[kennejp]

Treehouse Racing/ EuroTech- Ya I know that was really good advice

[kennejp]

when I am doing my head job should I port and polish it for a extra 500 or no?

[DU09]

when I am doing my head job should I port and polish it for a extra 500 or no?
do cams instead.

[Damo]

As the prev guys said, port amnd polishing work wont really doe much unless you have other mods to go with it.... It will flow a lot better thats for sure, but you wont notice much of a difference in HP maybe on fuel economy.....

I'd do cams if you have the $500 spare....

[87esir]

that shops full of horse puky, don't believe that. You can't hear that in different areas as fast as those valves are opening. The only thing even closely related to what their saying is that you can hold a dollar over an exhaust pipe and it will suck in if you have a burnt valve.
What they will do is grind your valves put your head back on, find out that wasn't the problem and then find out by them doing the valves your engine that probably has a lot of miles now has a lot more leak down and blowby because the rings can't handle the extra seal of the valve job. It will also likely start using oil. I would get them to put it in writing that they will fix your car if this stuff happens since their so sure the valves are the problem. They won't though.
good luck

[kennejp]

Well then what do you guys think is wrong with it- The car drives perfectly and I would have never known but I was about to put a turbo on it so I wanted to get a compression and leakdown test before I did- The engine runs and idles perfectly I guess I am just looksing alot of HP from the 6th cylinder....well if you guys dont think it is the head what do you think it is?

[SergeK]

im leaning towards headgasket.

[kennejp]

I believe I already had it replaced about 6 months ago.....maybe it went out again or something?

[87esir]

There is no way to know w/o taking it apart but it could very well be the cylinder wall or rings. How many miles do you have on it?

[kennejp]

It has 150k on it...

[SergeK]

Dunno, have you overrevved it at all lateley? Overheated? I dunno, im not too experienced in this.