The B20VTEC discussion thread

**dougie_504** · 07-12-2011 09:24 AM

Originally Posted by spetz

It would alter compression ratio if it was changed however logically it seems that sharp areas around the top of the bore would not be desirable?
I know the usually are not exactly the same as the bore and from looking at a few heads it seems sometimes the combustion area is not even a perfect circle.
I assume this means that the heads are not modified to take this into account?

True, not always a perfect circle. Mine for example are certainly not, having been modified when my head was built. This was done to increase flow/combustion but of course you need to be careful that you don't crease hot-spots and have it done professionally.

**Bludger** · 07-12-2011 09:29 AM

Originally Posted by dougie_504

True, not always a perfect circle. Mine for example are certainly not, having been modified when my head was built. This was done to increase flow/combustion but of course you need to be careful that you don't crease hot-spots and have it done professionally.

no need to get pro.

just sit there with a rotary tool & some beer.

needs lots of time and must know where to grind.

lol

**spetz** · 08-12-2011 07:34 AM

Does anyone know where the VTEC changeover point happens, and what rpm peak power is produced roughly with each respective head and standard cams?
ie, B16A, B16B, B18C, B18CR?

**mocchi** · 08-12-2011 07:36 AM

Originally Posted by spetz

Does anyone know where the VTEC changeover point happens, and what rpm peak power is produced roughly with each respective head and standard cams?
ie, B16A, B16B, B18C, B18CR?

are you asking the question based on head only or whole complete stock engine ?

**spetz** · 08-12-2011 06:34 PM

Well on the basis that all things are equal and the same with the only difference being the heads

**TODA AU** · 14-12-2011 12:16 PM

Originally Posted by spetz

Guys sorry if this has been covered, but I have not read all 77 pages.
Can anyone tell me considering the bore is some 3-4mm more than the B16/18, and the head comes from the B16/18, do any modifications need to be made to expand the combustion chamber or using it as is is fine?

Keep the chamber at 81mm as std, or better, use a CNC reprofiled chamber, but again keep it at 81.
Going bigger loses quench & compression, so don't go there.

**TODA AU** · 14-12-2011 12:18 PM

Originally Posted by GSi_PSi

Isn't that what a cnc Port job does

Damn!
You got a pic of the worlds 1st fully functioning android.
(That way his hands have computer numeric control

)

**GSi_PSi** · 14-12-2011 03:27 PM

Originally Posted by TODA AU

Damn!
You got a pic of the worlds 1st fully functioning android.
(That way his hands have computer numeric control

)

lol he could be a robot, nomsayin

better ?

**tinkerbell** · 14-12-2011 04:05 PM

maybe by:

would be an expensive headjob no doubt!

**GSi_PSi** · 14-12-2011 04:17 PM

Originally Posted by tinkerbell

maybe by:

would be an expensive headjob no doubt!

i see what u did there, asimo escorts ftw

**tinkerbell** · 14-12-2011 04:27 PM

either way, to answer spertz - slightly radiusing the edge of around combustion chamber to reduce hotspots would be all you should consider when using a 81mm head on a 84mm bore (unless you are designing the shape of the piston crown yourself...lol)