Go Back   Team-BHP > Under the Hood > Modifications & Accessories


Closed Thread
 
Thread Tools Search this Thread
Old 15th March 2006, 18:44   #1
BHPian
 
Kaizer Sozay's Avatar
 
Join Date: Apr 2005
Location: Melbourne
Posts: 333
Thanked: 4 Times
Default Engine Porting, Polishing & Valve Cutting

I have heard that after an engine does 50,000 kms. one needs to open the engine up. & the parts need to be machined and polished. Can anyone throw light on how this makes a difference in power / FE

Last edited by Kaizer Sozay : 15th March 2006 at 18:58.
Kaizer Sozay is offline  
Old 15th March 2006, 20:00   #2
BANNED
 
viper's Avatar
 
Join Date: Mar 2005
Location: Mumbai
Posts: 1,769
Thanked: 8 Times
Default

Hi,

There is no need to open an engine after 50,000kms you have heard wrong. As far as your subject matter goes Porting/polishing smoothens the flow of gasses and removes the casting irregularities found in the cylinder heads which results in better power.

Viper
viper is offline  
Old 15th March 2006, 20:05   #3
BHPian
 
Join Date: Feb 2005
Location: Stuttgart, Germany.
Posts: 815
Thanked: 96 Times
Exclamation

Quote:
Originally Posted by viper
Hi,

There is no need to open an engine after 50,000kms you have heard wrong. As far as your subject matter goes Porting/polishing smoothens the flow of gasses and removes the casting irregularities found in the cylinder heads which results in better power.

Viper
Ok, can a cast iron head be ported and polished????

What is valve cutting?
Edmund is offline  
Old 15th March 2006, 20:51   #4
BANNED
 
viper's Avatar
 
Join Date: Mar 2005
Location: Mumbai
Posts: 1,769
Thanked: 8 Times
Default

Quote:
Originally Posted by Edmund
Ok, can a cast iron head be ported and polished????

What is valve cutting?
Yes it can be done. Read this article which is interesting and should answer your question.

"Headwork entails enlarging the intake and exhaust passages in a head to allow for more flow. Good headwork entails subtle reshaping, not just hogging the whole port out bigger. Generally, good headwork leaves the floors of the port alone since most of the flow activity in a port is near the roof of the port. The roof is the outside radius of the bend going to and from the combustion chamber and by inertia, most of the air wants to flow up there. Good headwork usually rounds the floor hump which is the transition from the valve seat to the floor of the port. Stock, this is usually a sharp edge which causes non-laminar (turbulent) flow separation.

The object of good porting is to increase flow as much as possible while keeping the port volume as low as possible to maintain as high of a flow velocity as possible. Big ports have low velocity at low rpm. This results in a loss of bottom end power due to the lack of energy available in the moving gas column behind the valve. The gas column has inertia which helps fill the cylinder, especially at low RPM. Generally porting your head will cause some loss of bottom end power. Good head porters might be able to increase flow in the head up to 40 percent with no loss in bottom end but that is usually for American Iron heads which are terrible to start with. Modern Japanese engines donft usually see as big gains as their design is much better to begin with. Gains of 10-20 percent are typical with a modern Japanese motor.

The other major area of headwork flow gain is in the valve job. A large percentage of gain can be in the valve job alone. The best valve jobs are called multi angle valve jobs with three or more distinct angles. The main angles are the throat cut, which is a 60-70 degree cut that blends the port wall to the seating cut. The seating cut is a 45 degree cut which is the sealing surface for the valve. This critical cut should be 0.040-0.060 wide for a multi valve engine like an SR20. Finally there is the top cut which is a 30 degree cut which blends the seating cut to the combustion chamber. The purpose of these cuts is to help the air flow smoothly around the valve, especially when the valve is starting to open or close.

Another valve job trick is to place a 30 degree back cut above the 45 degree seating cut on the valve itself. This helps the air get around the valve better especially at low lifts. A five angle valve job uses two extra cuts to make the transition even smoother. The best valve jobs are radius valve jobs which are a 3 or 5 angle valve job which is hand blended after cutting for a perfectly smooth transition. The quality of a valve job is very important because it can contribute up to 50% of the flow gains that headwork will get you.

The best valve jobs are done on a Serdi machine. The Serdi is very high precision which insures that all the valve angles and depths come out equal. Most low price shops use stones. Stones can give a good valve job but the stones must be dressed frequently and dial indicators must be used to insure that the seating surface remains concentric. Stones require a highly skilled person who is conscientious of doing a good job. A butcher can make a big mess with stones.

Unshrouding the valves is an operation where the edge of the combustion chamber is cut back by about 25% of the valve diameter so that the wall of the combustion chamber does not block the air going past the valve into the cylinder.

Polishing the combustion chamber removes sharp edges that can glow red hot and trigger detonation. It also makes it harder for carbon to stick. Polishing should be limited to the combustion chamber and exhaust port. The intake port should be no smoother than 220 grit as maintaining some boundary layer turbulence is good for good bottom end. This turbulence makes the port virtually a little smaller at low flow velocities."(by Shaddoh international tuner)


Viper
viper is offline  
Old 15th March 2006, 23:06   #5
BHPian
 
Kaizer Sozay's Avatar
 
Join Date: Apr 2005
Location: Melbourne
Posts: 333
Thanked: 4 Times
Default

Quote:
Originally Posted by viper
Hi,

There is no need to open an engine after 50,000kms you have heard wrong. As far as your subject matter goes Porting/polishing smoothens the flow of gasses and removes the casting irregularities found in the cylinder heads which results in better power.

Viper

You have said better power what affect does it have on the FE?
Also i was told that this needs to be done as there will be carbon deposits after 50k
Kaizer Sozay is offline  
Old 15th March 2006, 23:20   #6
BHPian
 
Join Date: Feb 2005
Location: Stuttgart, Germany.
Posts: 815
Thanked: 96 Times
Default

Thanks alot viper.......great read......
Edmund is offline  
Old 15th March 2006, 23:36   #7
Team-BHP Support
 
Rehaan's Avatar
 
Join Date: Feb 2004
Location: Bombay
Posts: 22,381
Thanked: 22,601 Times
Default

Porting & Polishing (Porting and Polishing!!!)

Quote:
Originally Posted by ajayalphonso
Also i was told that this needs to be done as there will be carbon deposits after 50k
Decarbonization

Please continue the discussion in the existing threads, and please use the search feature before creating a thread on a topic that might exist

cya
R
Rehaan is offline  
Closed Thread


Thread Tools Search this Thread
Search this Thread:

Advanced Search


Similar Threads
Thread Thread Starter Forum Replies Last Post
8 Valve SOHC vs 16 Valve SOHC shineshine Technical Stuff 6 12th February 2016 22:23
Porting and Polishing!!! Edmund Technical Stuff 61 22nd November 2012 20:56
Looking for porting polishing & valve grinding in Delhi RedMM340 Modifications & Accessories 16 21st November 2008 11:31
Need Help for porting Yamaha RXZ ~ H O N D A ~ Motorbikes 42 10th March 2008 16:48
karizma porting redrage Motorbikes 1 27th April 2005 01:31


All times are GMT +5.5. The time now is 21:50.

Copyright 2000 - 2017, Team-BHP.com
Proudly powered by E2E Networks