Should I Port/Polish My 951 Head?
#1
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Should I Port/Polish My 951 Head?
Hi guys,
I've got my head off (why, do you ask? to replace the head gasket, of course!) and I'm thinking about doing a little porting/polishing while I've got it on the bench. I'm not a professional, but I do think I could smooth things out a bit without removing a ton of material. Would it be worth my while to do so? It will probably be more polishing than porting, but I figure it's got to help air flow a little, won't it?
Comments, suggestions?
TIA
I've got my head off (why, do you ask? to replace the head gasket, of course!) and I'm thinking about doing a little porting/polishing while I've got it on the bench. I'm not a professional, but I do think I could smooth things out a bit without removing a ton of material. Would it be worth my while to do so? It will probably be more polishing than porting, but I figure it's got to help air flow a little, won't it?
Comments, suggestions?
TIA
#2
If so,just remove any casting ridges and so on,and smooth the transition from the port to the valve seat....nothing more. Polish it is something I would not do for any amount of money...keep a slightly rough surface, no mirror glaze. The last thing you want in that engine is a bigger port...more flow without enlarging anything at all will help a little,but any enlarging will make it worse,especially in the low rpm range.
#3
Originally Posted by Skunk Workz
If so,just remove any casting ridges and so on,and smooth the transition from the port to the valve seat....nothing more. Polish it is something I would not do for any amount of money...keep a slightly rough surface, no mirror glaze. The last thing you want in that engine is a bigger port...more flow without enlarging anything at all will help a little,but any enlarging will make it worse,especially in the low rpm range.
How well does the Stock 951 head flow...when upgrading is it worthwhile to go with something like Lindsey Stage 2 head?
What kind of gains can one see when porting the head?
-Richard
#4
Since the turbo basically acts as a pump, it not only promotes a great deal of mixing via tumbling the air but drives the air mass against the restrictions in the intake tract. The porting and polshing the head in this application will allow the turbo ride the pump (turbo) system curve and provide more volume given lower restriction. More air + More fuel = More power
Jpr
Jpr
#5
Originally Posted by RogueM3
So you are saying that you wouldnt want to polish..but you would welcome a slightly bigger port?
How well does the Stock 951 head flow...when upgrading is it worthwhile to go with something like Lindsey Stage 2 head?
What kind of gains can one see when porting the head?
Last edited by Skunk Workz; 01-27-2005 at 08:54 PM.
#7
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So, Skunk Workz, If one wishes to gain from porting and polishing the head. what general components need to be additionally enlarged/ upgraded to make more power in conjunction with more corresponding torque? Are we talking about increasing bore and stroke? Doesn't the turbo need to have a corresponding capability? Wouldn't greater flow also require more fuel flow? Wouldn't we also need to increase the intercooling capability?
I ask all of this, because this would be good info for those that are new to our cars, and Turbo cars in general. Thanks E
I ask all of this, because this would be good info for those that are new to our cars, and Turbo cars in general. Thanks E
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#9
Originally Posted by Bengt Sweden
Polishing has zero effect.
A MIRA radius cut valve seat make big difference.
A MIRA radius cut valve seat make big difference.
#10
Originally Posted by ehall
So, Skunk Workz, If one wishes to gain from porting and polishing the head. what general components need to be additionally enlarged/ upgraded to make more power in conjunction with more corresponding torque? Are we talking about increasing bore and stroke?
Doesn't the turbo need to have a corresponding capability?
Wouldn't greater flow also require more fuel flow?
Wouldn't we also need to increase the intercooling capability?
I ask all of this, because this would be good info for those that are new to our cars, and Turbo cars in general. Thanks E
#11
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Skunk,
I don't really know about all this.
If the charge velocity becomes too high through an opening (port, in this case), pressure will drop. This will result in a net loss because the ram air effect into the cylinder will not out-weigh the static pressure loss through the head.
This is pretty much the basic idea that smaller holes favour lower engine speed VE, but do not allow for higher RPM breathing. Nothing new, really.
So yes, opening ports could result in more lag (all else being equal), but should increase full power potential (which really only would come into effect with more aggresive valve timing along with it).
I don't really know about all this.
If the charge velocity becomes too high through an opening (port, in this case), pressure will drop. This will result in a net loss because the ram air effect into the cylinder will not out-weigh the static pressure loss through the head.
This is pretty much the basic idea that smaller holes favour lower engine speed VE, but do not allow for higher RPM breathing. Nothing new, really.
So yes, opening ports could result in more lag (all else being equal), but should increase full power potential (which really only would come into effect with more aggresive valve timing along with it).
#12
Originally Posted by TurboTommy
Skunk,
I don't really know about all this.
If the charge velocity becomes too high through an opening (port, in this case), pressure will drop. This will result in a net loss because the ram air effect into the cylinder will not out-weigh the static pressure loss through the head.
This is pretty much the basic idea that smaller holes favour lower engine speed VE, but do not allow for higher RPM breathing. Nothing new, really.
I don't really know about all this.
If the charge velocity becomes too high through an opening (port, in this case), pressure will drop. This will result in a net loss because the ram air effect into the cylinder will not out-weigh the static pressure loss through the head.
This is pretty much the basic idea that smaller holes favour lower engine speed VE, but do not allow for higher RPM breathing. Nothing new, really.
So yes, opening ports could result in more lag (all else being equal), but should increase full power potential (which really only would come into effect with more aggresive valve timing along with it).
#13
To add to this, It was found in wet flow testing that the smoother the walls the better. It was also found that the bigger the ports the better the mass flow without much lossin speed. It was found that the boundary layer was almost stationary and the ceter of the port moving at high speed. The more lift the greater the boundary layer and the less flow thro the center of the port. It was also seen that the smoother walls helped in lowering the effect of the boundary layer, as the rougher walls seemed to promote the boundary layer build up.
The new technology in Flow testing with wet flow testing and computer generated port maps showing speed and mass in all the different quadants of the port, is showing what used to be thought of as good, now is showing up as not the best. If only we could see air.
The new technology in Flow testing with wet flow testing and computer generated port maps showing speed and mass in all the different quadants of the port, is showing what used to be thought of as good, now is showing up as not the best. If only we could see air.
#14
Originally Posted by Skunk Workz
what you need is to do on the 2.5 is to keep the flow and decrease the diameter of the port for more intake velocity...same amount of air going though on the flowbench,but in the engine it goes in at a greater speed
If this were the case however..why would so many aftermarket companies (of all cars) offer porting and polishing of the head as a performance upgrade...especially on turbo cars?
I know the more air=more fuel you can fit in the cylinder=more power...but following this logic you would want to open the ports to allow more air in (I understand that you are saying smaller ports will speed the air into the cylinder...but I would think this spped would come with a loss of air flow.
I think the polishing does have a solid effect....a decrease in resistance..no matter how small, will lead to an increase in airflow....and thus power.
I am torn here....I understand both sides..but because of aftermarket offerrings am leaning to the side that porting and polishing is beneficial for an increase of power.
-Richard