Hey all, I know on a N/A Motor bigger ports are not always better as you loose air velocity and bottom end torque and can be a slug untill you get up in RPM
But does the same go for a Turbo motor? as the air is being forced in... altho I can see it causing the motor to lag more untill its up on boost.
Or is it better to keep them smaller for the low rpm power and the turbo will force alot more air in anyway.
Head Porting on a Turbo Engine
Started by
_Viper_
, Apr 30 2009 08:38 PM
14 replies to this topic
#2
FastEHHolden
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Posted 30 April 2009 - 09:31 PM
It is a balancing act.....and its all related to flow and what you want the car for.
If its maximum power you are after then the ports are bigger..if you want it to have a bit more bottom to mid range and driveability the ports are smaller.
With a turbo you get a bit of flexibility with your port sizing...you can get away with having a smaller port as the air is going to be forced thru it...but its wrong to think you don't need to port a head and you can just increase the boost...increased boost does not necessarily mean more flow.
If its maximum power you are after then the ports are bigger..if you want it to have a bit more bottom to mid range and driveability the ports are smaller.
With a turbo you get a bit of flexibility with your port sizing...you can get away with having a smaller port as the air is going to be forced thru it...but its wrong to think you don't need to port a head and you can just increase the boost...increased boost does not necessarily mean more flow.
#3
_Squarepants_
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Posted 30 April 2009 - 09:33 PM
The trick to porting any head (turbo or NA) is to get the highest flow rate while removing as little material as possible.
The smaller the ports, the higher the air speed, meaning better fuel atomisation (for a better burn) and (in a turbo) less lag.
A lot of people will tell you turbos don't need porting, just run higher boost, but that's BS. The better the heads flow, the better it will perform.
The smaller the ports, the higher the air speed, meaning better fuel atomisation (for a better burn) and (in a turbo) less lag.
A lot of people will tell you turbos don't need porting, just run higher boost, but that's BS. The better the heads flow, the better it will perform.
#4
_Viper_
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Posted 30 April 2009 - 09:54 PM
Yea I understand port shape is the MOST important and the smoother the port the better (flow shape i mean not the texture) and having smooth transitions with no sudden changes etc
But yea just wondering about actual port size... oh and Valve size come to think of it... are bigger valves better in a turbo motor?
So sounds like I should still try keep the ports small to keep up velocity but with the smoothest flow.... but big valves?
But yea just wondering about actual port size... oh and Valve size come to think of it... are bigger valves better in a turbo motor?
So sounds like I should still try keep the ports small to keep up velocity but with the smoothest flow.... but big valves?
#5
gtrboyy
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Posted 01 May 2009 - 11:18 AM
A correctly ported head in most cases reduces lag when done right dude.
#6
_Squarepants_
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Posted 01 May 2009 - 03:41 PM
I'd say the valves are prolly the biggest restriction in the system so short answer - yes, big valves.Yea I understand port shape is the MOST important and the smoother the port the better (flow shape i mean not the texture) and having smooth transitions with no sudden changes etc
But yea just wondering about actual port size... oh and Valve size come to think of it... are bigger valves better in a turbo motor?
So sounds like I should still try keep the ports small to keep up velocity but with the smoothest flow.... but big valves?
It prolly depends on the motor and how much the standard valves are capable of flowing. A flow bench is the only sure fire way to know.
#7
_Allports_
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Posted 01 May 2009 - 09:34 PM
Yes to a point and no. If the port/valve/pocket relationship is out it may become turbulent or just be a poor performer. The valve size must be matched to what the port can feed. Some ports just cant keep up with what the valve may be able to supply the bore with. the min csa of the ports must be set up to match the bore/stroke/rpm range of the engine. If you have a port that goes into port choke @ 6000rpm for eg if the port is to small either in the P/R choke or the window area and you put say another .200" lift into it or a .125" larger valve that wont magically fix the problem for you. It may make or help to make some more power over what you had but in reality it's just going to mask the problem. The numbers must add up on many counts when porting a head not just the CFM on the bench, in fact thats the last thing we look for when prepping a cylinder headI'd say the valves are prolly the biggest restriction in the system so short answer - yes, big valves.
It prolly depends on the motor and how much the standard valves are capable of flowing. A flow bench is the only sure fire way to know.
#8
_Allports_
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Posted 01 May 2009 - 09:43 PM
Texture is of paramount importance, and a smooth port vs a rough port will lose in every count. And correct on the transitional changes, air is like a B double it doesnt like to turn, so in effect you must slow it down in order to make the req' turn/turns. A simple hydraulic principal. Air behaves like a fluid once in motion. A head is much the same as a cam if you cant decide between this or that 1 go the smaller 1. As for a turbo head specifically, keeping the ex ports a little on the smaller side will always help reduce your lag area to coming on boost area. Cam timings differ greatly as well. As for your velocity what rpm range do you want to use?? What bore/stroke are you running? What turbo? What inlet manifold? What G/box? What diff ratio? The list goes on.Yea I understand port shape is the MOST important and the smoother the port the better (flow shape i mean not the texture) and having smooth transitions with no sudden changes etc
But yea just wondering about actual port size... oh and Valve size come to think of it... are bigger valves better in a turbo motor?
So sounds like I should still try keep the ports small to keep up velocity but with the smoothest flow.... but big valves?
#9
_mumstaxi_
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Posted 02 May 2009 - 09:17 AM
Cam timings differ greatly as well. As for your velocity what rpm range do you want to use?? What bore/stroke are you running? What turbo? What inlet manifold? What G/box? What diff ratio? The list goes on.
I believe the cam profile is the big make or break factor with a Turbo head
regardless of valve size, porting, flow etc, if the cam is cr*p it wont make good power no matter what you do (found this out the hard way)
As Allports suggested , a lot of factors need to be taken into consideration if you want to do it right,
are you planing on going draw/blo-through or EFI ?
MT
#10
_threeblindmice_
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Posted 02 May 2009 - 12:02 PM
This is a few years old ,things might have changed a bit ,
#11
Tiny
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Posted 03 May 2009 - 09:08 PM
This Thread has been Cleaned up to remove the DRIBBLE.
Let's please try and keep on topic and not jump down each other's throats.
We are all here to ask questions and learn, and it's excellent for those who might know the answer - and even those who think they know the answer - to give their opinions in the effort to try and enlighten the question asker.
Please. Let's try and play nice.
Let's please try and keep on topic and not jump down each other's throats.
We are all here to ask questions and learn, and it's excellent for those who might know the answer - and even those who think they know the answer - to give their opinions in the effort to try and enlighten the question asker.
Please. Let's try and play nice.
#12
Stedz_lc
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Posted 03 May 2009 - 09:17 PM
I always thought you needed/wanted Rough on the inlet (to help atomisation of fuel and air) And smooth on the exhuast, i also thought u wanted the exhaust manifold just a bee's dick larger then the exhuast port to stop...the words not coming to me grr.. to stop it goin back in (in basic terms)
But im no pro on heads just prefer pay someone who knows what there doin and get the job done right! Its a major player on ANY engine i feel.
Cheers
ed.
But im no pro on heads just prefer pay someone who knows what there doin and get the job done right! Its a major player on ANY engine i feel.
Cheers
ed.
#14
Stedz_lc
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Posted 04 May 2009 - 02:04 PM
haha, thats the one. THANK YOU
#15
_Allports_
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Posted 05 May 2009 - 07:05 PM
Correct to a point, If the step to the ex is too large it exaserbates the reversion issue esp on the low pressure side on the pipe, and more to that if the bend is tight off the head it WILL get ex gas back into the chamber, which is almost the worst thing for making power or controlling detonation that could happen. You will find in most pipes the pipe is usually larger than the plate so it's kind of done for you anyway. So in most cases you just need to check that the plate isnt inside the port face window.I always thought you needed/wanted Rough on the inlet (to help atomisation of fuel and air) And smooth on the exhuast, i also thought u wanted the exhaust manifold just a bee's dick larger then the exhuast port to stop...the words not coming to me grr.. to stop it goin back in (in basic terms)
But im no pro on heads just prefer pay someone who knows what there doin and get the job done right! Its a major player on ANY engine i feel.
Cheers
ed.
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