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Discussion Starter #1 (Edited)
So whats the real story with having a ported head or not ported for a turbo?

Is it as important as it is for N/A?

Can anyone give some real world experience with this?

Anyone here ever step up to a better flowing head and made more power ( if so how much more per pound of boost ) with out changing anything else?

I just had to buy a new head after finding out mine was cracked. It was a CNC 320cfm port. They only flow 270 new out of the box. So im not sure if its worth the money to get the head ported or just go with the stock port.

Would luv to hear what other experiences/opinions on this are.. :confused:

Thanks...
 

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Discussion Starter #3
yes i plan on getting a good valve job. But im wondering how important the extra cfms are for making the most power with a turbo...
 

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Application specific and desired hp specific but everyone knows turbos are magical at making hp.

What cubic inch and intended hp goal?
 

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Discussion Starter #6
Its a 4 cyl 198ci.

So far its made 620 rwhp at 35 psi

Drive train is turbo 400 with 9" 3.50 ratio ..

Im looking to make 750 rwhp .

As for peak rpm, that so far changes as i turn the boost up ..

At 35 psi its 6500 rpms where at 20 psi it dont go past 6000..

But im really just wanting to know if porting the head from 270 to 320 cfm is going to make enough extra power to justify the 650.00 .....

Thanks
 

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Your words “most power” lead to the natural answer. Yes a ported head will make more power at the same boost level or the same power at less boost. But, ported heads generally have slower air velocity. So if responsiveness and lower rpm operation are important, the unported will have a bit of an advantage. You just have to run additional boost
 

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Discussion Starter #8
Your words “most power” lead to the natural answer. Yes a ported head will make more power at the same boost level or the same power at less boost. But, ported heads generally have slower air velocity. So if responsiveness and lower rpm operation are important, the unported will have a bit of an advantage. You just have to run additional boost
Im glad you say this because i wanted to ask that question next.

But will the increased cfm be the same gains as N/A?

As the psi goes up is there a point where just like N/A , the head wont flow anymore , or will the power keep going up with increasing psi ?So in other words, is there going to be a ceiling eventually ? Im sure that heat will be a battling fact as psi goes up though .. And i do need the velocity . One of my biggest problems was power before boost. The out of box head has 215cc runners . My 320 head was 234cc. Not much difference in cc's but maybe it will be enough to pick up velocity and make a difference . Idk...
 

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Here's the big picture. As boost goes up the actual CFM of air flowing into the engine doesn't change much. However, the increased density results in increased lb/hr of air entering the engine which means more O2 molecules. ;)
 

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Discussion Starter #10
I was hoping there would be someone that stepped up to a better head that could share there expereince with whether or not it was worth doing it ..

But thanks for all the replies so far..
 

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Whoever moves the most mass flow wins, everything else being equal. As long as we are talking strictly EFI drag race, as long as there is adequate port airspeed to keep fuel atomized I'll take the big well designed CNC port everytime.
 

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Anything different about a turbo head port job than we normally look for in a NA port job?
In my opinion yes, often times porting is not as specific as it should be. Everyone seems to be possessed with intake port flow numbers but I would gladly trade some intake flow to gain some exhaust port flow. In most cases getting air/fuel into the cylinders is no problem but getting it out efficiently is more difficult with a lopsided port job. Cam design is more difficult as is hot side design. I think in many ways a turbo engine is almost the opposite of a NA engine. NA intake is #1 - Turbo exhaust is #1 Just my $0.02
 

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Discussion Starter #14
Looks like ill just put the stock head on and see what it does.
I will be able to compare it to my old head and find out that way..

It will be interesting to find this out ..

Worst scenario ill just send the head to get done after i find out the truth on this...
 

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Its a 4 cyl 198ci.

So far its made 620 rwhp at 35 psi

Drive train is turbo 400 with 9" 3.50 ratio ..

Im looking to make 750 rwhp .

As for peak rpm, that so far changes as i turn the boost up ..

At 35 psi its 6500 rpms where at 20 psi it dont go past 6000..

But im really just wanting to know if porting the head from 270 to 320 cfm is going to make enough extra power to justify the 650.00 .....

Thanks
Yes. Anything gained to a pressure ratio of 3 bar. After 3 bar heat begins to escalate and gains slow.
 

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Yes. Anything gained to a pressure ratio of 3 bar. After 3 bar heat begins to escalate and gains slow.
You’re gaining 50cfm x .257 x 4 cylinders = 51.4 hp naturally aspirated multiplied by a pressure ratio of 3 = 154.2 hp under the same boost. Hp will move up and this 20 psi @6000 number will move up.
How much ? Depends on how dialed in the combo is currently and can the cam lobe support it.
Is the turbo out of breath, cam signing off ?
 

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This 20 psi @ 6000 number that planes out is an indicator something is tapping out already.
Find out this and the cork will be removed when the ported heads go on, jmo.
 

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In my opinion yes, often times porting is not as specific as it should be. Everyone seems to be possessed with intake port flow numbers but I would gladly trade some intake flow to gain some exhaust port flow. In most cases getting air/fuel into the cylinders is no problem but getting it out efficiently is more difficult with a lopsided port job. Cam design is more difficult as is hot side design. I think in many ways a turbo engine is almost the opposite of a NA engine. NA intake is #1 - Turbo exhaust is #1 Just my $0.02
You are absolutely right about the na focus being on intake. We spent very little time on exhaust. Maybe we should work on it. But does that mean that the header should perhaps be larger diameter primaries as well?
 

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Discussion Starter #19
Yes. Anything gained to a pressure ratio of 3 bar. After 3 bar heat begins to escalate and gains slow.
You’re gaining 50cfm x .257 x 4 cylinders = 51.4 hp naturally aspirated multiplied by a pressure ratio of 3 = 154.2 hp under the same boost. Hp will move up and this 20 psi @6000 number will move up.
How much ? Depends on how dialed in the combo is currently and can the cam lobe support it.
Is the turbo out of breath, cam signing off ?
The turbo is a precision 6870 so i dont think its out of breath.

The cam i dont think so but but maybe? It started out as 582 556 lift .050 251 242 on a 114. had spooling issues for a long time with that cam . Tried loosening the the converter but when i did it wouldnt hold the power upstairs. So i would tighen it up and back to the spooling problem. Then i changed the cam to a smaller one . It was all the same lift and spread numbers . Just changed the duration to 243 234. Surprised me to find out that it didnt really change my spooling problem or make less power, seemed to be at the same level .Just lowered my power band 800 rpms. So that sucked. Then i tried uping my compression ratio from 8.4 to 1 to 9.7 to 1. That really didnt help either. lol maybe alittle ,but nothing to get excited about. It did make more power at the same boost levels of the 8.4 ratio though. So now im at the point of putting my hands up. Then i find out my head is cracked and i end up having to get a new head. So im hear asking these questions about head flow . The thing is, with all the changed that i have done in the past that i just explained, Im afraid that porting the head will just be the same end result. Where it wasnt worth the money and effort of the change . Because i do know upping the boost is a game changer haha. But at what point will that just become a brick wall ? Maybe ill have to spend another 600 bucks on a real big cam and just spin the motor .. Idk ..

Hey thanks for all your thought out answers . Deffinitely made alot of sence....
 

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I'll agree with the above post too. 320 head should make power well above 6000 boost or no boost. The fact that your peak hp moved down with additional boost is telling you something. And that something is not that the head is too big. I don't think there is harm in trying the head unported. I would focus on other things as the cork right now. I think you will come back to the head and want to get it ported after you find the problem.
How are the valve springs?
How is the back pressure ratio?
Yes I think you need to figure out what is keeping you from making power at a higher rpm. It has been my experience that if you try to make uber power at low rpm, that's pretty darn hard on parts too. They aren't diesels. The torque that it requires to make big power at low rpms is very high. Cylinder pressure is very high. As long as your parts are ok with higher rpm, especially valve trane, then I think you really need to capitalize on making power at 7000 rpm. Once you find the cork.
The only problem with a high rpm small motor is that spooling is difficult and converter choice is tricky.
 
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