Can someone explain to me why porting heads is good for turbo setup??

I'm alittle confused about this. I know porting heads is good for NA for the engine to suck in more air. But for forced induction is that really an issue? You figure no matter how much porting you do the forced induction is always going to force not be pulled in. So what I'm saying is if you need more flow into the heads why not just turn up the boost? Wouldn't that be the same as porting heads? Am I making sense or have I lost it?

Porting heads will still allow more air to flow in, regardless of if it is being pushed or pulled. Higher boost isn't always a desireable thing.

Furthermore, porting the exhaust side will allow the turbo to spool faster because of increased flow on the exhaust side.

Originally posted by WannaBeZ28
Porting heads will still allow more air to flow in, regardless of if it is being pushed or pulled. Higher boost isn't always a desireable thing.

Furthermore, porting the exhaust side will allow the turbo to spool faster because of increased flow on the exhaust side.

To continue on what Wannabez28 said:

As you may or may not already know, is that all boost is, is a form of restriction and when you get that unrestricted air path going into your heads your going to maintain if not gain some horsepower. You will also see less bost but that doesnt mean your loosing hp. It just gives you an excuse to run more boost. :)

Ported heads/intake on FI setups just allow for the same amount of horsepower at less boost

crude example:

500hp @ 12psi stock heads
500hp @ 9psi ported heads

but the advantage comes when you raise the boost back up, another crude example:

500hp @ 9psi ported heads
575hp @ 12psi ported heads

Understand a little better?

I just got my heads ported on my T.A.(in sig) and it doesn't seem to be any more powerful at all, I went from 7lbs on gauge to around 4-5, can I put the 12lb pulley on it now and still kept the same diveablilty I had with the 7lber? I figure I'll see around 7-8 lbs with the 12lb pulley. I mean since boost is pressure and that can blow pistons then with less pressure w/ my heads ported be easier on my engine now? Hopefully someone realizes what I am trying to ask it is harder to type than say.

Originally posted by Burn_Out
I I mean since boost is pressure and that can blow pistons then with less pressure w/ my heads ported be easier on my engine now? Hopefully someone realizes what I am trying to ask it is harder to type than say.

stress blows stuff up.......and more power means more stress.............you can increase your boost again, and now youll make more power at that PSI, but that doesnt mean its gonna be safe, because now there is more power/stress.

one of the smarter guys will correct me if im wrong.

He isn't going to loose any boost with ported heads, he is running a turbo. Boost is not controlled by the crank.

Originally posted by SMOKNZ
He isn't going to loose any boost with ported heads, he is running a turbo. Boost is not controlled by the crank.


uhh........then why was he talking about swapping pulleys?

Originally posted by 89ProchargedROC
Ported heads/intake on FI setups just allow for the same amount of horsepower at less boost

crude example:

500hp @ 12psi stock heads
500hp @ 9psi ported heads

but the advantage comes when you raise the boost back up, another crude example:

500hp @ 9psi ported heads
575hp @ 12psi ported heads

Understand a little better?

OK I get that but then if you wanted 575hp than why not just turn the boost to 15psi with stock heads? It's more stress on the bottom end but if ityt can take it then hey.... So basically if you have a built bottom end ported heads is somthing that it isn't a must like it would on NA?

Also when we're talking forced induction porting heads can be done with any DIYers and still gain just as much and a pro right? Cause since it's forced induction the engine is not trying to pull in air, it's being forced so all that the heads would need is to be opened up. No special technique is really required right? Well I guess to a certain extent.

I'm trying to get more info on heads for forced induction before spending $3K on something that will only gain me 20hp or less, or even worst I can get somewhere else for $500

Originally posted by LT1RX7
Also when we're talking forced induction porting heads can be done with any DIYers and still gain just as much and a pro right? Cause since it's forced induction the engine is not trying to pull in air, it's being forced so all that the heads would need is to be opened up. No special technique is really required right? Well I guess to a certain extent.



well you have to choose which way you wanna make power.

good heads + medium boost

bad heads + high boost

i think high boost has too many cons (detonation, blowing gaskets, etc), so id rather get some good heads.

if going with the LT1 block.......id just get some well ported stock castings by someone like phil at advancedinduction or the guys at combo motorsports. that would be a good enough head that you wont have to run really high boost for good power.

Originally posted by SMOKNZ
He isn't going to loose any boost with ported heads, he is running a turbo. Boost is not controlled by the crank.

no, boost is not controlled by the crank, boost isn't controlled by anything but RESTRICTION. Less restriction in the heads, less boost or psi at the gauge, simple as that.

I just got my heads ported on my T.A.(in sig) and it doesn't seem to be any more powerful at all, I went from 7lbs on gauge to around 4-5, can I put the 12lb pulley on it now and still kept the same diveablilty I had with the 7lber? I figure I'll see around 7-8 lbs with the 12lb pulley. I mean since boost is pressure and that can blow pistons then with less pressure w/ my heads ported be easier on my engine now? Hopefully someone realizes what I am trying to ask it is harder to type than say.

i think i understand what you are saying. Pressure in itself doesn't cause things to blow up but it does put a lot of stress on parts, that is why if you only want to run Xpsi then you put a combo together to make the most power you can at that Xpsi. So in your case, yes you can put the 12lb pulley on the blower and it will produce more CFM to put into the motor (probably similar to your old pressure reading) but you will make more horsepower from my the explanation of my previous post. You just have to make sure you aren't over spinning the blower. they have a max rpm that they should be run at. As for drivability, i'd say yes and no. Since your car will be making more horsepower and will be injesteing more cfm, your computer should be re-programmed to handle it. So it may not run right until you do that. So factor that into the budget

OK I get that but then if you wanted 575hp than why not just turn the boost to 15psi with stock heads? It's more stress on the bottom end but if ityt can take it then hey.... So basically if you have a built bottom end ported heads is somthing that it isn't a must like it would on NA?

More restriction in the intake system puts more pressure on parts and the engine as a whole. It also depends on your comfort level of what kinda level of pressure you are willing to run to make a certain horsepower level. If you are comfortable running 15psi all the time and have a motor that can handle it, go for it. If you feel that you need 20psi to make the power you want but only want to have to run 11psi to get it, you're going to have to port the heads/intake. Hope that helps

Originally posted by 89ProchargedROC
no, boost is not controlled by the crank, boost isn't controlled by anything but RESTRICTION. Less restriction in the heads, less boost or psi at the gauge, simple as that.


A turbo is a pump, it pumps air. If it had no restriction it would develop ZERO pressure. pressure is a measure of the amount of restriction. When you have pressure in the intake you are cramming in more air than the engine can use. The turbo isn't limited on it's air flow by how fast a belt is spinning, thus won't be affected because it can speed up to flow the additional air to make the same pressure it did before the head swap.

All I was trying to say is that the pressure in a turbo system is controled by a pnuematic actuator, the wastegate, changing the heads on a turbo car will not make you loose any boost at all if nothing else is changed like it will on a supercharged car when the pulleys are left alone. Changing heads isn't going to spontaneously weaken the spring in the wastegate, it will compensate for the higher flow of the heads and maintain the pressure the same as before. I'm sure I'm not telling you anything new.

All that being said, you will make more power with the heads ported at the same psi. I guess It all depends on how much power you want to make. If you can make the desired power with stock heads, then do so!

Bill

OK I get that but then if you wanted 575hp than why not just turn the boost to 15psi with stock heads?

Don't forget, the more boost you run, the harder the turbo/supercharger has to work. Also, at higher boost levels, the air coming from the turbo/supercharger will be alot hotter than the air at lower boost levels.

Originally posted by SMOKNZ


All I was trying to say is that the pressure in a turbo system is controled by a pnuematic actuator, the wastegate, changing the heads on a turbo car will not make you loose any boost at all if nothing else is changed like it will on a supercharged car when the pulleys are left alone. Changing heads isn't going to spontaneously weaken the spring in the wastegate, it will compensate for the higher flow of the heads and maintain the pressure the same as before. I'm sure I'm not telling you anything new.




true, if your wastegate is within its operating range. Too many ifs but we're getting the same idea across, just want to make sure the original thread poster understands at least the "logic"

:)

thats all

later

Why is porting heads good for a turbo setup? Well first of all your boost pressure (PSI) is a measure of the inefficiency of your engine. It's basically a measure of how much pressure it takes to force X amount of air into your engine.

Take for example two of the same engines only that one is stock and one has ported heads. If your turbo provides X (CFM) amount of air, on the ported engine it might take 8 psi to FORCE that air into the engine, while on the stock and less efficient engine it will take 10 psi because of the greater restriction. It's the same amount of air going into the engine, but here is the one reason why the ported head engine makes more power...heat

Heat is one of your greatest limitations of creating power. Compressing air automatically creates heat, so by running a lower PSI but same CFM, you are picking up power right there. Now, when you increase the boost on the stock car you are further increasing PSI and heat...and heat/detonation is usually were you start to hit your limits. In the end, the ported head car has more room to increase CFM because it will gain more CFM per unit of boost increase/heat.

Next, there is also the exhaust side of the ported head car. It is being more efficient on the exhaust side, means faster spool and more power quicker. It also means more power because of the easier release of the great amount exhaust backpressure, which is VERY VERY important on a turbo car and will net you tons of power.

So, basically the ported head car will make more power while putting less stress on the engine. Plus it will make even more power if both ported and stock are pushed to their limits.

Finally, other things like the turbo efficiency, compressor maps, etc...come into play too, but you should be picking the proper turbo for your exact setup and needs...this is the biggest advantage of using a turbo.

here's how I understand it. Porting heads/cam/intake/whatever WILL cause a loss in boost, but not a loss in air volume. Remember the wastegate is not connected to the MAP sensor in any way, so it has no idea what boost you are running...all it knows is at XXX psi of EXHAUST pressure, I'm going to open...whether that pressure produces 10psi at the intake or 5psi. Since bost is created by restrictions in the intake system, the less restriction you have the less boost you will make at that exhaust pressure.

Sorry, but you got that backwards. The wastegate on a turbocharger IS controlled by boost pressure NOT exhaust pressure. So the pressure is constant and the flow is the variable based on the flow characteristics of the heads and cam, etc.

My experience has been that spending money on high dollar port jobs and expensive heads for a turbocharged setup does not net the same gains as it does on aspirated setups. Unless you have really restrictive heads or are making real high hp numbers the gains with high dollar heads may not be worth the trouble and expense.

We put down 522 rwhp and 620 rwtq on a LT1 with stock heads, cam and exhaust manifolds. We also put down 509 rwhp and 551 rwtq on a bone stock LS1 at only 8 psi boost. Not saying that heads and cams wouldn't make a difference because they would. Just saying that the gains per $ spent is not going to be as big of a bang for the buck as the turbocharger was. For all out race engine you want to optimize every aspect and gain any VE you can. For most guys, it is cheaper and easier to just turn the boost up 1 or 2 pounds on the turbo (which is free and takes just the flip of a switch) and pick up another 50 hp rather than spend a couple grand installing a new set of heads.

Best of luck to you on the project, Rick @ STS

Originally posted by Turbocharged


My experience has been that spending money on high dollar port jobs and expensive heads for a turbocharged setup does not net the same gains as it does on aspirated setups. Unless you have really restrictive heads or are making real high hp numbers the gains with high dollar heads may not be worth the trouble and expense.

We put down 522 rwhp and 620 rwtq on a LT1 with stock heads, cam and exhaust manifolds. We also put down 509 rwhp and 551 rwtq on a bone stock LS1 at only 8 psi boost. Not saying that heads and cams wouldn't make a difference because they would. Just saying that the gains per $ spent is not going to be as big of a bang for the buck as the turbocharger was. For all out race engine you want to optimize every aspect and gain any VE you can. For most guys, it is cheaper and easier to just turn the boost up 1 or 2 pounds on the turbo (which is free and takes just the flip of a switch) and pick up another 50 hp rather than spend a couple grand installing a new set of heads.

Best of luck to you on the project, Rick @ STS

Thanks for all the reply. Turbocharged's reply is what I needed to hear. I know I'll have th heads ported but just needed to know if I needed to send it out to a specialist or just do it myslef, got to start somewhere

As others have said, boost PSI, is just a measure of restriction and not a measure of actual airflow.

If you port the heads, you make more HP with less boost, or more HP with the same boost, creating less heat, less backpressure, and the ability to make more horsepower on a lower octane fuel.

So, IMHO, it's as important to have good heads on a FI motor as it is on any other.

Originally posted by Turbocharged
Sorry, but you got that backwards. The wastegate on a turbocharger IS controlled by boost pressure NOT exhaust pressure. So the pressure is constant and the flow is the variable based on the flow characteristics of the heads and cam, etc.



Could you explain this for me? The wastegate is connected to the exhaust inlet right at the turbo, and some wastegates operate on a pressure spring only...so I don't understand how it is controlled by intake pressure? And in fact, if it was relieving any sort of intake pressure, wouldn't that eliminate the need for a BOV?

The wastegate is a valve that dumps exhaust out before the turbo so that this exhaust "bypasses" the turbine. This enables you to control the turbine wheel speed which controlls the air output of the compressor. This wastegate valve has a diaphram with a spring that holds the valve shut. Boost pressure is plumbed into this diaphram and pushes against the spring to open the valve. When the boost psi overcomes the spring psi, the valve opens and lets the exhaust bypass the turbine. The only thing that exhaust pressure has to do with it is that it does put force against the surface of the valve but that surface area is very small compared to the surface area of the diaphram. The higher the boost goes above the preset spring pressure, the further the valve opens to let more exhaust out in an attempt to slow the turbine down and control the boost output of the compressor. Hope that helps.

Talk to you later, Rick @ STS

Originally posted by magius231
And in fact, if it was relieving any sort of intake pressure, wouldn't that eliminate the need for a BOV?
A BOV is not a devise for controlling boost. It is simply there to release boost pressure as the throttle closes. It saves the turbo's bearings.

Saving the turbo bearings, and the whales for that matter, is all fine and dandy. Most people are more excited about keeping the turbo spooled up during shifts so the boost comes back on quicker in the next gear and you don't get major turbolag with each gear change on the manual trans cars.

If you don't blow the boost out through the BOV, that boost has to go somewhere during closed throttle so it goes back out through the turbo and dramatically slows (can even stop) the turbo. Then it has to spool up from very low rpms back up to 100,000 r's again which takes a little time.

Automatic cars don't have this problem as the boost pops up with each gear change instead of down. Your wastegate will work really hard and open clear up on the shifts to try and control boost "POP" on shifts with automatic trans. I'm all for automatics with turbos! :D

Originally posted by Turbocharged
The wastegate is a valve that dumps exhaust out before the turbo so that this exhaust "bypasses" the turbine. This enables you to control the turbine wheel speed which controlls the air output of the compressor. This wastegate valve has a diaphram with a spring that holds the valve shut. Boost pressure is plumbed into this diaphram and pushes against the spring to open the valve. When the boost psi overcomes the spring psi, the valve opens and lets the exhaust bypass the turbine. The only thing that exhaust pressure has to do with it is that it does put force against the surface of the valve but that surface area is very small compared to the surface area of the diaphram. The higher the boost goes above the preset spring pressure, the further the valve opens to let more exhaust out in an attempt to slow the turbine down and control the boost output of the compressor. Hope that helps.

Talk to you later, Rick @ STS

That does help, thanks...but with that I don't understand the drop in boost people experience going to a less restrictive intake tract...wouldn't the wastegate just hold until boost was back where it should be, despite whatever increased airflow you might get?

turbocharged, I was told that without a BOV you will end up with less turbo lag for the next gear. I have talked to a well respected dyno tuner and he says he actually runs no BOV for the strip. Once the throttle closes all that pressure still builds until the turbo starts to slow down then pressure goes the other way. But he says that all takes a second to happen so it also depends on how quick your shifts are. On his 700rwhp RX7 he tried no BOV and said he usually gets full boost around 5500rpms but with no BOV he got full boost instantly. Of course this will kill your turbo for street setup.

With a BOV you release all the pressure but keep the turbo spinning. Without a BOV you build pressure and the turbo will only keep spinning for a second or so until pressure has built up so much it'll stop the turbo from spinning all together.

Originally posted by magius231
That does help, thanks...but with that I don't understand the drop in boost people experience going to a less restrictive intake tract...wouldn't the wastegate just hold until boost was back where it should be, despite whatever increased airflow you might get?

Correct, a wastegate will hold the boost constant. The loss of boost that you are referring to is experienced on supercharged cars, not turbo. The supercharger impeller has no way to compensate for an increase in the cfm of the engine due to heads/cam change, because it can only spin as fast as the belt/crank is, therefore boost pressure (measure of restriction, which is now less) will go down slightly. To compensate for this you must change pulleys thus speeding up the impeller on the supercharger.

Make sence now?

Bill

Originally posted by LT1RX7
turbocharged, I was told that without a BOV you will end up with less turbo lag for the next gear. I have talked to a well respected dyno tuner and he says he actually runs no BOV for the strip. Once the throttle closes all that pressure still builds until the turbo starts to slow down then pressure goes the other way. But he says that all takes a second to happen so it also depends on how quick your shifts are. On his 700rwhp RX7 he tried no BOV and said he usually gets full boost around 5500rpms but with no BOV he got full boost instantly. Of course this will kill your turbo for street setup.

With a BOV you release all the pressure but keep the turbo spinning. Without a BOV you build pressure and the turbo will only keep spinning for a second or so until pressure has built up so much it'll stop the turbo from spinning all together.

The way I think of it which may or may not be right is:

The higher the pressure in the intake before the throttle body, the more work on the air the compressor must do, which will require more work to be done to the turbine blades by the exhuast velocity thru the turbine housing. During shifting the throttle blades are shut, the exhaust veloctiy quickly heads toward zero = nothing available to do work to the turbine blades = nothing to do work on the air in the compressor... the air must go somewhere because you now have a large differential pressure between the intake tract and the atmosphere, and the air will head out back thru the compressor, because no work is being done by the compressor blades to keep it there, thus slowing the compressor down. However IF a blowoff valve is being used and it releaves the presure in the intake tract, no work needs to be done to keep a high pressure air in after the compressor and the turbo's wheels keep spinning due to inertia. Do they slow, yes, but not as much, and as soon as your back on the gas it will come up to full boost much quicker.

If you can powershift really, really fast then perhaps none would be required, however we all know that powershifting + a M6 don't = longivity.

Bill

The thing is once you close the throttle the compressor wheel doesn't automaticlly stop then and there. Pressure is still being built because the wheels are spinning pretty damn fast. Pressure gets built between the throttle and compressor wheel for a short period of time. After a certain amount of pressure is built it back out the other way of the turbo. I was saying if you can make shifts happen before you loose pressure to the other side of the turbo you're golden. I don't think you would have to powershift to keep the boost. I'm thinking it would take well over a sec for the compressor to stop spinning and if you can't make a shift within 1 sec you need an AT

when you run a BOV does it matter if it is recircurlating. i have been hearing from guys around here that have DSMs that if you run a BOV that doesnt recirculate the motor doesnt get the air that it is expecting and it make the car run rich while changing gears. does this hold true for a car that is not meant to have a compressor on it?

when you run a BOV does it matter if it is recircurlating. i have been hearing from guys around here that have DSMs that if you run a BOV that doesnt recirculate the motor doesnt get the air that it is expecting and it make the car run rich while changing gears. does this hold true for a car that is not meant to have a compressor on it?

This should only happen on MAF cars where the BOV is placed after the MAF sensor. You don't want to vent metered air because the computer is expecting it to go into the motor. If you place the BOV before the MAF you won't have any problem because you will be venting unmetered air and the computer will never see it. Clear as mud?

I have run the BOV before and after the MAF and had no problems with running rich between shifts. When your shifting the the throttle is shut and it doesn't cause any problems. The guy I sold my old kit to with the BOV after the MAF ran an A4 and also had no problems with rich conditions.

Well as for a BOV, If my past statements didn't convince you that a BOV is necessary, then take a look at your compressor map and find the pressure ratio your running at and the CFM for your entire rev range. Close the throttle sharply at that pressure ratio so the Turbo is now flowing 0 cfm and tell me if you exceed the surge limit of your turbo. Garanteed you will. Protect your investment, turbo's aren't cheap, BOV's are.

Bill

Originally posted by SMOKNZ
I have run the BOV before and after the MAF and had no problems with running rich between shifts. When your shifting the the throttle is shut and it doesn't cause any problems. The guy I sold my old kit to with the BOV after the MAF ran an A4 and also had no problems with rich conditions.

Well as for a BOV, If my past statements didn't convince you that a BOV is necessary, then take a look at your compressor map and find the pressure ratio your running at and the CFM for your entire rev range. Close the throttle sharply at that pressure ratio so the Turbo is now flowing 0 cfm and tell me if you exceed the surge limit of your turbo. Garanteed you will. Protect your investment, turbo's aren't cheap, BOV's are.

Bill

I'm not saying running a BOV won't help the turbo's life. In fact I know it will. People confuse a BOV as a device that will help with turbo lag between shifts. I'm just saying if you shift fast enough you will build boost faster than you would with a BOV.

"This should only happen on MAF cars where the BOV is placed after the MAF sensor. You don't want to vent metered air because the computer is expecting it to go into the motor. If you place the BOV before the MAF you won't have any problem because you will be venting unmetered air and the computer will never see it. Clear as mud?"


__________________
that is all clear to me, but what i dont understand is that a kid i know is venting metered air and the car runs the same (95 GSX) as it does when recirculating. since he is just venting and it smokes black between shifts, thats what he told me cause that. the comp expects to see the air being vented so it automatically adds fuel, when the air is not there its naturally going to run rich. does that make sence?

He said, she said is all fine and great. We actually have tried different maf locations and with/without BOV's and different BOV locations with our systems and our actual results on our applications have backed up what logic tells you that the maf will read the air and add fuel accordingly. If that air doesn't go into the engine but instead exits through the BOV into atmoshpere, then the engine will go rich if everything is working properly.

Also, if the MAF is located further away from the Tbody and no BOV is in place, the boost air will actually go through the maf toward the tbody and then upon closing the throttle, that air will exit back through the maf again and be counted twice, which also will cause a rich condition. This has been our experience for what it is worth. But all you have to do is think about it and it really does make sense.

Talk to you later, Rick @ STS

Originally posted by Turbocharged
He said, she said is all fine and great. We actually have tried different maf locations and with/without BOV's and different BOV locations with our systems and our actual results on our applications have backed up what logic tells you that the maf will read the air and add fuel accordingly. If that air doesn't go into the engine but instead exits through the BOV into atmoshpere, then the engine will go rich if everything is working properly.



How is that so when the MAF isn't sensing anymore air when the BOV is opened? If you install the BOV before the MAF than the MAF will not sense any of the air that is vented out, how would it? It is impossible . I have been around lots of turbo Supras, 300ZXs, RX7s, Eclipses, 3000GTs and the only car that has problems venting to the atmosphere are Eclipses. There stock BOV vents back into the air intake after the MAF. Other than that I have no experiences with any of those cars running rich when blow off happens

I think you may have misunderstood my post. When the BOV is before the MAF, that air just exits and isn't counted. When the BOV is after the MAF the air is counted by the MAF but doesn't enter the engine. I would suspect that those cars that don't have problems going rich don't have alot of volume of air between the turbocharger and the MAF.

For a car with a large intercooler that is between the turbo and the MAF as well as all the ducting associated with it, all that air will pass through the MAF so that it can exit through the BOV (some of it will vent back through the turbo as well) In this case you are counting lots of air in the MAF. For a compact system with small or no intercooler there isn't enough volume of air flowing through the MAF and exiting the BOV to dramatically effect fuel mixtures.

Assuming the boost is limited by detonation, wouldn't porting the heads reduce the possible boost pressure without detonating, but increase power?

I'm thinking that the compression pressure would increase (for the same boost level) when the head is ported, because the heads are more restrictive. Higher compression pressure = more prone to detonation.

But, this means you can still run the same compression pressure (with same cam, etc.) at a lower boost, which means lower heat in the intake air charge, which means denser air.

So, my vote is that ported heads make more power, even at less boost, but can handle less boost.