Boost is Not Just Boost
06-30-2012, 08:06 PM
#1
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Boost is Not Just Boost I'm reaching out to the experts here because there are too many people on here talking about running LQ4s or LM7 with 15 lbs of boost on 93 and a 'good' tune and everything is hunky dory.... they're pushing 600 horses and blah blah blah....
Maybe they are shooting straight, maybe not..., but....
In your expert opinions I believe we are can agree that boost is really a measurement of the resistance to forced induction moreso than a measurement of potential horsepower....
With that said....
If car A has a freer flowing (CNC-ported or whatever) intake and heads, isn't car A's 15psi different from car B's 15psi on a stock (although well breathing) intake and heads...?
Someone please chime in....
I have tried to include an Excel spreadsheet of head flow info for several different widely available heads to see the different flow rates...
https://ls1tech.com/forums/attachment.php?attachmentid=361474&stc=1&d=1341104 704
Maybe they are shooting straight, maybe not..., but....
In your expert opinions I believe we are can agree that boost is really a measurement of the resistance to forced induction moreso than a measurement of potential horsepower....
With that said....
If car A has a freer flowing (CNC-ported or whatever) intake and heads, isn't car A's 15psi different from car B's 15psi on a stock (although well breathing) intake and heads...?
Someone please chime in....
I have tried to include an Excel spreadsheet of head flow info for several different widely available heads to see the different flow rates...
https://ls1tech.com/forums/attachment.php?attachmentid=361474&stc=1&d=1341104 704
06-30-2012, 08:12 PM
#2
Of course it is. Boost is just a resistance to airflow. If a motor has better flowing components it can make more power with less boost. Or you can compare a tc76 turbo to a gt91. At the same boost level the 91 will make way more power because its flowing way more air.
06-30-2012, 08:53 PM
#3
A naturally aspirated engine runs under pressure, one atmosphere at sea level (14.7 psi). 15 psi should double your engines n/a horsepower disregarding any efficiency issues in the system. (14.7 + boost) / 14.7 = Pressure ratio. Pressure ratio x N/a hp = rough estimate of hp.
06-30-2012, 09:51 PM
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Yup that's how it works... Air volume is what makes HP, pressure is just a measure of how much energy it takes to force a certain volume of air through the engine. An engine that flows more air will take less pressure to make the same HP, or more horsepower at the same pressure level.
^ I think I used the correct terminology
^ I think I used the correct terminology
06-30-2012, 11:08 PM
#5
it is not rocket surgery
if an engine make 500hp na and you add 14.7 psi boost, in theory it will make 1000hp.
if you put better heads and now it makes 550 na, put 14.7 psi boost and it will make 1100hp.
so,no boost is not a measure of restriction. the intake valve is the restriction, and all ls engines, afaik, close the intake valve at least once per cycle
if an engine make 500hp na and you add 14.7 psi boost, in theory it will make 1000hp.
if you put better heads and now it makes 550 na, put 14.7 psi boost and it will make 1100hp.
so,no boost is not a measure of restriction. the intake valve is the restriction, and all ls engines, afaik, close the intake valve at least once per cycle
06-30-2012, 11:30 PM
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so in theory as your saying 500 n/a hp + 14.7 psi = 1000 hp so in theory adding 29.4 psi of boost = 1500hp or is this where intake temps and other factors come into play ?????
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07-01-2012, 12:59 AM
#8
and adding 29.4 psi to 550 base is about 1650 hp.
it is simple multiplication, not fancy math, and that is the correct answer to the OPs question.
in practice, 15 psi isnt quite 2x the na and 30 psi isnt 3x Na. there is a direct, calculable, relationship between boost, temperature rise, and air density. that is to say,
boost hp is directly related to the amount of power the engine makes naturally aspirated and that is all you need to know.
07-01-2012, 03:07 AM
#9
Why are people so caught up on boost? Boost is a measurement of restriction. Plain and simple. If you have a more efficient setup (I.E. better heads) you will make more power at the same boost. Why you ask. Because you're flowing more air. You need to be concerned about what CFM is your engine flowing/turbo pushing.
07-01-2012, 03:23 AM
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Thank you guys for chiming in. My reason for reaching out is that I have an LQ4 in my Tahoe and I can't really afford to have two cars, but I can warm up my truck a little. I have gone with the Comp XR269HR cam and I am convinced that I should also go with the LS3 heads and intake kit that I believe Jegs is offering sans the GM Hot Cam. After reading the posts about junkyard engines and turbo kits I got the bug, but I am willing to spend a little cash over a couple years to do it correctly, but it has to remain VERY streetable too....
07-01-2012, 03:57 AM
#11
Excellent discussion on flow (in cfm) vs density change (mass flow change).
Pressure is always causing the air to enter the engine the same way.
There is a negative pressure when the engine's piston drops in the bore.
There is always a positive pressure from the atmosphere but it can vary in how much density the air has vs altitude.
The engine consumes the same volume of air every revolution whether at idle or at wot but the density changes as the throttle blade is moved from idle to WOT.
The density will be what ever the conditions are at the entry of the intake system.
Hot air, lower density Cold air, higher density.
Boost allows you to increase the density of the charge artificially.
I can't take credit for this.
This is a copy and paste from a FI engineer that works for Ford Motor Company
that mods on TTF.
This is how it works.
Pressure is always causing the air to enter the engine the same way.
There is a negative pressure when the engine's piston drops in the bore.
There is always a positive pressure from the atmosphere but it can vary in how much density the air has vs altitude.
The engine consumes the same volume of air every revolution whether at idle or at wot but the density changes as the throttle blade is moved from idle to WOT.
The density will be what ever the conditions are at the entry of the intake system.
Hot air, lower density Cold air, higher density.
Boost allows you to increase the density of the charge artificially.
I can't take credit for this.
This is a copy and paste from a FI engineer that works for Ford Motor Company
that mods on TTF.
This is how it works.
07-01-2012, 08:04 AM
#12
with all due respect, this is very wrong
SAVE your cash because you dont need to spend money on cylinder heads to achieve anything you are trying to achieve. in a properly specd system, the turbo will be the ultimate limiter of power, and in the average street setup, one psi of boost, maybe 2 at most, will compensate for any gain you may have seen in heads.
cases in point
hank peabody stock heads stock cam on 14psi
71chevy stock heads stock cam on 5 psi
86lxnotch stock heads stock cam on 15psi
http://youtu.be/3Nqt2Db8eMg
i would venture to say you dont even need a cam to make some heat with a turbo
Thank you guys for chiming in. My reason for reaching out is that I have an LQ4 in my Tahoe and I can't really afford to have two cars, but I can warm up my truck a little. I have gone with the Comp XR269HR cam and I am convinced that I should also go with the LS3 heads and intake kit that I believe Jegs is offering sans the GM Hot Cam. After reading the posts about junkyard engines and turbo kits I got the bug, but I am willing to spend a little cash over a couple years to do it correctly, but it has to remain VERY streetable too....
cases in point
hank peabody stock heads stock cam on 14psi
71chevy stock heads stock cam on 5 psi
86lxnotch stock heads stock cam on 15psi
http://youtu.be/3Nqt2Db8eMg
i would venture to say you dont even need a cam to make some heat with a turbo
07-01-2012, 11:12 AM
#13
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71 Chevy I see where you are going.
My main concerns are trying to avoid using meth and the higher temperatures associated with higher levels of boost (especially since I am not racing). I was led to believe that 8-9 is safe on the street and maybe up 12 with an intercooler... All with a competent tuner of course....
I also don't have a hard horsepower number in mind, but I do want my truck to move out. Adding the XR269HR cam woke it up a bit, but it's almost 3 tons so it needs a little more help than just the cam....
denmah also alluded to the fact that a H/C/I combo will help, but only so much and that's why he went the turbo route as well....
What's your take...?
My main concerns are trying to avoid using meth and the higher temperatures associated with higher levels of boost (especially since I am not racing). I was led to believe that 8-9 is safe on the street and maybe up 12 with an intercooler... All with a competent tuner of course....
I also don't have a hard horsepower number in mind, but I do want my truck to move out. Adding the XR269HR cam woke it up a bit, but it's almost 3 tons so it needs a little more help than just the cam....
denmah also alluded to the fact that a H/C/I combo will help, but only so much and that's why he went the turbo route as well....
What's your take...?
07-01-2012, 11:39 AM
#14
my opinion is
1.the difference between doing heads and not doing heads may be 2 psi, so if you did heads and ran 8 psi you would need 10psi without the heads. imo, thats the same operating range.
2. there are other factors other than power that dictate quickness. a well specd converter is one of those and they aint cheap. set up the system well and you will be fine on low boost. ie if you are trying to heat up your engine, dont put a 91mm turbo on it because it will be no fun on the street. size the turbo right(76mm) and it will spool faster and also be in its most efficient range right where you want it to be.
spend the money on a good intercooler, or water setup. Im personally a BIG believer in water injection. mind you I didnt say water/methanol injection.
I used plain tap water injection in my last combo and temps went from 250+ non intercooled to 125 with the water.
WATER pulls even more heat out of the air than methanol and in some tests ive seen, when they added water injection, they couldnt find the knock limit of the engine , so lets just say if you add water, you will be able to run more boost without issues.
you can put together a decent water injection kit by yourself for less than $150 and the best part is tap water is free.
1.the difference between doing heads and not doing heads may be 2 psi, so if you did heads and ran 8 psi you would need 10psi without the heads. imo, thats the same operating range.
2. there are other factors other than power that dictate quickness. a well specd converter is one of those and they aint cheap. set up the system well and you will be fine on low boost. ie if you are trying to heat up your engine, dont put a 91mm turbo on it because it will be no fun on the street. size the turbo right(76mm) and it will spool faster and also be in its most efficient range right where you want it to be.
spend the money on a good intercooler, or water setup. Im personally a BIG believer in water injection. mind you I didnt say water/methanol injection.
I used plain tap water injection in my last combo and temps went from 250+ non intercooled to 125 with the water.
WATER pulls even more heat out of the air than methanol and in some tests ive seen, when they added water injection, they couldnt find the knock limit of the engine , so lets just say if you add water, you will be able to run more boost without issues.
you can put together a decent water injection kit by yourself for less than $150 and the best part is tap water is free.
07-01-2012, 11:56 AM
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my opinion is
1.the difference between doing heads and not doing heads may be 2 psi, so if you did heads and ran 8 psi you would need 10psi without the heads. imo, thats the same operating range.
2. there are other factors other than power that dictate quickness. a well specd converter is one of those and they aint cheap. set up the system well and you will be fine on low boost. ie if you are trying to heat up your engine, dont put a 91mm turbo on it because it will be no fun on the street. size the turbo right(76mm) and it will spool faster and also be in its most efficient range right where you want it to be.
spend the money on a good intercooler, or water setup. Im personally a BIG believer in water injection. mind you I didnt say water/methanol injection.
I used plain tap water injection in my last combo and temps went from 250+ non intercooled to 125 with the water.
WATER pulls even more heat out of the air than methanol and in some tests ive seen, when they added water injection, they couldnt find the knock limit of the engine , so lets just say if you add water, you will be able to run more boost without issues.
you can put together a decent water injection kit by yourself for less than $150 and the best part is tap water is free.
1.the difference between doing heads and not doing heads may be 2 psi, so if you did heads and ran 8 psi you would need 10psi without the heads. imo, thats the same operating range.
2. there are other factors other than power that dictate quickness. a well specd converter is one of those and they aint cheap. set up the system well and you will be fine on low boost. ie if you are trying to heat up your engine, dont put a 91mm turbo on it because it will be no fun on the street. size the turbo right(76mm) and it will spool faster and also be in its most efficient range right where you want it to be.
spend the money on a good intercooler, or water setup. Im personally a BIG believer in water injection. mind you I didnt say water/methanol injection.
I used plain tap water injection in my last combo and temps went from 250+ non intercooled to 125 with the water.
WATER pulls even more heat out of the air than methanol and in some tests ive seen, when they added water injection, they couldnt find the knock limit of the engine , so lets just say if you add water, you will be able to run more boost without issues.
you can put together a decent water injection kit by yourself for less than $150 and the best part is tap water is free.
Distilled water is like $1 a gallon so it's almost free XD.
07-01-2012, 12:06 PM
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07-01-2012, 01:14 PM
#17
A relevant story strictly for perspective.
In 1987 when turbo Regals were new (and I knew nothing about forced induction), there was a small group of us experimenting with GNs. Of course the first thing we all did was modify the waste gate controller to turn up the boost and all the bolt on crap and fuel systems. But after all the easy power was found, I took a different path.
Having more hotrodding pedigree than most of my contemporaries, I decided to tear into my motor. I ported the heads, intake and throttle body and installed a special turbo cam recommended by Crower. My reward: about 2 1/2 tenths and 3 mph.
So, there I was running slightly faster than everyone I knew in the Tampa area with a Turbo Regal in 1988 when a new guy showed up from Alabama. He wasn't the most knowledgeable guy I ever met, but he had a relationship with a guy named Conley of a company named Conley performance. The thing is, this guy was a solid 4 tenths and 5mph faster than I was and he had never had his valve covers off. The difference? A large front mount intercooler and a pretty advanced fuel system.
I was stunned. Heck, all the local guys were stunned. This guy's car was solidly in the 11s, full weight, stock heavy *** steel wheels and he never had his valve covers off.
So, I scraped and saved and bought a front mount intercooler kit. I was instantly rewarded with 4 tenths and 5+MPH at the exact same boost level.
Ever since those days, when it comes to forced induction, my focus has been on a cool dense air/fuel ratio first.
If a turbo is too small, one of the things that happens is that it heats the air far more than a turbo of the right size to move the same volume of air. This is true just the same as a super charger. In general, I don't think of it as a restriction, but more as efficiency. Same of heads and cam. The harder you have to work to push the air through there the more heat and inefficiency you create doing it.
In 1987 when turbo Regals were new (and I knew nothing about forced induction), there was a small group of us experimenting with GNs. Of course the first thing we all did was modify the waste gate controller to turn up the boost and all the bolt on crap and fuel systems. But after all the easy power was found, I took a different path.
Having more hotrodding pedigree than most of my contemporaries, I decided to tear into my motor. I ported the heads, intake and throttle body and installed a special turbo cam recommended by Crower. My reward: about 2 1/2 tenths and 3 mph.
So, there I was running slightly faster than everyone I knew in the Tampa area with a Turbo Regal in 1988 when a new guy showed up from Alabama. He wasn't the most knowledgeable guy I ever met, but he had a relationship with a guy named Conley of a company named Conley performance. The thing is, this guy was a solid 4 tenths and 5mph faster than I was and he had never had his valve covers off. The difference? A large front mount intercooler and a pretty advanced fuel system.
I was stunned. Heck, all the local guys were stunned. This guy's car was solidly in the 11s, full weight, stock heavy *** steel wheels and he never had his valve covers off.
So, I scraped and saved and bought a front mount intercooler kit. I was instantly rewarded with 4 tenths and 5+MPH at the exact same boost level.
Ever since those days, when it comes to forced induction, my focus has been on a cool dense air/fuel ratio first.
If a turbo is too small, one of the things that happens is that it heats the air far more than a turbo of the right size to move the same volume of air. This is true just the same as a super charger. In general, I don't think of it as a restriction, but more as efficiency. Same of heads and cam. The harder you have to work to push the air through there the more heat and inefficiency you create doing it.
07-01-2012, 02:36 PM
#18
Technically yes. Boost is a measure of backpressure in the intake manifold in relation to the atmosphere.
No. A 101mm Turbo will make more power than a 76mm turbo at the same boost. Why? Because it flows more air (CFM). That is what you should be concerned about.
No. A 101mm Turbo will make more power than a 76mm turbo at the same boost. Why? Because it flows more air (CFM). That is what you should be concerned about.
07-01-2012, 02:43 PM
#19
And, just to throw this out there, bigger does not always make more power. As the wheel gets bigger, it gets heavier and has a different point of efficiency. Turbo efficiency maps are as complex as they are for good reason.
07-01-2012, 03:32 PM
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A relevant story strictly for perspective.
In 1987 when turbo Regals were new (and I knew nothing about forced induction), there was a small group of us experimenting with GNs. Of course the first thing we all did was modify the waste gate controller to turn up the boost and all the bolt on crap and fuel systems. But after all the easy power was found, I took a different path.
Having more hotrodding pedigree than most of my contemporaries, I decided to tear into my motor. I ported the heads, intake and throttle body and installed a special turbo cam recommended by Crower. My reward: about 2 1/2 tenths and 3 mph.
So, there I was running slightly faster than everyone I knew in the Tampa area with a Turbo Regal in 1988 when a new guy showed up from Alabama. He wasn't the most knowledgeable guy I ever met, but he had a relationship with a guy named Conley of a company named Conley performance. The thing is, this guy was a solid 4 tenths and 5mph faster than I was and he had never had his valve covers off. The difference? A large front mount intercooler and a pretty advanced fuel system.
I was stunned. Heck, all the local guys were stunned. This guy's car was solidly in the 11s, full weight, stock heavy *** steel wheels and he never had his valve covers off.
So, I scraped and saved and bought a front mount intercooler kit. I was instantly rewarded with 4 tenths and 5+MPH at the exact same boost level.
Ever since those days, when it comes to forced induction, my focus has been on a cool dense air/fuel ratio first.
If a turbo is too small, one of the things that happens is that it heats the air far more than a turbo of the right size to move the same volume of air. This is true just the same as a super charger. In general, I don't think of it as a restriction, but more as efficiency. Same of heads and cam. The harder you have to work to push the air through there the more heat and inefficiency you create doing it.
In 1987 when turbo Regals were new (and I knew nothing about forced induction), there was a small group of us experimenting with GNs. Of course the first thing we all did was modify the waste gate controller to turn up the boost and all the bolt on crap and fuel systems. But after all the easy power was found, I took a different path.
Having more hotrodding pedigree than most of my contemporaries, I decided to tear into my motor. I ported the heads, intake and throttle body and installed a special turbo cam recommended by Crower. My reward: about 2 1/2 tenths and 3 mph.
So, there I was running slightly faster than everyone I knew in the Tampa area with a Turbo Regal in 1988 when a new guy showed up from Alabama. He wasn't the most knowledgeable guy I ever met, but he had a relationship with a guy named Conley of a company named Conley performance. The thing is, this guy was a solid 4 tenths and 5mph faster than I was and he had never had his valve covers off. The difference? A large front mount intercooler and a pretty advanced fuel system.
I was stunned. Heck, all the local guys were stunned. This guy's car was solidly in the 11s, full weight, stock heavy *** steel wheels and he never had his valve covers off.
So, I scraped and saved and bought a front mount intercooler kit. I was instantly rewarded with 4 tenths and 5+MPH at the exact same boost level.
Ever since those days, when it comes to forced induction, my focus has been on a cool dense air/fuel ratio first.
If a turbo is too small, one of the things that happens is that it heats the air far more than a turbo of the right size to move the same volume of air. This is true just the same as a super charger. In general, I don't think of it as a restriction, but more as efficiency. Same of heads and cam. The harder you have to work to push the air through there the more heat and inefficiency you create doing it.
I don't think there is a right or wrong way to go about any of this, but I don't live under a money tree and I want to get as much as I can for my money within reason. I drive about 5-6000 miles a year so mileage is only moderately important and I want my car to be a little more peppy (ok, a lot more peppy), but I am not trying to set any new records I just want it to get out of its own way when I desire..
The other thing is that I have time. Unless my truck get totalled or something I can piece this all together over time....
I honestly figured over the next three years or so I could get it together, but the last American 'performance' car I had was a used up '86 T/A with a warmed up 350 TPI. The junkyard motors you guys are using make damn near as much power after 200k miles of abuse than that 350 TPI probably ever did with all the bolt ons I did (especially with forced induction).... Times really have changed....