well i was thinking about turbos and hot air last night and i was wondering wouldnt it be better to get a bigger turbo so it doesnt have to work as hard a produce so much heat. like say u have a ta-54 and a ta-49 you have to push the ta-49 and it is going to make alot more heat then a bigger turbo like the 54. what is this going to do to performance? am i thinking right or no? i know u will need a stall and all but what else should i be looking at
TURBO's and HOTAIR
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mycarsucks
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You know what, I think you actually have it about right on. At least it makes sense to me. However, I do think that it would be better to go with a home made IC setup for the long run. Or, if you want to stay with your hotair heritage, maybe alky injection could be a better option. (a new turbo and converter seems hard to swallow to reduce heat for me)
However, I have also heard that alot of the larger turbos are very similar to eachother in low boost, and the big difference is in the 20+ range. Hopefully some experienced members will shed some light on this.
However, I have also heard that alot of the larger turbos are very similar to eachother in low boost, and the big difference is in the 20+ range. Hopefully some experienced members will shed some light on this.
I see what you're saying. I think the IC cars can get away with pushing a small turbo farther than a hotair. The thing I've noticed and correct me if I'm wrong but I've never seen a non-intercooled hotair run more than 21-22psi and get any benefit from it regardless of turbo size. I do think a bigger turbo is more important on a hotair. Another thing is I didn't feel much difference when I went from the 49 to the 64 until after 22 psi.
You know the old saying about a 10 deg change in air temperature being worth 1% horsepower? It holds true here as well. But the temperature that matters is the temperature of the air in the intake manifold, which for us is not the outside air temp but the turbo outlet temp.
Here's how it works:
1. The engine takes in a given *volume* of air on each revolution. 231 cubic inches for each 2 engine revs as a matter of fact.
2. Colder air has a higher density.
3. A given volume of air will have more pounds of air in it when it is colder.
4. Therefore lower air temps mean more pounds of air is flowing even though the engine is pulling in the same volume of air.
5. More pounds of air means more power.
So, what improvement can you expect to see?
Lets assume you are at 20 psi boost. And it is 80 deg outside.
The temperature of the air coming out of the turbo depends only on the efficiency of the compressor, the air temperature coming into the compressor, and the pressure ratio across the compressor (ie pressure out/pressure in).
If we have a poorly sized compressor, with maybe a 60% efficiency, then at 20 psi/80 deg ambient the outlet temperature is about 333 deg F. The air density at the discharge is 0.118 lb/cu ft.
If we replace it with a great compressor that has a 75% efficiency, then at 20 psi/80 deg ambient the outlet temperature is about 279 deg F. The air density at the discharge is 0.127 lb/cu ft.
The air density has increased by 0.127/0.118 = 1.076 = 7.6%
So you could expect a 7.6% increase in mass air flow (ie the MAF should read 7.6% more, maybe going from 225 gm/sec to 242 gm/sec), which would translate into maybe 5-6% more power (ie from 250 hp to 265 hp).
So, from an turbo discharge temperature aspect *only*, this better compressor is only worth 15 hp!
Using the old rule of thumb about 1% per 10 deg, (333 F - 279 F) = 54 deg change, or 5.4%, which gives about the same answer.
This is where you learn the beauty of the intercooler. Suppose you could get the temperature down to 125 F. Then 333-125 = 208 F, or a 20.8% change in hp. That would take this 250 hp engine to 300 hp.
So anyway, if a bigger turbo makes more power that what I've indicated above, where does it come from if it isn't just due to air temperature effects?
I think it is due to exhaust backpressure. It takes backpressure to drive that turbine wheel which spins the compressor wheel.
Using our same example, the 60% efficient compressor wheel needs about 50 hp to drive it, while the 75% efficient wheel needs about 40 hp to drive it. To extract more hp from the exhaust, the turbine needs either a higher flow rate of exhaust to go through it (ie less through the wastegate), or it needs a higher exhaust pressure coming into it, or (most likely) both.
A higher exhaust backpressure means more exhaust left in the cylinder when the exhaust valve closes, which means less room for fresh air/fuel to come into the cylinder, which means less power.
This is the same effect you see when you add a better exhaust, or remove the cat converter, or add a better downpipe, or swap that 0.63 turbine housing for a 0.82 housing. These things all serve to reduce the exhaust backpressure that the engine sees, which increases power. Well, a more efficient compressor wheel, turbine wheel, and turbine housing can also reduce the required exhaust back pressure, which again increases power.
I think this is where the rest of the power increase comes from with a better turbo. Don't get too tied up with the "air heating" part of it, it isn't the whole story.
John
Here's how it works:
1. The engine takes in a given *volume* of air on each revolution. 231 cubic inches for each 2 engine revs as a matter of fact.
2. Colder air has a higher density.
3. A given volume of air will have more pounds of air in it when it is colder.
4. Therefore lower air temps mean more pounds of air is flowing even though the engine is pulling in the same volume of air.
5. More pounds of air means more power.
So, what improvement can you expect to see?
Lets assume you are at 20 psi boost. And it is 80 deg outside.
The temperature of the air coming out of the turbo depends only on the efficiency of the compressor, the air temperature coming into the compressor, and the pressure ratio across the compressor (ie pressure out/pressure in).
If we have a poorly sized compressor, with maybe a 60% efficiency, then at 20 psi/80 deg ambient the outlet temperature is about 333 deg F. The air density at the discharge is 0.118 lb/cu ft.
If we replace it with a great compressor that has a 75% efficiency, then at 20 psi/80 deg ambient the outlet temperature is about 279 deg F. The air density at the discharge is 0.127 lb/cu ft.
The air density has increased by 0.127/0.118 = 1.076 = 7.6%
So you could expect a 7.6% increase in mass air flow (ie the MAF should read 7.6% more, maybe going from 225 gm/sec to 242 gm/sec), which would translate into maybe 5-6% more power (ie from 250 hp to 265 hp).
So, from an turbo discharge temperature aspect *only*, this better compressor is only worth 15 hp!
Using the old rule of thumb about 1% per 10 deg, (333 F - 279 F) = 54 deg change, or 5.4%, which gives about the same answer.
This is where you learn the beauty of the intercooler. Suppose you could get the temperature down to 125 F. Then 333-125 = 208 F, or a 20.8% change in hp. That would take this 250 hp engine to 300 hp.
So anyway, if a bigger turbo makes more power that what I've indicated above, where does it come from if it isn't just due to air temperature effects?
I think it is due to exhaust backpressure. It takes backpressure to drive that turbine wheel which spins the compressor wheel.
Using our same example, the 60% efficient compressor wheel needs about 50 hp to drive it, while the 75% efficient wheel needs about 40 hp to drive it. To extract more hp from the exhaust, the turbine needs either a higher flow rate of exhaust to go through it (ie less through the wastegate), or it needs a higher exhaust pressure coming into it, or (most likely) both.
A higher exhaust backpressure means more exhaust left in the cylinder when the exhaust valve closes, which means less room for fresh air/fuel to come into the cylinder, which means less power.
This is the same effect you see when you add a better exhaust, or remove the cat converter, or add a better downpipe, or swap that 0.63 turbine housing for a 0.82 housing. These things all serve to reduce the exhaust backpressure that the engine sees, which increases power. Well, a more efficient compressor wheel, turbine wheel, and turbine housing can also reduce the required exhaust back pressure, which again increases power.
I think this is where the rest of the power increase comes from with a better turbo. Don't get too tied up with the "air heating" part of it, it isn't the whole story.
John
Oh yeah, forgot to mention...
Air density is a much stronger function of pressure than temperature. Much stronger!
If boost is increased from 20 psi to 25 psi, the air density (and therefore air flow) almost has to go up, even if it is hotter.
For example, assume 70% efficient compressor at 20 psi. Outlet temperature is 295 F, air density is 0.124 lb/cu ft.
Now raise the boost pressure to 25 psi. Suppose the efficiency drops to 65%, the air temperature is 354 F, but the air density is still higher at 0.132 lb/cu ft, because the pressure is so much higher. Air flow should increase by 0.132/0.124 = 6.5% even with the lower efficiency/hotter outlet temps.
In fact, for the air density to be the same at 25 psi as it was a 20 psi, the effiency would have to drop from 70% to 55%. I find this large of a drop to be pretty unlikely.
I think if going from 20 to 25 psi doesn't show an increase in performance it is due to something else. The higher boost pressure does require a substantial increase in power extracted from the exhaust, and if the efficiency drops off some then that will be an even larger increase; perhaps the losses due to exhaust backpressure counteract the gains from the increased boost? Or maybe it is something else, I dunno. I just doubt that you don't see a gain only because of hotter air temps.
John
Air density is a much stronger function of pressure than temperature. Much stronger!
If boost is increased from 20 psi to 25 psi, the air density (and therefore air flow) almost has to go up, even if it is hotter.
For example, assume 70% efficient compressor at 20 psi. Outlet temperature is 295 F, air density is 0.124 lb/cu ft.
Now raise the boost pressure to 25 psi. Suppose the efficiency drops to 65%, the air temperature is 354 F, but the air density is still higher at 0.132 lb/cu ft, because the pressure is so much higher. Air flow should increase by 0.132/0.124 = 6.5% even with the lower efficiency/hotter outlet temps.
In fact, for the air density to be the same at 25 psi as it was a 20 psi, the effiency would have to drop from 70% to 55%. I find this large of a drop to be pretty unlikely.
I think if going from 20 to 25 psi doesn't show an increase in performance it is due to something else. The higher boost pressure does require a substantial increase in power extracted from the exhaust, and if the efficiency drops off some then that will be an even larger increase; perhaps the losses due to exhaust backpressure counteract the gains from the increased boost? Or maybe it is something else, I dunno. I just doubt that you don't see a gain only because of hotter air temps.
John
THANX
Thanx, thats alot to read i will probeley read it like 10 times before i get it all. but if u can keep the intake air cooler it wont det. as easy right. as u where saying force feed more in the air temp might rise wouldnt this cause more det. sorry just trying to understand.
brent
Thanx, thats alot to read i will probeley read it like 10 times before i get it all. but if u can keep the intake air cooler it wont det. as easy right. as u where saying force feed more in the air temp might rise wouldnt this cause more det. sorry just trying to understand.
brent
Jerryl
Tall Unvaccinated Chinese Guy
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Tune in folks! 
I understand what you guys are saying but at the end of the day the way i see it at least....the exhaust still powers the turbo which is what heats the air up. i see the point jde makes by making it more efficient to keep temps down but without that intercooler the air is always gonna be hottt. Ive seen many turbo cars whose headers glow from getting so hot so i just dont see it making that big of a difference without an intercooler. Dont get me wrong there are hot air cars that are fast and i once was one but in the point of the temp being changed enough by a bigger turbo to make a difference without an intercooler i just dont know how far we could take that with the 84 85 style setup.
just shoot it full of alky and hang on lol
just shoot it full of alky and hang on lol
T-Type85David
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I think the stock or TA33 should be fine, Alky, Cry o2 intake cooler, Should all help lower temps. Tho a Intercooler is hardware, not like alky or other ways of cooling. We all do what we can to work with the HA, Turbo wrap(or hi temp ) turbo, UP,DP, better flowing exhaust. Cold air intake. Now if some where to have their M10 rebuilt with Lighter turbines, 360 bearing, water cooled etc. I believe that should help make the turbo run at a better level then stock. Turbos have came a long way now. But not all of us want a T4 or 700hp. Just a turbo, a TR that works at peak performance. Thats what i've been trying to do.
The only way i see it to not use Hardware intercooling, water or air to air, of course is alky or CRY O2(which i havent seen anyone use yet!!!!!)
So with what can be bought now a days HA should be well on their way. Just takes planing i say.
The only way i see it to not use Hardware intercooling, water or air to air, of course is alky or CRY O2(which i havent seen anyone use yet!!!!!)
So with what can be bought now a days HA should be well on their way. Just takes planing i say.
Jerryl
Tall Unvaccinated Chinese Guy
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I think the stock or TA33 should be fine, Alky, Cry o2 intake cooler, Should all help lower temps. Tho a Intercooler is hardware, not like alky or other ways of cooling. We all do what we can to work with the HA, Turbo wrap(or hi temp ) turbo, UP,DP, better flowing exhaust. Cold air intake. Now if some where to have their M10 rebuilt with Lighter turbines, 360 bearing, water cooled etc. I believe that should help make the turbo run at a better level then stock. Turbos have came a long way now. But not all of us want a T4 or 700hp. Just a turbo, a TR that works at peak performance. Thats what i've been trying to do.
The only way i see it to not use Hardware intercooling, water or air to air, of course is alky or CRY O2(which i havent seen anyone use yet!!!!!)
So with what can be bought now a days HA should be well on their way. Just takes planing i say.
Guys, first off, look a the original date of the post.
Although your points have validity, they are not "on track" with this thread.
The OP never asked about an IC, alky, a HP number, or anything else.
Now, you guys may be smarter than John
, but John's technical points were made to gain better understanding of the “why”.The laws of physics do not change ……
I think you guys missed the point of the posts from John.
….. Oh well (sigh) ………Tell me "why" you think I ran into this tread? :tongue:
What was the point of writing " tune in" on a post from 2002 ?? It looked to me like you were having similar question as original poster and i was giving input to help. When i see tune in i usually think your looking for opinions guess i wasnt the only one as T-Type85David answered also. if it were to show the info givin at the time i would say write something different than tune in.
Jerryl
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Well, to put it simply
;"Tune in" may have been the wrong choice of words for some, but to me it implied: "Read and heed".
There are quite a few new people on this board, including the HA section and I am sure you would agree that an old tech thread or post, does not necessarily make the information "outdated".
dr_frankenstein
Mad Scientist
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the data is correct, but the changes arent as big as thought.
the thoughts of will the bigger turbo make a difference in terms of heat and efficeincy the answer is yes. While this data might not be available in HA world - it has been put to the test in the carbed world. theres alot in common to between the 2. JDEstill has hit it mostly on the head by saying its not nessacarily the size of the turbo, but where it is most efficient. Thus we have turbo maps and calculators. But the sheer volume of air the larger turbo produces has an effect, its just very small. A larger turbo will have a higher volume, thus requires less boost to devlop same amount of power........ theroetically!!!! this is a common line of thought.. and where it gets mixed up.
HOWEVER................... it would require the larger turbo to be just as effiecient or better as the small turbo at the same or less boost pressure to qualify as a real gain in change of temp. this of course, is rarly the case. Unless you want to talk journal VS BB...... a whole different can of worms.
But some simple laws do apply and the engineers at buick were on top of this. Looking at the early carbed system, the intake sucked! it was small and just had long winding runners - the HA was the first to incorporate short runners and a plenum to allow expansion of turbo discharge- this helps to lower temps, ever so slightly.......... later the 86/87 had a bigger plenum, and an improved runner system .....???? Hmm........ sneaky , sneaky. The ides, were there - the improvements while looking small, obviously made enough impact to replace its previous version.
So.... What you need to do, is decide what boost you want to run, and find the largest turbo with the highest efficiency at that particular boost pressure. You will see substancial increases - but it is limited to the size of the turbos peak efficiency window, which is key on a non IC car.
A.j.
the thoughts of will the bigger turbo make a difference in terms of heat and efficeincy the answer is yes. While this data might not be available in HA world - it has been put to the test in the carbed world. theres alot in common to between the 2. JDEstill has hit it mostly on the head by saying its not nessacarily the size of the turbo, but where it is most efficient. Thus we have turbo maps and calculators. But the sheer volume of air the larger turbo produces has an effect, its just very small. A larger turbo will have a higher volume, thus requires less boost to devlop same amount of power........ theroetically!!!! this is a common line of thought.. and where it gets mixed up.
HOWEVER................... it would require the larger turbo to be just as effiecient or better as the small turbo at the same or less boost pressure to qualify as a real gain in change of temp. this of course, is rarly the case. Unless you want to talk journal VS BB...... a whole different can of worms.
But some simple laws do apply and the engineers at buick were on top of this. Looking at the early carbed system, the intake sucked! it was small and just had long winding runners - the HA was the first to incorporate short runners and a plenum to allow expansion of turbo discharge- this helps to lower temps, ever so slightly.......... later the 86/87 had a bigger plenum, and an improved runner system .....???? Hmm........ sneaky , sneaky. The ides, were there - the improvements while looking small, obviously made enough impact to replace its previous version.
So.... What you need to do, is decide what boost you want to run, and find the largest turbo with the highest efficiency at that particular boost pressure. You will see substancial increases - but it is limited to the size of the turbos peak efficiency window, which is key on a non IC car.
A.j.
Jerryl
Tall Unvaccinated Chinese Guy
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Very good explanation.
Except :tongue: ..... on a HA, with only one turbo upgrade readily available, you need to determine where the turbo's efficiency is, and work the combo backwards. :wink:
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Jerryl
Tall Unvaccinated Chinese Guy
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I can calculate if you tell me the turbo you running.
I got one for you to see what the difference is. Granted it's a carb/turbo but???:biggrin: Going from the stock 83 turbo to a hybred of sorts. I'm using the exhaust wheel and housing off of an 86 with the inducer side off of an m10 301 TTA. How much more efficent would it be or will it? I got the idea off another member and he said it works great but I'd like some numbers if that's possible.
im running a TA54
Jerryl
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Ok, did some diggin' ....... The TA54 has a 60-1 trim wheel.
Here you go.
If you can tell me the wheel size, I can try.
Otherwise, I am not sure.
The output and efficiencies are very dependant on A/R and other factors as well.
The same wheel in a different housing will act very differently, and that is NOT taken into account.
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