Baja Resident
New member
Can someone explain what the difference is in A/R ratios when looking at turbos. Which is better a low number or high number (.40, .60, or 1.10, etc)? What does it mean exactly?
Turbo A/R ratio?
- Thread starter Baja Resident
- Start date
SeattleSy#1255
Category 5 Conservative
Off turbonation.com:
The exhaust and compressor housings on turbo chargers use a "scroll" design. For example, the exhaust housing's scroll is where the exhaust gasses enter the housing and are directed at the turbine. It's basically a smooth, tubular chamber that surrounds the turbine with a slot all the way around that acts as a nozzle to direct the exhaust gasses at the turbine. It's called a scroll because it slowly gets smaller in diameter as a goes around the turbine. This pressurizes the gasses, forcing them out of the slot/nozzle at a fast rate. In turbo-terms, the scroll is measured by the cross-sectional area of the scroll's "tube" (A) and the distance from the center of the "tube" to the turbine shaft (R). The values by themselves are not meaningful to the user and for the most part, R does not change much for different housings, but by dividing R into A, you get the A/R ratio. So, the A/R ratio of the exhaust housing refers to the size and shape of the scroll that is cast into the housing. It basically determines how restrictive the housing will be, versus how quickly the turbine will spin up. A lower A/R ratio (smaller scroll area, A) results in a more restrictive housing. This restriction speeds up the exhaust gasses and increases the amount that the gasses will expand. It's the speed and expansion of the gasses that causes the turbine to spin. So with a low A/R ratio, the turbine will spin up quicker, but as engine output and rpms increase, the restriction of the housing begins to build up too much back pressure on the engine, which reduces performance. A good rule of thumb for when there is too much back pressure is when the pressure in the exhaust manifold is more the half of the pressure in the cylinder. So basically, a larger A/R ratio will improve your engine's top end, while losing some mid range power and increasing turbo lag. A smaller A/R ratio will help the bottom and mid-range, but may effect the top end.
On the compressor side, the housing also features a scroll design, but it has the opposite function. The air leaving the compressor turbine has a lot of speed, but not much pressure. The scroll on the compressor housing starts small and gets larger as it approaches the compressor outlet. This collects the air and builds up air pressure. So, the compressor housing is designed to convert the speed-energy of the air coming off of the compressor turbine into pressure-energy, which is much more useful to an engine.
The exhaust and compressor housings on turbo chargers use a "scroll" design. For example, the exhaust housing's scroll is where the exhaust gasses enter the housing and are directed at the turbine. It's basically a smooth, tubular chamber that surrounds the turbine with a slot all the way around that acts as a nozzle to direct the exhaust gasses at the turbine. It's called a scroll because it slowly gets smaller in diameter as a goes around the turbine. This pressurizes the gasses, forcing them out of the slot/nozzle at a fast rate. In turbo-terms, the scroll is measured by the cross-sectional area of the scroll's "tube" (A) and the distance from the center of the "tube" to the turbine shaft (R). The values by themselves are not meaningful to the user and for the most part, R does not change much for different housings, but by dividing R into A, you get the A/R ratio. So, the A/R ratio of the exhaust housing refers to the size and shape of the scroll that is cast into the housing. It basically determines how restrictive the housing will be, versus how quickly the turbine will spin up. A lower A/R ratio (smaller scroll area, A) results in a more restrictive housing. This restriction speeds up the exhaust gasses and increases the amount that the gasses will expand. It's the speed and expansion of the gasses that causes the turbine to spin. So with a low A/R ratio, the turbine will spin up quicker, but as engine output and rpms increase, the restriction of the housing begins to build up too much back pressure on the engine, which reduces performance. A good rule of thumb for when there is too much back pressure is when the pressure in the exhaust manifold is more the half of the pressure in the cylinder. So basically, a larger A/R ratio will improve your engine's top end, while losing some mid range power and increasing turbo lag. A smaller A/R ratio will help the bottom and mid-range, but may effect the top end.
On the compressor side, the housing also features a scroll design, but it has the opposite function. The air leaving the compressor turbine has a lot of speed, but not much pressure. The scroll on the compressor housing starts small and gets larger as it approaches the compressor outlet. This collects the air and builds up air pressure. So, the compressor housing is designed to convert the speed-energy of the air coming off of the compressor turbine into pressure-energy, which is much more useful to an engine.
Baja Resident
New member
That is awesome info, thanks.
New question then...what A/R ratio comes on a syty stock? What do most people agree is the best A/R ratio for a good quickness and reliability combo? Also, who knows what the mitsu 20g A/R ratio is?
If you can't tell I am trying to compare what I had with what I may need to buy.
New question then...what A/R ratio comes on a syty stock? What do most people agree is the best A/R ratio for a good quickness and reliability combo? Also, who knows what the mitsu 20g A/R ratio is?
If you can't tell I am trying to compare what I had with what I may need to buy.
THEMADTYPH00N
Active member
Baja Resident said:
The 20G has the same exhaust housing as a stock turbo. It just has a bigger compressor.
Baja Resident
New member
and the stock A/R ratio is what?
Ian Turgeon
Cascading Inspiration
mitsu's dont measure using a/r, they use a cm2 measurement, which isnt directly comparable with a/r
stock mitsu housing is 8cm2, a 20g usually comes with a 14cm housing, although it can be mixed with an 8cm and 12cm with some machine work.
stock mitsu housing is 8cm2, a 20g usually comes with a 14cm housing, although it can be mixed with an 8cm and 12cm with some machine work.
Baja Resident
New member
Here's what I am currently looking at, maybe I can get some feedback.
I believe this one would be a direct bolt on for the blown 20G I currently have. It looks identical down to the flat surface and markings.
Mitsubishi TD05-20G - $999 new
http://www.turbocalculator.com/view-product.php?product=002-008-003
Here is what I believe will be my best choice to upgrade to for the money/power.
Garrett Master Power T61 - $649 new
http://www.turbocalculator.com/view-product.php?product=002-003-001
Now, it's a little strange the better turbo is so much cheaper, but I guess it may be used on a broader range of applications. Is it possible it's not water cooled or something? Maybe the Garrett requires an external wastegate? I am going to call them tomorrow for more details, but that's the best price I have found online so far.
Oh, it also mentions T3/T4 flanges. Any idea which the stock flange is rated at? I assume it's the same as stock since you said the 20G turbine was identical to the stock.
As always any help in this endeavor is greatly appreciated.
I believe this one would be a direct bolt on for the blown 20G I currently have. It looks identical down to the flat surface and markings.
Mitsubishi TD05-20G - $999 new
http://www.turbocalculator.com/view-product.php?product=002-008-003
Here is what I believe will be my best choice to upgrade to for the money/power.
Garrett Master Power T61 - $649 new
http://www.turbocalculator.com/view-product.php?product=002-003-001
Now, it's a little strange the better turbo is so much cheaper, but I guess it may be used on a broader range of applications. Is it possible it's not water cooled or something? Maybe the Garrett requires an external wastegate? I am going to call them tomorrow for more details, but that's the best price I have found online so far.
Oh, it also mentions T3/T4 flanges. Any idea which the stock flange is rated at? I assume it's the same as stock since you said the 20G turbine was identical to the stock.
As always any help in this endeavor is greatly appreciated.
here is some more info about mitsu turbo's that i caught off another forum:
When we talk about Mitsu turbo's, the actual number (9, 14, 18, 19, 20, or any other in between) has to do with the size of the compressor wheel, and nothing more...
Now, for the letter after that number, The letter determines the "style" of wheel. The number of blades on the compressor wheel, the height of each one, etc. are defined by the letter after that number... The farther the letter is in the alphabet, the more efficient, and newer a design it is...
When someone says "14b", they are actually leaving out most of the size of the turbo...
A more proper size would be TD05H-14b. Now, H is a compressor cover style (h for high flow) used by Mitsu, and the 05 defines the actual size of the compressor cover. Not sure what TD stands for or it's significance... Here's the kicker... on a Mitsu turbo, just like a t3/t4, you can mix and match hot and cold sides, so, a mixed turbo could read something like "td07h-25g/tdo6h-10cm2" Which is the designation for the Hahn Racecraft Super 25g. The TD06 in the back half designates the turbine wheel, and hot side design, whereas the 10cm2 is the nozzle area... (smaller turbos use a 6cm2 like in the 14b, and get larger 7cm2 for 16-20g's typically, however, certain vendors like HRC vary this and use a 10cm2 for their Super series of turbos, or the EVO8 turbo, which uses a 9.8cm2 stock, and 10.5cm2 as an upgrade, or on the new MR)
As far as being a "frank" turbo... mitsu builds the 19(b,c,g,t) it's just a matter of getting one... Typically vendors would just buy the compressor wheel, and match it with whatever, call it a "frankenstein" turbo, and be done with it, but Mitsu does actually build turbo's to size as well.
For the original poster: there should be NO similarity between a 19g and a 14b, other than they are both Mitsu designations... (they could ~possibly~ both use a TD05 compressor cover) Here's the easy way to tell if it's a "g" series turbo - look at the compressor wheel, and if there are 6 large/tall blades with 6 smaller blades "hidden" under each of the larger blades, then it's most definitely a "g" turbo... Evenly spaced, level compressor blades typically shows a b series turbo, but, I can't recall what C and T use (the other most common designations)
When we talk about Mitsu turbo's, the actual number (9, 14, 18, 19, 20, or any other in between) has to do with the size of the compressor wheel, and nothing more...
Now, for the letter after that number, The letter determines the "style" of wheel. The number of blades on the compressor wheel, the height of each one, etc. are defined by the letter after that number... The farther the letter is in the alphabet, the more efficient, and newer a design it is...
When someone says "14b", they are actually leaving out most of the size of the turbo...
A more proper size would be TD05H-14b. Now, H is a compressor cover style (h for high flow) used by Mitsu, and the 05 defines the actual size of the compressor cover. Not sure what TD stands for or it's significance... Here's the kicker... on a Mitsu turbo, just like a t3/t4, you can mix and match hot and cold sides, so, a mixed turbo could read something like "td07h-25g/tdo6h-10cm2" Which is the designation for the Hahn Racecraft Super 25g. The TD06 in the back half designates the turbine wheel, and hot side design, whereas the 10cm2 is the nozzle area... (smaller turbos use a 6cm2 like in the 14b, and get larger 7cm2 for 16-20g's typically, however, certain vendors like HRC vary this and use a 10cm2 for their Super series of turbos, or the EVO8 turbo, which uses a 9.8cm2 stock, and 10.5cm2 as an upgrade, or on the new MR)
As far as being a "frank" turbo... mitsu builds the 19(b,c,g,t) it's just a matter of getting one... Typically vendors would just buy the compressor wheel, and match it with whatever, call it a "frankenstein" turbo, and be done with it, but Mitsu does actually build turbo's to size as well.
For the original poster: there should be NO similarity between a 19g and a 14b, other than they are both Mitsu designations... (they could ~possibly~ both use a TD05 compressor cover) Here's the easy way to tell if it's a "g" series turbo - look at the compressor wheel, and if there are 6 large/tall blades with 6 smaller blades "hidden" under each of the larger blades, then it's most definitely a "g" turbo... Evenly spaced, level compressor blades typically shows a b series turbo, but, I can't recall what C and T use (the other most common designations)
SeattleSy#1255
Category 5 Conservative
If i was you i'd pay 3-500 more and get a PTE kit, probably a 44 if you are using stock TC. For a few hundred more you have a turbo that has more potentioal to it if you decided to do more later...such as a higher TC, alki, etc.
Just my two cents.
Just my two cents.
Baja Resident
New member
I think I may have found a winner here...
http://www.turbocalculator.com/view-product.php?product=002-010-002
It says it has a "T3 inlet and 5-bolt T3 outlet flange", will that outlet match up to my 2 5/8" downpipe? I read that the Garretts won't match up, but this says it is a hybrid. A hybrid of what? And if I do need a downpipe, where do I get *just* a downpipe. I don't need the crossover, cat, or whatever comes with a kit.
http://www.turbocalculator.com/view-product.php?product=002-010-002
It says it has a "T3 inlet and 5-bolt T3 outlet flange", will that outlet match up to my 2 5/8" downpipe? I read that the Garretts won't match up, but this says it is a hybrid. A hybrid of what? And if I do need a downpipe, where do I get *just* a downpipe. I don't need the crossover, cat, or whatever comes with a kit.
THEMADTYPH00N
Active member
Baja Resident said:
KB headers move the Turbo away from the stock location so you'll need a special downpipe. Lucky for you Mike Lee sells one.
http://www.raceprovenmotors.com/cart/product_info.php?cPath=21_88&products_id=145
Also with the build you have I'd get a turbo much bigger than a 20G. If I where you I'd just invest in a PTE kit, minus the downpipe.
Baja Resident
New member
I'm not sure I understand that? I already have KB headers and my downpipe fits fine now.THEMADTYPH00N said:
Is that "5 bolt T3 outlet flange" going to match the downpipe tho? As I said the 20G matches up even with my KB headers.
ghettosled
SYTY SUPERSTORE
no offense, but i would call up a company that specializes in the sytys and have them spec the right turbo. Its not worth the money you are attempting to save if there is any at all. In my opinion most of the guys who buy a turbo from a non syty vendor without knowing what exactly it is they are buying end up spending double in the end.
The KB header system was designed to bolt up to a stock turbo. Or stock configuration turbo such as the 20G. If you are looking to put a garett turbo on you will need a new downpipe, and turbine housing. The 5 bolt T3 outlet flange wont work with anything offered for the syty unless you modify your downpipe.
The KB header system was designed to bolt up to a stock turbo. Or stock configuration turbo such as the 20G. If you are looking to put a garett turbo on you will need a new downpipe, and turbine housing. The 5 bolt T3 outlet flange wont work with anything offered for the syty unless you modify your downpipe.
Ian Turgeon
Cascading Inspiration
mike is a vendor, but take what he says as a good tip. You dont really know what your looking at so you either need to read/investigate, or call someone up who can explain it and give you some suggestions.
About the price difference, Mitsu's are just plain more expensive then garrett parts. the 20g compressor wheel alone is about 2x the cost of a similar garrett wheel.
a hybrid defines that its not a normally configured turbo. It could be half mitsu, half garret, or just two mitsu parts that dont normally go together
Mike wont steer you in the wrong direction, so you could give him a call... or any of the other vedors on here would be happy to help you out im sure.
About the price difference, Mitsu's are just plain more expensive then garrett parts. the 20g compressor wheel alone is about 2x the cost of a similar garrett wheel.
a hybrid defines that its not a normally configured turbo. It could be half mitsu, half garret, or just two mitsu parts that dont normally go together
Mike wont steer you in the wrong direction, so you could give him a call... or any of the other vedors on here would be happy to help you out im sure.
THEMADTYPH00N
Active member
SyTyArchives said:
I agree, call Mike.
Baja Resident
New member
I don't plan on being able to accomplish this for another month or two so, so I am not jumping to any decisions right away. I just wanted to try to put it out there and learn as much as I can. That's why this site is so great, Appreciate all the help and info. I have been learning a lot.