12H-T performance Build
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- #202
Dougal: I bought a vacuum VNT actuator a few days ago off eBay. Typical Audi/VW type.
I also bought a while back a dual port waste gate adaptor. That was how I intended to increase the boost with rpm - by feeding the high pressure side to the top and the low pressure side (between the two turbos) to the bottom. This would cause the boost to rise with rpm.
It turned out that the dual port was rubbish and while it has "two ports" the lower section was not sealed, thus would require me to machine up something to suit. No problem really, just a pain.
I am not sure how much the force required to close the vanes will change with rpm, this is an aspect that will require some tuning.
I also bought a while back a dual port waste gate adaptor. That was how I intended to increase the boost with rpm - by feeding the high pressure side to the top and the low pressure side (between the two turbos) to the bottom. This would cause the boost to rise with rpm.
It turned out that the dual port was rubbish and while it has "two ports" the lower section was not sealed, thus would require me to machine up something to suit. No problem really, just a pain.
I am not sure how much the force required to close the vanes will change with rpm, this is an aspect that will require some tuning.
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- #203
Dougal: What is your opinion of BSFC change as it pertains to intercooling. How do you consider the relationship?
Within the bounds of keeping as close to the lean side of 20:1 as possible.
Within the bounds of keeping as close to the lean side of 20:1 as possible.
I did exactly the same thing. Bought a "dual port" actuator off ebay only to find the second port was only decoration. To make a seal for the shaft which would give it the movement requried was not worth the hassle.
It's still a cheap single port actuator and is currently fitted to my GT2256V, which isn't fitted to anything.
The stock vacuum acutuators have enough force to move the vanes, that's a given. So from there we only neeed to regulate vacuum to them. My recipie in the 4btswaps.com thread has potential for remote intervention, additional controls and more. Just keep adding more vacuum or pressure lines. The result is the sum of all of them.
BSFC with intercooling. The Diesel Engine Reference Book" has a worked example showing a 6% improvement for 60% intercooling. But it's not in any way linear, a large part is simply cooler charge = better efficiency.
Their results graphs show improvement from roughly 230 g/kwh to below 220. Both are curves, that's one point only.
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- #205
I complained to the seller and they gave me a complete refund on the dual port actuator on the basis it was not what I ordered. I really wanted the dual port option and still would be happy to find one. It is hard to tell actaul size from photos and I was a bit suprised how small the diaphram is! Anyway, I *may* machine up a seal that I would"Devcon" on. Just have to make sure that the air leakage rate is suffciiently low enough as to not impact on pressure in the diaphram without going to large diameter hose...
I am looking at the moment for cheap banjo fittings and the like, these are the types of things that put a slow down on my projects - just getting the right bits. I am not a thread expert and dont have any thread gauges (maybe I should by some, theres an idea) so I know that I am buying the right sizes.
Perhaps the twin turbo is alive after all.
Things to do to make it happen: Buy some TIG gas, buy oil/water fittings, machine up my 20G compressor wheel, machine up another clipped CT26 turbine, get balanced and take the compressor cover in to get machined to suit, make GT25 dump to CT26, make CT26 compressor to GT25 inlet section, make CT26 dump (I bought a new flange and will use expanded tube fittings to reduce turbulence - same for GT25 dump), find a way to to a bracket to hold it all nicely in place, make it. Set up VNT control of GT25, put boost controller on CT26, just in case it is needed and the easy part; install.
All sounds so simple!
I am looking at the moment for cheap banjo fittings and the like, these are the types of things that put a slow down on my projects - just getting the right bits. I am not a thread expert and dont have any thread gauges (maybe I should by some, theres an idea) so I know that I am buying the right sizes.
Perhaps the twin turbo is alive after all.
Things to do to make it happen: Buy some TIG gas, buy oil/water fittings, machine up my 20G compressor wheel, machine up another clipped CT26 turbine, get balanced and take the compressor cover in to get machined to suit, make GT25 dump to CT26, make CT26 compressor to GT25 inlet section, make CT26 dump (I bought a new flange and will use expanded tube fittings to reduce turbulence - same for GT25 dump), find a way to to a bracket to hold it all nicely in place, make it. Set up VNT control of GT25, put boost controller on CT26, just in case it is needed and the easy part; install.
All sounds so simple!
Sounding simple is easy, but I think your small GT25 will flow almost as much as the CT26. You need to find something bigger to get the exhaust out.
Remember the exhaust volume leaving the first turbo will be almost double the volume entering it.
I saw a picture of a CAT engine with factory compounds. The smaller turbo was wastegated with the boost signal taken off the bigger turbo. Simple and effective.
I still plan to fit this setup when time allows. It's that GT2256V for the small turbo and a T28 above with a modified T25 compressor housing. Been in planning for 2 years now and probably 1 more before I can make it happen.
I don't have the room for a bigger turbo.
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- #207
My GT25 has only a 42.5mm inducer, 60mm wheel = 40 trim! Bit small really on the inducer side, but would work well with a manual box getting boost nice and early. Lag wouldnt be an issue! Most importantly, it is a perfect mate to a bigger turbo in a twin setup and has a bolted flange inlet too!
The CT26 really is not a small turbo, the limiting factor is the exhaust. I figure the much larger supra exhaust housing with a clipped turbine should give me the flow I need. A 20G compressor can according to the map flow 650cfm at 1.3 -1.4 Bar and to me, this is perfect (at least the compressor wheel is) for the small trim VNT I have. Also, the CT26 is safe at this boost level.
I am listening to critque, hence I am justifying my rational so that it may be pulled apart.
I have seen dyno of stock CT26 up to 340rwhp and high flow compressor modded CT26 versions to 436rwhp. A TD06 20G did 460rwhp and this is what I would expect, since the exhaust turbines are very similar. Both at 20psi
Would it be reasonable to expect that 300rwhp might then be possible in the diesel with a 20G compressor wheel? I have been working off 1.3-1.4 Bar, which is where the efficiency is best on the 20G compressor wheel. No matter how many times I run the calcs, I keep coming back to it being a fairly good match. This is why I have persevered with the CT26
The CT26 really is not a small turbo, the limiting factor is the exhaust. I figure the much larger supra exhaust housing with a clipped turbine should give me the flow I need. A 20G compressor can according to the map flow 650cfm at 1.3 -1.4 Bar and to me, this is perfect (at least the compressor wheel is) for the small trim VNT I have. Also, the CT26 is safe at this boost level.
I am listening to critque, hence I am justifying my rational so that it may be pulled apart.
I have seen dyno of stock CT26 up to 340rwhp and high flow compressor modded CT26 versions to 436rwhp. A TD06 20G did 460rwhp and this is what I would expect, since the exhaust turbines are very similar. Both at 20psi
Would it be reasonable to expect that 300rwhp might then be possible in the diesel with a 20G compressor wheel? I have been working off 1.3-1.4 Bar, which is where the efficiency is best on the 20G compressor wheel. No matter how many times I run the calcs, I keep coming back to it being a fairly good match. This is why I have persevered with the CT26
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- #209
quote: "I saw a picture of a CAT engine with factory compounds. The smaller turbo was wastegated with the boost signal taken off the bigger turbo. Simple and effective"
That was how I planned to do mine!, but VNT for the primary and a difference - I planned to offset against the combined boost to give a "ramp" of boost with rpm.
That was how I planned to do mine!, but VNT for the primary and a difference - I planned to offset against the combined boost to give a "ramp" of boost with rpm.
A GT25 should have an exhaust wheel 53mm or smaller. My GT22 has a 50/42.5mm turbine wheel.
It's the exhaust side I'm wondering about. That dyno figure would be from a petrol which bypasses a lot of hot exhaust out an enlarged or external wastegate.
Can we assume the stock supra CT26 is similar to a GT2860RS (also capable of 340hp)? It can only pass 20lb/min out it's turbine.
TurboByGarrett.com - Catalog
On a diesel you need to push through around 14 lb/min of air for every 100hp. So the 34 lb/min of the supra CT26 would be choked at roughly 240hp diesel.
A GT25 will do 200hp alone, is it worth compound for 40hp?
The big question, what pressure range do you want each turbo to work under?
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- #212
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- #213
Good points,
The Exducer of the CT26 is 52mm/68mm, basically a GT30 Turbine
It isnt much of an increase, I know.......
I was proposing 2.3PR (@25lbs/Min) on the VNT, 1.9PR on the CT26 (20G compressor, 600cfm @ 1.8PR, 640cfm @ 2.0PR)
The GT2860RS has the same size turbine as my VNT (46.9mm exducer). I could probably put in the Disco compressor wheel, problem is poor surge line.
My cousins TD42 gets 202rwhp with this turbo (28psi in the midrange). VERY quick Patrol. Spins all 4 wheel dropping second high range in the mud with 37" Tyres.... Sideways around any corner you want. Probably less than 20:1 AF ratio. Haze smoke in midrange/top end. Makes around 600nm mark. Has been Dynoed for those figures.
Problem is, it surges when trying to make ~ 20psi at 1800-2000rpm range (overfuelling to build exh energy). Hence, I am reluctant to upgrade mine, especially with the VNT.
My VNT compressor, with small trim, big exducer is really well suited for low rpm high boost..... I am sure I posted the map a while back.
Based on the re-evaluation, my CT26 Turbine is definately too small. Probably 50% bypass..........
The Exducer of the CT26 is 52mm/68mm, basically a GT30 Turbine
It isnt much of an increase, I know.......
I was proposing 2.3PR (@25lbs/Min) on the VNT, 1.9PR on the CT26 (20G compressor, 600cfm @ 1.8PR, 640cfm @ 2.0PR)
The GT2860RS has the same size turbine as my VNT (46.9mm exducer). I could probably put in the Disco compressor wheel, problem is poor surge line.
My cousins TD42 gets 202rwhp with this turbo (28psi in the midrange). VERY quick Patrol. Spins all 4 wheel dropping second high range in the mud with 37" Tyres.... Sideways around any corner you want. Probably less than 20:1 AF ratio. Haze smoke in midrange/top end. Makes around 600nm mark. Has been Dynoed for those figures.
Problem is, it surges when trying to make ~ 20psi at 1800-2000rpm range (overfuelling to build exh energy). Hence, I am reluctant to upgrade mine, especially with the VNT.
My VNT compressor, with small trim, big exducer is really well suited for low rpm high boost..... I am sure I posted the map a while back.
Based on the re-evaluation, my CT26 Turbine is definately too small. Probably 50% bypass..........
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- #214
Seems the turbine in my small VNT is the same as the GT2860RS. Does that make it a GT28VNT then?
After a look through many of the turbos on the Garrett site, it seems the difference between a GT25 and a GT28 is the Turbine Trim. On that basis, mine is actually a GT28VNT and now that I think more about it, seems a great match for an automatic.
So, here is a project plan:
(1) Fit current GT28V and water to air intercooler, get VNT control working well.
(2) Upgrade compressor to Mitsubishi 19T, Small 16G or Disco Potato or ? Problem is shaft diameter is 5mm or 5.5mm (cant remember), very small. I would like 48-49mm inducer.
(3) Probably fit a 12HT to my 80 series at this stage
(4) Add second turbo
(5) Snap GT28V turbine shaft and or break conrod under heavy boost.........
#5 notwithstanding, this rational is a gradual approach that allows some learnings.
After a look through many of the turbos on the Garrett site, it seems the difference between a GT25 and a GT28 is the Turbine Trim. On that basis, mine is actually a GT28VNT and now that I think more about it, seems a great match for an automatic.
So, here is a project plan:
(1) Fit current GT28V and water to air intercooler, get VNT control working well.
(2) Upgrade compressor to Mitsubishi 19T, Small 16G or Disco Potato or ? Problem is shaft diameter is 5mm or 5.5mm (cant remember), very small. I would like 48-49mm inducer.
(3) Probably fit a 12HT to my 80 series at this stage
(4) Add second turbo
(5) Snap GT28V turbine shaft and or break conrod under heavy boost.........
#5 notwithstanding, this rational is a gradual approach that allows some learnings.
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The break point between the 25 and 28 series is 53mm overall turbine diameter. If you have a turbine wheel bigger than 53mm, then yes it's a GT28. Between roughly 50.8mm and 53mm it's a GT25, between 50.8 and 48mm it's a GT22.
Remember, model families are based on overall diameter, not trim.
There's appears to be a fair amount of BS in the VNT turbo naming conventions.
So, here is a project plan:
(1) Fit current GT28V and water to air intercooler, get VNT control working well.
(2) Upgrade compressor to Mitsubishi 19T, Small 16G or Disco Potato or ? Problem is shaft diameter is 5mm or 5.5mm (cant remember), very small. I would like 48-49mm inducer.
(3) Probably fit a 12HT to my 80 series at this stage
(4) Add second turbo
(5) Snap GT28V turbine shaft and or break conrod under heavy boost.........
#5 notwithstanding, this rational is a gradual approach that allows some learnings.
T28's wheels have a 6mm bore. So a disco potato (GT28RS) compressor wheel won't fit on your GTV. The reason VNT turbos have a small trim wheel is to prevent surge. If you fit a bigger trim wheel you might be right in the thick of it.
Hope that intercooler can filter out compressor blades.
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- #216
I havent actually measured the inducer of the turbine. I have only concerned myself with the size of the hole the ex must escape....
I have the housing off anyway at the moment, I shall measure it.
The exducer on my little VNT is identical to the exducer on the GT2860RS, thats why I thought it was probably a GT28....but I will get the vernier out!
The Mits 19T wheel has the same bore diameter, 47mm inducer (very similar to DP Compressor), I checked that a while ago. Problem is I dont want to go smaller on the exducer and the induicer is too small for the one turbo to satisfy my power appetite!
I think the intercooler will make a fine filter (no pun intended)
I have the housing off anyway at the moment, I shall measure it.
The exducer on my little VNT is identical to the exducer on the GT2860RS, thats why I thought it was probably a GT28....but I will get the vernier out!
The Mits 19T wheel has the same bore diameter, 47mm inducer (very similar to DP Compressor), I checked that a while ago. Problem is I dont want to go smaller on the exducer and the induicer is too small for the one turbo to satisfy my power appetite!
I think the intercooler will make a fine filter (no pun intended)
VNT's need bigger exhaust exducers because they don't have a seperate wastegate to dump gas out.
I can't see you making any improvement to a VNT turbo by swapping compressor wheels. Some poor engineer at Garrett would have spent months matching that compressor and turbine together.
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- #219
Hi Tapage, yes, many times have I measured the CT26 in variety of forms. Also I have many at home (4). The 1HDT has the same compressor wheel as the Toyota 3S-GTE found in MR2's and GT4 (Alltrac) Celica's. 43mm inducer compared to 7M-GTE 47mm Inducer. The Turbines are exactly the same, the exhaust housings are different. The 3S-GTE housing is a smaller AR, the 1HDT is next biggest and the 7M-GTE is bigger again. I have tried the Supra exhaust housing on the 1HDT, no good, much too big. Less than 3psi before 2000rpm.......
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