Limitations of CT26 power outputs

SilverGhost · Sep 20, 2004

Hey all,

Im writing from Sydney and I have done quite a bit of research over the last 12 months since the purchase of my 185 into the fundamentals of forced induction. I have read countless forums of people stating the same old thing (bigger turbo, FMIC, Custom EMS) and it just gets tired.

Dont get me wrong these are all ligitimate upgrades, but only depending on your goals.

Take the CT26 for example, love it or hate it, it is the beating heart of all but the newest shape gt-fours (alltracs) and yet people are so quick to rip it out or clip it, or put in a bigger trim compressor, or go through the above bracketed upgrades. This has always baffled me because I never see people posted that they run their cars at 16+ psi boost, which would be the only reason why you would need a bigger turbo.

Toyota did a brilliant job matching their ceramic turbine driven hairdryer to the rally bred, hard as nails 3S-GTE, because I personally have a turbo with atleast 50,000kms on it (just over 31000miles) and im getting 14psi strong right up to the redline.

Engine basics tell us that if your not increasing displacement with more cubes then you need to cram more air/fuel in under pressure. Hence, if your running a 2.0 litre 3S-GTE at 14psi boost with a CT26 it will make no difference than running a T04 turbo at 14psi boost.

My rather long winded point is that people believe that the CT26 will run out of air (actual volume of flowed compressed air) towards the redline at anymore than say 12psi boost, but I have found this to be un true.

Engines develop the most power from fuel when they are running to Stoichiometry. either side of about 14.7-1 air/fuel ratio you are losing power. So, the only way to increase power from a turbocharged motor is to increase displacement, or boost pressure, simple as that.

Upgrading your turbo is only really a feasible option if you intend to run 16+psi of boost on a balanced engine which would be revving beyond the stock redline. That is where, and only where a turbo with a higher flow rate would be required.

I write this to hopefully get many responses from people in this forum who have poured their blood sweat and tears into what i consider the best cars on the road, because I respect your knowledge and experience. Thans for reading!

OlyST185 · Sep 20, 2004

hi there, glad to see another GT-Four owner here.
first of all, why we upgrade the turbo or change it, its because the CT26 is small and isnt in ceramic here in north america. it CAN'T boost up to the redline. You have the more powered japan spec, we do not. America is a real pitty for japaneses cars.
So if we upgrade the turbo we can get power to redline. and bigger trim = less heat, witch prevent detonation.
The little CT26 will only push hot air beyong 16psi while a bigger trim will be able to do it no problem. and what, if we want more power, we gotta remove that ''turbette'' as i call it. The CT26 is big compared to a T25 or a WRX IHI turbo, but still very small for serious power gain.
but again its a matter of your goal, if your goal is 300hp, the CT26 will be ok. if you want more, you have to upgrade it or simply change that turbo.

AwdGte · Sep 20, 2004

You should read up on the physics behind how a turbocharger works

14 pounds from one turbo is in no way comparable to 14 pounds from another. Each turbo has a different compressor map, or a diagram of how well and efficient it compresses air based on pressure it is asked to make and rpm it is turning. A larger turbo has longer blades so that it can ingest more air per revolution and have more centripital force push it against the outter diameter of the compressor housing when it is rotating, to compress more air, longer. It does not work as well as smaller turbos at lower air volumes, because each turbo has a peak efficiency range or sweet spot at which it operates optimally.

This is a short undetailed explanation of how turbochargers create boost, I would recommend reading up on that and compressor maps. Let me know if you have any questions

SilverGhost":1537bf9p said:
Hey all,

Im writing from Sydney and I have done quite a bit of research over the last 12 months since the purchase of my 185 into the fundamentals of forced induction. I have read countless forums of people stating the same old thing (bigger turbo, FMIC, Custom EMS) and it just gets tired.

Dont get me wrong these are all ligitimate upgrades, but only depending on your goals.

Take the CT26 for example, love it or hate it, it is the beating heart of all but the newest shape gt-fours (alltracs) and yet people are so quick to rip it out or clip it, or put in a bigger trim compressor, or go through the above bracketed upgrades. This has always baffled me because I never see people posted that they run their cars at 16+ psi boost, which would be the only reason why you would need a bigger turbo.

Toyota did a brilliant job matching their ceramic turbine driven hairdryer to the rally bred, hard as nails 3S-GTE, because I personally have a turbo with atleast 50,000kms on it (just over 31000miles) and im getting 14psi strong right up to the redline.

Engine basics tell us that if your not increasing displacement with more cubes then you need to cram more air/fuel in under pressure. Hence, if your running a 2.0 litre 3S-GTE at 14psi boost with a CT26 it will make no difference than running a T04 turbo at 14psi boost.

My rather long winded point is that people believe that the CT26 will run out of air (actual volume of flowed compressed air) towards the redline at anymore than say 12psi boost, but I have found this to be un true.

Engines develop the most power from fuel when they are running to Stoichiometry. either side of about 14.7-1 air/fuel ratio you are losing power. So, the only way to increase power from a turbocharged motor is to increase displacement, or boost pressure, simple as that.

Upgrading your turbo is only really a feasible option if you intend to run 16+psi of boost on a balanced engine which would be revving beyond the stock redline. That is where, and only where a turbo with a higher flow rate would be required.

I write this to hopefully get many responses from people in this forum who have poured their blood sweat and tears into what i consider the best cars on the road, because I respect your knowledge and experience. Thans for reading!

SilverGhost · Sep 20, 2004

Hi Guys,

Im glad that my post brought some different view points to the discussion. I honestly thought that I would be beat down because I didnt cover areas like volumetric, thermal and mechanical efficiencies for power gains. let alone free flowing exhausts or optimal ignition maps.

But yes, you are correct about different turbo compressor maps. This was what I wanted to hit with my previous statement. I cant picture the difference between the 2 turbos creating the same boost at the same rev range except the difference in shaft speed.

OlyST185 wrote: So if we upgrade the turbo we can get power to redline. and bigger trim = less heat, witch prevent detonation.
The little CT26 will only push hot air beyong 16psi while a bigger trim will be able to do it no problem.

Im not sure I follow. The reason for heat build up in the charge air is solely because of the compresion of that air. Granted a bigger trim can compress more air more 'efficiently' for the want of a better word but trim size has nothing to do with heat buildup.

The only way I can see that working is if the higher rotational speed of the compressor itself causes more friction with the air that a larger trim. But that doesnt sound right.

My point is that your engine at a certain rev rate, throttle position and boost level will always use the same amount of air regardless of turbo size, so if the standard snail can hold that kind of boost pressure why upgrade it?

I appreciate your replies, this is becoming an involving hobby of mine as you can probably tell

Griffin · Sep 20, 2004

I have a CT26 and I run it at 24 PSI. Its clipped and has a larger compressor and its still not enough turbo - its way outside its efficiency island and while the car pulls to 8500 I could easily make better power and spool faster with a better turbo. It also is heating the air like crazy because its not running at peak efficiency.

mtbgael · Sep 20, 2004

SilverGhost":grclk7yk said:
OlyST185 wrote: So if we upgrade the turbo we can get power to redline. and bigger trim = less heat, witch prevent detonation.
The little CT26 will only push hot air beyong 16psi while a bigger trim will be able to do it no problem.

A larger trim allows exhaust to flow more freely past the turbine, making the turbo more "efficient" when large amounts of exhaust are flowing (high rpm). It will spool a little later, but it's ability to flow means it will hold power in high rpms better. Go too large though, and the turbo will never spool.

SilverGhost":grclk7yk said:
My point is that your engine at a certain rev rate, throttle position and boost level will always use the same amount of air regardless of turbo size, so if the standard snail can hold that kind of boost pressure why upgrade it?

It can't, that's the problem. Get an accurate boost gauge and monitor boost as you get to redline.

MrWOT · Sep 20, 2004

Griffin":2ykoq81l said:
I have a CT26 and I run it at 24 PSI. Its clipped and has a larger compressor and its still not enough turbo - its way outside its efficiency island and while the car pulls to 8500 I could easily make better power and spool faster with a better turbo. It also is heating the air like crazy because its not running at peak efficiency.

A CT26 at 24 psi....... that just ain't right :twisted: ... no matter what you do to it I don't see how you can get the internal wastegate to not creep at that kind of pressure/rpm. What did you do to that poor thing?

Griffin · Sep 20, 2004

MrWOT":3a6u8lw1 said:
Griffin":3a6u8lw1 said:

I have a CT26 and I run it at 24 PSI. Its clipped and has a larger compressor and its still not enough turbo - its way outside its efficiency island and while the car pulls to 8500 I could easily make better power and spool faster with a better turbo. It also is heating the air like crazy because its not running at peak efficiency.

Click to expand...

A CT26 at 24 psi....... that just ain't right :twisted: ... no matter what you do to it I don't see how you can get the internal wastegate to not creep at that kind of pressure/rpm. What did you do to that poor thing?

3 washers between the wastegate bracket and the compressor housing

The downside is that I can't make less than like 18 PSI even at 0 percent duty cycle on the solenoid, but thats not much of a downside IMO

RedCelicaTRD · Sep 20, 2004

What kinda duty cycles are you seeing at 24psi? I was only planning on running mine up to 22psi and 7250rpm. And are you using the stock boost control solenoid or the GM?

Mafix · Sep 20, 2004

you guys are nuts. i would never take mine over 20 psi. On the flip side is the japanese turbo different from the us spec?

RedCelicaTRD · Sep 20, 2004

Well neither one of us have stock ct-26s and we both have an aftermarket EMS. I think the JDM ones came with a ceramic turbine which can blow itself to pieces pretty easy at high boost......

MrWOT · Sep 20, 2004

Griffin":1x51jkn1 said:
3 washers between the wastegate bracket and the compressor housing

The downside is that I can't make less than like 18 PSI even at 0 percent duty cycle on the solenoid, but thats not much of a downside IMO

:doh:

24psi on a ct26, regardless of the compressor you cram in there that's got to be under 70% adibiatic efficiency, what the hell are you using for fuel? It's gotta be close to detonation even on 100 with the stock IC or even a decent sized fm with that pressure ratio.

Griffin · Sep 21, 2004

MrWOT":93zhtlm7 said:
Griffin":93zhtlm7 said:

3 washers between the wastegate bracket and the compressor housing

The downside is that I can't make less than like 18 PSI even at 0 percent duty cycle on the solenoid, but thats not much of a downside IMO

Click to expand...

:doh:

24psi on a ct26, regardless of the compressor you cram in there that's got to be under 70% adibiatic efficiency, what the hell are you using for fuel? It's gotta be close to detonation even on 100 with the stock IC or even a decent sized fm with that pressure ratio.

91 octane - my intake temps are about 115 F with the FMIC at 24 PSI and I have IK27s in there - knock is quiet as a churchmouse. Remember I have full control over timing and fuel with the AEM - anyplace knock was bad I just added a bit of fuel and backed out the timing a tad. I make a lot more power on 103 with more agressive timing, but I haven't made that map yet.

Griffin · Sep 21, 2004

RedCelicaTRD":2ql4tsbj said:
What kinda duty cycles are you seeing at 24psi? I was only planning on running mine up to 22psi and 7250rpm. And are you using the stock boost control solenoid or the GM?

Thats with the wastegate at 85% duty cycle. 0% nets me about 18 PSI max, maybe 20 under super high load in 4th. Thats with teh stock boost controller. I am pretty certain I can get more out of it if I get an aftermarket solenoid though - the stock one doesn't allow me to bleed off much air.

AwdGte · Sep 21, 2004

It will not ingest the same amount of air always, but will have the same volumetric efficiency rating. You need to take into account, the thermal efficiency of the turbocharger

The less heated the compressed air is, or the more efficiently it is compressed, the more dense it will be and more fuel is required to offset that.

SilverGhost":m4hh17hv said:
Hi Guys,

Im glad that my post brought some different view points to the discussion. I honestly thought that I would be beat down because I didnt cover areas like volumetric, thermal and mechanical efficiencies for power gains. let alone free flowing exhausts or optimal ignition maps.

But yes, you are correct about different turbo compressor maps. This was what I wanted to hit with my previous statement. I cant picture the difference between the 2 turbos creating the same boost at the same rev range except the difference in shaft speed.

OlyST185 wrote: So if we upgrade the turbo we can get power to redline. and bigger trim = less heat, witch prevent detonation.
The little CT26 will only push hot air beyong 16psi while a bigger trim will be able to do it no problem.

Im not sure I follow. The reason for heat build up in the charge air is solely because of the compresion of that air. Granted a bigger trim can compress more air more 'efficiently' for the want of a better word but trim size has nothing to do with heat buildup.

The only way I can see that working is if the higher rotational speed of the compressor itself causes more friction with the air that a larger trim. But that doesnt sound right.

My point is that your engine at a certain rev rate, throttle position and boost level will always use the same amount of air regardless of turbo size, so if the standard snail can hold that kind of boost pressure why upgrade it?

I appreciate your replies, this is becoming an involving hobby of mine as you can probably tell

furpo · Sep 21, 2004

i have found the limit of the standard jdm spec ct26. we made 280 wheel hp with a fmic, after market ecu, exhaust and 18 psi boost. any more boost than this and too much ignition timing had to be pulled out and power was lost. at 3000 ish rpm we could run up to 24 psi with big torque gains. yaaaaa for map-able boost controllers.

i came to the conclusion that the compressor side was the limiting factor. we monitored egt's and manifold pressure and they both started going through the roof at about 265 hp.

i would like to see how the supra spec ct26 goes but have not tryed it yet. we then did a back to back test of the evo3 tdo5 which made 320 ish wheel hp on the same engine with a manifold to suit. with this turbo imo the turbine was still the restriction.

roger

ps. 320 hp was pushing the std injectors aswell.

Griffin · Sep 21, 2004

furpo":14hd728n said:
i have found the limit of the standard jdm spec ct26. we made 280 wheel hp with a fmic, after market ecu, exhaust and 18 psi boost. any more boost than this and too much ignition timing had to be pulled out and power was lost. at 3000 ish rpm we could run up to 24 psi with big torque gains. yaaaaa for map-able boost controllers.

i came to the conclusion that the compressor side was the limiting factor. we monitored egt's and manifold pressure and they both started going through the roof at about 265 hp.

i would like to see how the supra spec ct26 goes but have not tryed it yet. we then did a back to back test of the evo3 tdo5 which made 320 ish wheel hp on the same engine with a manifold to suit. with this turbo imo the turbine was still the restriction.

roger

ps. 320 hp was pushing the std injectors aswell.

Wow that was completely unmodified? Those are some good numbers if thats the case.

furpo · Sep 21, 2004

the exhaust side of the turbo was matched to the manifold but nothing like a porting that would change the a/r rating. this was done because production tolarance is rather large, i have seen up to 3mm mis allignment. this exhaust housing represents the factory best case senario.

roger

OlyST185 · Sep 22, 2004

the best thing to do is to have an external wastegate and 18inches minimim before the wastegate's piping go to the exhaust line.
this way it will not have disturbances in the exit of the turbine.
this mean a better flow while providing a bit better low end performance with no boost.

alltracman78 · Sep 22, 2004

mtbgael":1itvpcmx said:
A larger trim allows exhaust to flow more freely past the turbine, making the turbo more "efficient" when large amounts of exhaust are flowing (high rpm). It will spool a little later, but it's ability to flow means it will hold power in high rpms better. Go too large though, and the turbo will never spool.

SilverGhost":1itvpcmx said:

My point is that your engine at a certain rev rate, throttle position and boost level will always use the same amount of air regardless of turbo size, so if the standard snail can hold that kind of boost pressure why upgrade it?

Click to expand...

It can't, that's the problem. Get an accurate boost gauge and monitor boost as you get to redline.

A lager trim would not necessarily allow more flow around it. That is the function of the ar ratio, which the turbine, or compressor wheel, has nothing to do with. It is all the housing.
If you got the turbine clipped, it would allow more flow around it however.

My 93 and 92 both held 10 psi on stock turbo to redline. My 92 now has a 50t compressor, and holds 12.5 psi to redline.

Limitations of CT26 power outputs

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