Question for all of you running T25's....

[AWDrift]

Like the title says, I've got a question for you stock turbo 2G owners.

Can you hold 15psi at 50% throttle?

I searched and didn't find much discussion of part throttle boosting. Now we all know that the T25 isn't good for much beyond 15psi, and my car is hitting that at half throttle. Is something not right? or is this normal? This will help me troubleshoot other things, and maybe find out if my car isn't as stock as I believed.

Thanks

 

[Defiant]

Boost isn't only a matter of throttle position. Much more important is engine load.

 

[AWDrift]

Boost isn't only a matter of throttle position. Much more important is engine load.

Sorry, should have clarified. Normal conditions: no hills, no wind, no additional weight, no a/c, etc. Nothing else that I'm aware of that would increase load.

 

[taylorspl]

I don't recall even hitting full boost at 1/2 throttle in any of the 5 gears. This is an odd question, why are you asking?

 

[OneFastEclipse]

A T-25 turbo is capable of 15 psi. Only going 50% throttle can get you there as well. It is such a small turbo it takes very little flow from the motor to get it there. Are you reaching this 15psi while starting from a stop? Are you reaching this at 50% throttle at 4krpm or more? Both of those would have more load on the engine making it very easy to spool the turbo with little to no gas. A good way to tell if it is in fact a T25 rather than just looking at the turbo is just plan down right floor it. If it holds 15psi to your redline without droping back to say 10-12psi by 6 or 7k rpm, there is a good chance it's not a T25. The only sure way to tell though is to simply look.

 

[Defiant]

Like the title says, I've got a question for you stock turbo 2G owners.

Your profile mentions mods. An MBC isn't stock. How's it adjusted?

 

[dalatinromeo]

if your curious whether it is a t25 is to do what OneFastEclipse mentioned. floor the car and if the boost holds to redline without dropping off then more then likely you don't have a t25. but if you really want to know if you have a t25 just look.

 

[AWDrift]

No, I'm not questioning if I have a T25. I was referring to 2nd gens with a stock turbo, not stock 2nd gen cars. I'm still playing around with my mbc, it is spiking 4+ psi and I'm trying to figure out why. It is currently set to spike to 16 then drop to 12.

Yeah I've shortened the vacuum hoses, boost leak test, all that stuff.

In pretty much any condition, It feels like at least the last 25% of throttle doesn't make the car any faster, because it already reaches maximum boost. Doesn't seem normal to me, and I was just confirming that.

 

[Attack Eagle]

normal. and perfectly fine.

t25 spools so fast with any decent exhaust it spikes by a few PSI extremely briefly before settling.

Yeah I could and would get full 14-15 psi with 50% throttle on the t25, without an MBC. Absolutely normal.

 

[AWDrift]

Thanks, thats the kind of thing I was hoping to hear. Although, I'm on stock exhaust and it is still spiking more than a few psi. Back to the drawingboard I guess.

Thanks for the replies.

 

[dalatinromeo]

when does your boost usually drop off? around what rpm??

 

[AWDrift]

With the way my mbc is set up now, I haven't checked. In the past it has never held 15psi past about 5500 rpms.

 

[Attack Eagle]

again, that is normal.

it's one of the reasons the t25 is nick'ed the t 2small. after 5500 rpms it has reached max ouput and the boost falls as rpms rise.

 

[dalatinromeo]

yup perfectly normal happens to me all the time. thats why tonight i will be so happy when i get my 14b, from a friend

 

[daren_p]

Yes the t25 is extremely small but boost is related to load & throttle. If your boost controller is set @ 15 then you should only see 15 when you are/close to wot. You shouldn't see full boost at half throttle with any turbo as far as I know (even with the tiny t25). If you are seeing max boost without wot check how your boost controller is hooked up & make sure it's functioning correctly. Do you disconnect the bcs when you installed the mbc?

 

[AWDrift]

BCS is plugged in but hoses aren't connected. MBC is hooked up correctly, I've taken it apart, put it back together, everything looks fine. Any ideas?

 

[Attack Eagle]

Yes the t25 is extremely small but boost is related to load & throttle. If your boost controller is set @ 15 then you should only see 15 when you are/close to wot. You shouldn't see full boost at half throttle with any turbo as far as I know (even with the tiny t25). If you are seeing max boost without wot check how your boost controller is hooked up & make sure it's functioning correctly. Do you disconnect the bcs when you installed the mbc?

It's normal onthe t25 daren for it to do so.

You have enough exhaust flow at partial throttle to get full boost. Part of the reason I am seriously thinking of dumping my now failing t28 and going back to a t25. I don't like having to floor it to get and use boost, and I sure don't like the delay.

 

[daren_p]

It's normal onthe t25 daren for it to do so.

You have enough exhaust flow at partial throttle to get full boost. Part of the reason I am seriously thinking of dumping my now failing t28 and going back to a t25. I don't like having to floor it to get and use boost, and I sure don't like the delay.

That doesn't seem right to me, you shouldn't be seeing full boost under part throttle conditions. It's been a while since I had the t25 on but mine didn't make full boost at part throttle (this is on level ground of course). Now I know obviously it made more boost at part throttle then my evoIII turbo (nowere's close to the same amount of airflow though ) I would see maybe 10 psi at half throttle when my boost was set at 16. This was with a proper functioning mbc hooked up from the comp housing to the mbc & then to the wg (bcs deleted).

I hope I don't have to say this but you are looking at a real boost gauge & not the factory in dash gauge?

 

[Attack Eagle]

That doesn't seem right to me, you shouldn't be seeing full boost under part throttle conditions. It's been a while since I had the t25 on but mine didn't make full boost at part throttle (this is on level ground of course). Now I know obviously it made more boost at part throttle then my evoIII turbo (nowere's close to the same amount of airflow though ) I would see maybe 10 psi at half throttle when my boost was set at 16. This was with a proper functioning mbc hooked up from the comp housing to the mbc & then to the wg (bcs deleted).

I hope I don't have to say this but you are looking at a real boost gauge & not the factory in dash gauge?

I never ran an MBC on the t25. And yes... or close enough, I'd pull 14 psi at part throttle and max boost was about 15-16(for about 1000 rpm ) I just wouldn't get the big spoolup spike at part throttle, only at 75%+ (I rarely have pushed it to the floor). It will spool like a little mofo, which is why I want it back for my daily driver. I don't like having to press the gas to near WOT to get boost or waiting the t28 to spool. I am going back as soon as I finda decent t25.

 

[daren_p]

I never ran an MBC on the t25. And yes... or close enough, I'd pull 14 psi at part throttle and max boost was about 15-16(for about 1000 rpm ) I just wouldn't get the big spoolup spike at part throttle, only at 75%+ (I rarely have pushed it to the floor). It will spool like a little mofo, which is why I want it back for my daily driver. I don't like having to press the gas to near WOT to get boost or waiting the t28 to spool. I am going back as soon as I finda decent t25.

Just as a side note, there must be something really wrong with your setup (turbo?) I never have to go near wot to spool the evo enough to pass etc. (unless I want too ) ~ 5 psi at part throttle pulls alot better then the t25 at almost max boost. I see 18 psi by 3300 rpms, 15 is around 3100 which is pretty much what the t25 spools at from factory (I used to see 16 psi by 2900 with all intake & exhaust restrictions removed & everything ported, obviously with all the factory restrictions the spool time is longer). Your t28 should spool faster then the evo, these are not laggy turbo's at all and at any throttle or rpm position will out preform the t25.

 

[Attack Eagle]

Just as a side note, there must be something really wrong with your setup (turbo?) I never have to go near wot to spool the evo enough to pass etc. (unless I want too ) ~ 5 psi at part throttle pulls alot better then the t25 at almost max boost. I see 18 psi by 3300 rpms, 15 is around 3100 which is pretty much what the t25 spools at from factory (I used to see 16 psi by 2900 with all intake & exhaust restrictions removed & everything ported, obviously with all the factory restrictions the spool time is longer). Your t28 should spool faster then the evo, these are not laggy turbo's at all and at any throttle or rpm position will out preform the t25.

I was spooling by 2200 on the t25. Light up all 4 leaving an intersection, boosting out of the corners with full boost power. I drive in the 10% to 50% range, not 505 + range, and in the 2000 to 5000 range not 3000-700k range. I jsut don't like it, I liked it better on my t25. Even if it is slower in the 1/4 mile it's not slower thru 40mph.

 

[daren_p]

I was spooling by 2200 on the t25. Light up all 4 leaving an intersection, boosting out of the corners with full boost power. I drive in the 10% to 50% range, not 505 + range, and in the 2000 to 5000 range not 3000-700k range. I jsut don't like it, I liked it better on my t25. Even if it is slower in the 1/4 mile it's not slower thru 40mph.

My listed spool up times seem longer then your because they were based off logs from dsmlink, giving me intake mani pressure which seems to take longer then when your boost gauge will read full boost. My t25 used to spool 16 psi right around the same as you 2200-2400 rpms (showing 2900 full spool on log) so from that my evoIII spools the same boost maybe 300 or 400 rpms slower, but you have to remember the evo @ 10 psi will flow more air the the t25 @ 15 so basically you are flowing more air no matter what rpms even if you don't reach full boost as fast. I've just never heard anyone say they want the t25 back for any type of driving WTF . If I never went over 5000 rpms or 50% throttle I'd still never want that POS turbo back on but thats just my opinion

Edit: Well I wanted to check for myself so I compared some logs on both the t25 & the EVOIII, it looks like from 2000 to 3000 rpms the t25 does have abit more airflow (2 lb/min or less, 1 lb/min is ~ 10 hp) but as soon as you hit 3000 the evo makes more and increases drastically. So if you always drive your car from 2000-3000 rpms, then stick with the t25 .

 

[Attack Eagle]

you know that is a myth right?

10 psi isthe same amount of air whether from a t25 or a e16g or a holset.

bigger turbos let you run bigger psi numbers over a larger rpm range, with out losing compressor efficiency.

The feel and instant boost ofthe t25 is what convinced me to get the 2g instead of a big v8 powered vehicle, or a Mk iV Supra. I hate not having boost instantly available midcorner.

Go slow down to 30 mph in 2nds and take a 90 corne, hit the gas mid corner and tell me if you get boost before you are out or not. That is what I am used to. Straightline 1/4 mile aceleration I could care less about. I mean c'mon do you really need a faster than low 14's high 13's car in traffic as a family car/daily driver?

 

[daren_p]

you know that is a myth right?

10 psi isthe same amount of air whether from a t25 or a e16g or a holset.

bigger turbos let you run bigger psi numbers over a larger rpm range, with out loosing compressor efficiency.

The feel and instant boost ofthe t25 is what convinced me to get the 2g instead of a big v8 powered vehicle, or a Mk iV Supra. I hate not having boost instantly available midcorner.

Go slow down to 30 mph in 2nds and take a 90 corne, hit the gas mid corner and tell me if you get boost before you are out or not. That is what I am used to. Straightline 1/4 mile aceleration I could care less about. I've never been to a drag race and never will.

10 psi is the same on a t25 & a 50 trim, your not serious are you? Sorry that is not a myth, they may be the same pressure but they are no wears close on volume of air.

So if 15 psi is the same on both the t25 & the evoIII how come my injector duty cycle was about 70% with the t25 & the same boost on the evoIII I saw 107% duty cycle .

 

[Attack Eagle]

cooler denser charge.


it's the same volume at the same pressure.

CFM incoming air > CFM consumed = boost psi.

same boost psi = same incoming air quantity/volume.