T25 turbo, 3" turbo back boost question

[Gamble97]

On my friends car 96 auto gsx he has the following mods:
Cone filter stock piping
dejon upper intercooler piping
1g crushed bov
bc272 cams

The car was spiking at 21psi on the t25. This past weekend we installed
apex downpipe
thermal cat-back
hks ssqv bov
injen intake pipe
very mild ported 02 housing


The car is now spiking and holding at 15psi. I remember on my car when I had the same mods and did the exhaust the boost would spike to 21psi.

Why is the car at 15psi and not spiking where it was.
Thanks

 

[h8r]

First off... WTF is he thinking running a BC 272 with a t-25? That turbo would be maxxed on stock fuel(as it is a stock turbo). The boost was lowered becuase it is more free flowing..less restriction and the car can now breath... a T-25 should not be ran higher then 16 lbs IMO.....and if you do not have a nice clean, no leak ic more like 12-14... Basically he has transplanted the heart of an Olympic runner into a 300 lb fatbody.

 

[h8r]

Besides.... you dont WANT BOOST Spikes... IMO I would have looked for a problem with your set-up for such a searious spike.

 

[G9S6T]

yea dude theres no point in those cams at all at this point. Boost creep is not ever a good thing. Thats how you'll blow a turbo. Porting the 02 housing wastegate and a bigger turbo will get rid of it.

 

[turbodsm18]

Most likely you are not experiencing boost spiking in theory. It is just that the turbo is falling off at high rpms cause well, its the t25.

Also, your friend has no need to be running 272 cams.

 

[laserspeeddemon]

On my friends car 96 auto gsx he has the following mods:
Cone filter stock piping
dejon upper intercooler piping
1g crushed bov
bc272 cams

The car was spiking at 21psi on the t25. This past weekend we installed
apex downpipe
thermal cat-back
hks ssqv bov
injen intake pipe
very mild ported 02 housing


The car is now spiking and holding at 15psi. I remember on my car when I had the same mods and did the exhaust the boost would spike to 21psi.

Why is the car at 15psi and not spiking where it was.
Thanks

Thats why. Porting helps control creep. The turbo itself can not really support more then 15 psi without sufficating itself.

As for the 272 comments from the rest of you, shame on you.

Cams are modification to get more of the air/fuel mixture into the engine. It has nothing to do with turbo sizing. Though ultimately the turbo will determine overall power. I've seen cars with stock 1g's with mild mods and HKS 272 installs net 40 whp gain, granted on a 14b, but still a small turbo.

 

[Gamble97]

Seriously you guys need to chill out about the cams. The timing belt and water pump were getting replaced so why not do cams at the same time?
Also a new turbo is on the way, we are just doing 1 think at a time.

 

[h8r]

Not shame on us..... You are taking about a turbo that RUNS OUT OF STEAM well beofre the Redline, and then Saying lets take it Much more out of it's efficiency range, and while we are at it lets go ahead and leave 20ft lbs of TQ on the table down low... for Horsepower that will never be seen because it may make more hp at 6k but at 7+ the turbo is just adding heat....So IMO.... you are back to square one, maybe even a bit worse.

Seriously you guys need to chill out about the cams. The timing belt and water pump were getting replaced so why not do cams at the same time?
Also a new turbo is on the way, we are just doing 1 think at a time.

Ok.... then why worry about "BOOST SPIKE" if a new turbo is coming?... port the heck out of the 02housing and manifold.

 

[laserspeeddemon]

Not shame on us..... You are taking about a turbo that RUNS OUT OF STEAM well beofre the Redline, and then Saying lets take it Much more out of it's efficiency range, and while we are at it lets go ahead and leave 20ft lbs of TQ on the table down low... for Horsepower that will never be seen because it may make more hp at 6k but at 7+ the turbo is just adding heat....So IMO.... you are back to square one, maybe even a bit worse.

There have been a DSM that has broken 10's with a T-25. Though I would not even attempt such a feat, because it really makes no sence. It can be done. So it shows you that over all power isn't limited to just a turbo selection, more of the combination or parts.

 

[gsxeclipse97]

10's on a t-25 maybe with a 200 shot of nitrous. Im going to have to agree with him 272 with a t25 just seems crazy 2g cams are bad but putting 272 with a turbo that can even hold its own in normal conditons. Then comparing a 14b to the t25 just wont work, the power from those two turbos is just to great of a gap also since the 14b can hold 20 psi to redline, so i could see you running better cams on the 14b just because its a much better turbo for preformance.

 

[Gamble97]

Ok.... then why worry about "BOOST SPIKE" if a new turbo is coming?... port the heck out of the 02housing and manifold.

Ok my question was which was normal, the way his car was boosting or the way my car was boosting. THAT was what i wanted to know. I don't want the car boosting at 21psi.

10's on a t-25 maybe with a 200 shot of nitrous. Im going to have to agree with him 272 with a t25 just seems crazy 2g cams are bad but putting 272 with a turbo that can even hold its own in normal conditons. Then comparing a 14b to the t25 just wont work, the power from those two turbos is just to great of a gap also since the 14b can hold 20 psi to redline, so i could see you running better cams on the 14b just because its a much better turbo for preformance.

Seriously what don't you people understand, the timing belt was changed so why not change the cams at the same time instead of doing it twice? And I said a new turbo is on the way so big deal if I he rocks the t25 for a week or 2.

 

[95CarbonEclipse]

Seriously what don't you people understand, the timing belt was changed so why not change the cams at the same time instead of doing it twice? And I said a new turbo is on the way so big deal if I he rocks the t25 for a week or 2.

He's got a point... who the hell even knows if the guy is going to be driving it. I say, let's stop passing judgement and start helping find a solution.

Typically the best way to get rid of a boost SPIKE is to make sure that you have the shortest length of hose routed for your MBC (ie. don't tap the BOV line). To eliminate boost CREEP, which is often most noticable with a 3" turbo back exhaust, would be to port the hell out of your turbo hotside, o2 housing and exhaust manifold.

By taking those steps to eliminate boost CREEP and boost SPIKES you should be able to hit your desired boost setting and have it stay there (unless the T25 is dying off). On a side note... I haven't heard of people spiking more then a few PSI on a stock T25. And 'normal' boosting shouldn't involve any spiking or creep, IMHO.

 

[G9S6T]

Make sure the wastegate actuator is opening up properly. Also make sure that type-s isnt leaking. Another way to get rid of boost creep with bigger turbo's is switching to an external wastegate.

 

[95CarbonEclipse]

Make sure the wastegate actuator is opening up properly. Also make sure that type-s isnt leaking. Another way to get rid of boost creep with bigger turbo's is switching to an external wastegate.

True... I forgot to mention that.

 

[h8r]

OK.... !0's on a t-25 is irrelevant to this situation... So what... a gutted car prob. weighing 2000 lbs with 350o hp At the wheels with a time bomb tune and a shit load of nitrous.. Who Really cares.. My point was why be flooring a car to redline with a turbo that is not being optimized... Boost Creep is not ideal... it has been answered many times.. You are over working a SHITTY turbo. CASE CLOSED.... To fix it... Do like what alot have said ALE|READY..... port the hot side, make all boost controlling hoses short as possible..etc...

 

[Gamble97]

Why in the hell would I port the t25 when i clearly said a new turbo was on the way. If you can't help they why are you posting?

 

[delta448]

Ok my question was which was normal, the way his car was boosting or the way my car was boosting. THAT was what i wanted to know. I don't want the car boosting at 21psi.

Make sure the wastegate actuator is opening up properly. Also make sure that type-s isnt leaking. Another way to get rid of boost creep with bigger turbo's is switching to an external wastegate.

I think hitting 21psi on a T25 is pretty pointless and not exactly a good thing, although it is probably a pretty typical result if you don't have cams, have a 3" turboback exhaust and disconnect the WG actuator. There is no way it will hold that much boost very high in the rpms and eventually you'll destroy the little turbo. It doesn't matter though since you are getting a bigger one soon anyways. I applaud you for making the turbo the last upgrade on your list.

I think G9S6T hit the nail on the head. If you are seeing that much boost and holding with a T25, especially on an engine with 272 cams, I am inclined to think that either your gauge is wrong or you are overspinning the crap out of the little snail. I say check the wastegate. A bigger turbo however will not be so much of a concern with regards to boost creep, just make sure you are able to maintain control of it, or have enough fuel and tune ability to run at the crept-to boost level.

 

[95CarbonEclipse]

Even with the new turbo you're going to want to port the hotside, the o2 housing, and the exhaust manifold. Boost creep is more prevailant on bigger turbos' compared to the T25. Mainly due to sheer size. I'm positive that once you get your new turbo installed, ported and polished and everything. You'll be hitting your 'dialed in' boost level and holding.

Congrats on the upgrade. You're going to LOVE IT!

 

[delta448]

Even with the new turbo you're going to want to port the hotside, the o2 housing, and the exhaust manifold. Boost creep is more prevailant on bigger turbos' compared to the T25. Mainly due to sheer size.

We should be more specific.

Port the crap out of the wastegate side if you're using a small internal gate on a turbo that needs more control. Running the WG to atmosphere also helps whether internally or externally gated. Bigger turbos are only a boost creep concern if the wastegate being used isn't large enough. Example: stock internal wastegated 16Gs. If you use an (appropriately sized) external WG, like most large turbos (> 50 trim) require, boost creep is far less likely to occur.

 

[daren_p]

On my friends car 96 auto gsx he has the following mods:
Cone filter stock piping
dejon upper intercooler piping
1g crushed bov
bc272 cams

The car was spiking at 21psi on the t25. This past weekend we installed
apex downpipe
thermal cat-back
hks ssqv bov
injen intake pipe
very mild ported 02 housing


The car is now spiking and holding at 15psi. I remember on my car when I had the same mods and did the exhaust the boost would spike to 21psi.

Why is the car at 15psi and not spiking where it was.
Thanks

Probably because the cams can increase the VE a good amount but the stock exhaust was still a big bottle neck so you didn't realize this increase in VE. Now upgrade the exhaust to a nice free flowing unit & the VE now jumps up a good amount. The puny T25 is no longer able to keep up to the demands, so no more boost spike.

I too would have said the 272's were a dumb move for the T25 but I also would have asked if there was a reason for adding these cams (ie turbo upgrade in the future) before saying so . Looks like your friend is on his way to a nice setup

 

[Gamble97]

Probably because the cams can increase the VE a good amount but the stock exhaust was still a big bottle neck so you didn't realize this increase in VE. Now upgrade the exhaust to a nice free flowing unit & the VE now jumps up a good amount. The puny T25 is no longer able to keep up to the demands, so no more boost spike.

I too would have said the 272's were a dumb move for the T25 but I also would have asked if there was a reason for adding these cams (ie turbo upgrade in the future) before saying so . Looks like your friend is on his way to a nice setup

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