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View Full Version : 2.5" or 3.0" Downpipe?



Inthered
08-25-2004, 12:15 PM
What is the better setup - 2.5" or 3.0" downpipe? This is for a TDO5H (2nd gen talon) turbo on a 4agze engine. I want it to spool quickly, yet still make good top end. I am going to be running about 10-12psi on the engine. What do you guys think I'll be making for power at the wheels?

I also want to ceramic coat the exhaust side of the turbo. I heard this spools the turbo faster, as well as keeping the engine compartment. Any input on this?

I know I'm limited power potential on the TDO5H, but I figured it would be a good match on my 4agze engine.

Any suggestions would be appreciated.

legendboy
08-25-2004, 12:52 PM
definatly no where close to needing a 3" dp

Inthered
08-25-2004, 01:05 PM
I thought that it might be a bit big. Thanks for the tip.

What about ceramic coating the exhaust side of the compressor for better spool?

legendboy
08-25-2004, 01:35 PM
Nothing you should bother doing to increase the performance at the power lever your gonna be at (<200whp)

EK 2.0
08-25-2004, 01:38 PM
IMO...a 3 Inch DP is MINIMUM for a turbo application...it will help turbo spool up time, AND as well decrease temps...

cycosis
08-25-2004, 01:40 PM
Originally posted by CycloneAWD
IMO...a 3 Inch DP is MINIMUM for a turbo application...it will help turbo spool up time, AND as well decrease temps...
what he said ***

tsi_neal
08-25-2004, 02:16 PM
Originally posted by CycloneAWD
IMO...a 3 Inch DP is MINIMUM for a turbo application...it will help turbo spool up time, AND as well decrease temps...

ill third that, you may not be anywhere near maxing out the potential of the 3", but you will notice some improvement over a 2.5".
Consider ceramic coating a heat treatment only, while it will give you "some" improvement over nothing were talking very very minimal gains

Oh btw the TDO5H is a 14b/16g (1G/JDM) compressor housing... im not sure what the T-25 (2G) uses but it's something different

DSMer4Life
08-25-2004, 02:44 PM
Are you talking about a first gen 90-94 DSM turbo (14B), or a second gen 95-on DSM turbo (T25)?

The 14B is larger (405cfm) and will give you more top end. The T25 will spool up quicker, but will definitely drop off at higher rpms. What compression will you be running? I don't think either turbo would appreciate more than 9.5:1 at 10-12psi. I have no idea what power you'll make though (too many other factors to say).

Regardless of which turbo you choose, a 3" downpipe will contribute to boost creep, without any porting done to the wastegate and a larger wg flapper door. This is something to consider if you don't plan on going all out and doing the porting and such.

For flow, yes, a 3" exhaust is the way to go. But be prepared to put in the time to do it right. Otherwise, you'll be reluctantly lifting your foot of the gas to control your boost!

Oh yeah, ceramic coating of the turbine side is beneficial to keeping exhaust gases flowing through the turbo and keeping temps down in the engine bay. Good luck with your project!

legendboy
08-25-2004, 03:03 PM
Oh I guess you better go 3" dp then lol :rolleyes:

Inthered
08-25-2004, 03:28 PM
The turbo says TDO5H on the side of it. I was told it was out of a 2nd gen talon?? The 4agze that I have has 8.0:1 compression. It also has forged pistons, so it should be able to handle a bit of boost.

I might be getting someone to make me a dumptube for the turbo. Since the turbo has an internal wastegate, I thought it would be benefitial to build a seperate pipe for the wastegate gases.

I was checking on the calgary dsm board and found the picture below. The turbo is off a dsm and has a nice looking dumptube attached to it! How's this for high boost?

Inthered
08-25-2004, 03:43 PM
I will be running a 2.25" exhaust w/cat. Down the road I might buy a 3" exhaust, but not right away.

BTW, how well would a manifold like the one pictured flow? Is it a good design? I would like to see some good designs if possible. I will be getting a buddy to build me one if he has time, so it would be good to give him something that will flow good.

What size injectors will I need to boost 10-12psi with a t25?

djfob
08-25-2004, 04:09 PM
Originally posted by legendboy
definatly no where close to needing a 3&quot; dp

I would also have to second this unless your planning on building the engine and upping the boost. A 2.5" dp and exhaust would be more than sufficient for your needs. I would rather trade off for a bit slower spool up time than having boost creep. And for how quickly the t25 spools up I doubt you'll even notice the difference.

legendboy
08-25-2004, 04:15 PM
Definatly going to be NO measureable difference at this power level. None of these proposed mods listed in this thread will have any effect whatsoever.

Inthered
08-25-2004, 07:38 PM
Thanks for all the replys everyone!

What sort of power output will make these mods effective? I'm assuming I'd have to be making over 250-300whp for those mods I mentioned?

tsi_neal
08-25-2004, 10:41 PM
a 3" exhaust wont start to be a restriction untill well above 500hp (crank) but it all depends on setup. But the thing is if your going to pay someone xxx dollars to fab up a 2.5" exhaust the 3" is only going to cost literally a few bucks more (say 50 bucks), and doesnt hurt anything so why not.

oh a 2.5" exhaust will start showing its weakness somewhere around 350hp (crank again)

and IMO the ceramic coating is just a engine bay heat thing... like figure a couple ponies on a well built maxing out the turbo setup. might help it spool 25rpm sooner sorta thing. you know the no matter what the seat of the pants feels nothing and a good dyno wont be consistant enough to relyably measure the difference. not to say its a bad idea tho, less heat in the engine bay is always good.

googe
08-26-2004, 01:03 AM
Originally posted by legendboy
Definatly going to be NO measureable difference at this power level. None of these proposed mods listed in this thread will have any effect whatsoever.

well if a 2.5" and a 3" is going to be the difference between boost creep or no, its obviously quite measureable.

Inthered
08-26-2004, 08:38 AM
Thanks for all the replys everyone!!

legendboy
08-26-2004, 09:13 AM
Originally posted by googe


well if a 2.5&quot; and a 3&quot; is going to be the difference between boost creep or no, its obviously quite measureable.

With a well designed manifold and thought out wastegate placement the downpipe choice won't effect boost creep. I would never use internal wastegates on any of my own projects.

I think what some of you guys are forgetting is that maybe dsm's get boost creep if this or that. Maybe subaru guys get this or that. But a custom designed turbo system, all of the factory design flawes can be eliminated.

googe
08-26-2004, 09:18 AM
Originally posted by legendboy


With a well designed manifold and thought out wastegate placement the downpipe choice won't effect boost creep. I would never use internal wastegates on any of my own projects.

Oh for sure it has everything to do with the wastegate, but cost goes up quite a bit when working with an external one, especially on lower budget project cars.

Just saying, if the 3" in this particular application allows boost creep to occur and a 2.5 does not have that problem, the 3" must be flowing significantly better.

legendboy
08-26-2004, 09:21 AM
Well, i guess cost goes up a bit. You can get the tial replica wg's on ebay for 150us.

I really don't think that boost creep will be a problem with this situation. Its not a dsm.


I'll put it like this, if i designed the manifold and downpipe boost creep would be a non issue, regardless of dp size.

legendboy
08-26-2004, 09:31 AM
I'm almost 100% sure that boost creep problems are caused by dumping the wg way to close to the turbine outlet, and at completely the wrong angle. (for more than stock boost) Should be dumping a minimum of 12"-14" further down. This would completely eliminate boost creep, with no porting or anything.

http://www.telusplanet.net/public/thanem/p1010002.jpg

EK 2.0
08-26-2004, 11:02 AM
Originally posted by legendboy
I'm almost 100% sure that boost creep problems are caused by dumping the wg way to close to the turbine outlet, and at completely the wrong angle. (for more than stock boost) Should be dumping a minimum of 12&quot;-14&quot; further down. This would completely eliminate boost creep, with no porting or anything.

http://www.telusplanet.net/public/thanem/p1010002.jpg


in this case...I would have to agree with Legendboy...this is one os the main resons DSM's suffer from boost creep...and is easily solved with mad porting or a different O2 Housing/Downpipe alvailable from MANY DSM vendors...


Oh and BTW...if the Turbo was out of a 2G DSM it is a T25...

googe
08-26-2004, 02:07 PM
Yeah but, the question wasnt how to prevent boost creep, it was whether or not a 3" is going to flow any better than a 2.5" in his application? :)

legendboy
08-26-2004, 02:08 PM
ya and the answers no :rofl:

haha i guess our conversation has morphed a bit but I guess we can chalk this all up to differences of opnions.

Jason Lange
08-31-2004, 11:22 PM
re you going mandrel bent or regular cheap-o bends, or are you buying already made. If you are using squish bent then I would go 3" if you are using mandrel bends use either 2.5 or 3".

method
08-31-2004, 11:23 PM
you can go 2.5 or 3" you're never going to utilize the potential of either on that engine.

cummins diesels use 3" as a performance downpipe for fucks sake.