*IC Pipe size Q:*

[IJ.]

This is cross posted from my rebuild thread as not as many people will see it there and I'd like opinions on this!

Question on pipe size please jump in if you have an opinion!
I currently have 2.25" IC pipes, the new IC is 3.0" in and out!

I can mod my existing pipes and use reducer couplers or I can fab up a new set of 3.0" pipes!

Just interested to hear if you think this will add too much volume to the system or increase lag (which at the moment doesn't exist).

New IC arrived this morning>>

 

[chevyeater]

Go 3".

 

[IJ.]

LOL Brian,

give me some reasons!!
(I won't take a LOT of convincing)

 

[oneandgone]

Heh, I said basically the same thing in your other thead, just not as to the point I guess! lol!

 

[IJ.]

LOL Brian's a man of few words!

 

[chevyeater]

I like to use the KISS (Keep It Simple Stupid) principle whenever possible.

It may delay your spoolup a really small bit but the payoff will be many fold.

 

[IJ.]

Thanks Brian,

In my head I know it makes sense but the lazy side of me was considering staying with the 2.25's as the outlet on the Compressor is around that size ID.

 

[GrimJack]

Depends. How much HP are you going to be pushing through it? Do my eyes decieve me, or is that a nice shiny new Air / Water IC?

 

[IJ.]

GJ: The aim is 400rwhp I'm running a GT30r 600 roller and yep it's a new water to air (I already run a smaller version on the car but it's choked at 9psi)

This one is rated at 650hp crank

 

[Cz.]

My understanding is that 2.5" is the best. If you're only going for around 400hp I'd think that 3" is getting too big. The increase in size will add a lot of volume which might might take longer for full boost. I doubt that having 2.25" pipes will cause any sort of "breathing" problem.

 

[GrimJack]

Well.... if your turbo outlet is 3 inch, I'd say swap to 3 inch, at least from the turbo to the IC. You can get away with a smaller one from the IC to the throttle body if you like, because cooler air doesn't take up as much physical space.

Your HP requirements don't need anything over 2.25 in either location, however. But you know what they say about power requirments... they grow!

Edit: Thanks to Furball for pointing out the flaw in my typing... note to self, don't post when you're dead tired!

 

[Furball]

Cooler air is denser. I think what you meant was cooler air doesn't take up as much physical space, therefore the pipes can be smaller.

 

[Mk3 TurboS]

what size is your Intake mani?

 

[IJ.]

CZ: Thanks!

GJ: The ID of the outlet is close to the ID of the 2.25 pipes (this is why I chose em) The only reason I'm considering 3" is the new IC in and out are both 3".

Furball: <nodding>thanks

Mk3TS: The flange on the Gas Carb is around 2.75" I have a silicone reducer to make a smooth transition.

I have a pair of 2.25>3.00 silicone reducers so that side of it is easy!

The new IC barrel is HUGE compared to the old one and if I mount it in the same place I'm going to have cooling issues as it will block all of the lower grill!

I'm considering recessing it into the back of the bumper but to do this with 3" pipes will be almost impossible!

I'm also bench racing engine swaps in my head as the gearbox was all that was holding me back from going high HP!

Short list is

2JZ
Toyota V8
Holden V8 (domestic)
Chev V8
Gen 111 V8 .

 

[Rajunz]

My understanding is that 2.5" is the best. If you're only going for around 400hp I'd think that 3" is getting too big. The increase in size will add a lot of volume which might might take longer for full boost. I doubt that having 2.25" pipes will cause any sort of "breathing" problem.

This post makes the most sense, the larger you make the piping, the slower the velocity. You are not going to loose any performance with the 2.25" piping, not at your performance goals anyways. I think you will be disappointed with the throttle response if you go to 3".

 

[IJ.]

RaJunz: Thanks for posting!

I'm leaning towards staying with the 2.25 pipes for the reasons in my previous post as being realistic this isn't a race car and 400 at the wheels will be plenty!

I think I've figured out a mounting position that will actually shorten the pipes a bit but will give it some thought before going ahead.

3.0" would be nice if I were chasing bulk HP but if I were to do that I don't think I'd stay 7m.

Really love the car in your sig does it actually get driven or is it a show car?
(only asking cos it's so clean )

 

[IJ.]

If I could find some compressor maps for GT series turbos I wouldn't have to keep asking questions!

 

[supraaddict87]

If my power goal is no more than 350rwhp would there be any increase in power from 2.5” pipes over 2”? I am running the stock intercooler and turbo.

I ask because I have some 2” left over from another project and will do all the fabricating myself. If I do someday increase my power goals and need to upgrade, the only money lost will be in my labor.

I do not want to hinder the power output of the car, but would like the most throttle response as possible.

mike

 

[IJ.]

Well that was an interesting evening here researching my question!

I managed to find some compressor maps and did some calculations to find the airflow requirements of my combination!

I then found some info on pipe flow and it appears that I'm fine with 2.25" pipe as the velocity is still under the critical speed for the CFM I'll be pumping through it!

Saddict87: Sorry I have no idea without doing all the calculations but I'm certain one of the guys here has experience/advice on the exact setup you're using!

(I'm too lazy to do the math and this is why I asked the question here )
(curiosity got the better of me)
(Siman will be happy I found the velocity info on a Hondah Forum!)

 

[Rajunz]

RaJunz: Thanks for posting!

I'm leaning towards staying with the 2.25 pipes for the reasons in my previous post as being realistic this isn't a race car and 400 at the wheels will be plenty!

I think I've figured out a mounting position that will actually shorten the pipes a bit but will give it some thought before going ahead.

3.0" would be nice if I were chasing bulk HP but if I were to do that I don't think I'd stay 7m.

Really love the car in your sig does it actually get driven or is it a show car?
(only asking cos it's so clean )

Yeah I drive the car, but it's not a daily driver.

On the topic, just FYI, at the TX2K5 SupraNationals, the 7M dyno winner had 3" IC piping, but had a long spool up time. At the TX2K5 SupraNationals, the quickest 7M drag race car had stock IC piping, including the 3000 pipe. The guy also had a 7m powered MKIII drag car that ran 10's. It was gutted, it had a Garrett turbo with stock IC piping including 3000 pipe. I questioned this and he said for a street car it wouldn't be as ideal because the higher velocities generate more heat, but for the 1/4 mile the smaller piping gives it a lot quicker throttle response. Also, a shorter routing (through the snorkle hole) will help throttle response.