Airflow

[daniel23a]

Hi all,

I am looking at reducing the restrictions in the intake and exhaust of my S2 R33 to allow for better flow, with more mods to come further down the track.

I am a mechanical engineer by trade, have done a bit of reading on air flow and how it is affected by change in direction. basically any small change in direction causes drag in the air flow, with more friction caused by sharper less gradual bends. before this point i was looking at getting an FMIC that utilised the existing piping but now that i have looked at it, the 180deg bed that runs under the cooler would greatly slow down the airflow in the system.

I work in industrial projects, and have recently been dealing with hose manufacturers. I am looking at using industrial hose (rated to 50deg and 2bar) to route from the J-pipe to a front mount and back to the turbo. has anyone done this before? what are the drawbacks? i assume there would be some pretty big ones otherwise it would be more commonplace...

I am retaining my stock front bumper, so will be looking to use a smaller core that fits the size of the intake in the front (800x150?) as i dont see any point in installing a huge front mount if it isn't exposed.

For the exhaust side, at the moment i have an HKS 3" cat back with Apexi control valve (for noise) but I am wanting to replace the dump pipe with a screamer pipe and a straight through cat. is this the best way to go about freeing up the exhaust? i know the screamer makes a horrible noise, but my daily driving is done off boost, one of the merits of having a RB25

Any insight or criticisms into my logic are welcome!

Cheers, Daniel

[MrStabby]

Hi all,

I am looking at reducing the restrictions in the intake and exhaust of my S2 R33 to allow for better flow, with more mods to come further down the track.

I am a mechanical engineer by trade, have done a bit of reading on air flow and how it is affected by change in direction. basically any small change in direction causes drag in the air flow, with more friction caused by sharper less gradual bends. before this point i was looking at getting an FMIC that utilised the existing piping but now that i have looked at it, the 180deg bed that runs under the cooler would greatly slow down the airflow in the system.

Since you're a mech eng why not just do the calcs and see how much pressure loss is caused by the 180 bend? My guess is that it wouldnt be much, and may even be negligible compared to the total pressure loss along the entire fluid path.

Interesting point about intercooler size tho - i guess depth would be more useful than having more height or width that's shrouded by the bar. Also make sure there's no gaps around the intercooler that will provide an easier path for the air to flow around instead of going thru.

[R31Nismoid]

Core design plays as much of a part as overall size... and piping.

Some flow better, cool less... some cool more, flow less... and some sit in the middle

The core design would play more of a part than a 180 degree bend in overall terms i would imagine and a place where you would definately notice difference

When people measure pressure @ the turbo and then @ the plenum with bends, coolers and so on and dont notice more than 1-2psi drop overall... would that really be noticeable vs a setup with a couple of less bends? and maybe a 1psi-1.5psi drop (for arguments sake say... its .5 psi better with less bends)

Probably not??? considering you can just add 1psi more and off it goes.

Also, how does pressure affect things? (im not good at this part). Id assume pressure would alter calcuations and so on in various ways as opposed to a N/A setup.

[daniel23a]

Since you're a mech eng why not just do the calcs and see how much pressure loss is caused by the 180 bend? My guess is that it wouldnt be much, and may even be negligible compared to the total pressure loss along the entire fluid path.

Interesting point about intercooler size tho - i guess depth would be more useful than having more height or width that's shrouded by the bar. Also make sure there's no gaps around the intercooler that will provide an easier path for the air to flow around instead of going thru.

hi, thanks for your input

Have found that in a 2.5" system, a 180bend is equivalent to 1.1m of straight pipe and a 90 deg bend is equivalent to 0.9m of straight pipe, surprisingly not much difference. an aftermarket kit looks like it has roughly about 7 90deg bends, but i do think in the end this will be negligible when compared to the pressure drop across the intercooler, so you're probably right.

my other positives are that flexible pipe allows for easier installation and greater flexibility in mounting. it is also cheaper. i guess i'm just a bit hesitant to do it as its not common! anyone else?

[KiwiRS4T]

hi, thanks for your input

Have found that in a 2.5" system, a 180bend is equivalent to 1.1m of straight pipe and a 90 deg bend is equivalent to 0.9m of straight pipe, surprisingly not much difference. an aftermarket kit looks like it has roughly about 7 90deg bends, but i do think in the end this will be negligible when compared to the pressure drop across the intercooler, so you're probably right.

my other positives are that flexible pipe allows for easier installation and greater flexibility in mounting. it is also cheaper. i guess i'm just a bit hesitant to do it as its not common! anyone else?

Probably not used because it doesn't look "cool". Can't really see any downside so long as you can secure it properly (although the 2 bar and 50deg don't really provide a huge safety margin - things can get pretty hot under the bonnet).

[Adriano]

Turbo outlet temps can get up to 300 degrees. bear in mind cubes is making over 300rwkw with stock 2inch r32 intercooler piping, so it cant be that restrictive at stockish power levels.

[Jet 20]

Turbo outlet temps can get up to 300 degrees. bear in mind cubes is making over 300rwkw with stock 2inch r32 intercooler piping, so it cant be that restrictive at stockish power levels.

Was just about to say that intake temps before the cooler are very hot. the more boost you make the hotter it gets.

50 degrees is not going to cut it..

[daniel23a]

Was just about to say that intake temps before the cooler are very hot. the more boost you make the hotter it gets.

50 degrees is not going to cut it..

thanks guys,

the exhaust temps would def be very high, so you're right i should increase the temperature rating of the hoses. i don't see that it will reach 300deg just from heat transfer from the hot side, does anyone have an indication of how hot intake temps get (and what i should allow for safety)? also i have allowed for 2bar of boost (with safety factor), realistically in the future i should be up over 1bar, anyone know of what kind of pressures these hoses will be under when boost spikes?

cheers, Dan

[gotRICE?]

Would the rubber piping start to flex under that much pressure? Bulge a bit?

You would be surprised how much the turbo heat will transfer. Under full boost/load it doesnt take long for the ex. manifold to start to glow, thus would the turbine ex. housing, and i could bet you that a whole sheetload of that would transfer into the compressor housing. Or intercoolers wouldnt be needed right?

[MrStabby]

the exhaust temps would def be very high, so you're right i should increase the temperature rating of the hoses. i don't see that it will reach 300deg just from heat transfer from the hot side, does anyone have an indication of how hot intake temps get (and what i should allow for safety)? also i have allowed for 2bar of boost (with safety factor), realistically in the future i should be up over 1bar, anyone know of what kind of pressures these hoses will be under when boost spikes?

Pretty sure Adriano (IIRC he's a mech eng as well) was talking about temps out of the compressor, not to/from the turbine. Ie air temps not exhaust temps. And there's no hoses for exhaust stuff.... If he says 300 degrees air temp then i'm surprised but I believe it. Mind you the stock piping is rubber so.... WTF? OR maybe i'm completely misunderstanding what's being said here

Re: boost spikes, i'd just build a system that doesn't spike appreciably so you dont have to worry about designing the hoses to handle it.

You would be surprised how much the turbo heat will transfer. Under full boost/load it doesnt take long for the ex. manifold to start to glow, thus would the turbine ex. housing, and i could bet you that a whole sheetload of that would transfer into the compressor housing. Or intercoolers wouldnt be needed right?

Compressors add a lot of heat as they increase pressure, and i'd guess that's where most of it comes from - not through the turbo from the exhaust. A bit like air con where you have compressor -> heat exchanger, in a turbo (or supercharged) car you have compressor -> intercooler as the heat added from the compressor needs to be removed.

[Jet 20]

most of the heat on the compressor side comes from compressing the air. this causes alot of heat.

touch the output line off a normal air compressor in your sehd. gets very hot. the turbo does the same thing..

[daniel23a]

I have looked at the intake piping, there are rubber bends in the system, in fact there is a rubber section coming straight off the turbo so I don't see any problems with this. I have talked to a few people and the main reason hard pipes are used is to avoid expansion in the pipes. The hose I will be using is steel wound and rated to over 10 bar so I do not see this as an issue.

As for the exhaust system, previously mentioned I have an HKS super drager from cat back. I am looking to replace the dump with an atmos venting and also a straight through cat pipe, will I need to replace the down pipe also? does anyone know what size it is? No point replacing everything else if there is a bottleneck in the system!

[STATUS]

you think too much

buy a decent off the shelf kit (blitz return flow) and i gaurantee excellent results... i have used just about every kit available from jjr kits to full custom top shelf items costing close to 3k and the blitz one still offers the best results.....

important note: Many focus to much on pressure drop accross a core, usually the better the core (cooling wise) the larger the pressure drop to some degree. Remmber for heat to transfer it needs to have made contact on the way through the core...

Edited January 30, 2009 by URAS

[gotRICE?]

you think too much

buy a decent off the shelf kit (blitz return flow) and i gaurantee excellent results... i have used just about every kit available from jjr kits to full custom top shelf items costing close to 3k and the blitz one still offers the best results.....

I like you

Make me feel so much better spending $1000+ on the front mount

GREAT piece of kit.

[daniel23a]

Thanks URAS/GotRICE

I think because thats what i do, i'm an engineer... I look at better ways to solve a problem, whether it be in terms of performance or cost. i just reckon that i'd prefer to pay less than a quarter for a kit that will prob perform better than go for a brand kit just because it has been done before.

Any ideas about the exhuast sizing?

[gotRICE?]

You could also argue that if it was better to do it how you think, that the Japanese engineers are stupid

They dont just design and build stuff for the hell of it.

for RB25 you cant go wrong with 3" turbo back yo.

[discopotato03]

If the people making front mount intercoolers for standardish plumbing were smart they have the IC tanks top and bottom rather than either side , that way both inlet and outlet face the direction the ducting comes from so no 180 bend and extra length of pipe .

Many won't agree but I'm with Corky Bell , the way to make a propper IC is to have more tubes not longer tubes .

From your fluid dynamics studies you can easily see why many of these brain dead intercoolers don't work properly , the tanks are too narrow and the ducts are often way to close to the cores end plates . As you say gas , particularly at high velocities , doesn't want to know about changing direction so you get a pressure rise where you don't want it .

If I had to use the std plumbing (RB25) I'd go with the vertical flow FMIC , if you don't mind the non standard pipe kits I think the 180 bend off the TB and across to the offside and through a std GTR IC is good value .

If you can go with a GReedy type inlet manifold this is much neater .

Just my 2c , cheers A .