Stainless piping diameter question eg plenum

[Mr Multivalve]

Hi,

If someone could give me some advice I would appreciate it, maybe tonight, well soon

I finish up at work this week and they just have crap loads of stainless they are pretty much throwing out, I have a acquired a bit but I have a question. Big sheets of the stuff, heaps of pipe, rated to 1000psi

If I am getting someone to make up a custom plenum chamber for me what is the best size pipe to get, for the pipes leading from the plenum to the mounting manifold on the intake side?
I know this may depend on who is making it and their level of experience but if someone knows what a good safe size would be for me to collect I would appreciate it. I was thinking about 1 1/4 inch, is 1 inch too small? What would be the best size?
This would be for a set up on a 1G-GTE. How much would I need length wise? They would be straight pieces might be able to get some bent stuff.

Thanks in advance

[LeeRoy]

what is the best size pipe to get, for the pipes leading from the plenum to the mounting manifold on the intake side?... I was thinking about 1 1/4 inch, is 1 inch too small? What would be the best size?

Are you talking about the runners or what? i assume you are because you are saying 1 1/4 inch and that would be too small for anything else. I would highly reccomend alloy but as it will dissipate heat alot better, will weigh less, and be easier to construct. If your getting the staino for nothing, sell it, buy alloy, then happy days.

As for plenum design you want something that is at least 1.5 inches from the last runner entrance and this should get larger as you travel towards the throttle body. A manifold that is round will be the best imo as it presents no hard edges which can result in poor air flow. I don't have any pics of mine atm otherwise i'd throw one up.

- LeeRoy

[thechuckster]

much bigger - 3" would be a good size.

plenum shoud be 100-200% of volume of engine (depending on which manifold theory/design you subscribe to)..

however ... how would you join this stainless up to the aluminium runners? and how much heavier that alloy would this be?

perhaps flog heaps of piping (2", 2 1/2" ??) that you can use for intercooler piping - bends/donuts will be v.useful.

[Mr Multivalve]

Thanks Leeroy and Chuckster,

I have a quite a bit of 2" 2.5" and some 3" and am acquiring some more every day hehehe got some good bits with a few bends should get them tomorrow.

I have never seen under a custom plenum so I thought they would use smaller piping, so on a custom plenum they would have six 3" pipes going to the inlets using a 1G as an example, I though even 2" would be plenty big, how does it normally work if you wanted a stainless plenum made does the bottom half normally have to be alloy?
Hmm just read the part about the pipes changing diameter, ok starting to make more sense in my head

Can alloy be polished up to look like stainless as I have seen a few custom plenums that I swore looked like stainless. I was really only thinking stainless partly because they are getting rid of the stuff.

[LeeRoy]

My manifold looks like this with the exception of my throttle body being on other side, i have straight runners, and mine isnt as tall, but the design and concept is the same.
- LeeRoy

[Mr Multivalve]

That looks cool, but it that alloy that has been polished up, if so it looks good! I do not have the equipment to make anthing like this, I was just trying to gather materials lol

[joecoolmk2]

that manifold is aluminium/alloy. you can tell by the lumpy welds.

seriously, go aluminium, stainless is shite.

[LeeRoy]

Yeh its just polished alloy. I would dare say that any fabrication shop could make that for you or you could even make it yourself and just get someone to weld it for you. Just get the right sized pipes and cut them to size, all you really need is a bandsaw, and get the plate for the flange to bolt to the head laser cut ($40 or less), then get 1 3" donut and about 1foot of 3" straight pipe and about 1 sq foot of sheet alloy.
Make the runners first, there are some good writeups floating around as to length and size then just fit the manifold to runners then to the base of the plenum. Now using the 3" donuts cut to size so you can have the manifold taper and be smooth at the back. then using the plate cut bits out to fill the sides in. You will also need an alloy cup for the manifold to taper at the throttle body end and another flange plate for the throttle body to bolt to.

I foundpic of my manifold getting built and one almost complete and you can get the gist of how it was done. It sounds pretty difficult but with the right tools and a little help anything is possible.



- LeeRoy

[LeeRoy]

Like i said before just get the stainless and sell it to buy alloy. Alloy is better in many ways and factory manifolds are made from alloy too. As for runners you could use the standard ones and make them shorter or just make new ones.

Also alloy can't be welded to steel (stainless or not)

- LeeRoy

[mullett]

Your runners want to be the same size and diam as your ports., and maybe slightly tapered. Biggest thing is to put bellmouths on the end of them, it'll rock your world.

RM.

[LeeRoy]

Cause i run standard runners a dont have bellmouths but they rock, rather where the runners enter the base of the plenum, it has been die grinded extensiely to resemble bellmouths and runs a nice taper. Match porting manifold to head also rocks worlds .

- LeeRoy

[30psi 4agte]

MR multivalve

like everyone is saying go alloy mate! I know the stainless is free but alloy is way better for a inlet manifold/ plenum.

The stainless will be good for exhaust work and possibly a new exhaust manifold

All i can say is if the stainless is free get as much of it as you can !!!!!!!! even if you dont think you will need it!!
That shit always comes in handy!!

[Mr Multivalve]

Cool thanks for the help, I will have a look for some writeups. I have never done metal work etc. but I am willing to learn and try to save a buck where I can.

I want to get an exhaust manifold sorted out too so I can look at going to a single turbo something common like a T3/T04 hybrid, but one thing at a time.

Thanks for the info, have some rep on me

[ReQuieM]

LeeRoy, Whats that plenum for? engine that is. Can I get a better pic? They're a little small to see. Also do you have some links to the mentioned articles on runner length?

In the (long term) process of maing up gtr ITB's to a 1jz and I'm making a custom plenum (and runners) to suit. Been finding it hard to find cold hard facts that arn't acompanied by 42 pages of calculations!

[LeeRoy]

The manifold is for a 3T-GTE and its running a cressida throttle body as well, Its my project. I havent read specifically any article on runner length but the standard 3T manifold has runners that curve up, similar to the ones in the first picture i posted (the shiny one ) but we cut them before they curve up and have made them straight (the picture will explain better). Yellorolla runs a 3T-GTE Ke20 (i think its a Ke20) and runs consistent 11 second 1/4's, i've read a few posts he has thrown up where his manifolds which he makes and does a fair amount of experimentation with have given him more power/quicker times by using narrower runners, longer runners, shorter runners etc. Do a search as i don't know the specific thread that it is in.

In short theory standard manifolds utilise long runners as they provide low rpm torque and power at a cost to high end power, alot of people run shorter runners although sacrificing low end, they gain top end hi rpm power and torque.

NB: These two images are just larger versions of the ones above



- LeeRoy