wakeech

i know that cost will always be an issue, but for you guys that are all "price is not an object" when building your monster street machines, why do i see so many setups using the stock intake manifold??? i mean, to make really good power at lower boost pressures (pressure DOES NOT equal rate of flow, don't forget: more power at less psi = healtheir engine) reducing the length of the runners into the engine, not to mention increasing the volume of the plenum of the manifold, will really help with breathing... so, i don't get it...??

ttpowerd

try searching....

wakeech

yeah, i'm no n00b... i'm actually a mod at rx8club.com, but i'm just gearing up for building a single turbo FC (in who-knows-how-long)...

anyways, i have found absolutely nothing about why the stock intake is used, and thus asked...
guys??

IRPerformance

iTrader: (41)

I don't think it becomes a restriction. I have seen a few motors running the cosmo intake though.

zyounker

On the S4/S5 motor alot of people use an S6 UIM and port match the LIM.


As for why not do a custom one? only reason is cost and the stock one has seen 400+RWHP. so most dont do it..



There are plenty of people who do put on a custom one though. Just not to often in the US

wakeech

the concern wasn't that it was "restrictive", or that it couldn't take the boost (any cast manifold could pull off some of the obcene stuff you guys do ), but about making the most torque at the right (highest possible) rpm... the plenum on the stock manifold also doesn't seem very big either...

all i'm saying is that why invest all this hard earned cash, but hold yourself back so much?? i mean, you wouldn't think it, but i know for some guys 20-50hp (or considerably more) could be tied up in the header setup they have.

...i asked in case you all knew something i didn't, like "the port phasing on the 13B is such that having a big pressurized plenum won't help/won't be as good as stock" or some other secret known only to guys who've worked on them...?? one thing's for sure: sorter runners will help you at higher rpms, large plenums help flow by maintaining a high pressure volume for the engine to draw on (like a velocity stack, but at 2-4 bar, however high you push it)

rotarygod

iTrader: (1)

I have a custom manifold with a big single plenum that I built

j9fd3s

iTrader: (3)

do tell

mike

rotarygod

iTrader: (1)

You never saw that thread?

wakeech

yeah man, what're your specs?? runner length, diameter, radius (of runner taper), plenum volume, etc??
what size turbo?? what volume of air at what psi??
...and most importantly, how much hp??

link please!!

rotarygod

iTrader: (1)

It still uses the stock T-II lower manifold. I have plans to build one of those yet but am so busy who knows when I'll get around to it. It is a single plenum of 100 cu. in. in volume. It uses a single plate Mustang throtllebody. It is not a mod that was ever intended for use with the stock ecu. It is also a little more harsh to drive on the street since all runners are always receiving air regardless of throttle position. I don't care though since it is a play car. Still works like a champ and makes good power. The thread was rought with flames from the uneducated on its practicality and functionality. If it is for a daily driven car then I would probably not use it but for power hell yeah! It is off the car and will probably be up for sale. I am working on a completely new design that I really don't want divulged yet since I'm not sure how well it will work if at all. The theory is sound though so we shall see later this summer.

The reason I built it myself as with everything else I have isn't because I like to spend alot of money on my car. It is because I am a cheap bastard and name brands mean nothing. I like creative engine bays that are home made. I also believe that I can make it faster myself for cheaper.

j9fd3s

iTrader: (3)

i saw the thread but this is a better one

mike

astrochild7

iTrader: (3)

i agree the stock s4 s5 s6 they are all restrictive. the angle at which the LIM hits the motor is the main problem. the manifold i'm working on fixes that . and still seperates primary's..... yes i'm a cheap bastard tooo and i can make it for very little above scrap metal costs.....

wakeech

in your design, have you placed the secondaries closer to the port, or the primaries??

600HP CLUB

you and me both. **** i'm so cheap i'm cheap, i'm in the process of building my own exhaust manifold for a bigger turbo, but no turbo , just waiting on the funds, then after that i'm going build my own roll cage. i already observed how they built it in a performance shop when they did my friend's civic who needs it because of rules (10.99-11.99 cars). i would too like to build my own intake manifold, because was about to build one for my friend with a honda but got scared when we plan'd how the injectors going to be seated, (thank mazda for the injectors not being on the upper intake manifold)

-mike

suganuma

after building an intake manifold for a formula SAE car and doing all the calcs and trying out some different things on that setup, i've been wanting to do this as well, but also having trouble figuring out how i'm going to get it to mate with the motor very well and get the injector bungs in there how i want them.....i need some tools that arent at my disposal anymore like they were at school.....

for you that have built these already.....can we break this into a discussion of how the formulas change for intake runner tuning on a rotary vs. piston engine??....PLEAAAAASE??? if you have to keep it under wraps for one reason or another, i'd still love to talk about it through PMs....

wakeech

...the equations are the same... it breathes air in the same way a cylindrical piston does, it has a BDC volume just like a piston engine, and the side/inter housing plates take the place of heads... phase timing, port cross section, plenum volume calculation (at least 80ci for a 13B... but personally my system would incorperate on 160ci, just 'cause it's still so damned small ) pretty simple, runner tapering, contouring, tapering, etc... it's all the same bag of tricks.

rotarygod

iTrader: (1)

Anyone that knows me knows that I am long winded. If you don't know me then you'll soon figure this out.

The thing that changes, and this is important, is that in a piston engine there is air traveling in a forward direction (towards the valves) only a quarter of the time. Compare this to a rotary. Air is almost constantly
(and sometimes always) moving this forward direction. This makes the pulses from the other chambers less dramatic. On a piston engine when air is entering a cylinder (actually always a few at the same time but staggered) it creates a vacuum on the other non-moving runners. On a rotary this phenomenom isn't nearly as great but it does occur. A rotary engines intake runners (and exhaust runners) move more air than the same sized runners on a piston engine for this very reason. All rules regarding port overlap and importance of a good scavenging exhaust still apply. The above mentioned greater amount of air per time in a rotaries intake and exhaust only make proper tuning all the more important. A good scavenging exhaust on a rotary has a far more dramatic or exagerated effect on power production than on a piston engine. A proper exhaust is just as important to have on a piston engine though. Since the 12A/13B family of rotaries come stock with a small amount of port overlap (as do most other engines) a good scavenging intake and exhaust are very important as they all effect each other. the more overlap the greater the importance. I suspect that the new Renesis with its lack of port overlap (64 degrees of dwell) will not respond nearly as impressively to headers as the 12A/13B's do. I do not doubt though that they will do something.

As wakeech has stated doing all calculations for a 1.3 liter engine will not work. He states that using 2.6 liters for a reference is a good point to use. If we look at a turbocharger compressor map and do calculations for a 1.3 liter engine based on airflow, we get a turbo that would be too small for a Honda Civic. As we all know that isn't even close for a rotary. If we do the calculations for a 2.6 liter engine then we start getting in the ballpark for a stock engine so he is on the right track. I have a computer program that lets me enter in engine volume in liters along with max rpm and then calculates the appropriate turbo size (compressor, turbine, and a/r) based on the T4 series of turbos. So far it has been right along with the 2.6 liter number on a stock port engine. However when we port our engines we do more than just increase cfm through the port itself. We also increase port timing and duration which gives us more time to shove more air into the engine. Now we have just greatly thrown the 2.6 liter air flow number in the trash and greatly increased it.

These are a few basic points of interest and really don't answer any questions as well as they do raise some more. It is late and I don't want to start contradicting myself because I can't think straight right now. I do that alot

suganuma

heh.....thanks for the reply

is there any good rotary specific reading on this i could get into?....i'd like to get some more info on both intake & exhaust manifold tuning on rotaries both from whatever writings there may be on the subject and also what people have found to work in their many years of experience....i figure that's the only way we can move forward with each generation. so if any of you with more experience would be so kind as to enlighten us younger 20-somethings, that'd be much appreciated. PMs work for me if you dont want to post for one reason or another....

Thanks for info so far y'all!