NeXtLeVeL_TyPe_R

I was told as far as turbo manifolds that smaller diameter pipes are better for various rpm street use as per say larger diameter pipes are better for drag use

Anyone care to comment as far as what effects the diameter of the turbo manifold pipe have?

Prod

Just going on logic here...

A larger diameter pipe will flow more but have a lower exhaust gas velocity
A thinner diameter pipe will flow less but have a higher exhaust gas velocity

From what I've seen, most of the manifolds seem to have the same size tubing anyways...you have the exhaust ports right there so I don't think ya can vary on size too much.

Other gains can be had by using equal length tubes, twin scroll turbine...thats all I can think of now...I'm sure someone else can add alot more

Prod

Bump

I'd like to see if anyone else has information / opinion on this...it could be interesting !

NeXtLeVeL_TyPe_R

I agree ! bump^

racerxadam

where's ffgeoff? i bet he could talk in depth about it

noel

I'd also like to know this. I'm curious as to why these equal length manifolds are so good. I wonder if it would be possible to effect of an equal length manifold by making the runners on 2 and 3 a tad bit larger to account for the different velocities of the gas if that's main point. I guess that could be more of a bitch than just welding together an equal length manifold. FFgeof always has some nice equal length manifold pics. Anyhow, enough rambling, bump

Prod

Equal length manifold will keep the exhaust pulses coming at a consistent pace, of course that's going to help get the turbo up to speed quicker and smoother.

pub

volumetric efficentcy. each pulse has a max (1.8liters) of displaced exhaust gas coming out. Honda pretty much engineered our exhaust ports for efficency (I would only assume). Just as long as you keep it as close to stock diameter, you should stay efficent. I guess under boost-conditions the most efficent flow would be with a slight boreing of the exhaust ports. But I'm sure it's involves a nice calculus equation for how much boost you're running.

cliffs notes: I don't know.

GB

I've also thought about this. Personally I'm pretty skeptical about the exhaust flow being smoothed out when the runners are equal length but rely on different angles and twists to achieve it. Anybody building a performance exhaust is gonna agree that a 90-degree mandrel bend is a no-no if it can be avoided. So if that's the case, then how is it ok then for the manifold to have one straight runner and one runner that twists over itself a full 360 degrees before they meet at the collector?

I've seen pictures of custom race headers that use varying-diameter tubing throughout different sections on each runner to compensate for the bends. Lots of effort and $$, obviously. While I think performance can be gained on a $30,000+ engine by going all-out with the fluid-dynamics engineering and CAD design of custom race headers, I don't think there's anything special for street-only applications about equal-length headers if they do not use staggered diameter tubing to compensate for the varying bends in each runner.


[Modified by GB, 2:05 PM 10/30/2002]

GB

This makes sense...for street use, the engine spends a lot of time without boost. The engine really needs the low-end torque to motivate the car without the aid of boost as well as overcome the restrictive properties of the turbo as it is spooling up. So the philosophy is to design a system that is more motor, less turbo. Since the emphasis is on motor, the exhaust should be designed to favor a wide-rpm N/A application (high exhaust velocities more important than high flow).

For drag, the engine rpms are always kept high and the turbo is at partial or full boost for the entire run. This means that the turbo is always contributing more than it is taking from overall performance, and the engine is never forced to move the car by itself...so its less motor, more turbo. Thus the exhaust is built to favor the turbo application (high flow is more important than high velocities).

Cliff notes:
street uses more-motor/less-turbo so use N/A exhaust.
race uses less-motor/more-turbo so use FI exhaust.

NeXtLeVeL_TyPe_R

very informative post.
Thanks just what i was looking for.

WA DA TA

yeh where is Geoff?

Full-Race Geoff

i strongly disagree with alot of what you say. I have to ship a ton of crap today so ill respond later.

NeXtLeVeL_TyPe_R

ill be waiting to here your disagreements - should be very interesting

lazerus

a turbo manifold should be the same size ports as what come off the head. and also, a equal lenth turbo manifold sets up the exhaust pulses to "suck" one another along through the exhaust system.

i've designed my own turbo manifold, and it's basically 4 pipes that meet up, and the tubes really are equal length, but it's a very short manifold, and the inside has been grounded to where there are "flow veins" which i've air grinded out to direct the flow of each pipe down towards the turbine to maximize spool.

Equal tube turbo headers work great too, you'll see lots of the real fast guys usin' them.

another thing that helps alot too is thermal wrap, and ceramic coating of the manifold, turbine housing, and downpipe/exhaust components. The idea is to have minimal restriction with tuned flow in the ehxaust header up to the turbine (where you want this to be your only restriction) and you want your exhaust to be as least restrictive as possible.

but with that least restrictiveness, if you loose a lot of heat because of the large diameter piping and everything, you nearly kill your gains from it. Hence ceramic coat/thermal wrapping.

so in the end:

Your goal of the exhaust system is to keep the exhaust gasses as hot as possible, for as long as possible, to reduce backpressure, and increase velocity.

equal length tube header with ports with similar to those that are on the head, that meet up the turbo flange, wherein it is port matched with the turbine housing being the same size as the flange off the header.

therin you have your exhaust off the turbo, my personal setup is a 2.5" pipe off the turbo welded to a 3" mandrel bend that is wrapped in thermal heat wrap. (no exhaust yet)

a good way to get more exhaust gasses is have as much timing advance as possible before boost, and on boost as well (but it will be retarded over no boost)

and also Antilag works WONDERS o the wonders of antilag. =] too bad it will blow exhaust components quickly if not done right.

some WRC Cars build 22 lbs of boost when they are at their idle giving them instant boost off the line. here's a short video of cars equipped with antilag.

Antilag...

hope this information helps some. OOH i just found something =] here is a graph i have of how to tune your exhaust ports (for N/A Applications...) here it is.



Now to use this graph, you need to find out the number of degrees your cams have between when the exhaust opens to when the inlet opens, then read up to the revs, then to the numbers on the left hand side, which give you the length of the exhaust in feet before you want to place your first (straight through) muffler. which ususally ends up right where you sit.

umm... i dont' really want to get into this too much but there is some ideas on exhaust tuning, turbo and N/a (and of course both) they are different beasts, but the same idea applies. Get the exhaust out of the exhaust system as fast and efficiently as possible.

Brad


[Modified by lazerus, 11:07 AM 10/31/2002]


[Modified by lazerus, 11:07 AM 10/31/2002]

NeXtLeVeL_TyPe_R

Thanks Lazerus for your thoughs

-although i am gonna have to read it a couple of times

lazerus

hehe, no problem. just trying to contribute

GB

Well let me know when you're done shipping that "ton of crap."

I'm interested in seeing why you disagree with my reasoning, especially since it looks like you are in a business to make/sell that stuff for a living.

CovertFI

i think most people forget the fact that it is the heat from your exhaust that creates the energy to spin the compressor. but this is a great topic to discuss

Full-Race Geoff

alright, things have been hectic as hell but i finally have a little time. Sorry i havent been able to get back to all of you.

The great tube debate. Many people ask me why i only use a 1.5" tube, why dont i use 1.75 etc etc, and then there is runner length, collector shape all sorts of stuff.

Most ideas brought up regarding bigger tubes = higher top end and smaller tubes = more torque do not apply to turbocharging. This is great for n/a cars but definately not turbochargers. If you want to change the characteristics of the powerband you should change the housing on the turbo. The common debate is the .63 vs. .82 housings, i dont think i need to explain which does what.

As far as runner volume goes, the cross sectional area of the scroll of a turbine is much much smaller than that of the 4 runners combined. As a result you want the air to be entering the turbine housing as fast as possible as it will lose a TON of energy in the turbine wheel, as it converts heat energy and momentum to mechanical energy as it spins the turbine. The turbine housing will always start off at the same size on a t3 (standard box) and it will neck down to the scroll at the housing's respective shapes.

Now the next part of the equation is obvious, if you want to keep the velocity as high as possible entering the turbine housing what should you do? Simple, keep the runners as small as possible. In this case as small as possible equates to keeping them the identical size as the port. It is very very important to maintain a constant size runner behind the valve so that both pressures and velocities will remain as close to a constant as possible. Anyone who makes varying runner diamaters is searching for gains in the wrong places in my opinion. Also, the opinions of the majority of other highly succesful header builders. Not import related here, but look at any of the older indy turbo manifolds, they all are slip fit, coated, expansion compensated merge collector manifolds.

Anti reversion manifolds are AWESOME for n/a cars. However, they really dont work very well on a turbo car. Its a nice idea, but what people fail to realize is that once the turbine is spinning quickly it starts to actually create a pressure differential with lower pressures being at the scroll. These lower pressures help to pull the air from the beginning of the manifold to the collector and into the scroll. Anti reversion chambers definatley cant hurt a turbo manifold, but their gains will be quite negligable on a properly designed equal length manifold

Next is runner length. Some say what is the point of making the runners longer and longer if the air has to bend? Well most bends are available in two forms, short radius and large radius bends. What we use (and swear by) is called long radius tube. This means that for a 1.5" diameter tube, the radius of the bend of the tube is 1.5". The same goes for our downpipes, this is 3" material bent on a 3" radius. Long radius bends are designed specifically to not have ill effects on air flow. There is a fluids formula which explains this all (javier stole my damn book and swears he will bring it back tonite... we'll see) but i did the calculations before, and long radius theory holds true. There is no need to increase the diameter.

In any turbocharged car i think the turbo should be made to do as much work as phsyically possible. Thats what its there for. If you build the system to take full advantage of the turbocharger, the motor may not make more power but it will live longer. The added stresses on the motor and tuning challenges brought about from a high compression motor are definately a hurdle and they take a lot of streetability out of a car. people love to hear the words high compression and high boost, becuase it inflates egos a bit, but its not worth it. I know one car that goes very very fast runing a 7.2:1 compression.

Heat makes a huge difference. Heat is super important in this equation and is another reason why people should use thickwall stainless. The thicker the wall, the better an insulator it is. Also the stianless insulates better than mild steel and will not flake off from repeated heat cycles. This being said, the runners from cyls 2 and 3 should always be longer than 1 and 4 becuase as is well known the egts here are always hotter. This makes sense because cyls 1 and 4 are surrounded by more water than the cyls 1 and 4. cyls 2 and 3 are surrounded by cyls 1 and 4 adding to higher egts. This temp difference means that a longer runner will keep it at a slightly higher energy level than 1 and 4 so its ok to keep the runner longer and lose a small bit of energy over cyls 1 and 4 so that the turbine gets hit with a series of smooth, pulsing pumps.

MOST MOST MOST important is the collector design. If that collector is not super efficent there is no point of making the runners long. The collector is what every manifold should be designed around. The long runners on my manifodls are mainly there becuase i want to use a perfectly designed merge collector and put the turbo in an accesible reasonable location. As a result i cant find any better way to put the merge collector there without using a runner that bends *smoothly* to get there.

ive got more to say but thats been 1 hour. go ahead and critique me on this and if javier brings my fluids book back we can get more technical. great discussion guys.

Prod

Great post Jeff...Thanks for posting this, it's good to hear someones opinion who's been making manifolds for awhile.

Full-Race Geoff

cmon i write this big huge post and no one will respond.

cmonnn make fun of me or something at least. ttt will do too

tony1

You don't know what you're talking about Geoff....

NeXtLeVeL_TyPe_R

Yea what a load of crap


jk...great post Geoff.

Particular what you said about making the turbo do the work and relieving stress on the engine


[Modified by NeXtLeVeL_TyPe_R, 5:05 PM 11/2/2002]

Quick 200k Mile Motor

Casted manifolds have shorter length runners for cyl's #1 & 4.

psyche!