Mike Rainbird

iTrader: (3)

Importance and effects of: Length, size (diameter), rotational firing order etc.

Discuss .

AlexF

unequal headers and funny firing orders sound better

Anonymous

Its so funny the thing that most people love the scooby for so much is one of its performance down sides

heeman10

Lazy bastard!

I'd be saying the lower the backpressure the better. The turbo'll be creating backpressure as it is, so the shorter the exhaust and the bigger it's diameter the better, ie fat screamer pipe would be the ultimate. Am thoroughly prepared to accept that as poor theory if someone can prove it

rsnissan

iTrader: (9)

pmsl sound like a convo we had last night

Anonymous

4 stroke petrol engines have no benefit in having any "back pressure" that im aware of.

Any resistance to flow is only ever going to lose you power IME.

you need an appropriate sized pipe (especially on an N/A car) to keep gas speeds up and hence help to scavenge the last fiew bits of exhaust gas from the chambers, but thats actually a negative back pressure at that point in the cycle (due to the vacuum created behing the gasses as they go up the pipe)

I cant picture in my mind ANY point in the cycle where having positive back pressure is actually a good thing?

AlexF

absolutly!!!!!

but its true of rover V8s as well

Alex

Mike Rainbird

iTrader: (3)

Turbo cars please - or can't you read? So far, zip . I was expecting to here some discussions on what effect length and diameter has to gas speed etc . I suppose for an interesting discussion on this, I'll have to wait for Karl or Stu to post .

Karl

Mike this is one topic I wont discuss in public as it is the KEY to making power on a YB. The std 2wd manifold is shockingly bad compared to what a good tubular can produce. However as I don't make exhausts in general (only occasional one offs) I don't want to help any companies out who may read this site who do make them!!

AlexF

my scooby is turbo'd

so is the only rover v8 I have worked on






Alex

Mike Rainbird

iTrader: (3)

Fair enough . I know how important it is and also how poorly designed the 2wd manifold is, so thought it might make a good topic for discussion.

Peeps, please don't confuse this with the exhaust AFTER the turbo, as it is irrellevant (apart from back pressure) on a turbo car. I am talking MANIFOLDS.

heeman10

Sounds like you're going to need to make about five manifolds up using different diameters and primary lengths then Mike, and then dyno the engine with different manifolds to see what effects they have. Only surefire way to find out I suppose!

P.S. Then tell us of your findings

rsnissan

iTrader: (9)

any gains to be had using a tubular with a fairly standard head on a t34? or is there no need until a bigger turbo/head work is done??

Mike Rainbird

iTrader: (3)

Already done, hence why the tubular manifold we sell can be purchased in different diameters .

Here are some pictures to kickstart the discussion .

foreigneRS

on a turbo car, i can't see a reason to specify a certain length, as i'd imagine that you can't 'pulse tune' the exhaust gas scavenging due to turbine back pressure.

i would've thought that lowering the back pressure as best as possible between the ports and the turbine is the priority , in which case bigger diameter is better, and as straight and short as possible, or at least gentle curves.

Anonymous

* NOT A FOR SALE POST *

Mike, why dont you get the ball rolling with your detailed findings and reasonings then?

That way Stu will have less to write when he comes along than if he has to start from scratch.

I dont have the depth of knowledge needed on the subject to feel i can contribute properly with an article on it im afriad, so its not laziness but a lack of experience that stops me posting an article on this one.

Intetesting topic though

Mike Rainbird

iTrader: (3)

Another clue as to why the design is as it is...

Anonymous

Mike, words or STFU

foreigneRS

does gas speed come into it?

is the work that the turbine can do a function of the gas speed through it, or the energy of the gas going through it?

the mass flow will be higher with a bigger diameter pipe as there is less pressure drop, but does that give more energy than a smaller mass flow with a higher speed that you would get with a smaller diameter?

heeman10

Because it was cheapest, and the shinyness meant you could sell lots of them attached to heads so you could clear up the mess in the back of that photo?


In fact, thinking about it, I'd say the shorter the primaries the better, because turbo's are more efficient when being bombarded by sharp "smacks" from individual exhaust pulses. A long primary builds in damping in the gases due to the volume, so the shorter the primaries, the more defined each pulse will be. That's more in relation to the way the turbo reacts to the exhaust gases though, as opposed to outright power production so, again, probably not the sort of discussion you're looking for here

Mike Rainbird

iTrader: (3)

Firing order... . Look at what collector shares what pair of tubes...

rsnissan

iTrader: (9)

Ohhh thats clever

Anonymous

My limited understanding is that speed is of little relevance as its so strongly governed by the hot side of the turbo anyway.

Keep tine heat in is a good thing, as it means higher pressures, so from a perfomrance point of view i would say shorter = better.

But there are other factors such as shorter means more heat held close to the head so the potential for heat related failures increases (ie valves failing or head cracks)

Anonymous

Mike, you seem to have TOTALLY missed the point of these threads.

The idea is to give the information you have, not to regurgitate a couple of small bits you heard from someone else and try and sound mysterious and clever by not saying the rest when in fact its cuase you dont actually know the rest

Either speak frankly and in detail, or just dont bother to speak at all!

Mike Rainbird

iTrader: (3)

Chip,
I was just wondering how much knowledge there is out there about this side of things, and it seems very little.

I was just having an arguement with someone about the length and how this moves the power band around like a normally aspirated manifold does....

Anonymous

Clue : its not the length, its the volume

rapidcossie

is the 2wd manifold really that bad??

was always led to believe that as far as standar manifolds go the 2wd is one of the best

its practically a equal length tubular manifold...well almost

Mike Rainbird

iTrader: (3)

It's still quite restrictive (above 550bhp) and isn't particularly efficient compared to a true tubular system.

foreigneRS

not convinced on the length, or the volume shifiting the power band

i could believe that by changing the length you are changing the pressure drop, as it may involve different radius bends.

RichardPON

I know NOTHING about stuff like this, but are you saying that the relevant cylinders are linked by the exhaust manifold to speed up the flow of gases?

Mike Rainbird

iTrader: (3)

This is my belief as well.

rapidcossie

thats what i thought mike....

karl sems to think a standard manfold that can be picked up for buttons and can run 500 bhp is "shockingly bad"

looks ok to me

Mike Rainbird

iTrader: (3)

It can certainly be improved upon and is not perfect - an acceptable compromise....

Anonymous

Lets cut out all this Tec jargon With a 3" one car does 201 with a 3.5" one car does 210.

foreigneRS

you have a manifold made from 3.5" tube Rod?

Mike Rainbird

iTrader: (3)

Rod,
LEARN TO READ BEFORE POSTING .

Garage19

So are you hinting at the pairing of the cylinders in a 4-2-1 config manifold being critical?

Stavros

Fudgey

iTrader: (4)

well all i see is that cyl 1/3 go to turbo, and cys 2/4 go to wastegate

is that right?

i aint got a fookin clue otherwise... lol

primary designs can do all the mafs for mine

heeman10

3.5" manifold? I don't think even MAD are that mad!