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Priamry and Secondary pipe lengths for exhaust manifold?
NS Dev - 18/12/04 at 12:34 AM

Does anybody have access to information regarding the "ideal" primary and secondary lengths required on a Vauxhall XE 2.0 16v engine. Peak power would be around 6000 rpm and I am using 1.75" primaries, 2" secondaries and 2.5" outlet.

Thanks

200mph - 18/12/04 at 12:36 PM

i have a book which explains all that kidna stuff.

you can borrow it if you want or i will have a go at working it out..

mark

ned - 20/12/04 at 07:06 PM

i'd be interested in this info too...

Ned.

NS Dev - 21/12/04 at 09:26 AM

I suppose I might be being a bit daft here!

I have an SBD manifold for fitting a 16v XE into a Manta (from when I built one like that) but I am worried that the primary lengths might be shorter than ideal to suit the car. His seven type bonnet exit manifolds seem to have longer primaries.

Thanks for the info, thanks Dave, I'll try it out, I doubt it will be bollox, and I can compare to my SBD RWD manifold and aim between the two if the calculated one is much longer!

Cheers

Nat

NS Dev - 21/12/04 at 09:31 AM

Thanks Dave,

that little sheet has answered my question!!

I was bothered because I had a value of 30-32 inches for the priamries in my head, and couldn't see how this would be possible. Now I see that is the combined primary and secondary on a 4-2-1 which is what I am making.

Perfect, thanks!

ned - 21/12/04 at 10:00 AM

So nat, what are your dimensions for primaries and secondaries? from head to first 'y' piece and first to second 'y' etc..

please....!!

I'm looking at doing/getting done a bonnet exit manifold in due course...

cheers,

Ned.

NS Dev - 21/12/04 at 12:10 PM

The dimensions I that I know are: 30 inches from head flange to the 2-1 Y piece in total (the distance from the head flange to the 4-2 y pieces will be copied from the SBD manifold, but I'm at work at the mo so I can't measure that!) and the pipe diameters are: 1.75" primaries, 2" secondaries and 2.5" outlet pipe.

I'll put the distance from the flange to the 4-2 y pieces on the SBD manifold on here later on when I go home.

ned - 21/12/04 at 12:46 PM

Thanks Nat. Are you making the exhaust yourself or getting the design together for someone else to make up?

Ned.

NS Dev - 21/12/04 at 03:26 PM

I am hoping to buy the bends and make it up myself (well, with a mate who does stainless stuff in his spare time, under the name "Custom Solutions" that way I can TIG it all up nicely)

I will get the bits from Milner Offroad, but I am a bit stuck on the 1.75" bends at the mo, nobody seems to do them in stainless..............any ideas anybody????

ned - 21/12/04 at 03:46 PM

type907 (paul) might now, he's the guy who's doing the lurvely stainless silencers at the moment...

Ned.

krlthms - 21/12/04 at 06:57 PM

This is all second hand, but may be of use nevertheless:
1. There is a good discussion about tuning headers in Beardmore brothers site (www.beardmorebros.co.uk ). As I understand it, there is no "ideal" design, it all ldepends whether you want to boost power high up or low down on the rpm vs power curve.
2. I have read somewhere that the cheapest source of pre bent SS tubes are firms that supply the dairy industry.
Cheers
KT

907 - 21/12/04 at 09:58 PM

Hi Chaps,

I get my bends from Hygienic Process Equipment.

www.hpe.co.uk

A 2" 90 deg 316 S/S bend is about £7.

Hope this helps. Merry Xmas

Paul G

Rorty - 22/12/04 at 04:48 AM

quote:
Originally posted by krlthms
This is all second hand, but may be of use nevertheless:
1. There is a good discussion about tuning headers in Beardmore brothers site (www.beardmorebros.co.uk ). As I understand it, there is no "ideal" design, it all ldepends whether you want to boost power high up or low down on the rpm vs power curve.
2. I have read somewhere that the cheapest source of pre bent SS tubes are firms that supply the dairy industry.
Cheers
KT

Shorter primaries = higher revs and longer = more torque and therefore, more flexibility.
The torque can also be moved around in the rev range by selecting different size tube.
Don't forget that primaries are measured from the valve head and not the outside of the port.
If it's of any help, I have some info on my site HERE.

Dave, thanks for sharing that excellent spreadsheet with us.

quattromike - 2/1/05 at 03:36 PM

quote:
Originally posted by 907

A 2" 90 deg 316 S/S bend is about £7.



I'm also building my own exhaust from stainless and i'm going to use long radius bends so that i will minimise the restriction on the gas flow through the exhaust, thats still the main objective isn't it ? or does any one think a little restriction is good?
As far as i understand you want the exhaust gas away from the engine as quick as you can to make way for more gas on the next combustion and also helps to keep the engine cool.
Does anyone agree?

Mike.

Rorty - 2/1/05 at 08:25 PM

quote:
Originally posted by quattromike
I'm also building my own exhaust from stainless and i'm going to use long radius bends so that i will minimise the restriction on the gas flow through the exhaust, thats still the main objective isn't it ? or does any one think a little restriction is good?
As far as i understand you want the exhaust gas away from the engine as quick as you can to make way for more gas on the next combustion and also helps to keep the engine cool.
Does anyone agree?

Mike.

Yes and no. Some engines perform better with more exhaust back pressure than others. It all depends on specific individual engine characteristics.
Tight radii have little effect on exhaust performance, it's restrictions and transitions that pose the biggest problems.
The one thing that can help is to iron out restrictions and easy any change of volume.
The gasses will flow faster around the periphery of bends and will flow much slower around the interior which can cause quite a bit of turbulence mid stream.
The current thinking is to increase the capacity of the header tube on the inside of the bends to speed up the interior flow to better match that of the peripheral flow.
To this end, several super bike and F1 teams now run D-section exhaust tube (with the flat of the D to the inside of the bends).
It seems to work very well, but makes the exhaust systems extremely expensive to produce. It's not easy bending D-section tube and smoothing its transitions to round section again.
I think it is Honda who actually use an oval section tube (flats towards the bend centres) on their new bikes to address the same problem.
If you wanted to duplicate this practice yourself, the easiest solution might be to make D-section bend formers from hardwood and apply traditional sheet metal-working techniques to fabricate mirrored halves from shet steel and then weld the matching halves of the header pipes together and to the remainder of the system.

mark_UK - 3/1/05 at 12:36 AM

Don`t know if this might help :
http://www.nightrider.com/biketech/calc_exhaustlength.htm

NS Dev - 3/1/05 at 06:10 PM

Any talk of "back pressure" being a good thing is basically wrong. Bigger pipe is not always better but this is not because it has less backpressure than samller tube, it is because it reduces the exhaust gas velocity, so decreasing the reflected pressure pulse from the collectors. (hence the use of D-section tube to get smooth flow over a large radius but reduce pipe volume to better reflect the pressure pulses.)


What I am unsure about is the relative importance of primary to secondary lengths on a 4-2-1 manifold? I understand that shorter theoretically gives better power (actually better pulse initiated scavenging) at higher revs (obvious really, takes less time for pulse to travel up tube!!)

Now this is all nice and obvious on a 4-1 system, but on a 4-2-1, is the reflection between cyclinders 1-4 and 2-3 more important, or the "cross pulsing" achieved at the secondaries between 1-2 and 3-4?? Or is it that both are achieved at different rpm due to the different lengths of primaries and secondaries, hence the "better midrange torque" statement, which would then seem to be due to having two tuned lengths, one for 1-4 and 2-3 scavenging (the primaries) and one for 1-2 and 3-4 scavenging (the primaries and secondaries combined)

If this is the case, then would it not make more sense to have the 1-4 primaries a different length to the 2-3 primaries? This way you may achieve a lower max power but you spread the scavenging more evenly across the rev range, so increasing the power spread????

My head is really going round and round now!!!!!

Having said all this whilst thinking aloud really, the conclusion has to be that a 4-1 manifold is tuned for 1 specific rpm level, a 4-2-1 is a hotch potch that helps the power spread (which is what I am currently trying to achieve with my new grasser exhaust manifold)

So therefore the ultimate answer is to bin the 4-2-1 and go for a variable-length 4-1!!!!

Hmmmm, tricky one to build perhaps!!!

quattromike - 3/1/05 at 06:37 PM

yes that would explain why the standard manifold fron the 20xe (at least on the one i have) th primarys for 1&4 are a diferent lenghth from 2&3. And the secondaries are also a different length.

Stu16v - 3/1/05 at 09:09 PM

...which brings us nicely to the Yamaha EXUP valve...

Rorty - 3/1/05 at 09:28 PM

quote:
Originally posted by NS Dev
Any talk of "back pressure" being a good thing is basically wrong. Bigger pipe is not always better but this is not because it has less backpressure than samller tube, it is because it reduces the exhaust gas velocity, so decreasing the reflected pressure pulse from the collectors. (hence the use of D-section tube to get smooth flow over a large radius but reduce pipe volume to better reflect the pressure pulses.)

You can't dismiss backpressure as being "wrong". It's a part of exhaust design and function.
Nobody suggested a larger bore pipe was better.
The function of D-section tube is to smooth out gas flow around SMALL radii (as found on most headers) and not large radii as you state.

quote:
Originally posted by NS DevSo therefore the ultimate answer is to bin the 4-2-1 and go for a variable-length 4-1!!!!

Isn't that what Honda's and Yamaha's electrically controlled exhaust valves do?
This is all fine in F1 and Superbike territory, but lesser mortals shouldn't lose any sleep over it. I've raced BECs for years and anyone running a Yamaha motor with an EXUP valve simply removed it.
I have always run 4-2-1 systems to enhance the low down torque and flexibility of the engine when fitted in a BEC. The results are quite noticable.

Stu16v - 3/1/05 at 10:18 PM

quote:

You can't dismiss backpressure as being "wrong". It's a part of exhaust design and function.


Mmm. I would tend to disagree there. Backpressure in the system means that the engine has to use (or more correctly lose) energy to expel the gases, which obviously means power drop at the wheels. Ideally, the exhaust should be as free flowing as possible (but in practise this is very hard to deliver with ever tightening noise reducing requirements)...

Rorty - 3/1/05 at 10:26 PM

quote:
Originally posted by Stu16v
quote:

You can't dismiss backpressure as being "wrong". It's a part of exhaust design and function.


Mmm. I would tend to disagree there. Backpressure in the system means that the engine has to use (or more correctly lose) energy to expel the gases, which obviously means power drop at the wheels. Ideally, the exhaust should be as free flowing as possible (but in practise this is very hard to deliver with ever tightening noise reducing requirements)...

Yes, OK, I'll wear that.

NS Dev - 5/1/05 at 02:10 PM

Dave, I wasn't planning on building a variable exhaust system, although my very poor F1 knowledge tells me they use a sliding "trombone" type system on their intake systems (I am willing to be corrected on this one!)

Sorry, can't do Ansty Arms, got urgent plumbing job to do!!! (no hot water!)

Cheers

Nat

ettore bugatti - 2/2/06 at 08:06 PM

quote:
Originally posted by Dave Ashurst
You could play with this: I wrote it based on some book formulae, but they might be bollox. (the macros are OK not viruses BTW)


Just found that when using this excel sheet. The lenghts of the primaries are always 15" long.

[Edited on 2/2/06 by ettore bugatti]

tks - 2/2/06 at 09:08 PM

the problem with an high exhaust gas speed is that you can suck out fress mixture! lets say the problem wich have the 2 stroke engines without the exhaust....

the trick is that the mixture is just in when you close both the valve's....

this valve overlap (the time both valves are open) is there just for that trick...

the speed of the outgoing gasses pull in the new mixture...but if you pull to hard the filling % will be less sow less power.

You pull to low and you are on the other side of the problem.

the trick to close the inlet valve when the gasses are in,
because if your piston goes up and your inlet isn't closed you get the problem that the mixture is pressed out..

a engine is a very complex thing, things depend on many many factors....

Thats the reason in F1 it takes sow long to gain 400rpm


Tks

[Edited on 2/2/06 by tks]

ned - 2/2/06 at 10:05 PM

I've been researching this (again!) lately for the design of my exhaust system that I'm having made in about a month's time.
I came across this thread on blatchat which might be of interest, as it mentions both lengths and diameters of high power vauxhall caterhams exhausts..

http://www.blatchat.com/T.asp?id=4016

When they say primaries do they mean the total length of 4-2-1 and the secondary as the 2-1 bit? 30 odd inches sounds a lot to me otherwise, ut i do have some pics I can post up to show examples of race spec bonnet exit 7 type exhausts which is essentially what I hope mine will turn out like..

Ned.

[Edited on 2/2/06 by ned]

NS Dev - 2/2/06 at 10:55 PM

The primary length on a 4-2-1 (as far as I know!!) refers to the combined 4-2 bit, not the entire 4-2-1.

If you measure a few long 4-2-1 systems from the valve to the 2-1 collector they should be around 30 inches. If you think rouchly 2'6" and look at a few this is around the length they all run.

Worked on my grasser, improved torque a lot from the std vauxhall tubular 4-2-1, which is too short.

ned - 2/2/06 at 11:07 PM

ok its late and i'm being stupid, to quote the caterham boys:

31" Primaries 1 7/8 header dia
15" Secondaries 2 1/4"
3" collector dia at silencer

thats 31" from valve to 4-2 join then 15" from 2-1 ?

I'm more likely to go along the lines of the other guy:

27" primaries 1 7/8" dia
10" secondaries 2 1/4" dia
2 1/2" link pipe to silencer this is only about 3" long.

these sound longer than the way you have described it Nat?!

Ned.

[Edited on 2/2/06 by ned]

NS Dev - 2/2/06 at 11:12 PM

They are! Think I may have it wrong then, but the lengths I used worked for me on the grasser, but then without rolling-roading a really long primary system I don't know if this would be better still!!!!

I think Simpson know what they are about, I'd be inclined to follow their suggestions!

Let me know what they/you find, and I'll follow suit with mine!!

ned - 2/2/06 at 11:15 PM

pah, that sort of info will cost ya

..but on the phone they generlised and said for an xe somewhere around 24-28" primaries and 8-10" secondaries iirc..

Ned.

[Edited on 2/2/06 by ned]

NS Dev - 2/2/06 at 11:17 PM

LOL!!