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#1115849 - 14/10/2010 22:38 20vt Exhaust manifold
fialcia Offline
Discoverer

Registered: 16/01/2009
Posts: 29
Loc: blackburn lancs
I am making a manifold is there an optimum or maximum size for the primery tubes on the exhaust manifold, also i am putting the engine in a kit car is there a maximum distance the turbo can be from the exhaust ports any suggestions welcome.


Edited by fialcia (14/10/2010 22:38)

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#1115997 - 15/10/2010 10:05 Re: 20vt Exhaust manifold [Re: fialcia]
Nigel Offline
Club member 123
Forum veteran

Registered: 16/12/2005
Posts: 16982
Loc: Staffordshire
Well done for having a go, but I fear you'll never get better results than stock - many professional tuning companies have tried and failed

As for the distance of the turbo from the exhaust ports, minimum is generally best as it makes best use of the gas speed - however you need to consider whether you're going purely for short header length, or whether you're going to attempt to get equal-length headers

As for primary tube diameter, you are again faced with a compromise - do you want to shift lots of gas, or do you want to shift the gas quickly?

A lot will depend on the intended turbo - some turbos need a high gas speed to prevent excessive lag, others will be less dependent.

You should probably make yourself a cup of tea and spend a couple of hours (or days shocked ) trawling through Guy Croft's excellent forum
_________________________


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#1116184 - 17/10/2010 11:50 Re: 20vt Exhaust manifold [Re: Nigel]
rmouthaan
Unregistered


Hi, in another post i just said i might be making an 20v manifold also. But now i read that its impossible? What is the problem?, or is the stock manifold just very well made?.

Sorry for all the questions

regards remco

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#1116256 - 17/10/2010 18:58 Re: 20vt Exhaust manifold [Re: ]
Nigel Offline
Club member 123
Forum veteran

Registered: 16/12/2005
Posts: 16982
Loc: Staffordshire
Originally Posted By: rmouthaan
now i read that its impossible? What is the problem?, or is the stock manifold just very well made?


It not impossible - there have been several versions over the years

However, the standard manifold has proven to be durable and capable of big power (lots of cars well over 400bhp with a standard manifold) It simply needs to be port-matched to the cylinder head and cleaned up a little around the collectors

I'm fairly convinced that the cause of the common cracking is because of a short heat/cool cycle - I'm still on the original manifold from my old Sprinty - its now done more than a quarter of a million miles
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#1116331 - 17/10/2010 22:06 Re: 20vt Exhaust manifold [Re: Nigel]
fialcia Offline
Discoverer

Registered: 16/01/2009
Posts: 29
Loc: blackburn lancs
Thanks for the reply i should have given you more info i am building a delta s4 replica and my engine of choice is a 20v turbo,the reasons for my questions is the turbo will not be in the original position it will sitt slightly forward of the front of the engine (ie cam belt end)back to questions is exual lenght pipes important on a turbo engine,i will now sit down for a night on the guy croft forum thanks mick.

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#1116435 - 18/10/2010 09:43 Re: 20vt Exhaust manifold [Re: fialcia]
rmouthaan
Unregistered


S4, very very nice. But yes equal length is important, but so it the pipesize, the numbers of bends(minimum), the degree of the bends,angle of collector, material etc. With trying to get an equal length manifold you are trying to avoid cilinder interference. But if the bends per runner differ to much then you will lose the gains you made with the equal lengths. For you, you might be lucky, as you move your turbo quite a bit, so you can make an nice manifold as you have all the room to play with. Dont go to large on the pipesize though, unless you are going to run big big power.

Regards and all the luck

remco

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#1117606 - 20/10/2010 11:58 Re: 20vt Exhaust manifold [Re: ]
GCRE
Unregistered


Never mind bend radius and weld/joint quality and static back pressure, too short and too small a pipe diameter will be an absolute disaster and the enemy is, oddly enough, the sonic exhaust pressure waves whose speed varies directly with temperature. These waves interact and superpose and boucne all over the place cylinder to cylinder especially on short 4-1 systems with a poorly laid-out collector: they are a menace and functionally useless on your turbocharged engine. It is the exhaust port static pressure and heat energy that drives the turbine on your engine not the pressure waves.

Worse is to come: lagging to keep temperature up compounded with a short, small bore system with even minor deviations in flow characteristics generated by unequal length and poor exectution of bends and joints plus too much exhaust event or excessive boost will cause the most bizarre and damaging effects - local and very high port and cylinder temperature, turbine failure, erratic firing, distorted and burned valves, valve seat loosening and fracture, detonation with blown gasket and ruptured piston etc etc.

This is an issue of critical importance and I have devoted much time and thought to it in my new book which I urge you to buy if for no other reason than you will likely not find the answers to your questions anywhere else incl my website. I have seen more damage caused to engines of all kinds by infantile design of exhaust system than almost anything else. The standard plenum (damper) manifolds are OK up to a point and beyond that, frankly, you should expect to pay over £1000 for something effective enough to work consistently well on a tuned engine and if you choose unwisely you may be in for a real shock.

GC



Edited by GCRE (20/10/2010 12:01)

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#1117615 - 20/10/2010 12:11 Re: 20vt Exhaust manifold [Re: ]
Nigel Offline
Club member 123
Forum veteran

Registered: 16/12/2005
Posts: 16982
Loc: Staffordshire
Guy - looks like your name alert is still working well! I'd hoped you'd spot this thread when I mentioned your name earlier

When you worked on Matty's head did you flow-test the exhaust manifold as well?

As I said above, several people have tried tubular manifolds and I'm fairly sure that all of them have reverted back to a standard cast manifold

You commented when you worked on the 20VT head that it was a superb basic design, with pretty much everything in the right place and at the right angle. On the assumption that Fiat's engine designers seemed to know what they were doing, I can't believe that they would accept a crappy manifold design. We know the engine can suffer from piston failure that can be attributed to excessive backpressure, but we believe this is caused by a tiny turbo and a ridiculous 2" V band downpipe adapter. Good for midrange torque, we understand, but less useful at allowing decent top end breathing

Other than the unequal length headers (caused, I assume by a packaging restraint, rather than any performance issues), the only aspect that has always baffled me is that the ports in the manifold are significantly smaller then the ports from the head - there's a huge step (2mm all round) which can't be good for gas flow

Nice plug for the book wink Any discount for FCCUK forum members?
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#1117663 - 20/10/2010 13:08 Re: 20vt Exhaust manifold [Re: Nigel]
GCRE
Unregistered


Discount? When you've read it and told me it's not worth the price I'll think about it!


GC

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#1117673 - 20/10/2010 13:32 Re: 20vt Exhaust manifold [Re: ]
rmouthaan
Unregistered


Who would have thought that the manifold was such an important factor. Had this discussion an long time ago, but without succes sadly enough. Actually i do try to take in account the pipesize/turbulance/temperatures/angles/collectors etc. But the biggest enemy is the room to make an sufficient manifold or atleast to make one that is a bit or a lot better then the std.version without having to reorganize the intire engineroom. That no single manifold will do, for all situations and enginesetups is very clear, but to make the best with the space there is, just pushes me to compromize a lot. For now i just let the manifolds flowtest staticly, its not much, but then i will have something to start with. What do you think about the sofware available at the moment, for example ricardo wave or simulair? Thanks for the reply, and hope to read your book soon.

Regards remco

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#1117684 - 20/10/2010 13:56 Re: 20vt Exhaust manifold [Re: ]
GCRE
Unregistered


True.

As for Wave or any other software the annual licence is so expensive (I mean really expensive) that you'll never get access to it and if you did it would take weeks to put in all the parameters and process it even for one single installaion. And what it would tell you is what I've in essence already said and what you've referred to directly, that unless the architecture of the vehicle really does permit an optimised manifold setup you can't tune the engine with much hope of success at all.

I am going to 'stick my neck out' and say (perhaps for the 1st time) that tuning of turbo engines must begin with addressing this issue above all others.

GC

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#1117694 - 20/10/2010 14:12 Re: 20vt Exhaust manifold [Re: ]
Nigel Offline
Club member 123
Forum veteran

Registered: 16/12/2005
Posts: 16982
Loc: Staffordshire
Guy Croft sticking his neck out? Whatever next wink

So, Guy - are you saying that our cast manifolds have significant room for improvement?

Clearly, the issue here is that the vast majority of Coupes are road cars, with rather tight engine bays that can't easily be extended to accommodate a "perfect" manifold. There's already a compromise in the downpipe design, as the exit from the turbo is very close to the aircon compressor - it has to take a fairly tight downward turn straight out of the turbo

Its interesting that you cite the manifold as a starting point for tuning turbo engines - is this in all cases, or does it only apply once the manifold is known to be a restricting factor?

As you have possibly read, there are many 20VTs with over 400bhp that are still running the stock manifold (although in all cases, it will have been port-matched to the head to get rid of the huge step I mentioned earlier)
_________________________


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#1117700 - 20/10/2010 14:21 Re: 20vt Exhaust manifold [Re: Nigel]
Nobby Offline
Je suis un Coupé

Registered: 16/12/2005
Posts: 9214
Loc: At a fancy jamboree
Guy - I'm happy to send you a standard (albeit cracked and now welded) manifold for you to have a play with).

I'll even chuck in a gasket and a spare head if you like.
_________________________
Daytona Grey RS6 Avant

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#1117742 - 20/10/2010 15:27 Re: 20vt Exhaust manifold [Re: ]
rmouthaan
Unregistered


Indeed the software takes alot of time to programm,but i dont really mind as long as the results are positive. Will have a look next week at mentor graphics, they have some maybe interesting and faster to work with programm. Glad you sticked your neck out, now i can give my already overstretched neck some rest. Thanks again for your time and thoughts.

Regards remco

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#1117767 - 20/10/2010 15:52 Re: 20vt Exhaust manifold [Re: ]
GCRE
Unregistered


The OE manifold will no doubt be good 'up to a point'. The Int 16v one (eg) is good for about 400bhp. Never seen a 20v one and don't care to.
Importantly there is a significant difference in mode of operation betw a cast item (designed to try and damp out the pressure waves) and a tubular one. If the tubular one is too short/small/hot it will have a very adverse effect on the firing and exhaust cycles - by comparison.

Selection of a SUITABLE exhaust manifold as a precursor to tuning is vital if you are aiming for much more than 1.5-2 x OE output and if you do bother to give precedence to that part you can get power gains per-se from a good system in itself with no_other_mods. Never believe, all that said, that because it's tubular - it's better than OE - it may well be a disaster whatever claims are made for them by the folk who produce them. To prove out a turbo header and sell it you have to do days of the most intensive calibration, run the engine flat out on full boost and power and then run it on a car for months to see it cracks.

GC


Edited by GCRE (20/10/2010 15:52)

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#1117781 - 20/10/2010 16:11 Re: 20vt Exhaust manifold [Re: ]
Nigel Offline
Club member 123
Forum veteran

Registered: 16/12/2005
Posts: 16982
Loc: Staffordshire
Hmmm - I'm running in your "1.5 to 2.0 x OE output" range and I still have nothing more than a port-matched OE manifold

However, I have no way of knowing whether the manifold is holding me back or not, so I accept that I might be giving better power with a better manifold (although I reckon my limiting factor is my turbo - I'm already at the upper reaches of what Garret say is possible)

I seem to recall that having tried and discarded a tubular manifold, JohnS reverted back to a lightly-ported OE item for his 2.4l Coupe - this was giving around 550bhp on pump fuel and over 600 on race fuel - surely this would suggest that the manifold is inherently capable?
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#1117819 - 20/10/2010 17:02 Re: 20vt Exhaust manifold [Re: ]
rmouthaan
Unregistered


I will give it some serious thoughts, have some tubular versions also, but for sure you cannot use them for any race applications or 1,5 or 2.0 times the std.power. Cracking is often an problem indeed, 321 or inconel might prevent this a bit more, but still its difficult to prevent on an new product. Sometimes they try to solve with bracing, or just use an large wallthickness. Shifting problems you would think. May i ask who you normally use for these custom headers and manifolds?

Now preparing for an full boost run to italy smile

Regards remco

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#1117823 - 20/10/2010 17:09 Re: 20vt Exhaust manifold [Re: ]
Marco20ValveT Offline
I AM a Coop

Registered: 03/09/2008
Posts: 12731
Loc: looking for another 20vt
if its going to cost £1000+ to make a manifold for the 20vt would it not make sense to buy a pre made manifold??
_________________________
Torque Automotive LTD

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#1117829 - 20/10/2010 17:19 Re: 20vt Exhaust manifold [Re: Marco20ValveT]
Sedicivalvole Offline
Club member 147
Forum is my life

Registered: 17/12/2005
Posts: 6546
Loc: Northampton England
All dependant on your desired specification I believe.
_________________________
Vinci Grey LE
Alfa 147 GTA 3.2 V6
BMW E92 M3 4.0 V8
Fiat Tipo Sedicivalvole 2.0 16v ABS

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#1117880 - 20/10/2010 18:50 Re: 20vt Exhaust manifold [Re: Sedicivalvole]
ktm450exc
Unregistered


tongue


Edited by ktm450exc (21/10/2010 02:14)

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#1117883 - 20/10/2010 18:59 Re: 20vt Exhaust manifold [Re: ]
ktm450exc
Unregistered


its the 20vt manifold in marcos link

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#1118054 - 20/10/2010 23:30 Re: 20vt Exhaust manifold [Re: ]
fialcia Offline
Discoverer

Registered: 16/01/2009
Posts: 29
Loc: blackburn lancs
All turbo manifolds wether they are 4 5 or 6 cylinder are usually into 1 collector dirctly at the turbo is this the best option or is it just down to space in the engine bay, as i have a lot of room in my engine bay is there any gain by having a longer single pipe from the collector to the turbo.

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#1118179 - 21/10/2010 10:56 Re: 20vt Exhaust manifold [Re: fialcia]
Nigel Offline
Club member 123
Forum veteran

Registered: 16/12/2005
Posts: 16982
Loc: Staffordshire
Originally Posted By: fialcia
is there any gain by having a longer single pipe from the collector to the turbo.


I don't want this to appear as though I'm putting your ideas down, but if you're asking a question such as that, you should really think hard about whether you are capable of designing and building a manifold

If you read Guy's comments above, you'll see that there are many critical aspects to manifold design that only a dedicated tuning specialist will ever be able to fathom out

By the time you've built half a dozen different designs and tested them thoroughly at all engine revs and loads, you would undoubtedly have been better off buying a proven design

And the answer to your question is that the turbo needs to be as close as possible to the exhaust ports in order to benefit from the high gas speeds - when the exhaust gasses cool, they contract, which slows it down and provides less drive to the turbine. This is a generalisation though - there are other things to consider.
_________________________


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#1118274 - 21/10/2010 13:15 Re: 20vt Exhaust manifold [Re: Nigel]
GCRE
Unregistered


Sorry, nice if it were true but it's not so. The energy to drive the turbine comes from the enthalpy of the exhaust gas and the main components are pressure and heat not gas velocity. The nozzle region of the turbine housing is there to convert pressure to velocity to generate torque via the blades, the converse of how the compressor operates where velocity is converted to pressure through a diffuser.

For the most practical of reasons the turbo actually needs to be as far away as possible - quite simply in order to achieve as much separation of the (extremely high velocity) primary pressure waves as possible. These travel through the exhaust gas whose velocity is more a function of piston speed during the (upward) displacement phase.

There are some good examples of very long headers in Google images of old F1 engines:

http://www.google.co.uk/images?q=%22f1+turbo%22&hl=en&num=10&lr=&cr=&safe=images&um=1&ie=UTF-8&source=univ&ei=IgvATM6lJofQjAeFq_ydCg&sa=X&oi=image_result_group&ct=title&resnum=6&ved=0CD8QsAQwBQ

Separation and long pipes helps to achieve damping and attentuation of the primary waves and their reflections that would otherwise interfere hugely with the firing cycles of the other cylinders. The closer the turbo (ie the shorter the pipes) the more modest the exhaust event (in its entirety) has to be and the converse is also true.

As far as primary lengths go the magic number you are all looking for is a minimum of 15" and preferably 18" OR MORE. On n/a engine it is 27".

With a twin entry turbine a useful degree of separation can be achieved in practice and primary pipes can be oriented to take advantage of the gap between firing cycles. On a 4 cyl one would pair 1&4, 2&3 but irrespective of the net benefit one could achieve length is still utterly critical. On n/a engines pressure waves are vital to power - on turbo units they are a confounded nuisance. Except on real pulse turbocharging setups where the pipe length is so extraordinarily long the use is pretty-well confined to very big (ship & powergen) diesels.

GC


Edited by GCRE (21/10/2010 13:18)

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#1118285 - 21/10/2010 13:28 Re: 20vt Exhaust manifold [Re: ]
Nigel Offline
Club member 123
Forum veteran

Registered: 16/12/2005
Posts: 16982
Loc: Staffordshire
well - with an answer like that, I have no problem being wrong! However, if its pressure that's driving the turbine, there will still be an adverse effect of pressure drop caused by cooling of the gasses - the further away the turbo is from the exhaust ports, the cooler the gas and the lower the pressure - can this be overcome by careful sizing of the primaries?

So - why did Fiat fit the turbo so close to the head (which in turn left us with a horribly restrictive downpipe bend)?

Surely, they could have dropped the turbo location by a few inches and solved two major issues in one go

However, isn't there also a lag issue associated with longer primaries? - clearly not an issue on an F1 engine or even some race engines, but its not a desirable characteristic of a forced-induction road car
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#1118309 - 21/10/2010 13:56 Re: 20vt Exhaust manifold [Re: Nigel]
GCRE
Unregistered


...so close to the head to suit their own installation and they can get away with it because the ex overlap valve event is so modest as to be almost non-existent and a cast header acts as a damper which a tubular system does not and the boost is restrained. If you don't fully appreciate the meaning of 'event' it is the ex phase - governed by the valve lift, valve size, ex port flow characteristic, ex valve open and closure timing, extent of overlap and alteration of any one of those will impact on the behaviour of the turbocharger and engine as a whole. And I do mean as a whole because the turbine runs the compressor so the inlet event is indrectly affected too.

You're asking pertinent questions and that's fair enough but you can cite this-or-that issue as often as you like (lag eg) but it won't alter the savage reality that the marriage of a turbocharger to a gasoline engine is a 'match made in hell' and there are 'up' and 'downsides' to every conceiveable issue with no happy medium that is all things to all men. And I've not even remarked on the numerous degrading thermal and mechanical aspects that arise in these installations or even the survivability of the damned turbocharger itself. And I say that as a former turbocharger manufacturer Chief Engineer.

GC


Edited by GCRE (21/10/2010 15:45)

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#1118318 - 21/10/2010 14:13 Re: 20vt Exhaust manifold [Re: ]
rmouthaan
Unregistered


:), glad you have time to reply on this issue. Made me smile again, not so sure about others though.

Watch your neck.

Thanks and regards

remco

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#1118375 - 21/10/2010 16:43 Re: 20vt Exhaust manifold [Re: ]
Nigel Offline
Club member 123
Forum veteran

Registered: 16/12/2005
Posts: 16982
Loc: Staffordshire
Guy - I'm pretty sure the answer to this will be "buy the book", but without giving too much away, what should we be doing to get reliable, usable extra power from our 20VTs? We can see from your answers above that you know what we shouldn't be doing, but what we really need to know is what we should be doing

I'm sure you've already seen the route that we have found to yield the bigger results, which tends to go something like this:-

Bigger turbo (GT28RS, GT2871, GT3071)
Cams (slight increase in duration and lift - nothing wild)
Exhaust (drop the V-Band and go for up to 3" from the turbo all the way back)
Forged pistons & rods to take the extra grunt
Head (usually a simple port cleanup and 3-angle valve seats for the intake)
Intake (decent filter, re-sited closer to the turbo)
Injectors (bigger, plus slightly increased fuel pressure)
Up the boost (1.2 - 1.4 bar is common, with the nutters amongst us running 1.5 - 1.7 bar)
And of course, some decent mapping

I'm sure you'll tell us that the majority of the above is simply making the best of an inherently bad job, but without spending barmy money, that's what we're stuck with, so we are looking for the most appropriate solution, not necessarily the very best solution.

I also accept that in your professional opinion, you may tell us that there's actually no point in ploughing serious sums of money into extracting more power from a turbo'd FWD car. However, that would be like telling the kids to keep their hands out of the open sweetie jar - it ain't going happen wink

Finally, thanks for taking the time to reply - we realise you're busy, but your input is valuable to us.
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#1118386 - 21/10/2010 17:11 Re: 20vt Exhaust manifold [Re: Nigel]
GCRE
Unregistered


There is nothing wrong with your tuning ideas per-se,that is the first thing I would say. The point about the book is this: for years and years I've been coaching folk about engines, not exclusively clients but prospects and others too. I know more than anyone how important it is to understand the engine as a whole before tuning it up and that is where I come in. Sadly more and more folk esp those with turbo installations are wrecking their engines because they have so little of this knowledge. The book tells you what I believe you_need_to_know. If you think (using the word 'you' in the general sense) you don't need to know all that, fine. I just happen to think you will enjoy the project a lot more (in every sense) if you find out first what makes the engine 'tick' - because there are so many more vital facets to tuning an engine and making it robust than our short list above covers. Most people who ring me about 'turbo projects' have never worked on anything more complicated than a bicycle in their lives. So often I've been asked 'why's that then?' as if I was trying to con them about something; they had no idea about many of the aspects yet still felt they wanted to argue about them. Thus another unhappy marriage in the making!

Anyhow I've put one on ebay if anyone wants to try for a 'discount' copy!

G


Edited by GCRE (21/10/2010 17:26)

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#1118455 - 21/10/2010 18:51 Re: 20vt Exhaust manifold [Re: ]
rmouthaan
Unregistered


Cant find it on ebay.co.uk, and no i am not in need for an discount smile.

Dont tell me its sold already now...

Regards remco

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