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Exhaust manifold design test result..

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Exhaust... Manifold, System, Design Options & test results.

After I failed to get my exhaust manifold re-manufactured cost effectively I was asked by Mark kassim if i would take a look at the Alunox design  of manifold. As I am always looking for those little tweaks that help refine the Esprit i said i would like to visit the factory and chat about the design parameters to asses whether there was any scope.... I was glad i did, the set up at Alunox was very professional and the manifold exceeded expectations. I felt chatter on other threads did not explain properly the design advantages or do it justice.

I was very interested in some cross over design points with my own which don’t follow the norm but work with the 910 engine. The main one was the larger diameter primaries ... The slip joints at the collectors are what I refer to as the Burns double slip joint , not just a slip connection most would be familiar with and as was implied in a previous thread . This design will allow the pipes to flex, expand and move at the joint without blowing. Once hot they will  seal totally.  By incorporating this in the overall design, cracking from flex fatigue is virtually eliminated. This was not part of the original design but introduced later......With these included the primaries can be bolted to the head on independent flanges which won’t be subject to expansion slip at the head as the single plate type are. This then facilitates the different gasket design instead of the original shim type.


I was so taken by its potential that i purchased one to fit test and compare to my already high flow unit.  When i got it in my workshop i spent a couple of days assessing the flow characteristics. The longer primaries are well designed considering the space limitations. Calculation and experience said gains were possible at the lower rpm end.. The secondary’s  are designed for the standard turbine housing retaining the primary diameter into and including the secondary’s, this will optimise the velocity with the VE of the standard engine.    This is absolutely ideal for that application as it will spool the turbo far quicker and should make lag a thing of the past.  However with my larger turbo and VE a greater flow capability was required as velocity is not an issue due to the volume but back pressure would choke over 6000 rpm. If left unchanged.  So to make a fair comparison i gave Leon my design for the larger secondary’s  to match the S138 turbine housing i have fitted.  This was a credit to him as he absorbed the extra tooling cost for this which will only be required by those going to the extremes I have.

The fitting was fairly straight forward with all the fixings accessible, nowhere near as difficult as the standard cast. It slips into place in one piece with the turbo or n/s drive shaft removed. The original heat shields fit but the top one against the chassis will need small mod as it is very tight to the manifold #3 primary.


Before I  give you my performance assessment along with the power figures off the dyno and test results, i think it more appropriate to explain some of the theory to those who may not be aware of what is actually involved in the design of an exhaust manifold and system to get the best from it. I think it is important to know why it works and how changing the flow dynamics can drastically alter how your engine performs.  I have spent a great deal of time maximising these flow characteristics on my engine along with everything else, any changes in my data will be down to the new manifold design managing that flow differently...


There are various factors that have to be considered to get the best from an exhaust system. Flow, velocity, temperature, pressure and volume. What makes things interesting is that some of these factors conflict but are still all necessary to obtain the best results. The trick is to find the best balance by design.

There are many theories and formulas used which all give reasons why a design should be done a certain way, there is even extensive software available that manufactures use. But at the end of the day it’s the practical testing that provides the results and design approval.

To appreciate the design format we should realise what is has to do.  I will start from the cylinder and go to the tail pipe and hopefully this will answer questions and give a more detailed understanding...sorry if its a bit long....


After the firing stroke is completed the cylinder is full of hot pressurised gas. On the back of the exhaust valve the pressure should be as low as we can make it. This is so when it opens the hot high pressure gasses will be drawn into the exhaust port and manifold at extreme velocity. The bigger the pressure differences across the valve the more efficient the evacuation. As the gas evacuates its momentum forms a low pressure area in the cylinder. Ideally by the time the piston is half way up the exhaust stroke the pressure should be down around atmospheric. This moving mass of gasses is what we refer to as the pulses. How we control and manage these will have an effect on overall performance potential.

By the time the exhaust stroke is near completion the pressure in the chamber should be as low as possible. At this point the inlet valve opens; the pressure on the back of the inlet valve will be at atmospheric or greater depending on boost level, this will allow the ingress of clean dense oxygen rich air to enter the chamber even though the piston is still rising. This is referred to as the siphon or scavenge effect. The more efficient this is at removing all traces of the burnt gas the better.. Failure to remove 100%  will reduce volumetric efficiency (VE) , (This is also one area that cam timing and design governs, by reflecting the degree of the valve overlap and duration)... When the scavenge or siphon is taking place some of the clean air can pass into the exhaust but should be minimised. This is a waste of energy and when adopting the wasted system on the injection some un-burnt fuel will go with it, this can result in higher HC levels... As the exhaust valve snaps shut, the pulse is completed but it’s velocity will carry it forward chasing the low pressure tail of the previous pulse helping form its own low pressure zone on the back of the closed valve.

Now we have the pulses lined up we need to manage them with the manifold design. The target is to optimise velocity/volume up to the turbine. This will give the best spool up and negate lag.  This is where the conflicts and balancing act starts.

Primaries that have small diameter will generate great velocity as the gas squeezes down, but at the cost of  increased back pressure effecting scavenge with reduced volume choking at high rpm. Go to large and the reverse happens, reduced velocity produces lag but free flow increases VE and top end rpm etc.  To arrive at the correct size you need to consider the mass volume of exhaust gas the engine will produce, this of course will be influenced by the VE on induction, boost level, temperature etc. Because there are so many variables you need to find the optimum points and calculate based on what you require. (There are several sites which will explain the formulas for those interested.)              The length of the primary also has an effect, the shorter they are the quicker the velocity gets to the turbine with minimum heat loss. The longer they are the potential for back pressure from complex design plus heat loss.  On the longer more complex primaries it is not unusual for 150-200’f  to be lost over its length through the tubular wall.   The result is reduced EGT=smaller gas volume=loss in velocity ...... However bigger gains can be made by having well designed collectors, better organising the pulses and scavenging quality.                             So to recap....... We want to maintain as much heat, velocity, volume with minimum back pressure whilst organising the pulses to arrive equally spaced at the turbine for best results.............................

Design Options

Manufacturers use the cast log system, This has good heat retention qualities and short runs to the turbine to achieve best velocity and quickest spool up. They work well but have their limitations.

The Tubular log style which I chose has a far better gas flow from the internal finish. The bore size is also larger to maximise volume while maintaining velocity on the short primaries. By using an expanded collector/secondary system minimum back pressure is achieved along with a siphon effect from each primary to better align the pulses. Great spool up is achieved with top end RPM capacity..

The long tubular with matched primaries has the larger smooth internal finish with the advantage of more gentle bends allowing the gasses to move freely while sustaining better velocity and maximising the scavenge effect. With this design the collectors can also be made more streamline, reducing any turbulence which would result in increased back pressure loss of velocity and volume. Temperature loss should not affect Esprit’s with standard turbo. Wrapping with insulation is an option for those going the extra mile but be aware this could reduce reliability so not recommended for road cars.


Another point not mentioned till now is the pressure waves which move independently off the front of the pulses, these are part of resonance frequency tuning. This is quite important on naturally aspirated engines but difficult to control on our turbo’s due to space limitations, however the LCB design does allow more control to dull the negative effects...This design can provide great spool up and increased torque with more evenly spaced pulses and better cylinder balance ,but may limit top end capacity on free flow engines...

Considering all these points it must also be remembered that the spacing of the pulses is important, too close and they will reduce the energy recovered from them and their effectiveness. So by keeping the gasses from cylinder 1-4 and 2-3 separated up until the turbo housing the spacing can be much better managed than using a four into one system.

Post Turbo.

To gain the best spool up and flow from all the design tuning of the manifold the post turbo exhaust is a major consideration. What we are looking to achieve is the biggest pressure differential across the turbine.  To do this we need the least restriction in the post system as possible. Ideally the post system will increase in volume with the use of a bell mouth. This will have the effect of allowing the hot gasses to expand quickly in a controlled fashion. As they expand they will lose pressure and with that temperature, as a result of temperature lose volume will decrease further reducing pressure allowing easier flow out the tail pipe. Some say hot pressure gasses flow better, which is true but in this case pressure and volume reduction has the greater advantage on turbo performance.

To achieve the best from your post system careful consideration should be taken on tube dimension along with the least restrictive cat, and silencer available.. Best results are obtained from de-catted systems with free flow silencers, However noise management must be a consideration also.


That concludes a very rough outline of some of the factors that have to be taken into account from a tuning point of view, not forgetting the manifold needs to be able to heat up to around 1000 degrees and cool repeatedly without distortion.  ( A bit more to it than you may think..)


It was apparent from first starting the engine something had changed in the flow dynamics from the sound... When we put it on the dyno for a datum run on old set up we showed over the 400 bhp straight away but fell well short of 424. On the positive side spool up was quicker and torque improved.  We then noticed that the boost was down at 1.32 bar plus a couple of fuelling points needed addressing.  The boost level was reset to as it was before with a small tweak on the fuel.  This was much better, however it was fast becoming obvious we were not going to see any major bhp increases.  This is probably down more to the fact that the engine in this design format is already maxed out at the top end.  After another few tweaks on various mapping points, the next power run seemed really impressive, you could tell by the way it picked up and squatted on the rollers, so  we were not surprised to see it matched the original 424 bhp..... but blown away by the torque.....409lb-ft.... After a couple more runs it was obvious that was where it was happy.  What was achieved was 38lb-ft more torque...What was more impressive was at 4500rpm we are generating 64lb-ft more torque, along with a much quicker and aggressive spool up. The power came up quicker and did not drop off at the top.  All of this is due to the change in manifold design nothing else had been done since the last dyno run.....  This was a detailed test at an extreme level to assess the full design capabilities of the Alunox manifold.         I am confident it covers all the bases and will provide performance benefits to anyone who fits it.





The road test that followed was interesting, Ok the road was damp but lighting up the back wheels at 70mph in fourth can always make you smile....

Foot note..

 Leon has advised me he will make these manifolds available at the special price for a limited time only. This is to allow enthusiasts and forum members the opportunity to save a bit of cash for other jobs. He will need a minimum order of Ten for it to be viable.

So If you are in need, want to upgrade or tune your Esprit , this is your chance, If you add your name to this thread Mark Kassim will take it over furnish you with the details and arrange the

group buy..


Thanks for your interest..

Dave (Changes) 

Edited by CHANGES
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Looks great Dave! 

Very nice outline (not that I understand much of it)

A replacement system for my NA is high on my lists of jobs on the horizon. This is inspiring.


The turbo guys will be queueing up I'm sure!!!

"Intellectuals solve problems; geniuses prevent them." Albert Einstein

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A replacement system for my NA is high on my lists of jobs on the horizon. This is inspiring.

They were looking at a N/A system. I had a email from them saying they were working on one at the beginning of december and would let me know prices and pics when it was ready.  Nothing heard from them since.  Ive just purchased a 2nd hand cast manifold to get me going but would still go for a system if its available and the right price.   

Edited by mdw
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Hi , I was present at the dyno run and managed to get some turbo shots under load. I know Dave has explained the results in allot of depth. The new manifold did give better throttle response and more torque with the same power. I do also have film of this which I may have to link to YouTube later.




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What would the freight cost be to Australia?

All we know is that when they stop making this, we will be properly, properly sad.Jeremy Clarkson on the Esprit.

Opinions are like armpits. Everyone has them, some just stink more than others.

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Having been able to get my eye around the manifold during Dave's pre dyno testing and look over the build and design of it, I was able to work out and satisfy previous questions I had raised in a previous thread on this item...some of the questions were satisfied purely by this being a newer more developed version of the original design, which I had concearns over.

I was also present at the dyno testing earlier in the week, which proved in the end favorable results with the unexpected bonus of increased torque early on in the rev range as described already by Dave. Now that proper testing has been done on it, and it has shown to he able to handle more power than the rest of us have, it will be interesting to see its long term reliability over the next year of aggressive use..i understand Leon is offering a two year warranty with the item which should go some way to promoting it further as a viable option for replacing the existing unit..

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Yes it was a good day on the dyno, we gathered really useful data and answered all of the

critical questions.   I personally do not see any reliability issues arising. I am very confident

in the design even with the abuse it receives on my engine while wrapped. On a standard or

slightly tuned Esprit it would only get a fraction of the stress i am putting it through, so the fact

a two year guarantee is offered with it will be just to cover the the unforeseen ..

In my opinion a great product at an attractive price..

OH and no i have not any financial interest in this, I have done this at my expense for fact finding..    

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I guessing it'll be staying on then? :)


A couple of Q's:


Have you spotted any issue with leakage around the double slip joint affecting the lambda sensor readings on a cold start?


What kind of time and ECT delay do you use before attempting to go into closed loop fuelling on a cold start?

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I guessing it'll be staying on then? :)


A couple of Q's:


Have you spotted any issue with leakage around the double slip joint affecting the lambda sensor readings on a cold start?


What kind of time and ECT delay do you use before attempting to go into closed loop fuelling on a cold start?

 Yes it certainly will,  The torque developed is fantastic, I thought it was really topped out before

 only expecting a bit more low down torque and hopefully not choke out the top end..

What i have now feels so much quicker with the new low down power which keeps going..


Q1... Absolutely none, not even at cold. I used stethoscope to very carefully check all joints.


Q2...Engine control temp is set at 50 degrees for cold start.



Hello, do you know what the price on these would be on a group buy?


I think it is as before but Mark will post the actual details soon.

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Hi , just to confirm after speaking with Leon that the group buy price for 10+ manifolds still stands at £850 . However the one off cost of £990 he only holding for 1 month and then its going up to £1080,this is due to the rise in material costs and he running on the last stock at the moment. Mark

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That made it look like hard work, :huh: especially the misfire bit in the middle  :rant: which was actually 

the light load run after the power runs...  For those interested and Sparky who was probably waiting 

for the click/bang ££££ at that point :sick: .. the misfire was caused by the fuel map around the 6k region. 

 With this system not running the factory ECU we have to manually re-set  the format to cover all the

running parameters not just the flat out power. :wallbash: It can run like a dog till you get it right but when all smoothed 

out its a delight... :thumbup:. the  anomaly at that point we think was to do with the change in b/pressure or scavenge on

 light throttle. :coffee:

 What it does show however is that I won't hold back on the this case over 3 hours of it...

 You can't beat a good bit of abuse  to give you confidence in the product... :ouch:



Edited by CHANGES
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So it can be reliable, if it's put together correctly.

What a potential, you make us all drool and fantasise what to change next


What Turbo are you using, from the picture it looked like a Ford RS500 Cosworth one.

Or is it a custom made one off?

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