Turbo Plenum Spacer Group Buy

[sailorbob]

For those who may not be aware of it there's a group buy being arranged on LotusTalk for a 1 inch wide turbo plenum spacer http://www.lotustalk.com/forums/f164/turbo-plenum-spacer-group-buy-361481/

Whilst the spacer is based upon an injection plenum cover and an OE plenum cover gasket it may not follow the contours of every plenum cover exactly due to manufacturer tolerances and the plenum cover being a cast part.

[Chillidoggy]

Is that a warning?

[sailorbob]

Yep, not to expect a perfect fit on every plenum. Not that "perfect fit" and "Lotus" usually go together

[Chillidoggy]

Ah, gotcha. Sounded a bit ominous!

+1 on the 'prefect fit' theory.

[Advantage]

Seems to be more than one person on that thread willing to buy something that they have no idea what it is or what it's for!  

[Andyww]

6 hours ago, Advantage said:

Seems to be more than one person on that thread willing to buy something that they have no idea what it is or what it's for!  

The car tuning accessory market relies on these people

I think Tony Rudd would have made the plenum bigger originally if there was a benefit. He knew what he was doing. Is there a comparative dyno plot including plot of turbo lag, for the addition of the spacer only, with no other change?

[andydclements]

I thought that (based on the contents of the discussion thread, not the group buy thread) that it was one of the "Changes" changes, but that doesn't mean it's been comparatively tested on a standard engine.

[Barrykearley]

I've got a whole bag full of magic feathers for sale ....

[sailorbob]

The airflow path in the OE plenum is, quite frankly, crap. From turbo to inlet ports Garry Kemp calculated 30 CFM losses (see Dermot's website) which equates to almost 5% on the chargecooler engine using the rough rule of thumb of 2.5 x HP estimate so anything that reduces the losses is no bad thing IMHO.

[Andyww]

I can see how fettling the inlet pipe and the plenum to enlarge the air path and avoid any step on the joint might theoretically improve performance (although only a dyno comparison would confirm) but thats a different issue to adding a spacer, which would also add another joint in the path. On a turbo engine a clean air path is not so critical, the pressure in the plenum is limited anyway. A chargecooler is a pretty restrictive path.

I am never convinced by this "armchair engineering" where people model and calculate theoretical improvements, unless its backed up by testing.

[sailorbob]

There are lots of impediments to the airflow but doesn't mean you shouldn't try to remove them where you can. The OE design means the air hits the near vertical wall of the plenum backplate, not a particularly good design.

[Chillidoggy]

I'll be interested to learn how things turn out. If it's 'free' power with no moving parts, then that's a good thing to have.

Presumably the ECU sorts out the fuelling?

[Andyww]

The air from the inlet pipe hits an angled-downwards face.

The turbo normally is capable of supplying more than enough air to keep the boost (which is measured on the plenum in a "worst case" location in a front corner) from dropping below the specified value despite the restrictions in the air path. There is a possibility that the boost might drop at really high revs. I doubt whether many people would rev their engines high enough to reach it. Has anyone observed the boost gauge dropping at very high RPM?

A larger plenum surely must increase turbo lag?

I am aware I am being an "armchair engineer" here which I criticised earlier, and could be completely wrong. But the proof would be testing.

[sailorbob]

The angled downward face is nearly vertical at approx. 22 degrees so it's not particularly good at re-directing the airflow efficiently.

The OE plenum cover has a volume of 1.65 l and the spacer has a volume of fractionally under 1 l so the volume increase is not huge and the total volume is less than consumed by the engine in a 4 revolutions when under boost.

[cammmy]

I think we've reached the cut-off. I've asked if they would be be kind enough to provide me with the CAD template and I'd see how much it would be to have some made here.

[jcslocum]

That would be up to sailorbob as it's his work product. Shipping to the UK would be about $55 or so, and the cost of the spacer waterjet cut from 1" material is about $130

 

 

[CHANGES]

If you followed the development progress on 412 thread for the 910, you will note I refer to the restrictions in the induction and exhaust flow being important to relieve, so as to achieve the best VE.  The plenum spacer is one of these restrictions..  It is high on the list of what should be done first..  To say it is the primary choke on a standard system I can not validate , but the flow data in that area before and after does show massive improvements.   I think the question being asked here is , without doing any other mod , will the spacer provide any benefits..  My answer to that is yes..  I base this on localised  flow quality rather than overall VE. 

If we look at how the spacer changes the flow dynamics the positives become clear.. 1. The volume increase is not over excessive for the standard turbo as to create lag, but I would move the actuator control to the plenum as apposed to the compressor outlet. This will generate better control of the boost where it counts and may help overcome some of the chokes between the compressor and the plenum..   2. By moving the deflector face on the plenum cover back an inch you reduce the massive turbulence and random swirl in that area. The entry velocity with the same volume is almost halved, this means more  air can flow freely if  not  pre-chamber restricted.  3.  This extra air along with the increase chamber area give a far more uniform delivery system for all four ports.. ( the standard set up showed less air flow was achieved at 1-4 as apposed to 2-3 especially at high rpm comparison.  )   4.  This extra air mass within  the chamber also allowed better distribution of fuel air when the secondaries were operating. It also allows each intake port to function far more efficient at higher rpm. 

As to will it improve performance of a particular engine is very dependent on that individual engines condition and spec, but in my opinion has no obvious negative effects that I have come across.

other points made were:-

On 22/05/2016 at 20:31, Andyww said:

but thats a different issue to adding a spacer, which would also add another joint in the path. On a turbo engine a clean air path is not so critical, the pressure in the plenum is limited anyway. A chargecooler is a pretty restrictive path.

1. Another joint is not a problem unless fitted badly..   2. As for clean air path not so critical on a turbo engine. Well this is old chatter that I dismissed from the start.  So many people believe this , but logic tells you clean air flow = efficiency = performance.. But is logic is not enough just look at the dyno result..  3. The standard charge cooler could be restrictive at higher rpm . which is why I would move the actuator control to the plenum chamber.. This will counter the turbo dropping boost based on backed up pressure from the C/C..or other restrictor prior to the plenum.

On 20/05/2016 at 16:23, sailorbob said:

Whilst the spacer is based upon an injection plenum cover and an OE plenum cover gasket it may not follow the contours of every plenum cover exactly due to manufacturer tolerances and the plenum cover being a cast part.

This point is not that important.  The peripheral flow is so ambient that contour discrepancies would have to be huge to have any effect..  It is only when you go to the next level as on page 12 on 412 thread that the spacer becomes an integral part of gas flowed set up effecting laminar..

Conclusion  

This is a relatively cheap bolt on part that has assets.  It Is easy to fit and remove for purists when selling on . It will definitely provide performance enhancing qualities when used with other tuning mod's..

Also

For the UK market,  Someone here should supervise and manufacture  in the UK,  provided as a quality kit with all the relevant gaskets and a set of suitable re-spec'd bolts,   also a  longer / modified stabilising arm which is also needed, 'but till now not even mentioned'. All of this, along with step by step instruction sheet to avoid the normal post delivery  problems on these sort of group buys..    In my opinion this is how it should be done..  '' volunteers ? '' 

No offence meant to USA supplier on this ...               

[cammmy]

If I can get a template to work with, I'll certainly have a look at the costs/putting together some kind of package.

 

Also, thanks jcslocum, I'll ask sailorbob if he's willing to provide the template If putting something together on a non-profit basis.

[CHANGES]

49 minutes ago, cammmy said:

 

If I can get a template to work with,

 

You already have one ... Your plenum cover will provide all you need, that is what I used...  It also makes a good drill jig when machining any prototype for fit approval prior to  design production run.. 

[cammmy]

Fair point! It'll be a little while before I'm willing to take mine off though. Want to get the ECU sorted and tuned then enjoy the car over summer before taking anything off again. I'd want to get it done in one go so I don't use more gaskets than I have to.

[Andyww]

The wastegate control is already on the side of the plenum, furthest from the intake on the original 910 engine. Maybe it changed on later engines when they changed to the integral rather than remote wastegate?

[andydclements]

The thing on the side of the plenum on early (LC) cars isn't a wastegate control, the wastegate is in the turbo casting and the control for it is the integral capsule that points downwards. The component on the side of the plenum is a pressure regulator for the carbs.

[Andyww]

On the LC cars the wastegate is not on the turbo casting, its a separate part. You are right though the control pipe, even for the remote wastegate is not from the side of the plenum, it comes from the mouth of the compressor.

I was getting confused by a mental image of the boost gauge take-off pipe which is on the side of the plenum.

But having said that, it does mean the boost gauge is going to give an indication of the pressure after all of the restrictions. The boost gauge appears to confirm that the wastegate opens at exactly 7.5 PSI as it should, when accelerating at full throttle, which seems to indicate the pressure is similar between the compressor outlet and the end of the plenum, furthest from the air intake. 

[andydclements]

The spacer plate is following Dave "Changes" mods, which were on a chargecooled engine, so a lot of the discussions would be different, for example.

Later, suffer from a potential restrictor of the cooler itself, earlier don't.

Later, use more air& fuel to get the higher power outputs, earlier therefore may not hit the same barriers.

Later use sensors which read pressure at the turbo and determine control over the wastegate's mechanical aspects from those, earlier don't have such an over-ride.

 

As such, you may well be right about the LC cars not having a restrictor problem, but the later ones have problems created by both the very fact they work at higher flow and have things added to acheive this.

 

As to seperate part/ not. Sorry, I always think of that second casting as being a part of the whole turbo unit, but yes it is seperate. 

[910Esprit]

Hypothetically, I wonder if the plenum was redesigned as more of a half round shape, rather than flat, (when viewed from one end) if this would resolve/alter some of the inherent design compromises?     What do you think Dave?  

I think a prototype could be quite easily be made from glassfibre.