wot do they do and are the worth having performance wise????

 

need a remap to make the most of the extra air intake

 

is it summet worth doin and wots the rough cost

 

what spec are you running reece?

the point of them is to increase the plenum chamber volume so that each cylinder has a better chance of getting the same amount of air in, not to particularly increase the flow.

 

mines just runnin stage 1 mate

 

As far as I’m aware I was the first to fit a spacer to my YB (At least here in Australia) way back in 1996. At the time my engine had a stage 3 Mountune kit running 22psi. I had a Pace RS500 ‘cooler and 3” Exh system. On the dyno it made an extra 16hp to the wheels. There was no need to remap the ecu.

The main idea of the spacer was to increase the distance between the trumpets and the inner wall of the plenum as this is only 10mm. The only reason a 15mm thick spacer was used was due to the fact that the “bosses” that the fuel rail bolts to are 16mm thick and once there is a gasket on both sides of the spacer the total thickness is approx 16mm meaning no need to add any other parts other than a modified an “L” bracket that connects the Throttle body to the engine mount cos the Throttle body is now 16mm further out.

The spacer plate days are now old school compared to the manifold we play with these days





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that's what it actually does, but what is the point of doing that? as i say, it's to give more even air flow to each cylinder.

 

foreigneRS,

I’m happy to go into detail about the effects that the plenum spacer has so you get a better understanding to how it works mate . The easiest way to look at the situation is as follows………..

Consider each trumpet within the plenum having an individual throttle body on the end of them. The amount the throttle body is open is determined by the distance between the trumpet and the inner plenum wall. For instance if the plenum wall was butted up against the trumpet this would resemble 0% throttle, when the distance between the trumpet and the plenum wall was at its furthest point this would be seen as 100% throttle.

When a plenum spacer is fitted, the distance from the trumpet face to the inner plenum wall becomes 26mm (10mm + 16mm). This would resemble 100% throttle. If the spacer was removed this distance would now become 10mm and therefore resemble a throttle opening of (say) 80% and reduce power output in the higher rpm range of the engine. NOTE; we all know that cossies don’t have 4 throttle bodies. This is purely a means of explaining the theory.

When you say that the plenum spacer is designed to achieve the following…………. “It’s to give even air flow to each cylinder” I totally disagree. Firstly everyone knows that when a cossie piston/s fails at high boost 90% of the time it is piston 3 or 4 that melts. This means that these Cyls are running leaner than Cyls 1 and 2. There are a few reasons to why this can occur BUT it’s obvious that it is due to uneven air distribution due to the elbow location on the stock plenum.

Firstly, when we did dyno testing, we monitored the EGT (Exhaust Gas Temperature) of each Cyl by taking a reading with a laser thermometer on the Exh runners of each Cyl. NOTE; when these readings were taken the engine was cooled by running the workshop hose over the engines radiator and NOT the fan due to the fact that if the fan was cooling the radiator it would also be passing air over the Exh manifold and result in inaccurate figures as the air would pass over runner 1 and pick up heat and pass the heated air towards the rear Cyls.

When the engine was held static at a given load/rpm, Cyl 3 would run 75 Deg C hotter (EGT) than the average temp of Cyl 1 & 2. Cyl 4 would run 60 Deg hotter (EGT) than the average of Cyls 1 & 2.

I considered the fact that the engine coolant enters into the engine from the front (Cyl 1) then continues towards the rear of the engine (Cyl 4). There is no doubt this would effect the EGT when comparing Cyl 1 to Cyl 4 however NOT by 75 Deg C (EGT) as there would only be a approx 3-5Deg C temp (water) variation from the front to rear of the engine block.

I also considered the fact that the fuel enters the fuel rail from one side only with the reg on the opposing end and considered the possible oscillation of fuel within the fuel rail due to the engines 1-3-4-2 firing order. To help counter react this I made/fitted a new fuel rail that feeds fuel into the rail from both ends and has the return to the fuel reg in the centre of the fuel rail. (In fact I still have this fuel rail on my engine). Back on the dyno and there was no improvement to Cyl 3 & 4. Also, when the injectors were removed to fit the new fuel rail they were individually checked to see if they all flowed the same amount and they did.


Now by fitting a plenum spacer there is no means of increasing the air flow to Cyls 1 & 2 ONLY without affecting the air flow to Cyl’s 3 & 4 hence indicating that the plenum spacer is not effective in your claimed …….“it’s to give even air flow to each cylinder” as you keep referring to. It is obvious that the irregular air distribution of the stock intake manifold is due to the positioning of the stock elbow.


The methods to achieve even air distribution to each Cyl would be by fitting “air deflector” plates within the elbow/plenum as I have on my custom made plenum.











When the plenum spacer plate was fitted/tested on the dyno we did not re map the ecu and had no problems what so ever. In fact the change in the air/fuel of the engine was negligible and I believe there would be very little if any gain in re mapping the fuel map and I seriously doubt there would be the need to alter the ignition map.


Another method to help this situation of uneven air/fuel ratios between Cyls would be via an after market ECU such as an Autronic as this ECU can trim each injector/Cyl individually to help balance the air/fuel ratio within each Cyl BUT not even out air flow to each Cyl. In this case you would be tuning each Cyl as a separate engine rather than a single engine.


When you think about it, it is commonly taken for granted that when a 3” big bore Exh system is fitted/removing the cat or removing the stock air box and replacing it with a pod filter or by fitting an RS500 intercooler that there is no need to re map the ecu. Id say that the performance increase of these item would be similar (but not exactly the same) as the plenum spacer and yet people fit these items without the need to a re mapped of the ecu.

After saying all this I am interested in your theory to how/why the plenum spacer can “give even air flow to each cylinder” For interests sake I would appreciate a “detailed” reply rather than a simple single sentence answer

 

BMEP

i'm sorry, but i don't have time right now to give a full answer

but from your explanation, i still don't accept it all. despite that, we are both entitled to our own views and i hope that we should be able to keep discussing it in an adult manner

you seem to be contradiciting yourself slightly. you accept that there is uneven airflow between the 4 cylinders, but say that fitting a plenum spacer was not to help with that but just to increase the airflow.

if the airflow was increased by fitting the plenum spacer, why did it not need a remap? and how could it gain 16 bhp?

 

Either way, it seems that for a simple mod and at a small cost, its deffo worth looking into?? Would there be any gain after the 15mm (+gasket thickness...will be using cometic gaskets which are quite chunky as well) sized spacer??

CheeRS,
Stu.

 

foreigneRS,

Mate, I totally agree that we are all entitled to our own opinions . I am in no way trying to “make” you agree with me as that would be childish and very anti productive of me I and am happy to continue the discussion on this topic in an adult manner not only for “our” benefit but also all the other cossie enthusiast that put in the time to read this topic.

Ok, getting back to it, I can’t see how I am contradicting myself . In fact this comment of yours made it clear to me that you may not be 100% clear on the two separate points we are discussing. In fact I feel that you may be considering the two separate points as one and I believe that this is the reason for your confusion.

Point 1 being, the power increase from the fitment of the plenum spacer.
Basically the increased distance from the trumpet to the inner wall of the plenum (10mm becomes 26mm) is the sole reason for the power increase.

Point 2 (I think this is where you’re getting confused) is the fact that the spacer plate does not aid/feed MORE air flow to Cyl’s 1 and 2 ONLY. It improves air flow to ALL 4 Cyl’s by the same amount meaning that what ever the problem was with the stock Int manifold is still present as it has not been rectified. For it to be fixed would mean that the spacer plate would have to DIRECT more air towards Cyl’s 1 and 2 ONLY and NOT Cyl’s 3 and 4 to balance out the air flow to ALL Cyl’s cos as it is Cyl’s 3 and 4 are being feed more air than Cyl’s 1 and 2.

To cover it once more. Let’s say Cyl’s 1 and 2 receive 100cfm of air and Cyl’s 3 and 4 receive 110cfm of air WITH a stock Int manifold. Meaning Cyl’s 3 and 4 flow 10% more than Cyl’s 1 and 2.

Once a spacer plate is fitted Cyl’s 1 and 2 NOW receive 110cfm of air BUT Cyl’s 3 and 4 NOW receive 121cfm of air. So this would mean that Cyl’s 3 and 4 are STILL receiving 10% more airflow indicating that the spacer does not “balance the flow” to all Cyl’s. It only increases the flow to all Cyl’s with a linier result.

To answer your own question that you asked………. ”if the airflow was increased by fitting the plenum spacer, why did it not need a remap? And how could it gain 16 bhp?”


Would be the same as asking you………..By fitting a 3” big bore Exh system you gain power but the ecu did not need a remap, Why?

The reason a remap is not required is simple because the power increase on a % basis is so small that the difference in fueling/Ign timing is minimally affected.

The reason the power increased is because the engine can now inhale/exhale more air hence make more power. Again the increase of airflow thru the engine is a small % gain compared to the TOTAL amount of flow the engine had prior to the mods.

This is my explanation to how I have seen/tested the effects of the plenum spacer. I don’t expect you to agree or disagree. I am interested in your thorough explanation to better understand what your opinion is. Thanks.

Cossie604,

That’s a good question . I had actually fitted/tested two spacer plates to see what the results would be and there was no difference in power/torque by fitting the second spacer plate.

I should also add that another “myth” is that a spacer plate adds more lag due to the increased volume of the plenum area. This is also NOT true. To prove the point is simple.

When your driving along a flat bit of road your Vac/boost gauge is obviously reading in the vacuum area, as soon as you put your foot down the gauge swings to 0psi or a few psi (depends on the rpm your driving at) basically the time it takes your gauge to go from vacuum to 0psi is the time it took to fill all the intercooler pluming, the ‘cooler and the plenum. Not a lot of time at all really

 

Ok cheeRS...will get serching ebay now for when they come up for aution again lol


CheeRS,
Stu

 

Brilliant explainations of "Why and how" thanks for that That new inlet BMEP looks funky

 

Cossie604,

Don’t laugh mate, I have seen them sell on eBay at very cheap prices, you couldn’t get them made for the cost that they sell for

Mr C,

Fantastic Obviously people do/can understand my explanation. I was starting to think that I wasn’t clear in my explanations

The Intake manifold not only looks good but works great. For more info look in the “Pics & Vid Gallery” under “2WD 11 second Saff”

I have posted a couple of vids of my1/4 mile run. On 205/40/17 street tires/ball bearing T28 turbo the Saff ran an 11.8 @ 124mph

 

So after the huge debate
Have we decided who makes a good spacer and what thickness they should be?.
I've seen plenum manufacturers say that "Their model is better than other companies as it has smoothed edges for better airflow" etc etc.
Anyone shed some light on this?.

 

lol its ok m8...I know they sell very cheaply on ebay....its just that about 90% of my cossie parts come from ebay..thats why I was laughing out loud....ebay is my home from home

 

BMEP
i,m tony perth in aus could u contact me bmep
cheers!!

 

cossie604....


tony perth.....you can always send me a PM....

 

sure i saw new ones of these on e-burgler for £14 about 6-8 weeks ago