Jump to content
SAU Community

Recommended Posts

If the thing flows a bit better, flows more evenly and is better at equalising cylinder filling across all cylinders...doesnt it stand to reason that a "weaker" cylinder will not ping earlier then the "better" cylinders...maximising the effeciency of the engine?

Don't forget a turbo acts like a fuel pump. It only pushes air. It requires a restriction to create boost pressure. It is moreso the boost pressure combined with the flow of the turbo which determines volumetric efficiency. The smallest area the air must get through is the valve space. There is no 'weak' cylinder as they are not all on intake at the same or similar times. It is the turbo which must continue to push air once the valve opens and there is a pressure drop in the system. If the turbo fails to provide a volume of air suffiecient to fill all cylinders at once then it will not be able to keep up at high rpm, air speed is reduced and power drops. What the design of the plenum does is maximise the 'efficient' space that the turbo can store air before the valve opens. Go too big and you will suffer in the lower end of the rev range for torque but increase your max rpm potential....go too small and the inverse is true. Usually a good plenum size is around twice the capacity of the engine. Runner length also has a major role to play in choosing a plenum/intake manifold as you want to achieve maximum torque at a desired rpm. The longer the runners, the lower the rpm you will have your torque band....and the same applies for this as the plenum in that you don't want to go too far. Runner design is important in that if you just weld some pipe to a barrel, you won't need to put it on a dyno for me to tell you it's not going to be efficient. Instead, bell mouth runners inside the plenum that taper down to the inlet port of the cyliner head to increase air speed as it enters the cylinder head is the better option. Once again there are more factors that play here and also protrusion of the runners into the plenum, diameter of runners, plenum shape, throttle body size in comparison to plenum size and then all of the above compared to engine capacity and whether or not it's forced inducted or not.

As you can see there is much more then just size and shape.....it's not always a case of what looks good, works well. I'm not saying that the aforementioned plenum does not work....I have not seen it or inside it for that matter. Just the usual educate the masses and help them make their own decision saga. Yunno the one about the 'teach a man to fish'. lol

  • Replies 63
  • Created
  • Last Reply

Top Posters In This Topic

Nice work, but how do you fish? That makes sense though what you said dan. I dare say it would make a difference, but to actually compare the before and after would be a better scenario, and also to compare b and a for any car for that matter would give a much better proven result so we can accept closure on this matter. On that note more than one car would have to prove this statement whether nay or yay it does actually improve results by that much. I dare say that IF there were more people willing to actually go through with this and share results of before and after would be of most benefitial for all of us not alone the plazmaman plenum dealer.

Cheers A

Don't forget a turbo acts like a fuel pump. It only pushes air. It requires a restriction to create boost pressure. It is moreso the boost pressure combined with the flow of the turbo which determines volumetric efficiency. The smallest area the air must get through is the valve space. There is no 'weak' cylinder as they are not all on intake at the same or similar times. It is the turbo which must continue to push air once the valve opens and there is a pressure drop in the system. If the turbo fails to provide a volume of air suffiecient to fill all cylinders at once then it will not be able to keep up at high rpm, air speed is reduced and power drops. What the design of the plenum does is maximise the 'efficient' space that the turbo can store air before the valve opens. Go too big and you will suffer in the lower end of the rev range for torque but increase your max rpm potential....go too small and the inverse is true. Usually a good plenum size is around twice the capacity of the engine. Runner length also has a major role to play in choosing a plenum/intake manifold as you want to achieve maximum torque at a desired rpm. The longer the runners, the lower the rpm you will have your torque band....and the same applies for this as the plenum in that you don't want to go too far. Runner design is important in that if you just weld some pipe to a barrel, you won't need to put it on a dyno for me to tell you it's not going to be efficient. Instead, bell mouth runners inside the plenum that taper down to the inlet port of the cyliner head to increase air speed as it enters the cylinder head is the better option. Once again there are more factors that play here and also protrusion of the runners into the plenum, diameter of runners, plenum shape, throttle body size in comparison to plenum size and then all of the above compared to engine capacity and whether or not it's forced inducted or not.

As you can see there is much more then just size and shape.....it's not always a case of what looks good, works well. I'm not saying that the aforementioned plenum does not work....I have not seen it or inside it for that matter. Just the usual educate the masses and help them make their own decision saga. Yunno the one about the 'teach a man to fish'. lol

LOL...yeh all very good. You have read some texts on manifold desing...but none of what you have said is specific to the RB25 or manifold in question :)

Doesnt change the fact that if you pull the plugs on a std RB they are never the same...you are tuning based around the average of the air the cylinders are consuming and the fuel youre dumping in them. Even then you are only tuning based around the fuel coming out of all the cylinders. One cylinder will be detonating before the others...that limits the ignition/tune you can get into the engine.

You dont need an engine dyno and Motec logging individual cylinders (though speak to those that have set up their RBs on dynos with Motec and they do actually use the individual cylinder injector settings)...the plugs tell you that not all is right. Could also be the fact that cylinder 6 runs the hottest, could be the injector rail isnt equal for all cylinders. Could be the airflow in the manifolds is a compromise....and a better manifold specifically design for a performance application on RBs can help get around this problem

Anyway...i dont really care...need to do some numbers and see whether i should go Plazmaman or jsut go RB26 head

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now



  • Similar Content

  • Latest Posts

    • Even more fun, leave all the ADAS stuff plugged in, but in different locations, hopefully avoid any codes!   And honestly, all these new cars with their weird electronics. Pull all the electronics out Duncan, and just shove an aftermarket ECU and if needed a trans controller in, along with a PDM. Make it run basic but race car styled!
    • To follow up a question from earlier too since I had the front bar off again (fking!) This is what is between the bumper and the drivers side wheel And this is the navigator side, only one thing but its a biggy! So basically....no putting coolers in the wheel arches without a lot of moving other stuff. Assuming I move to properly race prepping this car I'll take that job on and see how the computers respond to removing a whole bunch of ADAS modules
    • So I prepped the car for another track day on Wednesday (will be interesting to see coolant temps post flushing out and the larger reservoir, with a forecast of 3-14 being 20o cooler than last time I took it out). Couple of things to mention; since I am just driving the car and not taking a support vehicle, I took the rear seats out and just loaded the back up Team Trackday style. Look at all that space! To cover off removing the rear seat....it is weird (note the hybrid is probably different because it wouldn't have folding rear seats) Basically, you remove the lower seat base, very similar to a r series but it is a clip that pulls forward to release the base rather than it being bolted down. Easy Then, you need to remove the side section of the rear seat on each side. There is a 14mm head nut at the bottom of the side piece, the it slides upwards off a hook at the top to release; you also need to unhook the seatbelt from the loop at the top. Then the centre piece is weird. You need to release/fold the seats forward with the tab in the boot on each side From there, there are 2,x12mm headed bolts holding the rear of each seat to the folding bracket, under the trim between the rear seat and the boot (4x christmas tree clips there, they suck). The seat is out but you can see where the bolts attach to the bracket
    • As discussed in the previous post, the bushes in the 110 needed replacing. I took this opportunity to replace the castor bushes, the front lower control arm, lower the car and get the alignment dialled in with new tyres. I took it down to Alignment Motorsports on the GC to get this work done and also get more out of the Shockworks as I felt like I wasn't getting the full use out of them.  To cut a very long story short, it ended up being the case the passenger side castor arm wouldn't accept the brand new bush as the sleeve had worn badly enough to the point you could push the new bush in by hand and completely through. Trying a pair of TRD bushes didn't fix the issue either (I had originally gone with Hardrace bushes). We needed to urgently source another castor arm, and thankfully this was sourced and the guys at the shop worked on my car until 7pm on a Saturday to get everything done. The car rides a lot nicer now with the suspension dialled in properly. Lowered the car a little as well to suit the lower profile front tyres, and just bring the car down generally. Eternally thankful for the guys down at the shop to get the car sorted, we both pulled big favours from our contacts to get it done on the Saturday.  Also plugged in the new Stedi foglights into the S15, and even from a quick test in the garage I'm keen to see how they look out on the road. I had some concerns about the length of the LED body and whether it'd fit in the foglight housing but it's fine.  I've got a small window coming up next month where I'll likely get a little paint work done on the 110 to remove the rear wing, add a boot wing and roof wing, get the side skirt fixed up and colour match the little panel on the tail lights so that I can install some badges that I've kept in storage. I'm also tempted to put in a new pair of headlights on the 110.  Until then, here's some more pictures from Easter this year. 
    • I would put a fuel pressure gauge between the filter and the fuel rail, see if it's maintaining good fuel pressure at idle going up to the point when it stalls. Do you see any strange behavior in commanded fuel leading up to the point when it stalls? You might have to start going through the service manual and doing a long list of sensor tests if it's not the fuel system for whatever reason.
×
×
  • Create New...