spanners Posted September 22, 2010 Share Posted September 22, 2010 Ok so what are the rules, especially so that I dont confuse std ECU... I will keep the standard throttle body and air flow metering system, but the plenum doesnt fit. As far as I know the rules are... Keep intake runners the same length Make new plenum volume = OEM plenum volume Keep TB and AFM roughly same distance away Can I put big bends in the intake runners to move where the plenum sits? I was thinking of having an S bend or even twisting the runners around each other (think double helix) to keep horizontal length down to a minimum but actual runner length the same. Wanted to make a plenum from perspex, but may end up with folded aluminium or stainless. Just wanted thoughts on whether having runners on funny angles etc is going to hamper performance (or lean a clyinder out) Can you tell me why these wont work? Or maybe they will. I know TB placement is weird but so is the space available in my engine bay. I want a mushroom filter where my battery would usually be - theres no room to have it poking out the front of plenum as it would hit grill cheers guys Quote Link to comment Share on other sites More sharing options...
DJZ Posted September 22, 2010 Share Posted September 22, 2010 It's a very complicated science, from what I've read you really want the runners as straight as possible and inline with the port/back of the valve to keep the velocity up, or you want a runner with a very gentle bend if it has to be curved, so picture number one would be terrible and wouldn't work well at all. This is all hearsay and don't quote me on any of it. Quote Link to comment Share on other sites More sharing options...
mikuni Posted September 22, 2010 Share Posted September 22, 2010 Dropping the runner length down will be fine, all you will be doing is moving the torque curve torwards the higher rpm. This means you will lose a little mid range but peak power shouldn't be affected. Doing this won't confuse the ecu, but it may cause some difficulties with injector/fuel rail placement and some intake manifolds also have coolant running through certain parts, so just check off of that first. I would be inclined to just go as simple as possible for a custom intake, if you need to make one at all. Short runners, straight pipes, everything like that. Other option is "cut-and-shut" on the existing plenum to move the throttle body to a more suitable location? Quote Link to comment Share on other sites More sharing options...
Yowzer Posted September 22, 2010 Share Posted September 22, 2010 Although your 1st design definitly isn't ideal for all out power, I doubt you'll hamper the engines performance with it. If you were worried about optimum design you wouldn't be dealing with a factory ECU anyway. Quote Link to comment Share on other sites More sharing options...
westy Posted September 22, 2010 Share Posted September 22, 2010 Depends on the ECU/tuning. What is it? Quote Link to comment Share on other sites More sharing options...
kpr Posted September 22, 2010 Share Posted September 22, 2010 beams 3s i take it? changing inlet manifolds will usually mess up your tune a bit. but should be able to get away with more since its afm. not map. Quote Link to comment Share on other sites More sharing options...
spanners Posted September 22, 2010 Author Share Posted September 22, 2010 Yeah beams 3s. Even if I shorten the runners, there are still clearance issues with std plenum. Its huge, the wrong shape, and huge. I would love to keep the standard runners - inside the plenum they have nice bell mouths and I figure they are a good length (toyota knows best) so if I could keep and modify these then I would be off to a good start. Problem is they are all different shapes, so starts to get tricky. From what I understand making the runners short enough to fit this plenum in would be much too much of a change for the engine to perform the same. I would have to take like 100mm off or something ridiculous. I figure that I will try and keep the first 50mm or so (thats closest to the head) of the runners perpendicular to the head, then start a bend after that. Part of the reason for the bend is to bring the plenum forward from the firewall too. Does the TB placement actually matter then? No? I cant see why it would, as long as its not a maze of air to get to it you guys fucking rock with your opinions and hearsay - keep it coming, every little bit helps to make an informed decision Cheers Spandex Quote Link to comment Share on other sites More sharing options...
DJZ Posted September 22, 2010 Share Posted September 22, 2010 Throttle body position does matter, if you have it going straight on to the end of the plenum (which looking at your pictures you won't) it can be bad depending on how far away from the first runner it is, you can starve the first cylinder of air if it's too close. Aftermarket RB plenums have the throttle body angled, this helps with equalizing the amount of air each cylinder gets. I made the plenum for my 280Z, it's very simple but it seems to work okay. It was all guess work and no maths hah. Quote Link to comment Share on other sites More sharing options...
kpr Posted September 22, 2010 Share Posted September 22, 2010 straight will be better yeh, but bends wont cause too much issues. long as they arent too tight. not a fan of the cross over idea though. throttle placement wont matter too much. long as it isnt somewhere silly. i'd be more worried about throttle placement if it were turbo. definitely chuck some bell mouths of some sort back in there. quad throttles and aftermarket ecu please Quote Link to comment Share on other sites More sharing options...
mikuni Posted September 22, 2010 Share Posted September 22, 2010 If you are going to flag the existing plenum you could try just cutting it down so there is only a backing plate and runners, with the bellmouths left. Then get an alloy box made up in what ever shape and volume will fit. This is assuming that the length of the runners is short enough to stay the same, but you will know this as soon as you cut the plenum down. Welding to the cast alloy will be a bit of a cunt, but its definitely doable and might be the simplest solution. Quote Link to comment Share on other sites More sharing options...
spanners Posted September 22, 2010 Author Share Posted September 22, 2010 I do have a set of blacktop QTBs and brand new trumpets, but the cost of ECU wrecks it for me. I cant afford the extra $2k+ when i could just get a plenum and plug the whole lot in. Also if anything later down the track would be S/C so I would like to have a sealed system. I did just go out and cut plenum down. Well when I say cut I do mean beat the shit out of it with a hammer until it fell apart. Fits now, but obviously there are some new issues with this particular design! And my thoughts about where TB should go Yusssss, wrecked the whole thing so will have to get the whole lot made from scratch! plus firewall clearance. So I think I will just get a new one made up like my 2nd design, which has the runners pointing foward Quote Link to comment Share on other sites More sharing options...
kpr Posted September 22, 2010 Share Posted September 22, 2010 haha ruthless guy. can you not make the runners similar design as to whats there. and build a plenum to fit. chop that clutch cable thing off. i also relocated the brake reso to gain some more room Quote Link to comment Share on other sites More sharing options...
spanners Posted September 22, 2010 Author Share Posted September 22, 2010 Are your brakes still boosted? Im a retard so put a clutch Mcyl right in the way of everything too. Yea that clutch cable thing will get cut off, so all good, but the intake pipes are too close to the brake master cyl to get a decent box around them. The standard altezza plenum is so massive, its just ridiculous, so there is definately room for improvement. Looks like this might work out ok Quote Link to comment Share on other sites More sharing options...
nanarei Posted September 23, 2010 Share Posted September 23, 2010 Reverse pedal box, problem solved Quote Link to comment Share on other sites More sharing options...
spanners Posted September 23, 2010 Author Share Posted September 23, 2010 Yeah I wish I had done that. Any idea of cost of one? Quote Link to comment Share on other sites More sharing options...
nanarei Posted September 23, 2010 Share Posted September 23, 2010 Well if you want to do it on the cheap modify a L300 van pedal box or similar would do the trick. Otherwise Wilwood/Titon ones will set you back around 400-500 I think. Quote Link to comment Share on other sites More sharing options...
Mike-e Posted September 23, 2010 Share Posted September 23, 2010 please actually put a ramflow on it and penis customs. fuck I chortled fiercely Quote Link to comment Share on other sites More sharing options...
kpr Posted September 23, 2010 Share Posted September 23, 2010 yeh still boosted. i did the same thing with the clutch master also. relocated the reso for that too but still sucks sometimes. heres a better pic of the brake reso, dont gain a heap of room, but helps Quote Link to comment Share on other sites More sharing options...
R100 Posted September 23, 2010 Share Posted September 23, 2010 Fuck changing the pedal box. Just cut the intake tubes shorter and weld up a plenum. Dont get carried away with plenum science. It will be sweet as. If your worried you could still keep the runners the same lenght, just make them straight. Chances are everything will still fit under the bonnet if you make it fit. Thats all i would do anyhow. Quote Link to comment Share on other sites More sharing options...
spanners Posted September 23, 2010 Author Share Posted September 23, 2010 everything will still fit if you make it fit Never a truer word spoken... I have already put a bit of work into brakes so dont reeeeeally want to change them now. Just talking to my engineer about plan of attack now. He is a genuis and will make me something primo Dont think he will be keen on Penis Customs thing though. Waaaay off topic, but has anyone ever seen a white 323/Familia hatch around lower hutt with a big wonky fake speedtech sticker on the windscreen? Its possibly the worst car ever. Fake manual gearknob on an auto stick, blue rimmed guages to measure nothing, heaps more classic stuff I cant remember, basically I have never seen a worse attempt. It went well with his 323 owners club hat. I saw this like a year ago, maybe hes dead by now, but maybe hes macked his car even harder. More stickers maybe Quote Link to comment Share on other sites More sharing options...
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