rob Posted November 4, 2009 Share Posted November 4, 2009 ok.. so a while ago i picked up some ITB's from a silvertop 20v that have been butchered onto a smallport manifold which let me use the smallport fuel rail. only problem is that they're missing the idle bypass pipes that the factory 20v uses to keep the engine going when the butterflys are closed. from what i can tell, other "off the shelf" 20v-itb-to-16v manifolds suffer from the same problem - at least the one that t3 sells appears to... i briefly toyed with the idea of a stepper motor setup to operate the butterflies, but decided that it would probably be difficult to tune and was unnecessarily complicated when compared to an idle bypass setup, which would consist of some pipes and a single valve. i found some pictures of the factory setup: (came from http://www.my-acoustic.com/Car/vacuum/4_throttles'_vacuum/4_throttles'_vacuum.htm) but because of my fuel rail, theres not really any space to have the bypass holes coming in from above like the factory manifold, however there is enough space on the under-side of the manifold to sneak them in. the bypass holes would be going roughly where the black X is, indicated by the red arrows. this is the same layout as the factory setup, but coming in from the bottom, not the top. so, i have one question and need one favor the question is: can anyone see any problems running the idle-bypass holes in from below? and the favor is: does anyone have a factory set of silvertop ITB's laying around that they could measure the size of the bypass hole on? cheers, rob Quote Link to comment Share on other sites More sharing options...
BobbyBreeze Posted November 4, 2009 Share Posted November 4, 2009 Don't they have a butterfly bypass hole in the actual TB? there is a little screw to adjust how much bleeds through. You could also look at running an iac setup of another car. Either way i dont see any issue with what you want to do. My TB's are with T-rex at the moment so can't measure up but will be able to in a couple weeks. Quote Link to comment Share on other sites More sharing options...
Truenotch Posted November 4, 2009 Share Posted November 4, 2009 You could just adjust the throttle butterflies so they sit a little bit open? Works fine and means you don't have to do any more butchering. I also thought the TB had an idle bypass screw... it's a big flathead screw that is depressed into the bottom of the TB. Quote Link to comment Share on other sites More sharing options...
Spencer Posted November 4, 2009 Share Posted November 4, 2009 Yea i just cracked the throttle stop open a fraction, worked well. You should be using a some form of after market ECU to get this setup to work correcty. So just setup all your cold idle enrichments right and you should be able to get it to idle pretty low cold and hot Quote Link to comment Share on other sites More sharing options...
rob Posted November 4, 2009 Author Share Posted November 4, 2009 hi guys, thanks heaps for your replies my original plan was to set the stops to open the butterfly's a little to provide a "base" amount of airflow and then provide extra air (for cold starts etc) with a stepper motor operating on the linkage. so ive had another look at the TB's and you guys are right - there is a bypass in the TB itself! can't believe i missed it because its also shown on that page i found with the 20v itb info. thing is now i'm unsure why the factory setup has the additional bypass pipes built into the manifold.. something to do with having the engine being able to run in a *huge* range of conditions (like arctic circle/sahara styles) maybe? i had assumed that i'd need control over the airflow (either via stepper motor operating on the linkage or an electrically-operated valve) in order to have trouble-free cold starts etc, but if i can get away with richening up the mixture and just having the butterfly's statically set, then that sounds sweet to me. since you guys reckon it'll work fine with the existing TB bypasses and opening the butterfly's a bit i think i'll just roll with the TB's as-is. sounds like they should be work well enough to get it running at least - if it proves to be too much of a pain in the butt getting it to idle nicely i'll look at getting the extra bypasses drilled. p.s. i'll be using a megasquirt to do the spark and fuel on this thing Quote Link to comment Share on other sites More sharing options...
Spencer Posted November 4, 2009 Share Posted November 4, 2009 Yea mine worked fine with just a the throttle plate cracked abit, if you want factory style idle up the only way is with a bypass and stepper motor or similar. But mine worked well on coldish mornings I'd say in frost etc you will have to give it abit of gas for a minute or so to get it warm. There are a shit load of bluetops out there with the factory wax valve idle up removed and they run fine, once the slightest bit warm the idle away fine Quote Link to comment Share on other sites More sharing options...
kpr Posted November 5, 2009 Share Posted November 5, 2009 i also run mine with the throttles cracked open a bit. i didn't mess with the bypass adjustment. just readjusted the stoppers on the throttle plates so they started opening at the same time. but also have the stock throttle stopper dashpot thing rigged up to a solenoid. so it pushes the throttles open further, when the car is cold. its controlled by the link Quote Link to comment Share on other sites More sharing options...
rob Posted November 5, 2009 Author Share Posted November 5, 2009 my friend who is doing the megasquirt is concerned that slightly-opening the butterfly for idle may negatively affect the throttle response during engine deceleration, especially when under no load i.e. changing gears. considering that all of factory systems (that we've seen at least) set their butterfly's to close completely and use a valve that by-passes the butterfly, do any of you think that being able to close the butterfly's completely would improve the throttle response between gear shifts? maybe we're being too pedantic here..? cheers, rob Quote Link to comment Share on other sites More sharing options...
Spencer Posted November 5, 2009 Share Posted November 5, 2009 Go read KPR's build thread his engine build is pretty sweet, if cracking the throttles for idle control had any negative effects he wouldnt do it. My setup ran fine setup like this also Quote Link to comment Share on other sites More sharing options...
kpr Posted November 5, 2009 Share Posted November 5, 2009 shouldn't be any different running a slightly open throttle plate to a bypass. manifold pressure will be the same either way. there are a few minor issues, like if you were to adjust your idle speed via opening or closing your throttle plates, will effect the tps closed throttle setting. where as a bypass would not. but thats hardly a problem. a bypass is also easyer to adjust and possibly less likely to self adjust over time. but again nothing to worry about. its harder to get even airflow through all 4 throttles by cracking them open.(but no worse than using the stock bypass screws) i haven't been too concerned about this on my car, since it idles shit with the big cams anyway. you could always add your holes in the manifold an run a isc valve, controlled buy your ecu if you wanted cold start etc.. the hole size wont matter too much, main thing would be to get them all the same size. along with the plumbing to the isc. else you will get rich and lean cylinders at idle. id say 2-3mm hole in each runner would be plenty. i have a 20v manifold hanging about i could measure if you wanted. you could also just run a manual valve in place if said isc also. are you going to be running a map sensor or tps only? Quote Link to comment Share on other sites More sharing options...
Roman Posted November 5, 2009 Share Posted November 5, 2009 I'm doing the opposite, I am running a factory Toyota idle speed control valve which tees into all 4 intake runners. If on a race car I wouldnt care, but I want this car to idle nicely on cold mornings, etc etc. Only issue is that if you're still running an airlow meter, you need to make sure that the air that is getting sucked through for idle is still 'metered' by the air flow meter. I'm still running an airflow meter, without a fair bit of work setting it up, quads + map sensor is too inaccurate for a daily driven car IMO. With an airflow meter, it doesnt matter what sort of vaccum you can or cant make, more air = more signal. Quote Link to comment Share on other sites More sharing options...
rob Posted November 5, 2009 Author Share Posted November 5, 2009 roman: yeah - im still mulling over the approach i'm going to take. so far i've changed my mind from slightly-opened butterflys, to bypass pipes in the runners controlled by a valve, back to the opened butterfly's after reading that a bunch of people here are running them this way and now i'm leaning towards the bypass in the runners again - go figure my biggest concern with the lines tee'd in to each runner was that it would negatively affect the airflow through the runner, but after reading up and finding out thats how factory does it, i figure it can't be all that bad.. i have read that map sensor with itb's can be a bitch - but due to how my bodgey manifold is, theres very little space for an airbox of any kind - so running an afm would be a bit of a challenge too. kpr: if you could measure the diameter of those bypass hole's in the factory manifold that would be awesome! the engine is just a stock standard smallport - only reason i'm running the itb's is because i've pinched the smallport intake for another project i've also got a set of gze injectors laying around that i thought i might chuck on there... its just in a kp60 with a k50 - so its not gonna be a driftweapon or anything. it can get pretty chilly during the winter down here (chch) so i'm liking the idea of having a factory(ish) idle setup. going to be running the ms2 with the tps and a map sensor - and an additional map sensor for real-time barometric correction Quote Link to comment Share on other sites More sharing options...
NicT Posted November 7, 2009 Share Posted November 7, 2009 my biggest concern with the lines tee'd in to each runner was that it would negatively affect the airflow through the runner, I wouldnt be concerned about how they would affect the airflow through the runner when you have made an adaptor plate like the one you have. The welds and change in diameter will have more of a negative effect on your airflow then having a small hole drilled into them to feed idle air pressure in. A bypass valve is the nicest option. When fitting up a 3s in a rwd corona, i made vincent (dude from garagedori) run his bypass valve on his setup and it ran shitloads better then when he was trying to get it to run on a cracked butterfly. Flipside is i ran my 4age in my AE85 with no bypass and it cracked open with a lot of sucess. Made it easy as hell to do timing and tune cause of the easily adjustable idle. Really its up to you, ive had quite a bit of sucess with both setups. Quote Link to comment Share on other sites More sharing options...
mikuni Posted November 8, 2009 Share Posted November 8, 2009 I'm running 20v throttles on my setup and we kept aside an idle speed control valve to use incase it was too shit. Haven't put it in yet because its been alright at idle. At first I had nothing and it was a bit of a bitch to start, to idle and even when it was really warm (only at trackdays) but still wasn't too bad most of the time. When setting up the throttle bodys we put a small tube into each runner. The purpose of this was purely to get a steady vacuum signal for the map sensor. Unfortunately we couldn't get a reliable input so tried tuning it off the tps only, which worked well. Because of this I just disconnected the tubes from the map sensor but when that happened a pip came loose and created a vacuum leak. Since then the car idles perfectly and catches itself well when dropping from higher rpm to idle, which was the biggest problem I had. Long story short, that is the other alternative to cracking the throttles a little, but for the ease of that method, it may not be worth bothering doing it any other way. Quote Link to comment Share on other sites More sharing options...
rob Posted November 8, 2009 Author Share Posted November 8, 2009 I wouldnt be concerned about how they would affect the airflow through the runner when you have made an adaptor plate like the one you have. The welds and change in diameter will have more of a negative effect on your airflow then having a small hole drilled into them to feed idle air pressure in. the manifold has been buzzed/milled out, so no ug welds on the inside - it looks hoary-as-fuck from the outside, but the part that counts is nice-n-smooth it does change from round (the itbs) to oblong (the ports), but i dont see any way around that. the bypass valve would be controlled by the megasquirt - means i can adjust the airflow with a computer, easier than buggering around with the linkages imo im pretty much 99% convinced that an idle-bypass is the way i want to go - i'd like to retain the efi niceness of ease of starting/warm-up etc. if someone with some spare 20v itb's could measure the diameter of the bypass holes in their runners/manifold for me i'd be forever grateful cheers, rob Quote Link to comment Share on other sites More sharing options...
eke_zetec_RWD Posted November 8, 2009 Share Posted November 8, 2009 mine are also just set open slightly on the throttle stop, seems to work minto for me. can tune using tps as the load. Quote Link to comment Share on other sites More sharing options...
kpr Posted November 8, 2009 Share Posted November 8, 2009 if someone with some spare 20v itb's could measure the diameter of the bypass holes in their runners/manifold for me i'd be forever grateful i had a look at the one i had, but cant really measure properly without pulling the top off the idle circuit. even then may not be able to see the effective hole size. the actual hole into the manifold itself was bigger than i thought. 6-8 mm going by eye Quote Link to comment Share on other sites More sharing options...
rob Posted November 8, 2009 Author Share Posted November 8, 2009 sweet man, thanks heaps! sounds like im off to get some 6mm id pipe nipples will post updates/pics when theres some progress Quote Link to comment Share on other sites More sharing options...
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.