Getting Good Vacumn Signal from Quad Throttles to Air

[Garth AE86]

Seeing as i'll be doing the conversion from ae86 single throttle intake plenum to ae101 quads soon and ill be running them with pipercross dual sock-filters only, ill need a decent vacumn signal for the map sensor.

ill be tuning the EFI using a new Haltech E8 on TPS mode with a MAP+O2 correction for partial throttle/closed loop running AE101 injectors(if that makes any difference).

i intent to employ the vacumn distribution block method to get a decent signal so my vacumn taps are halfway down the 50mm runners AFTER the throttle butterfly (BF) so about 30mm from the original vacumn tap point.

ive been told to use a fuel filter in the line from the quads to the distro block to increase the signal and ive been told that the bigger the distro block the better. ive also been told that boh these things make no difference in the signal also.

does anyone have a definitive first-hand answer for me?

diagrams images would be great also! thanks!

[Hydra]

ive been told to use a fuel filter in the line from the quads to the distro block to increase the signal and ive been told that the bigger the distro block the better. ive also been told that boh these things make no difference in the signal also.

The fuel filter is there to dampen the potentially "rough" vacuum reading from the quads, which of course makes tuning easier and drivability better

[mrshin]

Remember to put a restrictor on the engine side of the fuel filter so that it can actually do something.

[takai]

Remember to put a restrictor on the engine side of the fuel filter so that it can actually do something.

Restrictor on the engine side? The 4A fuelrails come with their own regulators. That and the Haltech can run very large injectors at idle quite easily. My E6x is running GZE injectors at idle fine.

ae86drift, from your previous posts i gather that you are using the T3 manifold.
If this is the case then you wont be able to use the AE101 injectors, as they are side feeds. If you were going to butcher the AE101 manifold then you would already have a vacuum resevoir there.
You may as well setup an external vac resevoir elsewhere in the engine bay, run 4 lines, one from each throttle body, to it and then a little fuel filter on the exit of that res to dampen puslations.
You also seem to have some misconceptions as to the throttles. AE101 throttles are 42-43mm depending on how much gunk is built up and how tight the fit of the casting was. For a MAP sensor you can simply run the vac signal off the nipple on the "bottom" (in original configuration) of each throttle. The brake booster, which i cant see you mention may need a larger vac source. That said, mine was running off the two other nipples (1 & 4) and with a decent sized vac res.

[Garth AE86]

so like a tiny little inline one?

[oldcorollas]

think of it like this...

you have a high vacuum pulse (perhaps, depending on cam) from each runner, and so you get kind of a sinusoidal curve of vacuum. if your ECU does averaging over enough points, (depending on it's speed of sampling) then it may be ok.... but...

you can use a combination of vacuum canister (ie fuel filter or similar) and restrictors (like mig welding tips = cheap) to alter the signal.

the filter will provide a kind of buffer.. hmm... like an elestic buffer that the pulse has to work against to cause a change in the ECU line.. kind of like a capacitor in an electrical circuit.. so this will help with averaging out the vacuum signal.

the restrictor, place on engine side of reservoir, will reduce the AMPLITUDE of the pulses...

combine this with the filter, and then you have smaller pulses working against a large airspace, and you get very effective averaging..

a restrictor after the filter can also be used, but it is not as effective as having a vac canister or similar.

your ECU should have high enough sampling rates and logging to be able to distinguish the noisy nature of the Vac signal....

i did all this with my MS when setting it up... although i was using single TB, the signal was poor due to cam and low vac, but with simple carby fuel filter it worked very well..

we also used restrictor and filter on an Alfa 2L (ie 18RG) with quads and buggerall vacuum.. again, worked very well.. with the MS you could see how noisy the signal was and then change restrictor/filter to alter the signal...

have fun!

as for sizes... MIG tips are usually 0.8/0.9mm, but you can easily get 0.6mm tips too.. they are like $1 each and great size for 4mm vac hose (depending on gun style.. go to welding shop )
good old Ryco carby fuel filters are a very convenient size also, in terms of vac space..

[Bored?]

if your ECU does averaging over enough points, (depending on it's speed of sampling) then it may be ok.... but...

Filtering the signal in the ECU is pretty simple, so long as the readings you get are accurate.

This leads me to wonder, how responsive is the actual pressure sensor?

[oldcorollas]

as far as i know, ones like the motorolas are pretty sensitive and have fast enough response for the times we are talking about... their specs are available from places like digikey.com

as for filtering in the ECU, that comes down to how many points you average over, if it is too many, then transient response is affected, in a kind of laggy way.. doing it mechanically also results in a little lag i suppose...

not too many people have the option of reconfiguring the sampling rates of their ECU tho, but it would be interesting to see how much averaging affected things (fwiw, MS2 does this )

do any of the commercial systems allow you to change the rate or the number of samples for averaging the inputs??

[Garth AE86]

thanks for the info guys

ill be running TPS mapping mostly (coz i want 110% response) but with map/o2 for idle and closed loop stoichiometric

[oldcorollas]

thanks for the info guys

ill be running TPS mapping mostly (coz i want 110% response) but with map/o2 for idle and closed loop stoichiometric

does it give that much better response? previously i thought that the only place MAP was poor was for idle and very low throttle, but from mid to high, MAP was better? but after seeing a few installs, it seems that the MAP signal from quads reaches atmospheric quickly.. but then again, this means the ports are also seeing atmospheric pressure, so it is still a real measure of what is happening? esp since you have ports closer to head than original...

if you have big assed cams, maybe the ideal way would be TPS for idle and WOT (say 75% and more TPS) and then MAP + O2 for in between? can the haltech do that?

[takai]

Yeah, the Haltech can do that, but it runs like arse. Especially when you get larger cams in there. You end up getting too big of a flatspot on changeover when you nail the throttle. I ended up just going straight off the TPS and it runs a whole lot better.

[Garth AE86]

exactly takai
for response the only way is pure TPS

not only big cams but big overlap too.. not much mercury in that kinda situation.
ill try my best to get signal. thanks lads

[takai]

Personally i wouldnt bother. You arnt going to have much luck in getting much of a signal from it. When we were tuning mine i had a MAP sensor hooked up, and at anything above ~20% throttle we were getting atmo pressure on the MAP. So itll be idle, and bodgy closed loop at that as i dare say it wont have much of a time to settle at idle.

[Garth AE86]

well the tank and vac lines ive been given from a mate (part is from the USA, called eagle)
and everything else is tapped and ready, i need vac for brake boost anyhow, we shall test it and see.

[takai]

No harm in trying, just dont get your hopes up. And i would personally be reluctant to pay the $150 for the MAP sensor. I ended up using the one which the tuning shop had there for testing, and saw how bad it was.