Anybody Work With Cardboard?

[altezzaclub]

Ok, it's too effective!!

 

Arond town its no different, but this morning I got out into the hills around Ophir at 80-100kph and it was climbing hills at 16.8 to 1 mixture! So the extra air pressure leans it out too much at speed, which equals high exhaust temperatures and burnt valves. However easily fixed with the mighty SUs, I just pulled the choke out! :laff:

 

I'm happy to have it running down around 17 to 20 on over-run downhill, or cruising at 15 to 16, but I like it to richen back to 14point something when I slowly press the pedal going up a hill.

 

If you boot it the SUs always richen up, and its around 13 doing this, which is fine.

 

So I think I will put a pressure relief valve in the air box to stop the pressure pushing the petrol level down in the carb float bowls!

[ke70dave]

that is interesting!

 

how about making your contraption a little more complicated so that the air isnt rammed into the intake, but it still gets nice cold air?

 

so like a "maze" that the air has to negotiate before it enters your intake track.

[GJM85]

 

the 4a-fc used a get-up like this to regulate air pressure, though i've drawn a demo using your set up.

Edited November 8, 2010 by GJM85

[altezzaclub]

The simplest I can think of is to cut a hole in the top of the airbox and glue a rubber sheet over it as a flap, so I just glue the top edge. Where the yellow circle is.

 

When the car is stationary the rubber will seal the hole with its own weight, and it will be on the 'dirty' air side of the air filter anyway.

 

When its running over 80kph the air pressure will lift the flap and release the excess.

 

Its another one of those damm problems where I'd love to see under the bonnet while the car is running at 100kph, like watching the carbs to see if the pistons lift right up... I could cut a hole in the vertical face at the back of the airbox and hang the rubber vertically.

 

I might have to do some work with this stuff here- manometer tests!

 

http://autospeed.com.au/cms/A_0663/article.html

[Hiro Protagonist]

 

the 4a-fc used a get-up like this to regulate air pressure, though i've drawn a demo using your set up.

 

Isn't that just a warm-air induction? Pre-heating improves cold-starts (not really a problem in Aus but is overseas).

[Felix]

Isn't that just a warm-air induction? Pre-heating improves cold-starts (not really a problem in Aus but is overseas).

 

Probably not such a bad thing to investigate the 4afc setup. Think the aim here is a torquey economotor.

 

Altezzaclub have you got any books by David Vizard? Check out what he writes on "Torque Rams" in relation to mini A series motors. Might help in stabilising intake pressures and will really fatten up the torque curve (for your 3rd-4th gear issue).

[GJM85]

No. That's something different altogther and it's closed off unless the engine is cold..

 

On the ae92 4af-c the primary intake sits behind the head light. Between the bumber and right side wheel arch there is a air box that draws from the wheel arch.

 

This is the piece I removed from my seca and where I pulled it from.

[SLO-030]

Might be better off running the intake thru the inner guard as per factory?. Albeit thru a larger hole.

 

Still getting air that hasnt been heated in the engine bay and is fairly well protected from the ram effect and differences in wind direction.

[altezzaclub]

Might be better off running the intake thru the inner guard as per factory?

 

When I'm desperate after trying everything else! :laff:

 

GJM the Altezza runs something like that too, one intake from under the bonnet lip that joins one from the inner guard. There is a vac valve that switches from one to the other and various arguments about what revs it does it at... Anything that will give the carbs as much cold air as they can suck and dump the rest will do.

 

Felix I haven't seen a David Vizard book for many years, I might have to chase a copy up.

 

Overall I'm not convinced that I know why it leans out from the over-pressure, given that SU carbs regulate fuel by air velocity and they should compensate for it. I was thinking it must be pushing the fuel back down the jet, but that might not be it.

 

 

Maybe if I richened the top end of the needle it will run under a little boost quite well! That would make it too rich pulling the same 3-4000rpm in second as there wouldn't be the ram effect, but that's not really a problem.

[Felix]

Overall I'm not convinced that I know why it leans out from the over-pressure, given that SU carbs regulate fuel by air velocity and they should compensate for it. I was thinking it must be pushing the fuel back down the jet, but that might not be it.

 

Air velocity and air pressure are two different things. With higher air pressure you'd have more air molecules for a given volume, yet you'd still have the same air velocity through the carb. ie. denser air moving at the same speed, making it run leaner.

 

I'd be maybe looking into the blowthru variants of SU carbs (as in MG Metro turbos) and how they go about metering fuel for varying air (boost) pressures.

 

Might be easier to move the air intake point to a low pressure area like through the guard/wheel well as previously mentioned to minimise pressure variables.

[Hiro Protagonist]

No. That's something different altogther and it's closed off unless the engine is cold..

 

On the ae92 4af-c the primary intake sits behind the head light. Between the bumber and right side wheel arch there is a air box that draws from the wheel arch.

 

This is the piece I removed from my seca and where I pulled it from.

 

You sure that's an intake and not just a resonator? On all the EFI Corollas at least they run a closed-loop resonator in the front guard (except the EFI ones have the intake on the passenger side), it'd deal with pressure waves/pulses but wouldn't do a thing for ram-air.

Edited November 8, 2010 by Hiro Protagonist

[altezzaclub]

Air velocity and air pressure are two different things. With higher air pressure you'd have more air molecules for a given volume, yet you'd still have the same air velocity through the carb. ie. denser air moving at the same speed, making it run leaner.

 

That's what I was thinking, I couldn't see how having the air push down the fuel level would be all the answer, as with higher pressure the piston lifts higher which exposes a richer section of the needle. Probably both factors work together, the piston lifts up and more air goes in for a given throttle %, and the mix is slightly leaner again because the fuel level is lower in the jet if the jet is now in +ve pressure instead of neutral pressure.

 

I'll try and get some clear pictures of the options tomorrow when we take it down to West Wyalong. I'll run it with and without the scoop, with and without a 20mm gap between the plastic tube and the rubber tube, and with both rich and lean needles.

Edited November 8, 2010 by altezzaclub

[JedzWagn]

ill have to get the dyno sheet then 3k boy?

 

Hey KE20rollabus it seems clear you understand a few things about cars, now... please anyone correct me if I'm wrong but I think most people were taken aback by the way you just came in & openly sledged someone in a public forum ...so even if you are technically correct about anything to do with cars you'll always be viewed as wrong for sledging someone straight off the bat..

 

If you were trying to help the dude you've got a weird way of introducing yourself

 

Maybe you'll consider how to phrase your opinion next time.

 

We all dig cars, no one knows it all & curiosity goes a long way...

[7FOUR7]

how about runing the intake backwards into the wiper well? I have seen this done alot

[GJM85]

You sure that's an intake and not just a resonator? On all the EFI Corollas at least they run a closed-loop resonator in the front guard (except the EFI ones have the intake on the passenger side), it'd deal with pressure waves/pulses but wouldn't do a thing for ram-air.

 

The lower air box is situated in that front gaurd and it has an opening below towards the road. I believe it is effectively a resonator of sorts. It just balances the intake pressure by allowing excess airflow to exit instead of creating a ram effect, increasing pressure in the intake line.

Edited November 20, 2010 by GJM85