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Intake question for the experts

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Intake question for the experts

Postby benzino » Wed Aug 15, 2012 3:52 am

I recently had to change my intake pipe as it was splitting due to the stress of mating the leganza pipe with the lanos airbox.
My problem is that I have lost a ton of torque from the bottom end (and because my exhaust is so tiny, I have no top end either... :roll: ). I believe the torque was lost due to the resonator being deleted as it forms a large volume of air just before the TB and is easily available to the engine.

My question is, would there be some way of introducing a resonator to the new intake (as I can't go back to the stock setup, due to the reason above). I was thinking about measuring the volume of the old resonator and then finding a replacement (large mouth drink bottle, custom fibreglass, etc.) and have it going in at the 90* silicone elbow.

If I could weld I would just use the stock resonator but I need a solution that I can do at home for minimal $$ ;)
Any ideas on getting my torque back? The only other option is to wait for my exhaust to be done and hope that my lovely low down torque comes back with the 4-2-1 manifold :cry:

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Re: Intake question for the experts

Postby ls400x » Sat Aug 18, 2012 11:38 am

I've seen some clamp-around take off points for process piping but I think they would look a bit industrial. It certainly looks like Daewoo went to considerable effort in designing inlet pipework judging by what I've pulled out of my Nubira (I haven't seen a Lanos arangement).

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Re: Intake question for the experts

Postby PrecisionBoost » Sun Aug 19, 2012 5:28 am

benzino wrote: I believe the torque was lost due to the resonator being deleted as it forms a large volume of air just before the TB and is easily available to the engine.


To the best of my knowledge the additional resonators are only there to make the engine quiet, removal of them always gave very slight gains in torque and horsepower, I do not remember a loss in any area when comparing a cold air intake design versus the factory piping.

This testing was on a Dynojet with the Optra U20SED engine, which is nearly identical to the Daewoo T20SED engine.

The length and diameter of the tubes made slight differences at various areas of the power/torque curve during dyno testing of various intake pipe designs.

Most of your on demand air comes from the plenum volume past the throttle body, which is the same whether you have the resonator or not.

Daewoo was always concerned about the engine in the following order

#1 -- fuel economy
#2 -- engine sound
#3 -- engine power

They could have made the 2.0L push out 150-170hp with no problem, but yet they chose economy as their primary concern.

In short, are you sure the resonator made the difference in torque?

I assume this is a seat of your pants measurement of torque, perhaps it's more in your head than you think.

I know there has been many times where I change something and think it made less or more power, only to find out that it made absolutely zero difference on the dyno.

It's a total let down when you feel like the car is making more power, only to find out you lost 0.5 hp in one small area of the curve, which is pretty much negligible when considering the differences in power made during various runs on the dyno.
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Re: Intake question for the experts

Postby benzino » Sun Aug 19, 2012 9:32 am

A couple of pointers that led me to believe that it is for torque... firstly, the intake noise DID NOT get any louder after the removal of the resonator as I didn't have any of the pre-airbox resonators (if it's anything like the mx-5 miata, the pre-airbox resonators are purely for noise reduction but the post-airbox/pre-TB resonator is for torque);
Secondly, my fuel economy got worse after changing the intake (my hypothesis is the engine is working harder to do the same thing).

It is definitely a drop in <4000rpm torque that is noticeable.

I'm unsure if I have gained any top end as my 1.75" stock exhaust means that I have little power over 5000rpm anyway... and hence why the drop in torque has been so noticeable as that was all I had before! :lol:

So re. my options, do you think I could make a pre-TB air chamber/Helmholtz resonator or should I just wait and see when I get exhaust done?


LS400x> the leganza post-airbox intake is different to the nubira where it doesn't have the small diameter resonator/elbow just after the airbox, only the large one before the TB - I'm not sure what role the nubira one plays
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Re: Intake question for the experts

Postby PrecisionBoost » Tue Aug 21, 2012 12:12 am

I don't know what to say, I tested the stock Optra U20SED on the dyno and found little change when I removed the various components of the stock intake and converted it to a cold air intake system.

I did test it with the first half of the intake system removed as well as completely stock.

The only noticeable difference was a louder sound in a 300RPM band mid way up around 3500 RPM, which I attributed to a natural resonance of the intake pipe, which is normally absorbed by the factory resonance chambers.

Usually the resonance tuning used to gain power is done in the intake runner lenghts, which is why they use the dual length runners in the Lanos to increase low end torque with the longer intake path then increase high end torque with the shorter intake path.

The reservoir you speak of would slightly affect the intake flow, but it's more likely that it would give slightly crisper throttle response as opposed to a large gain in power.

The length and diameter of the intake pipe can affect the tuning of the intake runner length, which would affect torque, but to be honest I don't see it being significant based upon the testing I did.

It certainly wouldn't hurt to fool around with a few different intakes, all in all I think I made about 5 or 6 different ones when I was playing around, only one of them made significant gains, even then I think it was only 4-6hp in the top end
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Re: Intake question for the experts

Postby benzino » Tue Aug 21, 2012 5:35 am

how come wikipedia says the U20sed is rated at 89kw and 171nm http://en.wikipedia.org/wiki/GM_Family_II_engine#L34

that's 9kw less than the other 2.0l engines and 17nm less!
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Re: Intake question for the experts

Postby benzino » Wed Aug 22, 2012 3:03 am

also, what pipe diameters did you try? maybe going to 2.75" was too big?
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Re: Intake question for the experts

Postby PrecisionBoost » Thu Aug 23, 2012 4:59 am

benzino wrote:also, what pipe diameters did you try? maybe going to 2.75" was too big?


In my opinion you should not exceed the throttle body diameter ( 2.5" )

The general rules are:

1 ) Larger pipe diameter = power on top end, drop in torque on low end
2 ) Smaller pipe diameter = increased low end torque, drop in peak power on top end
3 ) Shorter pipe length = power on top end, drop in torque on low end
4 ) Longer pipe length = increased low end torque, drop in peak power on top end.

Increased diameter = lower air velocity = poor mixing of air in lower RPM but increased volumetric efficiency on the top end.
Decreased diameter = high air velocity = excellent mixing of air in lower RPM but decreased volumetric efficiency on the top end.


Personally I believe you would be best with a 2.5" intake pipe in the range of 24" in length between the throttle body and filter for the best mix of power and torque.

The intake designs were combinations of 2.5" and 3" tubing, I believe the best result was approximately 12" of 3" tube transitioning down to a 2.5" tube ( silicone reducer ) which was approximately 15" in length.

The 3" section was to match the cone filter and create a reserve volume, the 2.5" was designed to ensure decent intake velocity while maintaining the same diameter as the throttle body to reduce the risk of turbulence.

Some Formula SAE intakes manage VE numbers around 120% ( meaning they force 1.2L of air into a 1.0L cylinder )

Most of these intake pipes go from a primary throttle body diameter, taper slowly down to about 50% of Throttle body diameter over approximately 20" then taper back up to TB diameter over another 20"

The tapering increases the air speed dramatically and creates a unique resonance during a particular RPM band where it overfills the cylinders.

When it comes right down to it, the air coming in is smaller in volume and density than what is exiting out the exhaust.

If you don't have a 3" exhaust, there is not much point in having a larger diameter intake.

You need to ensure you don't create turbulence as the air comes to the throttle body, decreasing from 2.75 to 2.5" right at the TB will create a blockage of air due to turbulence.

Ideally you want a taper of roughly 7 degrees or less to reduce turbulence, unfortunately most silicone reducers are significantly higher than that.

This is why the 3" to 2.5" transition was done well before the throttle body to ensure that the air had some time to settle down before it hits the throttle body.
1994 Opel Calibra 4X4 turbo ( C20LET 2.0L 16V Turbo )
2002 Daewoo Lanos
2011 Mitsubishi Lancer Raliart --- SOLD! :)
1989 Passport Optima GSi (Astra MK2 ) --- SOLD! :(
1990 Passport Optima GSi (Astra MK2 ) ---SCRAP! :(
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Re: Intake question for the experts

Postby benzino » Thu Aug 23, 2012 7:03 am

as I'm going from the lanos air box to the TB, a long intake is not possible as the room to work with is approx. 16". The only way to go 24" is to convert to a cone filter.

I think upgrading the exhaust might solve my problem, my plan was extractors (42mm-45mm-51mm) then 2" pipe to a 2.5" metal magnaflow 200cpsi cat, then 2.25" cat back with 2 small resonators going into a Subaru STI rear muffler (for high flow/low noise).

And then if that doesn't make things good again, I will have another play with the intake; first by adding a volume of air pre-TB and if that doesn't work, by going to 2.5"

thank you for taking the time and effort to help me out Chris

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Re: Intake question for the experts

Postby benzino » Mon Sep 03, 2012 2:40 am

Chris, for the length of pipe I can use for the intake, would you recommend 2.5" or go even smaller like 2.25"?
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Re: Intake question for the experts

Postby PrecisionBoost » Mon Sep 03, 2012 10:38 pm

Given your looking to upgrade further, you might as well go with 2.5" and make it simple, then you don't have to worry about turbulence from diameter changes.

The lower the quantity of bends the better you will be, ideal situation is a cone filter in behind the headlamp, is there a reason you want to keep the stock airbox ?

If your concerned about a "factory look" you could always modify the stock box and move it forward towards the headlamp, but it depends on your fabrication skills.
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2002 Daewoo Lanos
2011 Mitsubishi Lancer Raliart --- SOLD! :)
1989 Passport Optima GSi (Astra MK2 ) --- SOLD! :(
1990 Passport Optima GSi (Astra MK2 ) ---SCRAP! :(
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Re: Intake question for the experts

Postby benzino » Tue Sep 04, 2012 4:23 am

Moving the airbox isn't an option due to the angle of the airbox outlet... It's only just right now...

I have a choice between 2.375" (60mm) and 2.5" (64mm), maybe the smaller diam. will be the sweet spot, or should I just get 2.5"?
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Re: Intake question for the experts

Postby benzino » Thu Sep 20, 2012 3:14 am

I ordered 64mm (2.5") as the stock TB is 62mm so I didn't want to go smaller with 60mm...

See what sort of difference it makes... and if I'm still not happy with it, I could join the 64mm and the 70mm together and stick a cone filter in the guard
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