Im am getting REALLY sick of all these CAI/pod/panel/snorkel threads. Not so much because of how many are started on a seemingly daily basis, but because they are full of opinions, misinformed understanding of how the intake works, and flaming. With all these threads there is a seemingly total lack of proof to back up anyones claims.

/end rant

In this thread I am going to take some measurements and try and prove or disprove some of the facts surrounding all these intake mods. To do this I am datalogging my EF with different intakes. To start off with I am just using the bits I have handy. The intake setup I have is an EL-GT snorkel, k&n panel filter, and a 3" pipe to the TB. I did 2 runs in 2nd gear from about 2500rpm to a bit over 5000rpm and averaged the results. I then replaced the el-gt snorkel with the standard I6 item and repeated. Finally just for s**t and giggled I pulled all the intake pipework off and ran an open throttle body. Here is the results I got



Note that the graph is bumpy because the intake in the manifold jumps around a bit (around 1 kpa) as pistons move etc. If I kept doing more runs and averaging the results they would get smoother, but you can already see the trends with 2 runs and i dont want to waste any more petrol than I have to. Ill might collect together more of my std intake, maybe a std paper filter and make some more graphs if people seem interested.

Any comments on the method or the graph?

i think this is a very f**k good idea and should be made a sticky and/or tech doco. Should help out many people who are wanting to upgrade there intake.

Keep the results coming. Pitty its not applicable to boxcars

Some great work as always Mark - its good to see a scientific approach taken towards this topic.

Just a couple of questions, more out of interest than anything else...

101.8kpa atmo - this is the reading with key on, engine off?

So the negative inclination of the graphs... this demonstrates vacuum increasing within the manifold?

Thats right. The pressure in the manifold without the engine running was a tad over 101kpa and without any other influence (like compression waves) this would be as good as it gets (0 restriction). The downwards slop in the graph indicates that as rpm increases the pressure starts to drop off. The open throttle body line basically shows how much restriction the throttle body is (and to some extent the shape of the manifold). The difference between that line and the others shows how much of a restriction the intake pipe, airbox, filter and snorkel are combined.

Some interesting analysis to be made of the standard intake run and the EL GT snorkel...

Seems EL GT has a comparative advantage in the low to midrange RPM... standard EF outperforms it at higher rpm??

that is an interesting graph. and as martin pointed out, it does look like the GT has more in the low down range (maybe why people "experience" more response? i could be way off here)

hopefully this will help people decide what they want to do and not ask again and not ask again and not ask again

Yep, thats what the results show which is not what I expected. If it is not an experimental error, the only way I could think of explaining it would be that the standard EF snorkel is not small enough to be a restrictionm, but its smaller size increases the velocity into the airbox which kind of forces the air through the filter. I will definately be running that comparison again so it will be interesting to see if this is always the case.

Can i make a sugestion.

Can you run the open tb test and then run with about 25cm of stright 3 inch pipe conected to the TB. (a pipe like the airbox pipe i use with my intakes)


Could you post a pic of your 3inch intake please?
and will you be doing a comparison of the 3inch pipe vs: the stock plastic pipe?



would be interesting to see the difference between fully stock with a paper filter and a complete 3inch pipe K&N filter and big snorkle.

I've updated the thread title - love your work man!!

dude nice work

if i knew how you did this id do it to

Ill see if I can find some pipe and give it a shot. I will be doing the stock intake, then with each bit replaced to see if I can find the major restriction (if any) in the stock setup. Ive got a few different 'performance' filters as well (no pods or paper filters though). I just have to go pick up all the stock bits and pieces that ive left lying around...

intake -

there was an article in street commodores mag a few years back where they tested intake tube length on a dyno.
they used that flexable ducting, so they could vary the length easily.

they found an open TB made less power then when it was fitted with an intake pipe of about 15cm or more, they tested to about 1.5m i think.

they also found the sharp 90degree bend the intake on a GEN3 has was a huge restriction to flow/power

stock standard, can I ask where u got that 3" intake pipe from?

Thinking about modding my EF 4.0l (95). Based on these results what do people think would be the best intake mod for EF 4.0l?
(In laymans terms for people as inteleeegent as me!)

cranborile - definately a 3 inch mandrel bent pipe