Sizing cold air intake

[thruthefence]

I hope I'm not breaking any rules, I posted this to "Automotive body" in error.

thruthefence (Aerospace) Aug 31, 2010
I'm interested in providing a 'fresh air' inlet for my Lotus Europa Toyota engine conversion. The engine is a twin cam four cylinder 1500 CC, mid engine configuration,winds pretty tight, I expect 7500 RPM or so "in anger" although this is not a race car. I am using the stock AFM, the inlet of which measures 2" X 2" at the 'swinging gate'.(sort of like an old Bosch). Is there a rule of thumb for the size inlet needed? I'm not expecting ram recovery, or any such nonsense, but the space limitations will require me to turn the airflow appox 90 degrees (through a filter box)to feed the actual intake plenum (using four individual throttle bodies) My boy-racer "naca like" submerged duct feeds two 3" flex ducts, which will terminate at the air filter enclosure. Is 1/3 greater area enough to prevent starving the engine of air?

 

[patprimmer]

I would think so, but it depends on the surface nature of the duct and how tight the bend is.

The bigger the plenum, the less restrictive the ducting will be as you smooth out pulses and therefore lower peak airflow velocities.

Regards
Pat
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[patprimmer]

Oh

You should red flag your other post so only one is running. I agree this is the more appropriate area.

It looks a lot better if you red flag the other one yourself before some one else does it to you.

Regards
Pat
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[thruthefence]

Red flagged, as required; thanks, Pat.

Steve

 

[thruthefence]

Replying to PatPrimmer, eg the ducting. I'm planning to use double wall "CEET" ducting, that has a smooth inner lining, as opposed to the spiral wound wire that is exposed on the single wall.

 

[patprimmer]

If it is smooth wall, swept radius, I think it is plenty big enough, however it can't be to big at that point from an airflow point of view. Gains re space and weight costs is another thing.

Regards
Pat
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[GregLocock]

I've never measured more than 1 kPa MAP at full throttle, but I've measured air intake temps at 60C quite often.

Might be worth thinking about which has the most effect on power.

Cheers

Greg Locock


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[patprimmer]

Ifit is NA, I suspect more surface area with lower air speed picks up more heat.

Insulating the air ducts and IM can help.

Regards
Pat
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[Lou Scannon]

Greg, can you please clarify? "1kPa MAP" makes no sense to me... typo?

 

[patprimmer]

I presumed 1kPa pressure drop.

Regards
Pat
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[AboveRedline]

1 kpa refers to plenum pressure, in other words atmospheric. Of course since you've spent some of your available energy on passing through a filter, and turning corners, don't expect a full atmosphere in the plenum.
Usually the diameter of the inlet is whatever the throttle body o.d. is, and the length and access to cold air is what tunes in the power curve. Up to 7500rpm, 30-34" should work well. A 2"x2" square is equivalent to Ø2.25 tube, so 2.5" (64mm) dia should be okay.

 

[evelrod]

Since I'm a long time Lotus racer, I find a twincam Toyota in a Europa just fine as long as it's replacing the Renault POS.

I have a 197+hp/132lb/ft Lotus 1600 twincam in our Lotus Cortina. Never used more than one 3 1/2" tube to feed the fiberglass air box over the two 45DCOE's and we red line at 8600 rpm.

We did put an 18RG in a MkII Cortina years back with a stock ~3" inlet hose. Street only, no problems.

Looking at the photos of a JPS Europa, I should think the stock twincam inlet and filter would perform adequately with your engine conversion.

Rod

 

[thruthefence]

Thanks, Rod, that's reassuring. I hope to make 150 HP, which is twice the Renault Taxicab engine has. I've seen some Gordini crossflow head Renault's make good power, but this Toyota came with my "basket case", so I'm committed.

 

[evelrod]

Is it a 2TG or some later model? I have a 165 hp TRD 2TC 1600 with twin 44 PHH's that I built in 1997 but have never even put oil in it. One of these days I'll find something to put it in. It's mated to a Lotus gearbox at the moment.

Rod

 

[thruthefence]

It's a 4A-GE 20 valve,(five valves/cyl), a Japanese domestic market engine. The head is a Yamaha design. VVT on the intake cam, 10.5 compression. There's quite a few of them in Europas these days, a guy in Houston has developed a bellhousing adapter & engine mount 'kit' that simplifies the process. I'm a year away from running, at best.

 

[evelrod]

Yes, I've seen that engine in both the injected and the carbureted versions used in the now defunct World Sportsracer class. We have a couple running in VARA since there is no other class for them to compete in.

I wouldn't mind owning one. Made a few years ago down here in San Diego and on the market for reallllly cheap considering how sophisticated they are.

Rod

 

[thruthefence]

Yeah, the boy-racer/drifters use them. Quite a few mods for the engine, as well as outrageous lies about horsepower.