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Cold air intake

Some of what is claimed and posted about cold air and ram air intakes is complete rubbish. In general, there are a few things that may help:     If the new tube has a larger bend radius and/or diameter than original ducting this will increase air volume slightly. The end of the intake (inside the filter) should be a 270° rolled-over radiused lip, not cut off flush. The radius should be 25 to 30% of the diameter (although the gains beyond 3/8” are minimal). For example: if the entry is 70mm to match the TB, the radius should be at least 17.5mm or .69”. None that I’ve seen are big enough. The difference in flow between a good shape and a bad one is over 5%. Click the picture for a larger view.

The tube (and the entire tract) must have a smooth interior wall - the bendible, conformable flex tubes are completely worthless - the spiral or corrugated inner wall drastically reduces air-flow.     Aluminum is almost the worst material for the tube (silver or copper would be worse) because it transfers heat too quickly. Steel tubing polished, plated, or painted silver is much better, the weight difference is only a few ounces. ABS such as used for DWV (available in many large sizes inexpensively at Home Depot, &c.) is useful here also since it’s a good insulator and the interior walls are very smooth. It can be constructed in sections using standard commercial shapes (45° bend, U bend, etc.), glued together and painted.     If the new filter area is larger than the OEM this increases flow slightly - but this is not always an accurate comparison, since not all filters flow the same per square inch of area.     A filter re-located to anywhere inside the engine compartment gets only pre-heated air from the engine (unless masked with an enclosure, &c.). Under WOT the heat throw-off from the exhaust and hot air pulled through the radiator by the fan is huge. A CAI located in the engine bay is in the “prop wash” of the radiator, and will getting 180+° F air continuously by convection. Air is also not an insulator to heating by radiation - luckily, this is minimal except at very low speeds.     The biggest power boost you can get from the intake duct is cold air - the difference between 70° ambient air from in front of the car vs. 150° or more taken from inside the bay is large. Ideally, an intake should have a remote tube ending outside the engine bay in front of the bodywork (grill, under bumper, &c.), and a water trap to prevent rain and road dirt from reaching the filter.     The duct from the entry need not be a continuous diameter, or even a continuous cross-section (as long as the minimum area is substantial). It can end in a big box containing the filter, then another tube back to the throttle body.     Pointing an external intake scoop forward does not produce enough “free supercharging” to make much difference, the dynamic (wind) pressure is only about 1.2% at 100 mph.     Even a K&N filter has to be big enough to work; for example: a 3.3 liter engine peaking at 6,000 RPM needs about 47 square inches of filter to work (6” × 8” panel, &c.). The K&N formula for filter surface area: (engine size in liters × RPM ÷ 418). 3.31 liters × 6,000 RPM = 19,800, ÷ 418 = 47.4 square inches. The K&N replacement filter for the 3MZ is 5-7/8” × 11” for 64.6 square inches, or sufficient for 8,000 RPM.     When you remove the original stuff (especially the resonators), you get a bit more intake roar (sounds nice, though!), but it cancels any benefits from the original tuned intake system; see above: .

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Throttle body     The original TB is 70mm (2.75”) inside diameter, which is more than adequate for the stock, or even a mildly modified engine. With test conditions of 95% VE, ambient air 29.92” Hg @ 75° intake temperature, 5,800 RPM peak power the 70mm TB produces a pressure loss at the manifold of only .219 psi (.446” Hg).     Substitution of a larger 75mm TB, widely touted as a power mod, reduces the loss to .164 psi (.333” Hg), but is only worth about ½ HP, and that at only at high RPM and full throttle.

As reported by Stefan Vince, SAE: “a TB increase will change the resonant RPM of the intake. It’s the same as enlarging the neck diameter on a Helmholtz resonator. That change may provide the bulk of any power increase seen at higher RPMs. The effect on the resonating system must be considered for any TB change on a plenum type intake. The OEMs’ use of large TB size is normally to reduce pumping losses.” Click the logo to visit Stefan Vince’s “Performance Engine Components’s web site.

Here’s a rough guide to selecting a throttle body by minimum intake pressure loss. Please note: do not use these pressure drops to determine carburetor size, where losses below .25 psi are not suitable for anything but race engines, and .75 psi for high performance.

Intake pressure loss guidelines
Psi	In., Hg	Application
1.473 psi	3.000”	Std. CFM rating for 1 or 2 bbl. carburetor
1.000 psi	2.036”	safe for any use, mild peak power loss
.737 psi	1.500”	Std. CFM rating for 4 bbl. carburetor
.500 psi	1.018”	high performance, leaves little power on the table
.200 psi	.407”	slight power increase, delicate throttle operation or modified controls suggested
.100 psi	.204”	race only, not suited for daily driver and traffic

Later models with “drive by wire” (electronic) throttle control cannot substitute a cable or linkage-controlled TB directly, since the control signal affects other computer functions.     Click here for comments on modifying older conventional TB linkage for better control: .     The optimum duct size to supply a throttle body is 25% larger than the TB’s area. The transition from the duct ID to the (smaller) throttle body ID is a radius, for which the formula is: R/D=.5, where “R” is the desired radius, and “D” is the throttle body diameter. This radius combined with 25% larger area leading to the throttle body reduces the velocity to exert more pressure on the throttle body. Here are some TB diameters vs. intake diameters:

Throttle body diameter vs. air inlet diameter

TB

56mm

58mm

60mm

62mm

64mm

66mm

68mm

70mm

72mm

74mm

76mm

78mm

80mm

Radius

28mm

29mm

30mm

31mm

32mm

33mm

34mm

35mm

36mm

37mm

38mm

39mm

40mm

Duct

63mm

65mm

67mm

69mm

72mm

74mm

76mm

78mm

80mm

83mm

85mm

87mm

89mm

TRD supercharger     The TRD supercharger kit, designed and manufactured by Magnuson Products from the basic Eaton M62 Generation IV· supercharger, was only available for the earlier 1MZ-FE engine. With the original drive pulley size, it produced 5 psi in the 3.0 liter engine, but required about 35 hp to drive it. The outlet (compressor discharge) temperature is increased 50-60° F over inlet temperature. If the drive ratio is increased to 2.5:1 (supercharger 15,000 RPM, engine 6,000 RPM) it will produce 10 psi. It has been discontinued and is now hard to find.     Here’s a picture showing a TRD 1MZ-FE installation by Solaraguy.com member ndeguzma. Click on the picture for a larger view; click here for the Solaraguy.com thread and more details:

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5 speed automatic transmission     This has overdrive (indirect) final gear, which lowers engine speed in 5th for reduced wear, noise &c. and increased gas mileage. Using the original P215/60R16 tires (26.16” tall), the internal ratios are:

Gear ratios RPM lost RPM recovered RPM after shift Overall ratio Speed per 1,000 RPM Speed in gears @ shift RPM 1st 4.235:1  Shift out of 1st at 5,800  13.94:1     6 Mph   32 Mph 2nd 2.360:1  -44.3% 55.7% into 2nd at 3,232  7.77:1   10 Mph   58 Mph 3rd 1.517:1  -35.7% 64.3% into 3rd at 3,728  4.99:1   16 Mph   90 Mph 4th 1.047:1  -31.0% 69.0% into 4th at 4,003  3.45:1   23 Mph 131 Mph 5th .756:1  -27.8% 72.2% into 5th at 4,188  2.49:1   31 Mph 181 Mph

It is readily apparent from the table that the nominal top speed of 130 mph is limited by engine power, not by RPM. At 130 Mph the engine is only turning about 4,150 RPM and in fact the top speed might actually be increased by raising the axle ratio from 3.291:1 to perhaps 3.500:1, which would raise the engine speed to 4,420 RPM - closer to its rated power RPM. Don’t have a U151E? Find your own ratios here:     All modern automatic transmissions have torque converters, and all torque converters have stall (maximum engine speed before the engine stalls or the car moves), there is no such thing as a “stall converter”. Engines built for increased power with radical cams suffer from reduced low speed power, and a converter with increased stall speed allows the engine to spin faster for a better launch. The increase can be done by either changing the angle, diameter or pattern of the fins, or reducing the diameter of the shell (outer body), or any combination of these.     There is a practical limit to this, since all FWD cars have weight transfer from the drive wheels on launch - if you have too much power or too much stall speed, you simply spin the tires.     Converters prepared for serious use (blower, nitrous) frequently have their fins, which are commonly crimped to the torus shell, brazed in place to prevent them from “laying over” (bending) from hydraulic pressure under severe load - expect to spend money on this.     In addition to the 1st gear torque multiplication, the torque converter also multiplies engine torque by perhaps a factor of 1.9:1 for the first few feet until the stator spins up to speed. This gives a brief but effective overall 1st gear ratio of about 8:1.     The U151E works well with the stock engine, but needs some modification when the engine is supercharged. These changes include: »    modified valve body calibration to improve shift quality »    additional friction clutches for more surface area »    internal oil passages ported and enlarged for better cooling and faster application of fluid pressure »    pressure regulator boost valve modified for response time »    generally, the line pressure is raised to apply more force to the clutches »    for sustained boost more transmission cooling capacity is needed, usually by adding a remote       radiator in series.

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