Intake runner length....technical question

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Mar 10, 2010 | 12:46 PM

06isDriver

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From: Louisiana

Intake runner length....technical question

So, as some folks may remember I've been designing an intake system thats gonna be really cold air and blah blah blah....but right now I'm focused on the intake length to keep the max torque in the 4800 rpm area just like stock.

According to my calculations the length from the valve opening to the tip of the intake tube should be about 2.6 ft. My question is this: what is the total length from the throttle body to the intake valve opening. I have no real way of measuring that and would appreciate one of you more technical fellas (**COUGH loboxracer COUGH**

) pointing me in the right direction.

Mar 10, 2010 | 12:51 PM

windex

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From: SFV 818

lol at your subtle name drop there hah.
Good luck with this

Mar 10, 2010 | 02:27 PM

Gaugster

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From: Illinois

Don't forget that the intake is dual stage and therefore the lenght is dependent on the baffle postion. Sounds like you want the maximum lenght regardless but it could be better to consider both low and high RPM conditions.

Mar 10, 2010 | 02:38 PM

lobuxracer

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From: Georgia

Total length from the throttlebody to the intake valve isn't the important part of this because you have a plenum supporting the intake runners. The length you're wanting to manage is the runner length. 31 inches sounds like a lot of runner - you might want to consider half wave (16.5 inches) from a packaging perspective.

Who's calculator are you using for this?

Mar 10, 2010 | 02:39 PM

lobuxracer

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From: Georgia

Quote:

Originally Posted by Gaugster

This is only true for the 4GR-FE, it is not true for the 2GR-FSE.

Mar 10, 2010 | 03:08 PM

06isDriver

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From: Louisiana

Quote:

Originally Posted by lobuxracer

well the original value was 16.5 but I didnt see any practical way to use that length with what I've already got goin on. So as I understand it you can double the length and still expect the stacked pressure waves to hit the open valve at the right time. Correct?

but then this would move the torque curve significantly below the 4800 mark.

Mar 10, 2010 | 03:25 PM

06isDriver

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From: Louisiana

now heres the funny thing...according to the calculations, with a displacement of 210.5 cubic inches and the supplied 4800 max torque rpm (from lexus) it says the frontal area should be 1.9 square inches. The stock intake frontal area is practically 3 inches squared. Why supply 1/3 more frontal area than is needed?

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Mar 10, 2010 | 04:30 PM

lobuxracer

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From: Georgia

Quote:

Originally Posted by 06isDriver

Good work. Now you know why I don't believe the claims people make for aftermarket intakes. The extra area is likely for sound control - the OEMs have specific db targets they must meet while the car is operating to meet federal standards (true for all vehicles), so you'll see stuff on intakes that just plain makes you scratch your head and wonder why - but it reduces noise, or allows them to make more noise somewhere else. It's also possible it allows for higher altitude operation, but that's just a guess on my part.

Yes, you can double the length and still have a viable piece, but you'll change the balance of harmonics at other frequencies. If the engine were designed to run at a specific rpm all the time (like a stationary generator set) then you could fully optimize intake length and gain some pretty impressive efficiencies. Since car engines have to run widely variable rpm, you have to make a best fit compromise. My bet is you'd be happier with the shorter length if you have any way you can make it work.