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#721772 - 09/08/09 09:21 PM Runner lengths on SBC single plane intakes?
MY FYN 79 Offline
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Registered: 11/12/02
Posts: 9761
Loc: N/E WI
Any one know the runner length of a typical height single plane SBC intake? A 2975 Victor Jr for example?

I'm trying to get my feet wet baselining my EFI setup myself, and its asking a lot of questions I dont know the answers for at the moment.... runner length being one of them.

Thanks in advance for any input!
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~Jeremy~
79 Monte - Sold 5-11-13
Welcome Natalee Mae 3-16-12

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#721814 - 09/08/09 10:38 PM Re: Runner lengths on SBC single plane intakes? [Re: MY FYN 79]
BadSS Online   content
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Registered: 05/30/00
Posts: 1230
Loc: Pearl, MS, 39208
Typical single plane intakes usually run in the 4.5" range. I measured a 2975 a number of years back,,,,,, but can't find the reference material. In case someone can't say for sure,,, I'm wanting to say it was 4.58".

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#721817 - 09/08/09 10:44 PM Re: Runner lengths on SBC single plane intakes? [Re: BadSS]
Bear88SS Offline
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Registered: 02/25/06
Posts: 1467
Loc: Yukon, Oklahoma
Runner length is from the end of the carb to the edge of the valve... I'd go to a parts house and ask if you can open a box and measure with a string from the center of the plenum to the edge of the runner, then call the manufacturer of your heads and bug them lol laugh
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#721875 - 09/09/09 05:31 AM Re: Runner lengths on SBC single plane intakes? [Re: Bear88SS]
BuzzLOL Offline
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Registered: 05/02/06
Posts: 5504
Loc: Toledo, Ohio
.... I'd say runner length is more from where the runner enters the intake manifold plenum... to the valve seat center... I'm thinking about 8"-9" as I recall for some carb'd intakes like single plane Torquers... longer for Victors... even much longer for TPI's/SuperRams (15"?)...

.... My SBC MoTown heads have 4.5" intake runners + ~6"-7" runners in dual plane stock intake = 10.5"-11.5" total...
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'86 Monte LS (total'd Fall '2013), '87 GTA TransAm TPI350 TH700-R4, '85 Fiero 5-speed, '75 MG Midget Buick Alum.V8 BW 5-speed manual, '77 Pontiac Astre Formula wagon 5-speed posi, '78 F150 4WD 351"M ==> 400" C6, '79 Caddy Seville Olds EFI 350" TH400, 19' Slickcraft 425HP 351W MerCruiser I/O

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#721890 - 09/09/09 08:03 AM Re: Runner lengths on SBC single plane intakes? [Re: BadSS]
BadSS Online   content
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Registered: 05/30/00
Posts: 1230
Loc: Pearl, MS, 39208
For paper calculations, the formulas seem to work better using TOTAL length by using the centered measurements from the valve seat to where the intake runners end/begin in the plenum. Most of the decent engine simulations I've used tend to mirror actual dyno pulls using the short side radius measurements. The better simulations ask for head and intake lengths seperately,, but some ask for TOTAL length.

The better simulations also ask about intake taper,,, because a tapered runner will act like a slightly shorter runner in comparison to a non-tapered runner (same for either a radiused entry edge vs a knife edged entry). Equally important in intake selection and calulations is the minimal cross-sectional area.

What these calulations do not consider is the effeciency of the intake. Again, the better dyno simulations will have a factor to adjust for a well designed, easy flow intake smooth entry into the heads vs an angled entry into the heads. A good example is the swung out runners of the FIRST (left) that lines up the air path to come in straight into base intake and the heads,, unlike the stock TPI (right) that slams air into the intake (from the runners) and the head at terrible angles.




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#722181 - 09/09/09 11:14 PM Re: Runner lengths on SBC single plane intakes? [Re: BadSS]
SS402 Offline
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Registered: 02/06/08
Posts: 4656
Loc: Beaverton, Oregon
I'd go out on a limb and say they are asking for Intake manifold runner length, not including the plenum, from the beginning of the runner to the end. The port length on cylinder heads is pretty generic, its the differences in manifold runner length they want, who knows, run it both ways and see where the 1st 2nd and 3rd order harmonics are falling..
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#722227 - 09/10/09 03:20 AM Re: Runner lengths on SBC single plane intakes? [Re: SS402]
BuzzLOL Offline
Member

Registered: 05/02/06
Posts: 5504
Loc: Toledo, Ohio
.... I suspect the formulas don't know what kind of heads you are using or brand of engine, so want total intake and head runner lengths... and in the case of Webers/Hilborn injection, even the carb./throttle body length and intake stack length...!!

.... FE Phord heads have very short head runners...
_________________________
'86 Monte LS (total'd Fall '2013), '87 GTA TransAm TPI350 TH700-R4, '85 Fiero 5-speed, '75 MG Midget Buick Alum.V8 BW 5-speed manual, '77 Pontiac Astre Formula wagon 5-speed posi, '78 F150 4WD 351"M ==> 400" C6, '79 Caddy Seville Olds EFI 350" TH400, 19' Slickcraft 425HP 351W MerCruiser I/O

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#723064 - 09/12/09 02:32 PM Re: Runner lengths on SBC single plane intakes? [Re: BuzzLOL]
MY FYN 79 Offline
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Registered: 11/12/02
Posts: 9761
Loc: N/E WI
Thanks for the input everyone. I agree that most likely they are looking for just the length of the actual intake runners, minus plenum and head. I'll keep this info, but for now plug away at tuning without using these numbers.
_________________________
~Jeremy~
79 Monte - Sold 5-11-13
Welcome Natalee Mae 3-16-12

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