SD Intakes vs. OBS Intakes

[Mike M]

I thought some of you would find this interesting. Since I plan to upgrade to the bigger intakes on my ’97 soon I wanted to collect some data.

Everyone knows the 3-inch inlet intakes outflow the 2-inch OBS ones, but I wanted to find out exactly how much more. And the answer is quite a bit more LOL

OBS intake: 241 cfm
SD intake: 538 cfm

They were flowed at Randy's Engine & Machine.

Here's a link with a little more info

 

[97BambiBasherPSD]

Wow I didn't think an inch would make that big of a difference


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[purpleheart350]

Yup.... Going on my list

 

[JD3020]

Wow I didn't think an inch would make that big of a difference


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LOL

But that is an amazing number difference. Has anybody ever swapped just plenums to see what actual gains there are?

 

[Mike M]

I agree it's a huge difference in flow.

But when you look at the total area of a 3-inch vs. 2-inch circle it makes sense. A 2-inch hole has an area of 3.142-inches, while a 3-inch circles' total area comes to 7.065-inches or so. More than double...

 

[96stacked&smoken]

somebody had to say that.lol

 

[Mike M]

somebody had to say that.lol

Don't blame him one bit either LOL

I'm an Office fan myself.

 

[SouthFlstrokin']

What does this mean performance wise?

 

[Worstenemy453]

I bet the heads are lower than the OBS number, in which case the intake is the least of the restriction.

 

[Mike M]

I bet the heads are lower than the OBS number, in which case the intake is the least of the restriction.

Very good point. An engineer at Navistar once told me he'd be more worried about opening up the 7.3L's heads before getting the stock, crimped downpipe out of the way...

Don't know if I believe that—but it was interesting to hear.

 

[Worstenemy453]

Ill have to get my hands on a 7.3 head, and do our hand porting to it and see what improvements are shown with some porting/polishing over stock.

 

[dave186]

He meant the heads flow less than what the OBS intakes do. FWIW, Ive had a set of 3" plenums waiting to go on for a long time now. have a 3" Y with adapter boots right now. Just dont see it being of enough gain to get me to rip it all apart just for the plenums.

 

[SouthFlstrokin']

Ill have to get my hands on a 7.3 head, and do our hand porting to it and see what improvements are shown with some porting/polishing over stock.

A member on here I think has ported heads , 238/80s, and a 38r.

He made 538 rwhp on the dyno using gearhead tunes I believe

 

[Worstenemy453]

A member on here I think has ported heads , 238/80s, and a 38r.

He made 538 rwhp on the dyno using gearhead tunes I believe

I was just talking about flow numbers, get flow numbers on a stock head, and then on a ported head.

I see no reason to upgrade to SD intake stuff, when its the least of the problems. Port/Polish the heads and the stock OBS stuff would be great. IF the heads could match that 500+ CFM that the SD stuff can push then id see it being worth it.

 

[Mike M]

I was just talking about flow numbers, get flow numbers on a stock head, and then on a ported head.

I see no reason to upgrade to SD intake stuff, when its the least of the problems. Port/Polish the heads and the stock OBS stuff would be great. IF the heads could match that 500+ CFM that the SD stuff can push then id see it being worth it.

I agree with you. Upgrading intakes just based on what they flow would be useless. No way would a stock 7.3L head even flow 241 cfm per cylinder. Probably more like 150 to 170-ish (don't have any data here). I'm simply upgrading them because the rest of my intercooler plumbing will be 3-inch soon.

I just posted my findings on the intakes as fuel for thought. I'll be looking into flowing a set of stock heads vs. ported in the future.

*Does anyone know what stock 7.3L heads flow? My 150-170 guess above is a shot in the dark.