EFI throttle body size questions

[BigBlockOlds]

I'm building a 425 Olds big block for my '87 Cutlass Supreme and will be converting it to EFI.

I'm using an Offenhauser Supersonic intake that requires a 4500 Dominator flange so I'm looking into the Wilson 4bbl throttle bodies.

My question is, how big is too big? They offer them in 1136cfm, 1388cfm, 1484cfm and 2008cfm. I'm sure the 2008cfm is too large but what about the others?



The engine will be around 500-550HP and I'll be turning it to 6300-6500rpm with a possible 100HP shot of nitrous on top of that.

Thanks for the help,

[TUBED]

Andrew,
The 2008 CFM might or might not be too big, but keep in mind that the linkage is a progressive design and the front throttle bores (primaries) are more likely where your normal operating range would be until the (secondaries) open up under harder acceleration.

The CFM ratings for a Carb. application differs from that of the CFM flow rates for EFI applications. Check with Wilson to be sure. Also keep an eye out on eBay for a good used Wilson or Force Fuel throttle body I believe they are the same design.

You should be able to find one for $350.00-$400.00 with a TPS and IAC provisions. Here's an ad on www.RacingJunk.com for 2 throttle bodies Ad#606967, take a look he has someone wanting 1 and is looking for another buyer for the other one to sell them seperately. I hope this helps.
Gerald

[John McIntire]

I've done a lot of research on this subject, as I too had the same question when it came time to inject my 572. According to many engine builders and shops the CFM you need is roughly twice the displacement of your engine.
With that said, you'll be looking for a TB with a CFM rating of at least 850. You could round that up to the nearest CFM that you can find.
I went with a Cobra throttle body, as I was having a custom sheet metal intake made. I went with this because it was an oval sedign, therefore lower in height, and flowed plenty of CFM.
I got mine from Accufab, check them out. I believe that they sell stock OEM type TB, but they might sell racing ones too.
Goog Luck!
John

[Hammered]

cfm = c.i.d. x maximum rpm x volumetric efficiency ÷ 3456

I believe a VE of about 1.1 would be a reasonable guess for an engine with a healthy cam and cleaned up heads.

For example,

455 x 6500 x 1.1 / 3456 = 941 cfm


John

[ProTouring442]

Just as a quick note; the throttle body that came witht he Holley Commander system I am using on the square port (LS6 crate) 454 in my 442 is 1000cfm.

Shiny Side Up!
Bill
'72 442 "Inamorata"

[BigBlockOlds]

Thanks for the replies.

I ended up going with a 4 bbl universal type throttle body for my engine. Mostly due to pacakging.

The hood on my car is a W-25 replica off my friend Angelo's '85 FE3X:

http://maytag87.dyndns.org:8081/angelo/firstpic.jpg

So this made it a lot easier to get the scoops hooked up to the engine.

I also probably went a little over board on throttle body size. I bought an Edelbrock 1600cfm unit. My intake is an Offy Super-sonic that has the 4500 Dominator flange. It was kind of tough finding a Dominator flange throttle body with something around 1000cfm so I went with this. I'll just have to build a bigger engine. ;)

Here's a few pics with it sitting on the mock up engine:

[ProTouring442]

Sweet! Are those Iron heads?

I love the W-25 hood... that's why I went with the Holley Commander on my BBC.

Now hurry up and get that thing finished!

Shiny Side Up!
Bill
'72 442 "Inamorata"

[BigBlockOlds]

Yeah. I bought them with exahust crossovers already filled, the center exahust divider welded and machined flush and set up for 2.100" intakes and 1.710" exahust valves.

I've raised the intake roofs about a .25", ported and blended the bowls and smoothed everything else out. They've been drilled for 7/16" rocker studs and tapped for external oil return lines.

But, I've decided to finish porting these to match each other and then I'm going to sell them.

I plan on buying a set of Edelbrock aluminum heads and having them CNC ported by BTR Performance.

My first 455 build (which was my first engine build ever) wasn't the greatest performer in the world. It got me to and from college everyday but I could only muster a 13.9@99mph out of it. So this time around, I want it to go. ;)

Thanks,

Sweet! Are those Iron heads?

I love the W-25 hood... that's why I went with the Holley Commander on my BBC.

Now hurry up and get that thing finished!

Shiny Side Up!
Bill
'72 442 "Inamorata"

[XCESSIV]

Nice pic at Brickyard are from around the Midwest would like to see your car in person. EJ:3gears:

[BigBlockOlds]

The pic of the car at Brickyard is my friends. But mine will look similar once its done.

I live near Dayton, Ohio.

Thanks,

[XCESSIV]

I LIVE NEAR MIDDLETOWN ARE YOU LOOKING FOR SIDE SKIRTS TRY
HONEST CHARLEYS www.elcaminoss.com
GIVE ME A SHOUT IF YOU NEED ANY PARTS FOR YOU PROJECT I HAVE A LOT SPARE STUFF. ERIC J

[Hammered]

Wow! I'm in Kettering between you two. Andrew: what ECM are you going with? I've got my Pontiac drivable, but not fully tuned yet. I'm running the Gen7.

Eric: I had an 86 GN and sold it for $3,600 with 167,000 mi. Best car I ever owned - stupid me.

John

[BigBlockOlds]

Wow! I'm in Kettering between you two.

Small world. I work in Kettering.

Andrew: what ECM are you going with? I've got my Pontiac drivable, but not fully tuned yet. I'm running the Gen7.
John

Thinking about using the Megasquirt V3.0.

[BigBlockOlds]

Another question,

Where are you guys placing the IAT sensor? Can it be placed in the base plate of the air cleaner?

I'll be running an open element style air cleaner that will be sealed to the underside of the hood.

Thanks,

[ProTouring442]

Another question,

Where are you guys placing the IAT sensor? Can it be placed in the base plate of the air cleaner?

I'll be running an open element style air cleaner that will be sealed to the underside of the hood.

Thanks,

That should work I would think.


Shiny Side Up!
Bill
'72 442 "Inamorata"
www.fquick.com/ProTouring442

[Hammered]

I put mine in one of the intake runners near the plenum. I've seen them mounted in the plenum most often, but also in the air cleaner base.

I believe that once the VE table is tuned in, the computer is looking for the relative difference in temperature change to make adjustments. I would put mine in the plenum if I had the space.

There are a lot of people running MS, you should be able to get a lot of support off their user board.

[ProTouring442]

I put mine in one of the intake runners near the plenum. I've seen them mounted in the plenum most often, but also in the air cleaner base.

I believe that once the VE table is tuned in, the computer is looking for the relative difference in temperature change to make adjustments. I would put mine in the plenum if I had the space.

There are a lot of people running MS, you should be able to get a lot of support off their user board.

You know what, now that you mention it, that's where mine is mounted.

I think it's been too long since I worked on the thing!!!

Shiny Side Up!
Bill
'72 442 "Inamorata"
www.fquick.com/ProTouring442

[64duece]

Let us know how that works out for you. With that large progressive setup, I think you'll be fine. We run alot of large 90-105mm) mono-blade style on our turbo stuff and they seem to be decent.