Edelbrock 2701 Intake

[Verdoorn Racing]

I'm wondering if anyone has experience with the Edelbrock 2701 intake with a carb bigger than a 4412 Holley. Would going from a gauge legal 500 Holley 4412 to a larger carb, something that's suppose to flow 620-650, be a noticable gain even with the Edelbrock 2701 Performer intake? Is that intake too small to warrant a bigger 2 barrel carb? On a 440 HP motor, how much of gain in HP would that make?

Thanks
Jeff V.

[stockcar5]

i saw a 10hp gain between a gauge legal 4412 and a 4412 gauge legal but with thin throttle shafts and blades. i'd say the intake can handle it.

[sj valley dave]

Don't forget when they flow rate a 2 bbl carb, they do it at 3" of mercury, where with a 4 bbl carb they do it with 1 1/2"..If you flow rated a 4412 the same as a 4 bbl, it only flows approx 350 cfm...Thats why a 390 cfm 4bbl will out flow a 500 cfm 4412 2 bbl.

[Verdoorn Racing]

Don't forget when they flow rate a 2 bbl carb, they do it at 3" of mercury, where with a 4 bbl carb they do it with 1 1/2"..If you flow rated a 4412 the same as a 4 bbl, it only flows approx 350 cfm...Thats why a 390 cfm 4bbl will out flow a 500 cfm 4412 2 bbl.

We have to stay with a 4412 2bbl, but can modify it. Any modifications are legal as long as it has Holley boosters.

[dynoman14]

As there are 2 different 2701's and 3 different versions over the last couple years, it would be best to have the manifold you plan to use flowed by someone that has some data and experience with them.

They have a variation of +/- 27cfm best to worst on my bench. Cylinder to cylinder balance is also critical for engines making over +450HP.

As far as the boosters go, do the rules say stock 500 holley boosters? Straight leg, down leg, etc...what size spacer is legal?

I have not seen many SBC's that did not like more carb as long as the fuel was right and the vacuum signal was good and the cam was correct for the RPM range.

I have some big baseplate stuff that is close to 490hp which is pretty close to the max I have made with a good flowing stock 2701 in an IMCA style application.

[dynoman14]

SJ Dave is right on the flow number for those that want to be able to calculate it;

When you compare the numbers you use the square root of the pressure drop that you flow at and divide it to get the ratio.
sq.rt 1.5 / sq.rt 3 =
1.22/1.73 = .705

Flow number at 1.5" = 500cfm x .705 =
Flow number at 3.0" = 352.5 cfm

Works for anything that you run on a flow bench as I have been running my heads at 25" for 25 years and all the rest of the folks out there use 28". 28" just makes the number about 7% higher than my numbers but the numbers can be calculated real easy. You can take the same head and run it at both numbers and it is almost dead on.

Once you get closer to the 50" range no you start to get the head close to "super-sonic" and you start hearing some wierd stuff but it makes them vacuum motors in the bench really hot and then starts to change your flow numbers.

My rule of thumb on carbs is you need about 1 cfm @ 3" for every HP you plan on making and about 1cfm in the head for every 2HP. These are just rules of thumb I have generated over 30 years of flow bench testing, engine dyno testing and chasssis dyno testing.

[sj valley dave]

Dyno, that is the number we have always used as a rough rule of thumb...2 hp per cfm for head flow to see what the heads potential is...I think you have the numbers flipped though for carb cfm..you need 1 cfm per hp at only 1.5" of Hg, which is what the 4 bbl carb rating is tested at...800 hp needs a 800 cfm 4 bbl minimum...You only flow your heads at 25"?

[cswitch11]

just trying to pull everything together for the new exhaust and edelbrock. Hm.. (not a nice word)(not a nice word)(not a nice word)(not a nice word), I wish I would've known that. I could've ordered you one from Tischer when I placed a large order 5 days ago.

[dynoman14]

Dave,
I use 25" because I have about 50 years of head flow data from Harold Bettes, Mike Chapman, Jim Feuling, Bill Jones and a couple other folks. Old school guys used 25" because that is what the Originial SF manuals said to use. I have gone as high as 50" with a double manometer system but it will blow everything in the room off the walls. It is good to listen to and see how nice your ports run close to super-sonic. Feuling told me once that he figured out that you needed to flow heads at 100" because when he was jumping out of planes he saw cool stuff happen like zippers open and close, buttons shear off suits and other cool stuff, and he told me he would show me when I came and made a jump with him, I wish I would have but he checked out too soon...

I was having serious problems with the idea of jumping out of a perfectly good plane.

Most head builders in the 70's / 80's changed to 28" and I think it was to jack the numbers a little bit kinda like recalibrating a dyno every couple years so your engine sheets can keep up with the rest of the world.
I have had my SF Bench and ChassisDYno for almost 25 years and have never once changed the calibration curve from my initial comparison set-up with the ones at Penske and Hendrick that were the only twins to mine.
If I want to compare my heads to someone elses I just add 7% to my numbers. I normally just leave them as is an know I have 30 more cfms than most other folks. When my SB-2 stuff hits 350-375cfm with the small ports I use, I stop.

[dirty white boy]

2701 intake will do well with a 650 carb,...up to 6,000 rpm,..sure other intakes might do better but if you just wanta pull off your 2 barrel an try a 650 4 barrel,..youll fell it good in low to mid rpms an have good vacuum too,..you wont like the 2 barrel afterwards!!!