750 cfm for 340?

[lilcuda]

jetted down tho?

It's still too much cfm for a midly modified 340. Sure, you can jet it down. You would have to. But the problem is that you have a weaker vacuum signal in the venturi, which leads to sluggish throttle response. The accelerator pump is going to cover up some of that sluggishness, but it will be more fun to drive with a smaller carb that provides crisp throttle response.

The biggest is not always the best!

 

[AdamR]

Jetting has nothing to do with carb size. You dont change jets to compensate for to big of a carb. Carbs are rated at air flow, Jets are fuel flow. You cant decrease air flow by decreasing jet size or fuel flow.

A 750 is not to much carb for a 340, It may be to much for his 340 though. For the street a 600 to 700cfm carb is fine. A 750 Vacume secondary carb like the Holley 3310 will also work just fine.

my 340 made more torque and had a lower peak with a Holley 950 then it did with a 750 Proform carb.

It all depends on the combo and your tuning skills.

 

[lilcuda]

Jetting has nothing to do with carb size. You dont change jets to compensate for to big of a carb. Carbs are rated at air flow, Jets are fuel flow. You cant decrease air flow by decreasing jet size or fuel flow.

I understand that cfm is airflow and jetting has to do with fuel flow. To say that the two are not related is ridiculous. Jetting has to do with the vacuum signal in the venturi. The vacuum signal in the venturi has to do with the volumetric efficiency of the motor, which is a combination of engine size, cylinder head flow, cam profile, intake & exhaust systems, rpm range, etc.

A 750 is not to much carb for a 340, It may be to much for his 340 though. For the street a 600 to 700cfm carb is fine. A 750 Vacume secondary carb like the Holley 3310 will also work just fine.

That's what I was saying.

my 340 made more torque and had a lower peak with a Holley 950 then it did with a 750 Proform carb.

It all depends on the combo and your tuning skills.

That's great! But your 340 is highly modified, correct? His is not.

I stand by my recommendation of a Holley Street Avenger 670.

 

[dodge freak]

A holley 950 is the same as a 750 but has 1 3/4 butterfly's as too the 750 1 11/16 plates.

Its really not 200 cfm better than a 750 and a 850 flows more than a 950 ! Its true..

 

[mullinax95]

Jetting has nothing to do with carb size. You dont change jets to compensate for to big of a carb. Carbs are rated at air flow, Jets are fuel flow. You cant decrease air flow by decreasing jet size or fuel flow.

A 750 is not to much carb for a 340, It may be to much for his 340 though. For the street a 600 to 700cfm carb is fine. A 750 Vacume secondary carb like the Holley 3310 will also work just fine.

my 340 made more torque and had a lower peak with a Holley 950 then it did with a 750 Proform carb.

It all depends on the combo and your tuning skills.

BINGO!

Exactly... it took awhile for me to figure this out but once it was explained to me it was easy.

I believe the 750 vaccuum secondaries would be the ticket. #3310

 

[AdamR]

lilcuda, I miss understood what you were saying and I agree that the 670 avenger is a good choice. I'm considering one for my mild 360 also.

 

[prostr340duster]

I had a 750 vac sec. on my 340 running 12.7's That was running the economy spring in the secondaries. I still have it, but it needs a bottom plate. Now I run a 650 double pumper and running low 12.50s

 

[69 Valiant Kid]

so should i go with a 650 double pumper or a 670 sa?

 

[Longgone]

I think for the street a good carb would be the Holley Street Avenger 670 with an electric choke and a vacuum secondary, leave the double pumper for the racetrack.

 

[69 Valiant Kid]

wlel, i guess im not gonna bother putting a vac booster in......

 

[Bill Crowell]

I will add the following to your database. I have a 360 with 10.5:1 compression, ported "J" heads, Edelbrock Performer intake and a Comp Cams "292-degree" cam. I called up Barry Grant to ask them how big a carburetor I should use. They ran the data thru their computer, and told me to use either a 650 or a 675 CFM unit.

 

[lilcuda]

lilcuda, I miss understood what you were saying and I agree that the 670 avenger is a good choice. I'm considering one for my mild 360 also.

No problem. That has a tendency to happen online. It's much easier to get your point across in person.

You'll like the Street Avenger. It woke up my friends' 340.

 

[Beatnik]

I'm running a 650 DP on a 340 w/ .508 MP cam, ported J's, Torker and Hooker Super Comps and FBO ignition. It screems from 4000 on but down low it's not the best especially w/ my 3.23 gears....

I've got a Eddy RPM I'm going with and I'm going with a 670 SA...better throttle response, and low end for the street. If I was going to go with a mech. secondary carb I'd go with a 650 Demon and have Don @ FBO tune it for me...but for my 90% street driving and for the $$...the 670 is getting my vote.

 

[69 Valiant Kid]

hey, thanks for the input guys...

 

[daves66valiant]

My Dad loves his 670 Street Avenger too on his 67 Chevelle 350

 

[Ace]

My 650DP experience seems to agree w/Beatnik. Once the revs rise, it really kicks in after around 3-4k rpm all the way on up, but feels a little soft on the bottom.

Definitely the more "track-friendly" option there.

 

[MtNemoMopar]

As I said in the first post. I run a 670 Street Avenger,Vaccum secondary carb, and it is great. I did run a 750, and it worked great also. If you go 750, you should go double pump to avoid a bog, and you will want to rev that sucker(tall gears,headers,etc).

 

[dgc333]

You are more likely to get the bog with a 750 double pumper than a 750 vacuum secondary. A vacuum secondary is much more tolerant of being oversize than a double pumper.