Holley choice for 400 w/mods

[Phansm72]

Alrighty I have a stock 400 b block auto in my 70 Satellite and I was looking at doing the smaller of the 3 Thumpr cams and lifters, Performer RPM intake , Flowtech long tubes. I was assuming I needed to put a 750 holley on it but the guy at summit says itll be too much , I need a 600-650. So now Im a little confused. What do Y'all think?

 

[rumblefish360]

A 650 would be good considering that engine is all ready a low compresion engine and the cam is going to make it worse. At 650 cfm, it will have excellent streetabily.

I've gone through this personnaly with my 400 in my Magnum, which is a '78 P code 400. A big carb you don't need. It did indeed work better with a 650 or a big TQ. The small TQ was down on low end power and I needed to step into the gas pedal far.

 

[1badgtx]

rumble fish has you covered...650cfm will work good...You can go to edelbrocks website or holley they have a guide for carbs for engines...You also need to stick to vacum secondaries...Your car and mine is too heavy for mechanical...
Petty Blue 67 GTX

 

[Phansm72]

Thanks for the input guys!

 

[Redpolara]

As a general rule of thumb> cubic inch displacement x max rpm.....divided by 3456 = CFM.

 

[Meep-Meep]

The key here is the low CR like Rumble stated. The first thing you need to do is pick a cam that will keep your Cylinder pressure at around 160 PSI. If you have a factory TQ carb (or the 600-650 CFM vacuum secondary as mentioned) and cast iron intake those won't be your limiting factors. You will get more bang for your buck by choosing the correct cam and adding free flowing exhaust.

 

[S.I. Coronet]

Wow If an engine can't handle a little ole 750 Vacuum theres something wrong.
My 318 made love to a 750!
I just installed a new 650 DP and it runs great!!!
Don't get one of those non adjustable 600s, theres no such thing as an adjustment free carb.

 

[Satellite65]

Wow If an engine can't handle a little ole 750 Vacuum theres something wrong.
My 318 made love to a 750!
It wore out and Im installing a 650 DP next week.
Don't get one of those non adjustable 600s, theres no such thing as an adjustment free carb.

I agree. If you have to have a Holley, a 3310 (750 vac sec) should work just fine. It will need a little tweaking, but so will any carb. A 650 vac sec, like an 1850 will work well too. It will have a strong low rpm signal but may make the engine feel like it has asthma at higher rpm's.

A good 850 Thermoquad will give you the best of both worlds but won't work with a Performer RPM manifold due to it's spreadbore design. The standard Edelbrock Performer or Holley Street Dominator would be the manifolds of choice for a TQ.

 

[hunt2elk]

I am going through this right now on a 383 with lower compression. I have a 750 Edlebrock and just purchased a 650 Edelbrock Thunder. The 750 was in my opinion running a little rich/rough at idle, but otherwise was ok with plenty of power. Alot of opinions are that a 750 is too big for a 383, which led me to try a 650. I put on the 650 and immediatly noticed a better idle, and throttle response from 1000-3000 rpm. But my wot went from easily smoking the tires in 1st for ever and then in 2nd for 10 feet to 10 feet in 1st with the 650. Big difference-but I bet I'm getting better mpg lol. So I called Edelbrock and talked to a tech for 1/2 hour. This was a very good conversation and I learned alot. He said either carb will work fine and a 750 is not too big for a 383. You have to decide if you want more top end power or a better responsive low end. You cannot easily change the idle jets on the 750 (they need to be soldered shut and redrilled smaller). So what he recommended is changing the secondary jets +.02 and metering rods one size up on the 650. This will keep my low end the same but should give more power at 30% to wot. Although he said it is not possible to make a 650 into a 750. Anyway I am picking up the parts today and hope to try them this weekend.

 

[S.I. Coronet]

I am going through this right now on a 383 with lower compression. I have a 750 Edlebrock and just purchased a 650 Edelbrock Thunder. The 750 was in my opinion running a little rich/rough at idle, but otherwise was ok with plenty of power. Alot of opinions are that a 750 is too big for a 383, which led me to try a 650. I put on the 650 and immediatly noticed a better idle, and throttle response from 1000-3000 rpm. But my wot went from easily smoking the tires in 1st for ever and then in 2nd for 10 feet to 10 feet in 1st with the 650. Big difference-but I bet I'm getting better mpg lol. So I called Edelbrock and talked to a tech for 1/2 hour. This was a very good conversation and I learned alot. He said either carb will work fine and a 750 is not too big for a 383. You have to decide if you want more top end power or a better responsive low end. You cannot easily change the idle jets on the 750 (they need to be soldered shut and redrilled smaller). So what he recommended is changing the secondary jets +.02 and metering rods one size up on the 650. This will keep my low end the same but should give more power at 30% to wot. Although he said it is not possible to make a 650 into a 750. Anyway I am picking up the parts today and hope to try them this weekend.

Kind of too much thinking.

I would use a Holley over an Edelbrock but I guess somebody has to buy Edelbrock to keep them in buisness?
You can get more CFM buy taking the whole choke horn off and polishing the insides.

 

[Junky]

I run a 383 out of a '71 Newport. Heads worked over with a XE262H Comp Cam and headers, and other stuff. I've tried five different carbs, both Edelbrock and Holley. The 3310 Holley 750 is the best one out of all of them! Took some tuning, but the end result was worth it. A 400 should like the 3310 Holley 750 just as much.