Carburetor suggestion needed

-
duster360

duster360

Well-Known Member
Joined
Aug 8, 2008
Messages
3,825
Reaction score
308
Location
Alabama
I need some opinions on what size cab to run on my combo. This is just a weekend cruiser with an occasional beating to clean it out. I want a double pumper, should I go 650 or 700 or 750 and why?

67 Dart
340 ci
Edelbrock 60779 heads
Edelbrock Air Gap intake
Hughes engines roller rockers
Lunati 268 cam

Hydraulic Flat Tappet. High performance street cam likes 2400 RPM stall, 700 CFM carb, dual plane intake and headers. Makes unequaled power to 6200 RPM with proper valve springs. Strong cam with great street manners for crate motor.
•Advertised Duration (Int/Exh): 268/276
•Duration @ .050 (Int/Exh): 226/234
•Gross Valve Lift (Int/Exh): .494/.513
•LSA/ICL: 110/106
•Valve Lash (Int/Exh): Hyd/Hyd
•RPM Range: 1800-6200

Part Number: 10200703
Previous Part Number: 60403

9.5:1ish compression
4 speed
3.91 gears ( will probably go 3.55 later )
 
My take on it is this.. You can have all the best parts in the world, it comes down to how well they play together.. In other words its the entire build assembly plus the "Craftsmanship" of the builder. The more OCD he or she has to the finer details the better, the cross your fingers and hope it all works out for the best whn yoi turn the key. I allways think that a street car should have a 3310 dual feed single pump. A 650 is magic. Ring and bearing life are key. A 750 is fine as long as you check the oil regulary. Anything bigger is just a bad move. I have a a 750 because it was new in the box for 100 bucks. My personal choice would be a 650cfm Quick Fuel Tech. I dig there stuff.

Just my take on it. I wish ya luck and hope all goes your way.

Woodie
 
Well, you probably know my set up from the other thread you have going on cams...

'68 340
.060" over with KB 243 hyper pistons, .018" over the deck, ~9.8:1
Forged crank, stock 340 rods, resized with ARP bolts
308 heads, 2.02/1.60 valves, 65 cc's chambers, stage II ported and flowing 264 cfm at .500" on the bench
Crane adjustable 1.5 rockers, Smith bro's pushrods
Lunati 60404 Hydraulic cam, .513/.533, duration @ .050" 234/242, advertised duration 276/284
Doug's Headers
Edelbrock Air Gap
Holley 750 Ultra DP

Also backed with a 4 speed.

I have the Holley 750 ultra DP on it now, but have also run a 770 Street avenger and a 670 Street Avenger. Of the three, the 750 Ultra DP was by far the closest out of the box. I went from 72's to 70's on the primaries and from 80's to 76's on the secondaries, and changed out the 6.5 power valve to a 5.5 (match it up with my 9-10" HG vacuum). Works very well, and that's monitoring everything with a A/F gauge.

The 770 ran richer and had to be jetted down about 4 steps, which it didn't like. The 670 was lean and had to be jetted up about 4 steps, which it handled ok, but I couldn't ever get rid of the lean bog transitioning to the secondaries. Cruise was fine with the primaries and even at WOT with the secondaries opened up, but the transition bringing the secondaries in was always lean. I played with the jet sizing, accelerator pump cams, accelerator pump nozzles, power valve, and the secondary spring (vacuum secondaries on the Street Avengers). Definitely improved things, but I couldn't get rid of it entirely. Decided I needed mechanical secondaries (and the extra accelerator pump), bought the Ultra DP, and viola, problem solved.

I'm sure the 650 DP would probably work, especially with the slightly smaller cam. Probably wouldn't need to change the power valve either. It might give up a little top end compared to the 750, but you'd probably only notice that on the dyno and not on the street. But I really like the 750 on mine.
 
I have used several different vacuum seconday holleys with an automatic. I figured since I am going 4 speed this time I would try a double pumper. It is my understanding that double pumpers have better response when changing gears.
 
72bluNblu said:
Well, you probably know my set up from the other thread you have going on cams...

'68 340
.060" over with KB 243 hyper pistons, .018" over the deck, ~9.8:1
Forged crank, stock 340 rods, resized with ARP bolts
308 heads, 2.02/1.60 valves, 65 cc's chambers, stage II ported and flowing 264 cfm at .500" on the bench
Crane adjustable 1.5 rockers, Smith bro's pushrods
Lunati 60404 Hydraulic cam, .513/.533, duration @ .050" 234/242, advertised duration 276/284
Doug's Headers
Edelbrock Air Gap
Holley 750 Ultra DP

Also backed with a 4 speed.

I have the Holley 750 ultra DP on it now, but have also run a 770 Street avenger and a 670 Street Avenger. Of the three, the 750 Ultra DP was by far the closest out of the box. I went from 72's to 70's on the primaries and from 80's to 76's on the secondaries, and changed out the 6.5 power valve to a 5.5 (match it up with my 9-10" HG vacuum). Works very well, and that's monitoring everything with a A/F gauge.

The 770 ran richer and had to be jetted down about 4 steps, which it didn't like. The 670 was lean and had to be jetted up about 4 steps, which it handled ok, but I couldn't ever get rid of the lean bog transitioning to the secondaries. Cruise was fine with the primaries and even at WOT with the secondaries opened up, but the transition bringing the secondaries in was always lean. I played with the jet sizing, accelerator pump cams, accelerator pump nozzles, power valve, and the secondary spring (vacuum secondaries on the Street Avengers). Definitely improved things, but I couldn't get rid of it entirely. Decided I needed mechanical secondaries (and the extra accelerator pump), bought the Ultra DP, and viola, problem solved.

I'm sure the 650 DP would probably work, especially with the slightly smaller cam. Probably wouldn't need to change the power valve either. It might give up a little top end compared to the 750, but you'd probably only notice that on the dyno and not on the street. But I really like the 750 on mine.
Click to expand...

72bluNblu, it sounds like a 700DP might be the way to go.
 
I have tried 2 carbs on my 4 speed/3.55combo;
An 1850/600/vac.secondary, and;
A 3310/750DP
The 600 was a pretty good all round carb, that was able to achieve some pretty good economy. But the rubberband effect was not for me.Waiting for the secondaries to open,seemed impossibly long. No matter how I tuned it,It was stab and wait. The manual trans does not flash up like a stall TC. I like to cruise at 1800 to 2000rpm at 30 mph. This is 3rd gear with 3.55s. At that rpm, the v-secondary is on vacation.

The next carb, the 750DP, was an instant hit! With all 4 bbls open stuff happens,even in third gear.This is where 360 cubes and a 224*cam, with a true static cr of 10.7, really shines....3rd gear torque.

I tried these two carbs because I had them. Tuning the 750 was not a cakewalk. On the street both of these pulled hard at the upper end. Yeah the 600 seemed a bet weaker on top. And yeah the 750 should have been weaker on the bottom.

So, for you and anyone with a manual trans,the DP is the way to go.
If you have the tools and skills, I might recommend the 750.It will grow with the combo. I say might, because at 9.5exactly Scr, and that cam with its 60*ICA, will net you a Dcr of 7.8, and the 750 might be a bit lazy on the bottom,at that Dcr. With 3.91s it would probably be ok. But if you are considering 3.55s, and your 1st gear is 2.66, then I think it will be a handful.So to be on the safe side, and since its going to be in a weekend cruiser, and if you've never had a 750 before, I would recommend something smaller. If you have to purchase a new carb, then I would recommend the 650DP. For all the reasons above, plus:1) it will be easy to sell or trade,if you feel the need for a bigger carb later and 2) the 750 really is too big, and 3)the 650 may be a bolt on and go kinda deal, and 4) carbs are like cams in that, for a streeter,its,always,ALWAYS, better to err on the smaller side.
This is my opinion.
Its also my opinion that with aluminum heads, you could run a lot more compression.Doing the math; at an Scr of 10.8, and using that cam, the Dcr works out to just under 8.8. and at 8.8 Dcr I run 87E10 all the time. I do however run a tight quench of .034. I run 32* to 34* power timing and a 205 Tstat. I am at 700ft above sealevel, and weigh 3650#.
I realize that its too late to change the Scr, so the trick is this; stick with that cam or any other size cam you find just so long as the ICA remains at 60* ABDC or less. If you go any bigger, that engine will begin to get soft ,out of the gate, with a stick.

PS you will love that combo. I had a similar cam to your226/494 cam, in my 366 fo about 4 years.Sometimes I still miss it. And I moved up only 1.5 cam sizes.The cam I had was 223*/549lift. My new cam is 232*/.571 . The difference in ICAs is just 4 or 5 degrees. Their personalities are very different.
 
340's like to breath, with a 4 speed you want a DP. 4779 Holley 750 is my vote. Have one on my 340, with a pro form main body.
 
I know one thing, the next holley I mess with is gonna have screw in air bleeds. But I like having a million things to mess with so I can really screw up the tune!:D

No, Honestly I have been reading David V's book on holleys and it seems that adjustable air bleeds and correct boosters are the key.

I have also read alot about how much of an improvement a DP is on a four speed. I say go for it.
 
I say....find a Craigslist 4777-2....buy it, tear it down.

Buy a HOLLEY 4777, 4779 double pumper rebuild kit.

Buy a Proform 4777 chokeless center section.

Buy Nitrophyl floats....jet extensions for the back float.

and Build your custom Double Pumper yourself.

Get some 72, 74, 76, 78, 80, 82, 84, 86 jets and tune it to your 340.

Mine only cost $300 turnkey to acquire, build, setup.

Performs flawlessly....built and tune it with 1 screw driver.

:farao:
 
I have a nice 650 DP (4777-4) sittin in the garage. I will put a kit in it before I use it, if that is what I decide to use.
 
I actually bought it when I was going to put the iron heads back on. But when I decided to get the Edelbrock heads I figured I better get some advice to make sure it would still be a good choice.
 
Dragonbat13 said:
I know one thing, the next holley I mess with is gonna have screw in air bleeds. But I like having a million things to mess with so I can really screw up the tune!:D

No, Honestly I have been reading David V's book on holleys and it seems that adjustable air bleeds and correct boosters are the key.

I have also read alot about how much of an improvement a DP is on a four speed. I say go for it.
Click to expand...

This man has it right!
 
You must log in or register to reply here.
-

Back
Top