Holley 650 Ultra double pump to big for a 302?

I currently have a Holley 670 street avenger with vacuum secondary,s and i am not at all happy with it. The secondary,s take for ever to fully open up. My personal opinion is the car is to light and the vacuum to low. So my plan is to use the street avenger on my wife,s 1977 F150 truck build we are currently doing.
I was planing on putting a 600 double pump on, but then I saw the 650 ultra double pumper. I like the blue anodize and the zink coated look of the ultra carb. But I'm not sure if it would be to big of a carb?

Car info
69 302ci
8.9 cr pistons
aluminum ProStar heads with 54cc chambers
crane cam .504in .520ex lift 110deg separation
Built C4 W/ B&M shift kit
Boss Hoss 2800rpm stall (actual stall 2300 rpm aprox)
3.55 gears

 

for fear of getting into the whole "mild 302's only ever need a 600 cfm MAX" debate again.. it would heavily depend on the type of intake manifold used for this combo. The 650 is not hugely different than the 600 from the standpoint of primary/secondary venturi sizing but no matter how you go here ANY carb needs to be tuned for the specific combo. Engines size, compression ratio, induction system(size and design), weight, gears, tire size, yada, yada, yada.. it ALL matters when it comes time to tune.

Basic rules are this. Single planes often need the doubled pump shot to fill the "hole" created when you abruptly go WOT. You can throw tons of squirter size and/or 50cc accellerater pump on a vac sec and it will sometimes have you running faster(improves throttle response under load) but comes at the expense of dirtier oil due to lack of adjustability that 2 separate accelerator pumps/squirters will allow.

Dual planes effectively split the engine into 2 halves(now each cylinder only sees 1 primary throttle bore meaning greater booster response(directly related to throttle response and AFR consistency) and gives far less cylinder to cylinder cross talk during overlap to cause increased reversion that is possible with a bigger camshaft and larger carb sizing. You can improve the top end breathing capability by using open spacers on this manifold design but it comes at the expense of more cylinder to cylinder cross talk. Which of course takes you back towards a single planes affect on the booster response as the open spacer "unsplits the motor" for the sake of gaining plenum volume to promote higher rpm breathing capability.

Not sure on exact parts spec's here but I would guess you're around 10:1 static compression. With that sized cam in this smaller stroked motor.. I would lean towards a dual plane any day of the week with those trans and rear gear ratios. And on top of that I would likely run a vacuum secondary carb that's been properly tuned/fuel curved. A double pumper can also be made to work here too but would need to be re-tuned to not flood the engine before those gears let the rpm/boosters come in. But if running thicker open spacer(1.5" or more) you'd want a slightly fatter initial pump shot to fill the bigger hole due to increased plenum volume it creates.

I would also like to see that cam advanced a fair bit to get cylinder pressure up just a bit earlier in the power curve. For a street car it's typically better to have a quicker AND fatter power curve than just worrying about a higher peak numbers arriving later on in the last 20% of the valvetrains available power band. Your gearing would be more towards wrong for that higher powerband anyways.

What is your current cranking compression?

Have you ever thought about getting it dyno tuned? Damned good bang for the buck, can keep you from tossing parts at it too, and makes the car funner and more responsive to drive no matter what size carb you decide to put on it.

Oh.. and PS. If you're testing secondary opening just by eye here?.. you'd never want a vac sec carb opening so early that it would be visible while winging the throttle open by hand. The engine needs to be loaded before even the lightest spring would allow secondary opening. Highly doubt that motor would need much more than a purple spring on the secondaries anyways.

 

First of all," pretty don't make fast". Don't worry how the ultra looks because once the air cleaner is on, nobody cares how it looks. How far have you tuned the 670? Secondary springs are the simplest tuning mods.

 

You should buy a Holley trick kit with an assortment of secondary springs and different cams, squirters and jets. From what you have a 670 sounds about right. As far as secondary's coming on, if you can feel them they're probably coming on too late. You also want to look at the power valve and invest in a vacuum gauge.

 

In other threads on this forum, I've heard that the Holley 670 is a troublesome carb on smallblock Fords, which corroborates my experience. Although I never tested it on a Dyno, the 670 I had on my 302 did not seem to produce any more power than the 570 that is currently on there, but got terrible fuel economy compared to the 570. It should probably also be noted that this was at high altitude (6000 ft.). It ran fine but the throttle response is more "crispy" with the 570. I've also had good results with the Edelbrock 600.

From my understanding, the 650 DP is not too big, but fuel economy will be reduced compared to a vacuum secondary carb. You really do need to consider all the things mentioned by groberts101, because proper carb selection really depends on many factors. It is my opinion that on a stock 289/302, anything bigger than a 600 approaches the point of diminishing returns. This all changes when performance parameters enter the equation. Compression, cam, valve & port sizes, exhaust system, ignition timing (we could go on & on). Any aftermarket carb will need to be tuned tor optimum performance based upon its application. Notice I said tuned and not "tricked out". For example, on a Holley, tuning involves changes to jet sizes, power valve ratings, accelerator pump discharge nozzle size, accelerator pump cam/position, float height adjustment, secondary springs (vacuum secondary models), & air/fuel mixture adjustments.

When you start drilling and machining stuff, and mixing parts from other carb models, you have entered a different realm of "hot rodding" called "tricking-out" a carb, which is quite a bit more work as well as more expensive. In my opinion, this should not be necessary for most street applications.

With that said, definitely take into consideration all the factors mentioned by groberts101 when trying to determine which carb is best for your application.

 

Sorry i forgot intake info. i do have a wieand stealth dual plane intake.
I used the paper clip method to see how far the secondary,s opened, they did not fully open until it hits around 75ish mph. I have the lightest spring holley makes in the vacuum pod.
I am planing on dyno tuning it this spring, and i have not done a compression check on this engine yet. its farly new. burned up my last motor last summer heading to the national round up.

 

Not trying to argue anything, but my personal experience with the Holley accel-pump cam assortment kit was a big waste of money and time. None of the cams in the kit worked as well as the original cam that came with the carb (the orange one). What solved the issue I was having was changing from a #31 discharge nozzle to a #28. In my case, I needed a smaller one, but someone else may need a larger one.

I agree with you on squirters, jets and secondary springs though.

 

My motor is pretty LOL and you can see the carb. i,v changed squirters, jets,power valves, spring. it,s been troublesome on this motor, the old motor was .060 over 11 to 1 compression it took a lot of tuning to it to run, just cant get it on this motor.

 

I've had luck with a kit and without. Some work better with a pump can swap but others fall on their face. Definitley worth a shot, it's a good learning experience also. I'd also recommend the Holley tunning book (little red book).

 

Also make sure to keep a log of the changes your making. Keep us posted

 

i love carb threads

 

I can tell you that there is absolutely no way in hell that little motors spec's needs all that carb at 130 mph.. much less at only 75 mph. I would highly suggest that you split that carbs fuel circuits up into separate systems to make tuning MUCH easier to do.

That involves running the stiffest black secondary spring to keep the secondaries closed, although even the black spring still allows some secondary opening, while you tune on the primary side. But first off you'd want to do the idle/transition circuits. Then the primary side.. then the secondaries fill in the gap for what the primaries and power enrichment circuits could not provide at WOT. This lets the engine/carb come up quicker and stay stronger/longer on the booster/s to help throttle response, torque production, and typically also aids overall engine efficiency.

How much timing advance does the motor have dialed in right now? Initial, mechanical, and total advance numbers?

and as a result of that initial timing advance.. what is the manifold vacuum at idle?

also still curious what the motors compression readings are too.

 

That,s not 75 mph cruising down the road. It,s dead stop floored till i hit 50 stop take a look at the paper clip then repeat seams to be fully opened at 75ish.
Vacuum at idle is 7 in
Initial timing is 12Deg its been a while since i set the MSD up but i think the mechanical is 18deg and total is 34deg
There is a tuning shop about 10 mi away from me, i think the best bet is after i dust the winter off of it in a few weeks, set it up to use there dyno. they only charge $80 and hour to dyno tune.

 

Although I haven't done a 670 as of yet, I use these on all my VS carbs as well as some DPs and some I build for friends.
http://www.quickfueltechnology.com/...ration-w--spark-185033104776477747784779.html

 

yeah, I knew what you meant and guessed at your rpm when running full throttle down the road up to about 75. Keep in mind that the secondaries would have opened up even more in a "hypothetical" third gear pull as the motor load increased due to loss of gear multiplication and aero drag.

Dyno time is easily worth the money but holy crap.. that's cheap! My car would be super-tuned all the time. $125 is about the cheapest around here and goes higher when you want them to tune it for you. And they don't seem to work the fastest when you're paying that hourly rate so I usually do all my own stuff with a buddy of mine to get more runs in.

And holy crap.. that's really crappy idle vacuum! lol

You need more initial timing.. big time. Ok, I'll stop with the corny. Seriously though.. give the engine whatever timing lead it wants up to the point that it leans out and you'll need to start monkeying around with bleeds and IFR's(obviously you'd need to still adjust mixture screws). Pretty tough to tune any carb to perfection when the timing is that far off. Bigger cams need more timing and respond well to vacuum advance pots supplemental assist. Unless somethings wrong with that longblock or the cams installed severely retarded, I bet you some cash that they can get that vacuum up to around 10 inches or better. I wouldn't be happy until I reached at least 12" of idle vacuum. Motor would be night and day responsive with the boosters coming on to make the motor come up on the gear and cam a bit quicker. More average power that's funner to step you foot into.

Also be sure you bring extra jets, shooters(32-36's should be pretty good), cam kit, and secondary springs. All bling aside.. the ultra HP would give extra tuning flexibility and help pay for itself while it made slightly better average power due to the more refined tune.

Good luck with it and be sure to post back the results for those of us needing to live vicariously through you until winter passes by. lol