Quick Fuel carbs

[ChargerST]

I'm about to buy a new carb for my 440 (915 heads, larger cam) and was told to get a 750 carb and ditch my 625 Carter. Is it possible to use a Quick Fuel Q-Series 750 vacuum secondaries on this setup? Or is there an advantage to use the Street Series (SS) carb (735 VS) over the Q-Series other than the electrical choke?

Another choice would be the Proform 750 Race carb with vacuum secondaries.

I wanna use a vacuum carb as my car is quite heavy (70 Charger R/T) and I have a 3.23 rear end, plus a low stall speed carb (factory piece?).

[firefighter3931]

How much cam ? How much stall ? 

I recommended a proform 750 vacuum carb for one of our members (66Chargertoy) with his mild 440 and after some tuning it runs fantastic. He has 3.23 gears and a Hughes 2400 stall. The cam is a Crower HDP271.

It's important to match the carb with the rest of the components for best results. 

I like both the QF and PF carbs.....I run a "Q" series 1050 on my 572 stroker 



Ron

[ChargerST]

Problem is that I don't know what cam and converter I have. engine was rebuilt several years ago and none of the previous owners I could track down knows anything about the engine.
The cam right now is pretty radical (in idle you can smell unburned fuel at the exhaust it sounds like a stone-filled washing machine ) and I plan on swapping it out for a smaller cam in the future.

about the carbs in general: you're saying it doesn't matter if it's a street or Q-series if they're both vacuum secondaries?

[66chargertoy]

Just as Ron mentioned, I took his advise and changed all three components in the engine so they can all work together properly (cam, carb & converter). The proform is a absolute work of art Almost out of the box bolt in. My old philosophy has been "When in doubt, throw it out ), so not knowing what kind of bump stick you have and also if not impressed with what you have now, change it out , then you will know exactly what is in the beast. The crower cam works for me .

[firefighter3931]

Problem is that I don't know what cam and converter I have. engine was rebuilt several years ago and none of the previous owners I could track down knows anything about the engine.
The cam right now is pretty radical (in idle you can smell unburned fuel at the exhaust it sounds like a stone-filled washing machine ) and I plan on swapping it out for a smaller cam in the future.

about the carbs in general: you're saying it doesn't matter if it's a street or Q-series if they're both vacuum secondaries?

It's probably got a 484 or 509 Purpleshaft judging by your description....that was what everyone used back in the day. Not a fan of those cams 

I guess you need to decide what direction to go with this car. 

If the car has manifolds as opposed to headers ; the MP purpleshaft is not the best choice.....the 484 cam is marginal but the 509 is definately a no-go with restrictive exhaust. 

How much vacuum is the engine making ? Where do you have the timing set ?

There are different carbs for different applications ; low vacuum/big cam needs an agressive fuel curve.

The Q seies are available in both vacuum & mechanical secondaries. The race carbs have a more agressive fuel curve.




Ron

[firefighter3931]

Just as Ron mentioned, I took his advise and changed all three components in the engine so they can all work together properly (cam, carb & converter). The proform is a absolute work of art Almost out of the box bolt in. My old philosophy has been "When in doubt, throw it out ), so not knowing what kind of bump stick you have and also if not impressed with what you have now, change it out , then you will know exactly what is in the beast. The crower cam works for me .

This is a well matched combo and runs like a champ ! Idles clean, cruises for hours and can light the tires up at will ! 

Here's a youtube of Denis fooling around      http://www.youtube.com/watch?v=t9xOgxgui54



Ron

[ChargerST]

Awesome video, awesome engine!

About my engine: the combination seems to be mismatched as I do have a large cam but then a Performer 440 intake topped with 625 Carter carb (I'm thinking that the intake/carb were swapped out sometime in the past). I do have headers though (old rusty ones). Vacuum seems to be low (haven't measured) as the new PB booster doesn't offer a lot of assistance.

Had the timing set by a mechanic - don't know the numbers. It has electronic ignition (orange box but USA made) an a vacuum advance distributor.

Unfortunately I don't have the funds to completely tear down the engine so I was thinking to go one step at a time starting with intake and carb - and soon after camshaft (might do i at the same time as I have to take the intake off for the cam swap). No specs on compression but it's rather high if the 906 heads were swapped for 915s (if crank was reused).

Thanks for clearing up the difference between the street and race carbs - different fuel curve was new to me.
What I like about the QFT/Proform vacuum secondaries is the easy adjustability with just a screwdriver - that would allow me to run the carb with lower vacuum now and run it after I've changed the cam. Or am I wrong?

[firefighter3931]

Thanks for clearing up the difference between the street and race carbs - different fuel curve was new to me.
What I like about the QFT/Proform vacuum secondaries is the easy adjustability with just a screwdriver - that would allow me to run the carb with lower vacuum now and run it after I've changed the cam. Or am I wrong?

The "race" carbs are set of differently ; with low engine vacuum the booster needs to be more sensetive for the correct amount of fuel. The fuel metering is also more agressive to compliment the cam/compression/cylinder heads etc....

You have to think of it in terms of increased airflow requirements (Modified engine) requires increased fuel.  

With a milder engine that produces lots of vacuum the venturi boosters don't need to be as sensitive and the fuel curve doesn't need to be agressive.

So a carb that works with one type of engine build won't work well with another.  



Ron


Ps. The carb i selected for Denis' 440 was based on the engine combination (mild 440 with lots of engine vacuum) The PF street series 750 vac secondary  works great with some minor tuning. 

[ChargerST]

The PF street series 750 vac secondary  works great with some minor tuning. 

Sounds good to me! What about the QFT 735 VS? 

[71bee]

 

Just go with a 4150 Holley. vacuum operated secondaries in your engines case, will not do you justice.