Carburetor suggestions - 625 or 750?

[RBCharger]

Finally got the 440 back together on my '74 triple black Charger. It fired right up. Carb leaks pretty badly - I need to break in the cam but don't want to use the TQ with the leaks. It looks like it's been "rebuilt" at some pint with lots of orange RTV. I think that carb goes into the original parts bin. Looking at Holley Street Demon as a replacement - either 625 or 750. Car has headers and a .488/.491 274/286 comp cams shaft. It's stock otherwise so compression will be fairly low (~8.5 to 1). I think the 625 will get it done - looked also at a 750 vac sec holley, but seems like more hassle. Any help/suggestions are appreciated. I think the stock one was 800CFM?

 

[493 Mike]

Personally, I would do a proper rebuild on the TQ. The 625 will do fine if no great expectations of high speed performance are on your mind.
Mike

 

[R413]

Rebuild the thermo. Orange silicone tells us that it needs looked at.

why did you choose that larger cam? To put around at part thrortle? A 750 should be minimum.

 

[topside]

TQs are great street carbs. Sounds like a damaged plastic body patched with RTV ?
At low street RPMs the 625 will probably have better throttle response, while the 750 will make more power at upper RPM.
So, it depends how the car is used.
I'm a fan of the Eddy AVS2, but the OP most likely has a spread-bore intake.

 

[wagonman]

IMO a Holley 750 3310 is easier to tune than a Carter/ Eddy. Both are good carbs though. Not the cam I would choose with 8.5 compression.

 

[RBCharger]

Rebuild the thermo. Orange silicone tells us that it needs looked at.

why did you choose that larger cam? To put around at part thrortle? A 750 should be minimum.

Why would I be putting around at part throttle? Agree on the 750 - actually leaning towards 750 holley vac sec. Easier to tune.

 

[RBCharger]

IMO a Holley 750 3310 is easier to tune than a Carter/ Eddy. Both are good carbs though. Not the cam I would choose with 8.5 compression.

I'm headers and 4.10s and factory stall is 2000-2350? so combo should be fine w that cam.

 

[R413]

Why would I be putting around at part throttle? Agree on the 750

Exactly, so why even consider a 625 for a 440?

this is where a thermoquad is good for part throttle with the small primaries, then plenty of flow when wide open.

 

[66Satellite47]

Since I'm a Holley guy, I would suggest one of the 3310 style Holley's. They are easier to tune in my opinion. But a smaller carb like one of the Carter style can work very well in most applications.

 

[Lefty71]

You've got more than a few suggestions already (wow, lol).. If it were mine, it would prolly go with the bigger is better theory cuz i dont care about gas mileage on a '440. But importantly, whatever you change to, get the trans kickdown set back up properly so you dont open another can of worms.

HTH. Lefty71

 

[RBCharger]

You've got more than a few suggestions already (wow, lol).. If it were mine, it would prolly go with the bigger is better theory cuz i dont care about gas mileage on a '440. But importantly, whatever you change to, get the trans kickdown set back up properly so you dont open another can of worms.

HTH. Lefty71

Yeah I was looking at that. Looks like I'll need some bracket to adapt everything.

 

[66Satellite47]

No sure if it's still true, the old 3310 Holley had the Mopar adapter for throttle & kickdown linkage. Maybe not today. Or the aftermarket styles may not consider that. Could take a bit of playing around. But the 3310 style is a really versatile carb.

 

[davek]

holley 750 DP

 

[Geoff 2]

Replacing a TQ with a Holley is a backwards move. Have a look at the extensive post on the FABO on TQs. Why the metering is better etc. Most likely cause of leaking TQ is missing/damaged O rings, easily fixed with a repair kit.

 

[rumblefish360]

750 cfm in the carb style you like and understand how to tune.
I use a 750 on my 340 w/4.10’s & 360’s w/3.55’s.
My wife’s 360 has a roller comp @224@050 intake. It’s the same advertised duration. Cam card below for her 360.

 

[RBCharger]

I did order a 750 Holley Vac Sec. The TQ is in pretty rough shape. There are a number of vacuum lines that I'd like to eliminate as well on this car so the TQ is going into the parts bin.

 

[RBCharger]

I was watching the metering rod bar on the TQ during break in - it kept bouncing up and down. Is that common on the TQ?

 

[493 Mike]

I was watching the metering rod bar on the TQ during break in - it kept bouncing up and down. Is that common on the TQ?

The metering rods react to vacuum changes. Put a vacuum gauge on and see if it follows the bouncing action.
Mike

 

[Geoff 2]

Met rods that move:
- if the cam is hyd, it could be because the lifters have not pumped up & vac is erratic. This scenario is unlikely to cause this.
- carb has leaking gaskets/seal
- I assume break in was fast idle, so met rods should have stayed down. If hyd cam, possibly wiped lobes.