[69z28freak]

I am looking at getting a carb for my 1970 LT1 motor. All stock factory, except running headers. I have been told by some guys that the Quick Fuel 780 is a much better running carb and half the price of a List 4053. Anyone have any advice. This is not a numbers match car.

Thanks

[SIDEWAYS]

I had a Holley Street Avenger 770 and then bought a QF 780 vs carb cause it "was much better" and tried it. The Holley went back on.

[bigblockragtop]

Isn't 780 big for a 350 I would think it would be much happier with a 650.

[Eleanor's Nemesis]

A 780 will be fine for a mild 350, been done for a long time.

The deal with most carbs-whether a q-jet, Holley, or Thermoquad-is how it is set up and tuned.

Almost never does a carb come out of the box and perform optimally.

As for the Quick Fuel I have been hearing rave reviews about them from racers. These are racers that have to use the 780 as a replacement for the original Holley 780 in stock type classes. The guys at QF, so I have been told, used to work at Holley. And, I was recently informed, that QF has been bought by a corporate entity that owns other perf parts companies. I don't know if that is true or not-just heard it this past weekend from someone at PRI.

[69z28freak]

The guy who built my motor has the same motor in 1970 Deuce Yenko, and he swapped his 780 Holley for the Quick Fuel and said it is night and day. The Quick Fuel would cost half of the price of a correct style car for that car/motor combo. He also switched the float bowls to Holley float bowls and used the standard 5/8 lines. He said it all bolted right up. He has been building motors for 30 plus years. He also has a 780 Holley he can sell me, but suggests the Quick Fuel.

This motor is around 400 hp. Will find out soon when I dyno it.

[ZLP955]

Originally Posted by bigblockragtop

Isn't 780 big for a 350 I would think it would be much happier with a 650.

Jet size has a much greater impact than the nominal cfm rating.

[ZLP955]

Mike, there was an article in a recent issue of Muscle Car Review, that compared a number of similar carbs to what you're asking about. Can't recall exactly which brands or models they tested (am at work now....) but I recall the best overall performer was a surprise, and that one of the old Holley designs that Summit bought the manufacturing rights to, was a great (and cheap) performer right out of the box. I'll dig it out when I get home.

[69z28freak]

Originally Posted by ZLP955

Mike, there was an article in a recent issue of Muscle Car Review, that compared a number of similar carbs to what you're asking about. Can't recall exactly which brands or models they tested (am at work now....) but I recall the best overall performer was a surprise, and that one of the old Holley designs that Summit bought the manufacturing rights to, was a great (and cheap) performer right out of the box. I'll dig it out when I get home.

Thanks Tim. My daughter says its hot down under right now.

[ZLP955]

Originally Posted by 69z28freak

Thanks Tim. My daughter says its hot down under right now.

Yes, Summer begins on 1st December here, the last couple of weeks of Spring warmed up nicely here (it hit 108F), but now back down a few degrees, so very welcome. Hopefully it will be a good season, I have lots of bodywork lined up for the Z and we are moving house, too - bad timing there maybe
Are you still planning a trip down here?

[ZLP955]

Hey Mike,
Found that article, and I misled you - it was in Car Craft October '12 issue, not MCR..... (blame that one on having too many subscriptions - surely it can't be my age?). They tested 7 carbs, including several Holley 4-barrel vac sec models, and the Quick Fuel Slayer (but the 750, not the 780). Might be of some interest.
Anyway, I searched and the article is available on the web as well as the printed magazine - here:
http://www.carcraft.com/techarticles...d/viewall.html

[dubs68camaro]

Comparing a QFT to a 4555 or 4053 (or 3246, 3247, 3910, and on and on since they are all the same) is not a fair comparison. You are comparing 45 year old tech to what we currently know about fuel delivery based on the newest testing equipment. For the most part, it's all in the blocks. The base plates and main bodies just about all to the same thing. Many Quick Fuel bodies have screw in air bleeds though most guys are not familiar enough with them to properly tune. Comparing a 45 year old casting with 2-3 emulsion holes to a billet CNC'd one with 3-4 can make a big difference. It is about mixing air and gas before filling the cylinder right? The billet blocks do a better job out of the box. You could take that swap meet carb that was in the article and make it kill all the other carbs by running it through the hands of professional. It will cost you but they will make mods to the carb to bring it up to what we know today about fuel delivery.

I too agree with the 650 recommendation. Just beause GM put a 780 on it doesn't mean it was the best way to go. Think about guys.....GM only had 2 carbs. It either got the 750 Q-jet or the 780 Holley. Small blocks and big blocks got the 780. Why? It didn't make sense for GM to pay Holley to build the correct carb for every application so they truly tried to build a "one size fits all" carb and that was the 780. Say what you want about the list number and block numbers but they are all the same castings/carb.

I also wouldn't get too hung up about an article testing "street" carbs on a dyno. Dynos do one thing.....test for idle to WOT. Although they can hold a given rpm, they certainly do not do a good job of testing cruise/part throttle.

[bigblockragtop]

I had a 650 blow thru on my 496 go ahead and laugh. I changed to a 850 I wish I had the 650 back but I sold it to get the 850 I still can not get the carb to act as good as the 650 did. The throttle response was amazing with the 650 so I left a few hp on the table. Atomization(big word) meaning turning the gas into vapor works much better with smaller venturi's due to the speed the air travels turning the gas into vapor which ignites much better. This is my experience. You can go with the larger carb it just takes a lot of tuning the circuit air bleeds etc. I think all carbs are pretty close in design it has to do with tuning.

[dubs68camaro]

Now Mike....I do have to say that a 650 is flat too small for a 496. Sure it had killer throttle response because you have crazy velocity running through the main circuit down low. You would actually be leaving more than a few HP on the table. A 496 at 6500 will need somewhere a tad north of 900 cfm. There was more than likely something not correct with the 850. Granted, you do give up a little down low on an 850 due to the huge 1 9/16th venturi. Do you know what your 496 was making. I'm building an aluminum headed one that should come in close to 650hp at 6,300.

[bigblockragtop]

I have a procharger on mine so I was told when the boost hits it actually almost doubles the cfm of the carb. So I may have lost 25-50 hp. I should be 650 to the wheels so maybe 750-800 to the flywheel. Also gobs of torque. The problem I have is I got the car to cruise great and wot is great it is just grumbly(if that's a word) in between which is a ral pain. I would like to roll into the throttle to not break the tires loose but the engine does not like that. It make the car frustrating to drive. I mean cruising is great at 14.7 afr but I have to use the gas peddle like an on off switch. So I do not even hook up until 3rd gear. If i ever race anyone I will get left behind until 3rd. Plus it makes the car a lot more violent to drive. I am seriously thinking of fuel injection but chaching!

[dubs68camaro]

Dear Lord.....are you running a stock 650 with straight leg boosters? Is the 650 and was the 850 set up for blow-thru?? If you are running a procharger with a hat, you are severely under carbed. You should have an 850 or 950 with annular boosters!! My buddy Paul, who owns "Superflow Carburetor Systems" is running an annular 950 on a little 434 sbc. He's pushing 900hp. I bet you are loosing WAY more HP than you think!! Boost needs so much more fuel. That's why 6:71's run twin 750s, 850s and more.

Oops! Sorry to jack the thread!