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Feeling Stupid......Am I Wrong About My Carb???

6K views 87 replies 16 participants last post by  Franks68coupe 
#1 · (Edited)
Hi Guys,

I always thought I had a 650 Holley....I might be wrong. Looked at the numbers again before I ordered a rebuild kit-- 80457-5 below that, a 1925 number. A quick look and I see that it might be a 600 cfm. If that's the case, I may just buy a 750 and tune with that. Thoughts??
 
#2 ·
HLY-65-80457

UPC: 090127333525
CFM: 600
Fuel: Gasoline
Number of Barrels: 4
Carburetor Flange: Square bore
Choke: Electric
Secondary Type: Vacuum
Fuel Inlet: Single
Carburetor Finish: Dichromate
Ford Kickdown: Yes
Booster Type: Straight-leg
Throttle Linkage Type: Universal

This would be ok on a stock 289 or 302.
 
#9 · (Edited)
it is made from a different material plus it has center hung floats. those are good carbs for what they are and i would buy that over the first one you posted without question.

heres a very cool carb with proform type body, adjustable bleeds, choke, vac secondary center hung floats. never used one though.

http://www.summitracing.com/parts/qft-sl-750-vs/overview/

ok, here is 2 killer carbs. first is 680, second is 735.

http://www.summitracing.com/parts/qft-ss-680-vs/overview/

http://www.summitracing.com/parts/qft-ss-735-vs/overview/

.
 
#12 ·
ok you have an auto, i forgot. i just now posted some cool carbs in my previous post.

you can not make them a kick down unless you changed the throttle shaft but you could probably change over to a 65 style pedal and kick down which is a pita.

i will look some more.
Yes, auto. Not looking to do a lot of mods as the car runs good--I just think it can be better and now we know it is under carb'd , we need to do something. I like the aluminum 750 Holley but it may be too big for our applic. Always open to ideas but kinda want to stay simple on this.
 
#15 · (Edited)
if you need the kick down for the later style, i think you can take the throttle rod out of yours and put it in the holley and possibly quick fuel. if so, i would buy the quick fuel 680 I listed. the carb you listed does not have the kick down either.

since the secondaries are adjustable, a 750 is not really too big but a slightly smaller 670 thru 735 might be a bit better. i run 750's on most 347's with around 400 hp and 6000 rpm.

this is a little known carb that has annular boosters, vac secondary, auto kick down, electric choke and its your favorite brand holley. i would do the 680 quick fuel, that body style will flow better than the std holley but this would probably be my second option. i would contact holley and ask for the tech supervisor and tell him what you have and ask if this will work or if you need a standard metering block. the metering blocks are not that much. you will have better throttle response, and more hp and tq with the annular boosters up to around 5800 rpm. right off bottom will be much better and it will compensate slightly for the vic jr intake you have if i remember right but that might be someone else.

http://www.summitracing.com/parts/hly-0-80681/overview/


this automatic throttle shaft set up fits 1850 style carbs.

https://www.holley.com/products/fue...ts/carburetor_replacement_parts/parts/20-48-1


this fits 3310 style

https://www.holley.com/products/fue...ts/carburetor_replacement_parts/parts/20-49-1


quick fuel high flow ford kick down throttle shaft. add this to the ss/vs 680 carb.

High Flow Primary Throttle Shaft/Ford Kickdown (C4-C6)


quick flow high flow vacuum secondary throttle shaft. if you want to go whole hog.

High Flow Secondary Throttle Shaft/Vacuum Secondary


the high flow shaft will increase air flow slightly [by around 8 cfm per shaft] and they cost the same as the non high flow shafts.

. . .
 
#16 ·
I have a 750 CFM Quick Fuel on my 347. It is a little large down low but near perfect at high RPM. If 700 CFM was a choice that's where I'd go. When I had it dyno tuned I asked if 650 would be a better choice and the guy said he thought it would run out up high. That's just one guys opinion but considering the numbers he was able to get out of the car I tend to trust what he is saying.
 
#17 ·
#19 ·
I have a 680 quick fuel on my stroker. It is perfect size Imho. Engine dyno ran 440hp and 417ft lbs and the motor was still pulling at 6200rpm when they stopped the run.
 
#23 ·
#26 ·
Usally run annular discharge on engines were there is no or blocked heat riser. Otherwise down leg booster is fine with heat riser not blocked.
Mpst of the time chevys annular discharge works best no matter blocked or not.

Ie NASCAR ford Hollys use down leg chevys annular.
 
#27 · (Edited)
Too much carb will never hurt as much as too little carb. Plenty of guys run 302s with 750s and get good times at the track. I know people will say "how often do you go to the track?" But these people are confused. Most of us build <6500rpm engines. A 6500rpm engine that runs really well at the track is going to run really well on the street. It's when you start building 9000rpm engines that run really well at the track that will get headaches on the street. If you build an 11 or low 12 second 347 it's going to kick *** even if your carb is a little more than you "need."
 
#31 ·
I have to disagree with your first statement. Too much carb WILL hurt your performance. An engine can only use so much air. Too big a carb will slow down the air coming in, ie awful performance AND gas mileage. A smaller carb will provide better throttle response and gas mileage. I'm not saying to go with an anemic 390 cfm carb, I'm saying that 650 will do very well on his build. Won't give the full potential of the top end, but will give him plenty of all around performance.

A 750 would be more than enough for a 347 if you want all more top end power. You might sacrifice throttle response though. Shouldn't be much of an issue on a stroker.
 
#29 ·
You can also get some better response with the secondary spring quick change set (I had that as well), for tuning your secondary opening much easier.
 
#32 ·
The question is when, and under what circumstances, will you reach "too much carb"? Is a 750 too much carb for a 347? Nope.

There's tons of guys running 650 double pumpers on 289s with tons of success over the years.

The point I was trying to make is there's a huge difference between more than enough and too much, you should err on the side of more than enough when it comes to carbs rather than too little. If you care about performance.
 
#33 · (Edited)
Quick Fuel 680 vacuum secondary with electric choke
down leg boosters, screw in bleeds if you wind up going more cam radical later on
4 corner idles
street carb with some drag strip features
besides all that, its beautimus
a little pricey at over $500


 
#36 · (Edited)
Hi Guys,

What about the Street Avenger 670 http://www.summitracing.com/parts/hly-0-80670
No...it's $90.00 more than the 750 you posted and won't flow enough or as much as the quick fuels i posted. if you want to save money, buy the aluminum 750 you posted and maybe have a couple burbles in the lower rpm range when you accelerate because it is a straight leg booster carb. as i mentioned, down leg and annular booster carbs are both better than straight leg ones. everyone will tell you that. you will not gain 40 hp by just bolting on a carb if your headers are only 1 1/2" and since you are restricting the engine, there is no piint in putting in a big carb but a 650 will help a little.

also, as i mentioned a few times now, if your header tubes are only 1 1/2" you will not get much benefit from putting a much bigger carb on it so if anything, just go up to a 650 cheapo aluminum holley. if you have 1 1/2" tubes and install headers with bigger tubes, you will likely gain 20 hp and 20 ft lbs of torque or more. if you put on a bigger carb after that like a 680 - 750, you will likely gain another 20 and 20 or more, so if you have around 350 hp now, you will have around 390 which is a huge increase.

it seems to me that you are too focused on thinking 750 cfm is way too big for your engine and that it will run like c__p off the bottom if you put one b on. you have 3.73 gears with a stall converter. a 750 will be no problem. if you had that engine with 2.80 gears, i would say leave the 600 on it. if you run 456 gears you can run an 1100 cfm dominator if you want.

if you want to have what imo is the best overall carb, buy the quick fuel ss/vs 680 or 735. i would buy the 735. all these carbs including the holley will require a throttle shaft change. they seem to not make carbs over 650 cfm with vs and auto trans kick down even though they sell the auto kick down parts. it seems like they assume that if you need a carb bigger than a 650, you must have a manual trans, lol. .
 
#46 · (Edited)
ok thanks for the info, unfortunately there is no advertised duration but it must be around 274, however, i can tell you that i use 750 carbs on engines with cams very, very, similar to that one with eddy rpm non air gap intakes and they run hard up to 5800 rpm and yours should do the same. if it is dying off and building rpm more slowly after 5600, it obviously has probs..

this cam is very similar to yours

35-518-8 - Xtreme Energy? Hydraulic Roller Camshafts, Computer compatible (E.F.I.) with O.E. hydraulic roller cams 1985-95
 
#47 · (Edited)
ok thanks, unfortunately there is no advertised duration but it must be around 274, however, i can tell you that i use 750 carbs on engines with cams ver, very similar to that one with eddy rpm non air gap intakes and they run hard up to 5800 rpm and yours should do the same. if it is dying off and building rpm motre slowly after 5600, it obviously has probs..

this cam is very similar to yours

35-518-8 - Xtreme Energy? Hydraulic Roller Camshafts, Computer compatible (E.F.I.) with O.E. hydraulic roller cams 1985-95
O.K. thanks!! Maybe I should give the 750 a try...............I'm new to the carb info so you guys obviously know a whole lot more than I about them (I'm coming from an after market FI background --sequential FAST system on the race motor, and low rpm drivability was not the first consideration-although that motor does idle nicely at 800 and pulls hard to 7500 at 27 lb of boost).
 
#53 ·
FWIW I would recommend a Holley Street Avenger 670 for your engine and trans set up, over a 750 cfm carb. If it were manual trans, then 700 to 750 might be better.

I like the features of the SA, and all three of mine have tuned very nicely, no problems (two 670's and one 770) My 69 Mach 1 with 351W has the Holley 600, and it is adequate for a FMX car, but nothing fantastic. I will be changing out to a 670 when I swap around a few other car combinations.
The SA is aluminum body, has 2 metering blocks, and dual fuel feed. Ford kickdown....
Pretty good out of the box, and good value in my opinion.
http://www.summitracing.com/compare

Might be worth talking with either a pro engine builder, or a dyno tuner. Chances are they have dealt with a similar engine/trans/model that you have and may have some value to add. At the end of the day it will need to be tuned on the car, regardless of what you get. No such thing as 'out of the box' performance with carburetors.

Good luck on whatever you decide
 
#56 · (Edited)
Here's the holley secondary spring chart specs for when they start to open and when they are fully open on a 350 ci engine. As you can see, you can set it up so your secondaries will never fully open yet because it’s a 750, you can have decent size primaries so your car doesn’t gasp for air off the line. This is the benefit of secondaries. The white spring is the "happy" spring.

color. . . . . . rpm

white . . - very early
purple . – 1950 – 6950
plain . . – 2240 – 8160
brown . – 2710 – 8750

. https://ac17cb7e3cc3506f0d23-7386afb7d61f5e5af0e5a817d2877bfe.ssl.cf1.rackcdn.com/199r8219-2rev.pdf
 
#57 ·
Just my $0.02 worth....

Stick with what you've got. My favorite CFM calculator (Wallace Racing's) calculates a need for a 515-670cfm carb (depending on many more factors than can be input in their simple calculator) based on 347ci, and 90% VE at a 5,700 rpm redline. My experience with Holley carbs is that they typically flow a bit better than advertised so if it were me, I'd grab a blue gasket kit, a jet kit and some jewelers drill bits and go for it.
 
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