: Carb Recommendation



wurstarme
07-24-04, 02:32 PM
I'm looking to buy a new carb for my 472 and was wondering what cfm I should go for. I'm going with a Holley for sure, but I don't know whether to get 750, 800 or 850. I don't want to overcarb and was wondering what you guys had success with... The engine is just a '74 472 with an Edelbrock intake and MSD pro billet distributor

davesdeville
07-24-04, 05:30 PM
I'd reccomend having the Quadrajet rebuilt. There's no reason to go with a Holley, really, you'll probably just lose some gas mileage. If you feel the need to spend more money to lose mileage and not gain performance, anything over 750 would be too much.

lux hauler
07-24-04, 06:36 PM
If you're set on a Holley, a 750 will be plenty. davesdeville's right though, for a street car, a Q-Jet is probably best. If set up correctly, it should give you all the performance plus better mileage.

wurstarme
07-24-04, 11:26 PM
Well my problem is that I don't have the original stock qjet.. so I'll get a 750 holley. Thanks

Ogier
07-24-04, 11:29 PM
I'd reccomend having the Quadrajet rebuilt.

Good idea. Although Q-jets can be tricky. Make sure you have a competant rebuilder do the job.



There's no reason to go with a Holley, really, you'll probably just lose some gas mileage.

Horseshit. If you go with a Holley and set it up properly, you will gain mileage not lose it. Same with any of the aftermarket carb manufacturers. Don't expect to buy one, bolt it on and have it run correctly out of the box. You actually need to do some homework.


If you feel the need to spend more money to lose mileage and not gain performance, anything over 750 would be too much.

Actually, anything more than 600-650 is a complete waste of time. If you go with the 750, you will encounter the following:

1) Boggy bottom end.
2) Sluggish midrange.
3) Really bad mileage.

Horsepower is created by a number of factors. One of which is air-fuel velocity going into the combustion chamber.

To properly make use of a 750 on a 472 motor you would have to spin it up to 5500 rpm consistantly. You will not be doing this on the street or even the freeway where the engine will only be running consistantly at around 2000-2500rpm.

Hope this helps.
Ogier

lux hauler
07-25-04, 12:41 AM
Good idea. Although Q-jets can be tricky. Make sure you have a competant rebuilder do the job.




Horseshit. If you go with a Holley and set it up properly, you will gain mileage not lose it. Same with any of the aftermarket carb manufacturers. Don't expect to buy one, bolt it on and have it run correctly out of the box. You actually need to do some homework.



Actually, anything more than 600-650 is a complete waste of time. If you go with the 750, you will encounter the following:

1) Boggy bottom end.
2) Sluggish midrange.
3) Really bad mileage.

Horsepower is created by a number of factors. One of which is air-fuel velocity going into the combustion chamber.

To properly make use of a 750 on a 472 motor you would have to spin it up to 5500 rpm consistantly. You will not be doing this on the street or even the freeway where the engine will only be running consistantly at around 2000-2500rpm.

Hope this helps.
Ogier
Anyone that I've ever heard talk about Q-Jets said that overall, when properly tuned, they will get better mileage than most......?

lux hauler
07-25-04, 01:20 AM
Well my problem is that I don't have the original stock qjet.. so I'll get a 750 holley. Thanks
Actually, when I said a 750 would be plenty......I meant that it would be more than enough.
Most people think that because most 350 Chevys have 750's, a bigger engine must need a carb bigger than a 750. That's not so. Unless that 350 is turning 7500 rpm's, a 750cfm carb is much too big. My mild 514 Caddy only requires around 725cfm's.
Use this formula:

Engine size (cubic inches) x maximum engine rpm's / (divided by) 3456
472 x 4500rpm(?)=2124000/3456=614.58XXXX

614.58 is cfm at 100% volumetric efficiency. You car is only capable of about 80% volumetric efficiency so you have to figure a little less.....a 600 should work well. A 650 will work but the bigger you go, the more throttle response you'll lose.

Ogier
07-25-04, 04:42 AM
Engine size (cubic inches) x maximum engine rpm's / (divided by) 3456
472 x 4500rpm(?)=2124000/3456=614.58XXXX

Hmmm, there seems to be an echo on this forum. :)

Ogier

davesdeville
07-25-04, 06:04 AM
Horseshit. If you go with a Holley and set it up properly, you will gain mileage not lose it. Same with any of the aftermarket carb manufacturers. Don't expect to buy one, bolt it on and have it run correctly out of the box. You actually need to do some homework.

If you go with a vacuum secondary Holley and set it up properly, you'll get decent mileage, DP Holleys will get less. If you go with a QJet and set IT up properly, you'll get better mileage anyway. And since the lowest cfm carb he listed was 750, that's what I reccomended, and yes that's still over-carbed. Although vac-secondaries will help that alot.



Hmmm, there seems to be an echo on this forum. :)

Ogier

There seems to be an echo all over the world, because that formula's everywhere.

Sasquatch
07-25-04, 08:43 AM
If you already have an Edelbrock intake why not go with the Edelbrock carb? I purchased a model number 1411 which is a 750 cfm and installed it in my 69 commercial chasis hearse with a 472 motor and it runs great. None of the problems listed above. Yes I did take it right out of the box and bolted it on and started driving. No adjustments necessary. Edelbrock does a great job of setting these carbs up before they leave the factory. We've had this discussion in other threads about a 750 cfm being considered "overcaberation" on the 472. I said it before and I'll say it again. EVERY time I take my hearse out there is never a bog, hesitation, throttle response loss, or problem of ANY kind. Just straight out haulin ass and lot's of fun with this carb installed. I replaced the old Q-Jet which was the original carb. I know this because I checked the numbers. I agree that the Q-Jet is a great carb. when rebuilt and set up properly no doubt about it. Especially for street driving. The Holley is a good carb. also but I would think more oriented towards the higher performance/racing setups. Since you already have the Edelbrock Intake the Edelbrock carb. would bolt right on. Make sure you have the hood clearance. I imagine if you already have the Edelbrock intake on the car with your Q-Jet mounted there is no problem. The Edelbrock intake adds 3 inches in height when bolted on. 750 cfm for me worked perfectly. Of course this hearse is 21 feet long and weighs in at 4300 lbs. Hope this helps and it really is a matter of choice and preference. The choice being 600 to 750 cfm's and which name brand. :coolgleam

lux hauler
07-25-04, 09:55 AM
Hmmm, there seems to be an echo on this forum. :)

Ogier
I had to dig around a little but I see that you have posted that formula here before in another thread. If you have some kind of "rights" to that formula, you might want to contact Holley......they have it posted on their site too.

BTW.....the "Horseshit" comment wasn't really necessary, was it?

Ogier
07-25-04, 11:58 AM
Yes, the formula is everywhere. I was merely making a poorly thoughtout joke. :)

As to the "Horseshit" comment, yes, I feel it was nessecary. carberation is a science. There are people who get paid a lot of money because they are really good at it. DavesDeville made a blanket statement that was not only incorrect, it was flat out wrong. So I labled the comment for what it was.

Ogier


I had to dig around a little but I see that you have posted that formula here before in another thread. If you have some kind of "rights" to that formula, you might want to contact Holley......they have it posted on their site too.

BTW.....the "Horseshit" comment wasn't really necessary, was it?

davesdeville
07-25-04, 07:43 PM
On the subject of horseshit, you're full of it. Sure, a new, properly adjusted Holley will get better mileage than a 200k, 35 year old Quadrajet. But a rebuild, properly adjusted Quadrajet will get better mileage than a new, properly adjusted Holley. Do you own stock in Holley or something?

Go find something that proves me wrong. Try it.

wurstarme
07-25-04, 09:07 PM
If you already have an Edelbrock intake why not go with the Edelbrock carb? I purchased a model number 1411 which is a 750 cfm and installed it in my 69 commercial chasis hearse with a 472 motor and it runs great. None of the problems listed above. Yes I did take it right out of the box and bolted it on and started driving. No adjustments necessary. Edelbrock does a great job of setting these carbs up before they leave the factory. We've had this discussion in other threads about a 750 cfm being considered "overcaberation" on the 472. I said it before and I'll say it again. EVERY time I take my hearse out there is never a bog, hesitation, throttle response loss, or problem of ANY kind. Just straight out haulin ass and lot's of fun with this carb installed. I replaced the old Q-Jet which was the original carb. I know this because I checked the numbers. I agree that the Q-Jet is a great carb. when rebuilt and set up properly no doubt about it. Especially for street driving. The Holley is a good carb. also but I would think more oriented towards the higher performance/racing setups. Since you already have the Edelbrock Intake the Edelbrock carb. would bolt right on. Make sure you have the hood clearance. I imagine if you already have the Edelbrock intake on the car with your Q-Jet mounted there is no problem. The Edelbrock intake adds 3 inches in height when bolted on. 750 cfm for me worked perfectly. Of course this hearse is 21 feet long and weighs in at 4300 lbs. Hope this helps and it really is a matter of choice and preference. The choice being 600 to 750 cfm's and which name brand. :coolgleam

Well hood clearance is not an issue because I drive without a hood. The hinges are busted, and I'm having the hood cut for a hood scoop because of the clearance problems with the Edelbrock intake. For now I'm running with a 600cfm Edelbrock and it bogs like hell when you hit the gas. The reason I suggested a 750cfm at the low end is that the 600cfm is running so poorly. Speaking of gas, I don't care about gas mileage at all. I budget a good chunk of my paycheck for gas already...

I'm looking for the best carb for performance, as in going fast. I realize I drive a 5,000-pound car not meant for racing, but I still want to make it as fast as I can. That's the whole reason I bought the car, to be different. The reason I suggested Holley is that everyone I talk to at car shows has a Holley and couldn't be happier.

A friend of mine has a 750cfm Holey double pumper w/ mechanical secondaries that he can sell me cheaply, so I will probably just go with that.

lux hauler
07-25-04, 10:38 PM
A friend of mine has a 750cfm Holey double pumper w/ mechanical secondaries that he can sell me cheaply, so I will probably just go with that.
You can do what you want but according to Holley, that carb is completely wrong for your car. A carb with mechanical secondaries is best for a car that is light, has low gearing (numerically high), manual trans etc. Have a look here..
http://holley.com/HiOctn/ProdLine/Products/FMS/FMSC/FMSC.html

wurstarme
07-25-04, 10:46 PM
You can do what you want but according to Holley, that carb is completely wrong for your car. A carb with mechanical secondaries is best for a car that is light, has low gearing (numerically high), manual trans etc. Have a look here..
http://holley.com/HiOctn/ProdLine/Products/FMS/FMSC/FMSC.html

Thanks a lot for the info.. I'll look it over

caddycarlo
07-27-04, 02:39 AM
sorry to but in but the holley 750 dp that I ran on my stock motor with a cam did very well and my car weighs 4200 lbs with me in it ......... the only reason holley says those things is becouse most people way over carb there little motors ..... with the caddy cid and low end torque it works just fine ...... also don't get to hung up on that math it does not work ......

imho ...... if you want hit the holley dp is hard to beat

if you want milage the q-jet or edebrock is better .... this has to do with how the fuel is mitered.......

but like dave said what ever carb you use has to work right .... a wore out carb of any type is no good ........

lux hauler
07-27-04, 05:05 PM
You're running a bigger engine in a lighter car with a manual tranny (?) and lower gears.......Do you think a dp will work as well on his car as it does in yours?

caddycarlo
07-27-04, 10:10 PM
You're running a bigger engine in a lighter car with a manual tranny (?) and lower gears.......Do you think a dp will work as well on his car as it does in yours?
sure .....I ran the same carb on my stock eldo years ago ......that was like 6000 lbs and auto and no gear ............ the big problem with a dp is not how it will run but the fact that you will have no milage .......... the holley is very tunable but it is hard to not have the part throttle rich and still have wot right ...... this is becouse the carb uses a power valve which is on or off instead of a needle that changes the fuel flow with load like the q-jet or edebrock ................ granted a stock 300 hp caddy motor would like a 500 to 600 cfm carb more then the 750 which should be on a 450 hp motor it is not that much of a over kill ...........

Imprl59
07-28-04, 11:39 AM
For now I'm running with a 600cfm Edelbrock and it bogs like hell when you hit the gas. The reason I suggested a 750cfm at the low end is that the 600cfm is running so poorly.

The carb size isn't causing a bogging problem. Check the accelerator pump in the 600 and the vacuum advance on the distributor.

Steve B.

wurstarme
07-28-04, 01:32 PM
The carb size isn't causing a bogging problem. Check the accelerator pump in the 600 and the vacuum advance on the distributor.

Steve B.


The vacuum advance is fine, I had checked that a while ago. I tried different settings for the accel pump, but it didn't really help much.

Imprl59
07-28-04, 02:01 PM
Is the accel pump working? If you manuallty operate the throttle you should see a good stream of fuel spray in to both sides of the carb.

Steve B.