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4 barrel carb question for my 73 RR

Posted By: bigdaddywiz

4 barrel carb question for my 73 RR - 12/25/09 05:32 AM

Hi guys. I've read from a few sources that back in the day guys were throwing 4 barrel carbs on their 318's that came with 2 bbl's on them from the factory to get a little performance boost. my 73 road runner is completly stock. i was going to just drop a bigger engine in, but didnt want to go through the trouble of changing the transmission and rear end out to handle the power.

would it be worth it to slap a 4 barrel on my car and would i notice enough power to make it any more fun? if so, is there a specific one that i would need that works with the 318 from 1973? also, what other mods could i do to that engine (without major tear down) to get more out of it? i'm not lookin to make it a fire breather. i know its just the 318. just want to make it a little more fun.

i've got a base model 73 road runner with the automatic.

thanks in advance!
Posted By: 4aThrill

Re: 4 barrel carb question for my 73 RR - 12/25/09 11:31 AM

you can do alot to that 318 change the intake manifold, carb, headers, spark plugs, wires, rotor and cap hell you change the distributor for a better output of power if it hasn't already been done. what are you running for the rear and trans? 904? and what rear? theres alot you can do to make it run better and have more power. best thing to do is alot of research on whats good to use for the combo you want. Have fun and Happy Holidays
Posted By: RapidRobert

Re: 4 barrel carb question for my 73 RR - 12/25/09 01:33 PM

I'd suggest attacking the most restricted area of the eng 1st which would be adding some 340 HP ex manifolds (or headers if you can live with their issues) and a mandrel bent ex 2.5 or 3" that way if you upgrade the eng (& you will eventually) your ex will be adequate. A 600 eddie would be a good choice and I would for sure right now play w the dist curve/springs. You have a heav(ier) vehicle w a small eng and a deeper gear would make a world of difference in performance AND economy as the inertia of all that weight to get it moving is what hurts you. EDIT 73 was a bad year for emission mods and another 2bbl carb (75 or later) would help and if it's a carter the primary jets from an eddie strip kit will work in your 2bbl & benefit you
Posted By: bigdaddywiz

Re: 4 barrel carb question for my 73 RR - 12/25/09 04:48 PM

its got the 904 and the weaker rear end (from what a buddy who is a bit more knowledgable about that stuff than i am said). will i run into problems with either of those "weak links" with a little more power?

i'd like to just do bolt ons. what would have the biggest impact in that category?

merry christmas guys!
Posted By: goldduster318

Re: 4 barrel carb question for my 73 RR - 12/25/09 06:45 PM

Exhaust is first i'd say
Then 4bbl...I like 600 holleys
Cam 3rd. You'll probably pick up more with the cam once you've done the other stuff than the others gave you.
Posted By: scratchnfotraction

Re: 4 barrel carb question for my 73 RR - 12/25/09 09:06 PM

headers & duels first,best bang for the buck

stock 360 intake and q-jet/600 eddy with eddy LD4B,2nd biggest bang for the buck

swap in a stock /6 high stall torque converter,120$ reman from local tranz shop,3rd bigest bang for the buck

swap in a small Lunati voodoo cam with comp 901-16 springs 4th and biggest gain for the buck with the other bolt ons

get some 3.55 gears to get the full gain with all the bolt ons

do it all at once and you will need to find a rear axle upgrade/spare ASAP

may want to swap on some late model #302 closed chambered 318 heads to up the CR and be a little more efficent then add all the upgrades

it will be a nice little daily driver with some pep and fun back into it
Posted By: DaytonaTurbo

Re: 4 barrel carb question for my 73 RR - 12/25/09 09:34 PM

I would check out the rear gears first. If you have some granny gears in the rear diff, your 318 is going to be soggy no matter what bolt-ons you throw at it. First thing I would be spending money on is building a strong and aggressively geared rear diff. Then build a hi-po motor/trans on the side and swap them in when the time comes.
Posted By: forphorty

Re: 4 barrel carb question for my 73 RR - 12/25/09 11:27 PM

Quote:

I would check out the rear gears first. If you have some granny gears in the rear diff, your 318 is going to be soggy no matter what bolt-ons you throw at it. First thing I would be spending money on is building a strong and aggressively geared rear diff. Then build a hi-po motor/trans on the side and swap them in when the time comes.

Posted By: James74

Re: 4 barrel carb question for my 73 RR - 12/26/09 05:06 AM

Quote:

its got the 904 and the weaker rear end (from what a buddy who is a bit more knowledgable about that stuff than i am said). will i run into problems with either of those "weak links" with a little more power?



did your buddy actually crawl under the car and verify it, or just assume that a 318 car had a "weak" rearend?

fyi, my old 74 was a factory 318 car, and had a 8 3/4 with it...
Posted By: bigdaddywiz

Re: 4 barrel carb question for my 73 RR - 12/26/09 02:13 PM

what would the "weaker" rear end be for my year?
Posted By: Wheeler

Re: 4 barrel carb question for my 73 RR - 12/26/09 02:19 PM

If you are not worried about keeping the car 100% original, I strongly recommend the 4bbl intake and carb swap. The 4bbl carb will be a huge improvement in performance and driveability.

For the carb, I would get either a spreadbore carb or a squarebore carb in the 500-600 cfm range. Here are some suggestions:

- Spreadbore carb: Rebuilt Rochester Quadrajet, new Holley Spreadbore

- Squarebore carb: Holley Street Avenger 570 cfm, Barry Grant Road Demon 525 cfm, Edelbrock 500 cfm, rebuilt Carter AFB 500 cfm.

For spreadbores, I personally like the Rochester Q-Jet. IMO, the Q-Jet is more reliable and less tempermental than the Carter Thermoquad. I would consider a Q-Jet ONLY if you can get one from a quality carb rebuilder that specializes in them (stay away from the rebuilt carbs you can buy at your local auto parts store). Otherwise, you should spend the extra bucks for a new carb.

If you are looking for a brand new carb, I like the Holley Street Avenger or BG Road Demon (providing the quality control on the BG carb is good). The Edelbrock 500 cfm would be a decent choice as well but Edelbrock carbs tend to have a heat percolation problem that can cause hard starting problems.

BTW - What happened to the old Carter AFB 500 cfm carbs you could buy at the auto parts stores?

For the intake manifold, it depends in what style of carb you want to use (spreadbore or squarebore) and how much money you want to spend. I like the following intakes:
- Factory 340 or 360 cast iron intake. Ideal if you are budget conscious and wanted to keep a stock look. 1968-1970 340 intakes have a squarebore pattern. 1973-up 340 and 360 4bbl intakes have the spreadbore pattern.
- Edelbrock LD4B (if you can find a used one in good condition). GREAT intake for a 318. Has the squarebore pattern.
- Edelbrock Performer: Will accept spreadbore and squarebore carbs. Performance wise - not really an improvement over a stock 340/360 intake. The Edelbrock LD4B and LD340 intakes are a lot better performancewise.
- Mopar M1

FYI - The factory 340/360 intake and most aluminum intakes for the small block Mopar have larger ports than a 318 intake. The port mismatch is nothing to worry about - just make sure you use high quality intake manifold gaskets. The only intakes (I am aware of) that have the smaller 318 sized ports are the Edelbrock LD4B and Edelbrock Performer intakes.

Hope this helps - good luck!
Posted By: MY340

Re: 4 barrel carb question for my 73 RR - 12/26/09 02:43 PM

Quote:

what would the "weaker" rear end be for my year?



8-1/4" rearend, just look for a 10 bolt cover on the back of the housing. It will be plenty strong for what you're going to do to the motor.

The 8-3/4" doesn't have a cover as it has a removeable center section.
Posted By: scratchnfotraction

Re: 4 barrel carb question for my 73 RR - 12/26/09 02:43 PM

could have an 8 3/4 rear axle,take a look at it,from the back it will have a round non-removable cover

I usally get a mid 70s chebby q-jet and tac weld the mopar throttle arm to it and run them that way to get a good non emissions carb that works well...327 and 318 are close for jetting

last reman one I got from autozone was in the 120$ range and still working fine

Posted By: RapidRobert

Re: 4 barrel carb question for my 73 RR - 12/26/09 02:46 PM

Quote:

what would the "weaker" rear end be for my year?

7&1/4 (it has a 9 bolt side cover).
Posted By: bigdaddywiz

Re: 4 barrel carb question for my 73 RR - 12/26/09 02:51 PM

Quote:

Quote:

what would the "weaker" rear end be for my year?



8-1/4" rearend, just look for a 10 bolt cover on the back of the housing. It will be plenty strong for what you're going to do to the motor.

The 8-3/4" doesn't have a cover as it has a removeable center section.



ok, thanks...that answers my question. mines got a rear cover on it, so its the 8-1/4" rear.
Posted By: bigdaddywiz

Re: 4 barrel carb question for my 73 RR - 12/26/09 02:55 PM

Quote:

If you are not worried about keeping the car 100% original, I strongly recommend the 4bbl intake and carb swap. The 4bbl carb will be a huge improvement in performance and driveability.

For the carb, I would get a
- Spreadbore carb: Rebuilt Rochester Quadrajet or new Holley Spreadbore
- Squarebore carb in the 500-600 cfm range: Holley Street Avenger 570 cfm, Barry Grant Road Demon 525 cfm or Edelbrock 500 cfm

For spreadbores, I personally like the Rochester Q-Jet. IMO, the Q-Jet is more reliable and less tempermental than the Carter Thermoquad. I would consider a Q-Jet ONLY if you can get one from a quality carb rebuilder that specializes in them (stay away from the rebuilt carbs you can buy at your local auto parts store). Otherwise, you should spend the extra bucks for a new carb.

If you are looking for a brand new carb, I like the Holley Street Avenger or BG Road Demon (providing the quality control on the BG carb is good). The Edelbrock 500 cfm would be a decent choice as well but Edelbrock carbs tend to have a heat percolation problem that can cause hard starting problems.

BTW - What happened to the old Carter AFB 500 cfm carbs you could buy at the auto parts stores?

For the intake manifold, it depends in what style of carb you want to use (spreadbore or squarebore): I like the following intakes:
- Factory 340 or 360 cast iron intake. Ideal if you are budget conscious and wanted to keep a stock look. 1968-1970 340 intakes have a squarebore pattern. 1973-up 340 and 360 4bbl intakes have the spreadbore pattern.
- Edelbrock LD4B (if you can find a used one in good condition). GREAT intake for a 318. Has the squarebore pattern.
- Edelbrock Performer: Will accept spreadbore and squarebore carbs. Performance wise - not really an improvement over a stock 340/360 intake. The Edelbrock LD4B and LD340 intakes are a lot better performancewise.

Hope this helps - good luck!




thank you so much wheeler and everyone else whos tryin to help this slightly un-educated guy get what i need!
Posted By: Wheeler

Re: 4 barrel carb question for my 73 RR - 12/26/09 02:59 PM

Quote:

thank you so much wheeler and everyone else whos tryin to help this slightly un-educated guy get what i need!



You're welcome, glad to help! Please refer to my post again - I made some changes and added more info.
Posted By: DART67GT

Re: 4 barrel carb question for my 73 RR - 12/26/09 10:17 PM

Quote:

Quote:

Quote:

what would the "weaker" rear end be for my year?



8-1/4" rearend, just look for a 10 bolt cover on the back of the housing. It will be plenty strong for what you're going to do to the motor.

The 8-3/4" doesn't have a cover as it has a removeable center section.



ok, thanks...that answers my question. mines got a rear cover on it, so its the 8-1/4" rear.



Those 8 1/4 rears aren't all that weak. I have a 318 w/360 j heads, holley double pumper, headers w/dual exhaust and a 904. I put a lot of miles on that back in high school. Many burnouts and never broke it. Sure the 8 3/4 is better, but not necessary behind a mild small block.
Posted By: ramrod

Re: 4 barrel carb question for my 73 RR - 12/26/09 10:36 PM

My first car was a 318 2-bbl '73 Road Runner. It wouldn't pull past 3500 RPM stock....

I got some 360 heads, had the intake valve seats cut for 2.02" 340 intake valves and had the heads milled .060" to get the compression up. Used stock 340 valvesprings and an early 340 square bore iron intake. Added a 650 DP carb and the smallest hydraulic cam from PAW. Threw on a pair of Blackjack Alumicoat headers and some header mounted glasspacks (hey, I was 15 years old!). Really woke the little 318 up. It would rev past 6K and spin the 3.23 peg leg as far as you wanted. I never broke the 8.25 rear, but after about 5 years and some trips to the track it was getting kinda sloppy.
Posted By: DaytonaTurbo

Re: 4 barrel carb question for my 73 RR - 12/27/09 03:10 AM

Even if you have a 8.25 rear, it still pays to jack up the back of the car and figure out what your rear gear ratio is. If you've got some 2.76 granny gears or similar, that 318 will still be a dog even with a 4bbl, heads, cam, headers, etc. You may need to evaluate whether it's worth doing $ motor mods or upgrading rear diff or even just upgrading your 8.25's rear end ratio.
Posted By: scratchnfotraction

Re: 4 barrel carb question for my 73 RR - 12/27/09 02:32 PM

pull the cover and change the oil on the rear axle

when you have it off,the gear ratio is stamped in the edge of the ring gear along with the date

no guessing that way

2.76 may be slow out the hole but it will fly on the highway

IMO,add HP to those gears and they will go fast...300mph dragsters use a 2.76 gear with 1400HP

Posted By: bigdaddywiz

Re: 4 barrel carb question for my 73 RR - 12/28/09 12:36 AM

so if i was just to go the 4bbl intake setup and other easy bolt ons, how much of an estimated gain will i be looking at?
Posted By: dodgeboy11

Re: 4 barrel carb question for my 73 RR - 12/28/09 01:07 AM

http://www.summitracing.com/parts/SUM-G9040/

http://www.summitracing.com/parts/WND-8007/

http://www.summitracing.com/parts/HLY-65-1850S/

http://www.summitracing.com/parts/CCA-K20-208-2/

This is what I'd use. Maybe more cam if the gears are in the 3.23-3.55 range. That manifold should match up ok with the smaller 318 port. Probably a little bigger, but if it bothers you that much, pull the heads and enlarge the runners to the 360 intake runner size.
The four barrel will pick it up though, those two barrels suck.
Posted By: DaytonaTurbo

Re: 4 barrel carb question for my 73 RR - 12/28/09 01:19 AM

Quote:

so if i was just to go the 4bbl intake setup and other easy bolt ons, how much of an estimated gain will i be looking at?



Depends on what you consider to be easy bolt-ons. By that do you mean just intake, carb and headers? Going into the engine to do cam and valve springs is a bit more work. If you were going to go that far I would suggest a magnum head swap. If you're just doing the simple stuff like intake/carb/headers, I would expect maybe a 20-30hp and torq increase. Stock cam and heads will kill performance.
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