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View Full Version : Carb Size for 318 ? ? ?


Skull-1
07-09-2004, 10:37 PM
What's a decent size carb for a 318 on its second overhaul? I have Electronic Ignition and a Holley Street Dominator Intake but I think this 600 CFM carb I have on it is a BIT too large for the motor.

Any suggestions? I like the 4 BBL setup. What CFM range should I be shooting for?

riverside
07-09-2004, 11:22 PM
I think the 600 is fine, doe's it have a vacuume secondaries?

67 Plymouthcuda
07-10-2004, 01:40 AM
Im running an Edelbrock 600 cfm on my car, and its running great. I have no problems with it.

rumblefish360
07-10-2004, 02:29 AM
A 600 cfm carb should be fine. If better throttle response and mileage is wanted, a 500 cfm Carter AFB or better yet (IMO) a T-Q will do wonders for the 318.
The T-Q has tiny primarys that run at about 200 cfm with biggger than big secondarys that are easier than easy to tune,
Click here for a great guy on this carb; http://www.thermoquads.com/
Tell'em I sent you. You'll won't be sorry.

Skull-1
07-10-2004, 02:11 PM
Yes it has VAC secondaries. I also have a mild CAM in it.

Which carb on the market is the least maintenance intensive? I am told Edelbrocks are the most carefree of the bunch. True?

usdart
07-10-2004, 09:12 PM
I had a 600 edel on my 318 with a mild cam and 2 1/8" exhaust. Found the 600 was too rich fo a 318 'out of the box'. I tried two brand new ones and was never happy.
I bought a 600 Holly w elec choke from Checker Auto Parts and it works alot better 'out of the box'.

I have since re-jetted the Holly for my 360 and am still happy with it. I only had it on the 318 for about a month when I swapped engines.

"your results may vary" LOL

dwc43
07-11-2004, 08:41 AM
Originally posted by Skull-1
What's a decent size carb for a 318 on its second overhaul? I have Electronic Ignition and a Holley Street Dominator Intake but I think this 600 CFM carb I have on it is a BIT too large for the motor.

Any suggestions? I like the 4 BBL setup. What CFM range should I be shooting for?

The 600 is too small. The stock carb in mid '70's was an 800 cfm thermoquad. That's what you need. It's ten times more throttle responsive than any holley ever thought about being. We even used them on our dirt track cars. :D

RAMKOTA
07-13-2004, 01:31 AM
I have a 318 with a 600 cfm holley with vac. 2nds and it does ok; small cam and the intake is a edl. performer. Also heard that the weight of the auto makes a difference, to big and it can bogged down.

rumblefish360
07-14-2004, 08:00 PM
This quote from DW. The 600 is too small. The stock carb in mid '70's was an 800 cfm thermoquad. Is not exactly an apple to apple compare. Heres why. The 600 cfm carb is a squre bore carb. It'll perform fine. The 318 really dosen't need more than that.
The T-Q is a spread bore design with primarys that flow less than the square bores 600 cfm unit. Ruffly, right around 200 cfm for the T-Q, around 300 (A tad less) for the Edel/holley designs.
The beauty of the T-Q is the secondarys. There massive and very tunable. You can do it your self if need be. The air door regulates the flow (Bendable air door for flow amount) and when it opens. (Spring loaded tension)
800 may seem like a lot, and it is, to a point. If it where a Holley/Edel design, I'd say way to much. Rediculas (sp) for the street. However, the 800 cfm T-Q is great for the street.
It's all in the design. Like a balanced power package, the T-Q will work.

sbddart
07-15-2004, 09:56 AM
you may feel the carb is a bit large, and not so. the problem may be in the intake you are running. an old street dom is a low single plane, and will be a dog down low with numeric low gear, small cam, and stock convertor in a heavier car. try a dual plane with your combo. the mopar engine book recomends a 650 for the 318. (i run a 650dp on a 77smog18 w/mild cam&j heads).
call me nuts, but a holley 500 2bbl will really wake the thing up!

Skull-1
07-15-2004, 03:14 PM
That is precisely what the problem is. It seems boggy down low but really ramps up when the RPMs go above 3,500 or so. Don't laugh, but I have huge gears in it (2.71:1) so the only way to get it to do anything is to manually shift it 1, 2, D.

I really like the gas mileage I'm getting (around 25 on the highway) but the power bog is a bit annoying. I was thinking I could delay secondary activation but there isn't anything on this Edelbrock to do it. :( I went with the 600 CFM Electric Choke and it runs way better than my Holley did.

dwc43
07-15-2004, 03:33 PM
Best way to fix this is install a Weiand action plus dual plane and a thermoquad. That will get your low end back, along with great throtttle response. :D

67 Plymouthcuda
07-15-2004, 08:17 PM
You can also add a spacer on the single plane manifold. That will make it act like a dual plane.

Skull-1
07-15-2004, 11:28 PM
I do have a Morosso (sp?) spacer on it. Not sure I want to swap intakes again, though. YIKES.

Anything I can do with this thing to alleviate the problem some?

On the Holley I put a really tough secondary spring on it to keep it from opening up until much higher RPMs. That did seem to help.

MoparMarcIdaho
07-15-2004, 11:42 PM
It MIGHT help but not that much.I have had quite a few eddy performers that were junk.A tin can with holes drilled in it would have done better.Any spread bore carb will have better vaccum and get better mileage.My crew cab came in with a preformer and it got yanked in favor of a qudrajet from a 425 caddie,kitted it and trimmed 1/4 inch from the metering rod spring and it kicks butt.18 to 20 pulling my boat and passes empty trucks going uphill.On a 318 auto.4.10 dana with tall tires.Not much tire left though,too many tire fires.:p

67 Plymouthcuda
07-16-2004, 12:17 AM
I was runnng a 318, bore 30 over. The heads and the single plane manifold from a commando 273. I have a spacer and a 600 Edelbrock carb. I had a 278 gearing in the rear, or was it 275? Anyway it used to roast the ---- out of the tires. Second gear would take my up to 95 mph, before I had to shift. All that time, that carb performed great, straight out of the box. Granted my gas mileage sucks, but the performance was there.:D

MoparMarcIdaho
07-16-2004, 12:29 AM
and yes you might have gotten a good one,that happens sometimes,I just seem to get the crappy ones I guess.:crying:

rumblefish360
07-16-2004, 12:02 PM
Thats the problem right there, tall gears.

67 Plymouthcuda
07-17-2004, 12:00 AM
I had tall gears, but I had no problem at all. The only problem I had was the tires not hooking up when I wanted it too.

Stoga
07-17-2004, 12:54 AM
Originally posted by 67 Plymouthcuda
I had tall gears, but I had no problem at all. The only problem I had was the tires not hooking up when I wanted it too.
Thats kind of the catch 22 with tall gears. If you hook up,, you'll accelerate slower, but if you lose traction, they'll spin the tires that much faster compared to engine rpm. It's part of the reason some cars are so much harder to hook up when e.t. racing than you'd think.
As for the topic, I used to use a SP2P Offenhauser on my old 318 72 Duster, it really helped the bottom end a ton and worked good with the stock heads and cam. But if you're going larger cam or more cubes, its kind of restricted in breathing though still better than a stock 318 intake.

Skull-1
07-17-2004, 02:51 AM
I rather think my 2 BBL carb had more pickup than this 4bbl off the line. Is that par for the course?

rumblefish360
07-17-2004, 06:41 AM
What 2bbl and what 4bbl? Sounds like a tuning issue.

MoparMarcIdaho
07-17-2004, 01:34 PM
on big blocks,smaller carb has more vaccum so its stands to reason that it would have better low end torque.;)

dwc43
07-17-2004, 03:51 PM
Originally posted by Skull-1
I rather think my 2 BBL carb had more pickup than this 4bbl off the line. Is that par for the course?

One, that holley has no throttle response to start with. @nd, it's mostly a tunning issue too. Get a TQ and you'll have the low end throttle response your looking for. :D

Skull-1
07-20-2004, 12:13 AM
How hard are TQs to keep in tune? That Holley was always requiring adjustment. I want a basically hands-off carb.

dwc43
07-20-2004, 12:15 AM
The TQ is what you want then. Just set it and forget about it. We very seldom ever touch our race car wit ha TQ on it too. It's just that reliable. A holley never will be. :D

Hobbes
07-23-2004, 12:27 AM
Got to go with dwc - Thermoquads have always been good to me, and you can still pick them up at the boneyards or on eBay for a song. You'll get the off idle response you're looking for at a fraction of the price of a new Holley, Edelbrock, etc...

Hobbes
07-23-2004, 12:33 AM
There was a thread concerning T-quads about a week or so ago in the performance talk forum that might be useful to you - it had some good info and links to relevant sights.

Skull-1
07-23-2004, 01:29 AM
I'll check on it.

Are there new ones available? I sound like a dork asking I bet.

DEMON SIZZLER
07-23-2004, 11:05 AM
Originally posted by Skull-1
I'll check on it.

Are there new ones available? I sound like a dork asking I bet.

'Only if you don't ask the question!":D

No new T.Q.'S since late 84' but occasionally you will find an NOS T.Q. on ebay or through other sources. Plenty of new parts are still available now.

My personal opinion is that the right T.Q. on a particular application is really hard to beat. Two examples:

1)my $425 318 build with totally stock 74' short block, stock 302 heads, very mild Crower hyd .423"-.441"/250-254 duration cam,
Performer intake, Hedman 78050 headers, 3.91 8-3/4 gears, 904 trans with stock converter in my 71' Demon Sizzler, 3,350 lbs with me in it. I have my full race 890 cfm T.Q. on it made from the last smoger 84' oem T.Q. and the car runs consistent 14.70's with 2.15 sec o-60 ft times spinning the tires about 40' at the track. I will be testing with American Racer L-60-15 tires soon and am confident that I will have my o-60 ft times in the 1.90's and qtr mi times in the 14.30's.

2)Jimmy S's 70 Dart, 408 stroker 360, roller cam, Victor intake, W-2 Econo heads, mild porting, about 10.7:1 compression, 1-3/4" od Hooker Super Comp headers, 904 trans, 4.30 gears in an 8-3/4
rear, with his T.Q. runs 6.494/104 mph in the 1/8 which is 10.20's in the qtr mi. He will soon be testing with my race prepped T.Q. I built for him and hopes to run in the 9.90's by the eng of the season.

These are just a few examples of the power that can be attained from a T.Q. from one end of the spectrum to the extreme!

dwc43
07-24-2004, 08:38 AM
Originally posted by Skull-1
I'll check on it.

Are there new ones available? I sound like a dork asking I bet.

Last time I bought one it cost 189 from Advance Auto. New bowls and parts, and built by Holley of all people. Go get you one. I ordered mine for a big block '72 Charger to get an 850 cfm carb. Just order one for a '76 Dart Sport 360 and you'll get an 800 cfm carb. They work great, and I have never had to take on back, yet. :D

rumblefish360
07-24-2004, 09:49 AM
See if you can get an earlier year carb instead of a '76. Ask for a 72 year carb for a 340. (For the smaller T-Q.) I don't know what advanced will give you.
It could be the correct carb for the year engine, it may not be. So, in this advent, read this by Demon sizzler. This should really help in a junk yard/swap meet search. http://www.moparstyle.net/forums/showthread.php?s=&threadid=6309&perpage=10&pagenumber=1

Skull-1
07-24-2004, 05:11 PM
Very informative. Thanks for the information, guys. :)

dwc43
07-25-2004, 09:48 AM
Welcome, anytime. :D

rumblefish360
07-25-2004, 09:51 AM
Ditto as above. :) LOL