View Full Version : 2 Barrel to 4 Barrel Upgrade

08-21-2001, 09:13 PM
Hi: Quick question, I have a 1985 bone stock 318 2 barrel with a whopping 140hp. I was wondering if anybody has just added a 4-barrel intake and a 600-cfm or so carb and what the hp gain was. I know eventually I would like to go with an upgraded cam and headers and do the heads etc. but I would like to know if it is worth the time just adding the 4 barrel setup before winter hits and continuing next spring or do the whole thing at once, ( I really don’t have that much money right now). Every mag article I have read about upgrading the 318 they didn’t do it a step at a time, always the intake with the carb with upgraded cam and took it from there. Thanks in advanc

08-21-2001, 11:03 PM
I have a 67 Belvedere II with a bone stock 273 2bbl. I added a 73 340 intake and a 600 Edelbrock. It made a huge difference in performance. Not sure of hp gain, but "seat of the pants" gain felt like it doubled. I still have the single exhaust as well. Theirs nothing wrong with doing it one piece at a time. Helps give you an idea what makes the bigest gain.

08-22-2001, 01:38 PM
I was watching Crank & Chrome on TV a couple of weeks ago and they had a car on there, I think it was an El Camino. They started off with a 454 bone stock and added headers and then did a dyno on it. Then they put on an intake and carb and did another dyno. They then added a cam and did a dyno again and finally they replaced the heads and ran the car. It was kind of neat to see each HP gain and really how everything came out. I think they started with 200 or so hp and ended up at 425 or so. I wish they would do one for a 318/360 sometime. I think I will put the intake and carb on the car before winter and see how I feel. According to the factory specs a bone stock 318 for that year was 144-145 hp which corresponds to my ¼ mile time and the 4 barrel version was 170 hp, not sure if they had a different cam or anything else different inside. Thanks for the input

08-23-2001, 11:23 PM
Did the same thing. First was the intake and carb, giving the car quite a difference in line jump. Next was to save for the dual exhaust. That made a huge difference. Next was headers, and I'm going to timing chain and cam next. 600 cfm is plenty on the carb.

Doug Wilson
08-24-2001, 02:08 AM
I think that if you're doing it a step at a time because of budget, you'd get the most return from: First- dual exhaust, Second-headers, Third-manifold and carb, Forth-cam and valve train. A lot of this depends on the shape of your engine now. If you have a lot of miles on it at present, you may be best just doing a timing chain - yep, doable in the driveway, and if you do need it, it'll make more difference than all the other stuff.

crud from the empty skull of...Doug

08-24-2001, 01:11 PM
I did the same thing with my 72 318 Satellite
Sebring. What impressed me with my Carter 625
and a cast 340 intake was the way the car
ran. MUCH BETTER with also very nice throttle responce. That alone mae it worth it.
I later went to dual exhaust and froma 2.71 to a 3.23 rear.
Now the car runs GREAT and had a little off the line SNAP.


08-24-2001, 05:05 PM
Fred and Doug Wilson and Ausydad what kind of gas mileage are you getting with your 4 barrel set up? I would assume that it would be about the same if not slightly better than a 2 barrel because the mains are smaller than a 2 barrel would be. I did the timing chain about 3 weeks ago because I was having a hard time getting the car to start at 15 btdc and the timing marks seemed to be jumping all over the place. Now the timing mark is solid and nice to start. Doing that kind of squashed my ambition to change the cam right now so maybe next spring. The dual exast will probably come after that if money permits.

Dart 65
08-24-2001, 05:34 PM
Didn't your mother warn you about watching that sort of crap? That GM junk will rot your brain, pal.

Doug Wilson
08-24-2001, 05:36 PM
In general, going from a 2 bbl to a 4 bbl will reduce your fuel milage considerably. Not because of the carb, but because of your FOOT! A 4 bbl makes more good sound and goes faster, so you are naturally into it more. If you have the discipline to stay out of the secondaries most of the time, the milage improvement can be a bunch - like 15 to 20 percent. In order of best milage to worst, the best carb would be the ThermoQuad, followed by Quadrajet, then Edelbrock, then Carter AFB and finally Holley. Although, different engines will get best milage from different carbs. Even in that case though, the spread bores - QuadraJet and ThermoQuad will yield the best results - oh, yeah, Holley also makes a spread bore, but I believe it only comes as a GM QuadraJet replacement.
Another consideration is the greatly improved low-end throttle response of the spread bore types, because of the tiny primaries. The Thermoquad also has the absolute best metering - it NEVER has to be re-jetted due to altitude changes, once it's set up right. It is utterly bog-free. I don't know if you've ever tried to tune out an off-the-line bog in a Holley or one of the AFB styles, but it can make you want to change hobbies - like from working on cars to joining a suicide club. It can be incredibly frustrating......this opinion is only from straight-jacketed Doug

08-25-2001, 09:16 AM
I have to agree with Doug. My right foot is sometimes heavy. The milage went up 10 %
in the city in my 3900 lb Satellite.
This is after I installed the 3.23 gears . My Highway milage was the same going from a 2.71 to a 3.23. This is good because I average 80 mph.
The legal speed limit in Alberta on most highways is 75 mph. BUT if I put my foot into it, the milage goes down, which I usually do.
Best of all the car is a real pleasure to drive now.


09-02-2001, 10:22 PM
I am currently in the process of doing the same thing to my '79 pickup with 318, except I am completely rebuilding the engine also. I purchased an Edlebrock Performer package, which includes 2176 intake, 1406 600cfm carb w/electric choke, 2177 cam and lifter kit, 7803 timing set, 1207 air cleaner, fel-pro intake set, 5877 valve springs and 1481 throttle lever adapter. Got this on-line from Summit for $676. I can't wait to get it all back together and see if it peps it up a little. My main concern is what modifications I will have to make to the throttle linkage.

09-03-2001, 12:34 AM
As far as mileage goes, mine sucked to begin with. With the 2 bbl., I got about 12. I now get about 6-7, but rarely go slower than any one around me. I guess my foot is made of cast iron!

09-03-2001, 12:51 AM
After I changed my timing chain I started to experiment with the base timing and so far I have the timing at 17 deg. BTDC and I am getting about 24-25 MPG in the city. Mind you I am driving like an 80-year-old grandpa, never speeding and just keeping with the traffic and no jump-starts. I think the 17 deg initial is ok so far but I guess I will see when it starts to get cold up here in Canada. I have tried the car at the full mechanical advance of 35 deg and it pinged badly so I had to drop it to 32 deg as a test so most likely I will have to weld up the advance bushing in the distributor to limit my advance. With all this said I have been looking for a good carb for this car so I can switch over to 4 barrel so I can drive like grandpa normally and I have the added assurance of being able to pass somebody if need be. So from what I have read on this thread in general I can sort of expect the same gas mileage as I am getting now as long as I keep out of the two extra barrels.

09-03-2001, 01:09 AM
The carb I'm running on mine is a Edelbrock model#1400 600cfm with electric choke. The model#1400 has the provisions for emission controls as I have to do that in California. Model #1406 is the same thing without emissions controls. Either way, 600cfm seems to make my 318 happy whether I drive it or my feather footed wife drives it.

09-03-2001, 10:26 AM
Hey all;

I had a '79 Dodge Magnum. (Boy I miss that car) It came with a 360 2bbl and the leanburn computer on the aircleaner. Single exhaust.
After getting this car up and running, I came to realize the grand total of 10 mpg hi-way was not going to do. The Holley 2bbl on top was shot. When I first started the car up, it would burn your eyes out. (Eeek, cough, gag.)
A trip to the junk yard offered up a '79 4bbl. intake for $20. Another $20 in a hot tank, beed plasting and a can of paint had it looking good.
Ordered up a 625 Carter. The 2bbl. linkage was given a nut and bolt to adjust for proper tranny workings. Later on, a swap meet '73-340 aircleaner with rear base trap door was added. $40.
The exhaust gave out shortly thereafter and duals were added. Under $300 with "H" pipe. Then a MSD set up.
After all was said and done, I was rewarded with 20 mpg, on any given day. Performance was good. The hwy. gears wouldn't let me get up and go quick, but that was OK to.