4BBL setup on a 2BBL 400
 

I have a '67 Full size Safari with the base 400 2BBL auto and a 2.41 posi rear end. I have a 4BBL intake and Quadrajet that I want to install. Eventually I will do a cam swap and exhaust upgrade. I also have a 3.42 posi rear end to swap in. My question is what can I expect to gain if I start with the intake and carb first? Will it be too much for the factory U code cam? Just to be clear my goal isn't to make a hot rod out of it. I just want to wake it up a bit.
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The Quadrajet won’t be too much for it, it will only give the engine as much airflow as it asks for.

You might have a little more top end power but maybe so little that it won’t really be noticeable until you at least have a dual exhaust.

I really wouldn’t bother with the intake and carb upgrade until you do the cam, exhaust and gear swap.

Thanks b man! I was kinda thinking along the same lines that I probably shouldn't bother now and do it all at once. It does currently have dual exhaust. My plan there is to add HO manifolds and 2.5" pipe. Currently 2.25". I havent picked out a cam as of yet. I'll probably go with a RV type cam that makes power down low to get this big beast moving.

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If there’s something you had to start with first due to budget I would go with the rear gears .

I say this with the back up from Jim Taylor who with a 421 tripower build in HPP a number of years ago proved that you can make 350 Hp running on just the center 2bbl.

What b-man said. But, how are you with the current performance? I was getting 15-16 mpg at 65 mph in my '67 GTO with a TH400 and a 3.36 rear gear. When I changed to a 2.56 posi 12 or so years ago, the numbers went to 21 mpg at 75-80 mph. The car now sips gas, keeps up with the Hondas, and runs cool. Since it's a road-tripper and cruiser, I would NEVER think of installing a 3.36-3.55 gear in it again. Just saying....with regular gas at $5.49 a gallon where I am, I'll take the extra 6 or 7 mpg's and 15 mph all day long.

https://m.youtube.com/watch?v=Nrgx5LA6TQI
Check out this video Richard Holdener just posted on a 2GC vs 4 barrel dyno test on a stockish 400 that showed a huge gain.
His engine has 62 big valve heads and 1-5/8” headers. Cam was unknown but had smooth stock type idle.

One other advantage to swapping the Q Jet is that the primary side of the carb is more efficient at fuel atomization than the 2 bbl is. The intake manifold is also more efficient as it has more height.

I've swapped plenty of 2 bbl Pontiacs for a 4bbl without a cam change, and they respond to the better intake tract.

Yes you'll get more out of the combination with all the attendant other parts, but Pontiac made thousands of cars with 4 bbl intakes, single exhaust and log manifolds over the years. The 3.42 axle is going to drastically alter your fuel mileage, but if you're fine with that reduction, that's fine.

It all depends what you want as an end result as to how you modify your car.

In reality if your starting off with a poor 2.41 gear with a very heavy car like a wagon if you don’t develop a lead foot with your new rear gearing fuel usage only goes up slightly.

It's a turd LOL! Granted it weighs 4500 lbs but if i were to guess 0-60 about 10 seconds. Mashing the go pedal at speed and it downshifts it basically just makes a lot of noise lol. Not worried too much about mileage. It's not a daily. I've never tried calculating the mileage but I know it isnt great.
My '67 4 spd GTO had a 3.08 when I bought it. Eventually I put a 3.55 in it. Great gear! I'm currently running a 5 spd Tremec TKO-600 and 3.73 12 bolt. With this setup just cruising the GTO gets around 15 mpg. The engine is mildly built making about 475 hp.

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Do you have a link?

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I have a real world test with a 2GC 2-bbl swap to a Q-jet, but on a mild 455 instead, and it is true, that you'll make more power with the 4-bbl induction. The difference in power on this 455 isn't as drastic as Richard's test, but eye-opening all the same. The 455 was a 1970 YH code out of a Bonneville, the standard 360 hp rated engine with the small valve heads with 9.95 to 1 compression which were stock (no porting), a Summit 2802 cam (224/234/114 @ .466"/.488" lift), stock log exhaust manifolds.

The 2GC made 323 hp @ 4500 rpm and 472 lb-ft torque @ 3100 rpm, while the Q-jet made 390 hp @ 4600 rpm and 512 lb-ft torque @ 3400 rpm. So, a 67 hp gain and 40 lb-ft torque gain pretty much throughout the rpm range of the pulls. You are definitely leaving power on the table all things equal...on the dyno. Those 2.41 gears won't let you use that power gain effectively until higher rpm, but you'll feel the difference. Adding a better cam, like a Summit 2802 with 9.5 compression, long branch exhaust manifolds, 2.5" exhaust system, 3.42 gears, along with the Q-jet & iron intake will net you 75 to 100 more hp over your current stock hi-compression 2-bbl engine.

Really nice wagon you have there, btw...

Dennis

It’s there, just click on it

I also forgot to mention the heads are small valve 8.6:1 c.r. I do have a set of 670 heads which are big valve 10 5:1 c.r. Using the formulas i found it appears that swapping to these heads should bring the static c.r. up into the mid 9 range with the dished factory pistons.

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TCSGTO, I've tried clicking on your post unfortunately I found no link.[emoji848]

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Since you have to pull the intake to do the cam might as well do that all at once.

Gears will even wake up the 2BBL!

Still nothing however I found him. He posts to YouTube?

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I know what you mean. Do it once! Honestly though removing the intake isn't really a big deal. I'll probably put the 4BBL setup on it and do the gear swap for starters.

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Sounds like a plan.

One other question, how many miles on the original engine? That originally came with a nylon timing gear in it, and if it is still in there the cam timing may be way off of spec. Retarding cam timing kills low end, so it may be sluggish because of worn timing components. Or you may have cam lobes going away, one or two nearly flat cam lobes pretty much kill power.

For sake of comparison I had a 68, 400 4 bbl Bonneville with the same gearing, got over 17 MPG on a trip, and would burn the single wheel as long as you wanted to hold your foot into it. Stock cam, and single exhaust.

I wouldn't go with 670 heads with the closed chambers, they have a tendency to detonate when running pump gas. If it were me I'd say with the lower compression heads with small valves. You're never going to be in the RPM range to make good use of larger valves anyway. The 389s used the small valves in them for many years in GTOs and most 4bbl engines previous to 1967. Unless you're building this car to be a street racer no need to build the engine like a drag engine is built, on the street you won't have much occasion to get in the 5000 RPM range very much.

Freeing up the exhaust, optimizing the timing curve, richening the jets up a few sizes, and mostly factory parts should get you some stump pulling torque to pull that heavy barge around.

I used a 1973 400 2 bbl engine with a 067 camshaft, and swapped to a Q jet and factory intake to pull around a 5800 lb Jeep truck. Low compression and small valve heads had more than enough power. Before I put the 400 in, I had a 350 Pontiac engine in it but broke a piston, and ended up swapping to the 400, because I had it already to go. Optimizing what you already have should be plenty to move that wagon around at a satisfactory pace.

I almost forgot, I had 2 of the 71-76 clamshell tailgate wagons with 455s in them, low compression, and I wasn't ashamed of how either of those wagons ran. I just optimized the stock parts on both of them, they are much heavier than a 67 wagon is by about 800 lbs, they weighed 5300 lbs.

Pontiac engineers excelled at making low RPM torque to pull their rather heavy cars around, and still keep the RPM down to get at least decent fuel mileage. Wagons have a higher percentage of rear wheel weight by the body construction, so if it won't spin the rear wheels, that's because you have more weight over them than a coupe has, figure accordingly.