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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. |
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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.
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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. |
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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.
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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. Sent from my SM-N950U using Tapatalk |
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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 |
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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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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! |
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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. |
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Didn't read through it all but an 066 cam would t take a 4 barrel... it's punchy with half throttle but if u dump it it will drown.. personal experience..
At 18 I pulled a 68 2 Catalina motor dropped it in a firebird and added a 4 barrel intake and carb... total fail.. |
Been there, done that
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I had a '67 wagon as my first car back in 1974 and did the same as you are doing. Q-jet, 4 barrel stock intake and dual exhaust. New timing gears and chain. Shift kit in the trans and spring kit in the distributor. Ran better but the 2.56 rear gear really held it back. It would go to 60 mph in 1st and 100 in 2nd gear. Stop watch 0-60 in 9 seconds. I was looking to swap the rear axle assembly to one with a 2.93 or 3.08 gear setup, but I was rear-ended at a traffic light and the car was totaled.
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Scott, I think that it was your lack of experience / knowledge at age 18 that made your 2bbl to 4 bbl adventure a flop, especially if it was Q-Jet swap over you did!
If nothing else assuming having in the ball park jetting conditions and having full throttle available the car should have had better drivability at low speed and at least 10 to 12 more hp. I know that would have been the case for me! |
Here are some dyno runs on a couple different intakes.....
https://m.youtube.com/watch?v=9AfeMtpi5pc In one of the videos he tested a Pontiac 2bbl intake as well...... |
Start with the gears, it'll make a huge impact.
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I used to own a 67 Catalina 2 door Sport Coupe with a 325 HP 400. It had a Carter AFB and dual exhausts with a 2.41 rear. The turbo 400 trans would shift out of 2nd gear at 90 mph. I learned 35 years after I sold it that Pontiac only made 1300 of that model.
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The 2GC was pulling 7” vacuum at WOT!! That’s enough to start kicking in the vacuum advance. If you already have the set up I see no reason not to throw the Q-jet and intake on. It’ll only cost $25 in gaskets and a few hours of your time. You’ll get more power AND better MPG’s when cruising. |
Those Holder videos are informative, and I like them, but man why do so many of these guys doing these videos have to so over animated!
Gez, it’s like he drank a 6 pack of Red Bull 20 minutes before the video shoot! I mean I like that he talks fast enough to get a lot of detail into the video, but to use a automotive term please throttle it back a little will ya!? |
Track73, not only low numbers with the the AFB carb for that year, but those 400s still used the 389/421 type heads also!
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Gez, it’s like he drank a 6 pack of Red Bull 20 minutes before the video shoot! People that know him say that’s just his natural personality. Certainly is enthusiastic about his work. |
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I could gain 9 HP with a sharp tune up, bringing the timing in sooner than stock, and richening up the carb and still run pump gas. I would guess that there is something fundamentally wrong with the OPs engine for it to be such a slug, I worked in a Pontiac dealership in 1970, those cars weren't as slow as he's describing his to be. I have seen some Pontiacs that someone changed the timing gears, and chain, that were 1 tooth retarded, and run like he's describing. They'll run smooth, but have no low end power whatsoever. Reset the timing gears, and it runs like a different car. Cutting dishes in pistons is pretty expensive when you can go with a larger CC combustion chamber, and run the stock short block with flat top pistons, but I tend to be practical, and try to save money, especially when it's my money. I've used Pontiacs from 326 to 455 in daily drivers, used them in Jeep Wagoneers and Jeep tow trucks, plus raced them on oval tracks for years, they aren't slow unless there is something wrong with the internal engine components, or the tune up is way way off. Almost all of my vehicles that were driven on the road would run on pump gas, and were under 9.5 compression ratio. A few of my GTOs were factory rated at 10.5 to 1, and the race car was 12 to 1. I got a lot of work done with relatively low compression Pontiac engines over the last 50 years. All had iron heads. |
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A very smart guy with boost. Tom V. |
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I grew up with a 66 Catalina station wagon. 3 on the tree, manual brakes. It had a 10-1 389 in it and my dad went to the junkyard and put a AFB intake and carb on the old girl that got us from CA to Oklahoma twice.
It ran great, got 20 mpg on trips. Still have the intake and carb. I have 2 AFB intakes, one is flat and one is more of a high rise. |
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ALL Horsepower is calculated, even at the dyno, its Never measured. You have a nice car, hate to see it get into "mission creep" and not enjoyed.. |
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Actually it is, and today's OEMs do. Modern engines use much higher compression ratios, enabled by direct injection. The higher SCR increases efficiency even at part throttle, thus increasing fuel economy (in addition to increasing torque under wide open throttle). They can get away with these compression ratios due to the charge cooling as the fuel is injected directly into the combustion chamber (especially with multiple injection strategy at under medium loads and low-mid rpm). This then allows them to downsize the engine displacement (if desired) to further improve fuel economy. This is why OEMs use DI even on small economy cars, not just performance vehicles. |
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I should have said, one of the reasons. The other of course, being emissions (with the exception of particulate emissions, which is actually higher than port fuel). |
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I had a '65 Lemans w. 326 2bbl and single exhaust as a kid. A dual exhaust was a big upgrade in performance. I then added a 4 bbl intake and Carter AFB which also made it even better with no other changes. I was amazed at the transformation which included basic, quality tune up parts. It was a 3 spd w. Hurst linkage and would chirp the tires in 2nd and 3rd with ease. If you're up to a cam swap, a Summit 2801 kit with lifters and springs and a new timing set will give a nice performance return on investment. The 670 heads aren't needed for what is just a nice torquey cruiser. The rear gears would be a better investment than the heads if you had to make a choice.
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Would be interesting if ANYBODY started Dyno mapping at 1500 instead of 3K . My Point is that some things were designed well, and do the job.. well.... |
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It's a bit complicated, but I'll try to simplify. The GENIII passenger vehicles (Corvette, Firebird, etc.) were in the low-mid 10s with aluminum block/heads premium. The small engine trucks 4.8/5.3 were mid-9s, the exception was the 5.3L HO which used an aluminum block and 9.9:1. The 6.0 LQ4 was only 9:1 but was meant for HD trucks that weighed more and would be used for heavier loads and 87 octane. There was a 6.0L LQ9 which was a 10:1 variant of the LQ4 but was used in Escalades and required premium. The GENIV LS (debuting with the LS2) were still PFI, and saw a bump in compression with passenger cars adding about 1/2 point. For the GENIV trucks, the iron blocks (and some aluminum) were typically 9.5:1, but often had VVT which bumped up the dynamic compression below 3500rpm. Some larger aluminum blocks (like the L92) were as high as 10.5:1 but recommended premium. With the GENV having DI, compression even with VVT, is typically 11:1 on trucks, and higher for passenger cars (but with premium recommended). And we haven't even talked about Super Charged cars, but the LT4 runs 10:1 with 9.4 lbs of boost. |
One can’t talk about modern engine specs as a reference to old car building without realizing the fast and powerful computers running them. ;)
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I killed a perfectly good 389 at age 16 when I rebuilt the carb.
The rebuild of my first carb went 100% fine, but then I found that I could get a bunch more idle rpm if a adjusted out the big center screw on the face of the AFB carb. This I came to find was the idle air adjustment. I left it that way and the motor ran so lean that the resulting detonation cracked two pistons! So much for the knowledge of a fledgling 16 year old hot rodder! |
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