1967 Skylark upgrade from 2 bbl to 4 bbl

Hi, I'm brand new to the forum and am looking for insight on these Buicks. I bought a 1967 Buick Skylark convertible 4 years ago and haven't done much with it. I got lucky and the previous owner (of 33 years) had rebuilt the engine recently, and done a lot of upgrades over the years. It has the 300 motor with a 2 bbl set up. I found a 4 bbl manifold for a reasonable price and snagged it for future use. I'm thinking about upgrading in the near future and welcome suggestions. What kind of carb should I be looking for? A neighbor that has a couple classic Chevys and literally rebuilt his race motor over a four day weekend suggested I upgrade the cam shaft to go along with the 4 bbl upgrade. Again, any thoughts or suggestions are very welcome. Thanks in advance.
 
Did you get the iron or aluminum 4 barrel? The aluminum one from 64 has smaller intake ports then the iron heads on your 67. It is actually restrictive comparatively. The original 4 barrel carb for the 300 was a Carter AFB (3826S) that flowed about 500 CFM. They are no longer made, but some remans are available (Rock Auto). Edelbrock makes an AFB (1406) that is 600 CFM and would work well with a 300. They also make a AVS that is 650 cfm that would work for you. You might want to look for one used or re-manufactured for the best deal. Elelbrock does re-manufacture their own carbs. Be prepared to deal with linkage and air cleaner changes as well. Only the Carter is a direct replacement.

Bigger cams generally make more power, but it is usually higher up in the RPM range at the cost of low end power. Without head porting, headers, more compression (67 300 was 9:1), better gearing, a higher converter stall and dual exhaust, you may not be able to take advantage of a larger cams power in the higher RPMs. It's all in the combination. A slight performance cam with a wide lobe separation and minimal duration and lift increases over stock will give you better performance throughout the RPM range with little low end sacrifice. A more aggressive cam would require all the changes listed above and would have poor road manners. Just don't let your neighbor talk you into too large of a cam!
 
Thanks for the detailed response Doc! I got the cast iron manifold to go with the cast iron heads. I'd been told they were hard to come by and expensive if you could find one. I found a gentleman that uses these engines in Triumphs or something. He wasn't interested in the manifold but had a good idea of the value. I grabbed it for a reasonable price I think. I realize this is not, nor will ever be a GS 400, but I'd like to get more out of the motor.

Falling on my sword here. I'm not familiar with the AFB, AVS references. I'm mechanical, but no mechanic. Still somewhat sweating the thermostat I'm replacing when the hoses come in.

I like the info regarding the cam also. I looked online but with roughly a bazillion options, I got lost. I read somewhere that the 300's have a fairly robust cam already as well. I'd like the move toward the slight performance cam with wide lobe separation option because I don't want to or have the ability at this time to do the required work for the other options. I'd appreciate it if you could point me in that direction with a little more focus as well. No worries about the neighbor pushing me in any direction. He's a great GM guy that races a 70's era love weekly, but he's the one that suggested I join a forum specific to Buicks. I do like to gather information without reinventing any wheels for sure.

Thanks again for the great info and any future response,

Eric
 
Eric, It is good you snagged the iron manifold for your 300. The 64 and 65 original equipment 4 barrel were the only performance manifolds ever made for the 300. There is a way to get a Rover manifold to fit with specialty spacers. AFB is simply aluminum four barrel. These were a square bore carb that fits the 300 manifold. There were larger and smaller square bore AFB bases depending on make and engine size. Make sure the model you purchase fits your bolt pattern and the butterflies do not hit the manifold when opened. AVS is adjustable valve secondary. This was an improvement in the ease of tuning the secondaries over the AFB. Either can be tuned to your car, but the AVS makes it a little easier.

Crower has a few grind for your engine as listed here. You can look at their descriptions as a whole on that page or look further into them individually. I liked the 50227 and 50229 for you. Click on them for specs. The e 50227 is pretty much for where you are at now with better low end torque and better throttle response. The 50229 will be usable currently, but will give you some room to grow into in the future. With a few more upgrades, it will extend your RPM and provide more low and mid-range power. The next one up, 50231 would require major changes to the engine and combination to get all of the power out of it. You can also look at Comp or Howard cams. TA performance has some 300 grinds and they are always very helpful in getting you on the right path. Comp is helpful, as well, if you talk to them. Once you have a few you think are interesting, give the tech line a call to go over it in your combination.

HTH - Steve
 
Last edited:
I would not be changing cams without knowing EXACTLY the particulars of the engine rebuild. The biggest mistake people make is over camming an engine, and the smaller the engine, the easier that is to do. The actual (not claimed) static compression plays into camshaft choices.


If you are sweating a thermostat and hose replacement, leave the cam shaft alone, especially if the engine runs well as is. It may already have a different cam if it has been rebuilt. You are way better off making the traditional improvements to exhaust and ignition timing. The 4bbl intake can be a big improvement combined with timing and exhaust. Definitely use the AVS, it will be easier to tune the secondaries.
 
Steve, sorry for the late response. Thanks for the good info. I have a lot to research and think about. I really appreciate the exact options you provided. "Crower has a few grind for your engine as listed here. You can look at their descriptions as a whole on that page or look further into them individually. I liked the 50227 and 50229 for you."

I'm glad I grabbed the manifold also, I felt like it was reasonable deal and I know I'd like to upgrade. Plus, I heard they were extremely rare at this point.

Larry, Good intel on not knowing the exact particulars of the rebuild. I hadn't thought about that. I may have oversold my sweating the thermostat, just humbly stating that I have a lot to learn. I have great resources such as my neighbor mentioned above for any general engine rebuild/repair concerns. I wanted to reach out to the Buick experts such as yourselves for specific Buick questions.

Thanks again Gents!

Eric
 
Eric, We have the 67 Chassis Service Manual here on this site. It has an extensive section (60-1) on the 300 and 340 engine with detailed specifications, operational descriptions, disassembly procedures, evaluative procedures and assembly procedures. I have a greasy hard copy that was a bible to this 17-18 year old 40 years ago and I still find it useful today. It is hard to go wrong if you read it carefully and follow the procedural sequences.

Steve


Manuals.jpg
 
I'm finally taking on the manifold and carb replacement. I've elected to not change the cam at this time. I ordered the "Auto line" C609 (#3826S CHAFB) Carter 4 barrel reman carburetor, carb gasket, and manifold gasket. I'm wondering if I will run into issues with the throttle linkage switching from 2 to 4 barrel. Any thoughts? Thank you.
 
I'm new as of today to the forum. I know this is an old post but I'm in the exact same position. Ant update on how it went or other information. Thanks Joe
 
Back
Top