2 to 4 bbl and exhaust upgrade questions

pennst8er

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Hey All, I am brand new to this site. I am purchasing a 1966 Delta 88 that has a 425 but has a 2bbl carburetor and single exhaust.

I read a 2020 thread about the Thornton exhaust manifolds for dual exhaust so will be purchasing those. One question that I have for exhaust is: should I go with 2.25 or 2.5 inch exhaust and why?

Also, I am thinking of changing the 2bbl carburetor/intake to a 4bbl. I would like to make it look stock but finding a stock 4bbl intake may be difficult. What do you suggest? Should I do the upgrade to 4bbl? If so, what all is needed besides the carb and intake and what are the best choices for those two items? Also, forgive my ignorance but will the air cleaner assembly from the 2bbl fit on a 4bbl (I am thinking not but here's hoping)?

Thank you in advance!
 

Olds 307 and 403

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Use 2.5" pipe if the exhaust shop can fit it. The Performer intake is taller but is also much better than stock and way lighter. You will need a different air cleaner. I actually made my own dual snorkel air cleaner with a 307 4bbl and added the snorkel off a 2bbl 260. Ironically the two different sized scoops looked exactly like what Olds did on certain years. A new Street Demon 750, custom tuned 800 cfm Qjet or a 750 cfm Quickfuel carb would all work well when tuned to your motor. Good luck.
 

pennst8er

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Oct 26, 2021
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Use 2.5" pipe if the exhaust shop can fit it. The Performer intake is taller but is also much better than stock and way lighter. You will need a different air cleaner. I actually made my own dual snorkel air cleaner with a 307 4bbl and added the snorkel off a 2bbl 260. Ironically the two different sized scoops looked exactly like what Olds did on certain years. A new Street Demon 750, custom tuned 800 cfm Qjet or a 750 cfm Quickfuel carb would all work well when tuned to your motor. Good luck.
Thank you for your answer. So the 2bbl air cleaner will not work on either of those carbs? Also, will I need a different linkage?
 

Olds 307 and 403

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The air cleaner won't work without a 5 1/8" holesaw😉. The bracket itself should work but the cable might not be the right length. Someone put a 260 in my 70 Cutlass that had a Dualjet vs the factory Quadrajet carb, original cable and linkage worked. But there linkage is more similar between than the 2GC and Quadrajet. Are you planning on a Qjet carb?
 

pennst8er

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The air cleaner won't work without a 5 1/8" holesaw😉. The bracket itself should work but the cable might not be the right length. Someone put a 260 in my 70 Cutlass that had a Dualjet vs the factory Quadrajet carb, original cable and linkage worked. But there linkage is more similar between than the 2GC and Quadrajet. Are you planning on a Qjet carb?
Yes, I plan on using a Qjet carb. Maybe I can find a 4bb air cleaner assembly somewhere (I know, good luck with that lol).
 

Olds 307 and 403

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There are usually some for sale on Ebay. Also check out parts for sale on the Classic Oldsmobile site.
 
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Olds 307 and 403

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'66 was still solid steel throttle linkage, with the electric kickdown and switch pitch convertor switch.
Is it the same from 2 to 4 barrel, will be the question, hopefully it is.
 

Olds 307 and 403

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Make sure you eat your wheaties or use an engine hoist to that 75 pound intake. Pulling an iron SBO intake was bad enough.
 

pennst8er

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Yes, I am in my 60s so may have to use a hoist. As much as I would like to keep this stock, I would really like to find an aluminum 4bbl intake but I have read on other posts on this site that state that there are no currently manufactured aluminum intakes for a 425 engine that is low enough for the air cleaner assembly to not hit the OEM hood. I just missed out on an Offenhauser intake on eBay. If anyone knows of one or has one that they would like to sell, please let me know.

Thanks in advance!
 

pennst8er

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You can buy them on Summit.com. The 400, 425, & 455 are all the same intake.
I saw that Edelbrock makes one. Is that the one that you suggest? They are out of stock on that one right now but if there is another one that you think is better, I would greatly appreciate your advice. Thank you in advance.
 

Olds 307 and 403

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The Performer is the best for a street car. It is definitely taller than a stock intake, doesn't have provisions for a hot air choke but will fit a Qjet.