That will be a nice upgrade. I have owned a few Catalinas with the 2 barrel carbs, but when I upgraded to dual exhaust I always upgraded to a 4 barrel manifold and carb. If it turns out you feel a problem, you can change the jets rather easily, with a sacrifice on gas mileage.
The 350 2bbl engine wasnt offered with dual exhaust as an option. Not sure why as the 350 4bbl engine did have duals as an option and both had the same exhaust manifolds so the systems would interchange. Given the restrictive size of the two barrel carb Venturi you might have no gain whatsoever by adding duals. I cant imagine any negative other than a slight loss in low rpm torque.
When I bought my 66 in May 2016 it had a real nice dual system with an H pipe on the 283. Ran fine, sounds great, never noticed an issue with it. I wouldn't be shy at all to run duals with a 2 barrel.
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1966 Strato Chief 2 door, 427 4 speed, 45,000 original miles
1966 Grande Parisienne, 396 1 of 23 factory air cars
A dual system will be loafing until you put your foot into it anyway. Reducing pumping losses (back pressure) increases efficiency. If you are as worried about noise as the GM engineers then you could run resonators with the duals like the factory did (if you can find them anymore).
Flipping the lid, great idea as your Parisienne is a prime candidate for such a shad tree modification. Just don't eat the decal.
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67 Chevelle Malibu Sport Coupe, Oshawa-built 250 PG never disturbed.
In garage, 296 cid inline six & TH350...
Cam, Toronto.
I don't judge a man by how far he's fallen, but by how far back he bounces - Patton
But he says the holes are worn in the casting. I'm with him, buy an assembly line rebuilt or else swap a 4 barrel onto, in which case I'd either buy a known working Quadrajet or else again, an assembly line rebuilt one.
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1966 Strato Chief 2 door, 427 4 speed, 45,000 original miles
1966 Grande Parisienne, 396 1 of 23 factory air cars
Somebody must have a decent 69 2 jet sitting around for Randy? Even a better baseplate? I bet Carburetor Rebuilders in TO could bring that one back by bushing the shaft.
What you will notice Randy is your gas mileage on the highway will go up significantly with the duals compared to the dorky pipe. Did you do a crossover?
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65 Laurentian post, 67 Grande Parisienne 4 door HT.
Somebody must have a decent 69 2 jet sitting around for Randy? Even a better baseplate? I bet Carburetor Rebuilders in TO could bring that one back by bushing the shaft.
What you will notice Randy is your gas mileage on the highway will go up significantly with the duals compared to the dorky pipe. Did you do a crossover?
Thanks Mark, I will look into them.
I left the piping up to a guy who has been doing this for a long time.
He asked me a few questions about what I was looking for and I trusted him do what he does best.
Very close to what a 1970 dual system would be like.
He has done 1969 styles before where the pipes wrap behind the wheels.
He even called me midway through the work, to make sure he had things right.
The funny part is that the guy with the 1968, 427 Impala in front of me, seemed to talk down to him.
I bet he gets that a lot.
When all is said in done, he knocked off $50 from the quote.
Hi Randy I have my 2 barrel off my 69 I don't think I need ? it ran very good with it just wanted more get up and go ! new ones are not expensive.but if you want a 69 one I understand that.message me and I am sure we can work it out Thanks..
-- Edited by Bill shuba on Monday 12th of August 2019 07:14:29 PM
Consider running an open element air cleaner when daily, switch back to the stock when show. With the new duals you'll gain a wee bit of mileage and power.
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65 Laurentian post, 67 Grande Parisienne 4 door HT.
I'm glad you saw no due cause to change to 4bbl; GM put alot of time into these drivetrains, and although a 2bbl doesn't seem as macho as a 4bbl, some people don't realize that some of the GM 2bbl carbs are monstrous compared to the primary side of a Quadrajet!
Although it was typical for GM to match single exhaust to 2bbl drivetrains, if you do some digging, you will find that there are exceptions; Often the 2bll/singe exhaust drivetrain had a slightly lower hp rating than the 2bbl/dual exhaust; often the exhaust is the restriction... The '73 Firebird Formula I owned was a 350/2bbl-dual exhaust; The same year optional on the base model, and std on the Esprit model was the same engine mated to a single exhaust gains twenty-five horsepower!?
As you found out, 2bbl stuff is out there, and by sticking to correct/replacement parts, you're keeping your headache level low.
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1970 Formula 400 Carousel Red on black (std) interior "no drivetrain option" car (same base drivetrain as GTO) 1:411 1970 Firebird Formulas originally sold in Canada
My experience is that the 2bbl carb works better than the Qjet on cars with tall gearing (2.73 in yours probably) in terms of normal driving, better response, smoother toe in. What you lose is of course WOT power. It's a matter of priorities. The 69 fullsize single exhaust had no resonator and a single outlet on the drivers side behind the wheel. The dual system had two resonators and two mufflers and exited under the bumper in back outboard of the frame rails.
-- Edited by North on Monday 7th of October 2019 11:40:08 AM
First off let me say, I'm generally a guy who stays with the factory equipment. The biggest exception for me is dual exhaust vs single. I've always believed it increases HP by 8 - 10. That was all I did when I have my 66 Laurentian. Now with my 62, which also has a 283, I went to the 4BBL, again looking for that extra 8 - 10 HP but most importantly for the smaller primary jet size you mentioned when compared to the 2 BBL. For this reason, the 4 BBL should give slightly better gas mileage when cruising, compared to the 2 BBL but it will be there when I want to put my foot into it and sacrifice economy over power.
Interesting! I remember some guys always thought some the engines, especially from the 70's, were choked off from developing their full power. That kind of power by simply changing exhaust seems excessive across the board. When I get mine on the road I had planned to dyno it with single and dual exhaust, even contemplating putting the 2 BBL back on vs the 4BBL. That might be too costly but we'll see, my curiosity is always peaked. I did check the site you provided for my '62, 283 but didn't see any reference to dual exhaust. Engines are basically air pumps, the more efficient you can make it at hauling air in and pushing it out the better it will perform, so it stands to reason the dual exhaust would add HP.
I actually did a test about 15 years ago with a bonestock pontiac 350 2bbl (in a 71 LeMans I believe). We ran it on a chassis dyno with a factory spec single exhaust (2" head pipe, single stock muffler and 2.25" tailpipe) and it put 145 horse to the wheels. Then we installed a factory correct dual exhaust (2" front to back with stock mufflers and resonators). HP rose to 157 with no other changes made. Btw, flipping the factory air cleaner lid added another 4 horses
I would imagine a 4bbl engine would benefit more than a 2 bbl since peak hp was at higher rpm where increased flow capacity of duals would be more beneficial. Most GM 4 bbl engines in the early 70's were rated as gaining 25 horse net with duals and most 2 bbl's gained 15 net horses. Mine only gaining 12 makes sense since I was measuring hp at the wheel.
Don't forget that net horsepower is still measured at the flywheel.
SAE Gross horsepower (SAE J1995)... stock engine without exhaust pipes, alternator, emission pumps, water pump, air cleaner etc. Some car companies used open headers during test, others used stock manifolds. Power was measured at flywheel
SAE Net Horsepower (SAE J1349)... stock engine with Air cleaner, exhaust system, water pump, alternator, emission pumps. However it does not consider things like power steering pumps or other optional draws. Power also measured at flywheel. The drop from gross to net hp was typically about 15-20% on vintage cars with dual exhaust and 30-35% with single exhaust
Drivewheel horsepower (no specific standard) is typically measured in a car fully equipped as in the net horsepower above but measured at the wheel after transmission, driveshaft and differential losses. Typically this also means things like Power steering and AC (turned off) compressordrag is also lost. typically the drop in vintage cars from SAE net is about 10-15% for manual transmissions and 15-20% with automatics.
