2 barrel question

ABC123 · Uber Guru

2 barrel question

gtodrive · Guru

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.

Bill shuba · Guru

My 69 had a 2 barrel and dual exhaust when I got it and ran great..went to a 4 barrel and hei after..just cuz a upgrade I guess

North · Guru

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.

ABC123 · Uber Guru

Thanks guys

"Dorky little pipe" is a quote from a member in fun.

I'm not really looking for a performance improvement but I have been warned about it leaning out the carb.

My single muffler is failing (actually cracking) so I decided to full system of all welded 2 inch with a small sound increase.

To my knowledge, my motor has never been touched other then a carb rebuild so for now,

The two barrel stays,

Maybe I will flip the lid on the breather L.O.L.

4SPEED427 · A Poncho Legend!

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.

CdnGMfan · Canadian Poncho Superstar!

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.

ABC123 · Uber Guru

The car sounds great !

Tommy's Custom Exhaust did a great job bending everything to look close to factory.

Factory on a 1970 Canadian Pontiac that is biggrin

The 350 seems to enjoy freedom from the single system.

I flipped the breather lid for more airflow, just to see if it ran better.

No noticeable difference.

Tips are Canadian Tire cheapies.

Forgive me Tommy !

ABC123 · Uber Guru

OK, now I have put my foot in my mouth,

The 2 barrel that I had rebuilt in 2017 just fell apart on the inside.

When you step on the gas, the throttle would stick and crunch 1/2 way.

After giving it a good look, I noticed that the arms for the choke and main butterflies were very sloppy.

Even the pumper arm hole is warn.

At that point I decided to do an autopsy since the arm casting holes are worn and not worth fixing.

This thing ran very well for sucking all that extra air.

The pumper assembly completely fell apart inside

Should look like this;

Image result for rochester 2 barrel pump assembly

This may be a sign from above !

May the 4 barrel be with me ?

Summit has a US made remanufactured 2 barrel.

I will sleep on this one.

seventy2plus2 · Canadian Poncho Superstar!

Rebuild yours. A carb kit should be pretty easy to source.

4SPEED427 · A Poncho Legend!

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.

cdnpont · Canadian Poncho Superstar!

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?

ABC123 · Uber Guru

cdnpont wrote:
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.

Todd knows what I did with that $50.00 wink

Canadian Poncho · A Poncho Legend!

Thanks Randy!

Bill shuba · Guru

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

ABC123 · Uber Guru

I ordered, UREMCO Remanufactured Carburetor 3-3214 from Summit Racing.

"United Remanufacturing Co. has over 60 years of experience in carburetor rebuilding.

As fuel system rebuilders with expertise and stringent standards, they ensure you the best quality at the best price.

They rebuild carburetors from most all automobile and truck manufacturers, and each one is,

individually inspected and rigorously tested on flow-bench engine simulators by seasoned and knowledgeable employees."

They told me "in stock" then "Back ordered until Sept 9th" but it then shows up Monday.

Today I got up early, before anyone had ideas of what I was to do with my day off.

An exact match.

Installed in no time.

It came with the factory correct fuel filter but I stuck with the in-line system.

I can not believe how well this car runs now !

Took it for a cruise and it's a totally different car.

As they state, each carb has been pretested.

My car fired right up and no adjustments are needed.

Not a real rocket, just a solid, smooth running machine.

The only tough decision I have now is whether or not to send the old one back for a $45.00 US core refund.

-- Edited by ABC123 on Wednesday 21st of August 2019 03:54:38 PM

cdnpont · Canadian Poncho Superstar!

Glad it worked out for you Randy.

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.

Bill shuba · Guru

Very glad it all worked out great for you Randy !!

unruhjonny · Guru

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!?

Look here for the specs page.

As you found out, 2bbl stuff is out there, and by sticking to correct/replacement parts, you're keeping your headache level low.

North · Guru

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 2017-03-14 090.JPG . 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

ABC123 · Uber Guru

Thanks North

Last week I was under the hood of a 1969 2 Barrel 2+2

The intake was more of a high rise style intake.

Mine is not.

To me it more like a truck intake or was a high rise intake used on a 2+2 ?

Glenn Musgrave · Addicted!

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.

73SC · A Poncho Legend!

This link has some engine specification data published by Pontiac.

http://www.oldcarbrochures.com/static/Canada/Pontiac/1972%20Pontiac%20Full%20Size%20Brochure/image13.html

There is one 2bbl engine shown that has both single and dual exhaust HP ratings.

You will see that Pontiac list the engine at 185 HP @ 4000 rpm with single exhaust then at 200 HP @4000 rpm with dual exhaust.

The difference is 20 HP or a gain of 11%.

Glenn Musgrave · Addicted!

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.

North · Guru

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.