A question about the 140 carbs and other 140 topics.

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Vamisk
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A question about the 140 carbs and other 140 topics.

Unread post by Vamisk » Wed Sep 13, 2017 12:05 pm

So when i bought my corvair i also got a van load of parts, including parts for a potential 140 head swap. I have a bunch of 140 parts including the sheetmetal above the fan and the distributor, i just need the heads.

My first question is about the carbs. I recieved a box of about 4 rochesters. All need rebuilt. Were the other two carbs on a 140 the same casting as like the ones on my 110? I know that they are supposed to serve as secondaries but were they just jetted richer?

I've heard that the 140 is kind of a dog down low and that the primary reason was that the intake valve is a bit too big for what the engine is doing.
Assuming i had all the money in the world but wanted to save a buck and get the best of the 110 and the 140, is it more efficient to try and open up the exhaust valve on a 110 head or try (is it even possible) to shrink the intake valve on the 140 head? Further, can a specific cam grind compensate for the intake on a 140?

I'm going to need to rebuild the engine sometime within the next two years if finances allow. I'm already chucking oil out of the driver's side bank. If i was going to rebuild it i would want to make it better then what it is now.
Thanks for your time.
1961 110hp Monza coupe

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bbodie52
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Re: A question about the 140 carbs and other 140 topics.

Unread post by bbodie52 » Wed Sep 13, 2017 1:09 pm

The attached DELCO ROCHESTER - Models H, HV Carburetor Service Manual contains a thorough description of the Corvair carburetors and the various functions. You will find a description of the 4×1 140 hp carburetor set up on page 12. The second attachment includes an illustrated description of the throttle linkage system. The third attachment includes details of the fuel line arrangement and other components. The fourth attachment is a section of the 1965 Corvair Chassis Shop Manual that describes the Rochester carburetors in detail. Page 6M-8 specifically addresses the Rochester H carburetors that were configured for use on the 4×1 setup as secondary carburetors. The secondary carburetors are easy to spot because they contain no choke mechanism, no vacuum ports, and no idle adjustment screws.

Both the 140 hp and 110 hp engines share the same 9.0:1 compression ratio. The differences in distributor advance curves are shown in the chart below…

Image

The attached 1965 Chevrolet Corvair GM Heritage Center Specs includes detailed engine specifications for comparison between the 110 hp and 140 hp engines. The two carburetor 110 hp engine produces 110 hp @ 4400 RPM and 160 foot-pounds of torque at 2800 RPM. 140 hp engine produces 140 hp @ 5200 RPM and 160 foot-pounds of torque at 3600 RPM. Both engines have essentially the same bottom end and same camshaft. The larger intake valves and dual exhaust system are designed to produce more horsepower at the high end with all four carburetors open. Both engines have a very similar pull at low end speeds, and I'm not sure you would notice the difference at low RPMs between the 110 hp and 140 hp engines. Both also get similar fuel mileage around town and at cruising highway speeds when the secondary carburetors are generally not in use.

I have also included several detailed photographs of the 140 hp cylinder heads. In addition to the additional carburetors, special linkage and fuel line arrangement, the exhaust manifolds also have a larger cross-section for improved exhaust breathing. A photograph of the 110 hp cylinder head combustion chamber is shown below for comparison…

Image

:chevy:
Attachments
DELCO ROCHESTER - Models H, HV Carburetor Service Manual.pdf
DELCO ROCHESTER - Models H, HV Carburetor Service Manual
(1.79 MiB) Downloaded 7 times
1965 Corvair Assembly Manual - THROTTLE LINKAGE SYSTEM.pdf
1965 Corvair Assembly Manual - THROTTLE LINKAGE SYSTEM
(1.92 MiB) Downloaded 7 times
1965 Corvair Assembly Manual - CARBURETOR & FUEL SYSTEM.pdf
1965 Corvair Assembly Manual - CARBURETOR & FUEL SYSTEM
(3.92 MiB) Downloaded 26 times
1965 Corvair Chassis Shop Manual - SECTION 6M - ENGINE FUEL.pdf
1965 Corvair Chassis Shop Manual - SECTION 6M - ENGINE FUEL
(8.87 MiB) Downloaded 18 times
1965 Chevrolet Corvair GM Heritage Center Specs.pdf
1965 Chevrolet Corvair GM Heritage Center Specs
(2.01 MiB) Downloaded 6 times
Corvair 140 HP Cylinder Heads (1).JPG
Corvair 140 HP Cylinder Heads (2).JPG
Corvair 140 HP Cylinder Heads (3).JPG
Corvair 140 HP Cylinder Heads (4).JPG
Corvair 140 HP Cylinder Heads (6).JPG
Brad Bodie
Lake Chatuge, North Carolina
Image 1966 Corvair Corsa Convertible

Vamisk
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Joined: Fri Apr 01, 2016 5:44 am

Re: A question about the 140 carbs and other 140 topics.

Unread post by Vamisk » Wed Sep 13, 2017 3:53 pm

Wow i wasn't expecting there to be that much information about the whole setup. I need to buy you a beer or something.
1961 110hp Monza coupe

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cnicol
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Re: A question about the 140 carbs and other 140 topics.

Unread post by cnicol » Wed Sep 13, 2017 9:32 pm

The 140 primary carbs are identical to 110 primary carbs. 140 secondary carbs are similar but on close inspection you'll find they're not machined for most of the parts you find on primaries; basically they're just a throttle and a main jet. Secondary main jets are the same as, or smaller than the primary main jet, depending on the year.

Going to a small intake valve isn't practical and wouldn't help anyway. What GM did to improve low-end torque for automatic trans applications was to employ the higher-torque cam from the 95hp engine. Since that cam's RPM range was too low for the 140, they retarded the cam timing so the cam's RPM range shifted upward about 400 RPM. This adjustment gave us the good bottom end and stretched the cam so it would still be effective when the secondary carbs began to flow. Another adjustment (mandatory really) was to alter the transmission governor so it would stay in low gear much longer (higher RPM/MPH)

I have a PG 140 engine and transmission in my Rampside (not original to that vehicle of course). Off the line it's just as good as a 110 PG (which is pretty good) but where it really shines in in the upper RPM range of first gear (35-40 MPH). There you can feel the effect of opening the secondaries. I live on a 35-40 MPH mountain road and I can go up our road over 10 MPH faster than I could with a 110. 45 vs low 30s.
'61 140 PG Rampside
'66 Rear Alum V8 4-dr
'60 Monza PG coupe (sold, sniff, sniff)
'66 Corsa Fitch Sprint Conv. (First car 1971, recently repurchased)

Vamisk
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Joined: Fri Apr 01, 2016 5:44 am

Re: A question about the 140 carbs and other 140 topics.

Unread post by Vamisk » Thu Sep 14, 2017 7:50 am

So i guess i shouldn't really be worried unless i have a PG? I actually have a set of 4 140 carbs but since the 110 primaries are just the same then I'm already a step ahead. Unfortunately the guy disassembled the secondaries down to the base casting so it's going to be fun trying to rebuild the throttle shaft and all.
1961 110hp Monza coupe

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cnicol
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Re: A question about the 140 carbs and other 140 topics.

Unread post by cnicol » Thu Sep 14, 2017 8:04 am

Right, for some reason I thought you had an automatic. The 140 with a manual trans (particularly a 61-3 4-speed with it's lower first gear) is wonderful right off the line. The ideal build (IMHO) is a 140 with a dual-pattern 280-duration cam (Otto Parts/Clarks OT-20, for example) and headers. That combination is about as good as Corvairs get for all-around performance.
'61 140 PG Rampside
'66 Rear Alum V8 4-dr
'60 Monza PG coupe (sold, sniff, sniff)
'66 Corsa Fitch Sprint Conv. (First car 1971, recently repurchased)

chris
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Joined: Fri Jul 02, 2010 5:25 pm

Re: A question about the 140 carbs and other 140 topics.

Unread post by chris » Wed Sep 20, 2017 4:44 pm

cnicol wrote:Right, for some reason I thought you had an automatic. The 140 with a manual trans (particularly a 61-3 4-speed with it's lower first gear) is wonderful right off the line. The ideal build (IMHO) is a 140 with a dual-pattern 280-duration cam (Otto Parts/Clarks OT-20, for example) and headers. That combination is about as good as Corvairs get for all-around performance.
Craig, that's exactly what I think about the engine combination. I'd even be curious about using the earlier trans (with the deeper first gear) with a 3.08 rear; seems it would be a great highway and all around cruiser (Craig, I MAY have read your older tech article and thoroughly agree with it!).

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cnicol
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Re: A question about the 140 carbs and other 140 topics.

Unread post by cnicol » Wed Sep 20, 2017 5:50 pm

chris wrote:
Wed Sep 20, 2017 4:44 pm

Craig, that's exactly what I think about the engine combination. I'd even be curious about using the earlier trans (with the deeper first gear) with a 3.08 rear; seems it would be a great highway and all around cruiser (Craig, I MAY have read your older tech article and thoroughly agree with it!).
I put the EM trans (3.65 first gear) with 3.08 axle into my '67. The engine was the factory "high torque" 140 originally found in 140PG models. The combination made for the best-driving Corvair I've ever had (and I've had many). I replicated the deal in my '66 except with a 304-cam 140 and that was merely OK.
'61 140 PG Rampside
'66 Rear Alum V8 4-dr
'60 Monza PG coupe (sold, sniff, sniff)
'66 Corsa Fitch Sprint Conv. (First car 1971, recently repurchased)

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