Holley 7855
- Thread starter rv2
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The car originally had the Carter ThermoQuad on it. The Holley R7855 is an OEM-replacement Holley for the Chrysler B/RB engine, which is why it came with the correct Chrysler throttle and kickdown linkage hook-ups on it. With the stud for the throttle/cruise control transferring from the original carb.
In my orientation, a better carb than the Carter. Holley model 4175 vac secondary spreadbore. Constructed and rebuilds like a normal Holley 4bbl 4160, just that it's a spreadbore carb instead.
Enjoy!
CBODY67
In my orientation, a better carb than the Carter. Holley model 4175 vac secondary spreadbore. Constructed and rebuilds like a normal Holley 4bbl 4160, just that it's a spreadbore carb instead.
Enjoy!
CBODY67
The number below the list number is the date code. First three digits are the day of the year, in this case the 172nd day of the year. The last digit is the year, in this case 0 is the year of manufacture, probably 1980. On that basis, the carb is likely not original to the car. Most standard performance big block Mopars had list 4160 Holley in the early '70's with some variations for CA mandated emissions. The 7855 650cfm was usually a carb used as a replacement on some Mopar engines that came equiped with a thermoquad spread bore carb. The plastic plenum on the thermoquad went to hell after a few years and many were replaced.
Dave
70bigblockdodge
Old Man with a Hat
Get a proper ThermoQuad built for your car from Woodruff's carburetor. Throw that Holley half breed in the trash (smash it with a sledge hammer first) so no other poor soul gets stuck with that junk.
If you insist on a Holley or a modern Edelbrock. Get a new manifold with a square bore hole on top and a new carburetor.
Those Holley spread bores were a half assed band-aid in eighties, 40 years later they are completely obsolete.
If you insist on a Holley or a modern Edelbrock. Get a new manifold with a square bore hole on top and a new carburetor.
Those Holley spread bores were a half assed band-aid in eighties, 40 years later they are completely obsolete.
Well, as much as I liked ThermoQuads, those Holley 4175s are better carburetors. Better venturi designs and such. I have a similar carburetor on my '77 LT Camaro and it works great. Since the 1990s. Even upped the mpg average from 17.44mpg to 20.00mpg. Same driving cycle and the night before the 305 became a 355, 23.5 in a 60 mile freeway loop. So, that OEM-replacement 9895 4175 was a good choice for me. It, too, was a direct OEM bolt-on. If that Holley needs some attention, send IT to Woodruff for rebuild, not "throw it out".
Not that Woodruff can't rebuild a TQuad correctly, FINDING a TQuad which might be worth rebuilding, at this point in time is the real issue to me. Not using a reman carb which is more "one size fits all applications" than having the specific fuel curve calibrations in it for the engine.
My one forray into TQuads was with their aftermarket 9801 in the late 1970s, when I bought that carb new. Putting it and a Torker 383 on my '67 Chrysler 383 4bbl. That combination, allegedly matched for just such an engine combination, offered NO significant improvements over the factory AFB and factory intake. Even bought a Strip Kit for it, too. Later went back to a used OEM Chrysler Holley 4160, which had a bit sharper throttle response than the spreadbore TQ. Tried different rods, too. Nothing seemed to work, other than "take it off". The TQuad did work better when a factory OEM carb insulator gasket was used rather than the "thin, inexpensive" base gasket all carbs and kits usually came with, back then.
When I saw the first Street Demon carb, my heart went pitter-patter, seeing a reincarnation of a TQuad, in all respects, other than the shape of the secondary throttle plate. Everything else looked pretty much as Carter designed it, including the tube going to the accel pump. THAT would be the only other carb I'd use instead of an OEM TQuad. Put some annular discharge venturis in it and it probably would be perfect. KEY thing with the Street Demon is that it will fit a spreadbore carb manifold as well as a square bore manifold, in this situation.
I always liked TQuads better than the Rochester QJets. But any later-design carb will usually work a bit better than a 1960s-design carb. Better venturi shapes and better accel pump discharges can mean better throttle response and a bit more mpg on the road. Just my observations and experiences.
CBODY67
Not that Woodruff can't rebuild a TQuad correctly, FINDING a TQuad which might be worth rebuilding, at this point in time is the real issue to me. Not using a reman carb which is more "one size fits all applications" than having the specific fuel curve calibrations in it for the engine.
My one forray into TQuads was with their aftermarket 9801 in the late 1970s, when I bought that carb new. Putting it and a Torker 383 on my '67 Chrysler 383 4bbl. That combination, allegedly matched for just such an engine combination, offered NO significant improvements over the factory AFB and factory intake. Even bought a Strip Kit for it, too. Later went back to a used OEM Chrysler Holley 4160, which had a bit sharper throttle response than the spreadbore TQ. Tried different rods, too. Nothing seemed to work, other than "take it off". The TQuad did work better when a factory OEM carb insulator gasket was used rather than the "thin, inexpensive" base gasket all carbs and kits usually came with, back then.
When I saw the first Street Demon carb, my heart went pitter-patter, seeing a reincarnation of a TQuad, in all respects, other than the shape of the secondary throttle plate. Everything else looked pretty much as Carter designed it, including the tube going to the accel pump. THAT would be the only other carb I'd use instead of an OEM TQuad. Put some annular discharge venturis in it and it probably would be perfect. KEY thing with the Street Demon is that it will fit a spreadbore carb manifold as well as a square bore manifold, in this situation.
I always liked TQuads better than the Rochester QJets. But any later-design carb will usually work a bit better than a 1960s-design carb. Better venturi shapes and better accel pump discharges can mean better throttle response and a bit more mpg on the road. Just my observations and experiences.
CBODY67
70bigblockdodge
Old Man with a Hat
Most old Holley's have been over torqued by the average car person so every flat surface inside is warped and needs machined, plus the throttle shaft is most likely loose. It could be fixed but it will not flow as well as a TQ and as usual a universal carb is just that universal based on GM requirements. That same carburetor that is feeding your 305 is going to work well on a 440? You have perfectly stated what the aftermarket has been doing since the 60s.
I'm sure it works excellent on your SBC.
For my money and time I'm sticking with a TQ. If I'm moving to a Holley I'm changing the intake to match.
I'm sure it works excellent on your SBC.
For my money and time I'm sticking with a TQ. If I'm moving to a Holley I'm changing the intake to match.
Your "over-torquing" orientation might be from your experiences, but on my 9895, they had changed to a metering block gasket with had a type of adhesive on it. Which meant it was very difficult to get it to break loose for disassembly. In my case, I did not go any farther than taking the front bowl off, because of that. On the one I did get the secondard metering plate to come off, the metal gasket got some waves in it, so that project just stopped.
On the Holley OEM-replacement carburetors, for Ford, GM, or Chrysler, they were meant to be a drop-in replacement item. Correct throttle linkage hook-ups, correct fuel line placements, and correct OEM choke attachments. Plus a fuel curve to match the intended application and be emissions-compliant as the orig factory carb was. That's why the 7855 has the correct Chrysler linkage attachments and no electric choke.
But when the carbs were later genericized, an electric choke was added and the fuel calibration could become a bit more generic too, as they COULD meet emissions, but not having to. Hence, the metering on the 7855 would not be the same as the early 9895s I bought back then. As GM had moved to electric chokes by 1979 model year, my 9895 came with a full-electric choke as a normal 1979 QuadraJet would have. Chrysler was using divorced, electric-assist chokes, so that's what the 7855 uses, too.
As any orig GM-application carb got older, sometimes they would adapt items which would be generic and need adapters for non-GM applications. Which generated the various adapter brackets for the aftermarket carbs to fit Chrysler linkages and such. Look at the more recent 9895 description and it mentions nothing about it being for a 1979 Corvette L82 as its original application, just "engines from 350-455cid" now.
In more recent times, one reason to NOT use a Holley 2300 2bbl of a 4bbl is that the accel pump diaphram's outside surface is in open air. When it starts to seep, fuel contacts the intake manifold directly below it. Not good, but Holley has released some diaphrams which are more ethanol resistant, plus teflon-coated gaskets. Which can make the Carter/Edelbrock AFBs and AVSs better choices, plus the Street Demon TQuad clone. Replicating the OEM metering calibrations with the related Calibration Kits (similar to the old Carter Strip KIts).
Enjoy!
CBODY67
On the Holley OEM-replacement carburetors, for Ford, GM, or Chrysler, they were meant to be a drop-in replacement item. Correct throttle linkage hook-ups, correct fuel line placements, and correct OEM choke attachments. Plus a fuel curve to match the intended application and be emissions-compliant as the orig factory carb was. That's why the 7855 has the correct Chrysler linkage attachments and no electric choke.
But when the carbs were later genericized, an electric choke was added and the fuel calibration could become a bit more generic too, as they COULD meet emissions, but not having to. Hence, the metering on the 7855 would not be the same as the early 9895s I bought back then. As GM had moved to electric chokes by 1979 model year, my 9895 came with a full-electric choke as a normal 1979 QuadraJet would have. Chrysler was using divorced, electric-assist chokes, so that's what the 7855 uses, too.
As any orig GM-application carb got older, sometimes they would adapt items which would be generic and need adapters for non-GM applications. Which generated the various adapter brackets for the aftermarket carbs to fit Chrysler linkages and such. Look at the more recent 9895 description and it mentions nothing about it being for a 1979 Corvette L82 as its original application, just "engines from 350-455cid" now.
In more recent times, one reason to NOT use a Holley 2300 2bbl of a 4bbl is that the accel pump diaphram's outside surface is in open air. When it starts to seep, fuel contacts the intake manifold directly below it. Not good, but Holley has released some diaphrams which are more ethanol resistant, plus teflon-coated gaskets. Which can make the Carter/Edelbrock AFBs and AVSs better choices, plus the Street Demon TQuad clone. Replicating the OEM metering calibrations with the related Calibration Kits (similar to the old Carter Strip KIts).
Enjoy!
CBODY67
fatmattress30
New Member
.I had a tq on my 440..got tired of the warped plastic body,..not dependable at all then I got the spreadbore..7855 bought it from Holley new 1983 holy **** ,like night and day best holley I ever had on that truck..totaled that truck ,rebuilt the carb and put it on my sb chevy...still kicking ***...those tq..sure you can send them out ..cost a fortune. ..they are about as worthless as a quadrajet....just saying
I have had a few OEM Replacement 4175s on SBCs. Changing from an OEM replacement 4160, it was very amazing. Much better off-isle response AND average mpg went up 2.5-3.0mpg. Money well spent!
Several years prior, I got a 9801TQ and Torker 383 intake for my '67 Newport 383 4bbl. With the better cyl-to-cyl mixture distribution of the Torker intake, plus the better venturi design of the TQ, as it was stated the 9801 was was calibrated for a 383 4bbl engine with the Torker on it, that combination did NOT run much better than the stock AFB and factory intake did. Spark plugs did not look "rich", but normal. WOT power was a little bit better after I put an OEM Chrysler base gasket insulator under it, but still mpg was nor improved. I WANTED the TQ to be better, but I was disappointed and later removed it for a used OEM Holley 4160 that I rebuilt.
When the Holley Street Demon 650s came out, I got one. Still in the box. It has the phenolic float bowl, too. Also got a new Edelbrock AVS2 when they came out. Still in the box.
QJs have their strong points, especially on GM engines. In general, Rochester carbs on GM engines have bulletproof drivability and good fuel economy. BUT they also have a very small float bowl capacity. BTAIM
I'm wondering how well a Rochester 1.69" throttle bore 2bbl might run on a Chrysler 383? One calibrated to run on a SBC400, for example. Other than the increase in max airflow from the larger throttle bores.
Just some thoughts, observations, and experiences.
CBODY67
Several years prior, I got a 9801TQ and Torker 383 intake for my '67 Newport 383 4bbl. With the better cyl-to-cyl mixture distribution of the Torker intake, plus the better venturi design of the TQ, as it was stated the 9801 was was calibrated for a 383 4bbl engine with the Torker on it, that combination did NOT run much better than the stock AFB and factory intake did. Spark plugs did not look "rich", but normal. WOT power was a little bit better after I put an OEM Chrysler base gasket insulator under it, but still mpg was nor improved. I WANTED the TQ to be better, but I was disappointed and later removed it for a used OEM Holley 4160 that I rebuilt.
When the Holley Street Demon 650s came out, I got one. Still in the box. It has the phenolic float bowl, too. Also got a new Edelbrock AVS2 when they came out. Still in the box.
QJs have their strong points, especially on GM engines. In general, Rochester carbs on GM engines have bulletproof drivability and good fuel economy. BUT they also have a very small float bowl capacity. BTAIM
I'm wondering how well a Rochester 1.69" throttle bore 2bbl might run on a Chrysler 383? One calibrated to run on a SBC400, for example. Other than the increase in max airflow from the larger throttle bores.
Just some thoughts, observations, and experiences.
CBODY67
Rustyrodknocker
Senior Member
I have found that people are tribal about carburators. They like what they understand the most. I have also found that they all pretty much work fine. The primary issue I have seen is the overall condition. Many can be warped. This seems to be from continued retightening. Many heat cycles of steel bolts in and aluminum structure. The long bolts in the Q jet combined with the soft base material leads to Many being over tightened. Many showing the sign around the head of the fastener. You can see the spalling on the carb. Of course the Thermoquad and internal leaks dripping on the throttle plates from epoxied wells... the best carb I ever had was the low mile one regardless of brand.
In terms of performance. That's it's own world. But they all can be found in a car with two wheels in the air. Proven time and again in class spec racing.granted some have been extremely modified.
In terms of performance. That's it's own world. But they all can be found in a car with two wheels in the air. Proven time and again in class spec racing.granted some have been extremely modified.
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