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Discussion Starter · #1 ·
Hell all, quick question for all the 122 gurus out there! Long story short, I have a bone stock (minus Bosch blue coil and Pertronix) 1968 VOLVO 122 B18B w/ BW35 with a set of rebuilt dual SU HS6s.

A friend of mine has the rather rare preheater assembly with a complete air box for the B18/B20B w/ SU HS6s, piping and the thermostat shutter. Is the preheater assembly a worthwhile upgrade or is it more of a hindrance than it’s worth? Was it designed more as an anti-icing system or an emissions control system? Will it rob any power over say the standard filters? Appreciate your thoughts. Many thanks friends.
 

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"rare preheater assembly with a complete air box for the B18/B20B w/ SU HS6s, piping and the thermostat shutter" a picture or three might help to identify it better...
 

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Discussion Starter · #3 · (Edited)
"rare preheater assembly with a complete air box for the B18/B20B w/ SU HS6s, piping and the thermostat shutter" a picture or three might help to identify it better...
Hi Ron, great to hear from you again! Here is a pic of the assembly (this one is a B20B) but the box and ducting is identical for the B18B cars. Information is scant but as far as I can tell the pre-heater option was available in April 1968. My car has the typical round filters and was made on April 23, 1968 so I seem to have just missed the option.

"Air filter with thermostat controlled preheating for SU carburettors is made available on B18 B in April 1968" according to ... http://www.volvoamazonpictures.se/modelyears/modelyears.php#1968


http://www.volvoamazonpictures.se/powertrain/images/B20B.jpg
http://i69.servimg.com/u/f69/12/79/77/41/140_su10.jpg

https://www.youtube.com/watch?v=eps6OzOTEUQ

Here is the thermostat shutter....https://www.cvi-automotive.se/en/articles/2.20139.53900/throttle-housing-240-b19ab20ab21a-75-78
 

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CVF;

Got it...that box and valving just draws warmed air from the exhaust manifold when cold, so minimizes the time needed to have Choke engaged...your info on years that it was fitted sounds right (you could check GCP.com parts lists which probably specify models and chassis for fitment)...it was also standard on post '68 140s with dual SUs and possibly ZSs, so if you must have one, look there also...that part doesn't do much for me...I want the coldest air being supplied under normal operation...Volvo even routed the cold air snorkel to in front of the Radiator...there has been some discussion if that give any significant performance advantage...I think there is enough cool air available from the hurricane under the hood when underway...

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Discussion Starter · #5 ·
CVF;

Got it...that box and valving just draws warmed air from the exhaust manifold when cold, so minimizes the time needed to have Choke engaged...your info on years that it was fitted sounds right (you could check GCP.com parts lists which probably specify models and chassis for fitment)...it was also standard on post '68 140s with dual SUs and possibly ZSs, so if you must have one, look there also...that part doesn't do much for me...I want the coldest air being supplied under normal operation...Volvo even routed the cold air snorkel to in front of the Radiator...there has been some discussion if that give any significant performance advantage...I think there is enough cool air available from the hurricane under the hood when underway...

Cheers
Thanks so much for the insights. I guess there is no real advantage with swapping.
 

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CVF;

Not enough advantage to warrant fitting, as far as I'm concerned (other may disagree), I like to see two big (3 1/2" high) Air Filters doing their duty...

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The advantage depends on how much cold / cool weather driving you do. The preheater assembly is a version (a really crude version) of the recuperator used on some large diesel and turbine drives. Preheating the combustion air with exhaust energy increases the amount of heat energy from combustion in the cylinder that is applied to useful work. So, in addition to improving operation of the carbs in cold temperatures (better atomization) you do get some improvement in the thermal cycle efficiency which theoretically should equate to some improvement in fuel efficiency when air temperatures are cold.

Volvo used thermostatically controlled air preheaters right through the 240 and 740 series. On the 740 the thermostat measured the air temperature inside the air box (so the blended air temperature). It probably changes with the models; but, my recollection was that during the summer time the thermostat on my 1987 745T was always operating in the 'cold air' position. So, if you are a fair weather Amazonite there may be no up-side to the air pre heater system since it may always be operating in the cold position.

If you drive in cool weather or the winter, then there should be a driveability improvement with the system. Pre heating the air offers a theoretical improvement in the thermal efficiency of the combustion cycle which should also materialize as improved fuel efficiency. Don't mistake improved thermal efficiency with increased power output because in this case preheated air reduces the air density which slightly reduces the mass of O2 available in the cylinder for combustion which slightly reduces the peak horsepower output. However, that effect is slight despite the advertising hyperbole associated with aftermarket cold air intake systems and the effect really only takes place at wide open throttle.

Perhaps the bigger problem with the preheating system is if the thermostat permanently sticks in the hot position. The B engine with its higher compression ratio is not exactly detonation resistant. Preheating the combustion air on a day when the air ambient air temperature is already 35 C is really going to exacerbate the tendency of the engine to detonate which is definitely a bad thing. I know about the 'bad thing' because the air box thermostats on my 745 turbo did have a reputation for failing in the 'hot' position and preheating already hot summer air was definitely a bad thing on a turbo. The other concern about the system that I would have is that the plastics from the late 60s - early 70s were not the most 'enduring'. I might be concerned that the parts might crack or snap off if you put them into service after close to 50 years.
 

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Discussion Starter · #8 ·
The advantage depends on how much cold / cool weather driving you do. The preheater assembly is a version (a really crude version) of the recuperator used on some large diesel and turbine drives. Preheating the combustion air with exhaust energy increases the amount of heat energy from combustion in the cylinder that is applied to useful work. So, in addition to improving operation of the carbs in cold temperatures (better atomization) you do get some improvement in the thermal cycle efficiency which theoretically should equate to some improvement in fuel efficiency when air temperatures are cold.

Volvo used thermostatically controlled air preheaters right through the 240 and 740 series. On the 740 the thermostat measured the air temperature inside the air box (so the blended air temperature). It probably changes with the models; but, my recollection was that during the summer time the thermostat on my 1987 745T was always operating in the 'cold air' position. So, if you are a fair weather Amazonite there may be no up-side to the air pre heater system since it may always be operating in the cold position.

If you drive in cool weather or the winter, then there should be a driveability improvement with the system. Pre heating the air offers a theoretical improvement in the thermal efficiency of the combustion cycle which should also materialize as improved fuel efficiency. Don't mistake improved thermal efficiency with increased power output because in this case preheated air reduces the air density which slightly reduces the mass of O2 available in the cylinder for combustion which slightly reduces the peak horsepower output. However, that effect is slight despite the advertising hyperbole associated with aftermarket cold air intake systems and the effect really only takes place at wide open throttle.

Perhaps the bigger problem with the preheating system is if the thermostat permanently sticks in the hot position. The B engine with its higher compression ratio is not exactly detonation resistant. Preheating the combustion air on a day when the air ambient air temperature is already 35 C is really going to exacerbate the tendency of the engine to detonate which is definitely a bad thing. I know about the 'bad thing' because the air box thermostats on my 745 turbo did have a reputation for failing in the 'hot' position and preheating already hot summer air was definitely a bad thing on a turbo. The other concern about the system that I would have is that the plastics from the late 60s - early 70s were not the most 'enduring'. I might be concerned that the parts might crack or snap off if you put them into service after close to 50 years.
Oh this is fantastic! Thank you both so much for taking the time to explain it. Yeah 98% of my driving is in fair Toronto weather the only cold weather the car really sees is when I'm shutting her down for the season (November) or taking her our the next spring (April/May). I was interested in the fuel economy benefit but seeing as it pretty much only sees very warm summer/warm-ish spring weather guess it'll do more harm that good.
 
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