Road Draft Tube ???
- Thread starter NITROFC
- Start date
The PVC replaced it.
A hose hanging down will not do the job. The engine needs fresh air entering (breather(s) of some type) and something pulling the contaminated air out. With a PCV system the engines intake vacuum draws the contaminated air out and back in the motor to be burned. The road draft tube was designed for its shape and positioning, to scavange or pull this contaminated air out and vent it under the vehicle. With out the baloney cut pipe angle and rigid correct angle placement, there is little movement or venting of the engine going on. Several good threads exist here for more detail.
Terry
A vent by definition provides a method to equalize pressure. The crankcase will vent through the hose but probably not as efficiently at speed as with the road draft tube. The angle of the cut on the bottom of the road draft tube is designed to enhance evacuation while the car is in forward motion but it will still vent without it otherwise it would do nothing unless the car was moving. The crankcase vent system through 62 used the road draft tube in conjunction with the oil filler cap which was vented on the low perf engines and non-vented on the high perf engines. My guess is that the non-vented caps on the high perf engines was to prevent any oil blowing back through the oil filler at high rpm. JMHO
Cecil, I dont know anything about the " correct" stuff, but I thought that the 62 409-409 used a simple vented push on oil filler cap. I thought the non-vented cap had to be used in conjunction with PCV system. ( 63 and later ) ??? Just not sure......
Ronnie,
I don't have any specific reference on 62 other than Corvette but the systems were similar through at least 61. The non-vented versus vented oil filler cap usage I referred to was true on the Corvette engines and I can't imagine why they would be different on other applications that used the road draft tube. I do have a 61 assembly manual that shows the road draft tube used on the 283, 348, and 409 engines. The RPO 242 Special Crankcase Ventilation Equipment was optional for all engines and showed the use of a pcv valve in the hose from the rear of the intake to the front of the carb. This option did not show any change in oil filler cap so I would assume that the oil filler cap that was called out for the specific engine application would remain unchanged. If the systems were consistent then I would expect that the high perf engine assemblies would have the nonvented oil cap regardless of pcv valve usage. Then again I could be wrong.
I don't have any specific reference on 62 other than Corvette but the systems were similar through at least 61. The non-vented versus vented oil filler cap usage I referred to was true on the Corvette engines and I can't imagine why they would be different on other applications that used the road draft tube. I do have a 61 assembly manual that shows the road draft tube used on the 283, 348, and 409 engines. The RPO 242 Special Crankcase Ventilation Equipment was optional for all engines and showed the use of a pcv valve in the hose from the rear of the intake to the front of the carb. This option did not show any change in oil filler cap so I would assume that the oil filler cap that was called out for the specific engine application would remain unchanged. If the systems were consistent then I would expect that the high perf engine assemblies would have the nonvented oil cap regardless of pcv valve usage. Then again I could be wrong.
gearhead, The fresh air enters those two round things on top of the motor!!!!
I may have to change my opinion on the nonvented cap on the 348/409s. I did some more research in my 61 Parts and Accessories Manual. and it does not show a nonvented cap for the 348. The nonvented cap 1552919 is cad plated and shows an application of 55-57 Pass w/dual 4BC, 56-57 Corvette, 58-61 PASS, Corvette w/H.L. Cam (exc. 348).
The vented cap 155233 is painted and shows an application of 55-58 all 8cyl (exc Dual 4BC, F.I.), 55 Corvette (8 cyl), 59-61 Pass (8 cyl).
The odd thing is there is no cap listed specifically for 348 implying that it may have used the vented cap 155233 regardless of hp rating. Maybe the high perf W engines weren't expected to get up into the RPM range of the HL cam small blocks so oil blowback out the vent cap wasn't an issue. If so then Ronnie is right for a different reason.
The vented cap 155233 is painted and shows an application of 55-58 all 8cyl (exc Dual 4BC, F.I.), 55 Corvette (8 cyl), 59-61 Pass (8 cyl).
The odd thing is there is no cap listed specifically for 348 implying that it may have used the vented cap 155233 regardless of hp rating. Maybe the high perf W engines weren't expected to get up into the RPM range of the HL cam small blocks so oil blowback out the vent cap wasn't an issue. If so then Ronnie is right for a different reason.
Thanks Gearhead, I guess I should invest in some 62-63 assembly manuals so I can keep up with you guys. I love this technical historical stuff.
BTW the reason may be because there were no solid lifter smallblocks offered in 62 pass cars so no need for a nonvented cap.
So which is better to have.
A factory style rigid steel tube road draft tube, or the conversion kit that
ShowCars sells ?
A factory style rigid steel tube road draft tube, or the conversion kit that
ShowCars sells ?
bubbletop, from an emissions stand point the non-vented cap with a closed PCV is far superior to the road draft tube. From a performance stand point, I don't think you will see any difference, however with the road draft tube and vented cap, you will be subject to blowby out through the vent cap at high rpms. Sure can make a mess under the hood.
Poocho
Poocho
NITROFC, You failed to mention if you had oil covering the bottom of your car or all over the engine compartment.
Ronnie Russell oil covering the bottom of your car or all over the engine compartment. :dunno[/QUOTE said:Thats the part I hate about the downdraft tube. I am tempted to change it out to pvc but keep all parts so it can be put back. I like to drive my car.
Dan, I only know two guys that have corret 62 409-409 cars. They both are members. They report that in all of their years with their cars , they have not experienced oil under the car or in the engine compartment. I have not seen an oily condition on a car with an unrestricted road draft tube. Please check with members who actually drive these cars . The cars from the late 50s and early 60s that were abused by infrequent oil changes built sludge. Oil quality was much worse then also. Sludge stopped up the road draft tubes and the only place left to vent was to blow out the oil filler cap. I dont think we have members who treat their car this way. If the road draft tube is open , the engine will vent. That is my opinion and certainly is an unpopular opinion, but it is from what I have seen. I suggest you make your opinion from researching cars that are healthy and well taken care of.
Road Draft Tube.....
Detergent oils and multi viscosity oils, did a lot to reduce the sludge that would build up in engines with road draft tubes.
For the most part, the road draft tubes worked pretty good, the proof being the black oily slick, they left on the side of the driving lane.:eek: Guys that rode motorcycles had to be aware of that area, at all times. Skip
Detergent oils and multi viscosity oils, did a lot to reduce the sludge that would build up in engines with road draft tubes.
For the most part, the road draft tubes worked pretty good, the proof being the black oily slick, they left on the side of the driving lane.:eek: Guys that rode motorcycles had to be aware of that area, at all times. Skip
NITROFC
Well Known Member
NITROFC, You failed to mention if you had oil covering the bottom of your car or all over the engine compartment.
FYI ..hose hangs far enough down not too make a big mess.
Skip forgot to mention that G.M. was not the only company to use the road draft tube. The oil that the motorcycles had to dodge was probably FORD oil!!!!