article on replacing carb with Holley spreadbore
Thread Starter
Team Owner
Joined: Jul 1999
Posts: 26,545
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From: Huntersville NC
article on replacing carb with Holley spreadbore
I was just reading an article on Corvettemagazine.com about replacing Qjet with a Holley. Pretty much a bolt-on job. Two things about the article bothered me (I have emailed the magazine). 1. They instruct you to use plumbers tape on the fuel line fitting. also the power brake vacuum fitting. My understanding (from others who have posted here) is that plumbers tape is bad stuff on fuel line fittings. First of all, the seal is not created by the threads but by the compression - so it doesnt help anyway, or shouldnt be needed. And secondly, the stuff can come apart, get in the fuel line, and really gum up the carb. I have found yellow teflon tape that is designed for gas, but according to point #1 shouldnt be used anyway.
2. At the very end of the article they tell you to set your torque wrench to 65 lbs/ft. You use studs for the Holley instead of bolts, but isn't that way too much torque for holding down a carb to the intake? Should it be 65 lbs/in ?
MJ
2. At the very end of the article they tell you to set your torque wrench to 65 lbs/ft. You use studs for the Holley instead of bolts, but isn't that way too much torque for holding down a carb to the intake? Should it be 65 lbs/in ?
MJ
Le Mans Master
Joined: Apr 1999
Posts: 6,134
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From: Raleigh North Carolina
Re: article on replacing carb with Holley spreadbore (MNJack)
You are right about the torque...
Standard torque figures for tightening down a 5/14-24 nut on a carb stud are:
Dry- 60 to 80 INCH pounds,
Lubed: 50 to 60 INCH pounds.
RE: The tape... I tend to shy away from using it on carb fittings only because it tends to vibrate loose, although I have used it on occasion. The tape is specified as a thread lubricant, not a sealant. At least, that is what all of my licensed plumber friends have told me. On an inverted flare fitting, the tape will have no effect on the seal. Same for a standard Holley sintered-bronze setup... the large, thin, metalic gasket does the sealing between the fitting and the fuel bowl. I have the 6211 spread bore currently on my 70 454 and I am not using any tape. I guess it depends on whether you trust the stuff to not allow the fittings to unwind. In the case of the standard Holley fitting, the tape could certainly get into the carb and cause problems. In the case of an inverted flare fitting, this could not happen unless you get the tape under the flared tubing where it contacts the seat.
Tom
Standard torque figures for tightening down a 5/14-24 nut on a carb stud are:
Dry- 60 to 80 INCH pounds,
Lubed: 50 to 60 INCH pounds.
RE: The tape... I tend to shy away from using it on carb fittings only because it tends to vibrate loose, although I have used it on occasion. The tape is specified as a thread lubricant, not a sealant. At least, that is what all of my licensed plumber friends have told me. On an inverted flare fitting, the tape will have no effect on the seal. Same for a standard Holley sintered-bronze setup... the large, thin, metalic gasket does the sealing between the fitting and the fuel bowl. I have the 6211 spread bore currently on my 70 454 and I am not using any tape. I guess it depends on whether you trust the stuff to not allow the fittings to unwind. In the case of the standard Holley fitting, the tape could certainly get into the carb and cause problems. In the case of an inverted flare fitting, this could not happen unless you get the tape under the flared tubing where it contacts the seat.
Tom
Safety Car
Joined: Aug 2001
Posts: 3,685
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From: Waterford Mi
Re: article on replacing carb with Holley spreadbore (Tom454)
I recently did the job on my 73. I had to use an adaptor for the brake vac tube and the air cleaner would not fit over the vacume secondary modual. I bought it from a Summit cat. #4175
I changed the shooters from the 40 down to a 31 and changed the pump cam to help stop it from running to rich on acceleration. I have a modified L-48 with a 3.55 gear. (9.5 compression, Cranecam, and Performer intake manifold). Runs good now
I changed the shooters from the 40 down to a 31 and changed the pump cam to help stop it from running to rich on acceleration. I have a modified L-48 with a 3.55 gear. (9.5 compression, Cranecam, and Performer intake manifold). Runs good now
Safety Car
Joined: Feb 1999
Posts: 3,631
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From: Fountain Hills AZ
Re: article on replacing carb with Holley spreadbore (MNJack)
I'll sometimes use teflon tape on fuel fittings, not as a sealant but to compensate for a mis-match between old or stretched threads and a new fitting. It's not uncommon for threads to wear or to be "pulled" from repeated (or over) tightening, giving a sloppy fit when mated to a new thread. If thread tape is needed on a fuel line fitting, start it from at least two threads from the end of the fitting so that none of it winds up in the carb, creating a bigger problem than it's solving.
