[ry57pont]

When are jet extensions needed? and are there any cons to using them? would you have to change jet sizes if using them? Thanks - RB

[Tom Vaught]

Originally Posted by ry57pont

When are jet extensions needed? and are there any cons to using them? would you have to change jet sizes if using them? Thanks - RB

On a passenger car that your 70+ years old uncle drives, they are probably not needed, unless your uncle's name is Beswick.

If the car is moving forward quickly and it has a Holley carburetor with race bowls on it, for the small expense of adding a pair of jet extensions and a "notched black float" you can get liquid fuel to the jets at all times.

Saying that a car has to do at least a 1.6 60 ft time to need jet extensions is a stretch. I will not bs you. Every chassis is different in tire, gear, weight, etc so this is one case where the jet extensions will not hurt you by installing them and could really help you on acceleration of your vehicle when using a Holley carb.

JMO

Tom Vaught

ps The stock jets screw right into the Holley jet extensions. The extension has a large passage so there is no flow restriction.

[455-4+1]

Tom, do you see any difference between the threaded extension that utilizes the jet screwed in at the end and the press on type that covers the jet in the original location ?

I personally use the BLP rears that have the extension machined into the jet and the restriction in the original location (at the metering block)

I was concerned with the extra volume of fuel "added to the well" after the restriction when the jet itself was relocated to the rear and its affect on the booster signal and emulsion.

[ry57pont]

is a notched back float required with jet extensions?

[Tom Vaught]

Originally Posted by 455-4+1

Tom, do you see any difference between the threaded extension that utilizes the jet screwed in at the end and the press on type that covers the jet in the original location ?

I personally use the BLP rears that have the extension machined into the jet and the restriction in the original location (at the metering block)

I was concerned with the extra volume of fuel "added to the well" after the restriction when the jet itself was relocated to the rear and its affect on the booster signal and emulsion.

Hello Mate,

Well if you look at the diameter of the main well and the expansion factor there vs the jet diameter and your "extra volume of fuel "added to the well" after the restriction when the jet itself was relocated to the rear and its affect on the booster signal and emulsion", I would think that the main well effect would be much larger vs the expansion in diameter on the typical Holley sourced jet extension.

I personally never liked the slip on jet extensions as they can bleed air around the outside of the jet unless it is a perfect fit. The leak would be right at the point where they slip over the jet.

Your BLP extensions would duplicate a factory jet location without the leak being possible BUT you would have some very expensive jets/ extensions over time unless you really had jetting deal dialed in.

Tom Vaught

[D. Miles]

Originally Posted by ry57pont

is a notched back float required with jet extensions?

Yes! a notched rear float should be used, otherwise your float cannot go all the way to the bottom of the bowl and allow the needle and seat to be "full" open.

455-4+1 I first tried the plastic tubes that press over top of the jet at the metering block. I had just started running a transbrake at the time when a buddy ask me if I had them, I told him no and he wondered how my car didn't bog off the line, I put the extensions on an the 60' times dropped .05 from 1.43-1.45 to 1.38 on the spot and started lifting both front wheels over a foot. Over that winter as I went through the carb, I bought a set of the nice brass screw in type that the jet screws into and the car ran totally different, it was harder to tune period. I assume that as you already mentioned that the carb has un-metered fuel available that is "stored" in the jet extension itself then as that flow begins to slow down once a negative pressure is met then the metering function of the jet comes into play, I went back to the plastic slip on deals and never looked back... D. Miles

[Tom Vaught]

My posted was related to the old copper/ brass swedged extensions.

I could see where a plastic extension would work fine and have no leakage unless a lot of jet changing was going on over time and the seal went away.

Tom Vaught

[455-4+1]

D.Miles, interesting info. Good to see some "real stuff" back up what opeople think "could happen" LOL

Tom, yes the BLP stuff is a little pricey but you only have to look at them for the rear and in a small range (10 jet numbers or so to cover the spread) , included PV and non PV tuneup.
They are very well made and have turned a few carbs from turds to outstanding in minutes

I plan to treat them carefully and have them a long time, I will possibly hand them down to my children also (if I have finished paying them off LOL)

As always, good to bounce a few ideas and theory's around for some educated feedback

Thanks all

[Dragncar]

If you race they are one of the best bang for your bucks out there. 20$ for the screw in brass extensions and the notched float.
Every car with a Holley and slicks should have them installed. No reason not to.