Holley Double Pumper - which way round?
- Thread starter Lee
- Start date
Pat Buckley
GT40s Supporter
Put it on whichever way is the most convenient regarding fuel line and linkage. The carb doesn't care.
Usually the inlets are on what we colonists call the passenger side, the right side of the car as you sit in the driver seat.
I remember one thread where another member asked a question regarding reversing the Holley. As I recall it was possible if primary/secondary metering blocks were reversed, too--something to do with the idle, I guess. I'm hoping those with more knowledge about these things than I will respond, too. It is entirely possible that 2124 is correct--let's hear from others.
Doug
I remember one thread where another member asked a question regarding reversing the Holley. As I recall it was possible if primary/secondary metering blocks were reversed, too--something to do with the idle, I guess. I'm hoping those with more knowledge about these things than I will respond, too. It is entirely possible that 2124 is correct--let's hear from others.
Doug
Pat Buckley
GT40s Supporter
Entirely possible?
LOL - thanks.
Actually I had the same question recently as I wanted to change the orientation of the carb I am using.
LOL - thanks.
Actually I had the same question recently as I wanted to change the orientation of the carb I am using.
YerDugliness said:
Not quite Doug, only the float bowls need to be swapped from end to end when reversing the carb, due to the slightly different fuel levels reqd ( measure the sight/level plug heights on each bowl you will see what I mean ). The metering blocks stay in their original positions relative to the carb body.
Also if your main jets use extensions in the [old] rear position these will now need to be fitted to the [new] rear position.
Jac Mac
Last edited:
Last year I had the same question for a Holley Street Avenger 4150 (#0-80770). After asking a number of experienced tuners I ended up with about a dozen different answers. I ask the same question of the Holley Telephone Service Tech Department on two difference occasions to check the information my “experts” had given and both times the tech person at Holley said it made no difference as long as the floats are set correctly. They also said it made no difference if the carb was tilted forward or level as long as the floats were set correctly.
I hope this discussion continues for a while and we can find out what really needs to be done for a "no compromises" installation if the carb is reversed 180 degrees.
Also, it would be nice to know the optimal carb level or tilt angle for a road racing car (not a dragster).
I hope this discussion continues for a while and we can find out what really needs to be done for a "no compromises" installation if the carb is reversed 180 degrees.
Also, it would be nice to know the optimal carb level or tilt angle for a road racing car (not a dragster).
I think this may be is the previous discussion that Doug recalled;
http://www.gt40s.com/forum/tech-engines-induction/17822-engine-angle.html
http://www.gt40s.com/forum/tech-engines-induction/17822-engine-angle.html
That's the one!
Right you are, Ben! The info on the jet extensions was the part I was intrigued with, but turning the carb backward doesn't appear anywhere in the thread, nor does switching the metering blocks.
Senior moments, senior moments.....
There can only be 2 explanations--too much loud rock 'n' roll or alien abduction!
Doug
Right you are, Ben! The info on the jet extensions was the part I was intrigued with, but turning the carb backward doesn't appear anywhere in the thread, nor does switching the metering blocks.
Senior moments, senior moments.....
There can only be 2 explanations--too much loud rock 'n' roll or alien abduction!
Doug
Only if the carb is a "Double Pumper" with the same size venturies primary/secondary can this be accomplished, and only if the (8) air corrector jets are threaded, removable and stay with the respective metering plates and float bowls to be able to be swaped from end to end. Don't even consider it otherwise, you'll have tuning and drivability issues that will never be resolved.
Pat Buckley
GT40s Supporter
Gee, I turned my Holley Double pumper around (which does not have same size venturis) and the car ran the same - just fine.
Can you tell me exactly why this shouldn't be the case?
Thanks.
Can you tell me exactly why this shouldn't be the case?
Thanks.
2124 said:
Yes!
What you've done is much too simple and easy for all the overkill/overthink guys on here!! LOL.
However it would appear there are differences in the fuel bowls front to rear and it wouldn't do any harm to swap them. Read Jac Macs reply carefully.
Cheers
One of my mates turned around a double pumper on a drag car and for ages this so called “engine builder” kept asking why he did it. Now my mate never told him why just to wind him up. One night at the track this “engine builder” came over and said he had worked out why it was reversed.
His theory was “As the driver nails the throttle, the primary throttle will be the closest to #1 cylinder, as it’s the first to fire and it will take off quicker”………..OK………I nodded my head and side stepped out of there !!!
The real reason why it was reversed, easier to connect to the throttle.
Clayton : )
His theory was “As the driver nails the throttle, the primary throttle will be the closest to #1 cylinder, as it’s the first to fire and it will take off quicker”………..OK………I nodded my head and side stepped out of there !!!
The real reason why it was reversed, easier to connect to the throttle.
Clayton : )
When you guys say "turn the carb around" what exactly do you mean?
The float bowls can be swapped end to end to change which side fuel is supplied from, or better yet buy bowls that have both bowl inlets drilled and tapped. The carb can also be mounted 180 deg from its "normal" position if you want the throttle cable to be on the opposite side. The thing to remember is exactly which holley list # carb we are speaking about, as this will determine what can actually be accomplished. I have a proform 750 cfm mechanical secondary carb on my ride and I can change anything on it except the power valve channel restrictors.
Regards,
Scott
The float bowls can be swapped end to end to change which side fuel is supplied from, or better yet buy bowls that have both bowl inlets drilled and tapped. The carb can also be mounted 180 deg from its "normal" position if you want the throttle cable to be on the opposite side. The thing to remember is exactly which holley list # carb we are speaking about, as this will determine what can actually be accomplished. I have a proform 750 cfm mechanical secondary carb on my ride and I can change anything on it except the power valve channel restrictors.
Regards,
Scott
Wow. A simple question, and I get 13 answers. Obviously not as simple as I thought.
I have a brand new in the box 4150 0-4781C Mechanical Secondaries Double Pumper.
I was not intending taking the float bowls off and swapping them to the other end. I don't mind if the primaries are at the front or at the rear, I'm just trying to plan the plumbing and throttle linkage. I can undertand if you want to swap the fuel delivery, while leaving the throttle linkage where it is, then you might need to do all that swapping of jets,venturis,accelerator pumps, or whatever, but I am happy to leave the throttle and fuel the same relative to each other. I just want to know if I have the entire carb assembled in my hands, does it matter which way I put it on the 4 studs?
Stuart
I can't compare before and after, because there is not a before.
In summary, I think it sounds like I can place it on either way to best suit the throttle brackets on the inlet manifold, and then plumb the fuel accordingly. I don't mind which side the fuel comes from, so I will leave the fuel bowls alone.
Thanks to everyone for all your input.
That then leads to the next question about setting up a double pumper for good idle emmissions (UK SVA test). But that can wait for another time.
I have a brand new in the box 4150 0-4781C Mechanical Secondaries Double Pumper.
I was not intending taking the float bowls off and swapping them to the other end. I don't mind if the primaries are at the front or at the rear, I'm just trying to plan the plumbing and throttle linkage. I can undertand if you want to swap the fuel delivery, while leaving the throttle linkage where it is, then you might need to do all that swapping of jets,venturis,accelerator pumps, or whatever, but I am happy to leave the throttle and fuel the same relative to each other. I just want to know if I have the entire carb assembled in my hands, does it matter which way I put it on the 4 studs?
Stuart
I can't compare before and after, because there is not a before.
In summary, I think it sounds like I can place it on either way to best suit the throttle brackets on the inlet manifold, and then plumb the fuel accordingly. I don't mind which side the fuel comes from, so I will leave the fuel bowls alone.
Thanks to everyone for all your input.
That then leads to the next question about setting up a double pumper for good idle emmissions (UK SVA test). But that can wait for another time.
Brought this one to the top again for an update. Was in christchurch (NZ) for a quick trip and visited Russ Noble. We had a quick look at the Race Demon carb he intends to use and found that the sight glass's on each bowl are at the same height, therefore the only thing that should need changed for back to front installation would be jet extensions and bowl vent 'whistles if installed.
Other makes/models may differ so check before you fit!
Jac Mac
Other makes/models may differ so check before you fit!
Jac Mac
as long as u have a manifold that accepts to turn the carb it is ok but dont use a dual plane manifold.if changing metering blocks check idle bleeds and high speed bleeds as they may vary.the 4by4 racers often use the foam in the bowls that works good with extensions on the jets
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