So you thought you could tune a Holley

[1987cp]

1040cfm total. Have you ever heard of a 260cfm four-barrel?

[P72Ford]

Under what standard condition do they flow 520 cfm?

The same standard condition that the 390 cfm rating was evaluated at?

By standard condition, I mean pressure/ vacuum? Usually inches of water depression for a carb rating, I believe.

We should all know that a flow rate doesn't mean anything without knowing what pressure drop it was achieved at.

[turbo2256b]

They flow them at the same depression as Holley. Back when I was putting front metering blocks, larger throttle plates on smaller Holleys, maching choke horns off and blending in the top, slabing throttle shafts swapping out booster venturies, hogging out carb s etc they started a busines doing it. Think they started out in the mid to late 60s

Now there is the question do they actually flow that much on my engine? Is my pump efficent enough to do it. At this point I dont realy know. I could even flow more if my pump is efficent enough.

What I do know is when the secondarys open and RPMs get up somewere over 4000 RPM give or take. When they close you think the trany just down shifted. It was so freeky of a feeling that it took me a bit of testing it out before I figured the trany wasnt having issues or had a 5 gear in it all of a sudden. Had me worried for a bit. Still is initally scarry when it happens.

[turbo2256b]

I'll be glad when you get this done. I've gone up 8 numbers on my jetting and it's close now but still screwy off idle.

Going up 8 jet sizes is usualy something that needs to be done with major engine mods like well portedd heads. You probably wont want to read this but on our heavy cars or any heavy vehicle its most effective to use a vacuum secondary carb. One thought I have is your signal strength through the carb is weak. This would be another reason that would require larger jets.

Also figuring your refering to off idle stumble mostly from a stop then light acceleration refered to as tip in but no issues at higher speeds tiping in the throttle?

[turbo2256b]

Best to down sizing the main jetting a couple steps at a time untill it runs bad. Started out at 55s dropped to 50s before it realy ran bad. 52s ran good. Possibly 53 would be better. Have to order some of them. I didnt have anything between 55 an 50 other than 52s. Have some 51 and some smaller than 50.


Here is whats going to happen jetting down untill light load and cruse crap out for your style of driving. Once that is determined a jet size or two bigger is going to be real close.

Next the biggest jet required for best full throttle acceleration has to be found. This can also be reversed find the best for WOT then the best for light loads and cruse. It s up to you. Records should be kept of what you have done so if things go wrong it can be reversed its going to happen. In fact your hopping it does.

You might think this is a pain but I have spent months with a tweecer doing the same stuff and its just as big a pain.

[Southern_Pride]

No like it has a dead lean spot barely off idle. The richer I set the idle the better it is. You add throttle and the rpms drop, then jump. But it will run all day at the lower rpm. It probably does have a weak carb signal. I get decent mpg though. The heads choke everything. At cruise going by plugs the mixture seems close. I like my manual secondary carb. Vacuum secondaries may make it faster, I just trained my foot not to mat it everytime I wanna take off fast. Rolling in the throttle on hard acceleration produce better results.

[Crownvicman289]

So are Holleys really that much better than Edelbrocks? I had an Edelbrock 600cfm/Weiand Stealth intake on my car up until early this year when I swapped for an Exploder intake manifold and Mustang EEC. The most frustrating thing about tuning the Eddy was the eventual compromise I had to make in the tune. As I'm sure you're aware, Eddy uses step up needles in the mains for the cruise circuit. At a high vacuum level, AFR's were a bit rich and gradually leaned out until the spring stepped up, at which point AFR's were rich again and gradually leaned out as vacuum decreased. I had to tune for the lesser vacuum levels which left everything else a bit fat, or else put a weak step up spring in there so no matter what, there was always a fat spot. This was after I blew $50 at OReilly's buying jets and rods to try to make it work for me. I'm assuming Holley's power valve is just like that step up spring that Edelbrock uses. Are you able to get spot on AFR's or is that just a fact of life with a carb?

[turbo2256b]

I have messed with the Eddys and Quadrajets. Their not my favorites on built moters. There is a reason why most all venues of high performance end up with Holley designs.

[1987cp]

All my carb experience is with AFBs, and while I still like them for their cheapness (especially the ability to buy a complete basic tuning kit as cheap as $35) and conceptual simplicity (at least to me ...), I agree that they're probably getting to be quite outdated. I guess they're not bad for a design that's probably seen minimal if any refinement in the 54 years since it was introduced, but my reading suggests that Holley-based guys have been working quite actively to make their stuff more responsive, more reliable, and even (supposedly) much more efficient. Even just thinking about the Holley pump cam arrangement and the ease of swapping secondary springs can make me extremely jealous if I let it.

The cost of Holley tuning parts was one thing that helped steer me away from them initially, but it's worth noting that I'm already well off the carb-model-specific tuning chart in the quest to get one of my AFB cars really responding well, and it looks like AFB stuff gets pricy anyway if you have to buy it separately from the kit (or buy multiple kits, or whatever).

[gadget73]

Holleys are a lot more tunable than the AFB design is. The AFB is a decent all-around daily driver carb but I've never seen one that was dead-nuts on. Its also a pretty old design. It was probably advanced in its day, but that was the late 1950s, and it hasn't changed very much since then. Qjets are more adjustable. Probably not the penultimate performance carb, but for a mild or daily driver application, they work very well. They also sound a lot cooler than square carbs, but thats just my opinion. I love the sound of a big spread bore opening. The Carter Thermoquad also sounded awesome with those twin mineshafts at the back of the carb body.

[import convert]

idk if i like he holley or the quad more. im finding that the quad needs more time and attention to detail to do small changes than a holley needs. like to change the primary rods you need to knock the pin out of the accelerator pump and then undo all the bolts to the hat and pull the rod assembly and then find a good rod while on a holley you just pull the bowl off and put diffeent jets in.

i do like the extra growl you get when the secondaris open and idk the car seems to run very well with the quad. i actually had more problems with getting the holley set up then i have with the quad. only issues ive had with the qaud was becuase i didnt quite understand how it worked and how each circuit worked and made it work. im still learning but yea all my holley stuff may be sitting around for a while. i do need different secondary rods though

[Crownvicman289]

My dad used to preach that a properly set up quad is a good carb, just that hardly anybody can properly set them up.

[1987cp]

"Quad" = Rochester Quadrabog? If so, I've heard the same thing about them having very good potential. Yet, if I ever leave AFB-land, I intend to go with a Holley based design for a variety of reasons, including parts availability and the fact that people are still developing them and making them better.

[1987cp]

No like it has a dead lean spot barely off idle. The richer I set the idle the better it is. You add throttle and the rpms drop, then jump. But it will run all day at the lower rpm. It probably does have a weak carb signal. I get decent mpg though. The heads choke everything. At cruise going by plugs the mixture seems close. I like my manual secondary carb. Vacuum secondaries may make it faster, I just trained my foot not to mat it everytime I wanna take off fast. Rolling in the throttle on hard acceleration produce better results.

Can't tune out your lean spot with squirters and pump cams? I know on my EDL-1404, I resisted taking the primaries really rich until I realized I was relying on a rich idle to try to compensate for them being too lean.

[turbo2256b]

No like it has a dead lean spot barely off idle. The richer I set the idle the better it is. You add throttle and the rpms drop, then jump. But it will run all day at the lower rpm. It probably does have a weak carb signal. I get decent mpg though. The heads choke everything. At cruise going by plugs the mixture seems close. I like my manual secondary carb. Vacuum secondaries may make it faster, I just trained my foot not to mat it everytime I wanna take off fast. Rolling in the throttle on hard acceleration produce better results.

Lean spot off idle. What to look for to begin with.

This will require pulling the carb. Does anyone know what the Curb Idle Discharge Hole is? How about the Idle Transfer Slot?