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Holley 4BBl Performance


porkbun

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The preferred carburetor of classiczcars and S30's all over the world! LOL

Ive run used SU's and ZTherapy SU's but they have never come close to the level of performance that my car was on when it had the 4bbl on it (when I first got the car). Ive got a close ratio 5sp, cam, clifford header, and a Crane XR700 ignition so it was pretty fast with the SU's but the 390cfm takes it to another level. Lightning fast startups with the electric choke is the cherry on top since this is a NE car and my daily driver(and only car!). I have the cartech adapter bolted onto the SU manifold but I have a BSR manifold on the way which should be a more permanent setup.

Definitely not the fastest it couldve been since Im new to Holleys and my tune is nowhere near perfect, the tires were spinning through ~30mph and I shifted late but it does show the Holley is certainly no slouch! 0-60 was in ~6.4 seconds and I plan on being well into the 5's once my manifold arrives and I take another video(hopefully!)

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Thats not quite what I was trying to say so I should probably clarify about my history of carbs on this car.

I bought the car with a Holley 4bbl and misdiagnosed a failing distributor and poor gas mileage as a problem with the Holley(I had only had experience with SU's up to that point and didnt really want to or know how to mess with a 4bbl). Turns out on top of the failing distributor the previous owner had it at ~30degrees of advance at idle. I bought a set of ZTherapy SU's and ran those on my car and I got 15/22mpg(averaging 80mph with both windows down). Traded the ZTherapy SU's for a non ZTherapy setup since I was short on cash and ran those for a short while while the 4bbl adapter and swap parts were on the way. Im assuming thats what you mean by poorly tuned SU's since I pretty much just slapped those on the car before I sold them.

The two videos are NOT meant to be a comparison which is why I didnt bring it up...but if we are talking questionable tests my car with a poorly tuned Holley is faster than the 71 240Z with an L28 "a Racer Brown cam, competition valves and springs, triple Mikuni 44PHH, Header to a 2.5 inch pipe with a Supertrap, and 'fat sticky Yokohama A001-R in 225-60-14e'"(I literally have the second cheapest all season tires Town Fair Tires offered. Big mistake I know) tested in an old car and driver magazine LOL

Why did I switch back? The 30 degrees of advance and failing distributor explained the poor gas mileage on the Holley. Everything else but that was great. No choke cables and I fire up in any weather like I have EFI (7 degrees was no problem this morning!). Throttle cable is butter smooth and the performance bump makes in town driving(which is what my commute is now) a lot more fun. Plugs were all identical. I switched back to find out what kind of fuel economy I get with a good distributor and proper timing and to see if the Holley was as nice as I remember.

I should also add that the Holley was a used eBay carb and the adapter a pretty beat up cartech example.

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That video was the same day I bolted the carb on and the only adjustment I made was the pump cam position. Since then ive learned that the power valve was the wrong size, the accelerator pump arm was not setup properly, floats werent setup properly and who knows what else had been changed but it was still good for ~6.4s 0-60 and ~14s 0-90. I only made this post because everyone seems to think that 4bbls on Z's are unusable and inferior. I dont want to start another theoretical debate since Ill bring more proof in the form of another video when all the new parts are bolted on

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man i would love to believe that the holley is the choice. i know holleys and learning su carbs buttt... If your speedo is anything like mine 60 is really 50 and 90 is about 74 . If they are so great why isnt everybody doing it . I AM NO EXPERT. but am really curious . I really have to question z therapy vs holley set up would love hear others chime in

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Im not trying to say that one is better just that the mods that have been done to my car react to the 4bbl very well contrary to what ive been told and what I have read (which is why im making this post). My speedo appears to be pretty accurate but im not sure what an acceptable method of testing it is. Its been "verified" at different times via GPS, "Your Speed" signs, in comparison to the flow of traffic, and comparison to newer cars. Perhaps next run Ill have some GPS on board?

I think the main reason people dont do it is because in theory it sounds like a horrible option. Had my car not come with a 4bbl I NEVER wouldve bothered putting it on since people talk about poor cylinder distribution, 90° angle air and fuel bend etc(no coolant lines hooked up btw so my atomization should be poor). and it all makes sense...but the overwhelming majority of people regurgitating these "issues" dont have or have never had a 4bbl on their car. The weird part is that pretty much everyone who has 4bbl parts wont part from them without a sizable chunk of money. I say try it out if you can, get your hands on an adapter. Its a quick swap removing the SU's and if you buy used its easy to sell your parts for close to what you paid for them.

If Im understanding this correctly ZTherapy carbs dont offer any additional performance but just assures that the throttle shafts never leak and that you get a better than new set of carbs with no vacuum leaks or problems that could affect old used SU's. That said my car may have been able to make use of SM needles but when I tried swapping in some 'SM' needles I got from a british shop, the car could barely idle it was so rich (even with the mixture screws bottomed out). For all I know when I install the Bob Sharp Racing manifold I may encounter all the problems I heard about :rolleyes:

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My first experience with domestic downdrafts on foreign in-line engine. 1969. An old drag racer I knew "fixed" his son in law's XK120 Jag, carb. problems, in an afternoon. He fabricated the flanges, found some exhaust bends, fitted & welded everything up, mounted a used two barrel carb. from a Ford engine of about the same cubic inches as the Jag and fired it up. Everyone loved the conversion. It's your Z, go for it. If you build the manifold it will be that much cheaper & a source of pride. We want photos. Mark in Portland

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There are a few stories of 4bbl success but you rarely hear it over the hubbub. I sold my all original 260Z to get a project so I could learn more about car and this car has taught me a bit and has gotten me more comfortable with working on cars. Learning how to weld is high on my list of priorities but it hasnt happened yet so I think itll be a while before Ill be able to build my own manifold. Not sure if you want a picture of my theoretical manifold or my setup but this is what my car looked like the day I drove it home. I think its a pretty clean look

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Funny thing, You put a downdraft on a Z and it's instantly the red-headed step child, still part of the family but,,,Well,,,,You know. Very few of the Zs on the street are 100% original, Most of us are trying to "improve" our Zs so we can enjoy them. If you're more comfortable with a Holley, do it, I think it would be a great conversation starter. Most people more curious than judgmental.

Mark in Portland

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Do you remember what kind of adapter/intake you had when you installed it? Not that I can diagnose your problem or anything, just curious.

The guy I bought the BSR manifold has run a number of different 4bbl/intake combinations on Z's before and he said the Arizona manifold is made better than the BSR manifold which is why he was selling the BSR manifold. He reckons that with a bit of porting the AZC manifold could make more power than the BSR manifold which is exactly what hes going to do. Aside from that and the throttle linkage mounting on the BSR, they are the same. A couple years ago on hybridz, the owner of AZC made a thread addressing the usage of a 4bbl on a Z. He was definitely right about "junkyard" carbs, trying to return everything to stock would put a massive hole in my wallet. BSR manifold should be installed on Friday!

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Bob Sharp manifold arrived today. Theres a little rib inside intake before the 3 & 4 runners that is not on the Arizona Z Car manifold that I think was put in there to prevent cylinder distribution issues? Just a guess but it looks pretty restrictive. Any ideas? Heres the inside view and the bottom view. You can see where it juts out on the inside view and its looks nowhere near as narrow from the bottom.

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  • 3 weeks later...

Ive had everything installed for a week or two and I think ive got the whole tuning thing down. Went from having to turn 2-3 screws on the SU's to 7+! Notice the sweet return spring setup!

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Much easier to install with no balance tube in the way (I had to do it twice since I had to tighten the coolant fittings on the bottom and my header was in the way). Most difficult part was the throttle cable install. The BSR manifold has the throttle linkage posts which just got in the way of the recommended spectre install hardware so I had to cut that up.

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The stupid black plastic piece that goes on the end of the sheath cracked as soon as I installed it and then I had to pull everything apart and bore out the plastic piece because it was preventing the cable from moving freely :finger:

I love the setup :love: pulled the plugs and they were uneven and so dark!! :cry:

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This explained my fuel economy and gave me some info about my mixture but it also happened to be the complete opposite of what people told me I would see, 3 and 4 were the leanest! Yesterday I cleaned the plugs, lowered the floats and also brought my timing down to 15 degrees from 20(so much for that supposed increase in fuel economy). Pulled the plugs again today and saw all the plugs were a light brown but 3 and 4 were a little richer than 1 and 6. Im hoping that by going to the FSM recommended 17 degrees (Not the random sources on the internet :stupid:) Ill have a nice even mixture across the board. 0-60 run will have to wait until there isnt as much snow on the ground and piled on the side of the road.

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The only time the engine sees at the initial timing point is when the throttle is closed, assuming ported vacuum is used for the vacuum advance, and the centrifugal is stock and working properly. Otherwise, throttle open applies vacuum advance and increased RPM applies even more. Those two will determine how the engine runs when driving.

In short, make sure your advance mechanisms are working properly and they're what you want for mileage and power.

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Zed Head, your post caused me to look up how my distributor actually works :). I read a couple places that advancing the timing a bit more could get me better fuel economy around town but I think it made it worse. This car has NEVER gotten very good gas mileage(compared to some of the numbers I see posted), I think the best ive ever gotten out of all the carb setups Ive tried was 22/15(shifting at 2k) with the ZTherapy carbs but I have no idea how much the cam/close ratio 5sp/3.90 affects it. Maybe I should take closer look at the distributor? Interested to see if the timing can really change the color of my plugs

With that super wealthy and advanced setup I had before I was getting ~10mpg but its also hard not to floor it with the pedal/throttle response (probably my favorite part of the swap). I think I might get this carb tuned up as well as I can and put in a super stiff secondary spring if my fuel economy isnt where Id like. My car is my daily driver and only car so I have to worry about these things

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Edited by porkbun
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Took some shots of the plugs today at 17° initial timing. I just cleaned up both electrodes before I reinstalled them last time. The white/grey looking stuff is anti-seize

(especially on #6!) that managed to get on a few plugs but wouldnt wipe away entirely

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Plugs 1 and 3

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ClassicZCars you saw it here first. Ive managed to run a Holley lean! LOL

Edited by porkbun
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  • 1 month later...

Porkbun, great work with the Holley et al. I'm a devotee to this way of thinking and I endorse completely what you've done to your engine!

I personally would love to see your theoretical manifold design for the four barrel carb. I've done my own research and looked carefully at several manifolds for the L and other engines and if I had the time and money, would've created that manifold.

As it turns out, I use an AZC on one of my cars and a Clifford 6=8 on the other. The Clifford intake supports 212 rwhp on my L28 normally aspirated!!

Keep up the great work, Cheers.

Edited by ozconnection
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  • 1 month later...

Its been a while since I updated! Regarding the manifold design, I emailed Dave @ AZC. The BSR has a lower divider, narrower runners, and those ribs before the #3 and #4 runners. Dave said "...The divider in plenum makes a dramatic improvement in low end response, I also opened up the runners for improved top end. Overall performance is excellent." So the AZC appears to be better than the BSR.

A couple months ago I realized that I was only getting ~11-12 mpg which didnt make any sense. I finally decided to get a vacuum gauge and hooked it up to the base of the carb: at idle I was pulling ~5mmhg (is that the right unit? I dont have the gauge in front of me and I just took a Chemistry final LOL). I had a 6.5 power valve in the car which means that the power valve was open as soon as I started the car (thanks a lot cam! My old carb had an 8.5 in it!). Went to a 2.0 power valve and #55 jets from #51 jets (each jet size is a 4% increase in fuel) and my fuel economy went up as well to ~14-15mpg city and but only 19mpg @80mph on the highway :( . I was getting decent fuel economy but the crazy speed was gone. I threw some #60 jets in got some oomph back but a big drop in fuel economy and the plugs were only the tiniest bit browner. Seems like I can jet wayy richer for performance but im learning that performance and fuel economy dont really go hand in hand. I would go out and get some 0-60 videos but I got wider tires and ruined my u joints after a couple of hard launches LOL. Im interested to see the 0-60 times as is, with the pig rich setup (#51 jets, 6.5 power valve), and the ultra wealthy setup (#55, 6.5 power valve depending on how the plugs look after the first run).

Thinking about switching back to SU's or maybe triples if a cheap set pops up. Nothing wrong with this setup but Id like to mess with SU's and see if I can get similar performance(and maybe pick up a wideband!). I just past the year anniversary of the day I got this car and ive done 5-6 carb swaps already :stupid: For some reason I just cant leave the car alone!

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Dont tempt me! Im going to go back to SU's and try and get it setup using a throttle cable (also going to ask a guy I know who restores E-types if he has any 2" SUs). Ill probably go back to a 4bbl eventually but its time for a change and some experimentation now that the weather is nice!

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  • 2 weeks later...

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