SLVRBLLT40 Posted February 6, 2008 Share Posted February 6, 2008 The ported dual SU's flow 360 for the two combined. I looked and found that a 44 Mikuni runner flows 211 cfm per tube. So x 6 that's a 1266cfm for the engine as a whole, which I've always heard is supposed to be extremely "over cabureted". How is that flowing less than a single Holley 390 that has to feed 6 cylinders through a relatively convoluted manifold? This is just more speculation here that doesn't add up. This whole thread is old, useless, and annoying. If someone wants to pony up some cash and actually TEST something, that would be great. As it is I'm pretty tempted to tool shed this one. Think about it for a second. The mikuni's your are talking about flow 211 PER TUBE. A 390 ontop of a common plenum, single plane intake manifold flows 390 PER TUBE. That equates to a total 3120 CFM V.S. the mikuni's 1266 CFM, which doesn't matter anyways, because all we care about here is flow per cylinder. Just take a look at a drag car running I.R. Hilborn versus one running a single quad ontop of a tunnel ram. The total CFM of the Individual Runner is WAY higher than what the single quad flows, due to the fact that each and every intake valve has access to the entire plenum full of air and gas when running a common plenum. So I didn't speculate on this one, I'd say I thought it through pretty well thanks. Quote Link to comment Share on other sites More sharing options...
JMortensen Posted February 6, 2008 Share Posted February 6, 2008 The way I'm seeing it, the flow rate of the carb is being taken into account, but the "suck rate" of the cylinders is not. In addition the flow rate of the runners, which is probably even more important is being ignored. Seems to me that the nicely tapered relatively straight shot runners of the triple carb manifold with a 44mm hole on the outer end would flow more than the log manifold that the AZC setup uses. I wonder how big the outer end of the runners are on that manifold. I'm guessing they aren't near 44mm... Quote Link to comment Share on other sites More sharing options...
SLVRBLLT40 Posted February 6, 2008 Share Posted February 6, 2008 And that is the main difference/point of argument between the two types of intakes I'd say. Quote Link to comment Share on other sites More sharing options...
madkaw Posted February 6, 2008 Share Posted February 6, 2008 I still would like to see a dyno day similiar to wind tunnel testing. I would think a dyno would rent much cheaper then a Nascar wind tunnel. Surely we could come up with enough combinations to test to make this worth while. More folks on this web site are concerned with HP then I believe areo efficiency. I realize this means a lot of wrenching and you would want to use the same platform(base engine) to get accurate results, but it could be done -couldn't it. It would be a Hybrid Myth Busters . I would think there would be more vendors that would get involved then was in the Tunnel testing. Things that could be busted 1) 4bbl vs. Su 2) Fuel Injection vs. both 3) n-36 manifold 4) header performance 5) electronic ign vs. points 6) mechanical fuel pump vs. electric 7) clutch fan vs. electric fan 8) triple webbers vs. all Just a thought- could it be done or would anyone else like to see this! Quote Link to comment Share on other sites More sharing options...
Guest TeamNissan Posted February 6, 2008 Share Posted February 6, 2008 The way I'm seeing it, the flow rate of the carb is being taken into account, but the "suck rate" of the cylinders is not. In addition the flow rate of the runners, which is probably even more important is being ignored. Seems to me that the nicely tapered relatively straight shot runners of the triple carb manifold with a 44mm hole on the outer end would flow more than the log manifold that the AZC setup uses. I wonder how big the outer end of the runners are on that manifold. I'm guessing they aren't near 44mm... The I.D. on the Cannon manifold in my basement is 38mm. I do agree with you that the I.D. on the AZC is smaller still though as I sold one back in nov. Quote Link to comment Share on other sites More sharing options...
JMortensen Posted February 6, 2008 Share Posted February 6, 2008 The I.D. on the Cannon manifold in my basement is 38mm. I do agree with you that the I.D. on the AZC is smaller still though as I sold one back in nov. If you're measuring the carb side, then you have a 40mm manifold. Regardless, the carb side should be bigger and will taper down to the head side. Quote Link to comment Share on other sites More sharing options...
Guest TeamNissan Posted February 6, 2008 Share Posted February 6, 2008 How many dif sizes are there? Quote Link to comment Share on other sites More sharing options...
JMortensen Posted February 6, 2008 Share Posted February 6, 2008 A BUNCH. In fact, after I posted I was thinking and I believe there might be a 38mm Weber. So 38, 40, 42, 45, 48, 50, and I think 55 are all out there, and there should be a manifold to fit each one. I'm guessing I'm missing quite a few. Quote Link to comment Share on other sites More sharing options...
Guest TeamNissan Posted February 6, 2008 Share Posted February 6, 2008 Wow, thats interesting. I was going to port it but hell, might as well just buy a bigger one. Quote Link to comment Share on other sites More sharing options...
Daeron Posted February 8, 2008 Share Posted February 8, 2008 My knowledge hoard isn't the sharpest, but I honestly thought that DCOE style webers went all the way down to 36mm diameter.. I did a brief net search (mostly google, wikipedia, and redline) and found enough to convince me 100% on the 38s, at least "once upon a time," but inconclusive evidence of 36 DCOEs. A few references to "36 dcoe" that may have been misconceived, and alot of co-incidence os "DCOE" and "36" where the 36 referenced a DGV. I really want to say I have seen 36mm side draft webers, or mikuni/solexes at least. If I am incorrect, then it is from confusing mikuni sizes with weber sizes. FWIW Quote Link to comment Share on other sites More sharing options...
ottoauto Posted April 23, 2008 Share Posted April 23, 2008 Hey. im just wondering if anyone knows the actual hood clearence height with the 4 barrel holler. considering scoop and filter options. Quote Link to comment Share on other sites More sharing options...
PanzerAce Posted April 23, 2008 Share Posted April 23, 2008 Hey. im just wondering if anyone knows the actual hood clearence height with the 4 barrel holler. considering scoop and filter options. Can't help you there, but I'm willing to offer up my car as a test bed for a triple Mikuni 44PHH vs. 4-bbl dyno pull if someone is willing to meetup and help with the wrenching and supply the 4-bbl. It ISN'T a stock L28, so we could see what the difference is on a larger engine. The ported dual SU's flow 360 for the two combined. I looked and found that a 44 Mikuni runner flows 211 cfm per tube. So x 6 that's a 1266cfm for the engine as a whole, which I've always heard is supposed to be extremely "over cabureted". Just wondering, where did you get those numbers? I've been trying on and off to find them... Quote Link to comment Share on other sites More sharing options...
JMortensen Posted April 23, 2008 Share Posted April 23, 2008 Just wondering, where did you get those numbers? I've been trying on and off to find them... Googled "44 Mikuni CFM" Quote Link to comment Share on other sites More sharing options...
ottoauto Posted April 28, 2008 Share Posted April 28, 2008 i just installed a holley 4 barrel with a arizona z intake. It's backfiring. It did the same thing with the su's. I've replaced rotor, wires, plugs, points, condensor, resistor, and played with the timing a little. I'm using a brand new holley 390cfm carb. The plugs indicate that it's running lean, but i was having the same problem with the su's so im pushed to think that this is an ignition or timing problem. I also just ordered a distributor off of a late 70's 280 with electronic ignition and i want to use this but i first want to figure out why it's backfiring. If it could be the vacuum advance then replacing the old distributor should fix this. Could any one maybe just give me a starting point. im pretty sure there aren't any vacuum leaks, but the brake vacuum lines do look a little worn. Quote Link to comment Share on other sites More sharing options...
brokebolt Posted April 29, 2008 Share Posted April 29, 2008 Remove the vaccum hose to the brake booster and plug the hole (do the same to all other vaccum taps). Do not drive the car in this condition it is just for analyst purposes. Start the car and check for the same problem. If the problem continues than varify the ignition timing to the crank. If the timing is good check the crank mark to the actual top dead center of the motor. Remove the valve cover and check the cam marks to the crank mark, and the top dead center on cylinder number one. If these three marks do not line up than you may have spun a harmonic dampener (very common) or your timing chain tensioner or slack guide is damaged/broken (also very common). A Chilton or Hayes manual will illistrate the location of the cam timing mark as well as how to determine the number one cylinder top dead center. If this all checks out than check the valve lash and cylinder compression numbers. It is possible their some issues with this area as they are adjustable and do need adjusting over time. Quote Link to comment Share on other sites More sharing options...
ottoauto Posted May 4, 2008 Share Posted May 4, 2008 The only problem im still having is that after rapid acceleration, unburnt fuel dumps out my exhaust. do i need to improve my ignition system. i have 280zx dist, new cap, rotor, wires, plugs, and will have my crane hi6 ignition in shortly. any known fix for this problem? Quote Link to comment Share on other sites More sharing options...
Clifton Posted May 4, 2008 Share Posted May 4, 2008 i just installed a holley 4 barrel with a arizona z intake. It's backfiring. It did the same thing with the su's. I've replaced rotor, wires, plugs, points, condensor, resistor, and played with the timing a little. I'm using a brand new holley 390cfm carb. The plugs indicate that it's running lean, but i was having the same problem with the su's so im pushed to think that this is an ignition or timing problem. I also just ordered a distributor off of a late 70's 280 with electronic ignition and i want to use this but i first want to figure out why it's backfiring. If it could be the vacuum advance then replacing the old distributor should fix this. Could any one maybe just give me a starting point. im pretty sure there aren't any vacuum leaks, but the brake vacuum lines do look a little worn. It sounds like you are throwing parts at it hoping you will get lucky and fix it. It will eventually work but it is expensive. Check your timing first. If you are asking if it could be vacuum advance, that tells me you haven't checked timing it yet. Quote Link to comment Share on other sites More sharing options...
Mr.INSANE Posted May 4, 2008 Share Posted May 4, 2008 This thread should be put in the tool shed honestly, So much misinformation. Especially since this thread is called the "facts" Quote Link to comment Share on other sites More sharing options...
ottoauto Posted May 4, 2008 Share Posted May 4, 2008 I have done my timing. all of the stuff i have put into it was stuff i wanted to do. the only problem i've run into was that fuel isn't buring after it speeds up rapidly. trust my i don't want to put any more money than i have to into this. so far i put elect fan on, removed A/C, put an electric fuel pump on, plated the mechanical pump, put my 4 barrel, and threw a glass pack on, but i know where there is a good set of headers that i will put on once i talk to a guy about bending my exhaust. now i would like to get it running as good as i can (without pulling or rebuilding) before i start puting some money into my interior, suspension, and drivetrain. and i have cheap access to parts Quote Link to comment Share on other sites More sharing options...
Clifton Posted May 4, 2008 Share Posted May 4, 2008 If you suspect your vac adv, put your timing light back on and disconnect it and see if it moves. You can also check total timing and see if your mech adv is working. Is it backfiring out the intake (lean or timing way off) or the exhasut on decel? Quote Link to comment Share on other sites More sharing options...
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