1 fast z Posted July 16, 2008 Share Posted July 16, 2008 Good Luck................................................................................. Quote Link to comment Share on other sites More sharing options...
duder280z Posted July 16, 2008 Share Posted July 16, 2008 Just a thought, I assume these are from a 750 4cylinder with 1.5 sets of carbs put together. If you multiply 750 x 1.5 you get 1150cc. The motor your puting them on is a 2800cc. Now I know the bike spins faster (old bike, maybe 9000rpm max) but are these gonna be enough carb to have any sort of top end? Bottom end could probably be great, but I'd think you'd hit a brick wall way before redline, even with boost. That was the first thing that came to my mind. If I'm way off here, someone please fill me in. If you get this thing running I'd love to see it sometime, Puyallup isn't that far from Lynnwood... Quote Link to comment Share on other sites More sharing options...
Daeron Posted July 16, 2008 Share Posted July 16, 2008 Just a thought, I assume these are from a 750 4cylinder with 1.5 sets of carbs put together. If you multiply 750 x 1.5 you get 1150cc. The motor your puting them on is a 2800cc. Now I know the bike spins faster (old bike, maybe 9000rpm max) but are these gonna be enough carb to have any sort of top end? Bottom end could probably be great, but I'd think you'd hit a brick wall way before redline, even with boost. That was the first thing that came to my mind. If I'm way off here, someone please fill me in. If you get this thing running I'd love to see it sometime, Puyallup isn't that far from Lynnwood... I can't find out exactly how many carbs the bike used, but it was originally a 3 cylinder. so if the bike used three carbs then he is using two full sets. Not that much difference, but I'm not sure the bike used three carburetors.. (maybe I'm just ignorant on motorcycles, heh) The Mikuni CV Mark II carbs he is using apparently came with bore diameters ranging at LEAST from 32mm to 40mm, so theres no telling without getting a bore diameter from the OP. What size ARE they? Quote Link to comment Share on other sites More sharing options...
speeder Posted July 16, 2008 Share Posted July 16, 2008 Check this out. I saw Eiji's car in person and its sound and looks are amazing. http://www.datsunspirit.com/240z.html Second the good luck wishes for the carbureted turbo. Quote Link to comment Share on other sites More sharing options...
duder280z Posted July 16, 2008 Share Posted July 16, 2008 I can't find out exactly how many carbs the bike used, but it was originally a 3 cylinder. so if the bike used three carbs then he is using two full sets. Not that much difference, but I'm not sure the bike used three carburetors.. (maybe I'm just ignorant on motorcycles, heh) The Mikuni CV Mark II carbs he is using apparently came with bore diameters ranging at LEAST from 32mm to 40mm, so theres no telling without getting a bore diameter from the OP. What size ARE they? OK, so they must be from a 3 cyl. 2 stroke. Those bikes were (are) legendary. I've heard countless stories from old school race bike riders that got to ride one of them and they all had the same reaction, freaky, scary, insane, retarded fast. That being the case, it makes more sense. If he can get it tuned right, it just might kick ass. Keep us updated dude! Quote Link to comment Share on other sites More sharing options...
Challenger Posted July 16, 2008 Share Posted July 16, 2008 OK, so they must be from a 3 cyl. 2 stroke. Those bikes were (are) legendary. I've heard countless stories from old school race bike riders that got to ride one of them and they all had the same reaction, freaky, scary, insane, retarded fast. That being the case, it makes more sense. If he can get it tuned right, it just might kick ass. Keep us updated dude! Also Id suggest buying a non webbed manifold... like mine.. Quote Link to comment Share on other sites More sharing options...
supertip Posted July 16, 2008 Author Share Posted July 16, 2008 Ok, they are 34mm, and yes it was a 3 cylinder bike, does it really matter that they came off a 2 stroke? But the cfm should be no problem. There is a forum about "6 carbs" that goes over the cfm requirements and these meet it. Can you post a picture of your manifold, I bought mine on ebay for $40. But also I thought that the webbed mani would provide more support. Quote Link to comment Share on other sites More sharing options...
duder280z Posted July 16, 2008 Share Posted July 16, 2008 does it really matter that they came off a 2 stroke? Well at least for initial tuning I'd think so. The carb requirements for a 2 stroke are pretty different than a 4 stroke in that a 4 stroke uses less air and fuel as a 2 stroke for the same given rpm. 4 strokes only need fuel and air every other revolution, 2 strokes need it every time around. The carbs on a 750 4 stroke of the same vintage would typically be smaller and jetted leaner. This may actually work to your advantage with a turbo (starting with richer jets that is). When time and money permits I'll be going Megasquirt myself, but I give you a big thumbs up for origionality. Quote Link to comment Share on other sites More sharing options...
Daeron Posted July 17, 2008 Share Posted July 17, 2008 well, whatever CFM they flow, a 34mm carb is NOT very large for a Z-car engine.. Keep in mind that the standard Weber/Mikuni/Solex "bore size" debate is between 40 and 44mm, with occasional bouts up to and including 50mm! I'm still not knocking anything, I am just trying to put it all in perspective. Quote Link to comment Share on other sites More sharing options...
2eighTZ4me Posted July 17, 2008 Share Posted July 17, 2008 Yes - but keep in mind the port openings at the head are roughly 34-35mm. So, theoretically, that would be a straight shot with no taper in the bore of the intake to the head. Secondly, you never run Webers wide open at 44 or 48mm. They have chokes that take them down in sizes ranging from 28-38mm. You can only stuff so much air in a 34mm hole, and also depending on what other mods have been done to the motor will affect jetting and choke size selection, as well as overall performance. He "could" have a pretty hot setup - never know until the dyno... Quote Link to comment Share on other sites More sharing options...
supertip Posted July 17, 2008 Author Share Posted July 17, 2008 Daeron, you said the webers are 40mm, but I only had two of them. Now I have 6 34mm carbs. What am I missing here? Not trying to argue, just trying to understand. Yeah I know a guy that runs a Kia club, ha a Kia club... but he puts on an event out here every year and dyno runs are only $20 Quote Link to comment Share on other sites More sharing options...
Daeron Posted July 17, 2008 Share Posted July 17, 2008 Yes - but keep in mind the port openings at the head are roughly 34-35mm. So, theoretically, that would be a straight shot with no taper in the bore of the intake to the head. Secondly, you never run Webers wide open at 44 or 48mm. They have chokes that take them down in sizes ranging from 28-38mm. You can only stuff so much air in a 34mm hole, and also depending on what other mods have been done to the motor will affect jetting and choke size selection, as well as overall performance. He "could" have a pretty hot setup - never know until the dyno... I am aware that the bores are tapered down by venturis in all the side draft carburetors installed on Zs, but I was referring to the standard six-throttle carb setup as it has been used on Z-cars for 40 years; six 40 or 44 mm bores tapered down by say, 36 or 40mm venturis respectively. (Am I overestimating? do that many 40mm carbs actually get 32mm venturis?) Understood, certain applications will see throats/venturis ranging from 28 to 42mm (I know I've seen 38mm venturis for 40s, I presume 42 on 44s) Given all of this, it stands to reason that a 34mm bore carburetor is more limited to its power potential than a 40mm bore carburetor, which these mikuni CV mark IIs apparently came up to (according to superficial google search by yours truly.) I have never seen an L engine where the carburetor venturi size was specifically chosen to match the intake valve size. As I understand it, the venturi is there as a restriction in airflow to generate the vacuum needed to suck the fuel up through the jet and into the engine. The valve size is taken as a given, and the carburetor inlet bore is sized to flow an appropriate amount of air into the engine. The venturi is sized to tune the carburetor to feed this engine the right air/fuel mix, and then the intake manifold runner and intake port in the head are shaped, sculpted, and sized appropriately to ensure that this given amount of air and fuel, achieve high (and highly tuned) velocity on its way through the intake, into the engine, and out the exhaust. To achieve this velocity, the size of the air channel usually starts out large and tapers down to the size of the valve gradually. In other words, the fact that many many L-series engines (four and six cylinder alike, cylinder size matters more than whether its an L6 or 4) have venturis sizes that are similar to their valve sizes is largely coincidence. And PLEASE understand, I am not trying to sit here with my arms crossed and explain why what you said is wrong.. I am trying to either explain why 34mm bore carbs ARE inherently a bit more limiting than 40, or explain MY misconception that keeps me from understanding your point of view.. so please, don't take offense. I wasn't trying to take any tone, just to explain as well as possible in as few words. I should also mention that 99% of my personal hands-on experience with these types of side draft carbs is helping my uncle with the carbs on his roadster engines, (U20 OHC 2 liter as well as 1600 OHV) but he runs triple webers on his Z, and we know plenty of 510 guys, so the discussions and lessons have run the gamut of 4 and 6 cylinder datsun concepts with sidedraft, individual throttle carbs. MOST of the time it has concentrated on max-effort power, but rarely (only two engines) has max-effort power meant "race engine" as opposed to street car use. Daeron, you said the webers are 40mm, but I only had two of them. Now I have 6 34mm carbs. What am I missing here? Not trying to argue, just trying to understand. Yeah I know a guy that runs a Kia club, ha a Kia club... but he puts on an event out here every year and dyno runs are only $20 I am not quite understanding this.. two webers? I guess you are saying that this is certainly an upgrade from stock SUs, which I would never argue against. I LIKE what you've done, and I need to emphasize that I suppose I am merely pointing out a "ceiling" of sorts. If you have six 34mm bore carbs, then you certainly have less flowing potential then someone who is running 40 or 44mm bores. or is 34mm the venturi size in the carbs you have?? If that is the case, then you are most assuredly running comparable sized carburetors to the "standard." Once again, I say above ALL else that I really like this setup for its originality, resourcefulness, and execution. I only wanted to point out the potential shortcomings and put them in perspective compared to the "standard wisdom," more conventional choices. In all honesty, I like the way these carbs look set up next to each other ALOT, (more each time I look at em, and I liked em in the first place) and with a nice airbox, a proper setup and tune, large venturi throats and a well-selected turbocharger, I am sure you would make enough power and look pretty enough doing it to make everybody talk nice or shut up Quote Link to comment Share on other sites More sharing options...
supertip Posted July 17, 2008 Author Share Posted July 17, 2008 Oh, so like a big funnel. When I said two webers I meant DVG's, the car had dual weber DVG's. Please don't take offense to my comment, any information I can get is greatly appreciated! Quote Link to comment Share on other sites More sharing options...
Daeron Posted July 17, 2008 Share Posted July 17, 2008 Oh, so like a big funnel. When I said two webers I meant DVG's, the car had dual weber DVG's. Please don't take offense to my comment, any information I can get is greatly appreciated! understood stinks how sometimes things like this can get misinterpreted over forum chats, good to know we are all on the same level. Quote Link to comment Share on other sites More sharing options...
2eighTZ4me Posted July 17, 2008 Share Posted July 17, 2008 Daeron - good points. (and Good Lord - it IS almost 40 years!!!) I was just trying to point out that this setup would be good for a torquey motor that's going to be limited on top end. Yes - it all depends on runner length, choke size, jet size, cam etc., but if he has a stock motor that he wants quickness out of, 34mm isn't a bad choice. The point I was trying to make is that the port size on the head itself is roughly 34.5mm, and yes - you want all the velocity you can handle for the effectiveness of the air /fuel charge. The stroker I'm building has the Canon intake that came with my Weber 40's. I have port matched the intake to the head such that there are no "lips" anywhere on any of my intake runners to obstruct the already moving air/fuel charge on its' way to the valves. Intake valves on these motors range from 42-44mm, so it's not the valve size I was referring to, but rather the overall size of the intake port on the head as the restrictive factor. You want the air/fuel charge moving as quickly as possible into the combustion chamber, and the less obstructions you have going into the intake port is going to yield higher velocity and greater intake charge. Being that the intake port size is roughly 34.5mm, a 34mm carb (without chokes) might not be a bad setup. I'm really curious to see how well it does on this setup. I just got a set of Mikuni 44's choked down to a 37mm (built by Rebello). That - in conjunction with my port matching work - I'm hoping is going to yield something a stroker can use around 4500-7000 rpm. It's probably not going to do well much over 7500rpm, but my goal is a track car that is torquey, such that I can get out of the corners quicker. Tony D states that a Z with more than 350hp is basically useless, as it's hard to keep it under control with that kind of power. I wanted something that can get up to revs quick and scoot past folks in the turns - relying on the handling characteristics of the car, rather than brute force power. The more I think about it, the less I'm leaning towards a turbo car. I think I'd end up more ticked off waiting for the boost to come on (in hopes of passing someone on the straights) than I would be if I could take position out of the corner and maintain down the straights. I'll use gearing to change top end characteristics. I'm a wuss with Z motors. I don't think I've ever revved past 6500 on a stock motor anyways - even though it can probably take it. I'd like my power band just a little below that and use gearing for top speed, rather than eat my motor winding it out trying to catch the guy in front of me. Meh - just babbling at this point, hope my post made some sort of sense. I'm just "stirring the pudding" on this topic - showing (what little) I know and hoping to glean more knowledge by throwing my thoughts out there. Quote Link to comment Share on other sites More sharing options...
supertip Posted July 18, 2008 Author Share Posted July 18, 2008 Well I am leaving for Annapolis for a 2 weeks in DC and the Academy on Saturday. My dad will be back from Afghanistan when I get back so hopefully I will post a video of it running. And 2eighTZ4me, your excuse for no turbo is nonsense, you just have to always being going so fast that the turbo is maxed out! Quote Link to comment Share on other sites More sharing options...
SidWell Posted July 18, 2008 Share Posted July 18, 2008 I am not much up on tuning multiple carbs these days but it seems to me that keeping 6 carbs in tune is a bit of a handful. As an earlier post said, you get full marks for creativity. I just wonder how many miles you will get between taking a screwdriver to the carbs. Quote Link to comment Share on other sites More sharing options...
MoNkEyT88 Posted July 19, 2008 Share Posted July 19, 2008 I'm glad my car has ITB's stock, they sure look cool. Quote Link to comment Share on other sites More sharing options...
Challenger Posted July 20, 2008 Share Posted July 20, 2008 Is that your BMW? Quote Link to comment Share on other sites More sharing options...
MoNkEyT88 Posted July 26, 2008 Share Posted July 26, 2008 No, mine is stock. Quote Link to comment Share on other sites More sharing options...
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