Guest butlersZ Posted July 15, 2003 Share Posted July 15, 2003 Does anyonehave any opinions on what works better and creates more hp, S.U.'s or the 4 barrel setup? I have a 74 260 with those damn flat-top carbs and have the choice to buy a set of 70 240 S.U.'s or the four barrel conversion manifold offered by Arizona Z Car with a Holley 650, which should I go with? Quote Link to comment Share on other sites More sharing options...
Drax240z Posted July 15, 2003 Share Posted July 15, 2003 SU's all the way. 650cfm is wayyy too much carb. The SU side draughts work very well if in good shape. (I've had them on a daily driver for 2+ years) They don't take much fiddling once you get them set, and they just don't have issues. Reliable, easy, inexpensive, and you can definately get some power out of them. (ask norm and his 12.88 1/4 miles!) The 4 barrel design has some inherent problems, greater initial cost, and is way too big for the engine. Quote Link to comment Share on other sites More sharing options...
brokebolt Posted July 15, 2003 Share Posted July 15, 2003 I agree that 650 is to large a carb for a stock or slighly modified in-line 6. SU's are an excellent choice for performance, reliability, fuel economy, and easy to tune. Down drafts take a bit more knowledge and parts to tune but don't discredit them. I have used every type of N/A induction and I do like the SU best for the reasons listed above. If your a quality tunner of downdrafts or know someone that is, you can get a set up for about $600.00 (last time I looked) using new parts, or online auctions sometimes sells good quality stuff at a cheaper price too. Mike Just checked, prices are lower than I thought, $500.00 at AZCAR. Quote Link to comment Share on other sites More sharing options...
Pop N Wood Posted July 20, 2003 Share Posted July 20, 2003 I have read a lot of very negative posts about the 4 bbl set up. The SU's are sweet, but make sure to get a set with a quality rebuild. The throttle shafts bushings wear out creating a vacuum leak. Quote Link to comment Share on other sites More sharing options...
DAW Posted July 29, 2003 Share Posted July 29, 2003 There is a night/day difference between those flat-top Hitachis and the earlier round-top SUs. Fuel distribution is going to be superior with the SUs than the 4bbl. I would use triple sidedrafts before a 4bbl. The SUs are highly tuneable and are simple and elegant in their design and function. Search for Norm's use of these carbs. DAW Quote Link to comment Share on other sites More sharing options...
Guest Nic-Rebel450CA Posted October 20, 2003 Share Posted October 20, 2003 The only real arguement here seems to be the size of that carb. I am considering this swap now as my round-tops are pretty well toast. I have good experience tuning 4-barrel carbs and and I am quite confident in my abilities to do so. I really cant see any reason not to consider this swap seeing that these SU's will need to be completely rebuilt or replaced. Is there any real reason not to consider this swap (4-barrel) if the parts can be obtained at a good price? A setup of tripples is much more expensive, and I am just looking for something to keep this engine running until I swap it out. I just cant see spending about $100 for a rebuild kit when that may not even get these carbs running good enough and I can probably get the 4 barrel manifold used and a good used carb for not much more. Fuel distribution is sort of not an issue because a 4-barrel setup is bound to be better than a pair of SU's that arent anywhere near balanced. Quote Link to comment Share on other sites More sharing options...
Guest Nic-Rebel450CA Posted October 20, 2003 Share Posted October 20, 2003 FYI, either ztherapy likes overcharging for their rebuild kits, or their kits include something special. I just got a kit for my SU for $15 (each). Quote Link to comment Share on other sites More sharing options...
johnc Posted October 20, 2003 Share Posted October 20, 2003 Z-therapy rebuilds include new roller bearing throttle shafts and bushings, matched dashpots and pistons, etc. They basically blueprint a set of SUs. The price is comparable to a blueprinted Holley 4 barrel sold be Demon and others. Quote Link to comment Share on other sites More sharing options...
brokebolt Posted October 21, 2003 Share Posted October 21, 2003 I've run every N/A induction system on the Z car. The 4 barrel can run well if properly tuned. Manifold and parts are readily available for what ever avenue you go. Personnally I like the trippple sidedraft for performance but for economy nothing is better than a set of well tuned bell top SU's. I've even run the bucket top SU's with relatively good success, although they are a bit more to tinker with. The four barrel is a good choice for performance but I think that a stigma follows that type of carb. Remember Dyno numbers don't lie! Mike Quote Link to comment Share on other sites More sharing options...
Guest Nic-Rebel450CA Posted October 21, 2003 Share Posted October 21, 2003 Z-therapy rebuilds include ... I was referring to just the price for their rebuild kit. $50+ each. Quote Link to comment Share on other sites More sharing options...
Clifton Posted October 24, 2003 Share Posted October 24, 2003 I've had round tops, DGV Webers and a 4 barrel with a 390cfm. I like the 4 as it had an electric choke and never needed minor tuning as the SU's seem to need until you get them right. You are going to need a unisyn also. If the prices were the same I'd go with the 4bbl but SU's are cheaper . As far as HP, I don't think there is going to be to much of a difference on a basicaly stock motor. Back in the day I beat an SU carbed Z with my 4bbl and crappy manifold that bolted to the SU manifold, not to say it's better, just isn't anyworse. I know that Az Z Car's manifold has a plenum seprator that others don't, I don't now the benifit of it though. Quote Link to comment Share on other sites More sharing options...
Guest bastaad525 Posted October 24, 2003 Share Posted October 24, 2003 The only real arguement here seems to be the size of that carb. I am considering this swap now as my round-tops are pretty well toast. I have good experience tuning 4-barrel carbs and and I am quite confident in my abilities to do so. I really cant see any reason not to consider this swap seeing that these SU's will need to be completely rebuilt or replaced. Is there any real reason not to consider this swap (4-barrel) if the parts can be obtained at a good price? A setup of tripples is much more expensive' date=' and I am just looking for something to keep this engine running until I swap it out. I just cant see spending about $100 for a rebuild kit when that may not even get these carbs running good enough and I can probably get the 4 barrel manifold used and a good used carb for not much more. Fuel distribution is sort of not an issue because a 4-barrel setup is bound to be better than a pair of SU's that arent anywhere near balanced.[/quote'] Yes there is plenty of good reason. Firstly, it is widely considered that do to the length of spacing between the cylinders and the central placement of any 4bbl setup, that even fuel distribution will be a problem. Most people who have tried this setup agree that you will run too rich at cylinders 3 and 4 (middle two) and too lean at the 1 and 6. There is too much difference in the length of the runners. How could one single carb in the middle of six cylinders distribute fuel as evenly as two carbs each in the middle of three cylinders? I would think the more throats the better... hence the performance increases gained with tripple webers/mikunis. Another problem is that you have a downdraft carb... the fuel gets pulled straight down, into a little catch/sump in the intake manifold, before being sucked into the runners... and some stays behind. I've heard 'stories' of fuel building up there and then somehow, some backfire thru the intake or something, ignites all this fuel in the manifold that stays in the manifold, and literally blows the manifold to pieces. I guess the possibility is pretty remote, but the design just doesn't seem to make sense for good performance. If you absolutely MUST go with a 4bbl, You shouldn't use anything bigger than like a 350... a 650 is WAY too much carb and I would bet money the car will either not run well or will take a TON of tweaking to get right. I ran a rebuilt set of Ztherapy SU's on my overbored 2.9L N/A motor... they are a bit on the pricey side but they run great, look great, are easy as hell to tune, dont ever really need to be fiddled with, and Ztherapy has redesigned the throttle shafts by putting ball bearings on the end instead of the bushings nissan used (which worn bushings are the most common problem on old su's, which causes vacuum leaks). Another option, that could save you some money, is to buy a set of dirt cheap used SU's, say $100 or so, buy the rebuild kit from Ztherapy (forget how much.. I think like $100?), and buy a set of their carb bodies (doesn't include the dome, piston, throttle linkage, float bowls and floats) that come with the ball bearing throttle shafts... I think these are like $150 for the pair... so for around $300-400 you'll have pretty much the same thing. The only thing you'd have to worry about, that wouldn't be replaced with the rebuild kit, would be the floats (if the hinges are okay and the rubber of the float isn't bloated) the linkage (just make sure it operates smoothly and doesn't look damaged) and the pistons and domes (make sure the dome is at least relatively smooth on the inside and the edges of the pistons are not excessively scratched up... if there is damage on either, they can be sanded/polished and fixed... the most important thing would be that they remain even... the pistons should move evenly between the two... this is all covered in Ztherapys "Just SU's" video, which I also highly recommend... they'll probably throw it in for free if you buy the rebuild kit and carb bodies). And who says SU's aren't balanced? I've heard that the stock, early 240 intake manifolds cause the cylinders to run SLIGHTLY unbalanced, and a recommended mod is to switch to the 260 manifold (the N36) which I did when I put the car together, and never had a problem with uneven running cylinders. I got the manifolds for $45, and they are a direct bolt on. Quote Link to comment Share on other sites More sharing options...
Guest Nic-Rebel450CA Posted October 24, 2003 Share Posted October 24, 2003 I just rebuilt my SU's and they run great! Now I dont have to waste money on a temporary solution before I do my swap. I sure would like to know why Z therapy sells the rebuild kit for $109 for the pair when I went to my local auto parts store and picked up a pair of rebuild kits for $15 each. This was a complete kit too, I cant imagine what Z therapy could include that this kit didnt have. The carbs were actually balanced as soon as I put them back on the car, didnt need to adjust anything. I was so happy. If I was still going to keep the L28 I think I would still consider switching to a 4barrel, but that is only because I had an idea for a custom intake manifold. I do agree now that these SU's are a nice setup, and it really didnt take much effort to rebuild. Quote Link to comment Share on other sites More sharing options...
Guest bastaad525 Posted October 25, 2003 Share Posted October 25, 2003 They are SUPER EASY to rebuild and maintain. That is interesting about the rebuild kit thing... I wonder what is and is not included. I know the Ztherapy kits are really thourough. You get: New needles New jets matched to those needles New float bowl to jet hoses, which have to be made of a soft rubber and preshaped... regular fuel line will force your chokes open all the time Grose Jets... which replace the needle and seat style valve in the floats and are considered by most to be far superior Gaskets Banjo filters And uh... I think that's about it... I've never bought a regular auto store rebuild kit so I dont know what more you're paying for. Quote Link to comment Share on other sites More sharing options...
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