> As much as I love my 240Z and the setup I
> have with my 390cfm Holley, I would suggest
> getting a set of High Performance SU's.
> Finding a jetting setup that doesn't run to
> rich or lean is a pain in the you know what.
> It also has a tendency to overthrottle if
> you stand on it(which my foot likes to do).
Go with the dual webbers. The 4bbl manifolds arn't designed worth a damm. I have ran 1, seen 2 others and 2 out of 3 had carb fires from backfires. The one piece manifold offered by motorsport is the worst by far, it doesn't offer balanced even flow to each cyl. 1,6 run lean, 2,5 run great and 3,4 run rich and nothing you do will fix this. I saw a little better result when someone welded a waterjacket to it but it has too much surface area under the carb and it puddles gas massively and are prone to backfire's and when combined watch out. The manifold that mates to the stock SU manifold is better but still it's throttle responce has a lot to be desired. The best carb I've seen work is the Carter (sorry holly fans) but it just flat out works better on the Z's. I've ran them both and got good results with a fairly built engine and a 500cfm Carter. And it doesn't have a damm power valve to blow out when the engine backfires. There is a fix for the holly's though at
www.jeg.com for around $7.95 kit, (they also have some BG carbs that are very nice). I prefer the weber dual 2bbl setup myself, great performance, easy to setup, great gas mileage potental with performance which you just won't get with a 4bbl conversion cuz they arn't built well to begin with. Also if you get the urge to add more carb you can always add 2 holly 2300 carbs (500cfm ea.). BG also sells a race 2300 that's polished, tuned in every aspect along with a 546.25 price ea..
But steer clear of the 4bbl setup, if you want that much power go with tripple weber/mikuni or for overall power and driveability, get the dual webers. I use a .460 lift/270 duration cam with header 2.25 exaust, dual webers and it's one fast car with great gas mileage when doing normal driving. I recomend this cam spec and exaust size also, you go much bigger on the exaust and you loose low end power. I also recomend the Nissan Motorsport's race header, expensive but it's the best you'll find anywhere for the Z. I replaced it from that garbage Motorsport auto's 6-2 header and the difference was noticeable. That one isn't tuned but it's still ok if your on a budget, anything is better than stock. Sorry about the long post.... Good luck with what ever you pick.