240z!!! Posted March 9, 2009 Share Posted March 9, 2009 ive been debating this for a long time and i know most of you are thinking...go with some tripple carbs....but im very old school and would love to do a turbo set-up with 4 screw su's...my plan is to use the original su airbox as a starting point...take out the air filter weld the box up then weld a piece of intercooling piping on it to connect to the j pipe...ill be using a zx e12-80 module distributor...a f54/p90 set-up a zx distributor...and will probably be using a stock j-pipe for a while because im not gonna run much boost anyways....other than the very obvious reasons...what would be the up and downs of using the setup? any helpful adivce would be apriciated...and this should be a mature thread i dont anyone going "thats just dumb" or "just get tripples" if you have those comments please dont post..oh and i have searched the forum and also searched google and some other places but nothing was very specific Quote Link to comment Share on other sites More sharing options...
Xnke Posted March 9, 2009 Share Posted March 9, 2009 Don't do it. It's been gone over before, Tony D has the most answers. Essentially, last time it was discussed, this is the conclusions we came to: Tunability: really really really effin' hard to tune. Get good at retapering the SU needles before even attempting. Even then, expect to spend $$$ at the dyno. Drivability: Not anywhere close to streetable untill you've already got the needles retapered, and spent a lot of time on the dyno, and you'll still get sneezes and coughs off idle and in the lower midrange. Reliability: Depends on how much you want to spend. Cool factor: OMGWTFBBQ WANT! Also, you'll have to figure out how to seal the SU's up for boost. We haven't even gotten to fueling requirements, solid floats, or any of that yet. NOW, that said, somethign that LOOKS like what you are describing, almost indestinguishable, CAN be done and run well: Throttle body injection, using the SU's domes to house a large fuel injector or two, and running a Q45 MAF in draw through mode, with megasquirt. There are a lot of places to hide all the sensors, the Q45 MAF is supported by MS, along with the cobra mustang MAF. I plan to eventually get this setup running using the 240SX IAT sensor, mustang MAF, and an SU TBI conversion. Untill then, I'll just run the SU's N/A, because there are a lot of parts to source. Quote Link to comment Share on other sites More sharing options...
240z!!! Posted March 9, 2009 Author Share Posted March 9, 2009 well i was thinking a getting a wide band so tuning wouldnt be a problem...i already have the custom box design i just have to make it...and ive been using su's for a couple of years now and have rebuilt and tuned at least a dozen of su's and made custom tapered needles for my buddys autocross 240z...so i have some experience with them and wouldnt mind the task of trying...ive got some time and a little money so experimenting wont hurt...if all else fails i have enough stuff to make a efi setup... as for the throttle body injection idea...i have also researched this option but it still doesnt satisfy my old school hunger enough...it does sound like a very nice and stealthy set-up...but just not for me has anyone actually done this or known anyone who has? Quote Link to comment Share on other sites More sharing options...
Xnke Posted March 12, 2009 Share Posted March 12, 2009 Yes, people have attempted it. But due to the design of the SU's, you just can't tune for a turbo. Carbs can be tuned for peak power ONLY, you can't realistically tune for other spots in the power band, so if you lean out at say, 3500rpm, but are pig rich at 2700, well, you're stuck with it and a blown piston. On top of that, you'll need new floats, which are going to be custom, since no one makes them. Throttle shaft seals, too, and you'll have to figure out how to seal the needle jet assembly to the bottom of the carb. BTW, I need to call you up and chat about getting your floors done. I've been really busy lately with work, and just havn't had time to call... Quote Link to comment Share on other sites More sharing options...
carguyinok Posted March 12, 2009 Share Posted March 12, 2009 Here are some links from CZCC that may help you. http://www.classiczcars.com/forums/showthread.php?t=31464&highlight=SU+turbo http://www.classiczcars.com/forums/showthread.php?t=22581&highlight=carb+forced+induction Quote Link to comment Share on other sites More sharing options...
Tony D Posted March 16, 2009 Share Posted March 16, 2009 The SU is boost irrelevant. Blowing air through them works the same as drawing air though them. They will react similarly. The largest problem you will have is sealing the fuel system. You have to revent the bowls. The brass floats in many SU's will collapse at 8-10psi. The old plastic floats may do similar. There are no composite composition floats avaialbe for SU's that I know of, so that is the upper level of pressure. If the fuel transfer hose doesn't blow apart first... Leaks of fuel/air at the jet. Hard sealing of the throttle shafts blowing fuel/air mix under boost. Heating of the bodies if not intercooled. And adding an intercooler for a 7psi system seems a waste of time and added complexity. It's a lot of work....and then throw in the modulation rings for float bowl differential to give more enrichment on-boost so you still have a relatively normal taper for N/A operation (which is more than you will think)... It's not the route I'd take. Neither is a blowthrough Mikuini/Dellorto... but oh well. "Some things you got to learn for yourself." Masochisim is not illegal! LOL Quote Link to comment Share on other sites More sharing options...
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