Nismo280zEd Posted September 23, 2003 Share Posted September 23, 2003 As many of you know my car was damaged in a freak fire accident. Since then i have aquired some parts, but can't decide which direction to take. Recently I have been pondering the idea of putting triple carbs on my L28 with N42 head. Does this sound crazy? The had has been ported and polished, harder valve guides, new valves, racing springs and cam. In my mind this sounds like a very easy and fun setup, but will I be looking at about the same power level i was at with my previous modified EFI? I was looking at the 40mm webers I started thinking about this as graphing a 76 280z wiring harness to my 78 engine doesn't sound very fun to me. Or rewiring all the EFI relays. Ideas anyone? -Ed Quote Link to comment Share on other sites More sharing options...
Guest NorCalZ Posted September 23, 2003 Share Posted September 23, 2003 from my observations I think 45s might be right for your setup, I think the 45s would probably make the cams really come to life if the lift is somewhat aggressive. I still need to do a cam upgrade but I think a tweeked out L24 works well with 40s and L28 to stroker are good for 45s. Don't listen to me completely, have someone confirm these facts. Quote Link to comment Share on other sites More sharing options...
ZR8ED Posted September 23, 2003 Share Posted September 23, 2003 Doesn't sound crazy to me.. but then I'm crazy.. 40 dcoe's are the way to go. 45's are too big for a street machine.. I have extensively rebuilt, tuned, jetted and modded 40's and 45's for many years on my Z. I ran close to 300hp (flywheel) from a 2.9L with 40dcoes with 36mm chokes. (not impressive?..well with 10.5:1 compression and 200psi across the board, and a 8000rpm redline, I hit 147mph @7400rpm in 5th gear with a 2880lb 280Z.) I didn't gain very much from switching to the 45's, and I found I lost more in the bottom end than I cared for. too much sacrifice for top end for my street car. I did extensive experiments with venturi and jet combos for differrent driving styles, weather conditions, and engine mods. with the 40's and 45mm dcoe's. I simply removed my stock fi fuel pump and put in a holly blue in its place (fits perfect) and used the stock fuel electrics, and fuel lines. Dcoe's are the no holds barred of performance carbs. they will outperform the z's stock fi (except for cold start up) They are not as fine tuneable as a quality aftermarket fi control system, but they sure get the job done. The GeeWiz factor let alone the incredible sound of those carbs under the hood are like pure perfection, should be enough to entice you. oh and i was getting 20-22 mpg with that set up as well. Quote Link to comment Share on other sites More sharing options...
Guest Anonymous Posted September 23, 2003 Share Posted September 23, 2003 Also nothing like the sound of the air getting sucked in thru tripple webbers. That alone is worth the effort to put the carbs on the car. Mark Quote Link to comment Share on other sites More sharing options...
JMortensen Posted September 23, 2003 Share Posted September 23, 2003 The How to Hotrod Book says 45's for an L28. I have 44 Mikunis and I love them. I wouldn't switch to 40's, but that is based on what I have been told from various tuners over the years, and you have to take that for what it's worth. I've heard that they don't flow enough for an L28, but ZR8ED seems to have had conflicting experience. I think a LOT of what you hear about triples is directly related to the skill of the tuner. I am getting pretty good, but still learning. My strongest suggestion is to install a single wire O2 sensor in your collector. Once I did that and hooked up my voltmeter, my tuning capability increased 100%. I went from seat of the pants and color of plugs (hard to read with MSD) to KNOWING what was wrong. The only drawback I can say for my setup is that I will bog coming out of very slow speed corners at autox, but my gearing is totally wrong, I just haven't come up with time/money/parts to fix it yet. 3:70's and 44's don't mix at autox. But I got the LSD! Jon Quote Link to comment Share on other sites More sharing options...
clarkspeed Posted September 23, 2003 Share Posted September 23, 2003 Ive got a set of triple 40's I'm getting ready to put on e-bay if you are interested. No manifold. I bought the set for my race car and then read everything I could about them. After pricing what it would take to tune them out I decided to go with an EFI system instead. Weber parts are not cheap!! There is a good book on them and worth the investment, "How to Build and Power Tune Weber & Dellorto: Dcoe, Dco/Sp & Dhla Carburettors" (not the HP book). From people I know that run them, 40 are great for the street, 45, 48 or 50's for all out race. Quote Link to comment Share on other sites More sharing options...
ZR8ED Posted September 23, 2003 Share Posted September 23, 2003 Most people with street Z's are way over jetted, and many who use the 45's complain of poor gas mileage, and some sort of bog somewhere in the power band. That is just poor tuning. Webers are adjustable enough, and when you understand the relationship of the different circuts and how and if they affect eachother, you can take this into account. I never had a bog anywhere in any rpm or gear. Just calculate the CFM of a set of webers, and it will tell you right away the flow capabilities. If my memory serves me correct, I did this calc with my 36 or 38mm chokes, and i found that I had 1100cfm worth of carboration on my 2.9L engine. WAY more than enough. Again most people just tune them around whatever chokes came with their webers, and many dcoe 40's came off small 6cyl engines from the 60 and 70's with low redlines and are therfore choked right down.. even 28mm chokes! I know some of the tuning books say 28mm chokes for a Z... well they are wrong for any kind of performance. changing choke sizes is like changing cams.. it just moves your power up and down the rpm range. (generally speaking) 45's and 50's are best left to the race tracks, for 9000rpm redlines. In GT2 racing, Z's would be limited to 40mm dcoe's and 34mm chokes, and they routinely hit 140mph and 8000rpm in top gears. Quote Link to comment Share on other sites More sharing options...
JMortensen Posted September 23, 2003 Share Posted September 23, 2003 I thought 240's in GT2 ran 50mm carbs. Could be wrong. We need Mark Belrose on this one. He just blew up his GT2 motor, he would know. John C would know too. Seen lots of L16's running 44's too, just to play devils advocate. Jon Quote Link to comment Share on other sites More sharing options...
Dan Baldwin Posted September 23, 2003 Share Posted September 23, 2003 I'm running 45mm carbs with 39 (maybe 38?) chokes. This seems to be pretty ideal for my setup (.550"/~305deg cammed 3.1). The torque reaches maximum at about 4700, and doesn't begin to fall off until ~6000, peak power is at around 6500 (rev-limit at 7000rpm). The "How to Modify" book seems to imply that much bigger carbs are better for my setup, but I really don't think I'd want to go bigger, and would definitely consider 40mm/36mm venturis for a milder-cammed 2.8 street or autoX motor. For maximum power, 44s or 45s. Quote Link to comment Share on other sites More sharing options...
Nismo280zEd Posted September 23, 2003 Author Share Posted September 23, 2003 From what i've read in the books, 45mm is ideal for my engine. But most people claim... 40's are better. This car is a big play toy for me, and my father and I have had a long history of trying to out do each other. My z vs his 911. When I was running my EFI I was beating him till end of third gear on my 5spd. I don't wanna spend 1500 dollars or more and come to find out that i bought too small a carb. I plan on modifying the engine even more, swapping heads, maybe even a larger cam than i already have... I just want to have room for upgrade on them. Are 40's going to be able to do this? or should i get some 45's and just put in some smaller main venturi's? Or... are the 45's going to be too radical for the street, ie never being able to properly tune... etc. Ideas are very welcome -Ed Quote Link to comment Share on other sites More sharing options...
Dan Baldwin Posted September 23, 2003 Share Posted September 23, 2003 Reading your last post, I say go with the 44s/45s. They can be made to run just fine on the street. Z vs. 911 is FUN at the track! Saturday and Sunday I had a GREAT time with an '85 911 with a 3.6 and HUGE tires (huge brakes, too). I had way more power to weight, and would really pull him towards the end of the straight (NHIS road course, South Oval configuration), but he could REALLY pull away going up the hill out of turn 3, where I was wheelspin-limited. I wound up beating him in time trials by hundredths! Quote Link to comment Share on other sites More sharing options...
JMortensen Posted September 23, 2003 Share Posted September 23, 2003 I agree with Dan. Z vs 911 is a very good roadrace. I used to go to POC events in CA. They were great! Very well organized, they rented transponders, the whole deal was awesome. I won the EX class (everything that isn't a Porsche) and they gave me a very official looking wall plaque, then a few weeks later in the mail I got a nicely engraved name tag for it. Ended up 12th out of 150 someodd cars that day. What a rush! I've been to a lot of different club events, but I like POC the best of those I've been to so far because they are so organized, and everyone is driving a Porsche so there is not too much "I'm gonna stuff my car into that corner under that Z" going on. They are fast but not fast at all costs. There were a few sneers from the other competitors, but most people came up and told me how the Z was their first sports car, and wanted to see under the hood, etc. Whatever you do with your carb setup, have fun out there and try a Porsche club event! Jon Quote Link to comment Share on other sites More sharing options...
ZR8ED Posted September 23, 2003 Share Posted September 23, 2003 The tuning manuals are very contradictory at times. I know of the graphs/tables you mention to figure what size venturis you need for our z's. My calcs also told me 45mm chokes (approx) Yet the carb kits mentioned for the 240 call for 28mm chokes. I think my car would have been a dog with chokes that large.. though at 8500rpm it would have screamed! In GT2 (at least here in Canada up until 5-7 years ago) you could run 45mm carbs, but you were limited to 34mm chokes, so it made no difference which carb body you used. If you drive this car on the street, and do any kind of tight track road courses, or autoX's, then you need that low end kick, and large carbs with large venturis are not going to work for you. You will end up with a broader hp curve with the smaller carbs. 45mm ++ are for full tilt cars. I ran 45's for two years on the street, and it actually hurt my 0-60 times.. my 50-90 times improved though..hehehe Some of my Z club buddies running 3.0 or 3.1's are using 31-33mm chokes, and are getting wicked bottom end power. on the tight tracks they could pull me, on the longer straights, ( 5000 rpm+ My car pulled much harder than theirs.. and this was their words, not mine.) My same engine (which was now 5 years old) when dropped in a 1970 240 with an lsd and 215/60/14 good year eagle tires, ran a jaw dropping 13.9 1/4 mile the first day of tuning after my motor was installed in this guys car. He ran a 0-60 in 5.3 sec. So yes I think that 40's can do the job for ya down the road as well. The carbs are pretty much the same as the 40's, and the jets etc, all fit, just the chokes are different. Like I said do a calc on the cfm of a set of dcoe's.. you'll be very surprised. Webers do like to breathe to work well though. They also like lots of initial advance as well, and the vac advance is useless on them. Mechanical balancing is very critical to getting them to run smoothly, so take your time setting up the linkages. 1mm difference is a big difference. Float settings are also critical, accuracy counts. the same size main jets flow very differently with different float level settings. Quote Link to comment Share on other sites More sharing options...
Nismo280zEd Posted September 24, 2003 Author Share Posted September 24, 2003 Ok, with numbers that quick you've got me convinced to go with the 40's, But i would like to know.. what size Main venturi's your running, what size main jet, etc. Since my source for getting these numbers is claimed wrong, or not street wise. Only book i have for getting these numbers is the HP book on modifying your Nissan/Datsun engine. This is where i got the 45 number from. Thank you very much, Ed BTW sourcandy@playful.com is my email. Quote Link to comment Share on other sites More sharing options...
ZR8ED Posted September 24, 2003 Share Posted September 24, 2003 Dcoe 40's 500 ft above sea leve. I had a lot of success with 34mm chokes and 36mm chokes. 17 initial advance. 38 degrees full 495 lift 290 duration msa cam Nismo 1 3/4" runner tunes header. with a 2.5" exhaust and supertrapp. 10.5:1 compression with flat tops. 240 rods 280 crank and lightened flywheel. N42 head and lots of P and P work. 3.9 r200 open diff. late model 5 spd. I ran a 145 main jet. F16 emulsion tubes 195 air correctors 60 accelerator pump jets 55f9 idles 36mm chokes 225 fuel inlet valve 7mm closed 15mm full open for the float settings. 3.5psi of fuel pressure using 1/4" id fuel lines with no return line No air horns, but used a custom aluminum air box with fresh air k&n filter. Quote Link to comment Share on other sites More sharing options...
Nismo280zEd Posted September 24, 2003 Author Share Posted September 24, 2003 Thank you very much for the info, I never really realized all you had to do was swap the rods from a 280 with the ones from a 240 to get the compression, I figured the cranks would be different sizes... silly me. Might have to do that since the engine is already out. Thank you again. -Ed your setup sounds really close to mine. Where did you find your intake manifold? Quote Link to comment Share on other sites More sharing options...
ZR8ED Posted September 24, 2003 Share Posted September 24, 2003 I've purchased, rebuilt and sold many sets. I used a cannon, then found an old nismo manifold. I just sold a setup with a nismo manifold 2 weeks ago. (in case you don't know Ed, I no longer run an l28. in my 280. I swapped in the vg30et from a 300zxt 3 years ago.) I still rebuild and tune webers for people. I also have lots of left over gaskets, seals, and misc weber parts from all the kits I have used... full rebuild kits usually have extra parts included, and I have a large coffee can full of bits and pieces that I sell off cheap to guys that only need 1 gasket etc.. as for the rods, yup its that easy, i only over bored my block, to get me to 2.9l My last engine is still running on the street. I sold it to a guy in anaheim CA a few years ago. Quote Link to comment Share on other sites More sharing options...
davidh Posted December 9, 2003 Share Posted December 9, 2003 i couldn't help but notice that some of ya said that ya toped out at 140mph?? is that as far as the stock trans will go?? even if it was a turbo?? and if it is, well all you have to do is get your gearing changed right?? and then after that though will it be able to still ride the streets. im kinda new to the carb scene here so any input is great! also i know this is a lame question but here go's....can you put a little nos on it to give you that neck snaping feel if you wanted, or no??thanks guys and like i said any input is welcomed Quote Link to comment Share on other sites More sharing options...
johnc Posted December 9, 2003 Share Posted December 9, 2003 2003 SCCA GT2 Carburation for the 240/260/280Z - 50mm with 46mm chokes. Quote Link to comment Share on other sites More sharing options...
Tony D Posted December 9, 2003 Share Posted December 9, 2003 I will agree with ZR8ED, I think the 40's will be enough. Also the specs he listed: 145 main jet. F16 emulsion tubes 195 air correctors 60 accelerator pump jets 55f9 idles 36mm chokes Were almost identical to what we ran in the 45's! The only difference being we swapped to a 135 jet (from my street car) for the run at altitude at Bonneville. Like John C posted, the GT spec calls for 50's, and with the 45's we had on the Bonneville car, the clear choice was 55's, but for the cost, we went with 45 TWM throttle bodies and TEC2 EFI. What we did was pick up HP in the upper ranges (extended usable HP to over 8500rpm). What I DID notice that suprised me was that the EFI had a somewhat "ragged" dyno curve, but the Weber curve was like someone took a felt-tip Sharpie Marker and drew a curve on the chart. Their atomization and power delivery is amazing. Even the dyno operator confessed he would have gotten the same HP we got from the EFI from the Webers (55's) but the ignition timing available from the Tec 2 gave us reliability, plus we could make adjustments in seconds with the laptop whereas changing mains in Webers to correct for altitude was kinda a pain... Tuning of the Weber Carbs is a dying art. Many people just drive a car in a "good enough" state of tune. And when they ride or drive someone's vehicle who has taken the time to dial them right into the needs of the specific engine it's like night and day! I have three sets of 45 Webers, what are they worth? One cannon manifold, one japanese manifold, one Skyline manifold (won't fit in a Z---DOH!) Maybe I should sell some of this stuff... Oh, and I'll also add that there's still a dollar in my pocket for a stock-bodied Z without a G-Nose breaking 150mph with a 3-litre Six or smaller N/A motor.... Quote Link to comment Share on other sites More sharing options...
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