rotorface85

ive been searching this forum with no luck i have a dcoe 48 carb and need to boost prep it. i would like someone that knows what they are talking about to point me in the right direction. is there a build thread on here that shows how it is done? if i can not figure it out by the end of the week i will send the carb to robert. i know that it cant be that difficult to do this. also what jets should i use? anyone have any ideas where to start? i already have plastic floats installed and i know i need to silicone anything that doesn't move. what is the best way to do this... money isnt a concern at the moment just want it done right. someone help

cfamilyfix

iTrader: (15)

I'm a little ignorant on the subject, but I believe you can run moderate boost on a dcoe side draft right out of the box...no mods necessary...

Shredduuhh

iTrader: (11)

yeah, ant it will fuel starve and spew fuel everywhere, car catch fire ... fun. ANY carb used for boost must be boost prepped!

Jeff20B

iTrader: (13)

The DCOE kinda sucks as a blow through carb. PercentsevenC tried it on his and it was never very good. Oh sure it had some power, but the downsides were very noticiable. A 4bbl carb would have been a better choice. 2bbls just don't work that well. If he catches this thread, he can provide first hand experience.

I have the carb now and will convert it back to NA use.

Shredduuhh

iTrader: (11)

thats funny, there was a company called cartech that sold thousands of turbo kits in the 80's.. 90% of the kits Corky Bell sold used 2bbl carburetors and they ran great..
a Japanese company called Sigma also sold kits using 2bbl carbs that ran well also....
not to mention the guy in chatsworth (robert) , ive seen cars at his shop with weber turbo kits... most of those guys are pleased with how the cars run..

rotorface85

just because one person had bad experience with a webber doesn't mean its a bad choice... i know there have been plenty of dcoe builds on here but no one wants to share how to prep it. what size jets and emulsion tubes to use.. i know you have to drill the carb to allow more fuel to flow. and bigger inlet. 4bbl carb wont make it easier. rx71king used a 4bbl holley and hated having to take the fuel bowls off everytime the temperature changed to change jets. 2bbls you can change jets way easier. im not looking for naysayers because those are the type of people i like to prove wrong. its all about tuning it properly to work well. i have a 4bbl carb and bought a 48 dcoe specifically because i know its better to run for a blowthrough app. where is the info on how to set it up is all im asking for. maybe precent7c just didn't do a good tuning job. what kind of porting does he have? i am positive that robert could get it done right but i dont want to rely on someone else to set it up when i know i am capable of doing it myself.

Jeff20B

iTrader: (13)

Two other examples on this forum from a few years ago: ioTus and hyper4mance2k. They both had a blow through DCOE and no longer run them. They both transitioned to NA for some reason. ioTus has been active lately. Ask him what he liked and disliked about his old setup.

Don't get me wrong. I am interested in blow-through and would like to set up two, but not with a DCOE. One will be a Holley double pumper (if I can make it work despite physical damage by the PO) and a Nikki.

I know the Nikki well enough, so I feel good about that, but the Holley is very foreign to me, plus it has some problems. So if that's too much, I may just grab a 4bbl TB and use my MegaSquirt. I don't like EFI but I'll make an exception if I must.

ioTus

iTrader: (5)

I would absolutely recommend sending it off to Robert to have him boost prep the carb, no question.

In terms of having an online "heres what emulsion tubes to use" or jettings, etc, I'm not sure thats fully possible. You may be able to get a set up that will get the car started for baseline, but I doubt there's a single recipe for the Perfect Tune that can be passed along online. So many factors affect a carb's tune - elevation, humidity, temperature, whether or not Mercury is in retrograde, etc etc etc. You really need to dial it in for the locale you'll be driving in.

I had an S4 stock port 45 Weber sidedraft setup. S4 turbo with ported wastegate, NPR front mount intercooler and HKS BOV. 2.5" full Racingbeat exhaust. My biggest problem was tuning - i had a narrowband Air / Fuel meter I was trying to use to tune, which as it turns out isnt very accurate a) to begin with and b) on a rotary in general. Always ended up running hella rich. Made for awesome fireballs on the downshift tho

I sold the car to CodeBlue and they've done quite a bit to it since, and from what I understand have done a lot to get it in proper tune.

My reasons for leaving the blowthrough setup:

• Mileage - 10mpg city 14mpg freeway. And that's being generous
• Performance - Decent peak HP. Note the word "peak" - thats exactly how I would describe the entire build. Not an inherently bad thing, but what I love so much about the rotary is its super smooth power band. This did not have that.
• Expense - seems like it will be cheaper but for just that little bit extra I could have gone EFI
• Drivability & Practicality - when it boiled down to it the thing was a pain in the *** to daily drive. Granted, this was mostly because I never got the carb tuning dialed, broke my OMP so i had to premix, and had a 12" steering wheel on a power steering gear without power steering pump.

It was hella fun overall, but not a car I could just jump in and go cruising in. It's interesting, as having chatted with DirectFreak throughout both our builds - he wishes he'd gone with a simpler 4bbl weber blowthrough. I wish I'd gone EFI I think the major factor there was DF went ALL out. A milder EFI setup would have been less hassle I think.

Currently I'm going for N/A EFI - when properly configured its as much peak HP as the blowthrough setup was, only with SO much more low end power and torque - which is where it matters in the twisties, uphill and downhill, basically 95% of all the driving I do. No turbo to spool or intercooler ducting to pressurize every time I accelerate.

But I'm not here to convince you one way or another. I'm SO glad I had that car and did that build, I learned so much by the time I was done. A 12a blowhtrough setup would be righteous. I think if I get another FB it will be a 12aT, with the two tone black / orange engine bay color scheme. But honestly a Renesis FC would be first

My advice to you is go through RotaryShack. Robert knows blowthrough and rotaries more than anybody I've chatted or worked with. I do the majority of my business through him. Top quality.

Hope some of this info is helpful!

~Geoff

rotorface85

thank you for the input sir, i will be sending my carb to robert next week.. i have a gt35r turbo custom built with a billet wheel designed specifically for rx7's, old school cast BAE turbo maifold. aem uego wideband. aem boost/vacuum guage, type rs 38mm wastegate. rebuilding the engine next week with solid corner seals and large pineapple racing streetport. i was totaling up the build costs and im close to the 4,000 mark already. i never thought it would be so expensive but hey i like quality parts. also did you have any spark upgrades? i currently have been running pertronics coils (similar to msd) on the n/a engine. was planning on running some ngk plugs recommended by robert for turbo engines. should i go full msd boxes or just individual coils per plug? i plan on removing the omp during rebuild and just pre mixing for safety. (ive had many oil injection pumps fail on snowmobiles and jetski's and now just run pre mix on everything) i understand that there is no specific jets to run for everyone (im around 5-6,000 ft above sea level) i have a lightweight steel flywheel and stage 4 clutch so daily driveability is already gonna be an issue. thanks again for the input. i will be pressing on with this build and will post video's and pictures when it is complete. oh yeah and my distributor is locked (welded)

ioTus

iTrader: (5)

Good choice on the AEM wideband I hear they're tops. I just got mine in last week, havent installed it yet. I'll be running the UEGO and an EGT. They also have boost and wideband gauge in one:
AEM Performance Electronics Wideband UEGO Failsafe Gauge - Wideband O2 UEGO, Water/Methanol, Stand Alone Engine Management, Piggyback F/IC, Tru Boost Controller, Gauges, Automotive Performance Electronics

Do it Right, do it Once is my motto these days. You wont regret spending the money to do it right.

I've never heard of Pertronics. Good stuff? On my setup I had only MSD blaster 2 coils and an MSD 6a for leading ignition. I've never really ventured into the realms of DLIDFIS or such, mostly because I've never seen one done that actually looks clean, and I've not felt too much of a diff from it.

Is the 6a worth it? Maybe not. But if you're trying to eek out every last ounce it might be a good option to throw a few hundred bucks at. Check out the Digital 6 as well, I think it might have an even better spark. Havent tried it tho.

If you're already a pre-mixer then you're set man. Is Pineapple tapping the front cover plate for oil return?

Sounds like you're set with the locked Dizzy. I had Robert prep mine and never had a single issue with my ignition setup.

Stoked on the project man - looking forward to pics!

PercentSevenC

My experience basically mirrors ioTus'. Crappy gas mileage, poor drivability, and I ended up spending the cost of the MegaSquirt I'm now using in tuning parts. And I even had a wideband.

As I've said before, I have no doubt that if you know what you're doing, it would be possible to get a blow-through DCOE rotary to drive pretty well. The trouble is that there's so little information out there that unless you're already a Weber expert, or know someone who is, getting to that point is going to be a process of trial and error. And as ioTus says, the settings that work on one car won't necessarily work on another. I eventually got tired of blowing money on jets and e-tubes and getting nowhere with it. EFI is its own can of worms, but that's a topic for a different thread.

Additionally, a single DCOE blow-through setup on a rotary has some issues that I'm not convinced are even possible to solve without re-engineering the carb. The fuel starvation problem, for one. The fuel inlet is just too friggin' small and there's only one of them. All you can really do to work around it is crank up the fuel pressure, which makes tuning for low-throttle driving that much harder to get right. In order to make more power reliably you'd have to somehow machine it out and install a larger needle valve.

All that said, I wish you better luck than I had. Robert at least seems to know what he's doing, so having him set it up is probably a good plan.

Regarding the boost prepping process itself, it's pretty straghtforward; you should be able to mostly figure it out just by looking around the carb. Much simpler than prepping a 4-barrel. Watch out for leaks around the threaded parts, like the venturi holder screws. Pipe thread sealant may be a good idea for those. Cold-start enrichment will have to be blocked off, and be sure to use a neoprene gasket for the carb top.

Those were draw-through setups, not blow-through. Big, big difference.

seanrot

iTrader: (2)

Sigma was a blow thru for an IDA carb... Mine ran really really well when I had it going on the last car. I would say that the Japanese used the IDA in most of their HKS and Sigma kits. Im currently building one that mirrors my last but this time going bigger.

PercentSevenC

I'm positive there was another old Japanese turbo kit that was draw-through; I must have been getting them confused. Cartech was draw-through for sure, though.

Shredduuhh

iTrader: (11)

nope, blow through... BAE and Arkay were draw through...

PercentSevenC

Cartech was definitely draw-through. Check this vid:

rotorface85

BAE made a draw through setup... i have one. just never intended to use it. i am selling the transfer plenum on ebay. the bae turbo is being sold to a friend of mine.(better than a turboII turbo) the exhaust manifold is the only reason i bought the kit. its a cast 12a manifold and robert at rotary shack told me its the best manifold you could find and that im lucky i found one. robert is building me a custom carb hat for a special birthday price.(not telling how much off i got) he is setting up my dcoe 48 for me and even jetting it so it will be close to what i need i told him im at 5-6000 ft above sea level so he can get it closer. he will be upgrading the inlet size and allowing it to flow way more fuel when necessary.. he seems like the guy to go to for any blow through setup. i have complete confidence in him. i wish i would have known that aem made a boost/wideband guage before i ordered mine because that would have been neat to put them into one spot.( im using the factory ac/ heater hole locations and they only need to be bored out slightly to fit the 52mm/ 1 1/16" guages) i dont have a heater or ac anymore because i smoothed the firewall and took all that junk out... will be buying a 2,000 degree egt kit from autometer this week and im going to build a 1" spacer/ riser for the turbo because the t70 gt35r will hit my intake manifold without it. i will tap a hole into the spacer for the egt probe so i dont have to drill the rare bae manifold. tuning may be an issue but i am aware of that and i will spend the long hours perfecting it. i might try the digital 6. i have installed one of those on my buddies old 63 chevy c10 pickup before when we built a destroked 350 pushing around 500 hp and that thing really made it snappy! pertronics coils are found in jegs or summit catalogs. they have the same specs as the msd coils. i just bought them because i wanted black coils so they looked stock and msd only makes them in red or chrome. summit also makes a msd stlye box now too for the low price of $150 but i think i would rather go digital for spark. gonna hide it under the dash though so i can still have a clean engine bay. my distributor has been locked and i will be playing with the timing when that comes around. robert told me i should be at 10 degrees advance to start with. not planning on too much boost but would like to be able to play around with it if i want. ive got a boost controller and will be buying a timing retard **** for whatever box i end up getting.

my recomendation to anyone in my shoes in the future is to just send your dcoe to robert. he told me $50 to boost prep it, plus a little for jetting. he is tapping my side draft manifold for extra bungs(boost guage, boost line, etc.) at no chage because he still has it. i dont know how anyone can talk bad things about this company, they have made me a very happy customer. rober has a lot of knowledge and experience in the whole blowthrough process and has built many succesful engines. even a 800hp 12a... not too sure how long it lasted though but when your pushing 8 times the amount of hp out of an engine you cant expect it to last as long... im hoping for a few years while i can get enough money together to build a 20b or (might be dreaming) a 4 rotor...

thanks for everyones input in this matter! i will share my progress with you all when it is complete!

rotorface85

oh yeah and i almost forgot.. the oil return bung is an easy tap job. i havent done it yet but intend to when i remove the oil pan and put the baffle plate in place. just going with a 10an fitting. not sure when thread size yet kinda gonna just go with what they have in stock at the local parts store. ive got a whole set of taps so it shouldnt be a problem.

zaridar

iTrader: (3)

Got my supposedly boost prepped sidedreft carb from robert brand new... as soon as i boosted it sprayed fuel everywhere from every orifice!!! had to do it myself... maybe he only did something to the throttle shafts... i think you have to add a seal or something.... i had a few threaded holes that i just plugged with small screws and thread sealant...

coldy13

I ran a 48dcoe on mine for about a year, it came from Robert and I didn't have any issues with fuel leaking out. The problem I had is it just couldn't keep up with the fuel delivery and the drivablilty wasn't as good as a blowthrough nikki. At the top of 4th gear was when mine would drain the float bowls and lean out. Fuel supply was good and no pressure drop, just the fuel inlet and float needles couldn't get enough fuel through to keep up. I gave up on it and went back to a modded nikki, no more problems and I could mash the gas and it wouldn't sputter and stumble like the weber. I tried a bunch of different jets with the weber and I think it ran best with F11 e-tubes, 235 jet, and 160 air bleeds, but it's been a long time so I could be wrong on that.

zaridar

iTrader: (3)

Well then you are lucky! I was fairly happy/comfortable with using carburetors, especially on older vehicles etc.), until this... now i will avoid carburetion at all costs. for the time, effort, and money i wasted trying to get the car to be somewhat tolerable to drive i might as well have dropped 3 grand right then and there and went efi. ==>> Done... no more headaches... instead i f'd around with a total of $1100 of parts that came over 6 moths after i ordered them. and it never ran like it should have...

Don't get me wrong, if you know carbs very well, then its its a different story.. but i think i was sold the wrong size carb and incorrect jettting and tubes... i tried many different combos and still could never the the hesitation out (if you cracked it open under 3500rpm)... I even purchased and read the whole weber carbs book and followed it to a tee to attempt to get correct size jetting, tubes etc.... since robert was so difficult to get ahold of... got very close, and very quick at 8 psi ( after i sealed all the leaks!). but never really practical to drive on the street,....

my 2¢

coldy13

I'm going EFI now, if I ever get the motivation back to finish the damn thing...it's definitely the right way to do it, but I'd recommend the nikki over a weber if you're trying to do it cheap. The hesitation and top end fuel delivery problems with the weber is why I switched back to the nikki. I could never completely get rid of the bog below 3500rpm either. Putting in the biggest accelerator pump jets helped, but it still had a bit of a stumble, had to crack the throttle a bit carefully to take off smooth.

zaridar

iTrader: (3)

exactly same problem as me... i think its just sizing of the carb... a two barrel cant do what a 4 barrel can... a two barrel in my case was too large so it suffered miserably in low end.. if its good on low end then the top end will not see the power gains that a larger carb would... so a 4 barrel cures that...(MOSTLY)...

i agree it may be a bit cheaper... but if OP/ you are anything like most of us FB owners... (from my experience) we dont plan on selling the car anytime soon.. and will eventually want more than a carb can deliver, this goes for streetability too, so you might/may as well do it right the first time...

I really wish i would have listened to the tons of people that told me to go EFi right away... would have saved me time money and heartache.. and my car might be running by now...