Project Fat Nikki
10-10-14, 11:02 PM
#26
Intake manifold
The best 12A manifold ever made is from the RX-3. Or maybe the rare 1976 reverse runner but I've never seen a 12A one in real life, just 13B ones. Maybe the 12A version is an urban legend, making the RX-3 manifold the best. The second best is the 79-80 but it requires some runner work to make it decent, also you have to fill the ACV port in your engine with quicksteel. The worst manifold is the 81-85 which sucks for flow but is very common.
I don't know how much TG worked on his manifold to get it to flow well, but I have some experience on the 13B versions of the manifolds mentioned above, including the RX-3 style (the 13B version from the 74-75 REPU) yes even the reverse runner (76 Comso), and even a 79-80 (J-spec NO) and they are all excellent. The power is there. The fun factor is there. It is better than EFI. It is better than a weber 45DCOE with the wrap around manifold. I think I'm making 130 to 150HP NA and close to 200 with an S5 turbo bolted on and a carb hat with no intercooler at stock boost level (around 7psi), but don't quote me on any of that because I've never dynoed it. It just "feels" like it is.
I don't know how much TG worked on his manifold to get it to flow well, but I have some experience on the 13B versions of the manifolds mentioned above, including the RX-3 style (the 13B version from the 74-75 REPU) yes even the reverse runner (76 Comso), and even a 79-80 (J-spec NO) and they are all excellent. The power is there. The fun factor is there. It is better than EFI. It is better than a weber 45DCOE with the wrap around manifold. I think I'm making 130 to 150HP NA and close to 200 with an S5 turbo bolted on and a carb hat with no intercooler at stock boost level (around 7psi), but don't quote me on any of that because I've never dynoed it. It just "feels" like it is.
10-11-14, 06:31 AM
#27
carb whisperer
I could almost feel your frustration in the first few posts, but It feels good to tinker and research and make carbs work, doesnt it?
You also could probably get away with that 95 main jet, depending on your air bleeds. I drove mine like that for over a year with no issues and a safe AFR reading.
I think the only things different about your Nikki and mine are the secondaries, and the throttle screws for the secondary butterflies.
I used vacuum secondaries for an EFI like smoothness, and my secondary screws were button head torx for flow :P
And +1 on the RB cleaner, it can be loaded up with the stock nikki's k&n filter, and its a decent piece. Only trouble I had with mine was the cheap decal on top not responding well to normal engine cleaners and collecting dirt and fading prematurely.
You also could probably get away with that 95 main jet, depending on your air bleeds. I drove mine like that for over a year with no issues and a safe AFR reading.
I think the only things different about your Nikki and mine are the secondaries, and the throttle screws for the secondary butterflies.
I used vacuum secondaries for an EFI like smoothness, and my secondary screws were button head torx for flow :P
And +1 on the RB cleaner, it can be loaded up with the stock nikki's k&n filter, and its a decent piece. Only trouble I had with mine was the cheap decal on top not responding well to normal engine cleaners and collecting dirt and fading prematurely.
10-11-14, 09:13 AM
#28
Here is my show stopper Nikki that I worked on for about 2 years. Has pretty much all the same modifications listed above. The primary and secondary Venturi's have both been opened up by sr motorsports. The booster venturi is received extensive smoothing by me. For all of the ports that need plugged I tapped the holes and used screws with epoxy to plug them. Also have the throttle shops machined down both primary and secondary. Teflon gasket sits between the carburetor and the rx3 manifold.
The RX3 manifold is the icing on the cake. I bought it from Jeff two or three years ago iand cleaned it up and channeled the ports.
TG you mentioned wanting a better air filter setup. Try K&N filter f 040 J 8. It has a rubber base. Fits right over the top of the Nikki. You may have to trim it down a little bit so the base isn't quite as tall but you can put a hose clamp on it to keep it nice and tight. I also drilled through the top of mine to let the stud come thru and put an acorn nut on top.
The RX3 manifold is the icing on the cake. I bought it from Jeff two or three years ago iand cleaned it up and channeled the ports.
TG you mentioned wanting a better air filter setup. Try K&N filter f 040 J 8. It has a rubber base. Fits right over the top of the Nikki. You may have to trim it down a little bit so the base isn't quite as tall but you can put a hose clamp on it to keep it nice and tight. I also drilled through the top of mine to let the stud come thru and put an acorn nut on top.
10-11-14, 09:32 AM
#30
My ultimate goal is to get the fully tunable air bleeds and incorporate these grose jets. I also have some rx3 floats that are supposed to eliminate the left hand stumble. I haven't installed them yet because I want to keep things as simple as possible until I get the car running. We can all see above how frustrating floats can be.
10-11-14, 11:35 AM
#31
Moderator
iTrader: (3)
Join Date: Mar 2001
Location: https://www2.mazda.com/en/100th/
Posts: 30,778
Received 2,563 Likes
on
1,823 Posts
just generally the fuel jet sets fuel flow, and then the air bleed controls how quickly the fuel circuit reacts. if you think about it the air bleed is a vacuum leak on the signal to the main circuit, and since it is a fixed size, vs the signal, which gets bigger as the airflow increases, its going to have its biggest effect at low rpm.
you can verify with the wideband, and on the weber its pretty obvious, yet everyone says something different....
the number 2, is that most jets are sized based on flow, and not on the literal size. so the weber jet might be stamped .80, which is .8mm, but it might not be exactly .8mm in size, but it should flow the same as the weber factories test 80 jet fixture.
number 3 the wideband is really nice, it lets you see where you are, but best performance needs a stop watch
10-11-14, 11:39 AM
#32
Moderator
iTrader: (3)
Join Date: Mar 2001
Location: https://www2.mazda.com/en/100th/
Posts: 30,778
Received 2,563 Likes
on
1,823 Posts
number 4, the air cleaner.
the Pro7 guys who did all these carb mods too, had to run the factory air cleaner, but they found that a duct to the front of the car worked better than drilling a bunch of holes in air cleaner housing.
i think the takeaway is that the hot air around the engine hurt power more than the open air cleaner helped.
number 5 is that you want a clean paper element, they flow well and actually filter the air. the other media do not filter as well...
the Pro7 guys who did all these carb mods too, had to run the factory air cleaner, but they found that a duct to the front of the car worked better than drilling a bunch of holes in air cleaner housing.
i think the takeaway is that the hot air around the engine hurt power more than the open air cleaner helped.
number 5 is that you want a clean paper element, they flow well and actually filter the air. the other media do not filter as well...
10-12-14, 01:27 PM
#38
You said K&N "f 040 J 8"? Is that the actual part number? I haven't seen that format on their site. Looks similar to this one... RC-5148 - K&N Universal Air Filters, Universal Chrome Filter
10-13-14, 07:36 AM
#39
Waffles - hmmm good
Thread Starter
iTrader: (1)
TG, just a quick note about air bleeds. I see above where you mentioned drilling yours out to be larger than stock.
...
But you really need to get a wideband to get better than about 60% tuned. I've gotten my carbs up to 80% without having the right jets and air bleeds available using the wideband. It gets nuts when you open the secondaries. Every 2bbl owner should drive one one these to see what they're missing.
...
But you really need to get a wideband to get better than about 60% tuned. I've gotten my carbs up to 80% without having the right jets and air bleeds available using the wideband. It gets nuts when you open the secondaries.
Every 2bbl owner should drive one one these to see what they're missing.to get it working then put I think it was 105s in for the primaries. Just wasn't sure
how far I could go without drilling. Sounds like 125 or so from your info.
I agree about the wideband or even a narrow band to get an idea of where its at.
Its all about the $$$.
10-13-14, 07:39 AM
#40
Waffles - hmmm good
Thread Starter
iTrader: (1)
Hey thanks, thats good to know. I want to keep the mazda blue top if I can, thats
what makes it hard to find. Used to be I could walk into advancedzone and find an
air cleaner no problem, but todays cars don't use carbs, so poor air cleaner selection.
what makes it hard to find. Used to be I could walk into advancedzone and find an
air cleaner no problem, but todays cars don't use carbs, so poor air cleaner selection.
10-13-14, 07:47 AM
#41
10-13-14, 10:54 AM
#42
You're right. I should have mentioned the narrow band. I've seen what a hogged Nikki will do in two vehicles with narrow bands and they are useful to know when it's lean and when it's rich. You just don't know by "how much" making tuning still a little guessworky compared to the wideband, but it's better than tuning blind or rather by spark plug color and/or by tailpipe.
Using a narrow band, I determined to swap from a set of stock 90 air bleeds (it was a 79-80 carb) to a set of 70s from an FB carb. Big improvement. The fuel jets were still too small at 118 (close enough to 120) that 125 would have been the next step in tuning. And then 130 but you'd probably need a wideband to know for sure.
Using a narrow band, I determined to swap from a set of stock 90 air bleeds (it was a 79-80 carb) to a set of 70s from an FB carb. Big improvement. The fuel jets were still too small at 118 (close enough to 120) that 125 would have been the next step in tuning. And then 130 but you'd probably need a wideband to know for sure.
10-13-14, 12:04 PM
#43
Speaking of air filters, I went to the store yesterday and looked around. All they had were stock replacements which fit the stock blue assembly but are too big to fit the RB spun aluminum assembly. So looks like I need to spend around 50 bucks for the K&N E-2700, or get RB's 20 dollar foam one, but foam doesn't flow very well.
10-13-14, 12:07 PM
#44
Moderator
iTrader: (3)
Join Date: Mar 2001
Location: https://www2.mazda.com/en/100th/
Posts: 30,778
Received 2,563 Likes
on
1,823 Posts
anyways, you want to start rich, preferably its almost too rich to even run, and then work your way lean. at part throttle (under 50% load), you can lean it out until it stops running.
if you keep track of what jet did what (note book is great), then it becomes pretty easy to tune. you want the best performance + a jet richer.
at WOT you wanna start rich, and then go leaner until it stops gaining power, and then go a little richer.
its always a good idea to be a little rich, as this gives a safety margin, and if your ignition is healthy it should be within 1-2% of peak power.
blue top can work really well, it flows enough for ~170rwhp,
10-13-14, 12:22 PM
#45
Waffles - hmmm good
Thread Starter
iTrader: (1)
you can tune without an o2 sensor, but you need to have a process. you need to start at idle, and work your way up the rpm band, the weber is nice here because you can remove the main jet completely, so you can get an exact idea what the idle jet does.
anyways, you want to start rich, preferably its almost too rich to even run, and then work your way lean. at part throttle (under 50% load), you can lean it out until it stops running.
if you keep track of what jet did what (note book is great), then it becomes pretty easy to tune. you want the best performance + a jet richer.
at WOT you wanna start rich, and then go leaner until it stops gaining power, and then go a little richer.
its always a good idea to be a little rich, as this gives a safety margin, and if your ignition is healthy it should be within 1-2% of peak power.
blue top can work really well, it flows enough for ~170rwhp,
anyways, you want to start rich, preferably its almost too rich to even run, and then work your way lean. at part throttle (under 50% load), you can lean it out until it stops running.
if you keep track of what jet did what (note book is great), then it becomes pretty easy to tune. you want the best performance + a jet richer.
at WOT you wanna start rich, and then go leaner until it stops gaining power, and then go a little richer.
its always a good idea to be a little rich, as this gives a safety margin, and if your ignition is healthy it should be within 1-2% of peak power.
blue top can work really well, it flows enough for ~170rwhp,
Thanks for the tip on the air cleaner. Maybe I need a CAI from the front of t he
radiator upto the blue can. Sounds like a winning combo. Just have to get a GSL-SE right radiator support or an old ReSpeed radiator support for the hole to route
it through.
I sense a new project coming on now.
10-13-14, 03:10 PM
#46
Moderator
iTrader: (3)
Join Date: Mar 2001
Location: https://www2.mazda.com/en/100th/
Posts: 30,778
Received 2,563 Likes
on
1,823 Posts
Yep, thats the old school way to tune a carby. Not many folks know it.
Thanks for the tip on the air cleaner. Maybe I need a CAI from the front of t he
radiator upto the blue can. Sounds like a winning combo. Just have to get a GSL-SE right radiator support or an old ReSpeed radiator support for the hole to route
it through.
I sense a new project coming on now.
Thanks for the tip on the air cleaner. Maybe I need a CAI from the front of t he
radiator upto the blue can. Sounds like a winning combo. Just have to get a GSL-SE right radiator support or an old ReSpeed radiator support for the hole to route
it through.
I sense a new project coming on now.
the old school tuning works on a carb, because you have ~10 parts to tune (idle jet, main jet, etc), and you can isolate each one (the weber is nice this way)
but EFI is 32x32 fuel table, which is 1024 points! big difference
10-13-14, 03:49 PM
#47
I'd go with the stock air intake if you can Tim.
In my opinion being able to use the stock air cleaner is the primary reason to go with a hogged Nikki over an aftermarket carb.
(especially one of them damned del Horto's).
No other air cleaner compares to the stock unit, with its classic "Mazda Rotary Engine" logo and its Mazda blue color.
Here's the nice minty unit that's going on the TGF Fat Nikki in the White One Project:
PS: I'm not completely sold on this CAI stuff.
They mutilate that beautiful stock look and just don't look right with the rest of an early '80's engine bay.
A CAI tube would need to be worth a significant increase in performance to compensate for the aesthetics.
I plan to do with- and without-the-horn testing, but if I can't feel or measure a difference I'm guessing this cold air and flow restriction stuff is just a bunch of hot air.
In my opinion being able to use the stock air cleaner is the primary reason to go with a hogged Nikki over an aftermarket carb.
(especially one of them damned del Horto's).
No other air cleaner compares to the stock unit, with its classic "Mazda Rotary Engine" logo and its Mazda blue color.
Here's the nice minty unit that's going on the TGF Fat Nikki in the White One Project:
PS: I'm not completely sold on this CAI stuff.
They mutilate that beautiful stock look and just don't look right with the rest of an early '80's engine bay.
A CAI tube would need to be worth a significant increase in performance to compensate for the aesthetics.
I plan to do with- and without-the-horn testing, but if I can't feel or measure a difference I'm guessing this cold air and flow restriction stuff is just a bunch of hot air.
11-30-14, 11:38 PM
#49
Lolicon*** of RX-7 World
Not gonna lie I really wanna do this with a spare Nikki lol I just really wanna make a fast N/A Build until after a rebuild breaking of 5k or so :P then start with the rest of my build again later man TG I think that Nikki would do great with a street port and some boost if applicable for such fun!!~ 
Other then that I really wanna see a Video of your car running in Perfect Driving weather not to hot or too cold but something that is Just right to get that perfect Combustion for maximum POWAH!!!!~
Other then that I really wanna see a Video of your car running in Perfect Driving weather not to hot or too cold but something that is Just right to get that perfect Combustion for maximum POWAH!!!!~
12-01-14, 10:01 AM
#50
First of all, outstanding work.
I do have a few questions. Would you say you are making more power using the nikki versus the Dell ?
Also in comparison to Dell is the nikki is smoother for the street?
I ask because i just built my own 13b using T2 irons with S5 na rotors. Its strictly a Sunday driver cruising winding roads to the mountains, etc. I also have a Dell 48 dcoe to pair with the engine. I am worried as to how smooth a big two barrel could possibly be.
Obviously i dont think a nikki would do me any good because of the lacking cfm i need. However, it does make me wonder about using amother 4 barrel such as a holley.
I too soda blast all my parts before reassembly and i have to say your carb looks fantastic.
I do have a few questions. Would you say you are making more power using the nikki versus the Dell ?
Also in comparison to Dell is the nikki is smoother for the street?
I ask because i just built my own 13b using T2 irons with S5 na rotors. Its strictly a Sunday driver cruising winding roads to the mountains, etc. I also have a Dell 48 dcoe to pair with the engine. I am worried as to how smooth a big two barrel could possibly be.
Obviously i dont think a nikki would do me any good because of the lacking cfm i need. However, it does make me wonder about using amother 4 barrel such as a holley.
I too soda blast all my parts before reassembly and i have to say your carb looks fantastic.