Tri-Angles

Thanks soo much for the insight mate. I really appreciate that because i wouldve went to holley and gotten some jets and been dead wrong. Lol!

LizardFC

iTrader: (1)

Since we have a good thread on Nikki mods going, I'll go ahead and post up my SuperNikki pics here.

Here's the gritty stock wonder I picked up at Pull-a-Part:



A top down perspective shows just how much airflow restriction there is. Yes, that's a beetle in one of the primaries. He's not helping low-end power.



The choke is removed and the walls of the air horn are all sharpened and polished. Sterling contends that flow tests showed nothing to be gained by airhorn modification, but I like to go all out anyway. If anything, it's aesthetically pleasing. And if it looks faster, then it must be, right? To get the mirror finish, I used a wire brush bit that came with my dremel along with some Meguire's Mag & Aluminum Polish. Just make sure you get all the polish out because it can really gum up a carb if you don't.



Here's a top down shot showing a much more flow friendly setup. The inner venturi arms were trimmed off completely, while the outer ones containing the fuel tubes were ground into an airfoil shape and polished. Be careful not to grind too far into the inner arms or you could cut right into the fuel tubes. The inlet of both main venturis was widened, and the secondary venturi diameter was bored out about 1mm. All booster and main venturis were polished. The oil metering tubes were also removed. Note that the bottom throttle body section was left off for this shot:



Here's one of the shafts, ground down and polished to a smooth airfoil:



And here's the secondary butterflies with a trimmed shaft and cut screws. I left the screw heads alone... for now.



I'll try to get some shots of my modded linkage this weekend.

LizardFC

iTrader: (1)

Holley jets are SAE which would've really screwed you up

bumpstart

the holley air jets fit as exchange nikki fuel jets without mods

1/4 - 32 SAE thread is very close to the metric thread used as the nikki fuel jet
-close enough to actually work-

in the same manner 1/8 BSPF ( 28 ) and 1/8 NPT ( 27 ) thread will exchange if you force the issue


if you look close enough,,you are going to find both the yaw carbs and the sterling also sometimes use holley air jets as nikki fuel jets

LizardFC

iTrader: (1)

Yeah, according to Sterling's site they'll fit well enough. I was referring to the size measurements... you have to convert the metric size to SAE or you're going to end up with some really oversized jets.

bumpstart

very correct,, not so easy to do the math on the conversion
methinks sterling at one stage posted up the relevant comparison cross chart

Oneiros

Hmm ok. All the primary airs I get are 90's - Aussie models. I think I remember something about the later models running richer down low (smaller air bleed = richer mixture) because they have other circuits which lean the mix out to compensate. Since everything emissions hits the bin I don't worry about it. If in doubt just enlarge the primary fuel jets to 100 and see how it goes, if you can feel it's too rich just drill the air jets out.

Very nice work on modding yours btw.

An idea I had on the side is to clean up the inlets a lot by running aluminium pipes down from the air horn. I was hoping for a bell-mouth shaped entry but the four inlets are too close together to get anything optimally shaped. When I get some time I would like to try it out and see how it goes.

Oneiros

http://www.sterlingmetalworks.com/th...carburetor.htm

Has stock jet size conversions

wesmcbride

iTrader: (2)

Question along these lines:

Are the Nikki fuel jets interchangable with the air jets? Sterling's page indicates that the Holley's are, but does not mention the Nikki's.

bumpstart

no
he mods the top of the nikki emulsion tubes to suit the holley thread for using the holley air correctors as nikki air jets

the nikki fuel jets however are already threaded close enough so to fit the holley air jets in their place

hope that is clear as mud

wesmcbride

iTrader: (2)

That was clear as mud. What I am getting at, can I swap my stock (82, manual) Nikki jets like this?:

Secondary Air (140) <--swap--> Primary Fuel (91)

This swap would most resemble the "Track" tuning, without buying any jets.

74RX4

iTrader: (10)

Nikki main air jets and fuel jets are different shapes. Sterling drills and taps the top of the air bleed jets so small jets shaped like the fuel jets can be screwed into them. You can't swap stock air bleed and fuel jets without doing the same. This picture shows the Main air bleeds. These are the "air jets". The fuel jets are not shown, but they are shaped like the Primary #2 Slow air bleed at the top. The air bleeds have a built in emulsion tube, fuel jets don't.

bumpstart

i thinks you would need to carefully re thread the top of the brass emulsion tubes for the same metric thread as the fuel jets ( or 1/4-32 )
as currently they are not the same at each end of the tube

edit,, gotta stop taking time in the replies,, am getting beaten to the punch

LizardFC

iTrader: (1)

That makes sense, you Aussies get the best of everything Japanese over there. Americans get the leftover scrap I haven't had enough pedal-down time with the new carb to see where the AFR's are at throughout the band. It seems to be pretty lean from what I've seen so far but I still have to tune the accel pump so that will have an effect.

Sounds like velocity stacks... that would be pretty cool.

LizardFC

iTrader: (1)

I took the first gen out to some country back roads and had a few good 3-7k WOT runs in 3rd gear. Wideband is showing lean as I suspected... high 13's to low 14's across the whole band. Not dangerously lean, but definitely not ideal for power. I went to Hobbytown today and picked up a set of tiny numbered drill bits. So tonight I'm pulling the carb back apart on the dining room table to rejet it - and put it back on the car tomorrow morning for autocross I'm thinking of starting with maybe 120 for the primaries.

Tri-Angles

Lol! indeed mate!

Tri-Angles

This thread is really wicked fam! Im really glad I asked these questions because this not only is helping me learn about carburetors, but also what all is involved in them. Ive decided to use my 12a carb on my 13b six port bridgey, but I cant find a manifold that will work for it nor do I know how to fabricate a adaptor that will work well with my 12a manifold. I can fabricate, but I want to get a good A/F mixture going into all the ports while im driving. Any suggestions and or pointers would be absolutely awesome. Cheers guys.

bumpstart

ASK used to make the adapters,, you should be able to find a 13b 6p to 12a or to a 13b carb manifold adapter on tweakit
http://www.tweakit.net/shop/index.ph...sort=2a&page=2

if you cant find 13b 6p to 4 port 12a manifold adapter then you could either use the 13bt to 12a manifold adapter and port it suit 6 port

or you can get the 13b 6port to 13b 4 port adapter, and an old 13b carb manifold,, and restud it to take the 12a carb on top
( requires some cross porting of phelonic spacers to suit )

LizardFC

iTrader: (1)

That's a pretty hungry setup for a Nikki. Even fully modified, I'm not sure it would flow enough for a 13b 6P-BP. Racing Beat sells a manifold to put a Holley on a 13b, which would probably be your closest bet to simply build an adapter for a Nikki. A machine shop could make it for you. If you did go with the Nikki, I'd recommend porting out the secondary venturis quite a bit and going with bigger fuel jets all around.

Speaking of rejetting, I drilled out the primary fuel jets on my SuperNikki. The largest bit in the set I bought was a #61, which converts to about .99mm. I felt that might be a little too small. So I found a thick paperclip that was larger than the #61 bit but still had plenty of wiggle room when put through a secondary air bleed, which is a 140. So I hogged out the primary jets with the #61 to the point where the paperclip could be forced through. I estimate the new jetting to be around 105-110. I left the secondary fuel jets and all the air bleeds alone. I also used the smaller bits to drill out the tiny holes in the air pump nozzle jet and adjusted the AP nut to lengthen the stroke of the arm.

That turned out about perfect. AFR's are now in the low to mid 12's from 3k on up, and there's no stumble when opening the throttle. The only downside is that my gas mileage is gonna take quite a hit. AFR's while cruising around are in the low to mid 11's, down from around 14. But hey, it runs cooler!

This weekend I got the chance to try out the carb at an autocross. It's a faster car now, hands down. The only problem I'm having with it is that it has a bad left turn stumble. There was a slalom just after a tight left turn that I just couldn't get any power through. So after reading a thread on here, I'm thinking of ordering a couple larger RX-3 floats. That supposedly fixes that issue.

Tri-Angles

Thanks alot mate.

Tri-Angles

Hmm... Well in that case I should just go with a holley 600 w/ a racing beat 6 port manifold all together. I dont want to have to do it that way because that means buying more parts but if that needs to be done then ill just have to do it. But if Crispen38 could run a monster port on his nikki carb then how is it that a bridged 6 port wouldnt be able to handle it?

Oneiros

It depends how you mod the Nikki. As Lizard said you will probably need to bore out the secondary venturis and possibly also the primary venturis as well. It can be done.

Tri-Angles

Well with that being said. How big would you say i would have to bore out the venturis and would drilling out the jets and a.c's i have now work good for this engine? This engine is mainly going to be lightfooted for the most part due to it being a daily. I bridged all the ports except the centre plate because im too lazy and I dont know if it will give me much of a gain. I could use it on one of my 12a's but one is monster ported at the plates and the other is a big bridge that cuts through the inner coolant o-ring groove but not inton the coolant jacket. Carbons are too expensive for me at the moment so thats why i opted to use me 13b. But i wanna keep my 12a soley because thats what the car had in it when i bought it. ( 600$ steal! ;-B )

LizardFC

iTrader: (1)

Bridgeport on a daily driver?? I haven't driven one so I won't even get into that.

The 13B is a fatter kid, and fatter kids eat more at the buffet. I'm not saying it won't work... I really don't have any data to go on. It seems like it would be stretching it though, since even the Sterling Nikki is only rated at 465cfm. Surely someone has tried it though, so maybe a search will shed some light.

I would bore the primary venturi diameter out by about 2mm, and the secondaries by even more... maybe 4mm if you can. As far as jetting goes, the jets can be drilled to any size you want, so as long as you have the air volume and velocity then the jets can be drilled to supply the appropriate amount of fuel (as long as there is enough pressure and flow from the pump.)

By all means, experiment

Oneiros

+1

The larger you bore them out, will improve peak air flow, but sacrifices fuel signal at lower air speeds, meaning a worse bottom end. If you can, optimise the venturi inlet and outlet angles as well - 16-21 degrees on the inlet side and 7-11 degrees on the outlet IIRC. If you want I can dig up the calculations I made when I first started doing them, it should help you out. Let me know.