Faking a Sterling (yeah, I went there)
10-15-12, 10:04 PM
#1
Faking a Sterling (yeah, I went there)
Since Sterling isn't doing this stuff anymore, and the other guy with a pistonated name I can't remember isn't around (cobra whatever), I decided to take on the task of Yawing a carb for my own personal use.
A pretty good candidate showed up on a waterlogged Pinapple Racing 12A. Streetported with a hogged 79 manifold.
Pics will speak for themselves.
You like this?
Smoothed air horn
Those venturis look big.
They are big! And look at the drilled air bleeds!
155 and 170? Stock is 93 and 160. Hmm...
Shaft is twisted.
It's dead.
Possible replacement candidate?
This took place in 2004. My prediction was since the accel pump was still stock, this carb would have a flat spot as you open the mechanical secondaries.
And now I've got a more recent update. I was right! And what's even more awesome is this carb is really powerful! You'd think the enlarged venturis would hurt low RPM vacuum signal, as Sterling always warned, but you know, I tried this carb in the blue car and it didn't have weak low RPM at all. In fact it pulled harder down low than my 22mm Hitachi and harder up top than a stock Nikki to 7.5k where I had to let off seeing as the engine was a fresh rebuild with around 100 miles on it (3mm apex seals, 74 ported R5 13B with Y plates and full RB dual pipe exhaust). It starts super easily without a choke too!
Which brings us up to the present. I decided to give this carb some Sterling treatment. I deburred the boosters and some other mods. Pics coming later tonight.
A pretty good candidate showed up on a waterlogged Pinapple Racing 12A. Streetported with a hogged 79 manifold.
Pics will speak for themselves.
You like this?
Smoothed air horn
Those venturis look big.
They are big! And look at the drilled air bleeds!
155 and 170? Stock is 93 and 160. Hmm...
Shaft is twisted.
It's dead.
Possible replacement candidate?
This took place in 2004. My prediction was since the accel pump was still stock, this carb would have a flat spot as you open the mechanical secondaries.
And now I've got a more recent update. I was right! And what's even more awesome is this carb is really powerful! You'd think the enlarged venturis would hurt low RPM vacuum signal, as Sterling always warned, but you know, I tried this carb in the blue car and it didn't have weak low RPM at all. In fact it pulled harder down low than my 22mm Hitachi and harder up top than a stock Nikki to 7.5k where I had to let off seeing as the engine was a fresh rebuild with around 100 miles on it (3mm apex seals, 74 ported R5 13B with Y plates and full RB dual pipe exhaust). It starts super easily without a choke too!
Which brings us up to the present. I decided to give this carb some Sterling treatment. I deburred the boosters and some other mods. Pics coming later tonight.
10-15-12, 10:13 PM
#2
i think Sterling was doing some secret squirrel stuff on these carbs that he really didn't advertise.. any idea what you may do to assist this carb in flowing more fuel other than continuing to run the larger jets and porting and smoothing?
10-15-12, 11:04 PM
#4
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I've only entered the rotary game for about a year, but Sterling's website states he isn't taking further orders.
A question to the OP, what diameter are the throttle plates on that pineapple racing carb? Sterling says he went from 20 - 22mm on the primaries and 28 - 29mm on the secondaries fwiw.
A question to the OP, what diameter are the throttle plates on that pineapple racing carb? Sterling says he went from 20 - 22mm on the primaries and 28 - 29mm on the secondaries fwiw.
10-15-12, 11:08 PM
#5
Zeik, Go check the good guy bad guy section for an update on Sterling and his customers. But keep discussion of that subject out of this thread.
I chose the title "Faking a Sterling" because a "Sterling carb" is more recognizable than a Yaw carb or a cobra carb these days. So Faking a Sterling is nothing more than modding a Nikki to get more performance. Or if you don't like my choice in title, you can mod your own carb and call the thread whatever you want.
mazdaverx713b , there are some mods I did to increase air flow based on stuff Sterling posted publicly. So there's no secrets as far as I know. I took pics of everything I modded. I'll upload tonight.
I chose the title "Faking a Sterling" because a "Sterling carb" is more recognizable than a Yaw carb or a cobra carb these days. So Faking a Sterling is nothing more than modding a Nikki to get more performance. Or if you don't like my choice in title, you can mod your own carb and call the thread whatever you want.
mazdaverx713b , there are some mods I did to increase air flow based on stuff Sterling posted publicly. So there's no secrets as far as I know. I took pics of everything I modded. I'll upload tonight.
10-15-12, 11:14 PM
#6
Noob with 50 posts, 
I found two business cards with venturi sizes written on them in a bag full of carb parts that came with the engine. I assume they represent this particular carb. The sizes are... I can't remember exactly. I took pictures of them. I'll post tonight. But I'll hint that they're a lot bigger than Sterling's with no apparent downside. hah
I found two business cards with venturi sizes written on them in a bag full of carb parts that came with the engine. I assume they represent this particular carb. The sizes are... I can't remember exactly. I took pictures of them. I'll post tonight. But I'll hint that they're a lot bigger than Sterling's with no apparent downside. hah
Trending Topics
has since been educated and will be following this closely as well.
10-15-12, 11:57 PM
#9
I just finished the carb and stuck it on an engine. But I might test run this carb on something else that runs and drives seeing as the engine is in a project vehicle that's not very close to running yet. So I'll just try this on the known running engine and let you know how it turns out.
On to the next carb! I was going to mod this next carb for boost but it has some serious problems inside. Upon air horn removal, I found some pretty disturbing problems inside. So Now I'm on the lookout for another Nikki...
But I might test run this carb on something else that runs and drives seeing as the engine is in a project vehicle that's not very close to running yet. So I'll just try this on the known running engine and let you know how it turns out.On to the next carb! I was going to mod this next carb for boost but it has some serious problems inside. Upon air horn removal, I found some pretty disturbing problems inside. So Now I'm on the lookout for another Nikki...
10-16-12, 02:32 AM
#11
I've got a couple more carbs around here. Thanks though.
Here's the project it's going on. One fake internet buck to the first person who correctly identifies it.
Here's the intake stuff. The 76 reverse runner manifold should help low end torque. The open hole spacer should help high end (but it may be causing a lean condition in midrange-need testing with an O2 sensor).
Right before tearing down. Notice the booster support arms are there.
The two business cards I mentioned. So it looks like they modified the shaft too? All I know is it was twisted which would make sense as a thinned shaft is obviously more fragile than a stock one. Sterling cautions about this.
Booster supports are trimmed and polished with an "aerofoil shape" on the remaining support. (Sorry no pics of that specifically). Upper part of boosters polished. Outside of boosters had casting flashed reduced and/or removed, then a quick polish job. Bottoms of boosters needed slight deburring.
Closeup of polish job. I wasn't going for Sterling levels of pretty. If it feels smooth, the air will think it's smooth too. Good enough for this former racing carb.
Thanks though.Here's the project it's going on. One fake internet buck to the first person who correctly identifies it.
Here's the intake stuff. The 76 reverse runner manifold should help low end torque. The open hole spacer should help high end (but it may be causing a lean condition in midrange-need testing with an O2 sensor).
Right before tearing down. Notice the booster support arms are there.
The two business cards I mentioned. So it looks like they modified the shaft too? All I know is it was twisted which would make sense as a thinned shaft is obviously more fragile than a stock one. Sterling cautions about this.
Booster supports are trimmed and polished with an "aerofoil shape" on the remaining support. (Sorry no pics of that specifically). Upper part of boosters polished. Outside of boosters had casting flashed reduced and/or removed, then a quick polish job. Bottoms of boosters needed slight deburring.
Closeup of polish job. I wasn't going for Sterling levels of pretty. If it feels smooth, the air will think it's smooth too. Good enough for this former racing carb.
10-16-12, 03:07 AM
#12
Enough gaskets for two accel pump mods. Notice the three screw sizes? Short is stock. Long is a J-109 ignitor screw. The middle is shorted by like 5 or 6mm. Fits well. Maybe 1mm too long still? There is just enough fudge factor, fortunately.
Drilled accel banjo bolt holes. I'm slowing down the stroke, so this helps keep volume high enough. It relies in the pot metal nozzle squirters more than anything now, which are left stock (tiny).
An adjustable steel bar. It's in the shortest position now. Sterling recommends 1 ¼" hole spacing. I did that and two others a quarter inch further apart each time. So I've got 1.25", 1.5" and 1.75". Not sure the other two were really necessary.
Shortened J-109 screws and three gaskets per side of the accel pump. The little pin is installed the other way for simplicity which is possible on this carb but may not be on an FB carb due to a plethora of linkage on those.
Ooh look at these floats. Many of you are salivating right now.
Grose jets. I don't think you can get these any more for this application.
Drilled accel banjo bolt holes. I'm slowing down the stroke, so this helps keep volume high enough. It relies in the pot metal nozzle squirters more than anything now, which are left stock (tiny).
An adjustable steel bar. It's in the shortest position now. Sterling recommends 1 ¼" hole spacing. I did that and two others a quarter inch further apart each time. So I've got 1.25", 1.5" and 1.75". Not sure the other two were really necessary.
Shortened J-109 screws and three gaskets per side of the accel pump. The little pin is installed the other way for simplicity which is possible on this carb but may not be on an FB carb due to a plethora of linkage on those.
Ooh look at these floats. Many of you are salivating right now.
Grose jets. I don't think you can get these any more for this application.
10-16-12, 11:11 AM
#13
10-16-12, 11:30 AM
#14
What is that bellhousing adapter for?
What is that bellhousing adapter for? It looks like a manual transmission except the clutch fork is in the wrong place for a Mazda unless they moved it for the RX8. Are you using someone else's 6 speed?
Is that a 4 port 13b?
Is that a 4 port 13b?
10-16-12, 11:53 AM
#15
That hole is for ACV. If you don't fill it in, you'll get a super heated manifold. Way too many people install freeze plugs but fail to fill in the ACV port with anything.
The coolant ports are there to keep the manifold COOL when exhaust is flowing through the ACV port. Just adding a block off plate to the outside of the intake manifold is not enough!
It's funny and sad how many misguided folks there still are on this subject. Think about it: You perform a rather involved mod for a noob (complete intake removal) and go through the gasket scraping ritual, install some freeze plugs which you believe will keep the manifold cooler for more power. Then add some new o-rings and a new intake gasket. Then you get it all back on and it runs funny. You feel the manifold to "See" how much cooler it is, and you burn your hand.
Aftermarket manifolds are less affected by this as they block the ACV and coolant ports. But you still wind up with some manifold heating if you don't fill the ACV port and block the coolant ports due to engine heat trying to continuosly heat the manifold wjhile the carb's venturi effect continuously cools it down. I'd personally fill both these bothersome areas in and let the venturi effect do its thing. You can also easily swap manifolds without losing coolant and you don't get a nasty carbon buildup and possible eventual leak from the ACV area. The gasket is really thin there. I've seen a few blown out.
If you're not emission controlled, do yourself a favor and fill the ACV and coolant ports! Otherwise leave them both open. Don't fill one and forget the other. It's both or none!
The coolant ports are there to keep the manifold COOL when exhaust is flowing through the ACV port. Just adding a block off plate to the outside of the intake manifold is not enough!
It's funny and sad how many misguided folks there still are on this subject. Think about it: You perform a rather involved mod for a noob (complete intake removal) and go through the gasket scraping ritual, install some freeze plugs which you believe will keep the manifold cooler for more power. Then add some new o-rings and a new intake gasket. Then you get it all back on and it runs funny. You feel the manifold to "See" how much cooler it is, and you burn your hand.
Aftermarket manifolds are less affected by this as they block the ACV and coolant ports. But you still wind up with some manifold heating if you don't fill the ACV port and block the coolant ports due to engine heat trying to continuosly heat the manifold wjhile the carb's venturi effect continuously cools it down. I'd personally fill both these bothersome areas in and let the venturi effect do its thing. You can also easily swap manifolds without losing coolant
and you don't get a nasty carbon buildup and possible eventual leak from the ACV area. The gasket is really thin there. I've seen a few blown out.If you're not emission controlled, do yourself a favor and fill the ACV and coolant ports! Otherwise leave them both open. Don't fill one and forget the other. It's both or none!
10-16-12, 12:04 PM
#17
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exhaust doesn't flow thru that port, it does go to the exhaust, but in a stock car, air pump air goes thru there and when you block it off, its just stagnant.
10-16-12, 12:10 PM
#18
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if you take a stock nikki and open the throttle and look in it, its really obvious that there is a bunch of stuff in the way of flow. the throttle plate screws take up like half the primary!
10-16-12, 12:18 PM
#19
Originally Posted by j9fd3s
exhaust doesn't flow thru that port, it does go to the exhaust, but in a stock car, air pump air goes thru there and when you block it off, its just stagnant.
But exhaust heat definitely does make its way into the manifold. I nearly burned my hand on a modded SA manifold that someone welded an S4 6 port flange onto. It had only been running for a short time so I felt the manifold to get a feel on how hot things were getting and ouch! I couldn't believe the heat build up in just a minute or so of running. Then I realized the ACV ports were "open" while the coolant ports were just bosses in the aluminum - never machined. So no way to cool the carbed manifold. Needless to say I filled the ACV ports with quicksteel in the S4 NA Luna engine.
10-16-12, 12:23 PM
#20
Originally Posted by j9fd3s
the secret stuff was saying there was secret stuff. i've actually got a rotary engineering catalog from the early 90's with a 465cfm modded nikki in it.
if you take a stock nikki and open the throttle and look in it, its really obvious that there is a bunch of stuff in the way of flow. the throttle plate screws take up like half the primary!
if you take a stock nikki and open the throttle and look in it, its really obvious that there is a bunch of stuff in the way of flow. the throttle plate screws take up like half the primary!
Yeah the screws stick out more on the FB shafts than SAs.
10-16-12, 12:35 PM
#21
Here is another racing carb. This is for some other class. Basically stock. I can use this to make a comparison. Check out how tiny the primary venturis are. They hug the booster with very little room for air to squeeze by. I'm half tempted to pull everything and see if I can yank the venturis. Then machine them bigger. I don't really know the first thing... but how hard could it be? I mean if Yaw, Sterling and that cobra guy can do it, why can't I?
10-16-12, 01:09 PM
#22
Waffles - hmmm good
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Here is another racing carb. This is for some other class. Basically stock. I can use this to make a comparison. Check out how tiny the primary venturis are. They hug the booster with very little room for air to squeeze by. I'm half tempted to pull everything and see if I can yank the venturis. Then machine them bigger. I don't really know the first thing... but how hard could it be? I mean if Yaw, Sterling and that cobra guy can do it, why can't I?
remove the boosters. Use some polishing compound or valve grinding compound
and a dremel with a buffer wheel the right size to fit down in the venturi and go
at it until your get it where you want it. Removing the venturis is not easy and its
easy to muff em up while doing so. Ditto for machining them once removed. I know
Sterling mentions this on his website at some point.
10-16-12, 03:08 PM
#23
Those are some good ideas. I noticed the hogged venturis in the other carb do look slightly uneven compared to each other. They probably left them in the carb.
I wonder if I should enlarge the venturis in a boost prepped Nikki? Is it even required? I don't think they need to be bigger as the boost will cover for shortcomings in the carb.
I think the rule goes something like this: An NA carb needs to be big to make power but a boosted carb can be small. An example is a boost prepped weber DCOE 45 which had 40mm venturis in it. It was recommended that a swap to 36mm should be performed to make everything work better. As it was, that carb never ran very well and it was suspected to be caused by the too-large venturis.
So for my Nikki I think leaving the venturis alone and just concentrating on the boosters (modded like above) and other boost-prep mods are where I should focus my attention.
I wonder if I should enlarge the venturis in a boost prepped Nikki? Is it even required? I don't think they need to be bigger as the boost will cover for shortcomings in the carb.
I think the rule goes something like this: An NA carb needs to be big to make power but a boosted carb can be small. An example is a boost prepped weber DCOE 45 which had 40mm venturis in it. It was recommended that a swap to 36mm should be performed to make everything work better. As it was, that carb never ran very well and it was suspected to be caused by the too-large venturis.
So for my Nikki I think leaving the venturis alone and just concentrating on the boosters (modded like above) and other boost-prep mods are where I should focus my attention.
10-16-12, 03:08 PM
#24
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Nice job on the carb. Also, I'm drooling over that manifold. Put them together and the result ought to be pretty impressive.
As far as boost prepping goes, the airflow works the same way whether turbo or NA (well, more or less). Boost just makes it so much easier to get the power you're looking for that you don't have to go all out and make lots of drivability compromises to get there.
10-16-12, 03:29 PM
#25
Jeff,
Forgive me if this is a thread jack, but I completed a VERY similar endeavor a few months ago. I spent about a year researching and copying what Sterling has done. I also had some help from COBRASTNGVSVT racing on my venturis. Here is what I ended up with as far as modifications:
-Channeled/ported Rx-3 Manifold (That you sold me.). I only ported the carb end, and kept the two rotors separate.
-Removed all emissions, choke, fast idle linkage
-Removed OMP tubes
-Mechanical secondaries
-Thinned throttle shafts
-Double gasketed accel pump diaphragm
-Full holley air bleed kit to allow tunability
-Removed unused linkages from throttle shaft
-Increased the diameter of both the primary and secondary venturis
-Trimmed and polished the booster venturis
-Plugged all extra ports and holes with set screws/jbweld
-Smoothed out the air horn
-Used button head cap screws with Red locktite to hold in the throttle butterflies
-Modified the accelerator pump nozzle and banjo bolt by opening up all holes to a larger size
-Rx-3 floats
-Grose jets
See my pictures here:
https://www.rx7club.com/1st-gen-non-.../#post11149071
Forgive me if this is a thread jack, but I completed a VERY similar endeavor a few months ago. I spent about a year researching and copying what Sterling has done. I also had some help from COBRASTNGVSVT racing on my venturis. Here is what I ended up with as far as modifications:
-Channeled/ported Rx-3 Manifold (That you sold me.
). I only ported the carb end, and kept the two rotors separate.-Removed all emissions, choke, fast idle linkage
-Removed OMP tubes
-Mechanical secondaries
-Thinned throttle shafts
-Double gasketed accel pump diaphragm
-Full holley air bleed kit to allow tunability
-Removed unused linkages from throttle shaft
-Increased the diameter of both the primary and secondary venturis
-Trimmed and polished the booster venturis
-Plugged all extra ports and holes with set screws/jbweld
-Smoothed out the air horn
-Used button head cap screws with Red locktite to hold in the throttle butterflies
-Modified the accelerator pump nozzle and banjo bolt by opening up all holes to a larger size
-Rx-3 floats
-Grose jets
See my pictures here:
https://www.rx7club.com/1st-gen-non-.../#post11149071