Weird Nikki 6 port 13B manifold
01-29-08, 04:08 PM
#1
Weird Nikki 6 port 13B manifold
Take a look at this abomination.
Did it work? It kinda sorta did on an RE-SI engine (like a J-spec GSL-SE but with smaller ports). The problem with the RE-SI is the intermediate ports are even smaller than a GSL-SE or S4 NA. So you have these monsterous channels at the top of the manifold, which squeeze down into normal FB runners, then which join into an aluminum plate that somebody cut for the 6 port 13B pattern, and since there are no aux port actuators, you must leave the sleeves out of the engine. No chance of using Pineapple sleeves or any of that. What you're left with is too much port timing at the end plates with poor flow, and not enough port timing at the intermediate plate with almost no flow. Couple that with US-spec early opening+early closing exhaust ports of the RE-SI (same as US-spec REPU, Cosmo, RX-4 and '81-'85 12As), choking off the engine, and you have one gutless wonder.
It was in my friend's REPU. It was pretty gutless so he got himself a Camden and I got this manifold and the Nikki that was on it. A '79-'80 style, but probably J-spec because it has a few feature sI've never seen before. Anyway the venturi boostrs are no longer glued to the main body and can be lifted up and removed from th ecarb. There is some wear from the metal to metal rubbing. Plus being an SA style carb, according to Sterling, is harder to dial in the air fuel mixture curve. It has a set of 106 Hitachi primary fuel jets, stock 160 secondaries, and 90 pri iar bleeds with 120 (yeah!) secondary bleeds. I'm going to try the carb on my nice trusty 12A to see if it's even worth fixing. If not, I'll harvest the good bits for an '81-'85 Nikki that needs some attention.
As for the weird 6 port manifold, I don't know yet. I'd appreciate your input.
Did it work? It kinda sorta did on an RE-SI engine (like a J-spec GSL-SE but with smaller ports). The problem with the RE-SI is the intermediate ports are even smaller than a GSL-SE or S4 NA. So you have these monsterous channels at the top of the manifold, which squeeze down into normal FB runners, then which join into an aluminum plate that somebody cut for the 6 port 13B pattern, and since there are no aux port actuators, you must leave the sleeves out of the engine. No chance of using Pineapple sleeves or any of that. What you're left with is too much port timing at the end plates with poor flow, and not enough port timing at the intermediate plate with almost no flow. Couple that with US-spec early opening+early closing exhaust ports of the RE-SI (same as US-spec REPU, Cosmo, RX-4 and '81-'85 12As), choking off the engine, and you have one gutless wonder.
It was in my friend's REPU. It was pretty gutless so he got himself a Camden and I got this manifold and the Nikki that was on it. A '79-'80 style, but probably J-spec because it has a few feature sI've never seen before. Anyway the venturi boostrs are no longer glued to the main body and can be lifted up and removed from th ecarb. There is some wear from the metal to metal rubbing. Plus being an SA style carb, according to Sterling, is harder to dial in the air fuel mixture curve. It has a set of 106 Hitachi primary fuel jets, stock 160 secondaries, and 90 pri iar bleeds with 120 (yeah!) secondary bleeds. I'm going to try the carb on my nice trusty 12A to see if it's even worth fixing. If not, I'll harvest the good bits for an '81-'85 Nikki that needs some attention.
As for the weird 6 port manifold, I don't know yet. I'd appreciate your input.
01-29-08, 04:13 PM
#2
Eats, Sleeps, Dreams Rotary
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Wasnt there a 6 port 12a? Not that savvy on the older (historic) rotary but I recall seeing a black and red stock air cleaner that had 6 port on it.
01-29-08, 04:36 PM
#3
Yeah, and my friend has one. Maybe this manifold came from one, or maybe it was a normal FB manifold. It looks like it because it had a shutter valve that somebody removed. I don't know that much about the 6 port 12As so I can't say for sure.
01-29-08, 04:48 PM
#4
I have one project car that needs a 13B. It is the GLC I've mentioned a few times recently. I was all set to build a 4 port 13B for it the other day and use a typical Hitachi carb and 4 port manifold. Even cleaned up the side plates and everything. I am, however, willing to entertain thoughts of an experiemental nature, namely figuring out a way to use this weird 6 port chymera. 
Some recent experiements with various Hitachis and a modded (by me) '84-'85 Nikki carb have convinced me the Nikki is a superior carb and does not suffer from the funky fuel curve problems of Hitachis and '79-'80 Nikkis. I was wholey impressed by the performance when switching from slightly larger than stock 94 primary jets and 90 primary air bleeds, to 100 jets and 70 air bleeds. It now has power up to 7k where before it would run out of breath up there, and the primary powerband seems to have gotten wider with more power down low. The carb used to only come alive when you'd open the secondaries above about 3800RPM. Now it has power pretty much everywhere and the transition has become smoother.
I was planning on cutting a set of Nikki stud holes in one of my Hitachi manifolds so I could take advantage of the Nikki's better power delivery when I realised upon test fitting a Nikki in my REPU the other day, that it won't fit under the hood. The Nikki is taller than a Hitachi, and the MOP lines and rod are about an inch too short. This is because the Hitachi manifold is about an inch taller than a Nikki manifold. Also the throttle cable was too long (at least that's how the weird carb was that came with the 6 port manifold; a normal Nikki might be different).
Since a Nikki on a Hitachi manifold won't work, I could either get a 12A to 13B manifold adaptor, or mod a Nikki manifold to fit. Or run without an air cleaner assembly. Still would need to mod the MOP lines and rod. Not sure about the throttle cable, but probably.
A better option would be to use a manifold that already has the right dimensions to allow the Nikki to sit lower. Since this 6 port mainfold is the only one like that, I'm considering it. It would need to be repaired, or course. I do still have the RE-SI end plates. I also have access to a '74 REPU intermediate plate with its short port runners and '74 spec port timing. That might work. It would provide much more flow than the RE-SI or a GSL-SE intermediate, and better match the non-sleeveable aux ports in port timing. Of course the low end torque would be pretty bad I'm thinking, but the GLC is a small light car. I bet I could get away with it.
Some recent experiements with various Hitachis and a modded (by me) '84-'85 Nikki carb have convinced me the Nikki is a superior carb and does not suffer from the funky fuel curve problems of Hitachis and '79-'80 Nikkis. I was wholey impressed by the performance when switching from slightly larger than stock 94 primary jets and 90 primary air bleeds, to 100 jets and 70 air bleeds. It now has power up to 7k where before it would run out of breath up there, and the primary powerband seems to have gotten wider with more power down low. The carb used to only come alive when you'd open the secondaries above about 3800RPM. Now it has power pretty much everywhere and the transition has become smoother.
I was planning on cutting a set of Nikki stud holes in one of my Hitachi manifolds so I could take advantage of the Nikki's better power delivery when I realised upon test fitting a Nikki in my REPU the other day, that it won't fit under the hood. The Nikki is taller than a Hitachi, and the MOP lines and rod are about an inch too short. This is because the Hitachi manifold is about an inch taller than a Nikki manifold. Also the throttle cable was too long (at least that's how the weird carb was that came with the 6 port manifold; a normal Nikki might be different).
Since a Nikki on a Hitachi manifold won't work, I could either get a 12A to 13B manifold adaptor, or mod a Nikki manifold to fit. Or run without an air cleaner assembly. Still would need to mod the MOP lines and rod. Not sure about the throttle cable, but probably.
A better option would be to use a manifold that already has the right dimensions to allow the Nikki to sit lower. Since this 6 port mainfold is the only one like that, I'm considering it. It would need to be repaired, or course. I do still have the RE-SI end plates. I also have access to a '74 REPU intermediate plate with its short port runners and '74 spec port timing.
That might work. It would provide much more flow than the RE-SI or a GSL-SE intermediate, and better match the non-sleeveable aux ports in port timing. Of course the low end torque would be pretty bad I'm thinking, but the GLC is a small light car. I bet I could get away with it.
01-29-08, 05:09 PM
#5
Sorry for all the reading.
What it comes down to is I want to use a Nikki because they are really great carbs. The only way to get one to fit in th eGLc is to use the 6 port manifold and build a 6 port engine. The downside is the manifold must be repared (I know a guy that can weld aluminum) and the low end driveability might suck *****. I want my dad to be able to drive the car when finished so I spent a lot of time researching flyweels and clutches so it will have easy pedal effort, but enough holding capacity for a 13B. (either the superlight steel 8 pound flywheel with a heavy pressure plate, or a Racing Beat light steel 13 pound flywheel with a light pressure plate)
I've built several 4 port 13Bs and I know they are great, but I feel in order to expand my knowledge base, I must venture into the 6 port realm. I'm running low on good hitachi carbs and manifolds these days, so I'm looking forward to experiementing with Nikkis and changing whatever needs to be modded to fit the different throttle cable, choke cable (for my dad) and other stuff.
I still have a trump card too; if the 6 port just doesn't work out, I can do a quickie rebuild and go with a 4 port.
So what do you guys think? 6 port? 4 port? The car already has a 4 port and it works pretty well with large street ports. The idle is a little lumpy and the carb is a little cold blooded. Also doesn't like to rev much because it's a Hitachi. My dad would not like it. If the 6 port turns out that way too, I'll do a non-ported 4 port.
If you like following my projects, you won't want to miss this.
What it comes down to is I want to use a Nikki because they are really great carbs. The only way to get one to fit in th eGLc is to use the 6 port manifold and build a 6 port engine. The downside is the manifold must be repared (I know a guy that can weld aluminum) and the low end driveability might suck *****. I want my dad to be able to drive the car when finished so I spent a lot of time researching flyweels and clutches so it will have easy pedal effort, but enough holding capacity for a 13B. (either the superlight steel 8 pound flywheel with a heavy pressure plate, or a Racing Beat light steel 13 pound flywheel with a light pressure plate)
I've built several 4 port 13Bs and I know they are great, but I feel in order to expand my knowledge base, I must venture into the 6 port realm. I'm running low on good hitachi carbs and manifolds these days, so I'm looking forward to experiementing with Nikkis and changing whatever needs to be modded to fit the different throttle cable, choke cable (for my dad) and other stuff.
I still have a trump card too; if the 6 port just doesn't work out, I can do a quickie rebuild and go with a 4 port.
So what do you guys think? 6 port? 4 port? The car already has a 4 port and it works pretty well with large street ports. The idle is a little lumpy and the carb is a little cold blooded. Also doesn't like to rev much because it's a Hitachi. My dad would not like it. If the 6 port turns out that way too, I'll do a non-ported 4 port.
If you like following my projects, you won't want to miss this.
01-29-08, 05:18 PM
#6
Wow, I must be inspired. Look at all the posts I've made in the last hour. That right there tells me it's worth exploring this 6 port Nikki thing further.
Here are the rotors I'd like to use.
One suffered broken apex seals in the RE-SI engine (right) as is the fate of all GSL-SE engines since they run so well for so long (one broke at 5.5mm). The other rotor came out of a water damaged nitrided R5 in my friend's garage. When he tried to get the side seals out, they were stuck and broke. He gave up and it sat on the floor for several years attracting bugs and debris. I was able to dig the side seals out in like 5 minutes using a special new tool I made out of an old box cutter blade.
Both are C weight, but just picking them up, the RE-SI feels a little lighter. They use the same counterweights and flywheels. Maybe I'm imagining it.
The Y side plates for the 4 port, should I decide to build it.
The 6 port RE-SI end plates are not pictured by maybe I can find a shot of the intermediate plate and its microscopic ports...
Here are the rotors I'd like to use.
One suffered broken apex seals in the RE-SI engine (right) as is the fate of all GSL-SE engines since they run so well for so long (one broke at 5.5mm). The other rotor came out of a water damaged nitrided R5 in my friend's garage. When he tried to get the side seals out, they were stuck and broke. He gave up and it sat on the floor for several years attracting bugs and debris. I was able to dig the side seals out in like 5 minutes using a special new tool I made out of an old box cutter blade.
Both are C weight, but just picking them up, the RE-SI feels a little lighter. They use the same counterweights and flywheels. Maybe I'm imagining it.The Y side plates for the 4 port, should I decide to build it.
The 6 port RE-SI end plates are not pictured by maybe I can find a shot of the intermediate plate and its microscopic ports...
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01-29-08, 05:34 PM
#9
Sorry to keep posting, but I found some 6 port 12A pictures.
EGR port.
Awesome cast iron header. Note the motor mount studs like a GSL-SE.
6 port manifold with a Nikki. Not sure how it flows yet, which runners etc.
'80 type dizzy. Short oil filter pedestal. Motor mount studs.
EGR port.
Awesome cast iron header. Note the motor mount studs like a GSL-SE.
6 port manifold with a Nikki. Not sure how it flows yet, which runners etc.
'80 type dizzy. Short oil filter pedestal. Motor mount studs.
01-29-08, 05:54 PM
#10
I think I just figured it out. The reason the carb seems to share features of an SA (main body, thottle body) and FB (top cover) and why it has 120 secondary air bleeds vs 140 on all the 4 port 12A carbs I've ever seen, is because the manifold and carb indeed are from a 6 port 12A. The 120 air bleeds keep the fuel meetering into the carb up to a slightly higher RPM and/or slightly greater CFM than a typical 4 port 12A would see.
There is a big difference in port timing though. The 6 port 12A has very late opening intake ports, with closing being about the same as a GSL-SE. The secondaries are also smaller than the RE-SI pictured above. The aux ports are um.. I can't remember what shape or timing they had. It's been a while since I saw a set of 6 port 12A plates.
Thanks to this thread, and the experiments I've done on my nice (4 port) 12A with a set of '74 spec ports I cut with my dremel, I now believe I can 'get away' with a '74 intermediate plate and the RE-SI end plates with their current port timing. The primaries will flow a little more since the engine is a 13B, and the secondaries will flow a lot more due to the timing of the aux ports.
The primary carb barrels should be able to flow well enough fuel with let's say 106 primary jets (as mentioned above) and perhaps some 70 or maybe even 60 primary air bleeds (they're worth their weight in gold!) and the 120 secondary air bleeds from the 6 port 12A carb (mentioned above, and worth their weight in uh silver, or something lol). I have a set of 170 and 190 secondary jets if I need to use them, but Sterling says the stock 160s are plenty big enough in his Sterling carbs with various levels of porting. Only experiements will bear this out on this engine, of course.
Wow, it's a real 6 port manifold and carb that somebody butchured to make it fit a 13B. Wow.
The 120 air bleeds keep the fuel meetering into the carb up to a slightly higher RPM and/or slightly greater CFM than a typical 4 port 12A would see.There is a big difference in port timing though. The 6 port 12A has very late opening intake ports, with closing being about the same as a GSL-SE. The secondaries are also smaller than the RE-SI pictured above. The aux ports are um.. I can't remember what shape or timing they had. It's been a while since I saw a set of 6 port 12A plates.
Thanks to this thread, and the experiments I've done on my nice (4 port) 12A with a set of '74 spec ports I cut with my dremel, I now believe I can 'get away' with a '74 intermediate plate and the RE-SI end plates with their current port timing. The primaries will flow a little more since the engine is a 13B, and the secondaries will flow a lot more due to the timing of the aux ports.
The primary carb barrels should be able to flow well enough fuel with let's say 106 primary jets (as mentioned above) and perhaps some 70 or maybe even 60 primary air bleeds (they're worth their weight in gold!) and the 120 secondary air bleeds from the 6 port 12A carb (mentioned above, and worth their weight in uh silver, or something lol). I have a set of 170 and 190 secondary jets if I need to use them, but Sterling says the stock 160s are plenty big enough in his Sterling carbs with various levels of porting. Only experiements will bear this out on this engine, of course.
Wow, it's a real 6 port manifold and carb that somebody butchured to make it fit a 13B. Wow.
Last edited by Jeff20B; 01-29-08 at 06:14 PM.
01-29-08, 08:55 PM
#13
Go ahead, Jon.
Latin, sorry I don't have any pictures of the 6 port 12A irons. I also don't any pictures of the RE-SI micro ports. I can however show the differences between the slightly larger GSL-SE/NO spec and '74 spec.
On the left we have a typical GSL-SE or NO or S4 NA primary intake port (they're all about the same). On the right is a '74 spec port.
Just imagine a port even smaller than the one on the left, and try to mentally compare it to the one on the right and how much greater the CFM potential is, without sacrificing much low end
I also included a 12A port for comparison.
Here we see a whole series of short runner intermediate plates. The RE-SI looks the same as a GSL-SE on the outside.
Here is how a typical Y casting 12A intermediate compares in runner height to a '74 intermediate.
And here is a quick comparison of port closing timing between a 12A Y casting and a '74 casting.
If you have a good eye, you can see a scribe line above the '74 port for a mild streetport. It was a little off so I didn't use it.
Latin, sorry I don't have any pictures of the 6 port 12A irons. I also don't any pictures of the RE-SI micro ports. I can however show the differences between the slightly larger GSL-SE/NO spec and '74 spec.
On the left we have a typical GSL-SE or NO or S4 NA primary intake port (they're all about the same). On the right is a '74 spec port.
Just imagine a port even smaller than the one on the left, and try to mentally compare it to the one on the right and how much greater the CFM potential is, without sacrificing much low end
I also included a 12A port for comparison.
Here we see a whole series of short runner intermediate plates. The RE-SI looks the same as a GSL-SE on the outside.
Here is how a typical Y casting 12A intermediate compares in runner height to a '74 intermediate.
And here is a quick comparison of port closing timing between a 12A Y casting and a '74 casting.
If you have a good eye, you can see a scribe line above the '74 port for a mild streetport. It was a little off so I didn't use it.
01-30-08, 12:51 PM
#15
Thanks for posting. Yeah, too bad the aux actuators have been removed from this manifold. It will be fill flow, full time.
With all the potential problems this setup could have, I'm having second thoughts.
I know I'll regret it if I don't try it. I can always rip it out and do a 4 port rebuild later, if necessary.
With all the potential problems this setup could have, I'm having second thoughts.
I know I'll regret it if I don't try it. I can always rip it out and do a 4 port rebuild later, if necessary.
01-30-08, 01:04 PM
#16
So, trochoid, what port size should I use on the intermediate plate? Keep in mind the size of the ports in the end plates and the lack of aux actuators. I can't even use sleeves because there is no way to secure them.
One of the end plates. (I could port it out a little if necessary)
Primary port comparison of GSL-SE and 12A on the left to '74 spec on the right.
Sorry, the pictures were a little scewed. I aligned them the best I could. The 12A and '74 spec are the same except for when they close. 12A spec flows well up to about 6500RPM. '74 spec flows up to at least 7k with a little headroom above. The GLC's current primaries are a mild street port. The secondaries are an extended streetport. Not much low end and they outflow the Hitachi (which is maxed out in jets and air bleeds) at mid to high RPM so it needs a bigger carb. No problem as it's getting pulled in a few days to make room for this 6 port beast.
The Hitachi will become available but I'd much rather use a Nikki. So, knowing it's getting a Sterling Nikki some day but will start out with a nicely modded stockish one, would you just go for the '74 spec ports? I'm thinking I should, but I want some opinions.
One of the end plates. (I could port it out a little if necessary)
Primary port comparison of GSL-SE and 12A on the left to '74 spec on the right.
Sorry, the pictures were a little scewed. I aligned them the best I could. The 12A and '74 spec are the same except for when they close. 12A spec flows well up to about 6500RPM. '74 spec flows up to at least 7k with a little headroom above. The GLC's current primaries are a mild street port. The secondaries are an extended streetport. Not much low end and they outflow the Hitachi (which is maxed out in jets and air bleeds) at mid to high RPM so it needs a bigger carb. No problem as it's getting pulled in a few days to make room for this 6 port beast.
The Hitachi will become available but I'd much rather use a Nikki. So, knowing it's getting a Sterling Nikki some day but will start out with a nicely modded stockish one, would you just go for the '74 spec ports? I'm thinking I should, but I want some opinions.
Last edited by Jeff20B; 01-30-08 at 01:16 PM.
01-30-08, 01:19 PM
#17
I just had an interesting thought. If I could figure out a way to secure the sleeves, what's to stop me from installing them and leaving them closed during break in? The engine would behave like a well mannered 4 port 13B. Then once its broken in, I could removed the manifold (both coolant ports would be blocked so no mess), rotate the sleeves to fully open and try it. If it kills power, close them up until I can get a better manifold. No need to pull the engine to do a 4 port rebuild.
Yeah, I've got nothing to lose. The sleeves are the key to unlock the full potential of this engine. Leave them in for my dad; take them out (or get some pineapple inserts) for me.
The last question is about port size. '74 spec intermediate? Should I port the end plates at all? If it runs well enough through all 6 ports, I'll let my dad drive it like that.
Then once its broken in, I could removed the manifold (both coolant ports would be blocked so no mess), rotate the sleeves to fully open and try it. If it kills power, close them up until I can get a better manifold. No need to pull the engine to do a 4 port rebuild. Yeah, I've got nothing to lose.
The sleeves are the key to unlock the full potential of this engine. Leave them in for my dad; take them out (or get some pineapple inserts) for me. The last question is about port size. '74 spec intermediate? Should I port the end plates at all? If it runs well enough through all 6 ports, I'll let my dad drive it like that.
01-30-08, 02:47 PM
#18
Once the aux ports are open full time, lowend torque falls off considerably. It kills me how many 2nd gen guys think thier car is faster with them removed or open fulltime, when they're not. You could leave them closed all the time then port the secondary ports bigger. I don't know if the actuators from the SEs or S4 could be adapted to open uours. Iirc, they opened through vacuum or something on the 12A 6-ports.
That engine, 12A-6port, was sold in Europe, perhaps the European forum can help you out on parts, info.
That engine, 12A-6port, was sold in Europe, perhaps the European forum can help you out on parts, info.
01-30-08, 03:00 PM
#19
Thanks trochoid. Yeah, I could leave them closed all the time and still get the advantage of running a '74 intermediate. I could also port the secondary ports bigger like you said. Maybe out to 12A spec? lol I'll have to think about it and compare port sizes.
Also the RE-SI aux ports are actually smaller than GSL-SE and probably S4 NA. This might actually be of benefit here. I've still got some stuff to think about.
Thanks for the advice about the European forum. I don't think it's wise to attempt to install aux actuators in this manifold since it's already been modified so extensively. To get them aligned correctly and sealed... Too much work. Even manual external ***** would still require proper alignment and sealing. The project is kind of rushed, actually, so I don't have a lot of engineering time. I could simply install the sleeves, maybe add a drop of sealant to steady them so they won't tend to rotate on me, and pretend the engine is a 4 port 13B which happens to have a Nikki in the proper location so it will fit under the hood.
If and when I do remove the sleeves, you'll be the first to know how it affects low end torque. Sound good?
Also the RE-SI aux ports are actually smaller than GSL-SE and probably S4 NA. This might actually be of benefit here. I've still got some stuff to think about.
Thanks for the advice about the European forum. I don't think it's wise to attempt to install aux actuators in this manifold since it's already been modified so extensively. To get them aligned correctly and sealed... Too much work. Even manual external ***** would still require proper alignment and sealing. The project is kind of rushed, actually, so I don't have a lot of engineering time. I could simply install the sleeves, maybe add a drop of sealant to steady them so they won't tend to rotate on me, and pretend the engine is a 4 port 13B which happens to have a Nikki in the proper location so it will fit under the hood.
If and when I do remove the sleeves, you'll be the first to know how it affects low end torque.
Sound good?
01-31-08, 06:45 AM
#21
Eats, Sleeps, Dreams Rotary
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Actually my previous motor (s5) had the aux ports open full time and it was very easy to drive on the street and ran like a bat out of hell with the pedal down! I can see how one can look at the port and say that the lowend suffers, maybe it does but to me it goes unnoticed. Top end sure as hell doesnt suffer!
01-31-08, 01:46 PM
#22
That is very encouraging, Latin. Thankyou.
I grabbed all the plates out of storage and compared the RE-SI secondaries to 12A spec. 12A are a little bigger. I bet I could leave the aux ports open full time since they are small too.
The bottleneck will be in the exhaust ports. We all know US-spec 12A exhaust ports are restrictive. These 13B ports have the same timing. They need to be enlarged. I could copy what I did in the nice 12A; leave opening alone but delay closing a bit. We cut upward 2mm until the closing bevel was gone. Then made a new bevel. We also widened the port 2mm on each side. The end result is a nice increase over stock but still small enough for excellent driveability.
I think I could do the same for this engine. The primary ports will be the same size but the secondaries will have more total timing and probably more flow (remember 6 ports are not as good as 4 ports for most porting potential etc). The main reason I'm doing this project is so I can use a Nikki carb without it poking up through the hood, as would happen on a 4 port 13B manifold. And since I don't want to build my own manifold or buy a 12A to 13B adaptor plate, I'm stuck building a 6 port 13B and using this manifold. All this fuss over a Nikki.
I grabbed all the plates out of storage and compared the RE-SI secondaries to 12A spec. 12A are a little bigger. I bet I could leave the aux ports open full time since they are small too.
The bottleneck will be in the exhaust ports. We all know US-spec 12A exhaust ports are restrictive. These 13B ports have the same timing. They need to be enlarged. I could copy what I did in the nice 12A; leave opening alone but delay closing a bit. We cut upward 2mm until the closing bevel was gone. Then made a new bevel. We also widened the port 2mm on each side. The end result is a nice increase over stock but still small enough for excellent driveability.
I think I could do the same for this engine. The primary ports will be the same size but the secondaries will have more total timing and probably more flow (remember 6 ports are not as good as 4 ports for most porting potential etc). The main reason I'm doing this project is so I can use a Nikki carb without it poking up through the hood, as would happen on a 4 port 13B manifold. And since I don't want to build my own manifold or buy a 12A to 13B adaptor plate, I'm stuck building a 6 port 13B and using this manifold. All this fuss over a Nikki.
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