fighting reversion
11-15-06, 04:16 PM
#76
'74 spacer on the left, '78 spacer on the right. Sorry, no picture of the J-spec spacer yet (just imagine a channel connecting both primary runners only).
J-spec and '78. They look similar. I'd need to study them to determine which has the smallest primary runners.
Left to right, we have '76 cosmo (with channels added), J-spec, '74, '78.
I had to reposition for the camera. '74, J-spec, '76 Cosmo, '78.
J-spec and '78. They look similar. I'd need to study them to determine which has the smallest primary runners.
Left to right, we have '76 cosmo (with channels added), J-spec, '74, '78.
I had to reposition for the camera. '74, J-spec, '76 Cosmo, '78.
11-16-06, 11:55 PM
#77
I swapped carbs and spacers on the REPU today.
The manifold is of the seperate runner variety, as was the spacer.
Rather than go through the hassle of changing manifolds, with the lost coolant, time involvement, cleanup etc, I swapped spacers instead. I'm sure the RX-4 manifold won't miss its channeled spacer (the blue one pictured above). Besides, I have other plans for it.
The truck runs very nicely now with no bogs. Its low end is surprising. I attempted to idle it up a hill. It began at 900 and chugged slowly up the hill until it started to putt down around 400 at the steep part. The whole truck was shaking and I didn't know how much longer I could torcher it. Satified, I slowly opened the throttle; paying close attention to any hickups or other anomalous noises. There were none. It climbed back up to idle and a little above without effort, cresting the top without incident. Not bad for a streetport. Of course the low gearing helped.
Then again, the REPU is kinda heavy, and there were two people in the cab. I believe that hill would have given the baja a little trouble in its current form. Ask PercentSevenC. He was with me.
The manifold is of the seperate runner variety, as was the spacer.
Rather than go through the hassle of changing manifolds, with the lost coolant, time involvement, cleanup etc, I swapped spacers instead. I'm sure the RX-4 manifold won't miss its channeled spacer (the blue one pictured above). Besides, I have other plans for it.
The truck runs very nicely now with no bogs. Its low end is surprising. I attempted to idle it up a hill. It began at 900 and chugged slowly up the hill until it started to putt down around 400 at the steep part. The whole truck was shaking and I didn't know how much longer I could torcher it. Satified, I slowly opened the throttle; paying close attention to any hickups or other anomalous noises. There were none. It climbed back up to idle and a little above without effort, cresting the top without incident. Not bad for a streetport. Of course the low gearing helped.
Then again, the REPU is kinda heavy, and there were two people in the cab. I believe that hill would have given the baja a little trouble in its current form. Ask PercentSevenC. He was with me.
11-17-06, 12:35 AM
#78
This info may interest Carl.
My REPU currently has a '77 Hitachi carb. Its specs are 20mm primary venuris, 106/160 fuel jets, 60/100 air bleeds, removed vacuum secondary spring (so they open sooner). The jets may be on the rich side. I have no means of testing air fuel mixture. Remember this carb is on a streetported engine (55° intake port closing)
The '74 REPU Hitachi came stock with 22mm primary venturis, 106/140 fuel, 80/160 air bleeds. According to Racing Beat, if you drop the primary jet size down to 105 and don't touch anything else, you gain power and fuel economy. The slightly rich factory jetting was for the thermal reactor.
My interpretation is this: '74 spec ports like 105 primary jets. I purchased a couple sets and tried them in my other Hitachis with nice results, including my '74 carb.
Further interpretation suggests 106 is ok on larger ports, like mild streetports as in my REPU. Experimentation has proved this correct.
I drilled some jets out to 117 (whatever SAE size drill bit I used). I tired them in 20 and 22mm venturi carbs and they behaved poorly. So 117 is too large for Hitachi carbs. You Nikki guys are lucky.
The '76 Cosmo also had 22mm primary venturis. Unfortunately my carb is a little messed up. Anyhoo it had 100/130 jets and 60/90 air bleeds. It had nice power up to high RPM on stock ports. It's a little less impressive on streetports. It developed an accel pump problem and one of the primary butterflies has a nick in it, disrupting the transition circuit (I think Hayes rotary damaged it when they 'rebuilt' it... the losers).
I tried a different '77 carb with 94/140 jets and 60/117 bleeds (I filled and drilled a set of 160 bleeds). It works well on the Cosmo, but I suspect it would work better with a channeled manifold.
My bro's RX-4 had a mild streetport and tried my J-spec carb before we installed a supercharger. The J-spec had 20mm venturis, and I rejetted it to 100/145 fuel and 60/90 air. Its low to mid RPM was very nice. It was only lacking in the upper RPM, but being a fresh rebuild, we didn't take it up there enough to worry about it.
So in conclusion, it seems 94-100 fuel jets work nicely on stock ported engines with tall primary ports. 100-105/106 work well on '74 spec (50°) and are useable on mild streetports (55°). I don't have any RB or extend streetports to try (60°).
It's probably just as well because I may've maxed out the Hitachis already. I won't know until I try a set of 110 jets. The 117s were certainly too big. I may not bother though. It's getting to the point of diminishing returns because a stock carb can only flow so much before it becomes a bottleneck. I'm sure the small air bleeds are thickening the mixture at high RPM too, regardles of secondary jets... to a point. It's good if it can extend the rev range and powerband, but not if it goes pig rich.
My REPU currently has a '77 Hitachi carb. Its specs are 20mm primary venuris, 106/160 fuel jets, 60/100 air bleeds, removed vacuum secondary spring (so they open sooner). The jets may be on the rich side. I have no means of testing air fuel mixture. Remember this carb is on a streetported engine (55° intake port closing)
The '74 REPU Hitachi came stock with 22mm primary venturis, 106/140 fuel, 80/160 air bleeds. According to Racing Beat, if you drop the primary jet size down to 105 and don't touch anything else, you gain power and fuel economy. The slightly rich factory jetting was for the thermal reactor.
My interpretation is this: '74 spec ports like 105 primary jets. I purchased a couple sets and tried them in my other Hitachis with nice results, including my '74 carb.
Further interpretation suggests 106 is ok on larger ports, like mild streetports as in my REPU. Experimentation has proved this correct.
I drilled some jets out to 117 (whatever SAE size drill bit I used). I tired them in 20 and 22mm venturi carbs and they behaved poorly. So 117 is too large for Hitachi carbs. You Nikki guys are lucky.
The '76 Cosmo also had 22mm primary venturis. Unfortunately my carb is a little messed up. Anyhoo it had 100/130 jets and 60/90 air bleeds. It had nice power up to high RPM on stock ports. It's a little less impressive on streetports. It developed an accel pump problem and one of the primary butterflies has a nick in it, disrupting the transition circuit (I think Hayes rotary damaged it when they 'rebuilt' it... the losers).
I tried a different '77 carb with 94/140 jets and 60/117 bleeds (I filled and drilled a set of 160 bleeds). It works well on the Cosmo, but I suspect it would work better with a channeled manifold.
My bro's RX-4 had a mild streetport and tried my J-spec carb before we installed a supercharger. The J-spec had 20mm venturis, and I rejetted it to 100/145 fuel and 60/90 air. Its low to mid RPM was very nice. It was only lacking in the upper RPM, but being a fresh rebuild, we didn't take it up there enough to worry about it.
So in conclusion, it seems 94-100 fuel jets work nicely on stock ported engines with tall primary ports. 100-105/106 work well on '74 spec (50°) and are useable on mild streetports (55°). I don't have any RB or extend streetports to try (60°).
It's probably just as well because I may've maxed out the Hitachis already. I won't know until I try a set of 110 jets. The 117s were certainly too big. I may not bother though. It's getting to the point of diminishing returns because a stock carb can only flow so much before it becomes a bottleneck. I'm sure the small air bleeds are thickening the mixture at high RPM too, regardles of secondary jets... to a point. It's good if it can extend the rev range and powerband, but not if it goes pig rich.
11-22-06, 11:51 AM
#81
Yeah don hold out on us post those pictures up.
I think there's not a lot to be added from people with less experience in tuning rotary's or ones that have less access to all the different motors you have. So its kinda tuff to add anything to this thread, but keep it up its greatly appreciated
I think there's not a lot to be added from people with less experience in tuning rotary's or ones that have less access to all the different motors you have. So its kinda tuff to add anything to this thread, but keep it up its greatly appreciated
11-22-06, 12:38 PM
#82
I was just hoping Carl would step in with his knowledge about carbs and maybe offer alternative explanations for the results I obtained after swapping carb spacers on my REPU, and any other insights.
Actually, Carl, I'd like to ask you specifically which intermediate plate I should use in my REPU engine. The stock 3B '74 plate or a tall port Y plate ported out to '74 spec. The only key difference is the port height on the outside. I'd also like to use a channeled manifold mainly to recreate the excellent results seen so far on my other engines.
Actually if I had more time and access to a dyno, I'd build the engine one way, break it in, dyno test it, then swap intermediate plates and test it again. Since that is not an option, I'd like to take what I've learned in this thread and build the REPU engine as a 'best guess'. I feel Carl's opinions would be invaluable in deciding which plate to use.
How well would T2 spec exhaust ports jive with '74 spec intake ports? I have access to two sets of '74 rotor housings. One is stock ported (and missing a little chrome). The other has lousy D shape ports with good chrome and needs to be corrected out to T2 spec at least (no larger).
I've gotta build two engines; for my REPU and MG. Both will have '74 spec intake ports because they can be used with Hitachi carbs and I have no plans on getting any more carbs (Hitachi actually fits in MG). Which vehicle should get the T2 exhaust ports, and should I enlarge the stock ports of the other set at all?
The stock ported missing chrome rotor housings were in the REPU engine. When that engine was briefly in the MG, it had tons of power. It never felt very powerful in the REPU. I suspect the restrictive exhaust, which I've since removed and will rebuild later, was the main reason. Man, the MG was ballsy with that engine.
I don't really want to disturb the low end potential now that I've gotten a feel for it. However the REPU should keep the small ports for more torque, but I know US spec ports are restricitive (at least at high RPM). Decisions decisions.
Any input is great. C'mon guys.
And now since you read through all that, here are some pictures as a reward for your patience.
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.
If you've seen the Scoot 4 rotor videos, they used at least one of these 6 port 12A intermediate plates.
The other two were J-spec GSL-SE (RE-EGI). Or maybe two 12A and one of the other.
I can't see the top of the rotor housings very well to determine whether they had oil injectors. That's for another day.
Actually, Carl, I'd like to ask you specifically which intermediate plate I should use in my REPU engine. The stock 3B '74 plate or a tall port Y plate ported out to '74 spec. The only key difference is the port height on the outside. I'd also like to use a channeled manifold mainly to recreate the excellent results seen so far on my other engines.
Actually if I had more time and access to a dyno, I'd build the engine one way, break it in, dyno test it, then swap intermediate plates and test it again. Since that is not an option, I'd like to take what I've learned in this thread and build the REPU engine as a 'best guess'. I feel Carl's opinions would be invaluable in deciding which plate to use.
How well would T2 spec exhaust ports jive with '74 spec intake ports? I have access to two sets of '74 rotor housings. One is stock ported (and missing a little chrome). The other has lousy D shape ports with good chrome and needs to be corrected out to T2 spec at least (no larger).
I've gotta build two engines; for my REPU and MG. Both will have '74 spec intake ports because they can be used with Hitachi carbs and I have no plans on getting any more carbs (Hitachi actually fits in MG). Which vehicle should get the T2 exhaust ports, and should I enlarge the stock ports of the other set at all?
The stock ported missing chrome rotor housings were in the REPU engine. When that engine was briefly in the MG, it had tons of power. It never felt very powerful in the REPU. I suspect the restrictive exhaust, which I've since removed and will rebuild later, was the main reason. Man, the MG was ballsy with that engine.
I don't really want to disturb the low end potential now that I've gotten a feel for it. However the REPU should keep the small ports for more torque, but I know US spec ports are restricitive (at least at high RPM). Decisions decisions.
Any input is great. C'mon guys.
And now since you read through all that, here are some pictures as a reward for your patience.
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.
If you've seen the Scoot 4 rotor videos, they used at least one of these 6 port 12A intermediate plates.
The other two were J-spec GSL-SE (RE-EGI). Or maybe two 12A and one of the other.I can't see the top of the rotor housings very well to determine whether they had oil injectors. That's for another day.
11-23-06, 12:40 AM
#84
Oops, I didn't clearly state that it is a 6 port 12A. So I'll do that now. Ahem.
The pictures directly above dj55b's post are of a 6 port 12A out of a J-spec or European 1st gen or HB Cosmo. It was imported and installed in some guy's 1st gen at some point. The tag on the waterpump says it was pulled in '94. The distributor looks like an '80 with the long pickup wiring harness and the reversed reluctor teeth (fast rising, slow dropoff past 0V, if I remember correctly - meant for J-105 ignitors). The oil pan, short filter pedestal and flywheel could have been swapped on at some point. Or maybe they're stock and the engine went into an '80 SA?
HOWEVER, and this is a big however, the oil pans of later 1st gen 12As actually had a missing section in the rolled over lip to allow for the motor mount on the intermediate plate between the exhaust ports, just like all GSL-SE oil pans. Looking at an '84-'85 12A oil pan in my garage, it too has the missing section in the lip. Earlier pans ('79-'81 at least) do not have a missing section on this side. This narrows the year of the engine down significantly.
If I had to guess, I'd say probably '83-'85. I'll know more if and when the owner wants to tear into it. I bet it'll have a high volume 17.5mm oil pump too.
Here is a video of the Scoot 23A. Note how the center intermediate differs from the other two. They had to block the EGR port. Now we know why, and which engine it came from. http://www.rotaryengineillustrated.c...ne-visual.html
The pictures directly above dj55b's post are of a 6 port 12A out of a J-spec or European 1st gen or HB Cosmo. It was imported and installed in some guy's 1st gen at some point. The tag on the waterpump says it was pulled in '94. The distributor looks like an '80 with the long pickup wiring harness and the reversed reluctor teeth (fast rising, slow dropoff past 0V, if I remember correctly - meant for J-105 ignitors). The oil pan, short filter pedestal and flywheel could have been swapped on at some point. Or maybe they're stock and the engine went into an '80 SA?
HOWEVER, and this is a big however, the oil pans of later 1st gen 12As actually had a missing section in the rolled over lip to allow for the motor mount on the intermediate plate between the exhaust ports, just like all GSL-SE oil pans. Looking at an '84-'85 12A oil pan in my garage, it too has the missing section in the lip. Earlier pans ('79-'81 at least) do not have a missing section on this side. This narrows the year of the engine down significantly.
If I had to guess, I'd say probably '83-'85. I'll know more if and when the owner wants to tear into it. I bet it'll have a high volume 17.5mm oil pump too.
Here is a video of the Scoot 23A. Note how the center intermediate differs from the other two. They had to block the EGR port. Now we know why, and which engine it came from.
http://www.rotaryengineillustrated.c...ne-visual.html
03-25-08, 10:29 AM
#85
Psalms 37**25
Jeff...all though its an old post ..nice work..
I will assemble a 12A this week using the smaller intermediate SE plates and a special mani..my goal is 30MPG ..
I will assemble a 12A this week using the smaller intermediate SE plates and a special mani..my goal is 30MPG ..
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