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1973 SU (flats) swap to 1972 SU (roundtops)...


mamba_888

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Hello everyone...

 

First and foremost, I have searched but found only a trickle of information on this so I am imploring for you SU gurus for help.

 

I have just purchased a 1973 240z (for 970.00 and almost rustfree) and it has the flat tops. Now I now these flat tops are basically boat anchors and so I went ahead and shopped for round tops and, lo and behold, good ole' local craigslist found me one for $25 bux!!!

 

I have a fairly good knowledge of the SU internals, how they work etc... and am doing pretty well dismantling and cleaning them up. I am confident that I will have a very good replacement once I'm done. I have checked the "clunking" sound and all's well with both front/rear carbs.

 

My questions... (finally!).

 

1) Should I use the E88 intake that came with my rounds or should I just replace the flat top SU carbs using the original intake already in the engine and just mount the 2 roundtops to the original intake? I would rather keep the 1973 intake intact if possible but I'll leave it up to y'all to tell me otherwise.

 

2) The other sort of thing I gathered using search is that the fuel feed lines differ from the '73 to the '72 carbs. The round tops I got have the intakes but is missing some kinda part on top of the two runners that join some holes on top. The round tops also the original fuel rail (fuel lines). Should I swap these or use the ones already in the 1973 engine?

 

3) My $25 round tops came with the heat shield also and I know that this is what I would need to use to that the springs mount naturally on them. Would these shields bolt up correctly into the 1973?

 

I also know about ztherapy and how good their products are but I just want to run my ride as is until I get the RB26DETT engine this one is getting sometime soon.

 

Thanx in advance for your input. :-D

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I'll answer each inturn.

 

1. Use either one. I have heard that the 1973 version has larger internals and flows better, honestly I have inspected them both and see no difference. I used the 1972 cuase smog wasn't an issue. If you want to keep it *cough* smog legal use the stocker than came on the car. The 1973 version will have, or at least at one time, had all the smog stuff mounted to the balance tube.

 

2A. I think your talking about the balance tube? It links the two manifold halfs together on the top and uses two bolts on each manifold. The 1972 will have no EGR port and the 1973 will have an EGR and it is ported for such. It also has water jackets for faster cold start warm ups. Unless your worried about smog you can use either balance tube.

 

2B. Use what ever fuel rail you like. I have seen no major advantage between the different fuel rails. But make sure you use a return line, all the stockers should have them but being 30+ years old good luck finding something that is in original factory condition, they are usually all rusty and such as they were covered with a insolation wrap to prevent vapor lockup and a host of other problems.

 

3. The heat sheild should bolt up fine. The only difference between the variations of the heat shield is that they are cut for a heat riser tube that is used on some of the 1972 air cleaner intakes. Those air cleaners usually had a winter/summer selector. The 1973 used an intigrated version but still used the heat riser tube from the exhaust manifold. DO USE the heat sheild (weather stock or aftermarket or home made) as it will greatly reduce carb heat saturation, especially in stop and go driving or long idleing.

 

Never used, Ztherapy so I can't comment on them but lots of others here have and they seem to have a good reputation. If the carbs you got work than, no worries!

 

Happy motoring.

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I'll answer each inturn.

2A. I think your talking about the balance tube? It links the two manifold halfs together on the top and uses two bolts on each manifold. The 1972 will have no EGR port and the 1973 will have an EGR and it is ported for such. It also has water jackets for faster cold start warm ups. Unless your worried about smog you can use either balance tube.

 

The round tops had no balance tube included when I picked them up. I'll have to find a 72 balance tube cuz I don't want to *cough* be smog burdened :sour: !

 

Also, you mentioned the water jackets and the round tops has a coolant line in the front carb, do I need to hook it up?

 

I also don't see an outlet for the coolant line. Where does the water exit to if I hook up this water inlet line?

 

 

 

2B. Use what ever fuel rail you like. I have seen no major advantage between the different fuel rails. But make sure you use a return line, all the stockers should have them but being 30+ years old good luck finding something that is in original factory condition, they are usually all rusty and such as they were covered with a insolation wrap to prevent vapor lockup and a host of other problems.

 

The fuel rail I got looks really really good so I'll hook them up.

 

3. The heat sheild should bolt up fine. The only difference between the variations of the heat shield is that they are cut for a heat riser tube that is used on some of the 1972 air cleaner intakes. Those air cleaners usually had a winter/summer selector. The 1973 used an intigrated version but still used the heat riser tube from the exhaust manifold. DO USE the heat sheild (weather stock or aftermarket or home made) as it will greatly reduce carb heat saturation, especially in stop and go driving or long idleing.

 

Will do! I like the heat shield that I've already cleaned and made shiny!

 

God bless, my friend!

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The water flows from the front carb (radiator side) to the rear carb though a passage pipe that should be between the two manfiold halfs. Sometimes these pipes have been removed. Basically each manifold half has a hole threaded for, if memory serves me correctly, a 1/4" NPT barb hose fitting.

 

The water inlet on the front manifold is feed from the thermostat housing throught the front manifold body and exits into the passage pipe (if still pressent). The rear manifold is feed from the passage pipe throught the rear manifold body and exits the rear (transmission side). This coolant will be returned to the other side of the motor to a 'T' fitting that is feed from the heater core return and both feed into the water pump pick up which has a large radiator hose connection and a 3/8" NPT threaded hole, again it memory serves me correct. The heater core is feed from the passenger side of the cylinder head in the rear (just a bit of info).Your car may not have this set up exactly as described as it is 30+ years old and people like to remove stuff, but that was how it came from the factory.

 

Both sets of inducitons you have should have water passages in the manifold. The 1973 version also had one that fed the balance tube and additional water passages on the carb bodies, if memory serves me correct. While I'm at it, they used a funny thermostat that when hot cut off the water feed to the manifold, remove that junk and toss it. It gives you nothing but problems as they never really did work well...at least mine didn't. The dealer no longer sells them and actually suggest that I do this years ago when I was looking to replace mine, smog reasons.

 

If the fuel rail is in good shape, great!!! I would disconnected the fuel rail from the car and use some compressed air and blow thourgh it to remove any bugs that may have made a home.

 

The non-smog balance tube may be hard to locate singlely but check out E-Bay and this sites 'for sale' posts for some good used junk. Also Zcar.com has a 'for sale' section. You may want to post a advertisement in the 'parts wanted' section.

 

Best of luck on the project.

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...The water flows from the front carb (radiator side) to the rear carb though a passage pipe that should be between the two manfiold halfs. Sometimes these pipes have been removed. Basically each manifold half has a hole threaded for, if memory serves me correctly, a 1/4" NPT barb hose fitting.Best of luck on the project.

 

brokebolt, you are correct again!! I see the passage pipe and it runs from the front to the end manifold halves and exits at the rear.

 

Ok... more questions. Why do people remove the coolant fittings? What does the cooling passage do beside the obvious answer I think of that it cools the charge? I don't get the engineering behind this since it looks like the whole coolant path just slings past through the passages.

 

Next question is that I read people block off the balance tube holes and not use a balance tube at all!! What is the thinking behind blocking them off. I know that the balance tube between the intake manifolds are spots for the brake booster hose, vacuum hoses, and PVC hoses to vent to and that blocking them only ruins the brake vacuum.

 

Thanx again for allowing me to ask questions.

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Blocking of the holes in the balance tube simply cleans up the top of the manifold. Look at the "Euro Manifold" Balance Tube and you will see something with only the Brake Booster threaded hole.

 

I don't know of anybody deleting the balance tube...it's agood thing to have for the operation of the engine (smooths things out).

 

People take the coolant hoses off the manifolds for any number of reasons...cool the intake charge by keeping the manifold cooler, etc.

There are actualyl two circuits on the later manifolds, one for the carbs to keep the throttle plate section of the carb from icing up in humid ocnditions and another that heats the manifold during warmup to help cold-running. Ignorance mainly dictates the removal of the whole system, really, as once the engine warms to 170F, the manifold heating section of the water passages is shut off by a thermostat at the rear of the engine as brokebolt says---it really helps promote faster warmups of the engine by allowing considerably more recirculation of the coolant within the block... but who am I to argue with everybody that looked at a 72 Manifold system and never looked any further???

 

I can see the anti-icing items being plugged, as well as the upper manifold portion when you aren't running EGR...but if the system is functioning it really helps with warmup and cold running cababilities of the setup. Biggest issue with the parts at the back of the engine is sedimentation from dolts who didn't use anti-freeze and sedimented up the thermostat...

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Blocking of the holes in the balance tube simply cleans up the top of the manifold. Look at the "Euro Manifold" Balance Tube and you will see something with only the Brake Booster threaded hole.

 

I don't know of anybody deleting the balance tube...it's agood thing to have for the operation of the engine (smooths things out).

 

People take the coolant hoses off the manifolds for any number of reasons...cool the intake charge by keeping the manifold cooler, etc.

There are actualyl two circuits on the later manifolds, one for the carbs to keep the throttle plate section of the carb from icing up in humid ocnditions and another that heats the manifold during warmup to help cold-running. Ignorance mainly dictates the removal of the whole system, really, as once the engine warms to 170F, the manifold heating section of the water passages is shut off by a thermostat at the rear of the engine as brokebolt says---it really helps promote faster warmups of the engine by allowing considerably more recirculation of the coolant within the block... but who am I to argue with everybody that looked at a 72 Manifold system and never looked any further???

 

I can see the anti-icing items being plugged, as well as the upper manifold portion when you aren't running EGR...but if the system is functioning it really helps with warmup and cold running cababilities of the setup. Biggest issue with the parts at the back of the engine is sedimentation from dolts who didn't use anti-freeze and sedimented up the thermostat...

 

Wow. I am a pilot and have never realized that carburator icing was a big issue on cars too. We have a lever inside the cockpit that re-directs exhaust to the carbs when flying and we detect carb icing!

 

Silly me, I guess I should not forget that they sold Z's in Maine, Minnesotta, Michigan, etc!

 

Thanx for the update. I guess I thought that the whole balance tube was removed but really, they just button up some vacuum stuff. Thanx for clearing this up in my head.

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  • 3 months later...
  • 3 weeks later...

I am working on something similiar. I just put the round tops on my '74 260. I bought a 260Z (engine in car did not have intake or carbs) with the car I got a set of rebuilt round top carbs and a doner engine with flat top carbs. The linkages from the original set of flat tops are too short for the round tops so I will need to make or buy a linkage setup. I am attempting to eliminate the balance tube - I am going to build my own balance tube that will also have the carb linkage attached.

 

The problem I have at the moment is what fuel line (at frame rail) is what? Line #1 = pickup from tank?

Line #2 = ?

Line #3 = ?

 

Could someone please post some pics of the fuel lines and the linkage setup for the SU carbs?

10870_thumb.attach

260Z INTAKE 141_thumb.jpg

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Hmmm. I'm not quite so familiar with the Flat top carb equipped cas, but the other 240Z's only have two fuel hard lines that come from the rear. The larger is the pickup from the tank and the smaller is the return line. In fact, the fuel rail I've got on my car came from a '73 that was in a junkyard, and I don't remember it having three lines, only two (there are only two lines going into the fuel rail anyway).

 

Here are a few pictures of my '72 roundtops mounted to squaretop N36 manifolds (from that same '73 in the junkyard). I took the liberty of welding the unnecessary vacuum holes in the maniflolds when I had them off.

carblinkage02.jpg

Here's another picture showing the linkage better.

carblinkage01.jpg

 

Here's a link to another thread where we went over the differences between the N and E series manifolds.

 

http://forums.hybridz.org/showthread.php?t=135702

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