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78 280z 4 bbl intake and carb suggestions


One Way

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The resurrection project is not even close to getting into the engine department yet, but I have an opportunity to pick up a 4 bbl ARIZONA intake manifold at a very reasonable price.

All of the original injector parts are in very rough shape-purchased the project car that had been off the road for almost 20 years-and I know all the components will need to be replaced.  Just some questions about the conversion.  Would it be less expensive, less complicated?  What do you do with the ECU component and wiring?  What type of lower pressure fuel pump would be required?  What about all the fuel and vapor return lines to the tank?  Any helpful comments will be greatly appreciated.  I have been picking up a few odds and ends for my Z that will not be needed until far in the future, but it is hard to pass up some of the good deals on certain items.  Thanks, John-Lugoff, SC.

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You can spend 300-$400 for a good carburetor.  So if that's not included, add that in.  It's pretty simple to convert though.  The EFI harness is separate from the man harness so all you do is disconnect it at the battery.  I think that you might need to work up some throttle linkage.  Cable is common.  The pump would just be a common low pressure carb pump, replacing the EFI pump.

Make up a list for both systems to see where the dollars balance out.

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two paths you can take: replace/refurbish your efi or go carbs. both have their plus/minus...

i did a complete rebuild/engine swap on my 78 280 and decided to go carbs because i wanted to be able to pick up performance with the engine mods (flat-top pistons, head work, header, etc.) and the stock efi is difficult to adjust - it runs quite well for a stock engine in stock configuration, but not as flexible as modern efi systems. the carb swap is not difficult, but there are quite a few things to consider:

  • swap fuel pump (efi pump is high pressure, carbs need low pressure)
  • choke cable, lever, mounting setup through firewall and into console (not cheap if it doesn't come w/carbs)
  • air filter (also not cheap if it doesn't come w/carbs - and the 4bbl is down draft so you'll have to find a very short filter to clear under the hood)
  • throttle cable revisions (takes a little doing - not hard, but certainly not just "plug-n-play")
  • fuel lines (i chose to completely re-route, you'll at least need to do some mods)
  • carb setup and adjustment (goes without saying, but it will take some fiddling to get right)
  • different manifold bolts (not a biggie, but ya gotta buy 'em)

that said, i love my su's because they are simple, rock solid dependable, old-school and the car runs great. but i spent quite a bit of time getting it right and i enjoy fiddling/fettling with my car...

if you want to go the other route and re-furbish your efi, you can either chase the issues (electrical gremlins, plenty of time with testing equipment on your hands & knees squinting at the pins on the ecu) or i have an entire re-built efi system i could offer at a very reasonable price which is completely re-built with all new parts. not trying to be a salesman, i just know it took me 6 months of dicking around w/the efi system (find the many threads, often w/a pic of my car hanging from a tow hook) and replaced EVERYTHING one part at a time at considerable cost to get it running right/dependable and i wouldn't wish that on anyone. if i could have bought the re-built system i have sitting in my garage up front, i sure would have. the plus with this route is the stock efi runs great and you just turn the key and drive like a "modern" car - no warm-up procedure, no regular carb maintenance, you will pass emissions testing if need be, better fuel economy, etc. when it's working correctly. others have different experience, just offering mine...

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I agree with Rossiz. I would keep the factory EFI...especially over a Holley conversion. I have built and Raced Holley carbs for many, many years, and I would never switch back to them over a factory EFI system.  Conversion to twin Su's or Triple Webers/Mikuni's sure. But a Holley 4 bbl would be a step backwards IMHO.

  • The Holley is not going to like being perched above a stinking hot exhaust manifold... the Holley float bowls are even more sensitive to fuel peculation than the factory SU's. A really good heat shield and phenolic base isolator are a necessity.

 

  • The installation position of Holley's with that manifold is 90 degree's to their design position and this can cause float level issues under hard cornering.  Mixture distribution to #1 and #6 carbs is less than ideal as well. This picture shows the improper " sideways" mounting and the lack of a heat shield. Bad design.4b1c.jpg

 

  • Holley aftermarket needle and seat are infamous for sticking open, causing massive flooding with raw fuel dripping out of the carburator.  Use of Genuine Holley Needle and seats along with a good fuel pressure regulator will help alleviate the sticking N&S problem. However, the modular float bowl design of Holley 4150/4160 carbs always tend to have some full drip from the float bowls. Right on to the hot exhaust manifolds or header Not good.
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  • BTW, the factory EFI system can work quite well with a mildly modified engine...with some limitations. Camshaft duration needs to be kept no larger than your typical 270 or  280 degrees advertised duration ( .230" to .236" at .050 lift )  A proper ignition timing curve WITH a tweaked manifold vacuum advance really helps smooth out the idle. The fuel pressure can be raised a bit to support a mild cam, headers, 2.5" exhaust etc and the AFM adjusted to compensate. ( Raise fuel pressure with adjustable FPR to eliminate lean spot after AFM tops out around 4,000 RPM and then adjust AFM spring tension to lean out mixture at cruise and low RPM's ). The DSM and Toyota boys have been tricking out Air Vane AFM's for decades using that method. The AFM does NOT fluctuate at idle as widely reported in various articles... as long as cam overlap is kept reasonable and idle at 1,000 rpm minimum   You are restricted with mild modifications with the Factory ECU as you really can't change injector sizing.. but it will support up to 200 HP with the right tweaks.

 

  • A stand alone ECU just eliminates ALL of the issues with the factory ECU and then the sky is the limit on HP.
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Thanks for the responses from the Z experts.  As usual, I was a day late and a dollar short on the intake manifold.  There are no intentions on making this resurrection project a high performance version, just a normal , easy to maintain, driveable street vehicle.  The engine will get a complete rebuild with stock internals.  Upgraded electronic distributor most likely will be needed as well.  I will cost compare new EFI components vs 4bbl conversion and see how that goes.  All of the injectors look very bad, as do all of the connectors, wiring, seals, etc.  I work for O'Reilly Auto Parts and they offer a very generous team member discount.  BWD brand injectors and connectors are still available through O'Reilly's as well as the Holley 390 CFM carburetor.  I also have a 68 Datsun 2000 with the SU carbs and not all that thrilled with

getting those to work properly.  It has been years since I worked on Holley carbs in my younger muscle car days, but always thought they performed well and were quite easy to adjust  when needed.  Also if I did do the conversion, I would be able to sell off some of the original parts to offset the cost.  There is quite a price difference in the Clifford manifold vs the Arizona Z version.  I have not really checked into any other brands that may be available. Any suggestions or alternatives ? Thanks again for the helpful suggestions, John-Lugoff, SC

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I picked up 6 brand new Standard Blue Streak FJ-3 injectors for $165 on E-Bay. That's hard to beat There are still some for sale.

http://www.ebay.com/itm/75-76-77-78-79-80-81-82-83-Datsun-280Z-Fuel-Injectors-FJ707-FJ3-/162241229221?hash=item25c654b1a5:m:mqP-kgYey2FHyrChcpHSIlg

Injector seals and injector holder kits are dirt cheap.

Most of the EFI issues are due to old injectors and corroded terminals. You can get a complete terminal replacement kit with Bosch spring loaded terminals for very little money. One of our members ( FricFrac ) sells a very nice kit. My 1976 280Z has an F54 block with flat top pistons, N47 head, 280 duration cam, headers. 2,5" exhaust and TWM 60mm throttle body. All running on factory ECU ( at present ). New injectors, good wiring harness ( perfect actually ) , new Airtex Fuel pump, Z31 Auxiliary Air Regulator

Car starts at first touch of key hot or cold. Cold idle speed of 1.500 and settles down to a rock stable idle with a nice lope at 1,000 rpm, mid range is perfect, Driveabilty like a stock Nissan  and I get 25 mpg on the highway ( 5 speed with 3.90 gears ). Stock L28's normally fall flat on their faces after 5,500 RPM. With the cam and other mods this one pulls HARD past 7,000 RPM. Having everything in good condition and smart tuning is the key.

I've got the car running so good right now, that I put a Haltech ECU project on hold for now. Was going to swap it in this summer, but ended up driving Z all summer ( My Audi broke and pissed me off. So I parked it ). Z ran so good all summer,  that it had me second guessing Haltech swap. ( That plus health and money issues ). I did get the car up and running with the Haltech controlling the fueling ...with ECU temporarily sitting on fender. 

But  I'm hesitant to swap over now, because the car runs so good on the factory ECU. It's not perfect. I'm sure I'm leaving some HP on the table. But this is a not a competition car. It's just a nice Sports Car that I can have some fun with. At 62 I find that I'm getting tired of working on cars. Plus my body has put an end to almost all DIY work... :(

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On 10/21/2016 at 5:10 PM, One Way said:

All of the original injector parts are in very rough shape-purchased the project car that had been off the road for almost 20 years-and I know all the components will need to be replaced.  

You won't really know what needs replacing until you get in to it.  If the cabin has been dry the ECU should be fine.  The injector quality will depend on the fuel that's been sitting in them.  If the fuel pump and FPR were in good condition when it was parked, the system could have stayed pressurized for years.  The connectors on the wire end are simple to replace.

Rossiz put a lot of effort in to getting his EFI right before he switched.  He didn't switch to carbs because it was bad.  He's your best bet for getting parts that are known to be good.  If you can determine what you need maybe he'll break it apart for you to save shipping costs.  I imagine he has the EFI intake manifold sitting in his garage with the rail, injectors, FPR, linkage, etc. all still assembled on it as it was when it was on the engine.

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Thanks so much for all the input and great offer on the EFI system.  As originally stated, the engine is quite a way down the road with this resurrection project and have been saving all the great info and trying to formulate a workable future plan for this project.  Sounds like the original EFI system is getting the most favorable opinions. I have no verifiable history on why this vehicle was taken off the road so long ago, but poor storage and several indications of it being water flooded at some time , do concern me with the electronics.  I will slowly progress with the project and have gratefully noted all the experienced opinions and recommendations.  Thanks, John-Lugoff, SC.

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