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SU fuel injection manifold conversion

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Hoping to get some imput from Z-ya and Derek and others who have looked at or have built their own injected intake manifolds. I'm getting ready to set up with megasquirt and have aquired some parts to get started, over a long term. (MS-1 basket case, EDIS setup, 275cc 11mm o-ring injectors, injector clips, other bits and pieces)


I'm looking at converting an N36 carb manifold to fuel injection, and have three options, as I see it.


1. Follow through like Z-ya did, and merge a FI manifold with a carb manifold.



-Commercially available fuel rails will fit

-Stock injector holes will all line up to hit the valve stem and back of the intake valve

-Less concern of welding distortion in the injector ports



-I'll have to get a FI manifold to butcher

-Lots of welding in hard to reach spots (between the runners is pretty tight for my spool gun)


2. Machine up some injector bungs and mount them on the carb manifold.



-Cheap. I can machine the injector bungs myself, they are not that difficult.

-Can place injectors anywhere I want

-No need to cut up a FI manifold I don't have



-Will have to machine my own fuel rail

-Concerns on where to place and aim injectors

-Welding distortion may be a problem


3. Throttle body injection with custom throttle bodies



-No manifold modifications

-Chance to do some more aluminum casting (YEEE HAAA!)

-Chance to produce a small run of parts



-Lots of time to produce patterns for casting

-Lots of time to produce parts to fit machined casting

-Injector placement concerns

-Need to get bigger injectors than what I have now

-Fuel rail issues


Anyone have any thoughts or ideas? Suggestions and ideas are most welcome.

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Why is casting involved in throttle body conversions? If you got SU's on the car allready...well:

Patton Machine has had SU drop-in GM TBI Conversion kits available for over two years now. I sent 52# of Datsun SU's off to him then and there is a set of his adapters running on a member's car in France at this very moment!



The Patton Adapters are very nice, and with a little work on the Suction Domes, nobody knows you modified anything! For $124 per carb, last the website was updated:




Because they use GM TBI injectors, the system is considerably lower pressure, so the stock fuel lines can be used, along with EFI rated fuel line for added security, making hookup a snap! No fuel rail needed, about a billion donor vehicles with a whole RANGE of injector sizes (get some for a 454SS Pickup and bet you have more than enough fuel for ANYTHING a Datsun will ever need!) and they are relatively cheap new at most auto parts stores.

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I considered that, and for a long time, that was the way i was going to go. I decided that I'd rather not bother with that, though, because it was starting to look cluttered, like the snakepit of hoses that came on the late 72/73/74 cars. I'd really prefer the clean look, if i an get it.

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Uh, define 'clean look'


When you don't use the SU's as an SU, you don't need the lines, a fuel rail between the two with fuel line coming in the back and out the front with a reg on it (or vice versa) is all the lines you need going to it. Wether you retain it or not in stock 'looking' configuration is up to you. I have seen plenty of 'sanitary' su setups.


The hoses on a 72 is the same as the hoses on a 69. I don't know what you're getting at by that comment. TWM makes SU bodies that use Bosch Style Injectors but they cost a hell of a lot more than $124 each.


Whatever. I'm sure when you make up you mind you will do something.

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My '72 had a LOT of hoses and lines running all over the place; it looked really terrible. Looked like a new car, once you take all of the plastic covers off.


Anyway, I just realized that I'll have to move my external water line; it's in the way if I go the port fuel injection route. I'm thinking i can run it up under the intake manifold, which would solve all the interference problems.


If I do go with the throttle body injection route, It will be with a custom throttle body; something that uses a pair of the 1680cc/min injectors from a RX7 turbo or similar. The idea is to make a pair of 50mm throttle plates, with a cam actuation for better tip-in response, that use a standard top-feed or side feed (top feed seems simpler so far) injector. The GM TBI injectors would work fine, I forgot that they came in the really huge sizes too.


Eventually, I'll be casting/fabricating a whole new manifold; but that's in the far field. Long way off.

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Hoping for 180RWHP NA, on a 2950cc bottom end, with a head that flows 171cfm per intake at my desired valve lift (.455" valve lift) and 25"WC. I have a bigger cam (.480" valve lift) waiting to be ground if this one does not get me there. (Have an opportunity to be doing some cam development, working with Delta camshaft.)


The large injectors are for if I get the "let's pressurize the whole system, and see what we can get" bug, since I've already got a ZXT manifold sitting on the shelf. I figure that for 200HP, I'd need 2 700cc/min injectors, at 80% duty cycle.


It's all just a pipe dream at the moment, but theorizing and working out the bugs is part of making pipe dreams reality.

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680CC or 1680cc?


I know someone who used 1000cc injectors in his TBI setup and they weren't idling as best as they could.


Eventually went down to 720's and got a decent idle.


I forecast 2 X 550CC's, as if they supported a 215HP Ford V8, I figure they could support my measly little Datsun. That works out to what? 110PPH, at 1/2 # per HP per Hr for an N/A, that's right around 220 hp, and with an 80% limit that's still 160-170HP. Though those Ford Injectors may be rated on the 'low' side. For a realatively sedate L6, a pair of 550's should be fine. For a Stock Conversion damn tootin enough. I doubt many would ever need 720, but my bud was ultra conservative and paid the price in idle quality.


I don't know if the TBI is governed by the same 80% duty cycle as port injection...

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That's a good question Tony, I don't know about the TBI duty cycle ratings. I'd still like to keep injector duty cycle under 90%, though.


Yes, 680cc/min. What a typo! (curiously enough, there are RX-7 injectors in BOTH sizes!)


I'm still up in the air; If i can cut and graft an EFI and a carb manifold together, I can lengthen the runners by about half an inch with no change in air filter location. Not sure if it's needed or if it will make a big change, still have not done the math on that yet, but it is a possibility.


The only thing in the way is the external water line from 5 and 6 up to the thermostat housing, I used 3/8" copper line. It's all held tight against the head, so if i change the bend near the thermostat housing from two 45* bends to a pair of 90* bends, the water line is no longer in the way, and port injection can be used. Or, if i redo the line and two of the 90* fittings to use straight fittings, i can route the line up tight against the manifold, and have a much easier time bleeding the air out of the line.


(Guess this means Photo Time, to get a good look at the system.)


In the end, I LIKE the way that Z-ya's manifold came out visually, and how it picked up 10HP peak and 20ft-lbs of low RPM torque. I'm not expecting such dazzling results, but like Derek's trumpets, the goals for this are:


Look Cool.

Look Really Cool.

Be Functional.


(paraphrased, of course.) I'm thinking to get to 180HP NA, I'll take all the help I can get, as long as the engine remains streetable.

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Here is another thing off my drawing board:

Spacers behind your SU's with counterflow injectors firing at the backside of the throttle plate.


I forget the thickness, but recall something like the same amount of the 'doublethick' thick spacers the AutoX guys run to boost torque on the SU's. You could use a gutted SU, or simply any air door. There is enough space to run DUAL injectors in there if you wanted, meaning twin Ford 370's (and no big injector idle control issues) on each adapter. Frankly, with a short air door you could make a real thick spacer for even more torque bump.


I actually drew out the spacer on my drawing board at home... It works, and there is plenty of depth to make bosch-style injectors fit in there.


With a 'thin' sandwich style butterfly, you could even keep the adapter at a minimum thickness required to fit the injectors at the requisite angle for proper impingement on the throttle valve, and leave lots of room for impressive spun aluminum polished air trumpets, two each, fully radiused and 3"+ in diameter with domed filters in the end...


Oh, and yeah, 680's will be more than enough. My bud's cammed Rebello motor is overwhelmed with the 720's. Just too damn big, but he refused to listen to me about trying cheap and available 550's first while in development... lead a horse to water, then shoot it!


Not that I ever gave that setup any thought before this very second, mind you...

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Now there's an idea. I have some 275cc injectors, (8 to be exact) and was thinking that if i was to graft manifolds, i could add a half inch or so to the runner length and put the injector up in the stock location. You've reminded me that I could add that half inch on the spacer too, and get the same effect, and have the injector pointed upstream, "pissing into the wind" so to say.


I bet I could probably trade those 275's to a N/A stocker guy, and get some 680's (RX-7 stockers) or 450's (DSM turbo stockers) to mount in the doublethick spacer plate, and likely could use VG30DE throttle bodies as air doors. Those TB's are pretty thin, front to back, and common.


So, best to aim them at the middle of the throttle shaft? With the injectors vertical, would it also be better to have the throttle shafts vertical?

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Oh, don't EVEN get started on Injector Placement. If it's an N/A engine, you want them on a stalk pointing into your velocity stacks at an oblique angle (5 degrees comes to mind), though each engine configuration should be optimized through dyno testing as to the exact best angle. For the close proximity of the spacer to an SU throttle plate it was best to have it hit the plate for cracked-throttle idle quality. It will impinge on the center of the plate, and as the throttle angle increases and air velocity increases (to a point) it will really pick up the fuel into the airstream homogenously, and keep from having any possible over-rich condition---better fuel distribution to all three cylinders on the branch. If the throttle opened any way but horizontal, I'm afraid the mix of a TBI setup would be biased to one of the cylinders during partial throttle. For port injection, of course it wouldn't matter... For max power with the injectors on stalks it might... Who knows? Build it and find out!


And yes, VG30 synchronised Air Doors with linkages shortened will be a snap to get it all going, using a simple cable throttle. You build it, it's been about 20+ years since I had that though the first time (at the Okinawa Naha Prince Distributor, looking at the VG30DE in the then-new Z32.)


It's terrible when you look at an absolutely new car, and the first thing you notice is stuff you could adapt to your own car. You don't see the new car and all the engineering, you see all the shiny new parts!!!


When we took tape measures to the preproduction Titan at a Car Show in So Cal the Nissan Handlers ran over and quickly wanted to know who we worked for and what we were doing. He just sat agape when we told him we needed to measure the height and width of the engine to see if it would fit into an S30...


As he walked back, he said incredulously 'These guys are insane, they were trying to see if this engine fit in one of those! They're insane!' (While pointing to John William's Turquoise and White 240Z)

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This project has come to fruition, I have the complete manifold and fuel rail, and linkage, all bolted up sitting on the couch. Just waiting on a fuel pressure regulator that I traded for with another member here to show up, and I'll bolt it on.


I was able to take the stock SU linkage I had laying around, heat it up so the brazed joints all sagged apart, turned a new center shaft in the lathe, brazed it all back up with new angles and bobbles, and got it all to fit in the stock positions.


I used two throttle bodies from Mitsubishi 4G93 1.8L engines, with 50mm throttle plates, Mitsubishi 4G64 275cc/min fuel injectors, (NipponDenso INP-065), and N36 carb manifolds. The most difficult problem I encountered was actually the fuel rail hold-downs.



Setting up for machining the fuel rail:







Cutting up parts and measuring, fitting, scheming:






35mm exhaust valve for my porting guide, set against the ports to check for clearance:





All parts layed out on the work table:




Balance tube:




Welded up and test fit on the kitchen table, before porting:










After Porting:






All assembled and ready to mount up on the car:












More photos as it get fitted to the car, and the water line finagled around. When that regulator shows up, video!

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Yes, this is the result of merging two manifolds, much like Z-ya's project, however to line up the two particular manifolds I had available (N36 and W24) I ended up with an 7.5" runner length.


It will be going on the car in a few hours.

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The manifold is tapered a little, and is matched to the ports. Here's hoping that when I get the car back driving again and get the Megasquirt tuned up that it'll be worth the effort!




It will be worth the effort every time you open the hood!



Trust me!


Looks great. Nice execution.  If it works out to your liking you can blend in the welds and then get a foundry to put it in their Wheelabrator machine. this will help give it a nice even finish and look more like a single casting.








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Getting it bolted up:




All bolted in and wired up:




Lots of room for future expansion, even with a 7.5" runner length. If I had been able to find some aluminum tubing that would have worked out, I could easily have stretched the runners another 2" and had plenty of room.



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Very nice work. I like the way you simplified the linkage. A lot more sexy than mine as I used the stock fuel rail. I like the idea of a steel fuel rail that wraps around the head on a race car. Looks weren't a priority.


Here is a fairly recent photo:





Stock EFI manifold vs dual throttle body.



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