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XplosiveLugnut

*hypothetical* "Bolt on" throttle body carb replacement

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I have an L24 with SU carbs. I've had this idea of the ability to go from carbs to EFI and back relatively easily.This would require a bolt on replacement for the carbs. I'd still be using the stock intake runners and air cleaner. I'd also try to keep the TBs the same length as the carbs. This is what I've doodled so far.

 

Throttle_Body_Sketch_zpsd1f5ed76.png

 

This uses a compact EV14 injector: http://www.bosch-motorsport.de/media/catalog_resources/Injection_Valve_EV_14_Datasheet_51_en_2775993867pdf.pdf

 

Some fuel rail I found the dimensions of: http://www.rossmachineracing.com/images/large/dash8wire.jpg

 

And the flange patterns from the SUs.

 

This drawing lacks stuff still. The idle air intake, I figure, could go on the sides of the TBs facing each other and be plumbed to a T where one adjustment screw handles both the TBs idle.

 

The placement of the injector is arbitrary. I just plopped it there and it worked out that the fuel rail doesn't interfere with the stock air cleaner (orange line). It's angle's just 45*. I'm not sure how evenly the fuel would be distributed down the 3 asymmetrical runners with this set up. Probably over thinking that though.

 

The placement of the throttle plate is arbitrary as well. I've merely spaced it 1 cm from the flange to provide room for bolting on the air cleaner. These should retain most of the stock throttle linkage too.

 

This drawing also assumes that both the front and rear of the SUs are 44 mm inside diameter and coaxial. I'm not sure about this.

 

I know next to nothing about injectors. According to some megasquirt literature though; If I want the capability to fuel around 150 HP then I need 2 injectors around 500 cc/min each.

 

Any reasons why this might not be feasible?

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^Yea, its basicly first generation fuel injection for most vehicles back in the day, specifically American companies. Honestly when I first got into these cars I was pleasantly surprised that the FI of the 77-78 models had an injector per cylinder.

 

One example would be the Chevy S10.

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Why not just look up Rick Patton at Patton Machine, drop in the conversion pieces where your suction piston and dome goes, hook up the GM TBI injectors and go from there? Why reinvent the wheel?

 

The links are on here...but googling will find it as well.

 

Andrew Jennings has 240Z SU's on his hot motored 510, and ran these adapters from BC Canada to Las Vegas and Back this past week. I pointed him in this same direction and he seems really happy with Ricks adapters.

 

I sent him 59 # of SU's to make up SU Adapters for every Datsun Ever Made...

 

http://www.pattonmachine.com/TBI-Carb-Chart.htm

Edited by Tony D

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The further the injector is from the port, the better it is for performance.

 

Head placement at the back of the valve was SOLELY for emissions concerns.

 

Look where F1 engines inject your fuel and tell me they're anywhere near the valve!!!

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The single fuel injector is where it is in F1 because of regulations.  Its must be in the intake tract, not the head which is where the engineers want it.  They are also fuel pressure limited to 100 bar to prevent direct injection.  If there were no technical regulations the designers would probably be at 500 bar for one or more direct injectors right into the combustion chamber.

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I was discounting direct injection as it's not even a passable reality for us at this point.

 

For atmospheric injection, I believe what I said holds true, and the additional mixing of the fuel air mass is accomplished with that, and not at the port, no?

 

Otherwise they would be port injecting at the back of the valve like the OEM's...yes?

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The further the injector is from the port, the better it is for performance.

 

Head placement at the back of the valve was SOLELY for emissions concerns.

 

Look where F1 engines inject your fuel and tell me they're anywhere near the valve!!!

Not just emissions, but drivability and fuel economy as well. It also makes it easier to tune.

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Nice, had no idea Patton Machine existed. I'll definitely look into that, thanks.

 

I initially thought of putting an injector in the top of the carb, but then thought having the injector pointed straight down on the external side of the throttle valve wouldn't be a good idea. Couldn't fuel end up in the air cleaner since it's side draft? Would that even be a problem? I don't 'spose so if these guys do just that.

Edited by XplosiveLugnut

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I am by no means a fuel injection or F1 expert.  But I think at 100 bar the injected fuel can be so finely atomized that any additional length of intake track beyond the minimum necessary to meet the rules would have fuel drop out of the air stream.  Also, there isn't much of an intake tract on F1 engines so we are talking a few millimeters of change in the position of the injector.

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After taking some more measurements and making some estimations it looks like the intake runner's bore is about 48 mm in diameter. So the carb's not 44 mm all the way through. It also looks like the piston and bridge(?) cause some restriction. Would a throttle body that tapers from 44 mm to 48 mm with no restriction, like the piston or bridge, be too sensitive? One of the ideas behind the EFI conversion is improved drive-ability and an on/off throttle is a step in the wrong direction.

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The piston and bridge are there to create a restriction. That's what creates the pressure drop that allows the atmospheric pressure in the float bowl to push the fuel out of the jet. I doubt that removing the restriction would make it too sensitive. I run triple throttle bodies with no problems.

 

I like the idea of replacing the suction dome with injector holders. There is a reason that factory throttle body injection puts the injectors upstream of the throttle. The acceleration of the fuel and air through the throttle air gap at idle and cruise helps atomize the fuel.

Edited by Sam280Z

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Not just emissions, but drivability and fuel economy as well. It also makes it easier to tune.

 I'd have to see the 'fuel economy' argument better documented, never seen that contention.

 

Tuning and drivability is related to tau layer, which directly relates to emissions as well. As John says, the move to direct injection eliminates all the bugaboos of atmospheric injection---but at this point is not practical for home conversions.

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I'm just speaking from my experience (and only about cruise economy - sorry, I wasn't very clear).

 

The tau layer is an issue with economy as well. Liquid and unatomized fuel doesn't burn efficiently.

 

However, you will be able to get higher maximum power fuel economy with the injector placed further away from the valve. There is not much of a tau layer with high airflows and with the injector placed further away, there is more time for mixing and evaporation with the associated charge cooling.

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Managing the Tau layer is what the OEM's spend their time on. Keep it constant and it's like it doesn't exist. But an increase in airflow increases it's evaporation into the airstream causing transient richness or other manifestations until metering catches up to the airflow change/load change.

 

Put it in chamber, it doesn't exist! Resultant problems eliminated, tuning now spot-on without delay on puts and injected volumes!

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Just throwing this out there but the Nissan NAPS head for the LZ motors has twin spark. If one is so inclined for a project, why not use one set of sparkplugs and make mechanical (or EI) injectors that screw into the other set of spark plug holes.

Probably wouldn't give you the best angle or spray but you work with what you have....

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They're out there.

Originally the post was "drop-in" and Patton's adapters fit the bill, in addition to being low pressure....GM TBI designed to be a step towards EFI utilizing existing legacy fuel components like hoses and wet flow manifolds.

 

It seems the closest thing to "drop-in" IMO.

 

They work great, Andrew Jennings drove from BC to Vegas for T he Meeting on ZBastardZ this past summer...SU Vapor Lock Weather, and using a PL510 with Z SUs usually isn't that great of a swap. But with Patton's adapters (especially considering the costs!) it was a successful journey.

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