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I'm doing research on converting my dad's '77 Spider to a MegaSquirt EFI system. I'm using the factory throttle linkage, manifold, and throttle bodies and boring out the injector mounts for late-model Bosch units. I'm going to use GM sensors for as mauch as possible. Only real problem I can't find an easy solution to is how and where to mount a TPS. Any ideas from people who have done this before?
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TPS for SPICA manifold

I'm doing a similar conversion on my '74 SPICA GTV, and I've found a few solutions.

First, I decided to mount the TPS on the rear manifold, since there's more room, and the rear thorttle body has an extra boss that'll be useful for drilling and tapping for a bracket mount.

I'm making a little 90-degree steel bracket that bolts to two of the studs that hold the throttle body to the manifold. It'll hold the TPS over the end of the throttle shaft.

Next, I'm taking the round steel bushing off the end of the throttle shaft (held on by a roll pin), welding a small lever arm to the bushing, and putting it back on the end of the shaft. Very convenient, and you don't have to remove the throttle shaft or have it machined or anything.

Various American and Japanese cars come with TPS sensors that are activated by a little lever arm on the throttle shaft, and don't need a D-shaped throttle shaft. But I've only found one GM application that rotates the right way to mount on the rear throttle body (most rotate the other way, and force you to mount the TPS on the front throttle body, where it can bump into the thermostat housing). It's from a late '80s GM FWD car with the 3.8-liter V6 and "multi-point injection" (Buick Riviera, Olds Toranado, etc.).

I've drilled and tapped the old thermostatic actuator hole in the manifold to accept a GM coolant sensor, and I've welded a 3/8 NPT bung to the back of the SPICA air box to accept a GM air temp sensor.

I'm also using Bosch injectors, but had a heck of a time sorting out the fuel rail layout to clear the SPICA throttle pulley thing. I ended up some offset injector fuel rail bungs off an Audi V6. I'm curious about your solution.

I'll try to post some pics as I make progress.

George

'74 GTV, SPICA/Megasquirt project in progress
 

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That helps alot. I haven't done anything, just trying to get everything sorted out before I start. What ECU are you using? I'm leaning toward the most basic Megasquirt (perhaps even the new Microsquirt) with the additional relay board for the main and fuel pump relays. No need for spark control right now since it has a Magnetti Marelli electronic conversion.
 

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Yes, I'm trying to keep this a simple installation, too. I've built other car and bike engines, and it's easy to get carried away with installing cool racing parts and AN fittings, etc. Before you know it, every system in the car is affected and needs to be built up and re-engineered, and the cost and time involved grows exponentially.

Luckily, my car came with the later electronic distributor, too.

I've yet to order the computer, but it'll be the Megasquirt 1, v.2.2 PCB. The PCB v.3 sounds neat, but thousands of cars have run just fine with the earlier board. The relay board is not really necessary, too. The car already has various relays screwed to the firewall; a few more won't look out of place, and are not hard to wire up.

The only non-essential spendy piece I'm ordering is the wide-band O2 sensor kit ($200) from DIY AutoTune.com. It'll allow me to dial in the VE table without spending time (and money) on a dyno. There's no need for a $400 wide-band O2 gauge kit, since the ECU collects all the data for later review.

The ECU kit and O2 sensor setup will cost less than $350.

If I were to build another intake manifold, I'd either spend the $175 for the cutting tool and drill the injector pockets directly into the casting, or I'd order the MSD screw-in or epoxy-in bungs for $50. I had fashioned my own injector bungs and had them TIG welded to the manifold, and this caused all kinds of fitment issues and hours of grinding and fiddling.

If you've got as much as a bench-top drill press, you can drill out the manifold yourself (with a bit of careful set-up and measuring) and epoxy in the ready-made bungs. Various local machine shops would do a similar operation for several hundred dollars, and the added precision is of negligible importance since the injectors seal with o-rings and allow a bit of mis-allignment.

I'm finishing up my fuel rail hold-down brackets, and starting on the TPS bracket (I've got it mocked up with cardboard templates so far).

I'll keep y'all posted on my progress.

George
 
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