3500 Engine Swap

At the end of July 2013, after about 3 months of work, I was finally able to drive the Fiero with a 3500 without any major issues.  Here’s the mechanical bits of the work involved.


Engine: 3500 – LX9

The engine started as a 3500 but slowly became more and more 3400.  Here are the big parts…

Throttle body: 3400 — The 3500 throttle body was electronic, so I had to ditch that guy.  The 3400 and 3100 throttle bodies across all years look similar, but there were at least 2 different sizes, 56mm and 52mm.  The end of the cable was a ring on the Fiero, but more of a bike brake cable stud on the 3400.  I found that using a drill and a Dremel tool with a cutoff wheel I was able to put a small hole and two slots in the cable attachment on the throttle body that let me use the original Fiero cable without any modification to the cable.  I did have to hack up the cable retainer bracket.  This required welding.  I don’t think there’s any other way to do this without welding.

Older 3x00 Throttle Cable  Cut Throttle Cable Attachment

Upper intake manifold: 3400 — The 3500 manifold fits the electronic throttle, so that has to go.  The 1999 and up 3400 upper intake manifold with the thicker runners was made with at least 2 different EGR designs cast into it.  One comes in on the bottom of the manifold by the throttle body and will not fit with the 3500 fuel rails, so it has to be cut off. The other EGR design (I know of) comes in on the side and does not need to be cut off, but it looks really ugly and useless, so I cut it off.  I had a buddy machine up a small aluminum cap on a lathe and then weld it in place since I don’t own a lathe and can’t weld aluminum at home.  There are also some 3400 manifolds that have an unusual looking crease in the mold on the bottom just after the throttle body.  You do not want that one.  The internet states that version starves cylinder 5 and 6.  GM eventually stopped doing that at some point.  Make sure you get the better version that has a smooth bottom leading away from the throttle body.

Wrong 3400 Manifold  This version of the 3400 manifold had the crease on the bottom.

Lower intake manifold: 3500 — The 3400 that I was working with before had the ECT sensor in the lower intake manifold near the thermostat.  The 3500 has the sensor in the cylinder head.  I considered changing the lower intake manifold to the 3400 so that I could add a coolant temperature switch (like the one the Fiero had to operate the coolant fan), but it is much cleaner to just let the Megasquirt ECU control the fan for me.  I think that his is an option if you are interested in it, but ask around first.  The 3400 LIM should swap onto the 3500.  If you need a dual element coolant sensor, the only one that I know of for the 3500 cylinder head is sold at www.britishcarconversions.com.  He actually starts with the original two element (3 wire) 3400 coolant sensor and machines it down to fit in the smaller 3500 cylinder head port.

Cylinder heads: 3500

Exhaust manifolds: Both are from a 2006 3500 front.  The 2004 and 2005 had an EGR port left in the casting that I didn’t like.  I noticed that 2006 was a different part number.  It is because this casing is removed and that port is left smooth inside and out.  Then I had mine ceramic coated.  It cost $70 each at ccperformance.com and I’m very happy with the results.  I don’t use any heat shields, but I do have most of the rest of the exhaust wrapped up to the muffler.

Block and internals: 3500

Oil pan: 3500 – I thought about swapping the 3400 pan (not totally sure it is a direct swap) to get a level sensor, but I figured oil pressure was a good sign that something was wrong.  Plus my gauge is setup to strobe at me when it gets low.

Clutch gravel shield: This has to be cut out a little more at the center close to the output shaft so that it doesn’t hit the engine block.  It’s thin so its easy to do.

Getrag 282 gravel sheild

Engine mount: The 88 Fiero has a different engine mount for the V6 than other years.  In the end to make it work on the 3500 you just have to hack it up to look like the prior years looked like.

Original and Modified 88 Engine Mount Bracket

Idler pulley: I think all the 3×00 idlers are similar enough that you can use any of them.  The key is swapping on a smaller smooth pulley.  I placed mine right above the crank pulley, the original location on the 3100 in my Z26.

Belt: Gates K060630 … 63-5/8″

Alternator: 3100 — There are at least 2 alternator bracket designs that look very similar.  One has a slightly lower clearance than the other.  As far as I could see, both brackets and alternators are interchangeable, but they are different parts with slightly different dimensions.  The electrical connection to both is the same.  I think the one I have is the whatever was being used in 1999 on 3400’s.  I cut mine up a little bit to make wiring look a little better.

Newer and Older 3x00 Alternator Bracket

AC compressor: I do not have one installed yet.  I am using an idler pulley to make this work.  I wasted a bunch of time during the swap trying to make this work only to get to the point where I said “forget it, I just want to get the car driving.”   One day I hope to get a compressor installed.  The 3400 compressor lines did not work well with the exhaust manifold pointing right down at it.  Plus I couldn’t find a high pressure cut out switch for it.  My guess was that a Hobbs switch would work, but I didn’t get that far.  I did wire the harness in the car for it, so that’s ready when I get there.

Fuel filter and pressure regulator: 99-03 Corvette — Lots of Fiero swaps use these.  They work well with the 3500 fuel rail because their output line is the same diameter as the 3500 fuel rail input.   ACDELCO Part # GF822 {#10299146, 19239926}

Fuel lines and fittings:

Attached to the 3500 rail and another on the filter inlet: FUEL LINE FITTING; 3/8″ X 3/8″ X 90 QUICK CONNECT

Attached to the filter output to engine: 3/8″ SAE Tube to 3/8″ barb, 1/8″ NPT port – You can add a pressure sensor here or cap the 1/8″ plug.

Attached to the filter, return to tank: Fuel Line Fitting, 5/16″ x 3/8″ x 90 Quick Connect

Fuel hose SAE 30R9: This is the right fuel line for 58 PSI do it yourself style.  You need 5/16 for the return and 3/8 for the main lines.  Amazon and Zex where what I used.  You might be able to find this at a local store too.  There is also 30R7 which has a lower working pressure.

Fuel pump: Walbro GSS340 — This is overkill for my needs, but why not?  I did a little dremel working on the bottom of the pump bracket so that it wasn’t rubbing on the sock filter attachment, but I might have been a little picky.

Modified and Original 88 Fiero Fuel Pump Bracket

Oil filter: 3500 — The 3500 came with an adapter for the filter that would have left it hanging right where the engine cradle is.  I removed it and put the filter right on the block. It took me a second to realize it, but the adapter had a removable threaded fitting that could be screwed into the block.  It was just an allen wrench and done.

3500 Oil Filter Adapter

Coolant lines: On the 3×00 there is a bleeder valve above the water pump to purge air out of the system.  I swapped this to a brake bleeder style.  Then I used a vacuum hand pump to pull coolant through the system carefully.  You probably need to be careful not to over do it or risk damaging a gasket somewhere.  The 88 Fiero also has slightly different coolant lines than the other years  from what I read.  I was able to keep the passenger side line the same, while only changing the hose to the water pump inlet.  The heater core line on the 3×00 that comes off of the bleeder and runs in front of the valve cover was cut off and then I put a rubber cap and clamp over it.  This is because the heater core inlet on the 88 Fiero is part of the main water pump inlet underneath the car.  On the other heater core line at the thermostat house I found a 180 degree 5/8″ bend, then a 5/8″ coupler, some generic 5/8″ heater  core line, and then joined that to the other existing 5/8″ line on the car from heater core with another 5/8″ coupler.  I think most of the parts for this came from HELP! / Doorman parts.  Just look in the underhood section, then heating and cooling.  Most stores carry some of these parts but not most of them you see on the website.  Take the part numbers and go over to Rockauto.com, do a part number search under the help brand to get what you want.  The couplers are part number 47094.  The 180 degree bend is Dayco part number 87653.  The driver side main hose is Gates part number 22231 (Astro/ Safari upper hose, 1996-2005), but it had to be cut to fit.  My memory is sketchy, but I think the passenger side hose is the Safari lower hose.

Filling the coolant system: I open up the line after the 180 degree bend, hold them up, and start filling both ends with the radiator cap off and the bleeder open.  Once that is full, then put the hose back together and seal it up.  Use a hand vacuum pump and the bleeder valve to slowly draw out air and suck in coolant from the overflow tank.  Once you are pulling out coolant at the bleeder you’re done.  Start the car and get it up to temp with it all sealed up.  Then somewhere a little above 200F you can open up the bleeder and purge out air.  It will steam so be careful.  If you open and hear hissing, but don’t see steam, then it might not be hot enough and you are letting air back into the system.  You know you have it full when it is at temp, about 210F, you open that bleeder, and liquid comes out.

Thermostat housing: There are at least two different styles of thermostat housings for the 3×00’s.  One has a barbed hose fitting (newer style) and one has a pipe thread fitting.  Another Fiero owner told me that you want the pipe thread fitting style.  That way you can install a bleeder screw which should help make filling and purging the system easier.  Unfortunately I had already assembled mine with the newer style and capped it off before I heard this idea.

Brake vacuum line: Again, get a HELP! 1/2″ coupler, some clamps, and 1/2″ coolant/vacuum line.  I actually found another brake vacuum line from another car in the junk yark with bends that helped make it look a little more natural.  I honestly don’t remember the car.  It was a GM for sure, possibly something with a 4 cylinder from the 90’s.

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