Challenge C4 - under new ownership.

Welding day!  I used my templates to mark up some spots, and used a fixture to keep the vertical pieces aligned.

Set the tubing in place, and adjusted it.

Finally, two welded up mounts.

I rechecked critical dimensions, and everything appears to have been at most 1/16" off.  Unfortunately, longitudinally, one mount was off in 1/16" in one direction, and the other 1/16" in the other direction.  I slotted the engine plate holes with a dremel grinding bit, but may want to do a bit more.

Time to reinstall the engine.  took a little extra work, since the new mounts were far stiffer than the original rubber mounts.  Ran into my next problem.

Passenger side:

Driver side:

It went from the engine mounts being too spread out to too close together.  I must have mis-measured or miscalculated something.  There really isn't enough meat on the frame mounts to grind them out, and I really don't want to cut, grind, and reweld the mounts.  I'd be afraid I'd end up messing something else up in the process.  Standing around staring at it, and debating if I could just stack a bunch of washers to get it to line up, it hit me.  I could just make offset bushings.  Its about 7/16" too wide, so if I make a set of bushings each offset by about half that, they should fit perfectly.  I'll want to mess with the print settings a bit, to make sure the inner and outer walls have at least a bit of infill, so there is some give on all sides. Thinning the walls down, and increasing the infill density should do the trick, and not cause problems.  Since this means the store bought bushings won't work as a substitute, these mounts will get a heat shield to protect them from the headers.

There is one other potential problem, and I need to investigate it a bit before making new bushings.  The engine is sitting about 1/4"-3/8" higher than I calculated it should be.  I completely forgot to take into account the rubber mounts would have collapsed somewhat under the weight of the engine, even when new, not that I would have been able to come up with an exact number for that anyway.  The bellhousing is close enough to the transmission tunnel, that it would be good to bring the engine height down as much as safely possible, especially if the back of the transmission ends up needing to be raised to attach to the C-beam properly.  However, while it is sitting where it is, it makes sense to recheck the power steering pumps for fit, and look into water pump clearance and anything else I can think of first.

Since I am planning on using the mounts as is, and am assuming the new bushings will be about the same weight, time to update my budget:

• 1985 Chevrolet Corvette:  $1000 purchase price.
• 2000 S10:  $300 purchase price - $0.50 change found in car - $260.25 sell off(as of 7/16/2025) = $39.75
• 2004 Trailblazer:  $800 purchase price - $1.78 change found in car - $1364.77 sell off(as of 9/5/2025) = -$566.55
• Transmission seal kit:  $24.99
• Swap oil pan kit:  $129.90
• Engine mount bushings, 1/4 of a spool of TPU filament:  $6.00
• Metal for engine mounts:  $35.25 (Have quite a bit of it left over so may be able to adjust price for amount used.  However, some will also be used in the C-beam adapter)
• Spool of MIG wire (only used a few ounces so far, so may adjust later):  $21.99

Current budget of $691.33

Couldn't you just cut the round section off the plates and move them up the face of the plate. This would spread them apart relative to each other and lower the engine at the same time.

In reply to vwcorvette (Forum Supporter) :

Yes, but I am concerned I'll screw up other dimensions in the process,  I welded the inside of the pieces that attach to the tubing, so I'd either have to cut the tubing off to get to those welds, or cut a lot deeper with the angle grinder from the outside.

I may still have to go that route, but 20 minutes in the computer to alter a design, then running a few prints seems a lot easier.  Even though each bushing takes a few hours to print, I can do something else while that is going on.

I didn't want to end today's garage time on a low note.  Grabbed the passenger side header and test fit it.

Looks like it should work perfectly fine if I don't get a smoking deal on some C5 exhaust manifolds.  A couple of observations:

1. I was thinking of flipping the stock truck fuel rail around so it would have a short run to the car's fuel line.  With the proximity to the header, I suspect it'll be wiser to run the fuel line across the firewall instead.
2. The front spark plug or two may need an angle head plug wire.  The 5.3 wires already have insulators, but I think they are bulky enough they won't fit.

Oh yeah, another good thing - stopped up at Patrick's this weekend, and ended up getting some drag slicks from him.  Still keeping an eye out for drag radials, since slicks might be overkill for my planned power level, but I'm really happy to have them, and they'll fit wheels that came with the Vette.

looking good Tim. Wahsers between the engine mounting plates and the block to get the alignment then replace with something more permanent or rebuild the mounts to that offset?

In reply to stafford1500 :

For expediency, I'm going to go with offset bushings for now, as I don't want to risk multiple passes of "does this fit right" when cutting and rewelding.  Once everything is fitted properly and the engine comes out, that may change.

One aspect of the updated mounts worked perfectly.  The rear of the transmission sits 3/8" forward of where it did before.  Once I cut down the 4L60E yoke, and attach it to the C4 driveshaft, it should be good to go.  It will need to be installed as the engine is going in, though, not enough room otherwise.

Transmission and differential angles are less than half a degree different.  The C-beam is still interfering with the yoke, but just barely, and if I pull it down to match driveline angles exactly, it has enough room.

As it sits:

With matched driveline angles:

While under the car, the engine and transmission seems shifted to the right, but I think it is just due to the shape of the transmission tunnel and floorboards.  It becomes more obvious when looking back at the differential and seeing how far the C-beam tucks around the rear yoke.  Also, the engine will sit a little under 1/4" further to the left once the bushings are replaced.

Still, I was concerned enough to give it a closer look.  From the front, it all seemed lined up, but I ran a straight edge across the front of the balancer, and measured back to front of the frame mounts.  The difference was 1/16" at the most, so I'm calling it good.  Not to mention, the passenger side measured back further than the driver side, so trying to "correct" that small of a difference would make the clearance worse at the back of the transmission.

In the engine bay, I test fit the driver side header.  It has even more room than on the passenger side, which is good, since it will be losing 1/4" of space.

Up front, the truck power steering actually fits now (the Trailblazer's doesn't), but the clearance is so small that it won't when the engine is shifted over to the side.  Remote reservoir or Volvo electric pump will be the plan.  I like the idea of the Volvo pump, especially if I end up with time/budget to build a controller, so it can be dialed up in the autocross and down in the drags.

Next up is the water pump:

It will definitely need a new thermostat housing.  I have misplaced my heater hose loop, so I can't test fit it, but I am pretty sure there is not enough room(Edit:  Found it, nope, it does not fit).  The usual way to deal with it on a C4 is to pull the hose outlets, thread the holes in the water pump, and use plumbing supplies to make them go up 90 degrees.  Seems like other people just plug them.  There does still seem to be some controversy over whether or not you need to have at least a bit of coolant flowing through there.  I'm inclined to believe it's better to at least have some flow across them versus just plugging them, but could be convinced otherwise by an expert.

Next up is redesigning the bushings.  I should have that done later today, but printing will probably take a few days.  Even though it'll make each bushing unique, I think I am going to try to lower the engine a bit, too.  I can drop it an 1/8" and still have at least 1/4" of bushing material between the inner and outer shells of the engine mount at all places.  In the interim, I may start playing with the wiring, and maybe pull the left side dash panel so I can temporarily install a gauge cluster.

Playing around in the 3D slicer.  Here's a cross section of the original bushing:

The yellow parts are solid material, and the red ring between them is infill(in this case at 60%).  The idea was to have a strong outer shell, and a little infill so it would have at least a little bit of give.  The thicker the walls and the heavier the infill, the stiffer the bushing will be.  I'm using Shore hardness 95A material, mostly because it is the most available, and it's pretty easy to print with.  

Here's a cross section of one of the updated bushings:

In order to keep the inner and outer walls separate, I cut their thickness in half (still considerably thicker than the default settings in the program).  To make up for that lost rigidity, I bumped the infill density up to 80%.  My wild guess is these will be fairly similar in effective performance to the original ones, but we'll see.  They are predicted to weight less than a gram different overall from the original bushings.  

I think the wall thickness in the original bushings may have been a bit overkill, since I am using a steel inner sleeve.  I'm printing an abbreviated version in PETG right now, just so I can look at it in person, instead of on computer, and see if gives me any additional concerns.  I also added a small vertical line on the end of each bushing, so they will be easier to visually align inside the mounts.

I noticed the river site has alt/PS brackets that tuck the PS pump up higher and closer to the block.  That may be cheaper than any other option I have come up with so far.  Not to mention, they are made of aluminum plate, so could potentially be re-drilled for a different style pump, like the one that came with the car.  

In reply to eastsideTim : Just checked that bracket kit out. Nice solution, good price at under $ 30. Don't need it now, but definitely could be handy for future projects. Did you find any indication of how much it moves the pump up?

madmrak351 said:

In reply to eastsideTim : Just checked that bracket kit out. Nice solution, good price at under $ 30. Don't need it now, but definitely could be handy for future projects. Did you find any indication of how much it moves the pump up?

 

Nope, but I should have it in my hands sometime tomorrow(Edit: or not, looks like it won't be here until some time next week).  I'll compare it with the original and put up the results in this thread.

The final offset bushing finished printing around lunch time today.

Once I had a little time, I pulled each mount one at a time, and swapped the bushings.  The result, no more engine crane!

With the intake manifold on, it looks like the hump on the hood will have to be extended for the air intake.  

Time to toss the radiator back on to see how everything will fit.

It looks like I should get a pressurized coolant reservoir, since the radiator cap will not be a high spot in the system.  The upper radiator hose routing is going to be interesting with the outlet the way it is.  Might see if I can come up with a way to redirect it with a threaded insert into the pump instead of the press fit piece.  Not going to look too intensely, but if a LS1 intake and a 98-02 F-body water pump fall into my lap cheaply, they'd solve multiple issues.

Now that the engine mounts are sorted, I think the two big time sinks will be the C-beam adapter and the wiring harness.  I'm a little tired of fab work(and it takes a lot of space), so I may take some measurements for the C-beam, but my bigger effort will be towards the wiring.  I am really hoping I can reroute everything to allow the PCM and the fuse box to be in the passenger compartment without too much fuss.  If not, there is a good amount of underhood space available.  There are also enough little jobs to do now that the engine is in place that I can switch around if I hit a temporary blocker, or just get frustrated.

Just out of curiosity,  how close is the back of the intake manifold to the firewall? If you have sufficient room for the intake to be rotated 180 degrees it can decrease the amount of hood clearance needed. Also helps to shave the top of the manifold if you do the rotation. The truck manifold is proven to produce more torque than the LS1/6 car manifold. Clearance is probably not there, but just a thought. Also this could be another time hole. Love the progress, keep up the good work.

In reply to madmrak351 :

I actually had considered it, but ultimately had passed on it.  My thinking was that even though a lot of cars have a high pressure zone at the base of the windshield, I suspect the C4 would be less so, due to the slope of the windshield. Turns out it didn't matter anyway.  There is just enough room that the throttle body would be jammed against the windshield and firewall.  If I did want to get a little weird with the intake piping, I think an LS1/LS6 manifold would be low enough that I could just drill a hole through the firewall and run it inside the cabin.  I'll keep that last bit in mind if it ever competes with a turbo, and I don't mind turning it into a one seater.

Understand,  I figured firewall would be tight, did not think about the throttle body being in windshield. With the C4 being a sports car that makes sense. My car E36 being a sedan has a higher windshield base.

Not a lot done today, but made some progress, and did a little organizing.

First mission was getting the gauge cluster installed. 

It's a "street" car again.  Now to see if I can get it inspected at home, or if I'll have to haul it somewhere.

Next planned work was to start in on the engine harness.  It was several bins deep in the storage side of the garage, so I got a little sidetracked.  I'm kind of hoping a_florida_man or stafford1500 or some Corvette expert can tell me what these shims are for.  They appear to be too narrow to be alignment shims for the upper front control arms, so I am kind of assuming they may be rear suspension related.

During the shuffling of bins, I also sorted a bunch of hardware that came with the car.  This should reduce the risk of me buying bolts I don't need.

Finally, I did manage to dig out the engine harness.  

Didn't have a lot of time left, but did get started on it.

I need to print out the instructions for which wires can be removed for a slimmed down setup, and get to work on that.  

De-pinned unnecessary PCM connections and un-loomed the wires.

I still need to go back and pull some other wiring from the loom, including some power wires related to what I yanked today.  The Trailblazer fuse box connector is different than the standard GM truck one, so it'll take a little extra work to make sure I keep what I want.  Will definitely be labeling everything as I go.

eastsideTim said:

I'm kind of hoping a_florida_man or stafford1500 or some Corvette expert can tell me what these shims are for.  They appear to be too narrow to be alignment shims for the upper front control arms, so I am kind of assuming they may be rear suspension related.

During the shuffling of bins, I also sorted a bunch of hardware that came with the car.  This should reduce the risk of me buying bolts I don't need.

 

If I recall correctly, those shims were for body mounting. Uppers use individual front and rear shims to allow caster adjustment.

I really should have sorted the hardware better.

At least I had labels on the remnants of the harness.

Spent a few hours looking at wiring diagrams and scribbling notes, then removed only a few power wires and connectors from the harness.  I kept the fuse block connector intact for now, but at some point, I'll label the wires that will be kept and cut it loose.  I do have the interior fuse box from the Trailblazer, and it could probably be adapted to work, but it seems like a lot of effort, as I don't need anywhere near the number of fuses and relays it has.  

Draped the harness over the engine, to see if it would fit the way I want it.

I think it is doubtful the PCM will go in the cab without extensive wire lengthening, but it may be able to be mounted on the passenger firewall, away from the engine.  Worst case, I find somewhere up front to mount it.  The fuse block connection may be worse, but as they are just power lines, instead of signals, I'm not as concerned with lengthening them.  The blue tape will have to come off, and we'll see if that gives enough length to run it into the cab.  The coolant temp sensor will almost certainly need to have its wires lengthened.  Otherwise, I think most of the wiring can be run to where it needs to go, but some of the runs may look a little odd. 

All of the split loom that was removed needs to be cleaned up.  Kind of tempted to just try to clean it in the sink with some dish soap.

The aluminum PS/Alt bracket kit showed up today.  

I tried to get a photo of it overlaying the stock bracket, but couldn't get an angle that showed the difference, so I scribbled on the picture in paint.  It appears the circled bolt hole stays in the stock location, and the other two are rotated a few degrees counterclockwise.  This should raise the bottom of the return line on the PS pump.  I'm not sure how much of an effect it will have, but will try to check it out after some other work is complete.  The alternator and idler pulley location appear to be designed to allow the use of a car intake.  I still need to dig out the S10's high pressure line to see if it has any chance of working with this configuration.

Interesting, thanks for the comparison picture.

No picture-worthy updates, but I have been working on the wiring harness.  Found an A/C circuit that was not connected to the PCM and pruned it.  I think I am pretty much done removing circuits, but will go over the diagrams once more.  I may have found a solution for mounting the PCM inside the cab.  The hole for the original ECM is on on the upper firewall in the center, and currently has a blank off plate.  I crawled into the car, and took a measurement.  It appears to be just under 2".  I think that will be too small to pull the PCM connectors through, but I may be able to start from the inside and pull the harness out through the hole, at least if I start with the largest transmission connector.  If that works, it should mean the harness can be fairly safely routed away from the exhaust, and there will be room on the firewall to run the fuel lines across to the driver's side.

Next time, I'll pull the plate, tape off the edges of the hole, and see if I can get the either the PCM or transmission connectors through.  A bit more of the interior may have to come apart first, so some more mapping of preexisting wiring should be done first.  If I can find a place to stash it, I was thinking removing the roof panel would make ingress and egress a lot easier while doing this work.

The roof panel is very light and mostly flat so should be easy to put out of the way somewhere. Be careful putting it back on and dont run the screws down too tight at the windshield. I cracked it before one of the events...

All the firewall holes are covered with thin sheet metal and rtv. Some may have screws or rivets too.

Maybe I won't remove the roof.  

Been sidetracked lately, but attacking the wiring still.  Mapping some of the wiring in the car, and still messing with labeling the individual wires on the engine harness.  Also put out a question on the main forum about alternator wiring.  

On a positive note, I was able to fit the PCM connectors through the hole in the firewall. 

Been spending time back and forth between the garage and my computer looking at wiring diagrams.  I have an idea about how power distribution and the fuse panel will work, but need to finish documenting everything so that when it doesn't work, it'll be easy to trace wires.

I played a little bit with cardboard today to get an idea of how the C channel adapter could work.  Used thin cardboard to represent the adapter, and corrugated for the C channel. 

I am hoping I can find some 3/16"-1/4" thick C channel for the part of the adapter that bolts to the C channel.  The rest of the material I'll take what I can get.

The inside of the C channel is 4-7/8".  I am thinking the adapter will be 4" if I can find channel, or a bit bigger if I have to make it out of flat sheet and some L-shaped pieces.  It'll give a little bit of room for some 1/8" shims to allow for adjusting pinion angle.

I'd rather have a solid design before I start building, but I think what I will need to do for this is get the C channel part of the adapter made and in its proper location, then attach it to a bracket on the tailhousing via the original transmission mount holes.  Once I've confirmed the spacing is correct, I'll have to brace and gusset by best guess.  At the very least, I want it supported by the two top bolts on the tailhousing, so it has support in different planes.  May also do so with the bottom two bolts.  From there, it'll have to be a matter of adding support until I think it'll be strong enough to hold together.  I think I'll let this percolate for a day, then run to the metal supplier tomorrow after having had more time to think.  Hunting down a C4 tailhousing and 4-to-6 bolt adapter would be ideal, if it weren't for the challenge budget.

I really need to get this built while we still have some decent weather.   Any other cutting/welding jobs should be a lot smaller, and should be able to take place during the occasional one off warm days in the winter.

Edit:  I also made a junkyard run recently.  Grabbed a Volvo electric power steering pump and a coolant reservoir from a Chevy Cruze.  I'm entertaining taking the budget hit to switch to a 2010-2015 Camaro water pump, to hopefully make radiator hose routing more simple, too.

The team stopped by this evening, in the hopes that four brains are better than one.  We reinstalled the front splitter and bodywork on the car, in an effort to figure out a way to make the splitter more easily removable. 

Several options were discussed, but the winning one right now is to not worry about it, and make longer ramps for the trailer. 

We also set the hood in place to see how bad it didn't fit.  The hump on the hood is tall enough for the intake manifold, but it looks like it'll need to be extended forward.  We'll deal with it later.  

A bit of wiring testing was done, and some ideas for the cutoff switch were discussed.  I need to do a little research to make sure it will be considered acceptable, but I think we have a path forward there.

Finally, I showed off my highly advanced mockup for the C channel adapter, and was met with approval, so will likely be buying metal soon.