Hey guys. I know to some this may be totally obvious but after watching Musclecar on Spike and seeing many LS conversion online I just gotta bring something up. I have noticed that quite a few of the GM muscle cars that receive a LS swap have all the electronics like the fusepanels and computers just bolted to the firwall or the inner wheelwells and well it really annoys me. Particularly the Firebird that Musclecar is building for Year One. The host I cant remember his name spent a ton of time making the engine compartment look like crap and Ill tell you why. He said that they couldnt make a hole big enough to push the connectors for the fusepanel and computer through the firewall. Alot of others using a GMPP conversion harness have done the same. Now this is were its just so obvious that it blows my mind.... MAke a small hole in the firewall and pull the engine harness from the inside out!! Every connector and the harness will fit through a hole less than 1.75" in diameter if its done this way and you dont have all that ugliness cluttering the engine compartment. I dont wanna make anyone that has done this feel bad but being an electrical guy by trade I have seen this done on so many engine swaps I cant count them on my fingers toes and the other guys in the shop fingers and toes. I know it may be kinda random but it really amazes me that guys will go through all the effort to make the sheet metal total smooth in the engine compartment just to scab it all up with ugly computers and fuse blocks with the harness looking like a bunch of spaghetti. Normally a hole right behind the intake manifold will place the harness up high enough that it cant be seen inside and looks super clean in the engine compartment. So I guess its a rant and a tip but if youre doing a swap and you havent wired it in yet please take some time to mount stuff inside where its hidden and cleanly route it from the inside out. The end result is a 1000 times better. Ok thats all thanks for listening

 

Good Rant Matty, I agree with you! I love a nice clean compartment

Pat

 

What do you use for a wire groment(sp?) then?

Just curious what everyone has used on a 1.75" hole.

 

I can see why they don't. If using the stock harness, its not that long, and its a buttload of work to extend all those wires in order to mount the PCM inside the car. In other cases, there simply isn't room as was the case with my swap. I don't even have a glovebox anymore after installing the 4th gen HVAC system - it's huge. But, things can be done to "tidy" it up as much as possible.

 

Matty, i agree, i soon will be doing my harness and have also smoothed out my firewall for a neat look ( not a showcar just neat do you have any pics? and what gromets did you use? Thanks JOHN

 

I did this very thing on my 77 vette swap. I tucked the computer behind the center console and used an existing wiring hole in the firewall to feed the harness through. Looks factory and cleans up the bay nicely.

 

http://www.sealsit.com

seals-it grommets work great. and Ive stuck pcms on top of gen 4 VA installs. Believe me you can find room, I have found room in model A's with AC so it can be done on anything. And other than a truck harness, any stock wiring harness for a 4th gen or corvette is more than adequate in length to route from directly behind the motor (with a small bend for engine movement) and then into the car. The GMPP harnesses are way long enough same goes for standard length S&P harnesses. Normally Ive found that the harnesses are a bit long and if anything would need to be shortened. Like anything it takes a little thought but it probably takes more planning to do a deep tub or actually smoothing a firewall than it does to find a home for the computer and a fuse block. IMO its either a lack of skill or a lack of motivation to find a nice home for electrical components. I really think that there are alot of guys that see a wiring harness and just flat freak out and dont know how to deal with it. When it comes to routing wiring I think of it like plumbing a car (but even that gets botched quite a bit). You wouldnt normally run you fuel line over the firewall to a regulator then double back to go to the motor and the same mindset should be taken when wiring as well. You wouldnt run a rubber fuel line across jagged metal or pinched between two parts or strung as tight as a tightrope but guys do that all the time with electrical and after going through a bunch of build threads I just couldnt take it anymore. I dont really understand why its considered acceptable practice to wire a car so haphazardly but then again Id be without a job if it was done correctly everytime

 

funny you ask about pics of my work, Im so busy doing it that I never stop to take pictures of my work. I dunno if anyone else has this problem but I find it hard to constantly stop to grab a camera while Im working. And as far as finished projects there really isnt anything to see cause you cant really see it so whats the point lol. Like I said I use Seals-it grommets or if my customer is paying alot I will use bulkhead assemblies from delphi. Those come in 24 up to 72 pin connectors that bolt together at the firewall but they arent cheap at about $75 for an assembly when you buy terminals and housings and locks and such but if youre paying 5-6k for wiring I tend to go the extra mile and use unique wiring products for a very one off installation. And I know this isnt the forum where most guys have the expeirence to cut a harness in half and be able to make it into a bulkhead and have everything work afterward but a nice grommet and some time is all it takes sometimes to go from average to awesome.

 

For a large grommet I used a door to pillar post grommet out of a late model caddy.

Look at all the cars in the junk yard with all the power adjusts coming up to the arm rests in the door.

Almost an unlimited supply and variety.

Jim

 

I'm doing the opposite. All the vehicles we got these motors from came with the PCM in the engine compartment somewhere...

I painted my PCM, and plan on mounting it right on the firewall where the A/C box used to be. For me its a "something else that makes the engine bay look anything but stock look, if they happen to miss the lsx motor that's in it look"... lol

 

that kind of reasoning is kinda scewed, Idk about you but when I look at the engine compartment of a 4th gen "beautiful engine bay" is not the first thing that comes to mind. If you got your motor out of a vette then I guess you should shove the computer down in front of the rocker behind the passenger wheel... why you may ask? Well simple, cause thats where GM decided there was room in a vette same goes for the 4th gens. Im more than certain that GM would have put the PCMs in the cabin if there was any room at all but in a vette its pretty hard up for space in there.. But hey at least you didnt grab a TPI motor out of a camaro or vette then youd have to stick it under the dash or in the pass. kick panel. Now Im not saying that you cant make it look good but IMO there is absolutely no reason for tacking **** all over the firewall at ruining the aesthetics if a simple engine compartment when you can do it so much cleaner. Personally sounds like a cop out to me, but hey thats why I was ranting. Its your car though and I dont have to like it. Now Year Ones tribute trans am car is different. That car had a smoothed firewall and was clean as could be. They stabbed an ls7 in there and then proceeded to paste the oil tank breather just right of center on the firewall and scabbed the computer and fusepanel to the inner wheelwell. I know what Year One was looking for and that was a very clean Pro Touring car, instead they are getting the televised construction of a visual monstrosity. The car should run just fine but if you have any respect for how your car looks I dont think you would do that.

 

Maybe GM wanted to keep them kind of cool? That was always my theory on why they were all in the engine bays instead of putting under the dash somewhere.

I wanted to put the PCM where the old one was in my 91 s10, which was right underneath the glove box. I would have had to extend all the wires about 2.5 feet, plus, the PCM would not fit in the hole for the old one.

On my s10 there is nothing on the firewall currently, except for the brake booster/master cylinder. By the time it’s done the only thing on the firewall would be the PCM and the fuse block. Everything else was discarded, and it was sanded and painted. From all the cruises I have been to this year, my truck is definitely going to have one of the nicest engine bays for sure, except for those "I trailer it to events" people.

 

No, not a Gen 4 VA setup... the ENTIRE 4th gen HVAC system out of a 4th gen. Its HUGE. No room.

Either way, I keep the hood shut. The Pontiac guys hate it, its not a "show" quality install, and I'm to busy driving it to show off with the hood up anyway.

 

I agree don't be sloppy.

But putting everything under the hood sure makes access a lot easier. Especially for us fat old guys. I hate getting under the dash to check a fuse.

You would die on a Navy ship. All the wiring is exposed, for good reason.

 

Jeff Georges recently left Year One & was their guru of wiring(among other things) on all their in-house builds for years. He had the same mind-set as you, insisting on super clean engine compartments, as evidenced in all the TV shows & magazine shoots & Power Tours he was also part of. Unfortuneately for Year One, he has moved on into a completely new line of work.

 

They put cooling fins on the PCM for a reason, when is the last time you found one hidden under a dash with no air flow? Pretty sure it had a replaceable PROM.

I like clean engine bays as well, but to overheat a PCM by hiding it inside a hot interior just so your engine compartment looks a little cleaner isn't always the best route either. I guess if you have a trailer queen it doesn't matter but if you actually use the car I would want some airflow on the PCM.

 

How do you explain the use of stereo amps, with cooling fins, inside the vehicle?

 

I can't explain them except to say they are not running complex algorithms that run an engine using several processors. Todays PCM's generate a large amount of heat. The cooling fines on the E38 2008 Corvette are about 19mm tall. I am pretty sure that GM puts those on there to cool the PCM, not to look nice.

The stereo amps just supply power to your sound system, nothing more, nothing less.
Some of the bigger ones do have cooling. They are also not factory installed, atleast ones that actually do anything. Your car will run with a dead amp, PCM dies, your on a rollback.

Not here to start an argument, just trying to clarify why hiding the PCM is not always the best thing to do. Hiding ugly wiring is a great idea.

 

Speaking of heat, which is warmer? Engine compartment or passenger compartment? Been my experience that a 200 degree motor with even hotter exhaust is much warmer to be close to. And since GM designed the ECUs to be able to withstand that heat, they should have no problem under a dash where is seldom goes much above 100. As for putting them where the factory does, design engineers have to make compromises for cost and ease of building. I think Matty's point is if a person is going to the amount of work that an LSx swap entails, why not make a little extra effort to make it look clean? Sometimes we as builders have to live with the same constraints the design engineers do, and for some folks, form follows function. So I can see it both ways. It's just when I see a really bitchin' car with a lot of work in it, seeing the electronics done in a clutter when it could be tucked out of the way detracts from the over all effort.

Pat

 

Supplying air circulation for a GM PCM, I would think, would be simple enough. If someone was concerned about this, Radio Shack sells all sizes of compact, very inexpensive, electronics cooling fans that could easily be wired to turn on with ignition. No problems...only solutions...