mil-spec v. auto-spec

[C. Ludwig]

We get a lot of guys asking about mil-spec wiring and connectors. My impression is that it's a buzz word a lot of people hear and they assume it's better. While mil-spec components certainly can be better, why are they better, do you need them, and is the added cost justified?

WIRE
First, let's look at wire and what the difference is between mil-spec and auto-spec (commonly referred to as hookup or primary wire). Mil-spec is actually a pretty generic term. For any given part (wire, heat shrink, connectors, etc.) there may be dozens of military specs outlining different characteristics for different purposes. A wire might have a mil rating for heat resistance. Another wire might have the same heat resistance but has a different mil rating because it has a different sheath that gives off a different chemical when it burns. Additionally, a wire that is not mil rated (auto-spec), may have similar characteristics in terms of heat resistance or load capacity, but it might not meet a mil-spec for vapor emissions when it burns.

What you generally get with a mil-spec wire versus an auto-spec, in terms of actually functionality, is a better conductor. Mil-spec wire, as used in performance auto applications, has tin coated copper strands that are better conductors than the copper standing of auto-spec wire. The individual strands of wire are usually finer, a given gauge of wire having more internal conductors, which results in a better conductor. What this means is that you can usually carry the same load with a smaller wire. For example, instead of using a 20 gauge auto-spec wire for an injector channel, you can use 22 gauge mil-spec. Additionally, the sheath, or outer coating of mil-spec wire is a different material than auto-spec. Usually Tefzel versus common PVC. Tefzel is a trademark of DuPont for ETFE. The Tefzel is tougher than PVC and this allows a thinner coating to provide similar, or better, protection of the wire from abrasion.

The downside to mil-spec wire is the cost. Mil-spec wire is usually 2 to 3 times the cost, per foot, of auto-spec wire for a given gauge. This adds up quickly when building a complete harness. Additionally, the hobbyist level ECUs (Haltech, Microtech, AEM, etc.) that come with auto-spec wire harnesses, generally don't have a mil-spec alternative available from the manufacturer. Therefore a mil-spec harness needs to be constructed from scratch. This negates any volume build discount associated with the manufacturer supplied auto-spec harness and creates an even larger price gap between an auto-spec harness and a mil-spec harness. Another bit of a downside is that the Tefzel coating, being thinner and tougher, requires a specialized stripper to properly strip the wire without damaging the conductors. If you're doing the work yourself, you'll need to invest in some new tooling.

So, essentially, what you gain with a mil-spec wire is a smaller, lighter wire over an auto-spec wire that will carry the same load. This is critical in cutting edge motorsports, where weight and weight distribution are highly critical. Formula car apps, where space is at a premium, are also an obvious application. For the hobbyist, auto-spec is good enough for auto manufacturers that guarantee their products for tens of thousands of miles, so it will work just fine, in terms of electrical performance, for anything you will want to do.

At LMS-EFI we consider value to be a key priority. We can build anything you'd like, but is your money being well spent? If you want mil-spec wire, shrink, and connectors, we can do it, have done it, and have many of those components on hand. Just don't be surprised if we try to talk you into something less expensive that will do the job just as well.

We'll talk about heat shrink tubing and connectors later.

[AnthonyNYC]

I'm currently changing ECU's and wiring and this info is very helpful, thank you.

When are we talking connectors and shrink tubing?

[C. Ludwig]

Working on it. Essentially, the story will be the same. Drop me a PM and I'll give you the basics on the heat shrink if you're ready to get started.

For connectors, we pretty much exclusively use the Deustch DT and DTM connectors. Here is a good run down on the DTMs. LINK For bulkhead connectors, there are a million different options.

[Whizbang]

ive used aviation grade stuff, mostly because of its variety and aircraft spruce has good prices.

[RENESISFD]

Good info, thanks for the post.

[AnthonyNYC]

Thanks Chris

[TitaniumTT]

I should probably take a few pictures if I can find the correct wire and post up the differences between Tefzel and the PVC variant that the Haltechs use.

Basically Chris is 100% right. When you buy a MoTeC harness you're paying $725 for what Haltech sells for 1/3 of that. The MoTeC harness is Tefzel wire, and it is smaller, thinner and lighter... but is it really worth it? For the hobbiest (and that's a great analogy btw Chris) the answer is simple, no. I'll be running a PS2000 in my turbo 'vert, and I have no desire whatsoever to erdo that entire harness in Tefzel. I will however be using nothing by deutsch connectors under the hood and I do plan on using a Mil-Spec 262857 ( I think) bulkhead connector. But that's just personal preference. I prefer to build the engine on the stand, build it completely, attach the tranny, and drop it in as one. Connect the fuel lines, coolant lines, oil lines, and go. But... that's me, that's my preference.

I am curious as to what you have to write about heatshrink though, Chris. I only use Raychem DR-25. I know there are other options out there but I haven't researched or tried them yet. My good friend Colin has, and he has a few different options that he's currently researching and trying out.

[Mazdabater]

One thing I have found (note I get aircraft grade wire and connectors for free from work) is that the special heat shrink on environmental splices requires too much heat for generic wire, it melts the insulation before the splice seals. And the mil spec wire certainly solders alot better if you choose that route.

[TitaniumTT]

I refuse to solder unless absolutely necessary. I can crimp some 20ga wire and you'll loose circulation in your hands before the crimp or the wire breaks.

[FerociousP]

Originally Posted by TitaniumTT

I refuse to solder unless absolutely necessary. I can crimp some 20ga wire and you'll loose circulation in your hands before the crimp or the wire breaks.

+1

I started down the "no soldering" path a few years ago. To me, its easier, cleaner, more controllable, and consistent than I was ever able to be with solder. Crimping with an uninsulated butt splice and heat shrinking leaves a bulge not much wider than the wire itself, and like TTT said... just try pulling it apart when done correctly. Hell, I use a $4 crimper from Harbor Freight! I just crimp in a way that ensures its integrity.

***With that said we already have a thread devoted to this argument

[Prodigy]

I just found this (sorry is repost)

http://www.apexspeedtech.com/the-dif...dtm-connectors

but I know the kind of connecters I want now... too bad they are damned expensive...

just wait and save up I guess.. lol


J.

[Mazdabater]

Well a majority of the aircraft stuff is crimped, that is what the enviromental splices are. Crimping is always a much better choice then soldering. But in saying that if I'm out of crimps I'm not fussed about soldering shit. It's pretty unlikely to fail really.