AMC V8 Shenanigans

[TyTheJeepGuy]

I had a perfectly running (at least) twice rebuilt '77 AMC 401. Most recently rebuilt by me (because I let a bolt fall into the intake on a test drive...), so I know all the juicy numbers and exactly what is in it now.

Dyno'd at 250hp (SAE corrected) at the 33" mud tires. Oddly, after adding fiberglass wrapped short tube headers, Holley Sniper EFI and HyperSpark ignition control with a professional tune, crossover x pipe on the exhaust, best dyno run was 249hp... go figure. The late 70s heads just do not flow air past 43-4500 rpm.

After getting maybe 14mpg on highway at best and you can bet more on 11mpg especially if holding 75mph, this didn't sit well with me. I want big power if I have to deal with all the cons of a big ('small block' based) V8. It certainly felt like plenty of power on the road but 250 to the tires just wasn't enough to tickle my pickle and brag about.

I also had issues in the summer, with a bed full of camping gear and a cab full of 2 humans or less, the truck would really struggle up mountain passes in terms of coolant temperature and apparently, fuel temperature.

There was a horrible clunking noise last time it was crawling in Moab. Made others uncomfortable. I didn't like it either.

So the shenanigans list was as follows:

• Mo powa baby (happy at any improvement to tires, very happy with 300, hoping for more like 315)
• Lower coolant temps in summer baby
• No more fuel pumps crapping out on me on the trail, making Karens in late model 4Runners mad that they were delayed by 2 minutes while I rub an ice cube on my external pump
• No more clunkity clunk on trail

[hiimmike]

How did you keep the ice cubes frozen in the Moab desert?

[TyTheJeepGuy]

Many of the shenanigan list items have been tackled in my garage but with it still being Spring, I'm not sure if the goals were accomplished. There have been some promising results however, starting with the fuel pump.

I think I've been through about 4 external fuel pumps. Heat is what kills these mostly. They dissipate some heat via airflow over them but *most* is from the fuel that they push through. For one, that isn't good for making max power, but mostly the rejected fuel that ends up back in the tank has now been heated by a pass through the pump. Through the cycle of a tank of gas especially going through the mountains in summer the fuel would get hotter and hotter and the pumps would fail. Generally, this was associated with high coolant and manifold air temps so it was super fun having your pump die and your engine go super lean right when it was getting hot. Then you'd pull over and shut off your engine and watch it heat soak to the moon and blow out the radiator. Even more fun when you just lovingly rebuilt that poor engine and you're watching it get melted. Even more more fun when people are constantly questioning the reliability of your old rig and its blowing steam!

So, I dropped the tank about 5 times and installed a "pump on a stick" sending unit. This way the pump is constantly suspended in the fuel and I think it goes a long way for longevity. I bought an assembly made for a CJ5, the tanks look pretty similar. It turned out to do well. It can pump the tank to nearly dry which is great, has a "hydramat" on it so it handles fuel slosh a lot better than previous iterations.

Reason I had to drop the tank so many times was I was trying to bend it to just the right shape. There's a hump in the tank where the float for the sending unit needs to clear, it would get pinned up against it and not read full. Very hard to see and mostly guess work in a black poly tank. I eventually hit the right bend with very minute changes and a lot of swearing and crawling around and getting soaked in fuel. Not fun.

Anyway, my gas gauge reads decent now and haven't had a fuel delivery issue since! We shall see on Loveland pass this summer!

[TyTheJeepGuy]

hiimmike previously posted:

[TyTheJeepGuy]

Now, the lower coolant temps. This has been bothering me since the rebuild. I've got the 401 overbored 40 thousandths over, its getting real close to the water jackets. It was at about 9.8:1 compression, 1.3 over stock, and both of these things means harder to keep cool.

Here's the disappointing part. When I went to have this thing rebuilt, I was aware that the stock cooling system might not cut it anymore, and I bought an aluminum radiator *and* fan/shroud combination and fan controller from BJs offroad. For those of you who don't know, you have about 2 choices for Full Size Jeep specific shopping: BJs Offroad and Team Grand Wagoneer. BJO is almost always insanely overpriced. I spent a lot of money on that setup and really believed it was the right choice especially since all of the reviews were overwhelmingly positive.

The BJO setup did do quite well in a couple of scenarios where you usually expect a radiator or fan shroud situation to be the culprits: high ambient temps idling in traffic, and decently when going down (flat) highway. The FSJs don't do well holding 75, and I don't mind that. There are always compromises in a 70s truck.

However, it was just plain getting too hot in scenarios where it shouldn't have been. Going about 35mph up Loveland pass, I think ambient temps were only in the 70s if that. Engine would slowly outpace the coolant system, up and up to about 230f before the fuel pump went...

A1gemmel from this forum (big Yella Yota pizza truck snow-wheeler) helped me out big time. He put a ton of work into chopping up my hood and making it a big ol cowled hood. Even less visibility when offroading now but should help vent that engine bay. The engine still outpaced the cooling system though.

So, after trying tons of other things (different tune on the EFI, spark timing, even hooking up EGR to try and keep combustion temps down), I finally questioned whether the BJO rad and fan were really what they claimed to be.

I've been watching a ton of Roadkill shows and they almost always ran into the same problems with different builds. I noticed the Mopar cars had very similar radiators, the lower models had I think 22" wide radiators, while the "heavy duty" cooling for stuff like big blocks had 26-27". I noticed the BJO radiator is actually 22" wide, the stock was 26" wide core. In one of the shows they simply found the bigger 26" wide, tossed it on and had room for two electric fans, boom job done.

I started with the fan situation. I assumed that BJO's description was accurate: they claim that even though its only a 2 core, it is 2 1" cores instead of I'm assuming 1/2" stock so it actually cools better. I now think this is BS but will elaborate later. So, assuming the rad was kick-ass, it must have been an issue with getting air over it. The "shroud" that I bought separately is specifically made for the BJO rad, and is expensive as hell. The shroud isn't really a shroud, imagine more like a mid-plate for an engine mount. It sits quite flat maybe an 1/8" over the rad core. I truly think it only pulled air over the surface area of the fan. I think results would be similar or exactly the same if you just zip tied just the fan to the core. I set out to try and do better, but there's a problem.

The BJO radiator solution is THICCC and it was near impossible to find any fan that could draw more CFM that would fit, dual fan setups were too wide for the puny 22" wide core, and again with low space to the engine, coming up with a better flowing shroud seemed impossible. I bought a few fans before eventually giving up and sticking with their solution.

The issue bothered me enough, and I had recently set about for making more power. Which means asking even more out of the cooling system. I decided to reject the teachings of BJs Offroad and their reviewers with puny stock AMC engines and set off on more research, this time into the radiator itself. I took some core measurements of the stock radiator I still had lying around propping my gate open from time to time and the BJO core. Crucial to cooling is total surface area and that's actually in 3 dimensions with radiators. The new radiator did in fact beat out the old one, but just slightly, and it seems that the cons of being railroaded into one fan setup that didn't have a very good shroud wasn't worth it. There is a *much* cheaper 3 row aluminum radiator that fits FSJ's (only listed under the AMC360 but, its the same truck) on RockAuto. I pulled the trigger on that. Also I found that there is a popular upgrade done by FSJ DIYers that involves using a turn of the century era Ford cooling fan assembly and it fits right onto stock AMC radiators (once you cut tabs off and find your own mounting solution): https://theamcforum.com/forum/contou...pic100667.html

I was super excited when the new radiator came in, and it fit! And has much more surface area for cooling. It also has more room to the engine so you can get fancy with cooling assemblies. If the Ford one doesn't work, I have a lot more aftermarket options, and a lot more junkyard cars should have them just sitting there waiting to be taken.

One thing with the RockAuto rad was that it did have a slightly more recessed mounting bracket, so the angle brackets used by the guys in that forum wouldn't suffice. I set about cutting up some corner brackets and drilling holes. I have a somewhat janky solution now but better for serviceability than the classic zip ties! The oil cooler for the transmission oil was back into the stock location so I trimmed up and remade my 6AN braided steel lines to go from transmission, to zip tied auxiliary oil cooler on front of core, to rad oil cooler, back to transmission.

This new setup is as yet un-stress tested but sure seems to move a great amount of air!

https://photos.app.goo.gl/DEBjhBjr3nwMp4gWA

[TyTheJeepGuy]

The eagle-eyed viewer may have noticed other happenings in the engine bay from the rad photos, that's the mo powa shenanigan. I'll be writing that up later.

[a1gemmel]

One of the coolest trucks out there! Here's a few pics of the cowl construction and the fuel cooler scoop. We were pretty amazed when we taped some string around the cowl/windshield and even at 10mph it was already inducting air!

[TyTheJeepGuy]

So for some context, that ridiculous fuel scoop was fabbed up (by A1gemmel) while I was installing my headers. I have a little fluid cooler (looks like an auxiliary oil cooler) that I had to tuck up under the truck and it got probably zero air flowing over it. Now it has air flowing over it for sure I think probably at the cost of 1mpg on the highway

[TyTheJeepGuy]

So for the clunking noise while offroading, turns out the transfer case I have (BorgWarner 1339) uses a drive chain for all modes: 2WD hi/low, 4WD hi/low. This chain got wore out over the years. I ordered a new one for the eye-watering cost of 340 buckaroonies from my favorite people, BJO. A1gemmel helpfully offers his shop for a more comfortable T case disassembly experience. I finally get everything apart and realize the new chain aint gonna work... turns out, my transfer case has an aftermarket kit that gives it 16% overdrive in all modes. This requires a different chain. Don't worry! BJO will partially refund you and make you pay a ton of shipping to exchange for the right chain.

When the new one finally came in I think I had that T case apart in about an hour in my garage, thanks to the practice run. Unfortunately also thanks to the practice run, it was well glued together by RTV and I had to use a jack to separate the halves. Cleaned it up, threw the new chain in on a workbench, heaved it back up into place and bolted back together with RTV instead of a gasket because the old gasket was disintegrated.

As with everything else in this thread, it is still unknown if this solves the issue, although there is a lot less violent clunking when shifting into reverse or downshifting now. Maybe if I stop tearing apart my running truck I'll be able to wheel it and see if the problem is resolved with a good ol loud pedal stomp in 4 low.

[TyTheJeepGuy]

Check out this impetus for roaming around my property looking for things to sell to try and afford some nice Eddy heads for my poor suffocating 409! Blue is best run from July 2023. Red is from March 2024, after: wrapped short-tube headers, EFI and spark control tune, exhaust crossover pipe, no air filter!

I think it was clear that all the upgrades to exhaust doing nothing meant it wasn't my bottleneck. Which I probably knew already but figured that surely the headers would unlock a bit of power. Clearly the heads weren't flowing as well as the chaps on AMC forums would claim. We shall see... anyway, I did spring for some Edelbrock heads, and with some encouragement from a1gemmel I even attempted some very light porting and cleaning up on them.

I'd seen an episode of Hot Rod Garage with Tony Angelo. They bought these same heads (Edelbrock Performer RPM for AMC), slapped em right on without changing a damn thing, to an AMC 401 that was .03 overbored (mines .04) and with deeper dishes on their pistons. They did have about as big of a cam as you can put with the heads, I think .550 to my .448 (Edelbrock Performer instead of Performer RPM level cam, which is really a specific Comp Cam in disguise). Anyway, mine should be about 10.3:1 compression ratio, I think theirs was more like 9:1.

They made 450 peak hp at something like 6k RPM!! Yeah, I bought the heads basically immediately.

I finally got it back together last night and fired it up. Itching for a test drive but I've got a lot of garage cleanup to do, and the power steering bracket was broken when I went to take it off. I have a new one but I've got to get that rounded off high pressure line off to replace and I'm not really looking forward to that.

More details on the actual head install coming.

[xaza]

What an adventure you are having. If you are still looking for an electric fan, I have a 2 speed fan out of a Taurus 3.8L. I was going to use it for electric fan conversion on XJ but never got around to completing. You are welcome to it if you want. Picture of it is in build thread of XJ very top of page 6.

[TyTheJeepGuy]

Ooh darn I would definitely have taken you up on that. I was scouring junkyards before just getting a new one from Dorman. They say nothing pulls air like the OEM ones but so far these seem pretty great!

[FINOCJ]

The fun of old iron....many days I am ready to sell the 58....the engine is making a concerning noise. Been going with the let it blow a rod through the block mentality as that means I can start fresh again and stop chasing unending issues. Good luck....I originally joined the group when the 70 was still a bit uncertain, but once it got all worked out, it's been pure joy to drive and wheel all these last 8 years.....except maybe when I do something dumb (say smashing the rear quarter - twice! - or drive it into a big hole breaking stuff so jim can test out his both his winch and new welder/inverter)!

[hiimmike]

Do you know how many spare parts I'd have leftover if I tried to take something apart? hahahah

Before I lifted my Jeep, I didn't know what a tie rod was or what it was for. I learned a lot doing that work, good because now I know things if I break down on the trail. That or I just take Jim along who just tells me to pull relays until my brakes stop locking up. I'm still dealing with that but I have a better fix, disabled all ABS systems/sensors with my Tazer.

[TyTheJeepGuy]

Short update: I'll still grab photos from the heads removal and replacement and do a better write-up of that. It was decently straightforward but a torn down V8 is always interesting to look at I think. Most of the interesting bits were actually to do with a mild porting job of the heads (at a1gemmels encouragement).

However the main update is, the new cooling system did very very well over the weekend. I was towing a snowmobile up mountain passes, holding about 3800rpm and heater off just to stress test it. On the way out the temps got up to I think 198 if I remember correctly. The ambient temps were low, snow was coming down near Eisenhower tunnel. The thermostat opens at about 185f, I turn on 1 fan with my fancy new relay setup and Holley Sniper output at 185f, then the second turns on at 190f. It rarely would overpower and climb past 190 in most situations where I was starting to hit over 200 easily with similar or lower ambient temps before.

Then on the way back, again holding about 55-60mph second gear going back up to the tunnel, no heater on to help, higher ambient temps this time, it climbed slowly to max of 214 and seemed to stay pretty stable there. This made me very happy.

[TyTheJeepGuy]

So, the mo powa shenanigan! The engine clearly needed to get more air. Since I had cooling issues anyway, some kind of power adder seemed like a bad idea. Even though we obviously live at elevation and play at even higher elevation I really like the simplicity of naturally aspirated engines. I came home from the dyno disappointed after upgrading exhaust (headers, crossover x pipe) and installing a fancy ignition timing system (Holley Hyperspark) and getting a tune. Same exact results on the dyno. I went looking for more info because when I was building my engine I remember the specs being similar to engines making something like 430 to 450 crank horsepower. My estimates based on the dyno put it to about 360 crank horsepower and that's being generous with the drivetrain losses. I did find plenty of internet evidence, for whatever that's worth, that the TH400 transmission is a power robbing slush box. Add to that some losses likely from the transfer case.

Anyway 360 crank I wasn't super excited about so I saw on an AMC forum that the Hot Rod Garage guys had an AMC401 that just kept asking for more and more fuel from the carb. This was surprising to me in 2 ways: for one I thought I'd seen all the MotorTrend shows I'd care about (mostly Roadkill based) and they almost always just stuck with Chevys, sometimes Mopars and rarely Fords, never AMCs. The second was that my engine was certainly not asking for more fuel, that meant they were getting more air than mine. I found the episode and loaded it up. There's a string of Hot Rod Garage episodes where they rip around that engine that I recommend watching, one where Randy Pobst (whom I've been lucky enough to meet on Pikes Peak!) tears it around a track. Basically they took a base 401 block, 30 overbored, put stock pistons in it and crucially, slapped Edelbrock heads on it. They claim that they did not touch the heads, just direct bolted on. The intake manifold is iron I think but some fancy aftermarket one, I'll chock that up to being pretty similar to mine (Edelbrock Performer). That thing revved up to 6k and made 450 horsepower. I'm pretty sure their compression ratio is maybe 9:1. So I ordered the heads that had been in my wish list for a while.

A1gemmel convinced me to do some mild porting or really just "clean up" on the ports and I'm glad he did. Not only do I think it probably unlocked some potential power here and there, but those things were DIRTY. Aluminum shavings coating all of the assembly grease. Valves were absolutely coated in aluminum dust. It probably would have been "ok" but who wants all that nastiness floating around their rebuilt engine? Not me.

Cleaned em up, reassembled, and set about tearing the truck down. I got it pulled apart pretty quickly, about a day's work if I remember correctly. Invited A1gemmel and my friend Zach over to help that evening. The help was nice especially for getting those crazy heavy iron heads out of there. Unfortunately, that was all that was left by the time they got there in terms of tear down, and I found out that I only ordered one head gasket and of course no stores are going to stock AMC V8 parts. Zach and A1gemmel and I discovered for me when we tried to at least install one head that I had also ordered the wrong head bolts. Edelbrock changed the head bolt patterns slightly. Luckily those arrived the same day the new head gasket did, and Summit was cool about refunding me for the wrong ones I sent back.

I had lost my help by the time the parts came back in, understandably (people have jobs and lives as it turns out). Luckily the new heads are nice and light, I think the truck literally sits higher in the front now. I was able to heave em carefully up into position and crank them down, 4 steps of torquing down all those head bolts. The rest zipped together relatively quickly and without issue; except I sliced my thumb open on the valley pan gasket that goes under the intake manifold. That made turning down all the little remaining bolts a literal pain!

Thanks to more help and my own efforts, I had really tightened down my wiring and vacuum lines in the engine bay. Some may say it still needs work but to me its great; I was able to put fuel and spark and accessories on relatively easily. Just a few minutes to get the Sniper back on there and ready to rock. I would find out literally last night (nearly a month and a trip to steamboat later) that through all this climbing over the engine bay I mashed a connection for the 12v power for the ECU. I'll elaborate on the intermittent issues that would cause later.

With everything back together it was time to fire it up. I of course had dropped the distributor back in 180* out, as is tradition. A couple massive backfires later and it was the right way, fired right up. Reset the static timing so the computer could take over and it was good to go. Of course at this point the hood is off and its raining but I couldn't help myself, I went for a glorious trip around the neighborhood. Aside from some stumbles here and there (12v power drop, as it turns out) the power increase was obvious to me. Big smiles per gallon!

I've got a busy May but I plan on a return to the dyno soon, and I'll post the results here. No matter how painful they may be its definitely the JMT now! (Jeep Muscle Truck). The Roadkill guys have a MMT (Mopar Muscle Truck) and CMT (Chevy Muscle Truck) so, I'm inspired.

[TyTheJeepGuy]

I forgot an important part that I think deserves its own standalone post on this thread. The Edelbrock instructions said I could reuse my stock rockers. I didn't know how that would work since those were held on by bolts, and the new heads used studs. Andrew didn't know how it would work either and spoke his mind, I unwisely ignored him while shrugging my shoulders. The sheet said its fine! Its fine! It wasn't fine. Turns out I need stock Ford small block rockers. Guess who happened to have them in stock for some unknown reason (he doesn't have any Ford V8s that I know of...)? Yup, Andrew. He brought them over and boom look at em! They're gorgeous. And they're roller tips so now I can rev to 7k no problem

[a1gemmel]

The empire of dirt hides many secrets

[TyTheJeepGuy]

a1gemmel previously posted:

[TjMike]

That 401 is starting to look pretty! Cant wait to hear you rev that thing to 7k rpm

Seems like Andrew has quite the pile of parts laying around.