Big Blue - 1975 C20

[willis_racing]

This truck only receives sporadic progress but right now I happen to be in a decent position to work on it for about a month. And so begins the thread about my BGMT

The truck's history: This thing started life as a 1975 Chevy C20 with a 2 bbl 350 and an sm465. At some point in the 80s it was built into a mud racer with front drivetrain parts from a k20 (spring hangers, axle, and steering). It was loaded up with a 454 big block, a turbo 350, and an NP203. Legend has it that it ran a 6-71 blower on top of the big block and got driven around new mexico to the mud racing series for a decade or so.

My personal history with the truck begins with its previous owner and my dad being pretty close friends in the early 00's. Our friend Paul bought it to use as a lake truck to tow his jet boat around on the sandy beaches of NM's biggest lake. Back before everyone and their sister had 5 tons, we had repurposed big gay mud trucks
I was around 4 or 5 at the time, and I spent a ton of time riding around in the thing pulling stuck people out, and I contribute a large amount of my love of trucks to being around this thing when I was a little guy and the tires were taller than me. I didn't know shit about trucks at the age of 4, I just knew that Big Blue was badass as fuck!
(Don't have any pictures from that time frame unfortunately)

At some point during this time, Paul broke an axle shaft in the 10 bolt and decided half ton axles are for pussies. He upgraded it with a 77+ Chevy KP60, regeared the front and rear to 4.88, and stuck in a pair of what I believe to be TruTracs. Not great on a crawler, but work awesome in the sand.

Sometime after this, Paul sold his jet boat and a couple of his jet skis and took up dirt bike racing as his main hobby, so Big Blue started sitting. It ended up sitting in his backyard for a little over 10 years before I happened to ask him about the truck on a whim. He had to ponder on it for a few months but decided that I was as worthy a new owner as anyone given my history with it. So on a trailer it hopped, and home it came.

My dad, Paul and I as he says goodbye to it. He's probably regretting all the life choices he's made leading up to this point

Anyway, a very short revival and a couple of cobwebs dusted off, and I started using the truck. I hauled my dirt bike with it, screwed a few girls in it, and most importantly, dragged my boat to the lake with it.

So there's a background on how I came to own a childhood dream truck of mine. Sometimes things in life are just meant to be
Stay tuned for shenanigans!

 

[willis_racing]

Alright, mushy shit's out of the way. This thing is plagued with a litany of issues, mostly stemming from being built with junkyard parts 40 years ago by people who are probably dead now.

Here's what I found:
-The front suspension is unstable, and gets into a slow but very pronounced wobble/hop between 10 and 30 mph.
-Steering geometry sucks (push pull with not enough pitman arm drop)
-The rear lift is a combination of lift blocks and add-a-leafs. Axle hops pretty bad.
-The front uses old school Burbank lift springs that feel like the axle is welded to the frame
-Valve stem seals totally shot, engine is a leaky bastard.
-Fuel pump setup has trouble pulling fuel from the gas tanks once warm. It has vapor locking issues after long periods of driving if the ambient temp is much above 60
-It gets 5 mpg no matter what you're doing with it
And this is the biggie
-The TH350 leaked fluid by pushing ATF out from around the vacuum modulator Has a cracked output flange that was spraying fluid errywhere. A lot of fluid. While moving from my college town back home and pulling a pretty heavy load, it gave up the ghost on me and nearly caught the truck on fire because the leak was so bad. (Because the tcase was getting ready to fall off)
-The crack on the trans appears to have been caused by the tension rod that it supposed to run from the output side of the tcase up to the bellhousing being missing from the truck. To my knowledge, it was never present.

Current Build plan:

1. Transmission gets fixed first, since that's what's keeping it off the road currently. I didn't see the point in rebuilding the th350 since it doesn't have an overdrive and wouldn't stand up to my long term goals. So I'm swapping it with a moderately built 4l80e. Still going to run the NP203 for now.
2. Re-seal and take measurements on the engine while gearing up for the trans swap. Verify bore, stroke, compression ratio, and main bolt count.
3. Scrounge up a tcase support rod or build another crossmember for tcase support to prevent future issues.
4. Holley Sniper EFI. This will force a complete fuel system makeover that the truck needs anyway, and it'll make it much more drivable compared to a 750 double pumper.
5. Undo and pare down a bunch of jicky wiring
6. Fix steering via crossover conversion
7. Fix front suspension wackiness with a chev 52 swap for the short term. Long term I think I'd like to see links and coilovers.
8. Ditch rear lift blocks with a shackle flip.
9. Big gay ass pulling truck style traction bars in the rear

 

[rugburn]

Subscribed 🇺🇸🍺👍🏼

 

[Sterlingfire]

Will be cool! Keep us updated

 

[350TacoZilla]

Please donate that TH350 to a museum so that it can be immortalized since it lived behind a 468 big block for that length of time.

 

[72blazer]

What’s the plan for the TH350? Shoot me a PM if you want to part with it.



Cool build.

 

[willis_racing]

Subscribed 🇺🇸🍺👍🏼

Thank you sir

Will be cool! Keep us updated

Thanks and I'll try!

Please donate that TH350 to a museum so that it can be immortalized since it lived behind a 468 big block for that length of time.

Not just that but I towed pretty goddamn heavy with it too. The thing was an absolute trooper. Rest in pieces

What’s the plan for the TH350? Shoot me a PM if you want to part with it.



Cool build.

Thanks!
From what I was told it has quite a few good parts in it. It's pretty beefy for a 350. I hadn't really gotten that far into planning what to do with it, so I'll definitely entertain the idea, we'll talk once I clean it up and have it sitting outside the truck.

 

[willis_racing]

After the truck bit the dust in May 2020, I fucked around for awhile and ended up temporarily moving to Green River, WY for a few months over the winter. While there, I managed to procure an 01 4l80e for $200. It was listed as an "inop core return" at the local junkyard, and after getting it to the shop to break into it a little bit, I could believe it. The oil in this turd looked like I drained it out of a diesel tractor engine.

I ended up moving back home to NM with this thing in the trunk of my car in about this state of half disassembly.
I built a little trans rebuild stand out of 2x4s and disassembled it the rest of the way, then took to pressure washing and cleaning the case.

 

[willis_racing]

At this point, because I like throwing time down the toilet making the drivetrain pretty under an ugly truck for some reason, I masked and sandblasted the case, primed it, and painted it, along with a coat or two of clear. All rattle ccan, so we'll see how it lasts.

I realize that I haven't actually said what the build sheet is for this trans yet so I'll try to recall what all I did to it.

The main brunt of the mods in this thing came from a Rebuild Kit Stage 2 from Jake's Performance. Here's what that entails:

• All bushings, seals, gaskets, clutches, steels, bands, pistons
• Additional friction disc mod for direct clutch
• HD intermediate snap ring
• Billet forward hub
• Shift kit with accumulator delete plate
• Rollerized output bearing

Mods I ended up buying separately from the Jake's kit

• Sonnax line pressure boost kit
• Sonnax "no walk out" top hatted output bushing
• Summit racing 4340 input shaft rated for 1200HP
• Circle D torque converter ordered to suggested specs by circle D for my build plan

I spent the next 6 months or so off-and-on working on it in my spare time. Between trying to race dirt bikes in 2 different series and me being a half retarded baboon trying to build a piece of modified race equipment in a cargo trailer, progress was slow.

Damn picture limit...

 

[willis_racing]

And the finished product:

With the trans 90% assembled, next step was to drop the NP203 out of the truck and prep it for being mated to the 4l80, which included swapping the input gear to a 32 spline unit, and redrilling the face from figure 8 to 6 bolt round.

About this time I started the build on my 2 stroke woods race bike so progress got even slower
I believe I also said something on Facebook to the effect of "Just a quickie transfer case rebuild and we're in business" which was a stupid, dumb, stupid thing to say. Little did I know how much of a massive pain in the dick NP203s are to rebuild. I still break out into a cold sweat and hives every time I see unattended uncaged needle bearings.

 

[willis_racing]

Aaaaaaand about another 6 months later I made them bump uglies.

 

[willis_racing]

This brings us up to about 4 hours ago. Rolled the bastard into the shop last night, and then got back around to wrenching on it this evening, with the help of my trusty shop assistant

 

[willis_racing]

So uh, 72blazer I don't think you're gonna have much use for this one.

Rolled the chassis out to wash it up so it's actually tolerable to work on and found that pesky leak.

Looks like this thing's always been missing the support rod that runs from the side of the tcase up to the bellhousing. Wonder if just something simple like that would have been enough to cause this carnage after years of abuse. Either way, apparently jumping ship to a 4l80 was the right move.

 

['84 Bronco II]

I didn't know you knew your way around a tranny


I've got a C4 for you to build

 

[willis_racing]

I didn't know you knew your way around a tranny


I've got a C4 for you to build

I would highly suggest waiting around to see if this one functions properly before saddling me with that responsibility.
There are a few things I know of in there I'm likely going to have to go back in a second time and fix because I'm stupid and cheap

 

[rattle_snake]

In for a BGMT single cab long bed.

 

[willis_racing]

Tore into the engine today. Interesting updates!

1. these heads are 3993820 castings, and there are many like them but these ones are mine. They have a sweet polish job on both intake and exhaust, as well as the intakes being port matched to the manifold gasket!
   
2. Roller rockers, which I already knew about. They have USA cast into them and they seem pretty quality
   
   In this pic you can also see the home made tray over the lifters and pushrods. Anyone want to comment on what the point of that is? Keeping oil from falling down onto the cam and crank or...?
3. MLS Head gaskets!!! Didn't get a pic.
4. Unsure on what to make of these pistons. I have no reliable way to measure how far they are in the hole at the moment, so I'll try to cook up something a little better tomorrow.
   One thing that's real nice is they have ".030" stamped right on top of them, so it's not a 468, it's a 460. Clearly it just aspires to be as cool as rattle snake's truck.
   
   Here's what I'm wondering about on these. What's up with that chamfered ring around the outside of these pistons? You can look down into the bore and stare directly at the top ring. Quite interesting, haven't really seen that before. Again, anyone got any comment on that? (This is my first time with a BBC)
5. Here's where things start taking a bit of a negative turn. The bores are all pretty straight, not an appreciable amount of taper to be found, no ring ridge either to speak of, still some crosshatch left. Here's the big kicker though. Looks like that 10 years of sitting did cyls 1 and 8 no favors.
   
   
   
   
   To me this looks like some water sitting in the holes for quite some time. Sucks to see this as I'm really not willing to do anything about it other than hone it at the moment. Even then, would honing help this damage out at all? If not I guess it's just gonna stay put.

Ran some rough calcs with a little bit of what I know and a couple ASSumptions.

Naturally I find that shit compression ratio to be less than ideal. This thing always sounded pretty healthy, I would not have guessed a static comp that low based on how it sounded while running and how much torque it had.



In conclusion so far, I'm pretty confident in the stories about this motor running a blower are true. It appears to me to be pretty well set up for it, and it has some pretty nice parts on it to boot! Bore damage and static comp ratio SUCK though. Feel free to give some advice or ideas.
Tune in tomorrow for popping the oil pan and checking out what's going on with the spinny bits.

 

[350TacoZilla]

Nice part of low compression is cheap fuel. With everything done to it though I wouldn't rule out the block being decked at some point in life so it might be bit higher ratio. I would certainly try to hone the cylinders and see what you get, hard to say how good they will clean up till you do it really or if your there personally to see the damage. I know you can't do anything about it at moment but good part is it can always be bored more but can't be less so be glad its not already like .080 over or something.

Tray is to keep oil from slinging around a bunch, basically to keep it down towards cam and off bottom of intake. Dunno if they help anything but I can't see where it would hurt anything either so since you already have it keep it lol.

 

[SLOWPOKE693]

That lifter valley baffle isn't home made, it's probably a Moroso or similar. It's an old school speed trick to keep hot oil from splashing onto the intake manifold. Was supposed to help make HP by keeping the intake charge cooler.

 

[willis_racing]

Nice part of low compression is cheap fuel.

True, this turd drinks so much anyway, I kinda gotta take what I can get.

With everything done to it though I wouldn't rule out the block being decked at some point in life so it might be bit higher ratio.

Piston to deck clearance at TDC seems to be indicating otherwise. In fact they're farther in the hole than stock

I would certainly try to hone the cylinders and see what you get, hard to say how good they will clean up till you do it really or if your there personally to see the damage. I know you can't do anything about it at moment but good part is it can always be bored more but can't be less so be glad its not already like .080 over or something.

Big thanks for this advice and I'm glad I took it, found another little fun thing in there today.

Tray is to keep oil from slinging around a bunch, basically to keep it down towards cam and off bottom of intake. Dunno if they help anything but I can't see where it would hurt anything either so since you already have it keep it lol.

That lifter valley baffle isn't home made, it's probably a Moroso or similar. It's an old school speed trick to keep hot oil from splashing onto the intake manifold. Was supposed to help make HP by keeping the intake charge cooler.

Ah, that does make some sense heat-wise. probably was worth the effort with a blower manifold, but with the air gap, maybe not so much
I do agree with Taco though, It's not hurting anything, it'll likely go back in.

And yeah SLOWPOKE693 you're right, the baffle itself is definitely a bought piece, the pallet band retention system was throwing me off though

 

[willis_racing]

Upon opening up the bottom end, I was greeted by 2 bolts mains, cast crank, melling HV oil pump, and stock rods. I guess if all you're ever going to run is like 6psi at our high elevation, it's fine. Rods appear to be balanced though, so that's cool.

It also has this cute little windage tray/baffle thing. I like it. It can stay.

I also spent like 20 minutes fishing all of my valve guide seals out of the oil pickup.

Big thing here I'm actually pretty impressed with is that these pistons are smooth on all surfaces, no casting indications. I think they're actually forged. That's cool. Also piston #3 apparently had a broken top ring that hit the ground while I was popping it out. Sure am glad the "hone it and see what happens" option got brought up or else I never would have found that.

Scope creep is beginning to set in, I was hoping this would be way faster. Gotta do whatcha gotta do though. Anyway, from my findings here, I'm going to go ahead and run the hone and see how the bores clean up. If they come out good, great. If not, I'll have to see about finding a trustworthy machinist and bumping up a piston size. Maybe it'll be an actual 468 at the end of it. Or not because I told myself I wouldn't let this get out of hand. Fuck me.

Either way, as stoked as I am about the forged pistons, I found that they sit about .032" down in the hole, which from what I was able to find online is about 12 thou lower than stock. As it is, the thin head gaskets were the only thing keeping the quench distance respectable. If I go back to a stock compression height piston with a 10.5cc dome and keep using .020 head gaskets, that would put me right at 9.5:1 static with a quench of roughly .040". That's looking like a pretty decent, cost effective option to breathe some new life into this thing. Time will tell after the hone.

 

[350TacoZilla]

Decent cost effective option would be a $100 366 out of an old school bus lol. It's all on how much performance your looking to get compared to what it had before. If you were happy with the performance before finding out the compression ratio I wouldn't let it ruin your fun type of deal but it is really sounding like it was made from day 1 to be a blower motor so maybe down the rd you could bolt on one of the small 177 kits or something like that for a jump in power. For getting it back together the main thing is finding out if you can save the current bore as that makes the difference between a trip to the machine shop or no lol. Also see if you can figure out chamber CC's since the motor has obviously been built before they may not still be 113.
Thin gaskets and heads decked would give you a small bump in CR if your able to salvage the current bores.
If it does need bored out then your looking at new pistons anyhow so you can pick your poison for CR depending on what fuel your looking to use and HP level your shooting for.

 

[arse_sidewards]

Make sure you are absolutely anal about taking a dozen measurements per hole before you hone so you know exactly what shape each bore is and know where does and doesn't need attention.

 

[rattle_snake]

Tore into the engine today. Interesting updates!

1. these heads are 3993820 castings, and there are many like them but these ones are mine.
2. Anyone want to comment on what the point of that is? Keeping oil from falling down onto the cam and crank or...?
3. 
   
4. Clearly it just aspires to be as cool as rattle snake's truck.Here's what I'm wondering about on these. What's up with that chamfered ring around the outside of these pistons? You can look down into the bore and stare directly at the top ring. Quite interesting, haven't really seen that before. Again, anyone got any comment on that? (This is my first time with a BBC)
5. Here's where things start taking a bit of a negative turn. The bores are all pretty straight, not an appreciable amount of taper to be found, no ring ridge either to speak of, still some crosshatch left. Here's the big kicker though. Looks like that 10 years of sitting did cyls 1 and 8 no favors.
   To me this looks like some water sitting in the holes for quite some time. Sucks to see this as I'm really not willing to do anything about it other than hone it at the moment. Even then, would honing help this damage out at all? If not I guess it's just gonna stay put.

Ran some rough calcs with a little bit of what I know and a couple ASSumptions.

Naturally I find that shit compression ratio to be less than ideal. This thing always sounded pretty healthy, I would not have guessed a static comp that low based on how it sounded while running and how much torque it had.

1.Nice FMJ reference. You will be faithful!

2. Prevent splash and oil burning on bottom of intake. cooler intake. better upper oil control.

4. Is the piston crown really smaller than the skirt? Mine became a 466. Once you go BBC, well...

5. I would take the time to measure and remove assumptions on static CR. CC a chamber or two. If heads were decked, the chamber may be smaller. measure deck on a few holes, both sides. Is it .020 or 0.032? I don't think those piston are -10cc. Probably less than 5. I'd call them flat tops. You may be closer to 8.5

8-ish to 1 is low but matched with appropriate cam, it will be torquey and run on 87. but quench sucks at (0.020 or 0.032 + 0.035 (HG) 0.055-0.067.

Big thing here I'm actually pretty impressed with is that these pistons are smooth on all surfaces, no casting indications. I think they're actually forged. That's cool. Also piston #3 apparently had a broken top ring that hit the ground while I was popping it out. Sure am glad the "hone it and see what happens" option got brought up or else I never would have found that.

Scope creep is beginning to set in, I was hoping this would be way faster. Gotta do whatcha gotta do though. Anyway, from my findings here, I'm going to go ahead and run the hone and see how the bores clean up. If they come out good, great. If not, I'll have to see about finding a trustworthy machinist and bumping up a piston size. Maybe it'll be an actual 468 at the end of it. Or not because I told myself I wouldn't let this get out of hand. Fuck me.

Either way, as stoked as I am about the forged pistons, I found that they sit about .032" down in the hole, which from what I was able to find online is about 12 thou lower than stock. As it is, the thin head gaskets were the only thing keeping the quench distance respectable. If I go back to a stock compression height piston with a 10.5cc dome and keep using .020 head gaskets, that would put me right at 9.5:1 static with a quench of roughly .040". That's looking like a pretty decent, cost effective option to breathe some new life into this thing. Time will tell after the hone.

Well you need all new rings. May want to measure bore and see what piston to wall clearance really is. A forged piston meant for boost should be looser than a hyper if you replace with those.

if heads are closer to 108cc and you get pistons that are only 0.020 down you are at 8.9:1

If you bore, deck the block to 0.005-0.000 get quench to about head gasket thickness (0.45). This gets you to 9.1:1 or so.

I would bore/deck/hot tank block, new pistons/rings. Valve seals (check guides). money well spent. Compared to total cost of build it will only add around $600. fixed CR, better cylinder seal, more power.

 

[arse_sidewards]

I would bore/deck/hot tank block, new pistons/rings. Valve seals (check guides). money well spent. Compared to total cost of build it will only add around $600. fixed CR, better cylinder seal, more power.

The $500ish spent cleaning, decking and boring literally doubles the cost vs a "just replace all the wear items and re-use my rotating assembly and block" type rebuild

 

[rattle_snake]

Agreed but shit adds up. $200 in gaskets and fluids. $100 beer
Then maybe cam/lifters, fuel pump, water pump, oil pump, plug wires, cap/rotor, coil, MSD box, nitrous, fan clutch, motor mounts, belts, hoses and whatever else is needed as you dig in.
Not always a cheap hobby we have ourselves in.

 

[McBastard79]

Cool truck

 

[willis_racing]

Alright, update time.

No physical progress as of late, but I'm ordering parts and I've settled into a somewhat coherent plan of action.

First and foremost, I know I said I wasn't willing to do anything about the cylinder walls, but plans change, and I can't leave well enough alone. I ordered up a set of .060 over hypereutectics with a 10cc dome. This will put me right around the 9.5:1 range, and should give me a sweet quench distance. Pretty stoked. Bore/hone, installing new pistons, and polishing the crank is going to run about $500.

Currently looking at the lower duration model of the Comp Thumpr. .498" int/ .483"exh Dur @ .050" :227/241 107* lobe separation angle.
Not dead set on this one, but obviously there's something to be said for me for a decently low lift cam that's going to chop at idle and give me a lot of midrange torque with the close lobe sep angle.

No other changes coming to speak of. These few little changes should bring this thing up to a more respectable power level while I save up for the aluminum heads.


To explain out my long term engine plans slightly better, If I get around to it, I hope to make 1000hp with this truck one day, hence the somewhat gnarly transmission build. A goal that lofty is going to require more than this little 2 bolt 454 can give me. However, what it's more than capable of doing is making some fun,rowdy sounding, usable midrange torque that will get the truck back on the beach pulling my garbage through the sand where it belongs. I wanted this to be a quick and dirty re-seal without really cracking into the bottom end, but that flew out the window when I found the bore damage and broken ring.
In a few years, I'll throw a set of AFR 265 oval ports and a bigger cam in this thing to bump up the power potential, and keep having fun with it. Maybe I'll like that setup so much I never get around to buying an aftermarket block and a couple of turbos, but that's for future me to figure out.

I'll be letting you all know when I get the machining done and start reassembly. It's gonna be awhile. Might be so long I start on the frame work before getting that shit back. Damn covid world.

 

[350TacoZilla]

If high hp is your goal I would be getting splayed main caps installed while at machine shop and it will be stronger than a factory 4bolt main block. No real problem with 454 block unless your going for big stroke crank in future where tall deck would be preferred.

 

[rattle_snake]

IMO you still need to deck the block to get good quench. The idea is to push the mixture away from the edges of the cylinder, into the chamber.
A dome piston and the outer crown down 0.065 is not ideal.
See how much it adds to the bore/hone machine cost. Plus the deck will be flat.

That cam at 227/241 is a bit high in duration for a big heavy 4x4, IMO.