Misunderstood Mopar tech 400, Thermoquad etc.

[The Professor]

I was thinking today about buying a mid/late 70’s Mopar to add to my collection and that got me to looking at the 400. I’ve read a few articles on it and think it’s got the makings of a really good engine.

I think it’s deeply misunderstood by a lot of Mopar folks and completely unknown to GM and Ford troglodytes. Most Mopar loyalists think of it as a “smog” engine and as such they discount it.

Looking at the 400’s specs like the bore/ stroke, rod ratio etc, it’s obvious to me it really can be quite the monster. It was burdened with a horrible cam from the get go hence its smogger reputation. It replaced the much loved 383 in a period where many thought that it did so because it was a weaker motor created to meet smog standards.

The 400 needs a real cam and some tweaked heads but the bore and stroke make for a quick revving engine. It has a 4.34 bore which is bigger than the 440 but its stroke is shorter at 3.38 vs 3.75. So it has the makings of a revy lil beasty.

The 400 was saddled with a small cam, a misunderstood carb (thermoquad) and a restricted exhaust, all things that are easily fixable. The heads are meh/ok but they can be woken up or better Mopar/aftermarket heads can be used.

Want a stroker? Put a 440 crank in it and you have a 451! Bore it 30 over and you are pushing 460 cubes of sweet Mopar justice! Add some 440 source stealth heads and a cam and your at 500 horsepower easy.

I use Hughes cams only, they are a Mopar only outfit and they understand that Mopar uses a 904 lifter that allows for a more aggressive ramp rate. Most cams are designed off of a Chevy grind so you are cheating your Mopar of free HP/TQ by not using a Hughes cam.

Anyway my opinion and 50 cents might get you a cup of coffee but there ya have it.

As always, Get Real….Get Mopar

 

[Geoff 2]

The short stroke 383/400 could have been a real screamer......if Chry had put some decent flowing heads on it.

 

[DanielSlocum]

The main problem w the stock 400 is the pitifully low compression ratio. Was advertised at 8.2,but doing the math reveals its actually only 7.7 .
Bringing it up to at least 9.0 really wakes it up. By the way,most stock advertised compression ratios are false and actually .5 to 1.0 ratio less.

 

[HawkRod]

Yes, awhile back the 400's were "discovered" and are recognized now to be a great building block (pun intended) for an excellent engine.

I have a 383 Road Runner. I took out the original, untouched numbers matching 383 to protect it and replaced it with a stroked 400 displacing 500 cubic inches, roller cam, . Back in the car, it still looks (mostly) like a stock 383 but it has torque galore. Awesome motor!

 

[Timmayy]

One of the things I remember hearing in my youth was that the 400 had thin walls and an overbore would cause over heating problems. Is this true or just an old wives tale?

 

[YY1]

I don't think so.

"Thinwall" casting was an engineering "improvement" but IIRC did not affect over boring.

If that were true, the 451 recipe wouldn't work.


The other issue most had was a pitiful final drive gear.

2.4x was pretty common as was 2.76.

I had a 77 400-2 from a van, and even with the 2 barrel, when I put it in my 70 Super Bee as a stand in engine, it screamed with the 3.55 gears.

The "problem" with 400 builds is finding pistons to get it to 9.x :1 that don't cost an arm and a leg.

BTW- if you don't over bore, and just use a stock 440 crank, IIRC you get a "444".

 

[bee71]

I had a 400 in my 76 Cordoba which was never going to be used as a street racer. It was very dependable especially when twice the water pump let go and sent the fan into the radiator. Both times I nursed it home and the engine was glowing when I opened the hood. Put it back together both times and it started right up. Nine years and over 200,000 miles I had to give it up due to MI winters and salt.

 

[BSB67]

I was thinking today about buying a mid/late 70’s Mopar to add to my collection and that got me to looking at the 400. I’ve read a few articles on it and think it’s got the makings of a really good engine.

I think it’s deeply misunderstood by a lot of Mopar folks and completely unknown to GM and Ford troglodytes. Most Mopar loyalists think of it as a “smog” engine and as such they discount it.

Looking at the 400’s specs like the bore/ stroke, rod ratio etc, it’s obvious to me it really can be quite the monster. It was burdened with a horrible cam from the get go hence its smogger reputation. It replaced the much loved 383 in a period where many thought that it did so because it was a weaker motor created to meet smog standards.

The 400 needs a real cam and some tweaked heads but the bore and stroke make for a quick revving engine. It has a 4.34 bore which is bigger than the 440 but its stroke is shorter at 3.38 vs 3.75. So it has the makings of a revy lil beasty.

The 400 was saddled with a small cam, a misunderstood carb (thermoquad) and a restricted exhaust, all things that are easily fixable. The heads are meh/ok but they can be woken up or better Mopar/aftermarket heads can be used.

Want a stroker? Put a 440 crank in it and you have a 451! Bore it 30 over and you are pushing 460 cubes of sweet Mopar justice! Add some 440 source stealth heads and a cam and your at 500 horsepower easy.

I use Hughes cams only, they are a Mopar only outfit and they understand that Mopar uses a 906 lifter that allows for a more aggressive ramp rate. Most cams are designed off of a Chevy grind so you are cheating your Mopar of free HP/TQ by not using a Hughes cam.

Anyway my opinion and 50 cents might get you a cup of coffee but there ya have it.

As always, Get Real….Get Mopar

Hard to imagine that any true Mopar enthusiast hasn’t know this for 40 years. In the early years, the piston was the challenge.

For the last 20 years, the 400 has been the go-to unless you’re going for original, or you already have 383 or 440 parts laying around.

 

[YY1]

Mopar 400 still gets talked down about as does the 360.

Still.

 

[Runcharger]

I bought several new 400's. They were a terrific engine stock (much better than the same year 440's). Because the 383's had high compression they had the reputation of being much better than the 400's but that wasn't a fair comparison. Back in the day when we got tired of street racing our cars we would go home and grab the trucks and race them. My 400's would stand up to 454's 460's and 440's. I don't recall good pistons being available for the 400, a set of pistons and some breathing mods would have made people forget about 383's altogether. All I did with my pickups was add a 4 barrel and dual exhausts and they responded well even without a camshaft and valvesprings.

 

[33 IMP]

Mopar 400 still gets talked down about as does the 360.

Still.

Possibly true..... but not by anybody that knows what's going on.

 

[lewtot184]

470!

 

[Virg464]

I have a +.030 bore, 400 in my 66 coronet, alum heads 10.5:1 CP, hyd roller cam that likes to be in the 3k to 6k rpm range and likes a lot of adv, with only miner tuning so far, foot barking, it jumps from 1500 rpm to 6500 right now! I think you would really like a 400 (408-ish), if you set it up right.

 

[YY1]

I wonder if the chevy 454 gets talked down as much vs the 427 as the Mopar 400 does vs the 383 and the 360 vs the 340.

gm pulled a fast one and didn't change the emblems to reflect the change from 396 to 402, or that would likely get talked down, too.

 

[33 IMP]

I wonder if the chevy 454 gets talked down as much vs the 427 as the Mopar 400 does vs the 383 and the 360 vs the 340.

gm pulled a fast one and didn't change the emblems to reflect the change from 396 to 402, or that would likely get talked down, too.

I'm not sure the 454 gets unfavorable reviews compared to a 427. There were definitely high performance versions of the 454 available, as well as WAY more 454s, than 427s. Both, in today's climate, are too small, and I haven't heard of a 396 being built for serious power in years, maybe a couple decades!
I think the comparable chevy would be the 400 small block. Never a high performance version, low compression, problems with overheating (supposedly). Yet the chevy boys love the 400 crank swap into a 350 block.
Anybody whose built a 400 properly, sbc or bbm, knows what they can do.
.

 

[YY1]

I'm not sure the 454 gets unfavorable reviews compared to a 427. There were definitely high performance versions of the 454 available, as well as WAY more 454s, than 427s. Both, in today's climate, are too small, and I haven't heard of a 396 being built for serious power in years, maybe a couple decades!
I think the comparable chevy would be the 400 small block. Never a high performance version, low compression, problems with overheating (supposedly). Yet the chevy boys love the 400 crank swap into a 350 block.
Anybody whose built a 400 properly, sbc or bbm, knows what they can do.
.

...but there are verifiable reasons for a sbc 400 to be "second fiddled" that don't apply to a Mopar 400 or 360.

1- no 4 barrel version ever offered. Not true of the Mopar 400 and 360.
2- oddball heads that don't interchange. The Mopar 400 does have different heads, but they are no worse than 383 heads and do interchange.

I'm NOT a chevy scholar, but those are the two that I know.

 

[BearDodge67]

...but there are verifiable reasons for a sbc 400 to be "second fiddled" that don't apply to a Mopar 400 or 360.

1- no 4 barrel version ever offered. Not true of the Mopar 400 and 360.
2- oddball heads that don't interchange. The Mopar 400 does have different heads, but they are no worse than 383 heads and do interchange.

I'm NOT a chevy scholar, but those are the two that I know.

Yes, overheating was an issue, and if you put the wrong head or head gasket on it without the "weep holes", the motor was doomed. and while you could put a 400 head on any other small block, and you couldn't take a set of 2.02 fuelies and put them on a 400. and while the siamesed cylinders did make them stronger, the weep hole made it a moot point.

Also, Once people realized you could do a crank/rod swap into a 350 and gain 33 cubes, and it was a nice, torquey motor and the 400 became like a Mopar land barge, you bought it as a donor. Most fun one I did was a S-10 Blazer,

 

[33 IMP]

I threw a set of brodix track 1's on a 406, without doing a thing about the steam holes. Ran with electric water pump and fan, never overheated.

 

[YY1]

I DO know the 350 gets talked down vs the 327, for basically the same reasons as the 360 vs 340.

I call it "mystique".

But the legions of 350 fans pretty much overpower the rabid 327 is way better than the 350 crowd.

 

[33 IMP]

....probably cause the "327s rev higher" is a myth. Nothing a 327 can do that a 350 can't, or a 350 probably better.
Just like a 340/360.
But you're right. "Mystique ".