4V carb on 2V manifold?

I'm thinking about using an adapter plate to install a 4V carb (a 575 Speed Demon) on my '71 Ford 400, which, of course, currently has a (350 CFM Motorcraft) 2V. My brother has the adapter to make the swap, but I'm wondering how effective it will be. I realize that the engine probably won't ever open the secondary throttle plates all the way, but I thought that maybe the smaller primaries may help with efficiency. 

Have you ever done this? Did it work? Will the 2V manifold flow enough air to allow this to make a difference?

Unless the current carb on the engine has problems, I can't see any advantage to doing this.  It will only flow what will fit through the two holes in the manifold.  You still can't fit 10 pounds of crap in a 5 pound bag.

In the CAM Falcon Wagon thread, they did a dyno run on a 289 with the 2v and 4v setups. Most of the difference was in the last bit of rpm. YMMV.

It looks as though you are looking for efficiency as opposed to more power from driving off of the smaller primaries as opposed to the two barrel. I understand your thinking, but I doubt you will see any gains that would be worth the trouble. 

I would swap a decent aftermarket 4 bbl manifold on instead. 

Speed demons are not known for their efficiency.  The only thing I could imagine helping you would be a Qjet or thermoquad, but adapting a spreadbore carb to anything is never a good idea.  The transition from the tiny primaries to the big holes in the adapter causes real velocity variations and the fuel doesn't stay suspended well.

The 75 400 is also really a wheezer.  Compression is around 8:1, the cam is something like 185 degrees of duration, and the head ports are pretty small.  Going bigger with a carb is not going to get you what you want.

If you want efficiency, try re-doing the timing curve.  It probably uses ported vacuum which you can switch to manifold and re-curve the rest of it.  Have it all come in by 3000 rpms and shoot for a total mechanical of 36*.  Or, the easy button there is to get an MSD spark box.  Doing that should let you trim down the idle circuit (which is still active during throttle open) and save you a wee bit of fuel.

The only carb I would switch to would be a Qjet.  They are really the only design out there that is truly "uses what it needs" kind of thing.  They were used in 750 and 800 cfm variations on everything from a 3.8L V6 up to a Caddy 500 and still passed emissions tests as late as 1989.  The tiny primaries do wonders for throttle response and part throttle torque.  BUT... I would never put a Qjet on anything but a 4V spreadbore manifold.  No adapters.

I do recall doing some experimenting with the Varijet.  Rochester did two variations of 2bbl carbs:  A dual jet which is like any normal 2bbl carb, and a Varijet.  The Varijet was like the left or right half of a Qjet with one small primary and one larger secondary.  The problem is that its only about 285 cfm.

Check out some Holden forums.  Some of those guys do two Varijets which effectively gives you about 525 cfms worth of Qjet-like performance.  Lots of complexity, but effective.

Oh... and don't ditch the EGR.  It only helps.  It doesn't affect power since it only operates at part throttle, but it allows for leaner cruise mixes AND more spark advance so it helps mpg.

Stage one is timing curve re-do.  Stage two would be a head swap to get closer to 9:1 and a mild cam to tailor it to the cranking compression.  Say, 195-205 intake duration?  THEN, Qjet.

I don't think that any Ford 400 made over 200 net HP.  I would keep the stock carb and maybe play with the jetting slightly if you're trying to get it to run a bit better.  A good exhaust and a really solid ignition system is probably going to be more useful than a carb swap on an otherwise stock Ford 400.  

noddaz said:

Unless the current carb on the engine has problems, I can't see any advantage to doing this.  It will only flow what will fit through the two holes in the manifold.  You still can't fit 10 pounds of crap in a 5 pound bag.

Not to be contrary, but yes you can. You just have to compress the crap first.

To the OP: Add boost.

Boost. Hmmmm. 

How much is 260 gross horsepower in net horsepower? 

The '71 400 ain't the worst engine ever. 9:1 compression, straight-up cam timing, no EGR or cats. The carb would be part of an incremental build, with the goal being to improve towing performance and efficiency, with a roller cam with a low-end/midrange torque grind, a tight torque converter, a little 4V carb, a 3" exhaust, and maybe some long-tube headers.

I've been playing with rhe timing already, trying to push it as hard as I can, without any spark knock when towing up a long hill. 

Here's what I have learned about the cam, from looking at the shop manual and doing math. 

We ran a smogged up 400 in our LeMons car before switching to a 460.  The 460 is better in literally every way.  

That said, the 400 isn't the most boat-anchory boat anchor on the planet.  Curtis is bang-on, as usual.  I would add  that the old motorcrap carb (which we also ran) can be ported and polished up to work rather nicely.  We ditched the choke on ours, too, to pick up a few extra CFM.  

And add a dual exhaust, if for nothing else than so that it sounds like a real American pushrod V8 instead of an Electrolux.  

We did ditch the EGR, but this was for racecar, so mpg wasn't much of a concern, nor was part-throttle or idle operation.  I also recall the EGR setup being very clunky and not likely very effective (especially after 40 years).  The EGR plate did, however, make a very nice carb spacer for the 2 bbl once we epoxied off all the EGR ports and smoothed it out.  

I recall 4 bbl manifolds being not terribly plentiful for these things.

Also, I have heard (but not actually proven myself) that Cleveland heads (specifically, the good 4V ones) will work on these engines with some modification.  Again, whether this is actually worth it, versus just swapping in a 460... 

Seriously, just swap in a 460.  You can buy a good running 460 that will make more power right out of the gate than what you'd spend to hop up the 400, and you can do the swap in a day.  It'll bolt right up to the same C6 trans as the 400.  

The ports on the 400 engine are not bad. Down under they cast Cleveland heads with the same small intake ports but better flowing exhaust and those heads were then imported by Ford guys who wanted better performance from their Cleveland V8's.  I remember the 400 I had as a good engine to move 4000+ bls of Ford Galaxie 500 around quite well and it would get up to 20 mpgs on the highway if you kept the speed below 65. Remember the national speed limit was 55 back in those days.

A cam change, milled head and better exhaust along with a recurved dist. advance would really wake up that beast and I would keep the 2 bbl if low to med. speed performance is all that's desired.

I accidentally read the OP as a 1975 motor... apologies.  A 71 would have more compression but not sure how much.

Gross-to-net conversions are really difficult to pinpoint, but a safe guess is 20%.  So a 260hp gross rating is likely around 200 SAE net hp.

From those .005" numbers, I would guess you're in the 195/208 duration range at .050" lift.

I will also echo Volvo's suggestion.  A 460 is a mighty fine motor, and you might be able to find a complete running motor for less money than the mods you planned.  Where my memory gets hazy is if the 400 has the BBF trans pattern or the SBF pattern.  That's the difference between a bolt-in swap and having to also getting a trans.

Our leMons car was a 400.  We swapped in a 460- the C6 bolted right up.  400 and 460 have the same bellhousing bolt pattern.  Engine mounts were pretty straightforward, too.  The main thing is to make sure the 460 has a "car" type oil pan (front sump).  Most 460's you will find came from trucks, which have an oil pan which won't work with the crossmember in your car.  Need to swap the oil pan and oil pump pickup.  I have bought used pans for $25 and the pickup is like $15 new on Rock Auto.  Or, you know, find yourself a car 460 and it's all ready to go.  If you get really lucky and find a pre '72 460 it'll be a pretty hot engine- 365HP gross or something.  Nearly 500 lb-ft of torque.  

Ford did a lot of weird things in the 70s...there was a 351W (Windsor, small block) a 351C (Cleveland, mid-size block) and 351M (Sort-of like a Cleveland, but a modified big block).  The 400 is the same block as the 351M.  There was no such thing, officially, as a "400M", though some folks call it that because there was a 351M and it was the same block.  _some_ parts from the 351C and 351M interchange, or are pretty close; others do not.  

Here's what our 460 sounds and runs like...

https://youtu.be/UbRBBbKWy_k

It's a 30,000 mile engine from a 1985 E350-based RV, with 429 flat top pistons, a cobra-jet cam (Thanks, noddaz!) a straight-up timing set, windage tray, some exhaust port work and a few other little tricks I'm sure I'm forgetting right now.  With a 3.50 9" rear with posi it'll boil both rear tires (Which are sticky racing tires) from rest, no brake stands or neutral drops required.  

Another trick I recently learned- look for a torque converter from an RV.  Apparently they're more stout.  

Curtis said:

I will also echo Volvo's suggestion.  A 460 is a mighty fine motor, and you might be able to find a complete running motor for less money than the mods you planned.  Where my memory gets hazy is if the 400 has the BBF trans pattern or the SBF pattern.  That's the difference between a bolt-in swap and having to also getting a trans.

The 351M/400 share the same bolt pattern as the 385-series engine (429/460). Although 90% of 460s that you find are also going to be low-compression, open-chambered, mid-200hp wheezers as well, and require some breathing on. 

You want complicated? 

Hand cast intake manifolds for each set of 4 carbs, aluminum polished bright.  Pretty sure the fuel rails are manifolds off a gas cooktop.  The dimples on the valve covers are spoons brazed on to clear the rockers, exhaust that exits the fenders in front of the doors is a big chrome pipe you could stick your head in.

Long tubes and a 3" dual exhaust on a torque motor?  Seems excessive.  These motors are also supposed to be somewhat detonation prone.

I think I'd rather find a much more recent 351W to build.

That took way longer to go full 460 swap than I thought it would.  

Why am I keeping the 400? First, the 4" stroke of the 400 (actually 402 CID) is longest of any Ford engine until the 5.4 Mod Motor came out.  It also has really long rods, somewhere in the 6.75" range.  Both of those say "torque" to me.  The heads aren't horrible, and it has the "canted valve" design of the Cleveland, and 2" valves.  The 400 is 200 pounds lighter than the 460, and I already bought and installed new Detroit Spring front springs for a 400.  

The 400 is known to be a little detonation prone. This is mainly because the pistons are .060" down in the bore, which was Ford's way of getting the compression down to 9:1. There are pistons that are zero-deck, with a little dish to maintain 9:1 and have better quench. I was thinking about trying to stroke the motor to get up to zero-deck, but that would be pricy, and end up with a ton of compression.

400s can be built to make 450 ft-lbs of torque pretty easily, and a '71 400 is more up to the task than later ones.

snailmont5oh said:

That took way longer to go full 460 swap than I thought it would.  

Why am I keeping the 400? First, the 4" stroke of the 400 (actually 402 CID) is longest of any Ford engine until the 5.4 Mod Motor came out.  It also has really long rods, somewhere in the 6.75" range.  Both of those say "torque" to me.  The heads aren't horrible, and it has the "canted valve" design of the Cleveland, and 2" valves.  The 400 is 200 pounds lighter than the 460, and I already bought and installed new Detroit Spring front springs for a 400.  

The 400 is known to be a little detonation prone. This is mainly because the pistons are .060" down in the bore, which was Ford's way of getting the compression down to 9:1. There are pistons that are zero-deck, with a little dish to maintain 9:1 and have better quench. I was thinking about trying to stroke the motor to get up to zero-deck, but that would be pricy, and end up with a ton of compression.

400s can be built to make 450 ft-lbs of torque pretty easily, and a '71 400 is more up to the task than later ones.

 

According to this, the 460 is only 100 lbs heavier than a Cleveland.

http://www.gomog.com/allmorgan/engineweights2.html

And I think the 400 is even a bit heavier than a Cleveland.  They are a different block, and the 400 was basically Ford's way of making an engine with enough torque to move a big pile of Nixon-era American pig iron down the road with some modicum of alacrity, while still meeting emissions.  

Stick an aluminum manifold on the 460 and you'll only be 50-60 pounds heavier than your 2V 400.

Long rods are nice, but still, a "built up" 400 as you're describing only barely makes the torque of a fully smogged out 460.  

A long time ago, I had the idea of building up a hopped-up slant six for a Dart.  Not turbo, mind you, but all the Super Six stuff and then some.  Then a mechanic friend of mine pointed out that I was going through all that work...to basically end up with the power output of a bone stock 318, which would swap right in.  

But hey, it's your car, and if you want to stick with the 400, we'll help you out.  

snailmont5oh said:

That took way longer to go full 460 swap than I thought it would.  

Why am I keeping the 400? First, the 4" stroke of the 400 (actually 402 CID) is longest of any Ford engine until the 5.4 Mod Motor came out.  It also has really long rods, somewhere in the 6.75" range.  Both of those say "torque" to me.  The heads aren't horrible, and it has the "canted valve" design of the Cleveland, and 2" valves.  The 400 is 200 pounds lighter than the 460, and I already bought and installed new Detroit Spring front springs for a 400.  

The 400 is known to be a little detonation prone. This is mainly because the pistons are .060" down in the bore, which was Ford's way of getting the compression down to 9:1. There are pistons that are zero-deck, with a little dish to maintain 9:1 and have better quench. I was thinking about trying to stroke the motor to get up to zero-deck, but that would be pricy, and end up with a ton of compression.

400s can be built to make 450 ft-lbs of torque pretty easily, and a '71 400 is more up to the task than later ones.

 

I agree with everything you say, except the torque/stroke part.  It is a long-debunked myth that long strokes make more torque.  Displacement makes torque.

For instance, if you set up two otherwise equal (flow, cam, compression, etc) Olds 455 and Buick 455 motors, they will make the same torque and horsepower at the same points regardless of the Olds' 4.25" stroke versus the Buick's 3.9" stroke.

In fact, the long stroke-per-displacement only ends up hurting hp potential (not that high hp is your goal, just speaking to this issue specifically).  Small bores mean smaller valves and/or more valve shrouding.

That isn't to say that your 400 isn't a wonderful choice for what you're doing, just speaking to this particular part of the discussion.

Another point to this (if you're tearing into it for pistons), always try to achieve your compression target with flat tops.  Domes kill flame front speed, dishes kill quench

Curtis said:

snailmont5oh said:

That took way longer to go full 460 swap than I thought it would.  

Why am I keeping the 400? First, the 4" stroke of the 400 (actually 402 CID) is longest of any Ford engine until the 5.4 Mod Motor came out.  It also has really long rods, somewhere in the 6.75" range.  Both of those say "torque" to me.  The heads aren't horrible, and it has the "canted valve" design of the Cleveland, and 2" valves.  The 400 is 200 pounds lighter than the 460, and I already bought and installed new Detroit Spring front springs for a 400.  

The 400 is known to be a little detonation prone. This is mainly because the pistons are .060" down in the bore, which was Ford's way of getting the compression down to 9:1. There are pistons that are zero-deck, with a little dish to maintain 9:1 and have better quench. I was thinking about trying to stroke the motor to get up to zero-deck, but that would be pricy, and end up with a ton of compression.

400s can be built to make 450 ft-lbs of torque pretty easily, and a '71 400 is more up to the task than later ones.

 

I agree with everything you say, except the torque/stroke part.  It is a long-debunked myth that long strokes make more torque.  Displacement makes torque.

For instance, if you set up two otherwise equal (flow, cam, compression, etc) Olds 455 and Buick 455 motors, they will make the same torque and horsepower at the same points regardless of the Olds' 4.25" stroke versus the Buick's 3.9" stroke.

Its funny that you use the Buick as the example, because of all the big GM 454/455 engines, it had the shortest stroke but made the most torque, eclipsed only by the Cadillac 500. It's not just displacement, either. Cylinder head design plays a large part too. Chevy 454s had those large rectangular and oval ports that moved a ton of air but gave up some velocity at lower engine speeds, killing torque down low but building more power up top. Meanwhile, Buick, Olds and Pontiac all used tall, skinny ports that had a ton of low-speed velocity but choked up top.

Also, rod ratio is one of those things that a lot of leading engine builders are saying is pretty much irrelevant these days. I know that one of the top racing engines, Pro Stock perhaps, have terrible rod ratios but have no real issues. If you go way too far off or are making a crazy high-winding naturally aspirated engine that is being run at top speeds for long periods of time, perhaps, but by and large it has no real effect. It's just one of those things that people got spouting years ago and has long since been cemented as a "fact".

NickD said:

Curtis said:

snailmont5oh said:

That took way longer to go full 460 swap than I thought it would.  

Why am I keeping the 400? First, the 4" stroke of the 400 (actually 402 CID) is longest of any Ford engine until the 5.4 Mod Motor came out.  It also has really long rods, somewhere in the 6.75" range.  Both of those say "torque" to me.  The heads aren't horrible, and it has the "canted valve" design of the Cleveland, and 2" valves.  The 400 is 200 pounds lighter than the 460, and I already bought and installed new Detroit Spring front springs for a 400.  

The 400 is known to be a little detonation prone. This is mainly because the pistons are .060" down in the bore, which was Ford's way of getting the compression down to 9:1. There are pistons that are zero-deck, with a little dish to maintain 9:1 and have better quench. I was thinking about trying to stroke the motor to get up to zero-deck, but that would be pricy, and end up with a ton of compression.

400s can be built to make 450 ft-lbs of torque pretty easily, and a '71 400 is more up to the task than later ones.

 

I agree with everything you say, except the torque/stroke part.  It is a long-debunked myth that long strokes make more torque.  Displacement makes torque.

For instance, if you set up two otherwise equal (flow, cam, compression, etc) Olds 455 and Buick 455 motors, they will make the same torque and horsepower at the same points regardless of the Olds' 4.25" stroke versus the Buick's 3.9" stroke.

 It's not just displacement, either. Cylinder head design plays a large part too. 

Very true, there are a few million factors in how an engine makes torque.  I tried to take that out of the equation by saying all things equal.  As in, if there were a way to bolt Buick heads to both the Olds and the Buick so that it were an apples to apples comparison, they would make the same torque curves.  Incidentally, the Caddy 500 and Buick 455 are my favoritest engines ever.

The real difference is HP potential (not important to the OP).  Small bores means small breathing.  Long stroke means lots of reciprocal inertia  Doubling the stoke squares the tensile loads on the rod, pin, and piston.

There is actually some power to be tuned in rod/stroke ratios having to do with piston dwell and the angle the rod meets the crank journal.at different points in the rotation.  Peak force on the crank happens at about 20-30 degrees ATDC.  Tuning the rod/stroke ratio with a shorter rod puts the most effective angle sooner in crank rotation... which puts it closer to peak cylinder pressure