I am getting ready to put a 400 block in the machine shop to make sure it's good. If it is, it's gonna get built. I am curious as to anything I might need to know when swapping to a 406 from the 350. I am going with my HSR setup on it, so it will be fuel injected. However I've heard that these motors are very hard to keep cool. Anyone have troubles with this? I know the 700R4 will bolt up, however I believe I'm gonna build a turbo 350 for it. Also, can you use the MAF sensor if you have it modified? Or will it hold the hp...? If anyone has done this swap, any advice or anything I might need to know for this, please let me know. Thanks in advance.

 

they over heat for people that don't know about steam holes. what's to modify about the maf? what problem would it have holding any amount of HP?

 

What is this "hold"? A MAF counts air molecules, so the ECM knows how many fuel molecules to add to the air. It doesn't "hold" anything.

I had a 400 in my 83 car for a short while. I ran it with the stock L69 cooling system except for a Stewart water pump and a later-model radiator. I never really had any overheating problems with it. Of course if I had left it in there longer maybe I eventually might; it was only in there for about 12 years and 140,000 miles as my daily driver. I did however leave the A/C intact, and ran it pretty much continuously for 8 months out of the year, since I lived in the South at the time.

 

other then the external balance flexplate, the dampener and possibly a new starter if the flexplate is a diff size... its no diffrent externally... so you dont need anything special there.


if you put the steam holes in the head (also no big deal) it wont overheat.... my 400 stayed cool all year long, and i also was in the south in high90* summer.....

 

Ummmm the MAF doesn't count anything, it measures the volume of incoming air by heating a wire and measuring the change in temp of the wire and converting that to volts and sending it to the ECU

 

and it does this to get the MASS of the AIR FLOWING thru it.

and that MASS is the molucules hes talking about.



just like the coolent sensor doesnt tell me engine coolent temp... it just changes the resistance of some thermocouple depending on the tempature of the coolent its in...

 

One of the guys I race with has a 400 block, runs all day at Pocono with no overheating issues.

As was said, you need steam holes machined into your heads and most shops know exactly how and where they go.

 

carbed 400sb and it runs at 180-200 due to the new hd fan clutch no problems at all

 

The 400 SBC is externally balanced, so you will need an aftermarket flexplate or you can have the one from your 350 "unbalanced" to work on the 400.

You will need a starter that fits the staggered bolt pattern of the 400. The one from your 350 will not work as the bolt pattern is in a straight line on a 350.

As the others have mentioned, get the cylinder heads drilled for steam holes and you shouldn't have any overheating problems. I took my radiator in and had an extra row added, it is now a 3 core radiator. This might not be necessary, but it's nice insurance.

 

Buy a new rad, for your new motor. Even a stock replacement one with plastic tanks and aluminum core.
Get a new water pump too.

I scooped up a nice factory oil cooler from a pickup truck
for my 400. Cost =$0 a gimmie.

 

you could also use a GM 400 flexplate... or a factory replacement one.. doesnt ahve to be aftermarket.... they're cheap anyway though..



and some 400s (like mine) can use a starter that has the bolts go straight across.... im running a summit ministarter like that right now.

 

I believe what you are talking about is the MAF sensor, even with the screens removed, is supposed to be good for only 300 rwhp. If I'm not mistaken, the flow is only good for 670 cfm. A well built 400 will easily exceed that rwhp. I have a carb on mine. Maybe someone else can speak to the MAF's limitations.

 

This is what I was asking about. I've heard that people have had problems with their MAF not "responding" right after so much hp. And I plan on exceeding that hp rating of 300...at least I hope... I do appreciate all the replies. I didn't think there would be much difference other than it being externally balanced, which I knew. I had planned on buying a bigger radiator as well, just to make sure, plus I already have my dual fans wired together with a fan switch. Thanks again, and anyone who has anymore info on the MAF situation, please let me know

 

the block is tapped for both

 

The MAF setup will support alot more than 300hp. I'd be more worried about the intake manifold its attached to.

 

I'm going with the HSR setup, so I'm not too worried about the intake it's attached to. Thanks for all the replies.

 

madmax,
Will the MAF support 300 rear wheel horsepower or about 385 at the crank? Every publication that I have picked up about Mass Air Flow systems always sees this as the weakest link to big horsepower...especially because of the fact the aftermarket has chosen to not to support the L98 TPI in this area.

 

The MAF will flow somewhat more than that.

The problem is the combination of that MAF and the ECM it goes with. The 2 things together cannot measure more than 255 g/sec of air. That's about 300ish HP. But, that's not entirely relevant, because the ECM doesn't use the MAF mesaurement at WOT anyway.

For those of you who didn't do well in high school chemistry, there's a number called Avogadro's Number. It's about 6.022 x 10^23. It is the number of molecules contained in a mass of any material that is the same number of grams as the atomic weight of the atoms of the material. In the case of air, which is about 80% nitrogen with an atomic weight of 14 and about 20% oxygen with an atomic weight of 16, that gives an average atomic weight for air of about 14.4. In other words, 14.4 grams of air contains about one Avogadro's Number of atoms. So, 255 grams of air contains about 1.07 x 10^25 air atoms, about 20% of which (roughly 2.13 x 10^24) are oxygen. Since oxygen molecules are diatomic, that means that the MAF will accurately meter about 1.06 x 10^24 oxygen molecules per second.

So now that you know that, if you care to calculate the number of fuel molecules that can be burned by that much oxygen, you can easily determine the HP that the MAF can accrately meter, since each fuel molecule releases a certain specific amount of energy when burned. All you have to know is the heat content of the fuel (about 5.1 million BTU per barrel, for gasoline), the efficiency of your engine (roughly 35% for internal combustion engines like ours), and a whole bunch of conversion factors; and you can calculate nearly exactly how many HP you can get out of your motor before you max out the MAF.

However, since the MAF measurement is not used at WOT, it doesn't really matter how much it can meter under those conditions. All it has to do is to allow the ar to pass through it. The ECM simply injects a pre-programmed pulse width of fuel per distributor trigger signal, which you can set yourself in the PROM.

To my knowledge no one has ever observed a MAF "holding" HP. I'm not completely sure what that would look like; or what would happen if it decided to put it down; or how it would pick it up in the first place; or where it would store it. If anybody knows how it could do these things, please enlighten us.

 

I had a 400 in my 85 z it ran about 140 in 85 degree weather, I followed lingerfelters modifications to the block and head gaskets. some of the 400`s had a extra coolant port that sits right in the middle of the deck betwwen the two middle cyl`s, In his small block mod book it shows how to make the mod if your block doesn`t have it, you drill the block to 5/8 on both sides and also the head gaskets. this mod puts cool water right between the two exausht ports in the middle of the head. I used a bolt on counter wieght from jegs with a 12 3/4 flywheel with my 400, the 85 had a two piece seal, so I ended up using the original 305 wheel with the 408. I`ll send you the scan of the page of the mod if you want.

http://www.cardomain.com/memberpage/487725

 

Okay, I don't think that was really necessary was it? I was just using the term "holding". Forgive me for not being very proper, but everyone else seemed to understand what I was asking. Would "handle" the hp be a little better for you??

 

Not sure what type, location, and weight rating the "handles" on HP are, so a MAFs ability to "handle" it is undeterminable.

 

When you swapped to 400, did it make the car guzzle much more gas, if youre otherparts such as heads intake exhaust stayed the same?

 

but i am running a way bigger cam than i had in the 305

 

What excactly makes a car gussle gas if one use efi?

 

Gas mileage is comprised of many factors but the biggest is RPM. Motors are just big pumps and the less you pump, the more gas you save. A 302 obviously has a smaller displacement than a 400 but if the 302 is turning a 4:11 rear gear and the 400 is turning a 3:00 rear gear, the 400 will get better MPG's considering they both have the same transmission. EFI, tuned properly, will get better MPG's than a carb but still needs an overdrive or low numerical gears to get the best MPG's, if that's your goal.