what is the stock length of a 400 connecting rod?
can i use a 350 5.7 rod in a 400?what i want to?any benifits of running a 5.7 rod?
what about using a 350 crank in a 400?
what other crank can be used in a 400?

 

5.56 is stock rod length, any length up to 6" can be used, double check what you have, pistons and clearance issues. longer rods exert less side preasure and are belived, or known, to make more power. you'd need "spacer bearings" or bearing spacers to use a 350 crank in 400. any crank you use will have to have the 400s diameter on the mains. you will also need to be careful about balance issues and make sure all your parts match and are balanced the same.

 

ok so what the benifits of using a 5.56,5.7 or a 6.00 rod

 

5.565" rod = stock; benefits are it's cheap, it's designed to fit (no clearance issues), disadvantages are it's cheap, gives higher side loading on the piston, and the piston spends a little less time right around TDC and BDC.

5.7" rod = stock 350; benefits are it's often cheap, parts are plentiful, it gives the piston more dwell at TDC, reduces the side load on theistons; disadvantages are that most of them require a significant amount of clearanc grinding, and require thinner rings, narrower lands between them, or puts the pin into the oil ring, or some combination of those things.

6" rod = totally non-stock, pretty much a max effort kind of thing, gives the most possible benefit of longer rods, whatever those may be; disadvantages are that they always require all 3 compromises to the ring system, and pistons are automatically expensive.

What are you really asking? i.e. Where are you going with this?

 

i'm just exploring all my options when it comes to building this 406.were trying to do this with as little money as we can.
thanks for the anwsers.

 

You can use a 350 crank in a 400 with special thick spacer bearings for the crank, since the 400 crank has bigger journals. This, combined with a .030 over 400 block will result in a 377. Think of it as an upscaled chevy 302. It is a big bore/short stroke motor, which results in high revving capabilities. I am thinking of doing this to my engine. Note that you will need to get the engine balanced if you do this.

 

here's what i was thinking
406
400 crank
400 rods
flat top pistons
500ish lift cam
about a 270-280 duration
lobe sep ??????
a set of 350 heads
2.02-1.60 valves
160cc runners
64cc CC
1.5 RR's
single plane intake
750 cfm carb

this will be going into an 85 Cutlass that will be maily for the strip but driven on the street once in awhile.
where thinking about mating a 700R4 to this because of the steep first gear.not sure of what gear we are going to run,maybe a 3:73 or 4:10.
our goal is a to run in the low 13's to high 12's.

 

160cc runners???? Isn't that wayyyyy to little?

 

You will need to spend some $$$ on that 700 for it to live very long behind a 400 running in the 12's.

Lonnie

 

Yea, 160cc runners with a .5 lift cam won't work very well together. The small runners will give you nothing but low end torque, while that cam would be better suited to high rpm.

 

Trash the Th700r4. use a th350 and with the money you save
buy an aftermarket head of about 215cc port volume.

Most bang for the buck... The th700 is useless to ya at the track
no advantage and costs more.
A 400 with flat tops and 64cc heads will have too much compression ratio.
use 76+ ccheads with flat tops or dished pistons with 64 ccheads.

 

If you're not turning over 6000 RPM on a consistent basis, the 5.565" "short" rods will work just fine.

For insurance, add new rod bolts ( ARP are good and not expensive ) and then AFTER the rod bolts have been added, have the rod ends checked to see if they need to be resized. Wouldn't hurt to smooth out any casting lines on the rod with a die grinder, but that's just me.

Cam selection in a 400 can be hit or miss. I've had good luck with cams in the 270-280 Duration range. ( advertised duration ). A cam that can be "wild" in a 350 or even sometimes a 383, will sometimes seem ALOT more mild in a 400.

The heads are a factor too. What's the casting # of the heads you're using? 882's and 993's were pretty common on stock 400 engines, and when being used in a street / strip 400 that won't see much over 5500 RPM or so, they are not that bad at all. What you want with the 400 is to take advantage of it's natural torque advantage. You want the cam, intake, heads to work together, can come in around before 3000 RPM.

As for the intake, a single plane, such as a Weiand Team G, Victor Jr style etc, work well on a 400, and because of the extra cubes you already have, you can afford to give up what LITTLE low end you might lose over a dual plane for the gain you'll get on the top end.

As for pistons....the flat tops will give you around 11:1 compression ratio with 64cc heads, and a normal head gasket, BUT ... you can possibly get by with this on a strip type / weekend duty motor IF you run a LARGE duration camshaft...bigger than 280 or so....

The larger duration cam keeps the valves open longer, and this will help bleed off the extra cylinder pressure at idle / part-throttle which will in turn help reduce the possibility of spark knock.

Wouldn't recommend it though, it's a fine line to get the quench area just right, and the cam big enough to make it run good like this.

If you're on a budget, look for a set of 882, 487x, or 993 castings. Try to stay away from the later model castings ( early 80's ) some were very thing and prone to cracking.

Clean 'em up, get a good multi-angle valve job, get the valves backcut ( ask your machine shop, if he doesn't know what this means, FIND ANOTHER ) and they should flow fine for what you seem to want out of the motor.

With decent heads, a single plane, a good cam, headers, and a 650-750 cfm carb, you shouldn't have any problem pushing 350-375 HP and even more torque.

Hooking up will then be your next concern. And IMHO, the 700 is not the greatest choice for the 400. Not because it won't live, it will with some mods ( as ANY stock OD tranny will need ) but the LOW 1st gear will hurt you for traction at the strip, as will the big RPM drop between gears. Use a good 2004R in that G-Body. It's a STRAIGHT BOLT IN ( you have to shorten the driveshaft for a 700 ) and with some mild mods will hold up fine behind a good 400.


HTH

 

I have a .020 over 400 block with a 3.48 cam (thats the size from a 350.) wich is a 375CI motor.

I have an eagle crank with "400" size main bearings, but otherwise you would need thicker main bearings.

I am running 6.2 rods but I would do 6" if I did it again.
I am running really short skirted pistons and 12:1 compression, but it is an odd combo and easier to find a 6" rod and piston combo.
The reason is more torque, with the longer rod, but there is a debate running if the 6.2 rod holds low end power down.
I only have an hour on the motor so it is hard to say right now.

the reason for the 375/377 is a higher reving/faster revving motor.
so you need high flow heads to make the package work, or just go with a 400ci 3.75 (stock) crank if you want bottom end and don't care about revving.
If you want to turn 9000 this is the motor to do it but you will need hi flow heads and a roller cam.