I got a 400ci block and I have been talking to my machinist about what I am going to have done. I am a little confused by the differences between them though.

From what I understand, the bore is larger on a 400, and you can put 400ci cranks in a 350 to get a 383 (minus .030 over i take it).

Also, the 350 is internally balanced and the 400 is externally balanced.

I know I will need to drill steam holes in my heads for the 400 block, but as I am looking around online to get an idea of what is available and the prices, I am confused.

It appears as though I need an actual "400" crank, and the pistons will also be slightly larger.

I am trying to price the cheapest (but good quality) rotating assembly kit I can find. I don't care much for more power at the moment. I just want to get this car back on the road. As long as it produces the same power as the stock engine did, I will be happy.

I found: https://www.motorpartscentral.com/Pr...tModelId=14969

and: http://www.usaperform.com/rotating-a...lat-p-439.html

Was about to check out Summit Racing. Can anyone else recommend any place else to buy the internals to rebuild my 400? Is a rotating assembly the best way to go or should I piece it together myself so I can choose exactly what I am getting?

Thanks much.

(This is my a 1990 Coupe by the way)

 

The 350 is a 4.00" bore x 3.48" stroke.
The 400 is a 4.125" bore x 3.75" stroke and has large main journals in the block.

So yes, the pistons are larger by an eigth of an inch.

The main journals on the 400 block are larger by about .200", so when you are shopping for cranks and see them specify 400 mains that means it is for a 400 block, regardless of the stroke of the crankshaft. The only way to put a 400 crank into a 350 block then is to grind the mains down to the 350 main journal size, which is what was done back in the day before all of the aftermarket cranks were available.

The other option for the 400 block is to use main bearing spacers which allows running a crank with 350 style mains in the 400 block.

You will definitely need steam holes in your heads.

Also note that the 400 block is a left side (driver's side) dipstick and you will need an appropriate oil pan, and also be able to accomodate the dipstick on the left side with regard to header flanges, etc. I run a block with a left side dipstick and it's no issue, just need to be aware of it.

And if you're planning on running the 153 tooth flywheel, have your shop check to make sure the block has the appropriate starter mounting bolt holes. Some 400 blocks are drilled and tapped for all 3 and will accomodate both types of startes, some only have the 2 starter bolt holes which only accomodates the starter for the 168 tooth flywheel, in which case you swap starters, or flywheels (depending on what you're plans are) or have the other bolt hole drilled and tapped in the block.

 

thank you. You clarified a lot for me.

 

 

I am wondering. Would a 400ci engine even increase the power at all if I left the chip and everything else stock?

If these are my stock engine specs:
Compression Ratio 10.00:1
Horsepower 250 hp
Torque 350 lb-ft

Then my HP/TQ per square inch would be .71/1 and 1/1, so by adding a another 50 cubic inches, as long as intake, heads and exhaust could handle the extra flow requirement I would get:
Extra 35HP
Extra 50TQ
For a total of 285 HP/ 400LB TQ.

That sounds waaayyy to easy though. I assume to even get half that improvement I would need better heads, intake and exhaust.

I am also trying to figure out the highest compression ratio my engine could handle if I use premium. if gas cost an average of 4.00 a gallon, and it's an extra 20 cents a gallon for premium, thats about an average 5% increase in cost for the gas. If you get about 4% or 5% increase in HP per compression ratio increase (like going from 10to1 to 11to1), then as long as that extra power translates into the engine not having to work as hard to go the same speed, and you get a 5% increase in MPG, then you would think it would be worth it right?

And if for some reason I put regular 87 octane in, would the computer just change the timing to compensate, lowering my power output?

I don't see any reason to not go with a slightly higher compression ratio as long as the engine is computer controlled to eliminate any detonation.

Any thoughts on this?

Oh, and one more thing. Do you think that doing a DIY port job on my heads and intake would be enough to support the extra 50CI from my block and give me a real 35hp and 50tq increase?

 

If you have Aluminum heads you can boost the CR up to 10:75-1 or really even 11:0-1 but you need to pay attention to the quench when doing this.

A good quench would be @ .045 with stock parts, tighter is better but with stock parts you have to be careful with not revving into the mid 6500 range to be safe.

My deck is .005 down and i use an .039 gasket

You could do a DIY port and have the valves backcut, which is cheap to do.