How much boost can a 2 bolt main 400 take, with the stock bottom end, and with 8:1 compression? This will be on the street so reliability is a major factor.

Digger

 

Theoretically you can put 15+ pounds of boost through a stock 400 with no problem.


But, that is only if a few things are and always stay perfect:

Fuel curve must not motor get lean or you will make piston paperweights.

Timing must never allow detonation or bent rods and more piston paperweights.

You must use a head gasket that won't blow out.

Don't ever (and I mean ever) attempt to rev the motor past 5500rpm.

Intercooled boost produces more power due to higher charge density.

Stud the bottom end and heads for extra protection.

I think it would be worth it.

 

what is the length of the connecting rods in your motor? 5.7 rod is a better choice here-technically speaking it will put a greater portion of the power produced over a wider spread of rpm-less "peaky" but i think what they do in terms of unloading some stress on the outer piston skirts and cylinder walls is the greater benefit. them short rods can scuff up cylinder walls something fierce-i agree with paul-5500 max and gear accordingly. set up your ring end gaps by hand

 

Dont go to anything over about 650hp/tq with that block with factory mains. You will yank the crank right out.

Id go 6" rods too. Less stress on the sidewalls that are already thin.

Plug the decks. (large holes in the deck)


I had a 400 block .030 over and I was running my vortech on it.
I swapped to the turbo and I didnt feel good about the block so i am in the middle of swapping everything over to the Dart Block now.

 

guido-what dart block are you going to be running? does it have a raised cam centerline? what is the displacement going to be when the thing gets finished, and finally-does the block utilize siamesed bores? when i built my 400 way back when everyone gave me poop about what a pile it was going to be, overheating and causing me troubles because of the siamese setup, but now i think most bowtie blocks are cast that way. and i have had no such troubles at all, and with a few lo-tech mods to the cooling system everything has been fine in the cooling system dept. the addition of the blower has increased the temps to more than i like to see which is saying that my margin of cooling capacity isnt there anymore so i am going to buy a be-cool asap. thx. frank

 

Like it says in my sig, im using the little-m. It is 406 cubic inches. It has the same dimensions as a SBC. Deck height. bore centerline, etc etc etc.

Ther major diffs are the oiling system. It sends oil to the mains first. It is simaessed too I think. It has a thicker deck on it as well.

It does not have a raised cam centerline however I think that it does have larger cam bearings to adjust for more radical cam combinations.

 

ah-i guess i was assuming that you were going to run 6 inchers in the new motor and i thought that starting at 5.7 rod length a couple rods would always contact a lobe or 2 on the cam and require clearance grinding on the big end and usually the top of a con rod bolt too. hence the cam c-line question.raising the cam fixes that "crutch" machining work. or do you know other ways around this problem,ways im ignorant of. and if you do -wouldya wanna share the info? sorry about all the Q's if its too much thats cool too and i understand keepin the combo in your head. t.i.a. for any help-frank

 

One question. How are you going to come up with 8:1 on a 400?

I would'nt run more then 10 lbs on a stock 400 block. Been there, done that. Ended up with #1 cylinder cracked.

 

I do have 6" rods

They cleared all the rotating components just fine in the factory block. I had to grind the **** out of the block to clear the pan rail and since it is internal balance, I had some problems inside too but it was all resolved with a file.

Ran flawlessly for a season. Came out as good as the day it went in.

They say I wont run into those problems with the Dart block but that remains to be seen.

 

I'm using the Dart Iron Eagle block for my SBC 427, which is the Dart version of the GM Rocket blcok. Dart actually casts and machines the Rocket block for GM. The Iron Eagle is the Dart block with the .391" raised cam, .800" spread pan rails (.400" each side). I also opted for the tall 9.325" deck, 400 mains, and BBC cam bearings.

I'm running a 4.00" stroke, 6.125" rods, and the pistons have a .300" upper ring land for good relaibility in my twin turbo application. To fit the 4.00" stroke crank, we didn't have to touch the pan rails at all. The bottom of the bores only required a small 1/4" notch to clear some ARP cap screw bolts in the Crower billet rods.

Naturally aspirated, the motor made 650hp/580 lb ft on pump gas. I recently replaced the JE's with some dished pistons to lower the CR from 11.27 to 8.3 and added 2 Precision PT-52 turbochargers. Running around 18-20 psi boost on pumpgas I'm looking at around 1200-1300 hp. If you're looking to go over 650-700, you'd be best served going with the aftermarket blocks - either the Dart or Rocket block.