I'm gonna build a 350 or 400 this summer to replace the 305 in my rx7. what i was wondering is if I wanna add about 100-150hp shot of NOS what would be a better motor? 350 or 400? I know the 400 would have more piston surface, but also less sidewall width. I plan on doing just a good cam,headers,vortec or ported heads and intkae and carb with some NOS. just wanna know 350 block or 400? thanks in advance

 

long rod 400 oh yes indeed

 

you mean a 400 with 5.7 rods and the special pistons right?

 

correctomundo

 

the 6.0 inch rod and pistons will be the same price and better for the motor..........but the 400 will be more likely to detonate over the 350..no matter what try and get some aluminum heads.

 

where you getting the pricing for the 6 inch combo? what pistons?

 

Well it's not a combo as you might put it, but you can get the 6.0 rods out of summit for 572.00 (Manley) and the same price for a 5.7. You're gonna spend 4 to 500 on good pistons anyway so get the Wiseco (Summit) for 463.00. Anyway I was just trying to give the guy another suggestion. Sorry if I offended anyone.

 

If you plan on using a lot of nos, the 350 will be cheaper to keep stronger... the 400 is somewhat weak unless it has real expensive innards in it

 

lil qwik, I'm not offended at all, thanks for telling me all that you know. Its cool, however I think I have decided on a 350, because parts are cheaper, stronger block, etc. and I'm just putting this in my 84 rx7 to replace the stock 305 I have in it now. I'm gonna try to get about 500hp outta it, fun fun :-) thanks again everybody for your help

 

Yeap, parts are definitey cheaper and more common.........Good luck. That ought to be an awsome feeling with 500 in that little car. Later

 

Sounds like it will be a wild ride!! lol

I would have chosen a 350 over the 400 too.

Knowing what I know now.

I have a 6" 406 motor. :lala:

 

ya I'm gonna put pics of it on my website here next week, I'm putting in the new motor this summer,( then probably a rear end) :-) lol

 

Why is the 350 stronger than the 400? I was under the impression that the 400's were stronger because of the siamesed bores?

 

They have thinner decks and cylinder walls. Plus, the 4 bolt blocks are even weaker yet due to the outer main botls not leaving enough material outside of the journal.

 

try checking out this semi-new part # from federal mogul (TRW) for these 400 with 5.7 rod "dished top" (reverse dome) forged pistons for pressed or floating pin rod setups (comes with circlips). these are for my interim blower 412 testing motor (.060). with the (.030) you get a 9.78:1 compression on 64cc heads and 8.80:1 with 76cc's, hell even 58cc 305 and L98 heads (niether recommended) will only net you 10.38:1 sorry the pistons are dirty from the mock up for final block machining and the tops are mildly deburred for a little nitrous adder.

 

heres the pic