TiNmAnTnTyTo

so i plan on putting an sbc 400 and a 700r4 in my 92 formula firebird and so my question is what kind of custom mount work do you have to do in order for it to fit right? any other issues i should be aware of? its carbd so no ecm or harness issues.

bradley23150

iTrader: (10)

An SBC is an SBC as far as external mounting points. It will bolt in just like a 305, 327, 350, etc..

zraffz

It is externally balanced. I do not know if it will clear the radiator support or steering properly. Physically the block and heads are the same size though. If their are any clearance issues you can simply get a internally balanced crank for $200 and solve the problem.

sofakingdom

iTrader: (1)

As said, it is a SBC (assuming of course that it's a Chevy 400); everything is the same externally.

It is "externally balanced". Therefore use a 400 crank damper and flex plate.

Since it is the same externally, it clears (or fails to clear) the EXACT SAME THINGS your 30 did/didn't. Everything is the same.

Changing the crank doesn't affect fitment.

TiNmAnTnTyTo

i appreciate everyones incite. i would rather stay with an externally balanced cranks o if anything goes wrong i dont have to rip apart teh whole block to fix it, but then again, i may have no choice if i have clearance issues although like sofaking has said, i also dont believe changing the crank affects fitment.. any other issues i should be aware of? keep in mind that this is going from a BOP setup to chevy if it even matters. im sort of new to the world of muscle.

sofakingdom

iTrader: (1)

Neither a 400 or a 700-R4 is BOP, so that's not an issue. In fact, unless somebody swapped it in, it wouldn't have a BOP motor anyway, as those were all long since discontinued by that time, and were never used in these cars anyway. Last year of the Pontiac motor was 81; last year of the Buick V8 was within a year or 2 of the same; last year for the Olds V8 was around 85 or so.

There's no reason why an internally balanced crank requires any different "ripping apart" than external, either more or less. That's not what it's all about. All it means is, you MUST use a damper and flex plate specific to the 400, can't use a 262.5 / 265 / 267 / 283 / 302 / 305 / 327 / 350 one.

Cerridius

I guess depending on the year of your 400sbc, the 3rd gen starter would not be able to bolt up... Thats the case with mine right now

gwarren007

iTrader: (1)

Bringing back an older post to clarify...


The starter in the picture is not a third gen "stock" starter, it is a mini starter (aftermarket). The stock starter would have offset bolt holes and would be able to bolt into place.

zenish

ive thought of doing this.will the 700r4 torque converter bolt to a 400 flexplate and crank?will the 400 oil pan clear everything including the crossover exhaust pipe?if not will the 305 pan bolt on to the 400 concidering the dipsticks on the wrong side?i have a 400 bottom end i may rebuild[scrapped the crappy heads and intake]using vortec heads.

sofakingdom

iTrader: (1)

You don't need a 400 flex plate, necessarily. You can use a 83-85 305 one IF you have the appropriate balance weight welded to it.

The starter bolt hole problem is FOR REAL. You CANNOT use a 12.8" (305 size) flex plate or flywheel without the hole Cerridius penciled in up there. The starter for 12.8" MUST have that hole, there IS NO magic starter that will sub for the lack of that hole.

HEre's a 400 block where I installed the hole in question.



You could possibly use a 400 flex plate (which would be for a Turbo 350), but it will be 14" dia which will move the starter about 5/8" outboard of where it is now which may interfere with the exhaust. Very risky. However it has the advantage of not requiring the extra hole or needing further balance work.

I STRONGLY suggest having the hole drilled and the corresponding flex plate made, as that GUARANTEES a trouble-free, 100% CERTAIN WORKING installation. Anything else you try, will probably bring you back here crying about "it doesn't fit what do I do now" at which time the answer will be, pull it back out and DO IT RIGHT. You MIGHT get lucky but in the real world, I wouldn't depend on it.

The 400 uses the same pan as any other driver's-side-dipstick block. Nothing special. Any pan from a F, G, or A body will work; ones from B (full-size) or trucks usually will not.

No your pass-side-dipstick pan will not work. Even more so, it will nto work because it's for 1-pc rear main seal, where 400s are all 2-pc RMS.

Yes you ABSOLUTELY SHOULD scrap the 400 heads and intake. Those are 2 of the 3 reasons that a stock 400 only put out 165 HP. Vortec heads are maybe not the "best" choice, but not a "bad" one either. If you put those on a 400 consider using a cam set up for nitrous but otherwise a little smaller than you think you should, as the problem they will cause is similar to what happens with the gas.

InfernalVortex

iTrader: (4)

Can you elaborate on this a little bit?

sofakingdom

iTrader: (1)

BIG intake port flow, BIG inches, LITTLE exhaust port flow.

Can't get more in until you get the used-up stuff out.

ryan.1e

if you are going to use the "vortech" heads i recommend drilling out the steam holes on a set of 305 heads. also, side note from experience, the factory third gen f-body exhaust manifolds will block off your dipstick tube. i used a set of flowtech headers and y-pipe.

spawnicus

i know im a little late on this thread, but i am currently doing this swap on an 87 formula, i have a SBC 400 out of a 79 C30, and seeing this starter problem got me wondering, why cant you just use the starter for the 400?, and shouldint you be using that starter anyway, i'm sure i need a higher torque starter to turn that 400 then my little 305 starter?

InfernalVortex

iTrader: (4)

Why on earth do you recommend using 305 heads? They may exist with the vortec intake pattern but they are not the same as the 906/064 vortec heads everyone knows and loves. They have a different, more traditional chamber design. Most of the benefits of 350 vortec heads are lost. Plus they raise compression, which is already a concern with a 383 or a 400 block and 350 heads. You're pushing the compression REALLY high for a set of iron heads. Plus the valves will be way too small on a set of heads that are designed for 300 cubic inches, not 400. 350 heads are bad enough in this regard, why choke it farther?

Edit: Are you just insinuating that he practice the drilling on 305 heads?

1gary

Capture the use of more cubes with appropriate aftermarket heads.The money is spent on overheads on all SBC's where the power is made.Otherwise why do the swap at all....

five7kid

iTrader: (14)

As stated, you can, but moving the starter farther outboard may cause interference with the headers.

The diameter of the flexplate has more to do with the torque to turn over the engine than the starter torque itself. If the 305 starter doesn't do the trick, the 400 starter won't be much better. A high-torque mini starter is more than likely required if you get into that situation.