jsanders

Ok, as some of you know I have in my possession a 400sbc that will have 350 vortec heads matched up to it. Through some reading I'm starting to wonder a few things now. I know there are differences between a 400sbc and a Pontiac 400 engine. I do know for a fact mine is a Chevy motor, so what I'm asking is. Will I have to modify my engine bay, motor mounts, or anything like that to get this 400 to go in to my 92 RS properly? Will this motor mate up to my 700R-4 without modification? Do I need to worry about my starter fitting on this block?

What I'm asking is this, what sort of things do I need to be looking at when it comes to swapping out my 305 for this 400?

sofakingdom

iTrader: (1)

No.

Yes.

Yes.



Have your machine shop add the hole that's circled in magenta, BEFORE putting the motor in, if it's not already there (won't be if the block is older than about 77 or 78). That's I believe a 73 400 block in the pic, that I drilled the hole in. NO starter can POSSIBLY work, if that hole isn't there, because a bolt in the inboard hole that IS there, down at the left end of the shorter cyan line, would have to go RIGHT DIRECTLY THROUGH THE MIDDLE of the starter drive. No such thing as some magic starter that will somehow not have its shaft and guts right where that bolt would be, no matter how many people who HAVE NEVER DONE THIS SWAP (yes some of THOSE are likely to post here with their infinite wisdom ) tell you what you want to hear. Anyone who tells you that doesn't know what they're talking about, no matter how attractive what they're telling you might be. Unless of course, you know where to go to get a bolt that has the middle section offset about ½" from the head and the threads. I used to, but that store (they also had the rectangular drill bits and the rear-end-gear anti-spacers that allow you to put 2 series gears on 3 series gears by taking space OUT) closed, and no place online has them any more.

You'll need the flex plate for a 83-85 F-body V8, and to have it "unbalanced" to the stock 400 spec, which is, if memory serves, about 25 oz-in directly in line with the dowel pin.

Cerridius

On the bolt hole that you drill how come you cant have all threads in the hole?

Apeiron

Starter bolts have a locating shoulder.

jsanders

Thanks for the info!

fireburdluvr85

id like to chime in here. i had a 74 caprice 400 in my 85 and never had any of these issues? i used the flex plate that came with the motor and bolted it directly to my 700. it had the offset starter for the engine. only thing that didn't work was the stock plastic cover. it got chewed up in seconds. also had to add spacers for the torque converter bolts. small washers if i remember. lasted me till i chopped it up 3 yrs later.

didnt read above clearly asking if he can use his starter.

why not just use the offset starter? i think i paid 35 new with a 1 yr warranty or something.

Apeiron

What exhaust did you use on it?

fireburdluvr85

me? i used some hooker headers i bought second hand. custom y pipe and 3 inch flow master system with 50 series muffler. you could use the stock exhaust if you had to but why? i just didn't think a 400 wanted the stock 2 1/4 y pipe. i make my own y pipes and weld them at work so i went ahead with 2.75 from 3" collectors to the single 3". flowed nice but woulda benefited from a better merge collector? i believe its called. i had roller rockers and some light machine work done. revved to about 6,000rpm then made some scary noises. really just enjoyed it cause the shaking of the car was rather intimidating to others...... put about 55,000 miles on this set up in 3 yrs and burned up 3 stock 700r4's. would love to build another but i would build it a bit stronger and more balanced with a bigger cam.

Apeiron

That'd be why.

LarryL

I used a 168 tooth flywheel. The stock 400 starter works. If the 153 tooth flywheel is used you must drill the block as above. I had a custom Y pipe made about $100.00 installed. The vortec heads work great. But if you run more than 470 lift cam, you will have to run LS6 springs and special retainers. If its roller. If flat tapet the 470 lift problem is still there.

fireburdluvr85

your saying the exhaust can interfere with the starter? i know i had to drop my y pipe whenever i burnt a starter. i thought they were all like that tho? i guess i learned something today.

Homer

iTrader: (1)

How is this accomplished? Is it something I can do, or can the machine shop do that? Why only those three years?

camarokracker

iTrader: (1)

wow.... It never ceases to amaze me how many times somebody asks about swapping to a 400 and everyone chimes in about redrilling for the starter and its a pain in the ***... etc etc etc... Have we forgotten how to just remind people to check instead of assuming there all the same... Oh and yes.. i have a 400 block in my car with an LT-1 starter for a 95 trans am.. with a 153 tooth flywheel for my manual trans... I didnt need to do any drilling or anything... the block is a 1972 400 4bolt main... I wish people would remember just because one person ran into this issue doesnt mean that there all like that.. Ok.. im off my soap box now.. carry on.

LarryL

You don't have to go crazy with this setup. As for trans jusy get a 168 tooth 400 flexplate bolt it on and use your stock 400 starter. The converter will bolt right up. As for the exhaust I did not like how close the Y pipe came to starter with the headers so I opted for a custom one. As for flywheel bottom cover the smaller one can be shimed to clear or get one on ebay. It is a stright swap no big deal. Only issue I had was cooling, but my stock 305 ran at 220 so I had it before the 400 install. I just pulled the electric fan and but old style fan runs off water pump, took the setup off 83 camaro. The dual electric fans did not cool, same as single electric fan. The car runs at 180 with A/C in florida. The 400 really likes the vette 2400 stall converter it makes a big difference. If you beat on it don't expect the 700 to last long. The stock one lasted me 2 weeks after that about 14 months per trans. But I was beating the H*** out of it. I don't beat it any more and this unit is fine going 3 years. I did my swap in 1 1/2 days myself. Pulled the engine and trans out together. Assembled engine and trans and dropped it in. Just watch the a/c box, it is a tight fit swinging the engine in with the headers bolted on.

sofakingdom

iTrader: (1)

Usually, by drilling holes around one edge.

You could do it, if you knew EXACTLY where and how much to drill out and could measure EXACTLY how much material you had removed by doing so, or could spin it up and see where you were. Otherwise, best to leave to the machine shop. I can tell you that it will take somewhere near about 10-12 ½" holes about ½" deep.

Because 86-up uses a 1-pc rear main seal, and the flywheel for that is different; 82 uses a 4-speed and I'm not sure the FW is the same; and 81-back uses a 14" FW, which won't fit in the 3rd gen bell housing.

Then you got lucky. Yay for you. Somebody who had the block before you, had already drilled it. It didn't come from GM like that because that bolt pattern was invented in about 77 or so; and if there's ONE THING I've learned about stuff like this, it's that the space aliens did not take a break from creating crop circles and Elvis sightings, and decide to visit a GM engine plant in the middle of the night, and randomly install "features from the future" into a few parts here and there. However some 400s starting in around 78 DID come from GM drilled. Which is why I always tell people things like

camarokracker

iTrader: (1)

Well all i can say is yay for you.. you would be one of the very few to actually mention about looking first instead of jumping to conclusions. Just about every post i see about this always seems to end up with the first reply post of "you have to do... its a pain in the ....." blah blah blah.. we dont seem to be much about helping people think around here as we are about jumping to conclusions and showing our asses... thats all im saying.. lets give advice and help... not a bunch of bs about it.... whos to say that by this point that 50% of the blocks have had the holes drilled.. and yes u mentioned it.. and you are one of the few that ever has from all the post i have read.. so... YAY FOR YOU...

Homer

iTrader: (1)

Here's mine. It seems to have an extra couple of holes, not the required one in question. I, for one, DON'T know what I'm talking about, that's why I'm seeking advice. I have an assembled block, 882 heads, cast iron Qjet manifold, oil pan, flexplate, balancer. Haven't opened it up yet. Want to get my ducks in a row first. Want to use my 700R4, year 1991. Since I have the 400 flexplate and rotating assembly, shouldn't I just use a 400 starter? What's the drawback to that?

sofakingdom

iTrader: (1)

Only, that it's a good bit farther out away from the crank, and larger besides; which makes for a problem opportunity with the exhaust which has to go right by there.

So yes, for an auto, you can just use a 400 flex plate; might need the converter bolt holes slotted slightly (bolt circle is just a little different, like a nice round metric dimension vs a nice round American one); but other than that, if whatever exhaust you use accomodates the starter way out in space out there, then you're good to go.

LarryL

You are going in all directions.
Setups that will work.
1.)400 flexplate 168 tooth,torque converter bolts to it. 400 starter. stock exhaust will clear.

OR

2.)older 350 or 305 flexplate 153 tooth and for 2 piece rear main seal(must be balanced for 400). If block has 3 holes for starter use your starter. If not you must drill. Torque converter will fit. Your stock exaust will clear.

Homer

iTrader: (1)

Thanks, guys. That makes more sense having it spelled out. I'll catalogue my build here once I start.

Later!