I got a 1985 Iroc and I am planning onbuilding a new motor for it.


My question is, should I build a 350 small block or a 400 small block. I want something for light to light acceleration and decent highway cruising.


Also wut would be a good trans and rear gear set up???

 

400's are torque monsters and perfect for light to light action. I'm building a budget 406 with Vortec heads, Comp XE274 cam and Performer RPM intake. CHP just did an article this month on a buildup very similar (a little less duration on the cam, 230/230 instead of my 230/236) and it made 525 tq. and 428 hp. Very impressive if I say so myself. If you do build that up a T56 will be needed to handle that power. You can temporarily use a T5, but it probably won't last long. Otherwise you could also use a 700r4 or th350 if you like autos. For the rear you'll need good strong gears like Richmonds, probably between 3.23 and 3.73 (I'm going with 3.73's). A heavy duty posi unit will be needed as well as forged axles. Auburn, Zexel, Eaton all make good posi units. You can get forged axles from Moser Engineering. Slicks are not allowed with this setup as the first time you hook you're rear will blow up with that much tq. The trick is not to be able to hook hard so street tires are reccomended.

This is the setup I'm going with. It's gonna be a beast. Hope this helped, and if you have anymore questions, let me know.

 

thanks for the input, any other opinions?

 

Bigger is always better

 

compromise and build a 377

 

I suggest using a tough 4 speed (ie. T-10) or a strong auto like a TH350 or TH400.

For rear ane gears, i'd suggest anything between 3.23 and 4.10

 

Or you can use a G-Force T-5 tranny. I just found out about them the other night, and they're an awesome tranny. They can hold like 600 hp with slicks and a moderate clutch. It's also cheaper than a T56 swap because you don't have to get all the parts off a donor car, everythings already there. This is the option I'm going with.

 

Were can I find out something about those G-Force trannies?

 

Right here...
http://www.g-forcetransmissions.com/default.htm
I just found out about them last night, they sound pretty good. I emailed them for some more info and haven't gotten a response back yet, but when I do I'll post that up.

 

What is a 377???? A punched out 350 or ????

 

It's a "destroked" 400. What are you looking to spend and what kind of mileage do you want? I have a friend with a 400 and I have a 383. They're good motors. But seriously ask yourself if you need the bigger motor. If you don't care about being faster than people, go with the 350. If you can afford it and want it, go with the 400. Just make sure you're not going to be kicking yourself down the road for building a bigger motor than you need.

 

Bigger motor than you need?? I don't think that exists .

Don't destroke a 400 (terrible idea) but if you do destoke it to a 350 (327 crank) the 4.125 bore on a 3.25 stroke is a great hp engine not he best for torque but still fun.

Later, Garrett

 

Motor too big????
To quote a song:
"It's like a girl too pretty with too much class, being too lucky, a car too fast, no matter what they say I've done, I ain't never had too much fun..."
But seriously, I'd build the 400. As long as you can keep your foot out of it all the time (which will be hard when you have that much power) you'll get decent gas mileage.

 

OK the singer is Daryle Singletary and the name of the song is "Too Much Fun"

And the 400 gas mileage is true, I got 17 mpg with a 406 a Holley 750 carb. putting out 383 horse and 456 torque. You just have to know how to drive one.

Later, Garrett

 

Thanks for helping me out on that one, I couldn't remember who sang it.

 

i've got a 400 thats almost done. mild cam, exhaust, stock heads (yeah, i know, but i'm a broke college kid), th350. biggest problem i'm going to run into at the moment is the fact tht i'm going with tbi for the time being. gotta do lots of programming (which i have yet to learn, no time). but this engine should be nice to play with

 

I think I'm gonna go with the 400, will any of the parts off of my 350 bolt up to the 400???


THanks

 

The carb, intake, headers, etc. will work, however you might want a bigger carb/intake, etc for your combo.

 

if you are going to go with the 400 then go buy this months issue of Chevy High Performance. and also, it costs about the same to build a 400 as a 350. if you dont beleave me, then add it up yourself. im going to build a 400, the same as CHP's, only difference is i got my 400 and the whole car for $100. and i'm going with the t-56 cause there is 6 gears, better gas mileage on the road(at least in theory).

Good luck,
Ryan

 

Are 350 heads the same as 400 and if so can I put a TPI unit from a 350 on a 400?

 

Actually most 350 heads flow better than 400 heads (maybe even the swirl ports!). They were pretty crappy, 400's w/ stock heads put out like 160hp. The only thing different about them is that 400 heads have the steam holes drilled in them, but that's easy enough to do to a set of 350 heads. You just get the 400 head gasket and mark the holes, then drill them at a 45* angle, IIRC. As far as using stock TPI on a 400, don't. It's barely enough to feed a 305, let alone an extra 95 cubes. If you want to go with fuel injection I would suggest a MiniRam, StealthRam or something of that nature (I'm not a FI guy, so can't really help you out when it comes to that). Accel also makes a nice DFI setup which I've heard good things about, but if it were me I'd stick to a carb.

 

I prefer 350 blocks to the factory 400 blocks. They are stronger, more durable, the parts are cheaper, and they require less work, and less of a cooling system for the most part.
350 heads are generally too small for a 400.. but if it's a low rpm motor it's not a big concern.


If you wanna use a version of the factory tuned port setup i'd go with a 350 definitly.

if you wanna use some nifty aftermaket setup i'd use a hot 350, or a 383, or the 400.

I'd be more apt to run a 383 than a 400. just not a fan of those motors.

The gearing is more determined by the camshaft, and transmission than what the motor is.

 

ive got a 406 with 64cc 350 heads that i drilled steam holes in, the motor has 5.7 eagle SIR rods, comp cams extreme energy 268 grind cam (.477/.480 lift), stock crank, edelbrock performer eps intake, edelbrock 750 carb, accell ignition and i am pretty happy with it, they are def torque monters, my powerband is from like 3000-5000 rpms, anything over about 5500 is pointless cause it just dosent pull as hard. I have a TH350 with a B&M 2500 stall, and 3.42 gears and i turn about 2500 rpms at 55.

 

How does that cam run in your motor? I'm planning on going a step up with the XE274.

 

it runs pretty good, you can def tell the car has a cam when it is idling. Like i said though not much power over 5500 rpms, but all in all im pretty happy with it. I wish i would have gone a little bigger but oh well next time around i guess. Oh yeah by the way i had to grind some off my rods to clear the camshaft just so you know before you buy it and try to slap it together like i did and find out that your rods hid the camshaft lobe. I guess you can buy a small base cam then you wont have to grind the rods... im using 5.7 rods also dont know how it would work with the stock 5.65 rods or anything else.

 

I should work fine with the 5.565" rods, but I'm not sure if I'm using them or the 5.7" rods. Kind of leaning towards the 5.7" rod though. Does it have lots of low end tq with that 268 cam?

 

yeah it has a ton of torque... very fun, just wish i could get some traction

 

400!

 

Well I've been talkin to a few guys around that I know and almost all of them said that I should build a 350, a stroker, or a 327.


The one guy I talked to really pushed me to build a 327......do these motors have a lot of potential??? Wut would be a good set up as far as cam heads etc.... for a 327.


The one bad thing I heard them all say about the 400's is they overheat very easy.

 

327's (IMO) aren't anything special. They have a shorter stroke than a 350, with the same bore. This theoretically allows it to rev higher (because of lower piston speeds), but with the right parts a 350 will rev just as high while having more low end and 23 more cubes. Strokers (383's I assume) have tons of low end torque with thier long stroke. Typically with the longer stroke they don't like to rev very high, but with good forged internals properly balanced they'll rev to 6500 no problem. As far as the 400's overheating, that's totally not true. The reason they "run hot" is because the guys didn't bother to drill steam holes in the heads. That loss of coolant flow in between the cylinders (which the walls are fairly thin cooling wise) caused them to overheat, along with the fact that they were probably running a cooling system that was barely adequate for a little 305. As long as you drill the steam holes and run a proper cooling system (which doesn't mean going all out, justy a good radiator, fan, and water pump) you won't have a problem. I know guys that have run their stock systems and it hasn't overheated once. I would reccomend a good electric fan though, the mechanical ones don't flow enough to keep a decent 350 cooled, let alone a 400. If it were me I'd build a 400, they have tons of torque.

 

400's run hot..... BS!! im so sick and tired of everything saying this from what they hear.... i have my 406 with 350 heads which i drilled steam holes in and i am using a bone stock cooling system, the only thing different than stock is the hoses. I am using the stock electric fan and a new stock camaro water pump. These engines do not run hot........ my car will not get over 180 with the fan on, i have a 165 degree thermostat and the car will not get over 180 even in the city. most of the time i dont even turn on the electric fan when i am cruising in clean air. Dont change your mind because you have "heard" these people prob though hey i can slap any old heads on here and be fine..... drilling these steam holes is extremely easy, get yourself a old headgasket and it is no prob at all. But now that you know they dont run hot!!! keep your options open for the 400

 

The big potential of the 327's lies in the Old 327's.

the old small journal pre-69 motors are the "screamers" with fairly "large" heads on them ie 350 heads, short strokes, and a lot less crank being thrown around they rev very quick and can sustain the high rpms, repeatedly

if you've got a motor with 350 journals it's rather pointless to run a 3.25" crank in there with the additional wieght of the crank. It will not support the rpm a small journal 327 will.

I still maintain the 350/383 is the way to go.. the building "block" is a much better base.. i share not the hardon of the factory400 sbc.

 

I have a 400 in my 1982 Suburban. In the winter, I actually have to place card board in front of the radiator to get hot water to my heater core. It has been explained to me that most factory 400's were in trucks. Most people treat their trucks like trash and many times run them without antifreeze causing the water jackets to rust out and the steam holes to clog. This is where the misconception that 400's run hot began. When I first acquired my 400, the water jackets were pretty grungy. I got some muriac acid from a swimming pool supply, blocked the water pump holes with steel plates and filled the water jackets to the top. I let it sit for a few hours, allowing the acid to eat away the rust and plaque. I washed it out with baking soda and water, then fresh water. I cleaned the steam holes with a hand held drill and slightly counter bored them. The acid trick will work on any cast iron motor. YOU MUST DO THIS BEFORE MACHINE WORK IS DONE. YOU WILL RUIN A FRESH BORE, BEARING SADDLE OR DECK SURFACE IF THE ACID GETS ON FRESHLY MACHINED SURFACE. The stuff is fairly mild but use neoprene gloves and safety goggles.

 

Another vote for a 400 and I agree the talk of 400s overheating is BS. Why on earth would anyone want to build a 327, really what are they good for?