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400 vs. 350

tiger9297

tiger9297

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Tupelo, Mississippi
Have a '90 K5 and am planning a rebuild. Still has stock 350 TBI. Want more HP and TQ with the new engine. I know I could build a 350 with much more power than the stock engine. I also know I could build a 383, but I'm concerned about having all the machining done to the block, as well as reliability issues. I have heard good things about the 406. My question is, isn't the 400 an old engine? How difficult would it be to find parts? And, most importantly, are these engines reliable? If I went with a 406 could I use the Howell/Holley 670 CFM TBI unit on this engine, or would it be better to go with a multi-point system? I'd like to stick with some kind of fuel injection so I don't have to "rig" all my computer stuff to keep engine lights happy, etc.
 
i'm not an authority on this, my last engine recipie got shot down hard but from most people i've consulted go with a 383, they can be built to make great power and be very reliable, i got distracted by more cubes and wanted to punch out a SB350 to 427cu in. to make 500+ hp, the SB 400 club seems to be a love it or hate it crowd
 
It's a great, strong platform. Parts are pretty easy to find and are supported by most good speed shops (Jeg's, PAW, Summit, etc)

I think the biggest problem you're going to run into is the fuel injection and the computer. My buddy has a mildly built 383 and it's just on the edge of throwing a code on the stock system. Any more can and I think he'd be asking for trouble.

My .02 and YMMV
 
If this is your DD then first things first check local smog laws. No use building it up if you cant pass inspection.
Second is to see what your budget will be for this engine. I started with a 350 because they are plentiful, parts are cheap, lots of different power combinations, and still fairly decent on gas. LOL
 
400 V 350

The 400 blocks have siamesed cylinder walls, so they will only take so much of an overbore. Pockets of steam were an issue also with this, so holes were drilled into the block and heads to allow the steam to escape. if you can find a good sound block that will not need too much of an overbore, you should be good to go. The heads used on these didn't have a great reputation either, but a combination of sound block and aftermarket heads can make some serious HP and torque. I think World Products makes heads with the steam holes already drilled in them, and parts are easy to get since it's still considered a small block. You may have to upgrade your injector (Usually big block injectors work fine), and maybe have your PCM reflashed, but if the smog police are an issue, you will need to be careful. The 409 on the other hand is a big block, like a 396, and you'll have to spend alot more for pulleys and brackets, etc etc, and are not that easy to find. 400's came in everything from Blazers and trucks to Monte Carlos, and can be found with enough looking.
 
I'm assuming you want to overbore a 400 +.030' and create a 406cid engine.....cool, that's not a stroker.
engine design involves a lot of variables that must work with each other, when stroking a 350 out to 383cid block machining must be done at the pan rails to allow for rod clearance and small base circle cams are a issue as well.
Reliability issues are based on the strength of installed components and the rod ratio.
Long rod vs short rod...they both have their ups n downs and both combinations will produce decidedly different personality's that must match intake manifold design, lobe separation angles, .050" cam duration and intended rev limit.
Big inch strokers larger than 383cid based on the 350 block are powerful but unless you employ a tall deck block and bring the rod ratio up then the motor will not enjoy revving above 5,000 and places very high loads on the con rod and sides of pistons, excessive cylinder wall scuffing and decreased ring seal will result.
Long rod motors will always make more power than a short rod motor but sacrifice bottom end torque in doing so,
they will also last longer are inherently more reliable.
400 blocks are rare but make a great platform for a thumper.
you could install longer lods and raised ring pistons with a overbore and build a 406cid screamer..........or
you could add a 350 crank with some really long rods and build a 377cid giant killer.
go for it man ....you only live once..!
 
When hunting for a block check for cracks between the steam holes and the head bolt holes. They were known to crack there when they got hot. When I was looking for a 400 block, finally on the 5th motor there was no cracks. If your going to all out race it doesent matter because you just pin the holes anyways but on any street application you had better find a good block. Or fork out $2000 for a dart block. Id go with a 355 or a 383. The 400's just gets to warm for my taste. Unless you get a Dart block.
 
I have always heard that the 400 block was prone to problems because the cylinder walls are too close to eachother. when rebuilding the block for performance, this can lead to cracking, and other heat related problems.
 
400 Block

They're called "Siamesed" cylinder walls. Each side of the wall is the inside of the cylinder, which is why you can't bore them too much.
 
What I'm hearing on the 400 is kind of what I was afraid of. It just doesn't seem like the wisest way to go. You basically begin the process with a platform that has problems that have to be worked around. I have also heard of the heating issue with 400's but didn't know if it was really much to it. Mississippi summers at 98-100* with 95% humidity towing with an engine that already has heating issues sounds like a bad idea. I tow my camper and boat alot during the summers with the wife and soon to be, daughter on board. Can't have an "iffy" engine. The 383 on the other hand really sounds good, but I have no idea where I would have the machining done, and there are so many different ways to build a 383 that it seems kind of overwhelming. As you can tell I have no where near the experience that some of you have. I certainly appreciate your input and welcome it. I will continue in this learning process. I'd want an engine that will pull my camper with no problem whatsoever. My TBI350 does ok but I always feel like I'm having to push it too hard. I don't want "adequate" power. I want MORE power than I need.
 
LongIslander26 said:
You could probaly cobble together a 383 cheaper and easier than you could a 400, since you already have a 350 to use as a starting point. :waytogo:
Click to expand...

How do you know which rods, and crank to go with on a 383 build? Also, I was thinking of using Vortec heads. I know there are better heads, but it seems that these are good heads for the money.
 
383

A 383 is a 350 with a 400 crank in it. Adding a littl bit of bore (About .030) and some stroke with the 400 crank gives you 383 CI. :waytogo: You can still use the 5.7" rods that are in your 350. You'll probably have to get new pistons though, after the block is bored. Since this is such a popular combo, 400 cranks new are pretty cheap and easy to find. The Vortecs heads will be a good choice, you'll just have to get a Vortec specific intake manifold.
 
LongIslander26 said:
A 383 is a 350 with a 400 crank in it. Adding a littl bit of bore (About .030) and some stroke with the 400 crank gives you 383 CI. :waytogo: You can still use the 5.7" rods that are in your 350. You'll probably have to get new pistons though, after the block is bored. Since this is such a popular combo, 400 cranks new are pretty cheap and easy to find. The Vortecs heads will be a good choice, you'll just have to get a Vortec specific intake manifold.
Click to expand...

I understand that this is a basic 383. However, in an earlier post by "Mad-Dog" he mentioned long rod vs. short rod. Would a 383 with a 400 crank and the stock 5.7" 350 rods be considered a long or short rod 383? He mentions that that long rod will be more reliable. That is most likely the one I would want, seeing as how I travel in this truck and don't want to constantly have to be working on it.
 
Rods

5.7" are short rods, 6.0" are long rods. You're only talking 3/10th's of an inch difference. Alot depends on the pistons you end up using as to what rods you can use, because of how high into the rings the wrist pin will be. There really isn't any difference in what rods you use. Alot of old hot rodders say the longer rods will give you more power because the piston will "Dwell" at TDC longer, but this debate has gone on for as long as there have been hot rods, either one will be fine, and rods generally aren't too cheap either. Considering you're going to need new pistons, rings, crank, and bearings to get this conversion done, plus the heads you want, a new intake, injectors, a PCM chip or reflash, and paying for the machine work, you're looking at $1500.00- 2 grand EASY right now. If you look at Chevy's 383 crate motor, I'm 99% sure it's got 5.7" rods in it.
 
5.7 rods in a 383 give you a rod ratio better than a stock 400 but not as good as a 350,
6" rods in a 383 create a rod ratio equal to a 350...
IMHO the 350 is not a long rod motor by any means, not when compared to 302 or 327.
most engine builders are happy with 5.7 rods in a 383 and so would you...this would make a fine powerplant for your truck with more than enough torque to pull you up the grades.

Here is a couple of links to help you understand the confusing rod ratio thing..
http://www.hotrod.com/techarticles/pit/index14.html

http://www.hotrod.com/howto/69883/
 
Never had a problem with my dads 400 (1970 blazer) over heating. Just made sure the heads were drilled, put a good water pump on, and a good clean 3 core radiator. The thing never gets above 185 with the AC on, even when its 110 out. well it did almost hit 200 when it was 118deg here. I think 400s are great engines.
 
Bunch of directions you can go for your build, as to heads, I think there are better out there than the Vortecs for certain applications.
 
i apologize for confusing you....
You would do fine just beefing up that 350, start with the exhaust.....full length small tube (1 5/8") hedders, 2.5" duals with a h-pipe or crossover behind the transfer case and flowmaster mufflers.
Work on the air filter system and let that motor breathe (ram air is a good thing) some cool air.
The intake is very restrictive and should be replaced with a Edelbrock unit (very nice)....this would allow to install the Holley TBI unit which outflows the stock unit and really kicks butt.
Stock TBI heads are the worst flowing heads that chevy makes so upgrading to set of World SR Torquers (expensive) are worth 50HP and AFR's (real expensive) are worth nearly 100HP.
Intake runners should be around 180cc and the chamber size can be decreased to 64cc and raise the compression w/o changing the pistons.
Changing the cam to a comp roller with 210/220 @ .050", 266/276 advertised , .500/.510" lift on a 114 dgree lobe center would be the icing on the cake and will push the motor to the 350HP mark easily with the other mods installed.
You would spend a lot less going this route and you don't have to pull the engine........the motor will have more power than you need cause a 350 HP 350 aint nothing to sneeze at....
lemme know what you wanna do and i will put together the part numbers for you....!
 
This is what i have learn on the battle between a 350 and 400.

A 350 will beat a 400 USUALLY on the strip. A 400 however will bet the pant off of a nice 350 in the mud due to the larger crank stroke. So if your into the mudd. 400 or 383. (the only problem with 383 are the are costly to build). On the strip, 350.
 
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