400 ci, 6.6L vortec, Can/has it been done?

90halfton said:

To the point of cracking s###

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that's why i got me a Vortec 383.......6.3L

I run 3 400 sbc none run hot. That's bs that was started years ago by people that did not know what they where doing.
like swapping heads and not drilling steam holes.

884x4310ci said:

I run 3 400 sbc none run hot. That's bs that was started years ago by people that did not know what they where doing.
like swapping heads and not drilling steam holes.

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i've only had one in my life and the truck ran HOT.....it was my first K/5, a 1975 that i got in '82 or '83. was a forest service truck from ME if my memory serves.......

looking back i can't say as to why it ran hot, the guy that helped me swap it out for a a 350 told me they do run hotter than the other small blocks, something to do with the cylinder walls.....i was a kid and he was a mentor of sorts, i took it for gospel. the roof leaked above the windshield too......

so i'll amend my post and state that MY 400 ran very hot. after the swap i had no more heat issues in the truck up till i sold it for a '78.

michael hurd said:

If you really want to proclaim a 6.6 L vortec... buy some stickers if it makes you happy. Trying to rationale spending thousands to upgrade a basically obsolete product is kind of insane, especially to a newer obsolete product.

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A bit dramatic.
Stock 400 shortblock, cam and all, with the trucks oem top end after drilling steam holes, will work just fine. A little computer tuning and its done. This isn't anything major, people build strokers that do the same thing daily, and its not like the 400's going to be making huge power.

Swapping a 255 HP ( net ) 5.7 L Vortec for a low compression motor that began life with ( net ) 150-180 hp. Sound great?

Even in top shape with great ring seal, the 350 heads will make about 50 hp more? That's IF you don't have issues with the compression increase, and detonation.

That's equivalent to running a 305 instead of a 350.

Shorter 5.565 connecting rods ( 400 ) 350 Vortec rods are 5.7 inches

Stock 400 - lame hydraulic flat tappet, slow opening / closing ramps. Stock L31 350, lame hydraulic roller, much quicker opening ramps. Regarding area under the curve, the roller cam reaches full lift earlier, holds the valve fully open longer, then snaps the valve shut faster.

64 cc heads on 400 = higher compression ratio, about 1.72 points more if you have the stock bore size. More if the bore is increased. More if thinner head gaskets are used than OE equivalent. More compression yet if the pistons are aftermarket and have less valve reliefs and no chamfer.

1970 400 had a stock CR of 9-1 from this source:

http://www.nastyz28.com/sbchevy/sbsum.php

Other years had 8.5-1, so dropping chamber size from 76 cc gets you to either 10.22 or 10.72 with the OEM compressed volume gaskets and the newer 64 cc heads, keeping the bore size 4.125"

If the pistons are OEM factory pistons in +0.030", advertised 8.5 to 1, you can take that 10.22 and raise it to 10.36 to 1 CR. If you had an original 400 with 9-1, and is + 0.030", you will have 10.86-1. Like what would have been GM service replacements from the stealer. Race fuel anyone?

If the engine sat for any length of time with old oil in it, the rings will be stuck, and the bearings will be pitted from the acids in the crankcase. You aren't going to take a stock engine that has sat for many years and expect to put it back to work without doing some work. It will need to come apart, unless you want to play hot potato with a grenade.


KB9907HC piston ( stock bore size, no oversize ), flat top with 2V relief , Fel-Pro 1045 gaskets, stock stroke, 0.010" machined off the block ( deck height ) and 64 cc chambers, I get 12.74 to 1 compression. Anyone else care to check the numbers?

With large swept volume, and small-ish combustion chambers, iron heads, you will need deep dished pistons, likely custom to get the CR down to a streetable level... like 9.5 to 1.

"building a gen 1 is like putting square wheels on a truck" i can see your against the idea, but your looking heavily negative towards it, it can be done, and quite well. i certainly wouldnt be using the crappy stock cam from 1970 thats for sure, sure most of that may be truck with the exception of race fuel on 11:1. timing a fueling can be adjusted on premium perfectly without the need for more than pump gas. other than that your numbers are right.

Yes, you could run 11-1 compression on pump premium, with retarded timing, absolutely. You would also need aluminum heads, an overkill cooling system to go along with retarded timing, and a camshaft large enough to bleed off cylinder pressure.

The 2 points in compression is absolutely not worth the squeeze.

More on compression ratio: once you get to a certain level, power output for one point increase falls off.

To go from 9-1 to 11-1 will give you a 6.7% increase. Jumping another 2 points would only get you 5%.

If the original configuration was 9-1 making 200 hp, your hot 11-1 would make a whopping 13.4 more horsepower, for a total of 213.4 hp. It will not run well at all on any kind of pump fuel, if it doesn't self destruct.

http://victorylibrary.com/brit/compression-c.htm

High compression is only a small part of the equation in making power. Reliable power increases can be made, but it needs to be thought of as a systems approach.

I've seen dozens of motors that have sat for many years without issues. Besides, the OP never said this is an old, poorly put away motor.
Yes, compression can be an issue. A hone, some pistons and rings and that's fixable. Yes, your combo comes up to over 12:1- 2v relief flat tops gave me over 11:1 on my 388, why would he choose those for a street build?
Yes, the original camshaft is weak. That's $200 to upgrade to a mild grind that will at least mimic the power of an anemic stock vortec roller.

When we're talking swapping engines, there some work to be expected. When modifying and swapping, even more so. Still, this isn't much work or money. But perhaps I'm jaded at this point....