Okay I have heard so much crap about the chevy 400 that its not even funny. Some people say they are torque monsters, and some say they will last forver, and others say they will throws rods easily and they have overheating problems and so on. Why (and why not) is the 400 a good motor? This is tech related, since I am looking for technical answers...

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1983 Pontiac Firebird SE
LG4-Based Chevy 400
700R4 Tansmission
Modified 4 Barrel Q-Jet Carb
Accel Super Stock 8mm Wires
Edelbrock Pro-Flo Air Cleaner
3.23 Posi Rear
14X7" Cragar SS/T Wheels
35X4 CD/AM/FM Head Unit
100WX2 Amp
2 Pioneer 12" Subs in Custom Box

 

In my opinion the major difference between the beloved 350 block and the 400 block is the siamesed bores that the 400 has. I believe this makes the cylinder walls thinner but it also causes heat to concentrate where the sides of the bores touch. Personally I think the 400s are fine as long as you take some precautions and not bore them out too far and make sure the heads have steam holes.

 

The 400 two bolt is better than the 400 4 bolt. This does not hold true for the 350 though, only 400. Kevin

 

LG4 based motor!
Get some better parts

 

These guys are correct. reason for 400 2 boltbeing stronger, is the large journal size on the crank. When you put the extra 2 bolts outboard, it weakens in that area and can crack.

Also, the reason they run warm is because the cylinders are siamessed and cant get water between them as such.

If you can keep it cool, its an AWESOME base for a powerplant. The bore is bigger so more torque, plus you pick up the cubes along with it.

Good luck

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-86 IROC
Vortech stuffed EFI 406 in progress
-=ICON Motorsports=-

 

I like them. I've got 2 in my garage right now.

I've had the best luck by decking the block, surfacing the heads, (no matter how good the surfaces are on either one.) and using 350 castings drilled for the steam holes.

Throw away any 400 heads you have.

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ASE Mechanic/Machinist/Smog Tech

1999 NBM Trans Am, flowmaster,FRA,Pro Kit,BMR STB, polished calipers.
1986 Chevy 3/4 ton pick up,flowmasters,4.10s,
1981 corvette FOR SALE
1995 ZX6R,Yosh,D207s

GO #3

 

in my opinion the 400 can be a sweet motor. since the bore is larger than the 350, the cylinder walls have to be thinner. Just keep it cool and it will make crazy torque. There are a few ways to set up good cooling systems but I dont know enough of the details to tell you how to do it.

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ice

 

I won't have anything less than a 400 if I can help it. It's an excellent street motor because of its torque, which is directly a result of cubic inches. I have no particular overheating probles with mine; like engineboy said, I have a set of the old 350 HP350 heads from 69 & 70, with the steam holes drilled in them using a 400 head gaslet as a template. The factory never made anything close to a high-performance 400; in fact, they were all 2-barrels, with the same garbage 76cc heads that came on 350s in the mid 70s (882 is typical). With good heads, the 400 is an excellent motor.

You really need to find out for certain if you actually have to keep the same carb and distributor. That LG4 stuff is killing any possibility of decent performance, and by keeping the timing too retarded for performance and making it run way lean all the time, it's contributing to your overheating problems too. If there is any possible legal mechanism for ditching that crap, you need to lose it, in favor of something like a Holley spreadbore 4-barrle and a non-computerized distributor.

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"So many Mustangs, so little time..."

 

Let's clear some things up here:
1) 400 cylinder walls aren't thinner than 350s. The larger bore requires the siemesed cylinder walls in order to maintain wall thickness. Different castings have been used through the years to maintain good wall thickness (SBC's started out in '55 as 265's, remember).
2) You can keep a 400 cool by, like RB83L69 says, drilling the steam holes in the heads. You've got more cubes, so put in a better radiator.
3) Better than factory 400 heads are required for performance. Good factory 350 heads will do, LG4 heads probably won't. World 2.02/1.60 valve S/R Torquers would be good street/strip heads. Go up from there wherever your dreams take you. AFR's, anyone?
4) The LG4 carb and distributor will work fine for the street, possibly even the intake, with proper tuning. Headers would be required to get the most out of it, along with the rest of the exhaust system.
5) 2-bolt main blocks tend to be stronger than 4-bolts from the factory, whether you're talking 350s or 400s. The strongest configuration is a 2-bolt converted to splayed 4-bolt.

I've seen a quarter million mile 400 in a '70 Impala; and a stroked, 12-second, smooth-idling 400 in a Vette (at this altitude, remember). So, don't try telling me 400's can't be made to last, or to run.

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82 Berlinetta, orig V-6 car. Rescued w/86 LG4/TH700R with all harnesses, sensors, ECM, etc. 3.08 open, cat-back from '91 GTA, Accel HEI SuperCoil. AMSOIL syn lubes bumper-to-bumper. Daily driver, work-in-progress (LB9 w/ZZ3 cam, World 305 heads, exhaust, paint, etc.).
57 Bel Air, my 1st car. Currently 396 .030 over, Weiand Action+, Edelbrock 1901 Q-Jet, Jacobs Omnipack, 1-3/4" headers, TH400 w/TCI Sat Night Special conv & shift kit, 3.08 10-bolt, AMSOIL syn lubes bumper-to-bumper. Best 15.1 @ 5800' Bandimere. Daily driver while Camaro was being put together.