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sbc 400 heads

6K views 23 replies 7 participants last post by  gmtony55 
#1 ·
Hey guys, I am new to this forum and have a question. first some background,I have a 1983 chevy elcamino with a 305 engine with 226,000 miles and only has 145hp. I want to have a little more power but dont have plenty money to spend right now. I have a 1971 400 with matching heads that my brother law pulled out of a 68 camaro It was running great when he pulled it to put in a zz4 crate engine. he gave me the 400..I have researched and everyone says throw the heads away they are useless but it seems there all looking for 400 plus horsepower, I am not I want to drive this baby everyday and if I can get 300 to 325 that would be great..What do you guys recommend?
 
#2 · (Edited)
The early 400's used a 2-bbl carb and were rated at 265 hp (gross hp from 1971 and previous years of production. As of 1972, hp ratings were based on net output, so that 265 hp figure would be lowered to 170. That would be the number that you would compare to the 305 hp from the factory) That would be a step up from your 305 motor, but of course, we don't know if that would satisfy you.
Are you capable of disassembling the motor, buying different parts, having machine work done (align bore or align hone the main bearing bore, bore and hone the cylinders for +0.030" pistons using a torque plate, cutting the block deck height to arrive at a close squish) and then re-assembling the motor with new parts? If not, install the 400 as is and enjoy.
 
#3 ·
Even a stock 2 barrel 400 will bring a massive injection of torque without necessarily bringing big horsepower numbers, so you will feel this right out the first stop sign you meet.

The 400 is an externally balanced engine where your 305 is internal. The difference being the 400 needs a 400 offset balance damper on the front of crankshaft and it needs a 400 offset balance flywheel or flexplate depending on whether your El Camino is a stick or automatic. Beyond that it's a bolt in.

Unless you're looking for some fantastic level of performance I wouldn't start by replacing anything especially the heads as heads, cam, pistons, intake and exhaust systems are really integrated parts of the whole, when you change one of these all should be touched if optimal power solutions are the goal.

Bogie
 
#9 · (Edited)
I do have another part to this question. Is the stock carb on my 83 elco something I can transfer over or not?
It is a 4 barrel Q-jet
To the best of my knowledge, Q-jets came in 750 and 850 cfm varieties, so yeah, a 750 is plenty of carb for a street-driver 400. In my opinion, it's the finest OEM fuel/air mixer ever bolted to a manifold and is nearly as good as EFI when properly set up. Get the proper manual to rebuild it yourself or have Cliff Ruggles or one of the other professionals set it up for your particular application. If you're gonna do it yourself, get Cliff's book....
Cliffs High Performance Quadrajets :: Qjet Carburetor Rebuild Kits, Parts, Quadrajet Rebuilding, Quadrajet Parts, Bushing Kits, Carb Tuning
I would bolt it to an Edelbrock Performer RPM #7104 intake manifold.

As far as cam, stay very conservative with a near-stock unit. If the motor is stock, then it's a low-compression motor and you will kill off all the low-end grunt if you use too much cam. I'd stay under 200 degrees duration @0.050" tappet lift. Resist the urge to use an extreme type of grind, choosing instead a reasonable rate of lift. Subtract the 0.050" duration from the advertised duration. If the result is a "hydraulic intensity" of 56 or larger, you'll have a nice, easy grind. The larger the difference, the easier the cam will be on the lifters. The smaller the difference, the more violent the cam/lifter interaction, with a better chance of roaching a lifter.
 
#10 ·
Have to disagree with its hard to over cam a 400, you can over cam ANY engine, I over cammed my 406 & it had iron eagle heads & 10.4.1 compression, It was a bear to tune, sure it would rev too the moon, but it ETs & MPHs exactly the same with the mild cam that i had originally put in it & i shift it at 5000, not 62-6300, So if you choose a cam, choose wisely, I'd just keep it on the cheap, you could re-ring it, clean up the heads, all new gaskets/chain/oil pump, mild cam, then just install headers/intake/carb, It'll run very strong, even with the stock heads. This was the cam that i installed that hurt my 406.

510/510, 245/245 @50, 108 LSA, installed at 104*, even tried 102*

I have 4.11 gears & a 4200 stall.
 
#16 ·
thanks cobalt..extremely good info. I will need an adapter because it had a holley on it before.

I been reading up on porting heads, It doesnt look hard to do at all just time consuming work. but I recarpet boats on the side so I am used to that..Do you think I should bother with that? porting that is.
 
#17 ·
Smoothing and blending the lip that's just below the seat helps (see arrows below). I wouldn't go much beyond that and cleaning up any casting flash or irregularities, though. Once you get in too far you can easily do more harm than good unless you're experienced.

Click on image for an article w/some porting info:

 
#20 ·
ok guys I am learning a little,now I'm in trouble.lol..I have some decisions made but have a few still questions. As I said before I have the performer RPM intake,but As I read it seems as though it is for a high rpm engine which I dont have. a 400 I am told to build for lower rpm. Keeping with low budget should I buy a performer intake that would fit my quadra-jet carb and just sell my RPM intake? Or would the money be spent better on a new carb and use the RPM intake?
 
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