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Old 11-07-2012, 10:29 AM
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sbc 400 heads

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?

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Old 11-07-2012, 12:32 PM
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Quote:
Originally Posted by gmtony55 View Post
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?
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.

Last edited by techinspector1; 11-07-2012 at 12:44 PM.
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Old 11-07-2012, 01:02 PM
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Quote:
Originally Posted by gmtony55 View Post
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?
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
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Old 11-07-2012, 01:41 PM
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A lot of great info thats for sure. I did leave out that the previous owner installed a cam, too big in my opinion i was told 282 and an edelbrock performer rpm intake. this engine has the heads off of it and the oil pan off as well. I do have the dampner and flywheel also. The short block is all assembled and I would like to just put it all back together and install it. But something keeps telling me, You all ready have it out and down and the 305 is running fine "save up some money and build it up right". With that said I do not want to bore this engine anyway as it will get expensive. with the right cam, headers and carb I should be ok. Thanks guys
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Old 11-07-2012, 02:43 PM
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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
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Old 11-08-2012, 08:52 AM
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Street ported?? Is this expensive? the cam is out of engine and was not put up with oil or grease on it so I think I better get a new one anyway, It has some surface rust on it..
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Old 11-08-2012, 10:56 AM
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the lifters are not marked..but you mean dont look at cam right? not the engine?
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Old 11-08-2012, 03:38 PM
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Thanks! One last thing, do you think I will be ok with my quadrajet carb? what size cam would you recommend? oops that's two things.lol
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Old 11-08-2012, 03:39 PM
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Quote:
Originally Posted by gmtony55 View Post
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.

Last edited by techinspector1; 11-08-2012 at 04:08 PM.
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Old 11-08-2012, 05:30 PM
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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.
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Old 11-08-2012, 05:40 PM
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I never seen the casting numbers on the heads some are better than others do u have casting numbers
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Old 11-08-2012, 08:18 PM
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this is very helpful and I apprieciate your time. the cam figures I must admit is over my head but I do get the keep it close to stock. I will definitely get the book you recommended. thanks again
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Old 11-08-2012, 08:20 PM
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Techinspector..this is very helpful and I apprieciate your time. the cam figures I must admit is over my head but I do get the keep it close to stock. I will definitely get the book you recommended. thanks again
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Old 11-08-2012, 08:27 PM
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Originally Posted by LJM97Z View Post
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 is hitting it on the head.This is what I am going to do.

my head casting number is 3973493
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Old 11-08-2012, 08:28 PM
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Quote:
Originally Posted by gmtony55 View Post
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
Yes, the Q-jet will work fine. You might want to tune it to match the engine its going on, but that would be the case regardless of what carb you were going to use. But if you want to use the Performer RPM- which is a very good intake- the Q-jet won't bolt up w/o using an adapter unless it's the Q-jet model RPM. In most cases an adapter will not be something I'd recommend. But unless you wanted to use another intake or a different carb, that's the route you'd have to take. And there is at least one test that shows only a very small loss using an open adapter to mount a Q-jet on the squarebore RPM intake.

If you DO use an adapter, use something like Edelbrock p/n 2693. Summit sells a similar one for a lot less although it might not move the carb back 5/16" like the Edelbrock adapter does. What you want to avoid is the 4-hole jobs (like Proform p/n 66253).

The Q-jet carb will almost surely be the 750 cfm casting, not the 800 cfm casting, although in practice there's very little real-world difference in the performance between the two. The 800 cfm casting does have a slightly larger primary bore and venturi, but compared to most any other similar size carb the primaries are still smaller- which equates to good throttle response and potentially better mileage.

BTW, it's a little known fact that the V6 4.3L GM trucks in the later years (up until '86) used a non computer controlled Q-jet w/the 800 cfm casting. I have one right here from a '86 4.3L V6 Sierra! Good place to source a Q-jet.

Good luck.
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