How do I achieve 500hp from my stock 396/325hp? - Impala Tech
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post #1 of 16 (permalink) Old 10-21-2017, 09:41 AM Thread Starter
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How do I achieve 500hp from my stock 396/325hp?

Just what it says. I've recently torn out the motor/trans out of my 65. The idea was, i'd take the motor to the engine shop near town and let them take a poke at it and tell me what needs to be done. Sort of like a shopping list if you will. Just trying to price things out and get an idea, quite frankly.

But here's what i have. A stock 396/325 hp. It's a numbers matching motor to my car. The heads are stamped 3856206. Which after looking that up, puts me at 2.06/1.72 CLOSED and 97cc on the heads?
There is an aftermarket air gapped intake on there and (Professional Products?? Made in China)
There is a wore out Holley Street Avenger 670 on there as well.
There is also a set of Hooker headers on there as well.
The head gaskets are still orange on the outside. I'm only ASSUMING the heads haven't been taken off this car before. So, do know what CAM is in there? No. I'm assuming a stock CAM. Valves, lifters, etc... are all stock.
I'm also assuming it's NEVER been bored out before.

The only thing not numbers matching on this car is the TH400. That's numbered out to be on a 73 Truck.

So i'm curious, what would i need to do to achieve a reasonable number? Could i do this keeping these heads? I'm looking at 500hp as my end state at this point.

I'm sure I'm missing other information.

I appreciate your information!
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'65 Impala SS
'71 Super Beetle
2011 Dodge 2500 6.7L Cummins
2013 GMC Acadia
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post #2 of 16 (permalink) Old 10-21-2017, 11:11 AM
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With your 396 you would need a 250 horse shot of nitrous-oxide. Or you could pull your nearly numbers matching engine and store it (because those numbers are important to you). Then you go find a numbers matching 1973 454 out of a truck or car and stroke it out on rebuild to make a 496 (thirty over 454 with a quarter inch increase in the stroke by way of a Scat or Eagle crankshaft).

That will get you your desired 500 horsepower with bigger valves and a little port work in the open chambered oval port heads that came on the '73 454. That and a different cam because you don't need a big long duration rumpity rump cam to make 500 horse power with a bigger engine; but you do need to run a roller cam with today's motor oil.

From the outside you can not tell a 454 from a 396 unless you craw under the car and check out the harmonic balancer for the extra external weight a 454 uses. So your 396 decals will look right in place.

The Holley carb can be made new again with a rebuild kit and carb cleaner soak. Rebuild kit costs about $30 bucks which is a lot less than the cost of a new carb.

Big Dave
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post #3 of 16 (permalink) Old 10-21-2017, 11:42 AM Thread Starter
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SO... be on the hunt for a 454. Why from 1973? IS that just pulling out a number as it was the date to the Tranny? or the fact that the heads are open chambered? Then bore .30 over and a different crank. As well as a little valve/porting work and a roller cam.

I see where you're going with storing the original motor on moth balls because its a numbers matching SS?

'65 Impala SS
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2011 Dodge 2500 6.7L Cummins
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post #4 of 16 (permalink) Old 10-21-2017, 12:54 PM Thread Starter
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Just how much more value does this get me having the original motor?

Can't i bore out the original motor to the same specs you're saying on the 454 donor?

And do some work on the heads?

What's the difference and/or advantage to CLOSED/OPEN port?

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post #5 of 16 (permalink) Old 10-21-2017, 01:07 PM
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1974 was the last year the BBC appeared in cars, and you have a '73 tranny so why not a '73.

The open chambered heads didn't appear in production engines until 1971 (they were used in production motors to improve emissions, even though it was sold since 1969 as a performance part in the Chevy parts department). Starting in 1975 Chevy went to the peanut port heads where the port volume feeding a 454 was the same size (190cc) as the high performance SBC head feeding a 350 (regular 350 head is 170 cc).

Peanut ports are great for building torque way down low in the RPM band to pull stumps or 10,000 pound trailers; but rotten for deep breathing required to make lots of power. Since the BBC was only available in three quarter ton or heavier pick-up trucks after 1974 (because they were exempt from emission testing). The BBC's heads were redesigned with the "peanut port" head to compete power wise with diesel engines, that cost three times as much to install in a light truck giving GM a sales advantage.

Under 500 cubes you want a 230 cc oval port head, not the bigger (320cc) rectangular port head. Because under 500 cubes or under 4,600 RPM the motor isn't sucking in enough air to keep the velocity up in the intake runners so gas fell out of suspension. Liquid gas doesn't burn, so you waste fuel and loose power.

Power is made in the heads. You want power buy the best heads you can afford. Match a cam to the power band of the heads (not to make noise) and you will make your power goal and enjoy driving it as well as it will respond to the throttle. A 670 cfm Holley will feed a 454 up to about 5,600 RPM. Above that power falls off and the carb becomes a choke point. If you run a hydraulic roller that is as high as you can spin it anyway before the valves float. With a solid roller you can hit 7,800 RPM before you have to go to exotic parts (triple wound valve springs with 800 inch pound spring rates, half inch push rods to prevent bending, and Jesel roller rockers to stay on top of the valve stem at high RPM).

A 396 is the performance equivalent of a 305 cube SBC. It has a tiny bore that restricts breathing which is why no one uses them.


View from the oil pan looking up a 305 bore to see 1.94" size intake valve. A 2.02 valve will hit the top of the block.

A 396 has to have the top of the bores notched to let the valve pass the top of the block because the bore is so small. Unlike the SBC the valves on a BBC are canted so they open towards the center of the bore as they come down.





a 427 with it's eighth inch bigger bore doesn't need the notches.

The 396 was built as a replacement engine for the 409 because NASCAR had imposed a 427 cube limit on new engine designs (further limited by GM's executive board to 400 cubes in all cars except the full size and the Corvette which had bigger a 427 cube as an option) to reduce the cost to racers who where buying a newer bigger engine every year as the manufactures fought over the win on Sunday sell on Monday advertising war.

Big Dave
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post #6 of 16 (permalink) Old 10-21-2017, 07:20 PM
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I'd pull the 396, fog and bag it, and throw in a brand new GM performance big block crate motor. Write the check for a ZZ502. It will be more reliable, has a warranty, and will make more hp/$ than throwing money at your 396. When you want to sell your car, drop the numbers matching 396 in, and sell the ZZ502 for close to what you paid for it.

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post #7 of 16 (permalink) Old 10-21-2017, 09:57 PM
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Quote:
Originally Posted by safetysoc View Post
Just how much more value does this get me having the original motor?

Can't i bore out the original motor to the same specs you're saying on the 454 donor?

And do some work on the heads?

What's the difference and/or advantage to CLOSED/OPEN port?
The value is determined at the time of sale. At that time the person buying your car could want the original engine under the hood, but it might be worth a lot more with a better engine already installed and drivable and the numbers matching motor in the trunk.

A 396 is a thin wall casting (to save weight) which is the same as all of GM's motor castings. You can not safely exceed a 0.060" over bore without the motor over heating or risking cracking the block. A 427 and a 454 share a common 4.250" and as such the largest safe bore is 4.310" (0.060" overbore). A 454 block is already at standard bore dimension 0.125" inches larger than a 396. If you tried to cut a eighth inch out of the cylinder wall you would break into the water jacket.

Any one can port heads. You just need the burs, and carbide bits, as well as cartridge rolls to remove material and some idea as to air flow and where to cut. I would buy three thousand dollar per head Big Chief aftermarket heads and send them out to a professional porter to have them worked over.

On the other side; I ported my customer's heads (whether stock cast iron or aftermarket aluminum heads) in my own shop and I would periodically take them to town to have them tested on a flow bench at my machinist's shop just to check on my progress. And I got to be pretty good at it after thirty years of trying. Still had my race car heads professionally ported by someone who knew what they were doing which cost me as much as the five to six grand over the cost of the heads. But heads are what makes your power.

Open chambered combustion chambers combined with a half dome piston to fill (why the BBC is sometimes called a semi hemi) where what powered Top Fuel, & Pro Stock at the drags, CanAm racing, and SCCA-USAC road racing in the seventies. They where developed for Chevrolet's model shop by an engineer named Warren Johnson (aka the professor). They made a lot more power than the bath tub shaped closed chambered heads because it improved breathing by unshrouding the valves (remember that 396 block notch). In production the heads where changed because the BBC couldn't pass California emission testing with closed chambers. The BBC was dropped from cars in 1975 because it flunked the 1975 testing standard which was getting harder and harder to pass each year as the limits allowed where reduced (which is why they stopped making the SBC in 2004).

Can you make 500 hp with closed chambered heads? Yes I did it for a number of years with a L-88 powered Camaro up until I bought my first set of open chambered ZL-1 heads in 1970. My Big Chiefs have a tiny little 56 cc combustion chamber by comparison, but they are also 12 degree heads, not 24 degree heads the way the stock valve angle is. So you can make power with a closed or open chamber head, you just have to work with what you have until you can afford to buy better.

Big Dave
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post #8 of 16 (permalink) Old 10-22-2017, 11:08 AM Thread Starter
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Here is a motor I'm looking at right now.

I didn't write the ad. Keep that in mind. I'm COPY/PASTING it. Is this more in my wheelhouse????

"454 HI PERFORMANCE BLOCK AND HEADS....bbc tore down to put new cam in it crank piston rods were left alone i have new performance cam lifters and new timing chain and gears i got complete kit with gaskets i have set roller rocker dress up kit after market intake 800 gets it all it hi performance pass heads block hi nickle"

Interested in your thoughts, y'all!

Mark

'65 Impala SS
'71 Super Beetle
2011 Dodge 2500 6.7L Cummins
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post #9 of 16 (permalink) Old 10-22-2017, 11:12 AM
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With a ZZ502 costing ten thousand dollars, they aren't an option for most people, and selling it used is financial suicide around here. Maybe in Canada, but where they are more prevalent, you MIGHT get half the original cost when selling.

The most cost effective way to improve the heads is to replace with aftermarket aluminum, for about the same cost as upgrading and improving the stock heads. You can etch and paint them to match the block, if you want the original/sleeper look. With today's cam profile technology, flat top pistons provide a better flame travel for more efficient fuel burn and hence more power.
Using your stock block with a stroker kit and piston pins spec'd for zero deck height, you can easily reach 450hp and maybe the goal of 500 for about half the cost of a new ZZ502. A reputable engine builder should provide a warranty for their work, if not, find the door...fast.
If you would prefer to save the engine and go 454, which will get you 494 C I, after .030 bore and stroke, the 454 was installed in pickups and suburbans well into the 80's and are far more easily found than a '73 specific car engine.
Remember, horsepower doesn't get the car moving, torque does that and 500 lb ft of torque is child's play for a big block with mild upgrades, even your original 396.
If you have a "specialty" engine builder in your area, talk with them to get an idea of how to build what you want and cost. There's also a huge difference in the way a high torque/low rpm street engine is built compared to a race only engine. A shop that only does, "rebuilds" may not have the knowledge for making effective upgrades that work together.
One other very important point on your '65 block is, the cam HAS to have a groove in the rear journal and most cam builders will do that, on request, but out of the box cams don't have that and will starve the top end for oil and destroy the lifters, rockers, etc.
Oh, and toss the carb. It was too small to start with. An engine build of the sort you are looking at needs at least 780 cfm. Again, a knowledgeable builder will know what size carb it needs to feed the selected internals.

Just noticed you are in NC...being in NASCAR country, you should have a plethora of reputable builders within a reasonable distance to talk to and compare builds and prices. Happy building !!!

'62 Impala SS 409 TH350
'66 Chevelle SS 496 M20
'70 Chevelle SS 396 M20
'67 Camaro ss/rs 350 PG
'38 Chev coupe street rod
'54 Chev 210 2 door
'69 Chev C10
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post #10 of 16 (permalink) Old 10-22-2017, 11:58 AM
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The ZZ502 with it's Bow Tie (cast by Caterpillar) 4.5 inch bore block runs new from $6,500 to $14,500 in price (above list) so demand must factor (otherwise no one would pay above list price).

There are a lot of them for sale used on the web, but most are at 80% of the price of a new one with no warranty or promise of reliability.

I have one out in the back yard in my Suburban that replaced the worn out 454 I had in it from the factory. Saving it for a blown 540 motor project in the future. At 370,000 miles on the Suburban I replaced it in 2011 with a new pick-up.

Big Dave
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post #11 of 16 (permalink) Old 10-22-2017, 12:00 PM Thread Starter
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How bout that 454 I'm looking at? I've asked him for more info. Waiting on a reply. In the meantime, id be interested in what you all think of that 454 I'm currently looking at.

'65 Impala SS
'71 Super Beetle
2011 Dodge 2500 6.7L Cummins
2013 GMC Acadia
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post #12 of 16 (permalink) Old 10-22-2017, 12:36 PM
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I used to build engines. Had a fair reputation, and customers lined up wanting them. I was put out of business by GM crate engines. They offer one thing I could not. That was a factory warranty.

With a GM crate motor if anything happens to it you drag your car to any GM dealership (Buick, Caddy, or Chevy) and they will fix or replace the motor for free for one year from the date of purchase (not when you actually get around to putting it in, or starting it for the first time; but the purchase date, which means while it is being shipped to you the clock is running).

All of the remaining engine builders offer you their word as far as warranty. You have to get the motor back to them for them to think about if they will fix it or not. You are without a motor while this takes place and the odds are not in your favor as to the outcome. Most disallow any form of racing (and those that build race engines rent them to you for the cost of buying 20 engines from anyone else, because they know what happens to race car engines in competition, and they are sealed to keep you from discovering their secrets).

Here is a pile of parts that cost $13,600:



Here is that pile of parts installed in a SBC '509 block:





Here is the same same engine for $5,760

https://www.summitracing.com/int/par...make/chevrolet

So you can see if you find a motor for less money than a GM crate motor then something isn't right. They are either selling you used junk with a rattle can rebuild, or the components to build the motor were made in India or Pakistan and are not worth installing them.

GM crate motors are made with all new American made parts assembled in Mexico to keep labor costs down. Heads and intake are from Edelbrock, crank (and rods for a BBC) are from Lunati, cam and rockers are from Crane; the rest is off the assembly line parts that would have been used to build a new engine in Detroit

Big Dave
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post #13 of 16 (permalink) Old 10-22-2017, 12:52 PM Thread Starter
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So.... Don't get a used engine but now buy a crate?

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post #14 of 16 (permalink) Old 10-22-2017, 01:43 PM
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Quote:
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So.... Don't get a used engine but now buy a crate?
A used engine that you buy locally from a salvage yard is the way to go. A relatively new pick-up providing your used engine (even with nearly 100,000 miles on it) will still run for years because the TBI kept fuel from washing the oil off the cylinder walls prolonging the life of the motor. A big block has a nearly indestructable bottom end; which is why they lasted as long as they did in Top Fuel when the Hemi heads were far superior in making power. The BBC outlasted many a Hemi in the chase to the finish line.

If you are going to buy it used it needs to be running, and you want to witness it running as opposed to a standard "it was running when we pulled it" you normally get from a salvage yard.

It probably was running three to five years ago when they pulled off the front end off the vehicle to sell to a body shop; leaving the engine exposed to the weather, until they finally got around to actually pulling it for you. They are not lying, they just aren't telling you the whole truth.

Even if it is running when you buy it they only offer a thirty day warranty so if a problem is discovered after that it's yours. If within the thirty days they won't reimburse you for the labor to replace the motor for a second time (usually six hours at $130 an hour for most shops) they just give you another motor without extending the thirty day warranty if they have another in stock.

With older motors you have to worry about a decal upgrade. A 402 looks like a 454 and many people swapped decals when the car was new. Comparison of the casting numbers, or an examination of the balancer for the external weight added to a 454 crank can save you from buying a 402 thinking you are getting a 454.

All Mark IV four bolt main BBC blocks have external oil cooler lines machined into the block (because the Corvette has an oil cooler stock). Look for the two big oil line pipe plugs as well as the tiny oil pressure gauge line plug above the oil filter pad to get a quick check against an inflated four bolt block price charge. All Gen V and Gen VI blocks are four bolt main, but they have a one piece main oil seal (to prevent oil leaks). Gen V block will not have a fuel pump boss (requires an electric fuel pump), Gen VI will have been machined to accept a mechanical fuel pump.

Big Dave
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post #15 of 16 (permalink) Old 10-22-2017, 03:37 PM
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Quote:
Originally Posted by safetysoc View Post
So.... Don't get a used engine but now buy a crate?
A used performance engine can be a crap shoot, The engine ad you posted has no casting numbers to research or pics to see what it is. At $800 it could be a smoking deal, BUT how long has it been for sale ?? same with Dave's statement about seeing engines for sale at 80% of new...how long have they been on the market and no one will pay the price ?? You can ask any price you want for a part, but it's only worth what someone is willing to pay. I see stuff like that on craigslist here for many months.

Having the casting numbers of the ad engine would tell you if it is a hp block, in some cases 2 or 4 bolt main, what the heads are and whether the crankshaft is a forged or cast piece, cast being the least desirable in a stock crank. What is the cam he has and is it what you want for a street engine, or race ?

If you have the financial ability to buy new, then by all means pursue that avenue, I was just pointing out there are less expensive roads to take to get where you want to be.

'62 Impala SS 409 TH350
'66 Chevelle SS 496 M20
'70 Chevelle SS 396 M20
'67 Camaro ss/rs 350 PG
'38 Chev coupe street rod
'54 Chev 210 2 door
'69 Chev C10
'89 Chev R3500 roll back
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post #16 of 16 (permalink) Old 10-23-2017, 06:48 PM
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The warranties associated with GM crate engines are not exactly a cake-walk to get them the fix the issue. I know someone with a 350/290 HP that had an issue with the engine using oil. They pin-pointed it to two if the cylinders and only authorized fixing those two --> new rings. And this was after arguing with the dealer and dealer's zone.

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