600cfms big enough - Impala Tech
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post #1 of 11 (permalink) Old 02-10-2018, 09:08 PM Thread Starter
 
 
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600cfms big enough

Have a '65-396/425 with a 282h8 Crane cam, "sat. night special".
Rect port 208 heads and a 4150 Holley 600. Mechanical advance.
I also live at 5000', have a M22 with the 2.2 first gear and 373's out back. THe car seems a little underpowered, but the numbers seem to say the 600 is enough even with 90 efficiency. THis is in a 66 chevelle, although the motor is from a full size chevy.
It's not a strip car but didn't the 780cfm sit on top of the L78? Wonder why the 600 works out on paper then.
Suggestions?
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post #2 of 11 (permalink) Old 02-10-2018, 09:17 PM
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I run a 600 on a 350. Dave will have more advice, but I think that a 600 is a bit small for a healthy big block, especially at that altitude.

Two doors, four doors, wagons, and ragtops.
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post #3 of 11 (permalink) Old 02-11-2018, 05:25 AM
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Where do I start?

600 cfm will cover 400 cubes on the street, but not the strip. The higher you rev the engine the more cfm you will need to cover it.

This is where I get prople mad at me. The 396 is only good for scrap metal. The SBC 400 cube motor will run rings around it for half the price. The BBC was designed to be a HIGH compression race car engine that would run all day long (12 hours to 24 hours) at 7,800 RPM. You can not run high compression with today's gas-ohol. Because of this you need a BIG big block. 500 cubes is a good start.

Rectangular port heads require 500 cubes or more displacement to begin to make power across the engine RPM range. They are duds on the street and a set of "Peanut Port" truck heads will out perform them on the street because they are the same size as a SBC 400's heads (190 to 220 cc in volume depending upon year made). To get any power out of a 375 horse 396 (it was rated at 425 horse only in 1965 at a higher RPM than the 375 horse was from 1966-70 because Chevrolet's marketing people wanted to sell the idea of a 396 replacing the venerable 425 horse 409) you have to spin it to it's red line and hold it there while you turned left.

The 375 horse 396 came with 320 cc rectangular port heads and a radical for the day mechanical (solid) flat tappet cam with a high rise manifold and a 780 cfm Holley carb. It had pop up pistons with 11.0:1 static compression and closed 90 cc combustion chambers. If you were to recreate that motor you would have to run it on 100 plus octane race gas; it would not run on today's gasohol. It was replaced a year later by the 427 that made 425 horse at the same low (compared to it's racing potential) RPM.

A 396 has bores that are so small that it has to have notches cut into the deck to clear the valves. It is the equivalent of putting money into a 305 when a 350 was available for the same money. Both the 305 and the 396 are small bore engines that were designed not for racing but for use as a truck engine. It was ultimately produced as a 366 not a 396 in a truck block for medium duty trucks and school buses. The smaller bore 366 makes torque with a long stroke small bore. The 396 has a half inch longer stroke than the legendary 409 did (which was a big bore short stroke race car engine to race at Dayton's high bank track). No one has written a song about the 396.

Now back to the 500 cube motor. For the same money you have in your 396 you could have built a 496 (the 383 equivalent of a 350 rebuild). You would have started with a 454 donor motor out of a light truck (not the tall deck medium duty 454 truck engine). Add an even longer stroke crank, eight thirty over pistons, and you are close to the 500 cubes those rectangular port heads need to run at the RPMs encountered on the street. With open chambered (121 cc combustion chamber), and the smaller 230 cc oval port heads found on the 350 horse 396 and you could make 500 to 600 horse on your pump gas street driven motor.

Your cam and head choice prevents your car from having any pep, aggravated by your small bore. A modern BBC can make up to 1.2 horse per cube. Only way to make power with a BBC is to go big; but in every case, it is the combination of parts that you choose that is important.

Crane Energizer 282 H08 Flat Tappet Hydraulic 2,200-5,600 RPM operating range with degrees of duration at 0.050" 226°, valve lift 0.533", 108° LSA, auto trans requires 2,500+ converter, 3,000-3,400 cruise RPM, 9.5 to 11.0 compression ratio advised. This cam needs a notch ground into the rear journal of the cam to run with your 1965 block. Without that notch you will not get oil to the top of the motor burning up the rocker arms and push rods and destroying the valve guides and valves.

Big Dave

Last edited by Big Dave; 02-11-2018 at 05:46 AM.
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post #4 of 11 (permalink) Old 02-11-2018, 07:19 AM Thread Starter
 
 
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Thanks Dave, You sure did your homework and I appreciate all you wrote, thank you. Thats allot to take in about this 396/425. I know they didn't make many of this particular engine, like about 2000.
Well shucks, basically what you are telling me is to start over. heh heh.
I can't see replacement with this engine as it runs very well. It just is what it is at this point. I know some folks would love to have it as it's kind of rare. THis particular one has never been bored. A guy might call it a transition engine inbetween the 409 and 454 as the engineers figured out what best worked.

Back to the carb and the 600cfms. Will I gain anything with a 750 on top vs the 600? What about the altitude factor as well?

Now I know that if funds were available, an upgrade might just be in store. I kind of like this engine, as it's still running after 50 years and in its day it was a pretty good performer with the solid cam etc.
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post #5 of 11 (permalink) Old 02-11-2018, 01:23 PM
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As to altitude this is one time when the factory settings are not good enough to work. Your reduced atmospheric pressure will affect the fuel air mixture. You are actually running rich at this point, as you are getting more fuel than oxygen to burn it. A bigger carb will reduce what little throttle response you have now.

Today people talk about port velocity, but back when your rectangular port heads were designed the thinking was the bigger the port the better. Racers learned in the late sixties that rectangular ports didn't suck. They were too big to suck. The air flow through the ports was slow (lazy) until the motor was spinning above 4,600 RPM. This is why the factory cam was a flat tappet. A hydraulic cam not spin above 5,600 RPM without valve float due to the lifter pumping up. So you have only about a 1,000 RPM to make power and it is too high up to be of use on the street.

Chevy learned this and introduced the Peanut Port head back in 1975. They are called that because the ports are so small in comparison to a rectangular port head. Chevy did this because in 1975 there wasn't a motor made with a solid tappet to take advantage of the larger port. Chevy wanted to make more torque with the 454 than they could with the oval port heads as the only vehicle with a BBC in it after 1974 was a light truck. Chevy was selling the 454 as a poor man's "Diesel engine". It was making diesel like power (but burning a lot of gas to do it) for a third of the price of a diesel engine. This gave Chevy a price advantage to compete against the Cummings engine in the Dodge and the International diesel engine (called a PowerStroke) used by Ford.

If you could find some Peanut Port heads (older ones where larger than newer ones) for scrap metal prices it might be worth while having them reworked with larger Manley intake and exhaust valves. Peanut port heads are unloved and few want them making them cheap, but cutting new valve seats for the bigger 2.2"/190" valves and buying all new swirl polished valves won't be cheap so it might work out cost wise.

One final thought. Your 1965 396 might in fact be a 409. For the first three months of production the 396 block was cast with incredibly thick cylinder walls because six months into the 1965 production schedule the executive board at GM had not made a final decision on the displacement of their new Mark IV engine (the 396 as you know it). It was cast so that it could be bored out to be a 409 replacement with the new Mystery Motor's heads canted valves, but at the old 409's short stroke. They ultimately decided that the longer stroke 396 was the option they wanted, but since they were already making cars and wanted the 409 out of production to break with the old body style, the Chevy foundry made that thick wall compromise.

Professional racers loved that block as it could be bored out to a 409 bore with a 396 stroke to make a 481 cube sleeper motor for match racing. As such most where bought up and used up in racing making it a very rare find today.

Big Dave
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post #6 of 11 (permalink) Old 02-11-2018, 01:43 PM
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Told you Dave would have something to say, lol

I agree with you, don't change it for the sake of change. There is always something better. If it were mine, I would simply put the carb on it that GM designed it with. Then, tune really well for your altitude. A small investment, and it will pay off in performance, mileage, and reliability.

Two doors, four doors, wagons, and ragtops.
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post #7 of 11 (permalink) Old 02-11-2018, 06:08 PM Thread Starter
 
 
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quote from big Dave. "One final thought. Your 1965 396 might in fact be a 409. For the first three months of production the 396 block was cast with incredibly thick cylinder walls because six months into the 1965 production schedule the executive board at GM had not made a final decision on the displacement of their new Mark IV engine (the 396 as you know it). It was cast so that it could be bored out to be a 409 replacement with the new Mystery Motor's heads canted valves, but at the old 409's short stroke. They ultimately decided that the longer stroke 396 was the option they wanted, but since they were already making cars and wanted the 409 out of production to break with the old body style, the Chevy foundry made that thick wall compromise.

Professional racers loved that block as it could be bored out to a 409 bore with a 396 stroke to make a 481 cube sleeper motor for match racing. As such most where bought up and used up in racing making it a very rare find today."

Thanks Big Dave again for all the info again.
Yes. it is a March '65 casting date on a 962 block which is what you spoke of with the thicker walls. It is a desired block to some as you stated. It has the 4 bolt mains as well, with matching 208 heads date wise. Has the external oil cooler plugs by the oil filter as well. The intake is very close to that date as well and is the snowflake winters. So, I think that all these parts are date wise, close enough, to be original to the engine.
The info you gave on the compression, solid cam and octane are all factors in basically dumbing down this engine to what it is now,(a street driver on 91 octane and a hyd cam with a 600Holley 4150, with the low first gear M22.
I like the engine for it's originality and rareness, and the fact that when I was a kid this was the big engine that was in the Corvettes. I didn't buy the car for the engine though. It just happened to come along with the Chevelle.
My how engines and gasoline have changed.
What to do? Probably nothing as Jay old school suggested. I just use it to cruise and am fairly content with how the engine behaves. But in her day I have heard stories about this particular engine and what she would do. In 65, she was the one to have. When it comes time for a rebuild, that's the time to sell it, recoup some money and move up to a 500+ inch motor and it could even be a break even deal moneywise. I'm sure there are some 65 impala guys that would love to have this particular set up and have at least, a date correct motor that runs well on 91 and needs no constant valve adjustment.

Thanks again Dave and Jay for your thoughts on this.
Boyd
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post #8 of 11 (permalink) Old 02-11-2018, 08:36 PM
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Yes, I'm one of those 65 guys. I'd love to have a correct 396 for my 65 ragtop! You don't want it, keep it for me. Mine is completely numbers matching, I kept the dated 1965 fuel pump when I changed it last year, lol.

Two doors, four doors, wagons, and ragtops.
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post #9 of 11 (permalink) Old 02-11-2018, 09:37 PM Thread Starter
 
 
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Quote:
Originally Posted by jayoldschool View Post
Yes, I'm one of those 65 guys. I'd love to have a correct 396 for my 65 ragtop! You don't want it, keep it for me. Mine is completely numbers matching, I kept the dated 1965 fuel pump when I changed it last year, lol.
Well, once you have the #matching, you have to keep it that way to insure it's value. I'm a retired guy who doesn't need 500-600hp, and has to plan for making the money last well into the future.
Makes me wonder what the actual hp and torque are the way it sits now?
any comments on that? Like Dave says it's all done at 5600, but from 3800-5600 she's in her groove. THe car originally had the 360hp but that has been long gone for years. It was raced in the early years.
Boyd
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post #10 of 11 (permalink) Old 02-12-2018, 01:35 PM
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Quote:
Originally Posted by boyd66k20 View Post
Well, once you have the #matching, you have to keep it that way to insure it's value. I'm a retired guy who doesn't need 500-600hp, and has to plan for making the money last well into the future.
I used to think this way, but then I started looking at the value of numbers matching cars that just are not that desirable.

My 63 Impala convertible SS is a numbers matching car, but the 283 with a 2 barrel carb and a powerglide transmission just isn't desirable. If I put a stick in it and a 409 the value goes way up even if the 409 and transmission don't numbers match. I could use the new aftermarket 409 block, people just want to say they are running a 409 "W" engine. If I built a 409 boring it out and stroking it they love it all the more.

Almost and V8 swap into a I6 or the rare I4 car increases the cars value. I still wish I would have bought the old 4 door 63 Impala that had the little Iron duke and 3-speed on the column. It was a just a neat combination that probably would have kept teenage me out of a lot of trouble. That my 66 impala with 327 got me into, that car loved 6000 RPM.
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post #11 of 11 (permalink) Old 02-12-2018, 01:51 PM Thread Starter
 
 
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Quote:
Originally Posted by Deadwolf View Post
I used to think this way, but then I started looking at the value of numbers matching cars that just are not that desirable.

My 63 Impala convertible SS is a numbers matching car, but the 283 with a 2 barrel carb and a powerglide transmission just isn't desirable. If I put a stick in it and a 409 the value goes way up even if the 409 and transmission don't numbers match. I could use the new aftermarket 409 block, people just want to say they are running a 409 "W" engine. If I built a 409 boring it out and stroking it they love it all the more.

Almost and V8 swap into a I6 or the rare I4 car increases the cars value. I still wish I would have bought the old 4 door 63 Impala that had the little Iron duke and 3-speed on the column. It was a just a neat combination that probably would have kept teenage me out of a lot of trouble. That my 66 impala with 327 got me into, that car loved 6000 RPM.
I see what you are saying with the 283 and glide. Personally, the 63 is one of my favs too. My buddy had one in the Navy and coming back from a weekend he fell asleep and went into the center grassy area and hit boulders. That car was totaled.
It "would" be more valuable with the 409 and particularly the 4 speed. Folks just have to have something to do while driving and many kids today can't even drive them. Funny how the market varies with different vehicles. The chevelle world loves the numbers matching stuff, probably cause the chevelle is in demand so much. Non numbers matching, a guy can build what he wants and the way engines have improved over the decades, I could be in this school of thought as well.
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