Thread: 396 375hp build question

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Well it looks like I got my hands on a 454 block for me for Christmas, ho ho, but I got to get mama's 396 humming before I can start my buildup. I have the 3969854 block which shows 396/402, 69-72 use. The block says hi perf pass bossed into the block. I calipered it out to 4.11" across the top of the cylinders. Since this is only .007" above the std 396 bore, I can only assume I"m measuring the wear and its a std bore 396. I want to take it to the 375hp version. Can you tell me what the cam profile was on those, and compression. Was there a steel crank in those? And last but not least I have the 3999241 heads to work with. Will they work, or will 2.19's and a little bowl blending in order? Street car and b-day present for the wife. Thanks guys.

Originally Posted by jimmyjeep

Well it looks like I got my hands on a 454 block for me for Christmas, ho ho, but I got to get mama's 396 humming before I can start my buildup. I have the 3969854 block which shows 396/402, 69-72 use. The block says hi perf pass bossed into the block. I calipered it out to 4.11" across the top of the cylinders. Since this is only .007" above the std 396 bore, I can only assume I"m measuring the wear and its a std bore 396. I want to take it to the 375hp version. Can you tell me what the cam profile was on those, and compression. Was there a steel crank in those? And last but not least I have the 3999241 heads to work with. Will they work, or will 2.19's and a little bowl blending in order? Street car and b-day present for the wife. Thanks guys.

I say use the heads you have and do your bowl blend and gasket match,and install new stock valves.
I don't know the cam specs. but I would use a more modern cam grind.
If the crank has a wider parting line then it is the steel crank,if it has a narrow parting line then it is a cast crank.

The 375 HP 396 was the L-78 motor, with mechanical-lifter cam, large-port iron heads, 11:1 compression ration, 4-bolt mains, forged Tuftrided crank and forged pistons. 11:1 on the street today is a problem because of detonation.

The cam timing was 40-86/88-38 (306/306 duration at 0 lift), with .500/.500 lift. (Casting #3863143)

You've got the same block used in the L-78, but not the heads. The heads you have were used on the 396/275 HP LS-3 engine, have a larger combustion chamber and smaller valves.

Here's a link to a page with the full L-78 and LS-3 specs.
http://www.nastyz28.com/camaro/z27396.html

Cam grinders make reproductions of the cam, but there are probably better grinds out there for what you have.

I can tell you what you have, and what the L-78 had, but there are other folks who can tell you how to build a strong engine with your parts. Erik Erikson or Pat McCarthy.

Myself, I'd be wary of duplicating an engine for the street with solid lifters and an 11:1 compression ratio. You can get massive HP out of a BBC without going that direction. Get down around 9 to 9.5:1 with your heads and pick a good hydraulic cam, and you can get your 375 hp easily.

Thanks guys, I saw on a different site earlier tonight the info on the solid cam setup for those critters, no thanks. Your right, a good hydraulic cam around .500 or so and something domed to get me 9.5 to 10.0 should get me in the ball park (I'M TALKING YANKEE STADIUM HERE). If I'm barkin up the wrong tree, let me know. I like the 2.19 idea, if it wont kill my bottom end.

Personally, I'd go with about 9.5:1, do a good high-performance valve job on the stock size valves, replace the seats with hardened ones, and install a complete hydraulic cam and kit. Perhaps a cam with 220 to 230 duration (@0.050 lift) and 0.500 to 0.520 lift. The effective power range would be from 1500/2000 RPM to 5800/6000 RPM. I had good luck with the Comp Cams Magnum series - like the Magnum 270H - but it's a matter of choice.

HYDRAULIC: Good for daily driven street machine, works with stock converter, likes headers. 396 needs 3.55-3.73 gear. Slight rough idle.

But that's just me. What you use depends on your goals. You know what they say about free advice. Sometimes it's worth what it costs .

I am glad people are realizing....there is no'good pump gas fuel' and I will
agree 10/1s are stretching it as far as detonation..I had a sbc 350/4 bolt main
with 300 heads,had a crower 480 lift cam,great to drive and 89 octane to boot
on 9.8/1 compression!You are asking for trouble with true 11/1 compression..
engine maker try to get you to buy these'trouble makers'but you have to mix fuel
etc etc etc...to get octane up..nothing like a ping motor or laboring motor
that you can not fix 'even with timing addjustments' people need to live in the
'now' unless you l;ike headaches..GFD.....

Another easy way to tell if it's a forged crank or not is to hit the counter weight lightly with a hammer. If it sings like a chime it's forged, if it makes a "thud" sound it's cast.

I'm currently building a 396 350HP for my '69 El Camino. Block and heads are from '67, heads are closed chamber oval port, pistons are a 19cc dome, solid cam with 240@.050, 10-1 compression, ported heads flowed 270cfm @.550 lift, has the forged 366 truck crank(rebalanced), 750 holley, Air Gap RPM intake, desktop dyno said 480HP-490Torque not accomadating the port work. The heads also have the chambers polished so I'm hoping to run on 91 pump gas. Just can't wait to drop it in. Hope this info helps on your build.

Another easy way to tell if it's a forged crank or not is to hit the counter weight lightly with a hammer. If it sings like a chime it's forged, if it makes a "thud" sound it's cast.

. . . and if it breaks, you forgot to read the "lightly" part.

I agree with those that recommend the hydraulic cam and lower compression. To coin a trite phrase, "back in the day" I had the 427 version of that motor (L-72). It was my daily driver and it was a beast. Had to adjust the valves at least once a month, gulped high octane leaded fuel and went through plugs pretty fast. Back when banks had drive thrus, it would vibrate quarters right across the tray while I waited for the teller. It would definitely run hard, but like the others said we have come a long way in 35 years. I also think you are better off with the oval port heads for general street use. The square ports are great from 4000-6800+ but for throttle response on the street and power under the curve, a good set of ovals ports might be better.

Good on ya for building a hot rod for your sweety! I'd do one for mine if I thought she would drive it.

Pat

Originally Posted by 69elko

Another easy way to tell if it's a forged crank or not is to hit the counter weight lightly with a hammer. If it sings like a chime it's forged, if it makes a "thud" sound it's cast.

I'm currently building a 396 350HP for my '69 El Camino. Block and heads are from '67, heads are closed chamber oval port, pistons are a 19cc dome, solid cam with 240@.050, 10-1 compression, ported heads flowed 270cfm @.550 lift, has the forged 366 truck crank(rebalanced), 750 holley, Air Gap RPM intake, desktop dyno said 480HP-490Torque not accomadating the port work. The heads also have the chambers polished so I'm hoping to run on 91 pump gas. Just can't wait to drop it in. Hope this info helps on your build.

Don't be hitting any cranks with a damn hammer.
If I saw this in my shop I would have to use the hammer on someones head.
Like I said before wide "parting line" it is forged narrow "parting line" and it is a casting.

Originally Posted by erik erikson

Don't be hitting any cranks with a damn hammer.
If I saw this in my shop I would have to use the hammer on someones head.
Like I said before wide "parting line" it is forged narrow "parting line" and it is a casting.

What you cranks at the shop made of glass???

Originally Posted by pat mccarthy

What you cranks at the shop made of glass???

Bad Pat,Bad Pat.
No I would be to afraid someone would miss and hit a journal.

Originally Posted by erik erikson

Bad Pat,Bad Pat.
No I would be to afraid someone would miss and hit a journal.

that ok i do not read jounals just short stories and also paper backs with lots of pictures

Originally Posted by pat mccarthy

that ok i do not read jounals just short stories and allso paper backs with lots of pictures

Pat, did I ever tell you about the time I dated the librarian?
Before anyone ask's the librarian was not a man.

did you get book worms from her