Baxter

What's the difference in these two engines?, Camshaft?, or ???. Also any Idea the torque difference between 396 and the two 427's?

Blkblt

I presume you are referring to the 1966 427s. The 425 hp version (L72) initially came out as a 450 hp engine, but (in a nutshell) the insurance industry got nervous so GM just backed the rating down to 425hp (less than 1 hp/ci). They didn't change the engine specs at all... :lol:

The L72 had a solid cam and lifters, aluminum intake and a 780 cfm Holley carb. The 390 version was a hydraulic cam and lifters, cast iron intake, and a smaller Holley (not certain, but maybe a 580 cfm). The L72 was, and remains, a high rpm screamer.... :yesnod: :yesnod: :D

*************

********************
Jeff
Ô66. Demonized L72
ÒThe Silver BeastÓ
Keep on :seeya :seeya :flag

Baxter

So what I guess I want to know is, how hard would it be to convert a 390hp to the 425/450? Do they both have 4 bolt mains?

WADE1965

The 390 also had oval port heads so to do the change you would have to change the heads,intake,carb along with a different cam and lifters. I don't know if the 390 was a two bolt block or not or if it had a forged or cast crank.

427Hotrod

The 390 hp was a 2 bolt motor. The rods in both engines had 3/8" bolts but the 425 hp had a slightly different forging. They were "dimple" rods meaning they had a small dimple on the beam to identify them. Even though they were different they weren't much stronger. Many folks found that when they revved the 425Hp engine into the range the rectangular port heads started making power at, the rods failed occasionally. That's why later on you see the L-88 rods with 7/16" bolts and a much heavier forging. The weight was a penalty but they are strong!

425 hp had TRW/GM forged pistons with pressed pins. Closed chamber iron heads with rectangular ports. It also had the "143" GM solid lifter cam that was used in the 396/375 (or 425 if it was in a Vette), and the 454/450 engines. It's actually a pretty decent mild street cam that can run 11's when tuned right.

Do you want to make a real "clone" or do you just want to outrun an original 425 motor?

The right setup of cam and intake and headers on a 390 hp engine can keep up with any stock 425 hp car.

jim

67HEAVEN

390hp L36 / 400hp L68 (these two are the same except for intake, carb and air cleaner)
===============
10.25:1 compression
hydraulic lifters
valve lift .4614 inlet; .4800 exhaust
L36 - Holley 4bbl / L68 3x2bbl Holleys
2-bolt mains
single-breaker ignition
2450-2750 lb. clutch
oval-port heads 2.060-2.070 inlet valve dia.
oval port cast iron intake manifold
pistons - cast aluminum alloy
connecting rods - drop forged steel

425hp L72 (1966) / 435hp L71 (1967) (these two are the same except for intake, carb and air cleaner)
===============
11.0:1 compression
solid lfters
valve lift .5197 inlet; .5197 exhaust
cam .3057 inlet & exhaust
L72 - Holley 4bbl / L71 3x2bbl Holleys
4-bolt mains
transistorized magnetic pulse
2600-2800 lb. clutch
square port heads 2.185 - 2.195 inlet valve dia.
square port hi-flow aluminum intake manifold
pistons - aluminum impact extruded
connecting rods - high alloy steel

There are several other differences in bearings, clearances, etc. All in all, it would be quite a job and lots of expense to convert a 390/400 to a 425/435.

six-T-six

Like the guys said above...

On the bottom end:
The 390HP has 2-bolt mains and cast crank, and lo-perf 3/8"-bolt rods.
THe 425HP had 4-bolt mains, forged crossdrilled crank, and hi-perf 7/16"-bolt rods.

It depends what you are trying to do. If you are trying to replicate a L72, it wouldn't be worth it. If you just want some extra power you can easily get those gains and still be pretty reliable with the low perf bottom end and heads, if your engine is in good shape now.

I had a 2-bolt, cast crank, cast piston engine with 10:1 compression and it probably made similar power as an original L72 (ran high 12's/low 13's) in stock trim. Nothing fancy: just changed the cam, carb and heads and tuned it a little. Used a Holley 750 double pumper, Competition Cam Hydraulic 292 with open-chamber oval port heads and a dual plane manifold. The exhaust and the spark was the stock. This motor was great around town, idled great and had great torque.


[Modified by six-T-six, 6:36 PM 11/19/2001]

Baxter

Thanks for all that info guys, what about the 65 396? is this built like the L72? Or in other words is the L72 a bored out version of the 396? Also it is easy to find HP ratings for these engines but what about the torque ratings??? I stopped by a chevy dealer and they couldn't find that info, though the said they would research it. I figure you guys can come up w/ it sooner! Thanks again for your help as I try to sort out which car to drop 40g's +/_ on. I only got 1 shot, don't want to screw it up!!! Hey one more thing anybody know how a 375 HP fuelie s/b stacks up against these b/b bad boys side by side?

67HEAVEN

Baxter,

Here's some more info.

The 1965 L78 396-425hp engine is the same as the 1966 L72 except for cu.in.

Horsepower (notice that the big cube engines get their ratings much lower down in the rpm ladder):
L84 (327 Fuelie) - 375 @ 6200 rpm
L78 (396) - 425 @ 6400 rpm
L72 (427) - 425 @ 5600 rpm
L71 (427) - 435 @ 5800 rpm

Torque (you want torque.....get cubes):
L84 (327 Fuelie) - 360 @ 4000 rpm
L78 (396) - 415 @ 4000 rpm
L72 (427) - 460 @ 4000 rpm
L71 (427) - 460 @ 4000 rpm

You asked about the difference between the Fuelie and the big blocks. No contest. Even the '65 L78 396 took it. The L72 and L71 did further damage.

Car and Driver tests in 1965
L84 (Fuelie):
0 - 30 mph - 2.9 sec.
0 - 60 mph - 6.3 sec.
0 - 100 mph - 14.7 sec.
1/4 mile - 14.4 @ 99 mph

L78 (396/425):
0 - 30 mph - 3.1 sec.
0 - 60 mph - 5.7 sec.
0 - 100 mph - 13.4 sec.
1/4 mile - 14.1 @ 103 mph

One final comment. If you accept the 425hp rating given to the L78 - 396 in 1965, it's obvious that the same engine with 31 more cubic inches (1966 L72) should make more horsepower. Therefore, the original Chevrolet rating of 450hp seems reasonable for the L72. Further, if the L71 is worth 10 more horsepower than the L72 (due to the 3x2bbl carbs and intake) then the L71 should probably have been rated 460hp.

Not that I'm partial or anything. :blueangel:


[Modified by 67HEAVEN, 3:56 PM 11/20/2001]

Kid_Again

"help as I try to sort out which car to drop 40g's +/_ on"

...did i see that right?.....you can get a 390hp for about 30K, of course, depending on condition, add about 5-8K more for a fouranaquarter (same caveat).....the fouranaquarter is a great car but if you get a good deal on a 390, you can easily warm it over with today's goodies, show nothing but tailights and still have a few bucks in your pocket :D

six-T-six

If you've got some play money....and if you're going to have fun with the car, I say get one and pull the original engine for safe keeping and drop in a new GM 502 to play with.

Blkblt

six-T-six wrote:
"If you've got some play money....and if you're going to have fun with the car, I say get one and pull the original engine for safe keeping and drop in a new GM 502 to play with."
______________________
I know there have been previous threads regarding just this trade, but refresh my memory....is a 502 a "drop in", or are there major structural and suspension mods required??

*************
Jeff
'66. Modified L72
"The Silver Beast"
Keep on :seeya :seeya :flag


[Modified by Blkblt, 6:51 PM 11/20/2001]

Vetterodder

I think there were some games played in hp ratings back then and one of the most common was to advertise the output at different rpms. The L88 was probably the most extreme example of this, advertising it's output almost 2,000 rpm before it's actual peak power. Another example is the difference, or the lack of, between the rating of the L78 and the L72. As already posted, both engines had the same specs except for the the L72's extra cubes. To get the numbers they wanted, they simply advertised the L72's power at 800 rpm less than the L78. A reading closer to the 396's 6,400 rpm would put it back to the 450hp it had started with. They wanted the L71 to show a little more power than the L72 so they used a reading taken at 200 rpm higher than they'd used for the 425/L72. Another example that comes to mind is the original Z28 302. Compared to the 365hp 327, it had the same cam, compression ratio, a much bigger carb, better intake, but 25 less cubes. It was rated 75 hp less than the L76 due to it's reading being taken at a much lower rpm than it actually peaked at.

six-T-six

I've never done it myself so I can't say. But I believe the Gen VI long block is similar enough to the Gen IV long block in weight. Unless you're going to race, I wouldn't think structural and suspension mods are required for a daily driver since the Gen VI blocks were capable of making big power also.

oger

They are 2 motors with the same size that are made for completely different uses. The 390 HP is a smooth running motor with lots of low speed torque that will work fine with a PG. The 425HP has much less low speed torque but moves the power band up 1000rpm and really needs a 4spd and at least 3.55 gears.

396 RAT

You asked about the difference between the Fuelie and the big blocks. No contest. Even the '65 L78 396 took it. The L72 and L71 did further damage.
--------------------------------------------------------------------------------
396? "Poor little feller, aint no bigger than a squirrel."
MMMM HHMMMMH, Aint that right Carl.... (Sling Blade)

I think the heads & carb were different on the 396 V.S 427, combustion chamber in the heads as I recall. The 396 does not get much ink as most folks think about there friends Chevelle from high school, and have never been in a 396 Vette.
(Only 2157 produced in 65)
My car ran a 427 69-71 2 1/2 yrs, (out of 22 yrs racing 65-87)
Prev owners said there was no advantage with the 427.
Car still has its orig 396.

Just playing the under dog here.

(here's an old Vette joke. Q: Whats the difference between a 425
396 and 427? A: 1/8" :lol:

With modern cam's , heads, intakes, single carb & exhaust you can pass up any solid lifter 65-67 BB with ease, even if it is a 2 bolt.
What you wont get is a BB that likes to REV like a small block.
Thats what I like about these old boat anchors, is the top end.
That magic tranformation from 3500 to 6500. Its hard to explain.
Like Dr. Jeckle and Mr. Hyde.
You might even fall in love with the 390, most folks dont even come close to running these old cars at the red line anyway. You should run it for a while
prior to making any changes.

(sorry, I was just in a smart a s s mood tonite!) no hard feelings... :)
:cheers: :cheers: :cheers: :cheers: :cheers: :cheers: :cheers:


[Modified by 396 RAT, 11:45 PM 11/20/2001]

MassVette

If you want an 'original' style car, then buy it ALL DONE. You CAN'T- do you hear me- CAN'T do it for what you can buy one for. If you want a Big Block 'project' car, then either use a GM crate engine, or a Bill Mitchell 'Merlin' crate engine, with a Richmond Overdrive 6 speed. The GM gen. VI BBC is a bolt-in for the C-2 and C-3 Corvette. I believe the 'Merlin' is a MK.IV design block, so it has the mechanical fuel pump boss. and the correct clutch pivot locations. Also, the GM gen.VI 454/425 HP has the mechanical pump boss, and the correct pivot holes. This is the EASIEST 'Replacement' style motor for a BB 'vette.The 454/425 can be bought COMPLETE for a little over 4K.
THe Bill Mitchell Merlins go from around 6K to 16K; they are from 500 hp to over 800 hp., and will also fit.
It ALL depends on how much $$$$$ you can spend. My 2c.
:yesnod: :chevy :chevy :chevy :yesnod:

427Hotrod

No question... a 396/425 is an absolute blast to play with. I've done it. I still think a well set up 396/425 or a 427/425 would be an absolute blast to play with in these pure stock (appearing) drags that are happening.

I believe some "new tech" guys could get surprised!

I've also played alot with oval port 396's and 427. Also easy deep 11 second potential without much trouble. They just have a whole 'nuther character as compared to the square port motors.

As was mentioned.... the only thing better than a 327 at 7000 rpm is a 427 at 7000 rpm!


Jim


[Modified by 427Hotrod, 12:39 PM 11/24/2001]