The original '68 396/325 mill that I'm about to have rebuilt needs plenty more torque, but must be able to get by on premium pump gas and not have an unseemly idle through cast manifolds. I'm going for the bone stock appearance with this one, but looking for a lot of extra grunt -- something that can push a Chevelle convertible into the 13s/14s when it's asked to.

I looked at the performance archives and got a lot of good info, but I still have some questions:

1. This is a two-bolt block with a cast crank. Has anyone got any misgivings about bumping up the power a bit using these parts?

2. Can anyone suggest a good power-building combo using the stock intake manifold and stock factory exhaust system? The car is heading for a full resto, so I want to do things right but add a bit more pull to the car.

3. The rear end is a posi unit connected to a TH400 up front, though I'm unsure of the rear gearing. I'll need recommendations here too. It will not be a long-distance car but I'd like to be able to get by with going to a distant cruise without the fatigue of driving at 4000rpm at 65mph in the slow lane.

All of you good folks with knowledge in this area, your views would be welcome. Thanks again! graemlins/hurray.gif

The L35 396-325 was seriously under-cammed for any kind of performance duty. For use with stock intake and exhaust manifolds, a hyd cam with a duration in the low 220's at .050 lift should wake it up nicely and allow you to retain the stock pistons with 10.25 CR and run on pump gas. To keep the idle fairly smooth and keep good vacuum for pwr brakes use a 112 or 114 LSA (114 smoother) cam. The actual CR from the factory was probably closer to 10.0-1 anyway. So don't deck the block or mill the heads any more than a light clean up if necessary with those pistons. The stock Q jet is plenty good with a little secondary valve tweaking. Also a good ignition recurve and electonic trigger such as a Pertronix in the stock dist. Low restriction mufflers would help too. The quietest performance muffler is probably the Dynomax Hemi Super Turbo, wich is about the same length and shape as a stock muff. All this would still appear as original on the outside but have noticably more power and sound a little healthier too.

A while back Dan the Impala man had the same exact Q, I'll try and search the thread down...basically blueprinting ( VERY EXPENSIVE IS STUFF IS OUT OF SEPC!), some mild porting, a really good valve job, opening the seats for bigger valves ( ONLY BY A PRO!!!) a cam going .500+ lift at the valve, etc....

But with all that if you put the snorkel air cleaner on, you migth as well just throw the motor together and put a cheap cam in it. That air cleaner REALLY DOESn'T suck!

Framer has a 325 hp with a comp 4X4 cam, nice pull for a stock ride UNTIL you put the snorkel on. No wonder they used an anemic .395 lift cam. You would never notice a real cam with that thing on.

Here's one of Dan's posts., but not exactly the one I recall....

http://www.chevelles.com/forum/ultimatebb.php?ubb=get_topic;f=9;t=007848;p=2#0000 16
From his user # ( in the profile) keep running searches. Hopefully the thread I recall wasnt deleted.

Retire the 396. Install a 454+ with all the stock-looking stuff on it. You can make much more torque with less noise and strain.

Over here, dude. (does anyone remember Sean Penn having his pizza delivered to Mr. Hands' class? Never mind.)

Anyway, to your question - or quest. Getting some beans out of a 396 while having it look completely stock can be a challenge - depending on how much extra ya want. In a 68 Chevelle convert - which I suspect weighs something close to 3900 (my Impala still has you by, say, 3 bazillion pounds) you're gonna want all you can get and it depends on how much you want to spend.

To your first concern, yes - from everything I've learned on this board your 2 bolt block and cast crank are easily up to the task of handling an increase - even a sizable one. Have 'em both checked and run them.

Leaving the stock manifolds in place makes this a challenge. Any increase you go for will have to be had by 5000, 5500 RPM's tops because the intake and exhause manifolds just won't support anything higher. It'll certainly spin past that, just won't make more power.

So, from the bottom up. Stock volumn oil pump with a higher pressure spring. Typical machining and balancing of the rotating assembly, high quality rod bolts, stock rods. Forged pistons are not necessary in this application but are nice to have. If the block needs to be bored - which means new pistons, here is one thing you can do: have the cylinders sonic tested to see if you can safely bore it to 4.250 (427/454 bore size). It probably can't go that wide but it's worth a check because it's not going to cost much more - if any, to bore it to 4.250, piston selection is greater, the valves get a little extra breathing room (which probably off sets the need to install larger valves in the heads), and you pick up 30 CI's. It's all good.

Since you will be looking for incremental gains where ever they can be found pay special attention to your piston-to-deck measurements (get them all as close to whatever deck height you are shooting for) and ensure you CC at least one combustion chamber - you'll need the info to correctly select a cam and set the quench. Because of your idle goals you'll want a static comp ratio right around 9.5 to 9.75:1. Anything much higher and you'll have to run a bigger cam to bleed the pressure.

Have the heads cleaned up in the bowls and the short turns, have a most excellent performance valve job done, and have the valves back cut a bit - all will work in concert with the cleaned up bowls. With the mild cam you are going to need to run to hit your goals I'm not convinced that there's a need to install larger valves in the heads - but they certainly won't hurt either. Then all the usual head prep.

The cam. Again, because you're limited by the intake and exhaust manifolds, there's not a lot to be gained by going with a huge lift cam. As Von suggests, something in the 220 duration - depending on your actual static compression, and .500 to .520 lift range, give or take. Consider a single pattern cam, opposed to a dual pattern. The single will make more torque up to 5k or so, exactly where your exhaust manifolds will start to give up. Also consider a solid over a hyd. Finally, one ground on a 112 or 114 will have a wider torque curve, and idle smoother, but may feel a little lazy.

Not a lot you can do with the intake or exhaust manifolds. The intake is way better than the exhaust so maybe match the exhaust manifold ports to the head ports. Either remove the heat riser valve or - like I did, have it gutted (mine looks completely operational from the outside). Have the distributor recurved as was suggested. The QJ is perfect when set up right. Like Gene pointed out, if you are running the stock single snorkle air cleaner consider running something else. Look at the secondaries on the QJ, look at the opening of the snorkle. You see the problem. I have a dual snorkle (Z28 reproduction) that I use for putting around - still looks nice and stock, and I keep the actual stock single snorkle for shows.

2.5 inch pipes off the manifolds and into the mufflers, deal with the heat riser as mentioned, decent flowing mufflers as big as you can fit. Consider running an X pipe before the mufflers to help scavenge the exhaust. Tail pipes bigger than 2.25 are unnecessary - bigger is your preference.

I can't comment on the TH400 or a converter, I run a 4 speed. Rear end gears will depend on the diameter of the tires you plan to run. For example though, I'm running 3.31's with a 28" tall tire. At 70 it's right in the neighborhood of 3k RPM's, give or take.

Good luck!

Dan

"Don't worry dude.... I can fix it!"

As far as your rear end decoding, look on the passenger side of the axle tube on the side that faces the engine. Along that tube somewhere will be a small code and date I.E.: CF 922 , which in my case decoded to a 3.31:1 Posi, built September 22nd. If assuming your rear end has never been changed you can find the code and decode it here: http://www.chevelles.com/years/68/68rearcodes.html

He, He!!

And while sonic checking your block, check and see if a complete stock bore 454 rotating ass'y won't drop right in b/c there are some 396 blocks that will swallow one easy!!

AND my 454 core block swallowed a 496 rotating ass'y AND I never touched it!!

pdq67

BTW, a good old CC 268HE, 270 Magnum or Isky 270 Mega on 108 LCA for a definate thump or a 270-HL on 114 LCA for a smoother, wider power band with less thump should do you fine imho...

Remember, you need to build max. midrange grunt b/c of the cast-iron exhaust manifolds!! I would go for max. T from say 3500 to 4500rpm, imho!!!

pdq67

Man, I hate to give away how OLD I'm getting, but in 67 I had a 360HP 396 Chevelle 4 sp. 4:10 posi. Only 1 year deal. That was fast street car for those days. The only diff between 325 HP is cam (same as 390 HP 427 vette) intake & carb(600 single feed Holley) It would destroy 325HP 396 and 375 HP could not get you till mid 3rd. gear.In my opinion all you need is good hi-rise intake, just a little more cam and a good Holley carb. Almost forgot(can't believe I still remember this stuff !) Before I changed rear gears(came with 3.55 open) car got 17 mpg at 70 mph.
Sorry for the rant, this was like remembering first sex deal !

First sex, you mean the ability to reload ad-infinitum! Thnks for sharing and thanks Dan.

simple
Use your 396 block and stuff in a 454 crank to make 434 inches, the longer stroke helps move the big old barge and the thing will look stock . Since you will not have to spin it that fast it will work with your exhaust manifolds.

You can use a cast crank, a set of reworked rods and KBs "KB361" pistons. These will work with open or closed chambers and give you some CRs you can run with pump gas.

God, this is a great place. graemlins/beers.gif

Thanks for the replies, all. I'll discuss all this with the engine shop and get back to you on what I decided.

I ran the same combo as old66ss back in '69. A '67 Chevelle SS396-360 with a wide-ratio 4 speed and 3.73 gears. I went through the stock motor (cc'd and ported oval heads, decked block, end gapped rings, good valve job, etc.) loosened up all the clearances, and put in a factory 396-375hp solid cam advanced 4-6 degrees. Kept the stock iron intake and stock holley. Stock cast iron exhaust and Hemi turbos with 2.5 exhaust system.
People used to call the car "the freak" cause it ran so hard and looked so stock. It was one of the fastest street cars in the area from 69-72. And it would KILL 396-375's all day long.

Randy

ok.........how about this.....my 396 was a factory 402 out of a 1970 c-10 pick up.....the old engie was beaten to the ground and it used oil......well off to the machine shop it went.

it was built to these specs, why? just because. maybe we didnt know any better 13 years ago.

heads stock...just cleaned up(tanked) and valves reground with a 3-angle valve job.118 cc open chamberd 2.06 1.72 valves. factory style replacement spring el'cheapos

intake stock low rise

carb....600 vac. sec. with carb adapter

bottom end stock, cast iron, cast el'cheapo pistons, 2 bolt main, and of course nothing balanced.

cam 272 crane cam 216 @ .050 with .515 lift.

compression ratio worked out to be 7.7 to 1 real downer....... the pistons was down like .055 down the hole the domes on the pistons was not worth the crap for nothing ...and the heads were to damn big (chambers) and on top of that we put .039" headgaskets on too.

but in all surprise this combo was good enough to haul a 3800 lbs 81 camaro down the track with 2.56 gears and stock stall to 14.40's right at 99 mph with a 14" open air filter and open stock exhaust manifolds........sounded like crap....I put headers on it open.........NO change...60 ft times was still 2.15-2.20 range and mph never fell below 99 mph. but sounded so much better.

5500 rpms was the shift point.......it didnt make do difference between the open stock exhaust manifolds or the headers i got for 25 bucks. crap i spent more time finding an exhaust manifold to clear my firewall then i did for those headers.. the one truck manifold wouldnt clear my firewall.

You know, another angle on this, although a bit disingenous, is to source a 454 block. Any will do. Grind off the casting numbers. You can then use "Steel-Bed" from Brownell's ( gunsmith supply house) or any sintered steel epoxy compound ( including JB Weld I suppose) to reinstall the casting numbers.

On the top side, have the block decked professionally, to give you a good deck height, like .005". Then have the numbers stamped back on the pad. If going through this elaborate "immaculate deception", I would drop the dime on a SCAT 4.25" internally balanced crank. Using hypereutectic pistons with a slight .100" dome with your oringal heads should get you 10:1. Here I havent done the research yet, it might be that flattops will achieve a 9.5:1 compression with a 4.25" stroke.

Fit the block with a modern hyd cam, ala the Lunati 280/88.

Bolt the original topside on, heads, intake QJ etc.

Save your orignal block. Run a 480 ci rat under there. NO ONE will be able to tell.

You can probably do the whole shortblock for $2000. You wont need anything trick in terms of rods, etc, since you'll be shifting that phatty at 5000. Keeping internal balance will allow use of all your orignal flywheel, etc.

If I ever do a full resto on Old Red, this is the "396/325" that will go into the car. Should work OK with an M20 and mild 3.08 gears, huh?

First - Decide how much performance you really want! I was faced with the same decison when I took on my own project. Decided to go with the 402 block that was in the car. In my case, the engine did not need boring or new pistons, if it would have, I probably would have went 454. There is plenty you can do to a base 396.

The oval ports on these are good to 5500 rpm in stock form.

A good freshening up of the engine is in order.

For a big performance gain, go with a modern high lift cam, you can go hydraulic, short duration solid or hydraulic roller. For stock heads keep the lift to <.540", the 2.07 int valves don't realy flow that much more above .500". Run 10 degress additional duration on the exhaust side.

Make sure to run a non-restrictive exhaust system. You can get a full 2.5" system that will bolt up to the factory manifolds.

Performance curve ignition timing

Different gear ratio. [if it has a 3:31 now, that will probably do]

TH400 = New Stall Converter. The stock converters are really tight, put a 2400 - 2600 converter in there, just that change alone will feel like 100 extra cubes.

There are many things you can do before you go for the bigger motor. At least that's the way I prefer to do it.

And last, you could do all of the above except use the 454 block & crank - SIT DOWN, BUCKLE UP, SHUT UP & HOLD ON!!!!!!!!!!!!!!!!!!

Latest Update:

The restoration shop got my unassembled 396/325 long block back from Dugan's last week, and it's sitting in a crate down south waiting to go back in the car when the body and frame return. They tell me that Dugan's 'does things right' and has had a lot of his shop's work appear in show cars and drag cars, and he's highly respected in SoCal. Can anyone back that up? :D

They found that my oil ring on #5 was sitting in the oil pan. Still, the bores only needed to go thirty over. On another thread I mentioned that they determined that the crank was .010/.010 over but the bores were never touched. Coulda been a factory job, they tell me.

They've said that their rebuild recipe for pump gas 396s amounts to 375 horsepower with factory exhaust using some model of Crane cam. All new rotating assembly except for the stock crank. They've used forged 427 pistons with the domes cut down to get the new CR of 10:1. I've had the heads tooled on, relieved in the turns, polished in the bowls, and port-matched, so I hope that I get an appreciable increase in torque even with the stock intake/exhaust hardware.

That's all I know at the moment, and that detail assembly of the motor begins soon. I hope to run a 2.5" exhaust and a new Quadrajet. For ignition, I'll take the advice above about the Pertronix module in the stock distributor.

Does anyone know about running the freer-flowing Corvette big block cast exhaust manifolds on a Chevelle? Does this work? I have PS, and no AC.

This motor will be a lot stronger than I remember it, I am sure. When I got the car, the motor was ailing badly. I didn't have this car on the road but for six months maximum before I garaged it for 15 years after the motor and tranny went bad.

graemlins/hurray.gif Oughtta be fun.

You asked "Does anyone know about running the freer-flowing Corvette big block cast exhaust manifolds on a Chevelle? Does this work? I have PS, and no AC"

The answer is NO
Corvette manifolds will only fit Corvettes and trucks,not any other passenger cars.

This'll help a little---

http://www.speedomotive.com/396%20TO%20434%20BBC%20BUDGET%20STROKER%20KIT.htm

Greybeard,thats a pretty awesome link..that would be fun to do to a 396/402..with closed chamber heads and use the Lunati 280/288 or 288/296 cam

Corvette manifolds will only fit Corvettes and trucks,not any other passenger cars. Mr 4-speed... I thought the Corvette manifolds WILL fit the Impala/full-size cars... I recall that the 1966 427/425 HP L72 in the Impala used the same Corvette exhaust manifolds as the 1966 BB Vette, and they were a different part number than the standard BB full-size manifolds...

I could be wrong..I know they won't fit an A body

The big block sits back further in the Corvette chassis. The BBC Vette Manifolds look more like shorty headers and will interfere with the crossmember.

When I first got the 70 it had a stock 69 396/325 in it. I put in a TRW remake of a LS-6 cam with a c396 dual plane/331 gears/11"converter/stock exhaust manifolds and a 2-1/4" exhaust it ran 14.0s@96mph (with a smooth and quiet idle). IMO the pistons are the weak point, add good rod bolts and a decent piston and 450+hp should be no problem for the bottom end.

Years ago I changed the factory 360HP cam with the 375 HP cam. The car ran much better with the 360HP cam (much more torque) The 375HP would rpm much better but the engine simply ran out head before the bigger cam really helped.