gruveb

What are the 396 big block's tendencies?

Does it have a relatively wide bore compared to the stroke? A 302 or 327 revs easily and I am wondering if a 396 does so for a big block b/c it's displacement is low.

Also, is $150.00 for a short block a good price on a 396?

Any other info on it would be welcomed!


Happy Thanksgiving.

AlkyIROC

First of all think of a 396 as a heavier 400 SBC since they can produce roughly the same amount of power.

The 396 has a 4.094" bore that can be bored out to 4.250 if there's no core shift. The stroke is 3.76. Boring the block out that much and still using the 396 crank makes a 427.

If you're going to invest in a big block then you might as well get some displacement out of it and go with a 454. The bore is 4.250 (can be safely bored out another .125") and the stroke is 4".

So theoretically you can bore the 396 block out to 4.250 (if the block has no core shift), install a 4" stroke crank and have a thin walled 454.

1982chevycamaroz28

but if u bored the 454 out and have the thin walls wouldnt the engine run really hot? becuz ive read where if u bore out an engine alot u will have problems withthe engine running hot becuz of the heat from the combustion chamber goin right to the water/antifreeze in ther block where the water/antifreeze is suposed to help cool but yet ur heating it up becuz the walla are too thin

Ions91Z28

This is something I've always wondered. Although cubes are often looked at as how much power you can produce or ease of producing power. With BBs you can run a head that'll outflow any SBC head, not to mention the advantage of running 1.8 rockers, I've also heard their cranks are much stronger (I'd assume due to size, I know you can fit bb cranks in sbcs) as well as capable of running higher lift cams.

Of course much of my information may be off, although I'm pretty sure about the heads. If so, wouldn't this technically give the advantage to a big block?

Not looking to start an arguement, just curious.

AlkyIROC

Since all BBC blocks can be safely bored out .125" over it's better to start with a real 454 block.

Boring the 396 block to the absolute maximum can make a 454 but it's still not a 454 block. The 454 block can be bored out an aditional .125" and probably more if there's no core shift.

Factory BBC heads can flow as much air as good aftermarket SBC heads so the ability to get more air into the engine will produce more power. The BBC can easily use 2.19/1.88 valves to also get more air in and out of those cylinders.

The BBC has 6.135" long rods compared to a 350's 5.7" rod. Both engines can have long rods installed and the BBC will still have a better rod/stroke ratio.

Assuming aluminum heads are not used, the BBC will add 100-150 more pounds to the front of the car but the extra torque it can produce should easily overcome that.

ede

302s and 327s don't rev any higher or faster than any other SBC

gruveb

No, it's not that they rev higher more safely, that's not how I meant to word it. Sorry.

I was referring to the effects of a wide bore / shorter stroke opposed to a narrow bore long stroke.

five7kid

iTrader: (14)

Not all 396s were created equally. The rear cam bearing oiling was different on '65 & '66 BBCs than all later versions, and therefore different than all aftermarket cams. Just have a grove machined in the back journal if '65/'66 block.

Aftermarket heads typically don't work well on 396s, since they are open chamber and 396s were closed chamber. Plus, the larger valves are shrouded by the smaller bore cylinder walls, limiting flow potential.

It's easier and cheaper to make power with a 454 than with a 396. But, you can get factory BBC heads to flow more for the dollars than you can with SBC heads, so if you find some factory small chamber heads, do some "normal" porting and valve work on them, you can make a pretty good running 400. It'll weigh more than its SBC cousin.

FWIW, my car weighs 3900 lbs with me in it, is a fairly mild build. A good second faster (at altitude) than the 350 that preceded it.

zippy

they are certainly right, the 454 is the better way to go, but if you can get a 396 cheap and don't mind the swap work it's worth it. evenly compared it has been done a few times the big block works over the small block of the same cubic inch since there is much better head flow. more than a few tests have had 408 small and big blocks against each other and the big block will win. a 396 with properly selected parts does quite the job for a street car and a consistant reliable drag car.

F-BIRD'88

Forget all this theory about bore and stroke and rev this and rev that.

Bunch o' houwie.

The motor will want to rev based on the cam, induction tuning
port volume/flow and cubic inch displacement relative to each other.
A short stroke will want the same rpm as a long stroke motor of the same cu in under the same head. (induction)

All push rod valvetrain motors are limited by the valvetrain
RPM way before the bottom end.
Now that we've put that bunch 'o **** to bed:
A 396 is a good motor to build. But needs carefull machine work
and good assembly and balanceing. You'll need to enlist the help of a good qualified machinist. It will cost a little more to build than a small block, but will be worth it. More durable and powerfull motor.
You can make 700+ horsepower with the stock open chamber oval port head.
ya just have to max port it and use bigger valves.
Big blocks love valve lift. Get a solid roller cam.

As stated above most 396 blocks can be bored to 4.25".
I think all 396 cranks are steel but some are not cross drilled (oiling). This would build a 427 cu. in motor. Cost is the same.
I'm pretty sure a 396 block will not accept a 4" stroke crank without main web relieving. I'd stay with the 3.76" stroke.
HP/$$$ You need to upgrade the stock rod bolts- minimum.

gruveb

I don't want to get in an arguement over this b/c I think what you are saying is very valid and I'm not that knowledgable, however, but the longer the stroke the more pressure put on the piston walls. I was reading a book about engine building and they had a chapter of the geometry of the crank, rods and pistons and the effects on longevity. Since the book wasn't trying to sell me anything and everything else I read panned out, I'd trust it to be true.

Now the Seat of the Pants testing probably won't show too much, but I think there is an effect.

With that in mind, if the guy ever calls me back I think I'll pick it up. It'll be a long time coming, but I'll get it in there eventually.

Any other ideas?

gruveb

I just got off of the phone with the guy. He isn't sure what year the motor is, he bought it for a project from somebody who used it for a circle track car.

It has one burned piston, but the block is unaffected and you can burn the motor over with a breaker bar.

It includes block, crank and pistons.

$150.00 a good price?

If I understand correctly, get a set of factory heads and have them ported right? What do I look for?

I'm a complete idiot here, so if I wanted a streetable cam, carbed setup, what would be a good starting point?

I'd want a decent idle, factory vac brakes and so on.

One last thing, what is the typical gas milage difference between a slightly modified small block and a slightly modified big block?

F-BIRD'88

Hate to rain on your Libary of Big Block knowledge but:

More overgeneralized bull****
Bigger cid motors have more friction than smaller cid motors.
The crank stroke has little (in itself) to do with this.
A big bore creates just as much friction / cu. in, or more.

*Just about* all the power/ potential/$$$ is in the cylinders heads.
Don't waste money on long rods or destroked crank.
* Unless you've got $$$corporate sponsorship$$$.
Look at the theroreticaly crappy rod to stroke ratio of todays modern Pro Stock motor. By your theory they should have hit a horsepower
"brick wall", yrs ago.
The only advantage a big bore/ short stroke motor has over
the same motor of the same size with a bigger stroke/ smaller bore is the bigger bore allows bigger valves. Period.
Bigger valves= more airflow which = more volumetric efficiency @ high rpm/ cu in. = more horsepower

Burn that book your reading and spend your money on the cylinder heads/ cam/ induction/ exhaust.

gruveb

It never claimed that the larger the CID the more friction. It never said anything about anything like that. It was referring the advantages of gaining displacement with wider bore versus longer stroke. It was referring to longevity, friction and so on. Had nothing to do with CID. By no means did it suggest destroking would produce more power and neither did I.

The book was referring to longevity, NOT racing. There's no replacement for displacement. Granted. However, sometimes there are cheaper, more effective ways to get it. I was originally merely asking if the bore/stroke ratio is more similar to that of say a 383 or 305 or if it was more like a 327, 302?

You're a little touchy.........CHILL OUT!

Ditto on the cylinder heads. The smallest area to get airflow in and out of is in the heads. That's why big blocks usually outperform small blocks.

The book also suggesting putting money into cylinder heads opposed to a longer stroke crank.

F-BIRD'88

$150 for useable block and crank is a great deal.
The pistons will make nice ash trays.
If your on budget, the stock oval port , open chamber heads
are all you'll ever need. 1971 to 1975+/-
Certainly all you'll need for a good street motor.
The best casting # to look for are 049 and ???____
Drawing a blank here.

Yes they'll need bigger valves and you can do a decent job of porting them your self.

gruveb

Thanks.

F-BIRD'88

Not getting touchy here. Really. Just trying to steer you clear of some of the biggest B*******t and waste of wood(print) or internet bandwidth that ever was.

It is not uncommon at all to dissassemble a old greasy 454 just to find thoses poor cylinder bores that have beem ravaged by that big old 4.00" stroke crank for 150,000 miles. Just as pristeen as
they were when 1 week old.

Bore wear is mostly caused by dirt.

The notoroius '70's smog motors used to wearout the bores because fo a combination of poor maintainace and lean mixtures
and retared timing. (primitive emmissons tuning) and bad gas.
this is where the short rodded 400 small block got its bad reputation for wearing out the bores and overheating. Thus the popularity of your theory.

gruveb

Point taken.

I wouldn't NOT turn a 350 into a 383 in favor of a 327 because somehow the 327 may make more power because of a shorter stroke, I know that's total bull****. And the stroke of the 383 isn't long enough to cause trouble.

However, when people start stroking a 305, the are starting to get into the dimensions that can cause trouble. The book was also talking about how in a V pattern stroke engine the effect is minimal.

My question was only out of curiosity though.

Sorry for the touchy remark, my kids are driving me nuts at the moment. I'm ready to sell them off! Only thing I hate about the holidays is putting up with cranky, over-tired children!

F-BIRD'88

Good luck on your big block buildup. Thery're a lot of fun.


this is my old 1970 454 bb Bird

gruveb

What times do you run?

F-BIRD'88

Lets just say TOP SECRET!

A matter of National Security..... My insurance broker may be browsing this board......

five7kid

iTrader: (14)

Not sure I can go along with the larger valve part. The top of the cylinders are notched for 2.065" valves, so how would larger valves help? A better bet would be to go with Manley Pro Flow style valves with your basic performance valve grind. That's my plan for the winter improvements on my 396, along with the porting.

If you do go for the 427 bore job, the cylinder shrouding would be reduced, so larger valves would be of more benefit.

F-BIRD'88

True the hi perf 396 and 402 motors had notched cylinder bores
to allow 2.19" valves on the hi perf square port motors
Once you bore to 4.25" this is not nessessary.

Not going to a larger 2.19 x1.88 valve set woul seriously limit the potential of a port job on your heads. The stock valves are
under sized for the size of the port.

Daz

iTrader: (1)

049 vs. 781

How would you compare bolting on a 781 vs a 049 heads on a stock 5445 block(1990 TBI SS)?What about 045 compared to the two?Im bolting it on for now with cam/intake/headers/carb cause of $$ constraints..Also you got any of the said heads handy..ported??The ultimate goal is to have 450-500HP,should I just wait for rectangular heads?What would be the most streetable cam(or combo) that can go well over 450HP..Im in Mississauga

Daz

five7kid

iTrader: (14)

My 325 horse, oval port, 2-bolt block is notched. I believe they just notched all of the blocks, regardless of version. Of course, my block also has "Hi Perf" cast on it (even though the engine isn't...).

I'll have to scribe the heads & block w/head gasket when I pull the heads and check dimensions, but I was under the impression that even the smaller valves needed the notches for higher lifts. And, as previously mentioned, high lift is what Rats like, anyway.

This discussion is more proof of the lack of information/developement on the smaller cube Rats. These days, you just don't start with anything smaller than a 454 in the aftermarket. In the late-'60's/early-'70's, there were a bunch of hot 396's out there, and most of them started out as the barely-streetable factory 375 horse version. Like what happened to the 302/327 when the 350 came out, the 454 eclipsed the mousy rats and the rest is history.

F-BIRD'88

I believe the 049 and 781 are the two popular open chamber
oval port heads that every one starts with for a oval port build up.
I don't know what a 045 casting is.
The recent 454's from the SS 454 pickups have tiny peanut port
heads. A small volume version of the earlier oval port.
I don't know the factory chamber cc volume on these heads.

The 049 and 781's have large 122cc chambers resulting in low compression if used on a stock 91 SS motor.
They need a 21/25cc domed piston to give 10:1 on a 454.

Look at the Edelbrock Performer RPM package for an idea of the power potential of a street friendly oval port 454.
A Comp Extreme Energy 274 or 284 hydraulic cam would be a good choice for a 454 street motor with ported heads.
Another sweet running street cam is the factory 1970 454 LS6
cam from the 60/70's. It's a nice streetable solid cam.
Easy to live with but a real performer.

I do not have any BB heads now. But a buddy of mine does.
If you're serious about a build up, let me know.
Another alternative is to get good performance oval port heads with smaller combustion chambers for use on a flat top 454 (91 SS)
is to start with a set of 66 to 70 396 oval port heads (96cc)
and work with these. The ports and chambers can be reworked to match the open chamber head's performance. Best casting # is "915" among others.
When your done you'll have the right compression ratio for
the street with a stock 91 454SS bottom end.
The factory tiny peanut port heads are good for mild torque type build ups up to about say 430 hp or so. So if you only want that much power, you can play with the stock heads. But these heads do have a practical power limit.

www.mortec.com
www.compcams.com
www.edelbrock.com
www.professional-products.com
www.cranecams.com