The Grumpy Grease Monkey mechanical engineer.
I have a 1971 402BBC that I want to put in a 65 Impala. It has low compression in 3 cylinders. I have taken it apart and the cylinder walls look good. The engine has 820 heads.
I want to build this engine into a strong street runner, lots of low RPM torque. I value reliability over high performance.
I have a new Performer RPM intake and carb.
I have ordered some BBC rebuild books to read. I would like to hear some opinions.
I have a 4L60 tranny I could put in. I was hoping to do a manual tranny swap but don't think the budget can support this with the engine rebuild.
The car has a 12 bolt rear end but I currently don't know rear ratio. I have a set of 355 gears that I plan to get installed.
many guys will tell you that a 402 cubic inch BBC engine re-build is a waste of time and effort, simply because the component cost and machine work required, too get it rebuilt, correctly could better be spent buying a 454 short block as the cost vs potential favors the larger displacement.
Id say that you need to keep your mind clear and check all options, blindly jumping into a rebuild , and opening your wallet without a precise well thought out plan is looking to waste time and cash!
a 402 BBC has much more potential than many people realize, simply because the blocks and the rotating assembly are much stronger than the SBC 400 and the oval port heads in many cases provide much better air flow than even the vortec heads.
rectangle port heads generally work best on 500 or larger displacement engines
with at least 10:1 compression and cams with at least 245 duration at .050 lift and valve lifts over .600 to take advantage of the potential port flow rates
btw even un touched stock oval port big block heads significantly out flow the SBC vortec heads everyone seems to rave about, so its no wonder that a 396 BBC can be built to out power a 400 sbc.
The correct cam bearings for the engine you have is very impotent some take a grooved rear cam bearing #396 Clevite SH615S 65-66 only!!!
Clevite SH616S 67-93 396-427.
It generally pays off to step back mentally and think carefully about your goals, budget skill level, and access to parts and tooling before jumping into any major car repair work!
youll want to make a rational choice, getting 500 plus hp and/or 450 plus ft lbs of torque out of a 402 bbc is not that difficult, and you can build a 433 stroker with a 454, 4" stroke crank and aftermarket pistons,
but youll want to check the cost vs value of the components and machine work against your other options.
will very likely come very close too the cost most machine shops charge to sell you a basically stock 454 short block assembly, carefully consider your options vs the potential power per dollar, youll likely have once its rebuilt.
and before you start , any engine build project, you'll want to get out a legal pad and stop by your local machine shop and price out the cost of having your 402 BBC or any other engine rebuilt and the option of just cleaning up the block, installing new cam bearings, freeze plugs, a new set of rings bearings , cam and lifters, is their but then ask about what new pistons and rings and the cost to bore and hone the current block if the current bores will require that to get a good ring seal.
(if they suggest over a .030 over standard bore size its generally a good idea to have the bore walls sonic checked for thickness.)
3993820....71......oval...OPEN...402, 113cc chamber, 255/114 ports
you have hundreds of options but those are decent cylinder heads that respond well to a well matched set of headers with a low restriction exhaust, add a high rise dual plane intake like a
especially once you get the compression up in the 9.5:1-to-10:1 range and use a fairly mild flat tappet hydraulic cam with about .480-.520 lift with a cam in the 210-220 duration at .050 lift for the rpm/power band your indicating you want.
the 3.55:1 rear gears and a 4l60 trans will work well with a mild 402 or a 454 built to operate in the 1600-rpm-5000 rpm power band.
obviously youll want to have good basic ring seal and new bearings for a rebuild.
don,t assume the bores are good as they currently are, have a local machine shop you trust, clean out the oil passages and coolant passages and carefully measure the bores for size and roundness, and inspect the block, for cracks , and if it checks out ok, have new cam bearings and new brass freeze plugs installed
a 402 BBC can be built to give good low and mind rpm power , with decent aftermarket pistons that get you in the 9.5:1-10:1 compression range
a simple cam swap to a decent hydraulic flat tappet cam similar to something similar to this
want a bit more?
if the bores on that 402 require an over bore you may want to find a good used 454 crank, damper and flexplate and get the correct pistons to build a stroker version with about 10:1 compression.
14096209 Hydraulic Flat Tappet "502"
This hydraulic flat tappet "502" is a good street high-performance and marine cam used in the Gen V 502 H.O. engine P/N 10185085. (Use spring P/N 3970627.) The duration at lash point in degrees (intake/exhaust) is 328/324; duration at .050" tappet lift (intake/exhaust) is 220/220; and maximum lift with 1.7:1 rocker ratio (intake/exhaust) is 500/500. Valve lash is zero/zero and lobe centerline is 115 degrees.
Technical Notes: Distributor P/N 1104067 or melonized distributor gear P/N 10456413 must be used on all crate engines with steel camshafts.
don,t jmp into any project without totaling up the potential cost and time required,
you may easily find that its cheaper and faster to buy a 454 short block assembly and get those cylinder heads a 3 angle valve job than to have the current block bored, honed and new pistons, rings etc.
a 402 BBC can and will generally produce better power than a 406 SBC built on a similar budget if you know how to go about it if you need the same type of machine work done to both engines, yes the BBC costs a bit more to machine but the heads you have will easily out perform vortec SBC heads once they are properly cleaned up, and get minimal port and bowl work.
If your intention was to maximize lower rpm torque in a 396-454 with peanut port heads , for use in towing a heavy load, at lower speeds,
they are certainly designed to do that, I.d say peanut port heads and a mild cam (similar too but certainly not limited to this one)
and ideally about 9:1 compression would be about ideal for your intended application.
wieand makes a specific intake to maximize peanut port head flow, in the lower and mid rpm ranges
346236 1975-87 454 Open 113cc . combustion chamber PEANUT port
dynamic compression should ideally be in the 8:1-8.1:1 range
try to get the quench distance in the .040-.044 range
with the 113 combustion chamber a 15 cc-17 cc dome gets you near 9:1
hyper-eutectic pistons would be fine here.
I would try to find a 4.20-4.3 diameter head gasket
obviously ask the manufacturers tech dept, if they have any suggestions and if they have had and clearance issues using your part number cylinder heads with the pistons your about too order, just to reduce any potential problems, yes youll want to manually verify piston to valve and piston to combustion chamber clearances
A couple days of
reading the linked and sub-linked info
could save you a great deal of wasted time and money
and money spent on wrong or un-necessary parts
read the links and sub links below
a day or so spent doing reading and research,
(reading links and threads)
will frequently save you thousands of dollars and weeks of wasted work.
if you want a fast dependable car you will need to either do the research required to know exactly how and why things should work, or pay someone else to do the work that has taken that time and effort.