don,t ignore the potential of a 402 BBC rebuild, but think things through


The Grumpy Grease Monkey mechanical engineer.
Staff member
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

related info


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.
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if you find a machine shop selling a rebuilt ,454 short block, or if you look around ,
Its not un-common to find machine shops that have a few pre-built or un-claimed, and recently, re-built short or long long-block 454 BBC engine, for sale.
you might want to look into that option, if your looking at rebuilt or used 454 engines ,
get the guy who is selling the used engine, too let you hear the 454 BBC engines that hes selling run, if you can, and do a compression check ,on all cylinders, and test the oil pressure , look at the oil on the condition of the oil, on the dip stick look for rust and sludge, or moisture in the oil, try to look under the valve cover if you can,and check the 8 spark plugs condition.

link too bore vs stroke info on hundreds of engines
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Pit Stop: Edelbrock 100cc Big-Block Oval-Port Heads—A True Bolt-on?
Written by Marlan Davis on December 15, 2016
Edelbrock - Photographer;

Which Edelbrock Head Yields 9.5:1 Compression on a Stock 1971 402?

I have a 1971 Chevelle SS that I bought new. It is a 402 big-block, four-speed car with 3.31:1 gears and is stock. I want to freshen the engine up by increasing the compression ratio from 8.5:1 to about 9.5:1 (I still want to run pump gas). I am thinking of a Comp Cams 280HR Magnum hydraulic-roller cam and kit, an Edelbrock Performer RPM oval-port manifold, and Edelbrock Performer RPM oval-port heads—either PN 60435 or 60455. My stock heads are open chamber with 113cc chambers. The 60435 head has 100cc chambers, with 60455 having 110cc chambers.

Which head can I use to achieve about a 9.5:1 compression ratio? I have gotten all kinds of opinions on this; they are all over the board and I am totally confused. My stock piston has casting No. 3995849 and the Sealed Power stock replacement is PN 402P. I am told that the Edelbrock heads won’t work because the piston will hit the spark plug because the plug has been relocated.

—Larry Musto


For Larry Musto to truly get to 9.5:1 with modern Fel-Pro gaskets on his existing short-block, even Edelbrock’s 100cc heads require milling—but by now it’s time to refresh that tired original motor. With the right head gasket and block deck height, 9.5:1 is easily obtainable with stock (but better quality) Speed-Pro forged replacement pistons.
Likely, neither head will do it out of the box. Your 1971 402 will only achieve its rated 8.5:1 compression ratio if the block, the rotating assembly, and the cylinder-head combustion chambers were blueprinted to the exact minimum design dimensions—and that’s with the original thin, steel-shim, 0.021-inch, compressed-thickness head gaskets! In the real world, an original, nonrebuilt, stock, unblueprinted engine could easily be at least a half-ratio lower than “it’s supposed to be” because, for example, the blocks are not machined to minimum to allow for “worst-case” tolerance stack on the non-blueprinted internal components.

That said, whatever your true compression ratio is now, the 110cc 60455 won’t come close to meeting your target on the existing short-block. The 100cc Edelbrock 60435 has the potential to raise the compression ratio just shy of a full point compared to your existing 113cc factory head—assuming no other changes, including the use of that OE-type, thin head gasket. But with aluminum heads, you’ll need to use a “thick” composition-type head gasket to reliably seal them on the block. (In fact, I frown on shim-type head gaskets even with iron heads with in-service engines unless the block and head decks are dead-nuts flat.) A “thick” gasket will lower the static compression ratio about 0.3 point on your 402 compared to a thin shim gasket.

By a “thick” gasket, we mean a modern-performance, aftermarket, composition-style head gasket (such as Fel-Pro PN 1027 or 1037). These 0.039-inch-compressed-thickness head gaskets have a reasonably small 4.370-inch bore, so they yield the smallest compressed volume (9.7 cc) of any of the gaskets in Fel-Pro’s composition-type big-block Chevy performance head-gasket line. Which of the two gaskets should be used on your engine is based on the block deck’s cooling hole locations; 1971 was a transition year, so compare the gasket photos on these pages to the deck holes in your block.

But will the 60435 100cc head hit the pistons? Edelbrock says the 60435 head develops “9.2:1 compression with flat-top pistons,” but that’s on a 454. Your small-bore 402 piston still has a slight dome, so we now need to address the question of chamber configuration and spark-plug location.

According to Edelbrock, only its E-CNC oval-port big-block Chevy heads, as well as all of its rectangular-port big-block Chevy heads, have revised spark-plug locations that may require pistons designed around the specific cylinder head. Edelbrock’s Performer and Performer RPM oval-port big-block heads (including the part numbers you’re considering) are said to maintain the standard spark-plug location. But in the case of the 100cc 60435 head, there’s a catch: To reduce chamber volume from the normal 110cc Edelbrock chamber to 100 cc, Edelbrock rolls over (angle-mills) the head decks 1½ degrees from standard. This design improves intake-port alignment and provides a smaller combustion chamber without shrouding the valves, but yes, it does effectively relocate the spark plug slightly.


This is a standard 110cc combustion chamber in Edelbrock’s big-block Chevy oval-port head, PN 60455.

This is the combustion chamber in Edelbrock’s 100cc “rolled-over” 60435 oval-port big-block Chevy head. Compared to the 110cc chamber in the previous photo, this head has a slightly rotated chamber to unshroud the valves. Also note how the 100cc head’s far-side wall is pulled in slightly.
The old-school rule concerning domed piston head compatibility on big-block Chevys is: Closed-chamber pistons usually are OK with open-chamber heads, but open-chamber pistons shouldn’t be used with closed-chamber heads. But, again, we’re in a gray area: Your stock iron 1971 113cc factory chambers are neither fully open nor fully closed. The Edelbrock chambers are considered to be semiopen; normally, closed-chamber domed pistons work fine with the larger-chamber versions.

In the case of the rolled-over 100cc head, the best information I have is your existing 1971 factory piston or aftermarket equivalent should be OK, but—because the head is angle-milled—don’t exceed a 0.150-inch dome height on a zero-decked block (piston deck is flush with the block deck at TDC). If the piston deck (the flat part of its top surface) is below the block deck at TDC, the amount the piston is below the deck can be added to the allowable dome-height value. If the heads are milled to reduce chamber size from the as-delivered 100 cc, subtract the amount milled from the allowable dome-height value. Nevertheless, prudence dictates claying the piston to check for interference, then grinding or machining the piston for clearance as needed. Of course, piston-to-valve clearance should be checked with any big aftermarket cam. Remember, Edelbrock heads also have bigger valves than the ones installed in your OE heads. These rough rules assume use of a typical “thick” head gasket.

How, then, can you reach 9.5:1? The easiest way is to mill the 100cc Edelbrock 60435 heads. Edelbrock says up to a 0.060-inch cut is safe; every 0.005-inch reduces the 60435’s chamber volume about 1 cc. Again speaking hypothetically, let’s say your existing pistons are 0.018 inch below the deck at TDC, typical for an uncut production block. Sources differ on the dome volume of the stock pistons (and so-called stock replacement pistons are not always exact duplicates of the OE piston), but NHRA specs claim the stock cast piston’s dome volume is 12.10 cc. To get to 9.53:1 with these specs calls for a 95cc chamber—therefore, the heads require a 0.025-inch cut to reduce chamber volume by 5 cc’s [(100 cc – 95 cc) × (0.005 in/cc) = 0.025 inch]. The OE piston supposedly has a 0.112-inch dome height, which should provide sufficient clearance: 0.150 dome height allowance + 0.018 deck height – 0.112 piston dome height – 0.025 head mill = 0.031 allowance remaining.

All this is by doing the math. But the only way to know for sure what your compression ratio really is would be to remove the heads and cc both a cylinder with piston as well as the cylinder head combustion chamber. You must cc and measure everything on your assembly, then figure out how much to mill the new heads to reach your goal.

I do hope by “freshen up” you mean that you are rebuilding the bottom-end, because that high-mileage rotating assembly won’t last very long with 150 or so more horsepower. That opens up many more ways to get to your 9.5:1 target. For example, you could blueprint the bottom-end, boring the cylinders 0.030-over. The relatively affordable forged Speed-Pro piston (PN L2383F30) is NHRA-accepted for your model year as a stock-replacement part and is stronger than a cast stocker, while its 13.90cc dome volume is close to OE specs. Square and deck the block to put the piston 0.010-inch below the block deck at TDC. This piston has a “should-be-safe” 0.110-inch dome height (0.050 remaining tolerance with a 0.010 deck and no head milling). Depending on crank stroke and rod-length variations, a 0.010 deck may require machining the block 0.005-inch below the block’s theoretical 9.800-inch blueprint deck dimension (crank centerline to top of block deck), but that’s OK; as I’ve said, your block is almost certainly taller than blueprint, so it will need decking).

Just tell your machinist what you’re trying to achieve. With the 100cc Edelbrock head and either of the listed Fel-Pro head gaskets this puts your now 408ci engine’s compression in at 9.52:1. Of course, with that big roller cam and modern aluminum heads you could run up to 10.5:1 on pump premium gas on a near-zero-decked block—but that’s a whole ’nother discussion.


Speed-Pro/Federal-Mogul piston L2383F30 is a close analogue to the stock cast piston but as a forging it’s more durable. A set of eight goes for $508.99 at Summit Racing. Using Edelbrock 100cc heads, compression will go up nearly a full point, assuming no other changes.

These Fel-Pro head gaskets illustrate the different coolant circulation patterns in early versus later big-block Chevrolet engines. See text for details.
These Fel-Pro head gaskets illustrate proper Mark IV big-block Chevy head gasket selection. For improved cooling, most (but not all) 1971–1990 Mark IV Chevrolet big-blocks use parallel-flow coolant circulation. They have three cooling holes on the block-deck’s exhaust side (A through C), and small single coolant holes at the rear of each deck (D and E). Any big-block Chevy head gasket with the appropriate bore size and thickness can be used—although a gasket with only the small water passages at each end (top, Fel-Pro Performance 1037 or Fel-Pro marine PN 17046) is recommended (only the gasket’s rear hole is “active” on each side). Prior to 1971, most (but not all) Mark IV Chevrolet big-blocks had series-flow cooling. At most, the block decks have only one lower coolant hole (C on the passenger side; A on the driver side), and there are double coolant passages at the rear of each deck (D through G; only the rear holes are “active”). Series-flow blocks must use Fel-Pro PNs 1017-1, 1017-2, 1027 (shown, bottom), 1057, or 1093. Although all big-block Chevy Mark IV heads and the performance gaskets shown here have the extra lower holes, they are nonfunctional without the extra holes in the block. Parallel-flow blocks can be converted to series flow by adding the missing holes using the appropriate gasket as a template.

a few related threads that might help you build a better car
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