I am John Nijssen.

I build performance V8 Engines.
I am not a salesman I do not sell crate engines.
Comparing my pricing with Proformance Unlimited and the Engine Factory I find I make more power for less money.

I use AFR heads because they are fantastic.
I build what you want and can afford.

The cost of any engine is the parts and the labor.

I do my best to beat Shaffiroffs pricing, usually a little less, but I do not show fixed combinations as I don't build "crate formula motors" rather build according to your requirements and budget.
You can write to me at


You can phone me on 760-508-4562.

The following is an attempt to provide useful information about big blocks 


Currently a guy I know is wanting to sell this. We are asking $10,000


427 Tall Deck Block Bored .030 Over Truck Block New Forged Pistons Steel H Beam Rods Steel 4" Stroke Crank Race Aero Manifold Water Cooled Turbos Twin Holley Carburetors Plummed For Nitrous


I also have a stock 427 bus motor with a small single turbo for $3500.




860Hp BBC




I build quite a few big blocks. The most popular is the 489 (.030") or 496 (.060")

The price is adjustable to some degree based on the parts used. Cast steel crank verse forged steel. Hydraulic roller cam verse flat tappet. AFR CNC ported heads verse as cast iron heads.

If I know how much money you want to spend, I can show you the options available to you.

The lowest cost turnkey 489 is about $7000

A Dart block motor set to rev over 7500rpm will cost as much as $22,000

Just like you I look around online to see what other builders are offering. I can match any of their prices, but not always their deliver time, as I don't keep partial engines just waiting an order for completion. I build all the engines myself, and seldom the same thing twice. Most of the orders I get are specialized.


While I don't advertise it, I do build a 660cid motors. The short block is $6500. I requires specail fitted parts to complete, but it does bolt in same as a 396, but plan on custom made headers.

I also build over 700CID street motors. To do so I use block height extenders, custom made rods and billet crankshafts. 760CID short blocks cost over $10,000


The question "What will it cost?" should first be address with "How are you willing to spend?" Then we can come up with a combination for you working together.

A typical 540 street build cost about $12,000 turnkey

A 540 with a short hydraulic roller cam with 315cc AFR heads will make 700Hp at 5500rpm and as much torque.

700Hp @ 5500 RPM 540 BBC

 These two builds show some of the cost differences extremes.

$400  GM 2 BOLT BLOCK 
$280  CAST STEEL 4.250 STROKER CRANK (Forged Steel Crankshaft $550)
$300  4340 6.3852 RODS          (H-Beam Rods $420)
$550  KB FORGED 9.6:1 PISTONS (Cast Hypereutectic Pistons $400)  
$2920 / $2920 TOTAL
$120   3/8 PUSH RODS
$2410 / $5330 TOTAL
$90   6qt. OIL PAN
$40   OIL PUMP
$15   PICK-UP
$615 / $5945 TOTAL
$85    8.8mm  SPARK PLUG WIRES
$950 / $6895
$400    MACHINED
$1500  AMERICAN MADE 4.250-4.750 CRANK
$225   RINGS
$7785 / $7785 TOTAL
$200     PUSH RODS
$6135 / $13920TOTAL
$300 OIL PAN
$100  OIL PUMP
$45   PICK-UP
$1715 / $15635 TOTAL
$200    OIL FILTER
$150    ASSEMBLE
$2920 / $18555

Most of this page is useful big block tech. If you are seriously looking for a motor write or phone me to discuss what you need.. Then do the same with other engine builders you are considering. If you are looking for the lowest price be sure to looking on ebay first.

Here is a magazine 496 motor named Coolest Rat
These 2 test show the improvement made by AFR 315cc CNC ported heads over Holley heads. Lifters collapse at 6500rpm .
496315.jpg picture by johnnijssen
 496 AFR 315 255/265 @ .050 10.4:1
The power curve is very similar to the results I got with less cam duration, but the same heads.
I built AFR 315 236/236 @ .050 11.0:1
Then the Coolest Rat motor with a change to Beehive springs which allow for higher without lifter plunger collapse
   RPM     Torque   Horsepower
A-P22.jpg picture by johnnijssen


 Here is a Blown 496

3500 639.9 426.4
3600 626.2 429.2
3700 623.8 439.5
3800 624.0 451.5
3900 635.9 472.2
4000 652.1 496.6
4100 694.3 542.0
4200 702.3 561.5
4300 746.3 611.0
4400 785.5 658.1
4500 797.2 698.2
4600 806.4 721.6
4700 815.1 745.0
4800 836.7 780.6
4900 832.5 806.2
5000 826.3 818.5
5100 814.0 833.1
5200 801.8 844.6
5300 787.2 855.2
5400 772.8 853.4
5500 759.4 848.0
12.5 PSI
3500 578.0 385.2
3600 584.0 400.3
3700 587.9 414.2
3800 592.8 428.9
3900 595.0 441.8
4000 605.8 461.4
4100 623.4 486.7
4200 632.0 505.4
4300 626.8 513.2
4400 631.8 529.3
4500 640.9 549.1
4600 671.1 587.8
4700 674.0 603.2
4800 680.6 622.0
4900 688.6 642.4
5000 682.4 649.7
5100 675.2 655.7
5200 666.9 660.3
5300 662.9 669.0
5400 652.7 691.7
5500 647.1 698.6
5600 639.5 690.4
5800 618.0 678.2
5.5 PSI

What does it take to make 1000Hp?
15:1 Compression 450cfm Airflow, and 7200RPM.
That and $15,000

Why I recommend heads

  Iron Stock Edelbrock Dart TFS Brodix
3,200 595 363 610 372 605 368 612 373 619 377
3,300 594 373 609 383 604 379 612 384 614 386
3,400 594 385 611 396 606 392 614 398 615 398
3,500 595 396 613 408 608 405 617 411 618 412
3,600 595 407 613 420 610 418 619 424 621 426
3,700 593 418 615 433 612 431 622 438 623 439
3,800 592 428 616 457 614 444 624 452 624 452
3,900 591 439 618 459 615 457 626 465 625 464
4,000 590 449 618 471 615 468 626 477 626 477
4,100 589 460 617 482 614 479 625 488 626 488
4,200 587 470 615 492 611 489 622 498 623 498
4,300 585 479 612 501 609 498 619 507 620 507
4,400 581 487 609 510 606 508 616 516 616 516
4,500 577 495 607 520 604 518 614 526 613 525
4,600 572 501 605 530 603 528 613 537 611 535
4,700 565 506 602 539 602 539 610 546 609 545
4,800 558 510 598 547 600 548 607 555 606 554
4,900 551 514 593 553 597 557 604 563 602 561
5,000 543 516 587 559 593 564 599 571 598 569
5,100 534 518 582 565 588 571 595 578 593 576
5,200 525 519 576 570 583 577 590 584 588 582
5,300 515 520 570 575 578 583 583 589 583 588
5,400 507 521 563 579 572 588 576 593 576 593
5,500 496 519 555 581 566 593 568 595 569 596
5,600 487 519 546 582 558 595 558 595 560 597
5,700 476 517 536 582 549 595 547 594 550 596
5,800 465 513 527 582 538 595 537 593 538 595
5,900 451 507 518 582 528 594 527 592 528 593
6,000 438 500 510 582 519 593 517 590 517 591
6,100 423 492 500 581 506 588 505 586 507 589
6,200 407 481 487 575 494 583 490 579 495 584
Peaks and Averages
  Avg. TQ Avg. HP Peak TQ Peak HP
Iron 541.1 475.0 595 521
Edelbrock 582.1 514.9 618 582
Dart 584.2 517.7 615 595
TFS 590.3 522.5 626 595
Brodix 590.8 523.0 626 597

Read more: http://www.carcraft.com/techarticles/ccrp_0803_big_block_cylinder_heads/viewall.html#ixzz2FAwBtpsI

  John I got the Chevelle running. It is very strong, 600 horsepower makes it feel like a race car. It takes some skill to drive. I have scared everyone that I've taken for a ride in it.
Thanks. Benny S. Texas.



Notice the camshaft is advertised to make peek power at about 6400rpm, but in fact made peek BHP at 6100 this is a result of the longer .250" stroke.
A solid lifter cam was chosen  to create more torque and horsepower than a similar hydraulic cam would produce.
A flat tappet hydraulic cam  would require special race lifters to maintain power beyond 6000rpm.
A Hydraulic Roller cam will make significantly more power and torque than the solid cam, but require a Rev Kit to maintain power beyond 6000rpm.
A Hydraulic Roller cam will cost $450 more and the Rev kit $175
The 274 is recommend to use with a 2500rpm stall speed torque converter, however you can get by with a 2000.
Longer duration cams will increase the peek BHP and lower the torque values below 3500rpm. They will also reduce vacuum and require higher stall speed converters.
A single plane manifold will also increase BHP and lower TQ at low RPM
Using a Mighty Demon Carb will lower the price $330
To further increase power and torque I recommend AFR 305 CNC chamber headswith 11.0:1 compression, add $750. These are excellent heads. Larger port heads will increase peek horsepower but lower torque



Comparing Big Block Heads

 Holley SysteMax

Comparing Manifolds

Comparing Cams

740BHP AFR BBC Magazine FeatureBBC_AFR_740.jpg


565CID 1000BHPBBC_565_sm.jpg


705 Magazine Build




12370850 - ZL1 Aluminum Big Block $5600

The Chevrolet aluminum big-block is back and better than ever. This block was first introduced in the 1969 Corvette and Camaro. It was one of the rarest production engines ever built. Now the improved version is available. This block is based on the original tooling. The new casting is made from 356-T6M aluminum alloy and has a 4.250" cast iron liner that can be bored to 4.300". The bottom end has also been improved with new 4-bolt splayed steel main caps with dowel pins to locate and hold the caps in place. This block includes screw-in freeze plugs with o-ring seals and a two-piece rear main oil seal. the new block has a provision for both dry sump or regular oil pump systems and mechanical fuel pump. All GM Performance Parts cylinder heads will fit this block and it weighs only 110 lbs. The maximum stroke is 4.375".



Engine Size Stock Bore +.060"-over Stock Stroke
366 3.935" 3.995" 3.760"
396 4.094" 4.154" 3.760"
402 4.125" 4.185" 3.760"
427 4.250" 4.310" 3.760"
454 4.250" 4.310" 4.000"
Mark 5 — 502 — Mark 6 4.468" 4.530" 4.000"

454 Engines 3.760" 4.000" 4.250" 4.500" 4.750" 4.875"
Stock bore = 4.250" 427" 454" 482" 511" 539" 553"
Bored .030" = 4.280" 433" 460" 489" 518" 547" 561"
Bored .060" = 4.310" 439" 467" 496" 525" 554" 569"
Bored .090" = 4.340" 445" 473" 503" 533" 562" 577"
Bored .100" = 4.350" 447" 476" 505" 535" 565" 580"
Bored .125" = 4.375" 452" 481" 511" 541" 571" 586"

502 Engines 3.760" 4.000" 4.250" 4.500" 4.750" 4.875"
Stock bore = 4.468" 472" 502" 533" 564" 596" 611"
Bored .032" = 4.500" 478" 509" 541" 573" 604" 620"
Bored .062" = 4.530" 485" 516" 548" 580" 612" 629"
Bored .092" = 4.560" 491" 523" 555" 588" 621" 637"

Aftermarket Blocks 4.000" 4.125" 4.250" 4.375" 4.500" 4.625" 4.750" 4.875" 5.000"
4.500" bore 509" 525" 541" 557" 572" 588" 604" 620" 636"
4.530" bore 515" 532" 548" 564" 580" 596" 612" 628" 645"
4.560" bore 523" 539" 555" 572" 588" 604" 621" 637" 653"
4.590" bore 530" 546" 563" 579" 596" 612" 629" 645" 662"
4.600" bore 532" 548" 565" 582" 598" 615" 632" 648" 665"
4.625" bore 537" 554" 571" 588" 605" 622" 638" 655" 672"
Free Counter  6410-1029 






BBC Background Story Click Here





This guide is intended to help you sort out the more major differences among Big Block Chevrolet engines produced since 1958.  Chevrolet has designed and produced several different "big block" engine families.  Within each family, there can be evolutionary changes, and special parts designed for competition use which may not be directly interchangeable with the regular production items.  I don't intend to cover every possible variation.  For practical purposes, all big block Chevrolet engines use a cylinder bore spacing of 4.84 inches although note the one exception below.

Early engines were designated as Mark I, (Mk I) Mk II, Mk III, and Mk IV.  Later engines continued the numbering system as Generation 5 (Gen 5), Gen 6, Gen 7.  There are some conflicting theories as to the reason for the change from "Mark" to "Generation".  My first guess:  "Gen 5" sounds much more modern, hi-tech, and trendy than "Mk V".

Mark I:  The original "Big Block Chevy", also called the "W" engine perhaps because of the layout of the valves and therefore the shape of the valve covers--although another possibility is that GM chose the "W" prototype for production rather than the competing "X" or "Y" prototypes, and therefore it's a convenient coincidence that the valve layout is in the shape of a "W".  It should be noted that this engine became "Mark I" only after the Mark II was being designed years after the "W" was introduced.  Whatever the origin of the name, this engine family was installed in vehicles beginning in 1958, as a 348.  In 1961, it went to 409 cubic inches, (as immortalized in the Beach Boys song "She's so fine, my 409") and for one year only (1963) a few well-connected racers could buy a car with a 427 cubic inch version called the Z-11.  The 427 version was all about performance, and had special parts which were not directly interchangeable with the 348/409.  While production of the 427 was severely limited, both the 348 and 409 were offered in passenger cars and light- and medium-duty trucks.  The truck blocks were somewhat different from the passenger car blocks, having slightly different water jackets and of course, lower compression achieved by changes in the piston in addition to more machining of the top of the cylinder.  A novel feature of this engine is that the top of the cylinders are not machined at a 90 degree angle to the bore centerline.  The top of the cylinder block is machined at a 16 degree angle, and the cylinder head has almost no "combustion chamber" cast into it.  The combustion chamber is the top wedge-shaped section of the cylinder.  Ford also introduced an engine family like that in '58--the Mercury/Edsel/Lincoln "MEL" 383/410/430/462.  The "W" engine ended it's automotive production life part way through the 1965 model year, when the 409 Mk I was superseded by the 396 Mk IV engine. 

Mark II:  This is more of a prototype than a production engine.  It is the 1963-only "Mystery Engine" several of which ran the Daytona 500 race, and in fact won the 100-mile qualifier setting a new record.  It is largely the result of engineering work by Dick Keinath.  Produced mainly as a 427 but with a few 396 and 409 cubic inch versions, all in VERY limited numbers.  Even though it was intended as a NASCAR-capable engine, it had 2-bolt main caps.  This engine was never installed in a production-line vehicle by GM, it only went to racers.  And even though it was available in 1963, it has very little resemblance to the 427 Mark I "W" engine of the same year.  The Mark II was a "breakthrough" design using intake and exhaust valves that are tilted in two planes--a canted-valve cylinder head, nicknamed the "Semi-Hemi" or "Porcupine" because it is "almost" a hemi head, and the valve stems stick out of the head casting at seemingly random angles.  The engine was the subject of an extensive article in the May, 1963 Hot Rod Magazine.  Because of NASCAR politics, Chevrolet was forced to sell two 427 Mark II engines to Ford after the '63 Daytona race, (to "prove" that it was a production engine, and therefore eligible to race in NASCAR events) and so this engine is not only the grandfather of the Mark IV and later big block Chevies, it's also the grandfather of the canted-valve Ford engines:  Boss 302, 351 Cleveland and variants, and the 429/460 big block Ford.  The bore and stroke of the 427 MK II is not the same as the 427 MK IV.

Mark III: Never released for production.  This was rumored to be the result of GM/Chevrolet's proposed buyout of the tooling and rights to the Packard V-8 engine of the mid-to-late '50's.  The Packard engine was truly huge, having 5" bore centers.  The former president of Packard wound up at Ford after Packard folded, perhaps because of that, Ford was also interested in this engine.  Ford wanted to make a V-12 variant from it just as Packard had once envisioned.  One way or another, neither GM nor Ford actually went forward with the purchase.

Mark IV:  The engine that most people think of as the "big block Chevy".  Released partway into the 1965 model year as a 396, superseding the older 409.  It is a development of the Mark II and using similar but not identical canted valve (semi-hemi/porcupine) cylinder heads.  It was later expanded to 402 (often still labeled as a 396, or even a 400,) a 427, a 454, and a few "special" engines were produced in the late '60's for offshore boat racing as a 482.  There was a 366 and a 427 version that each had a .400 taller deck height to accommodate .400 taller pistons using four rings instead of the more usual three rings.  These tall-deck engines were used only in medium-duty trucks (NOT in pickup trucks--think in terms of big farm trucks, garbage trucks, dump trucks,  school busses, etc.)  The tall-deck blocks all had 4-bolt main caps, forged crankshafts, and the strongest of the 3/8 bolt connecting rods.  All-out performance engines used 7/16 bolt connecting rods, along with other changes.  This engine family was discontinued in 1990, with the Gen 5 appearing in 1991. 

Gen 5:  General Motors made substantial revisions to the Mark IV engine, and the result was christened "Gen 5" when it was released for the 1991 model year as a 454.  There were 502 cu. in. versions, but never installed in a production vehicle, the 502s were over-the-parts-counter only.  Changes to the Gen 5 as compared to the Mk IV included, but are not limited to: rear main seal (and therefore the crankshaft and block) were changed to accept a one-piece seal, oiling passages were moved, the mechanical fuel pump provisions were removed from the block casting, the machined boss for a clutch bracket was eliminated, the cylinder heads lost the ability to adjust the valve lash, and the coolant passages at the top of the cylinder block were revised.  The changes to the coolant passage openings meant that installing Mk IV cylinder heads on a Gen 5 block could result in coolant seepage into the lifter valley.  Frankly, the changes (except for the one-piece rear main seal) were all easily recognized as cost-cutting measures which also removed some quality and/or utility.  All told, the Gen 5 engine was not well regarded by the Chevy enthusiasts because of the changes to the coolant passages and the lack of an adjustable valvetrain.  As always, the aftermarket has provided reasonable fixes for the problems.  The Gen 5 lasted only until 1995.

Gen 6:  GM recognized that it did not make any friends when it designed the Gen 5, and so they chose to revise the coolant passages again when designing the Gen 6, allowing the older heads to be used without coolant seepage problems. The boss for the clutch bracket returned, but was generally not drilled and tapped.  The non-adjustable valvetrain remained, as did the one-piece rear main seal.  Some but not all Gen 6 454 (and not 502) blocks regained a mechanical fuel pump provision.  Production engines installed in pickup trucks got a high-efficiency cylinder head, still canted-valve, but with a modern heart-shaped combustion chamber of about 100cc.  The intake port has a "ski jump" cast into it to promote swirling of the intake air flow.  All production vehicles with a Gen 6 used a 454 version, but over-the-counter 502s are available.  The Gen 6 is sometimes referred to as the "Gen Fix" because it fixed a number of issues that disappointed enthusiasts when the Gen 5 was released.  As an added bonus, most if not all Gen 6 engines use hydraulic roller lifters.

Gen 7:  A very major revision of the previous engines resulted in the 8.1 liter/ 8100/ 496 cubic inch Gen 7 in 2001.  The block gained .400 in deck height so it is the same height as the previous "Tall Deck" truck blocks, wider oil pan rails, and the cylinder heads have symmetrical port layouts instead of the previous 4 long/4 short port layout.  Very little interchanges between the 8.1 liter engine and the previous Mark IV/Gen 5/Gen 6 engines.  The head bolt pattern and even the firing order of the cylinders has been changed.  There are some things that remained true to the previous Mk IV/Gen 5/Gen 6--the bellhousing bolt pattern, the side motor mount bolt pattern, the flywheel bolt pattern, and the exhaust manifold bolt pattern are the same.  Note that the bolt holes are threaded for metric fasteners.   The 8.1 is internally balanced, so you could install a flywheel/flexplate from a 396/427 Mk IV provided you use the correct bolts to suit the 8.1 crankshaft.

I have had a chance to compare Mark IV, Gen 5/6 and Gen 7 head gaskets.  It seems to be possible--but very difficult--to install IV/5/6 heads on the Gen 7 block.  GM did this on one show vehicle, it IS possible.  You must move three head bolt holes in the block; and as the holes only move about 1/2 their diameter it would be difficult to plug the existing holes, re-drill the new holes, and still have enough strength in the deck surface.  There are cooling system differences as well that must be addressed.  I have NOT done this conversion; but I do have comparison photos of the head gaskets.

(sorry if this table loses it's formatting:  I don't know how to fix it.  It looks "ok" at full screen width on my computer)

Engine family    Displacement    Bore      Stroke      Rod length

MK I                   348                    4.125     3.25            6.135

MK I                   409                    4.31       3.5              6.010

MK I                   427                    4.31       3.65            6.135

MK II                  427                    4.31       3.65            6.135

MK IV                366                    3.938      3.76            6.135   (Only offered as a medium duty truck engine)

MK IV                396                    4.094      3.76            6.135

MK IV                402                    4.125      3.76            6.135

MK IV                427                    4.250      3.76            6.135   (Offered in passenger car and medium duty truck versions)

MK IV/Gen 5/6   454                    4.250      4.0              6.135

MK IV                482                    4.250      4.25            6.405     (very rare, made only for offshore boat races.  Used tall-deck block)

Gen 5/6              502                    4.466       4.0             6.135      (Over the parts-counter only; not installed in production vehicles)

Gen 7                 496/8.1              4.25         4.37

Specials:  GM has sold many special-purpose engines, partial engines, blocks, cylinder heads, etc., "over the parts counter" that were never installed in production line vehicles.  It is very difficult to track all the various items--suffice to say that heavy-duty "Bowtie" blocks and cylinder heads in various configurations--Mark IV, Gen 5, etc, have been produced.  Oldsmobile used the Big Block Chevy as a baseline when designing the first of the Drag Race Competition Engines (DRCE) so that the early DRCE engines have an Olds Rocket emblem cast into the block, but it's Chevy parts that fit inside.  There are special high performance blocks and heads, in either iron or aluminum, produced by GM and by aftermarket suppliers to suit almost any racing need.

Coolant Routing Mk IV/Gen 5/Gen 6
There are two different ways that coolant can be routed through the engine:  series flow and parallel flow.  Both ways work just fine.  There may be a slight preference for parallel flow, but it is not a big deal.  Series flow has the water exiting the water pump, flowing through the block to the rear, it then transfers through the head gasket and into the cylinder head through two large passages on each cylinder bank at the rear of the block.  The coolant then travels from the rear of the head, forward to the front of the head, into the intake manifold water passage and out past the thermostat and thermostat housing.  The water cools the block first, then it cools the head.  The coldest water (coming out of the water pump) is directly below the hottest water (having already picked up the heat of the block and the head) as the hot water transfers into the intake manifold.  By contrast, parallel flow has the water exiting from the water pump into the block, where a portion "geysers" up into the head between the first and second cylinder, another portion "geysers" up to the head between the second and third cylinders, another portion geysers up to the head between the third and fourth cylinder, and the remainder transfers to the head at the rear of the block.  The coolant temperature inside the engine is more even that way.  The differences in coolant routing is having (or not having) the three additional coolant transfer holes in each block deck, and three matching holes in the head gasket.  The heads have passages for either system, and are not different based on coolant flow. 

Be aware that gaskets that DO have the three extra holes between the cylinders often have restricted coolant flow at the rear

but not all

--instead of having two large coolant transfer holes at the rear,


there is only one, and it's the smaller of the two holes that remains. fel-17046_w.jpg

This is important because if you use a parallel flow head gasket on a series flow block, you can have massive overheating and there's NOTHING that will cure the problem except to replace the head gaskets with ones that don't restrict flow at the rear of the block, or to drill the block decks to allow the coolant to flow into the head between the cylinders

Here's why they can overheat:  A series-flow block doesn't have the openings between the cylinders, no coolant can flow up to the head there.  The gasket may only have the single, smaller opening at the rear, so the amount of water that gets through that opening is greatly reduced from what the block designers intended.  The result is that the coolant flow through the engine is only a fraction of what is needed.

Most, but NOT all Mk IV engines are Series Flow.  ALL Gen 5 and Gen 6 engines are Parallel Flow.  A series flow block can be converted to parallel flow by drilling 3 holes in each deck surface, and then use parallel flow head gaskets.  You can use the parallel flow gaskets as templates for locating the additional holes.  It's really easy:  Put the parallel flow gaskets on the block, mark the location and size of the three extra holes.  Remove the gasket.  Grab a 1/2" drill and a drill bit of the correct size, and pop the extra holes in the block.  There is NO modification needed on the head castings.  Some blocks have one of the holes already, but it needs to be ground oblong to properly match the gasket.  Again, very easy with a hand held die grinder and rotary file.

Please check out my guides to GM small block engines , and Olds, Pontiac, and Buick big block engines, Mopar V-8 engine familiesFord V-8 engine families since 1932 or HEI distributors , too.

If you feel this guide has been helpful, please give me a "Yes" vote by clicking the button below.  If you have suggestions for improvement of this guide, you can contact me through the "My Messages" feature of eBay by first clicking on my user name at the top of the page, then click on "Contact Member".  Thanks, all!

Entire contents copyright (C) 2007, 2008 Camino3X2  






The head bolt holes line up. The steam holes line up just like stock. (Four holes in gasket, three line up and are functional on each side.) I see NO place where the holes in the block or heads could overlap the gasket and leak into the lifter valley. The holes in the Gen 6 head are oddly shaped, and there is an "extra" one, but this is all properly covered by either a Gen 6 gasket or a Mk IV gasket. "Should" be no leakage.

The benefit of this conversion is to use the tiny-chamber L-29 Vortec heads on all those old 8 to 1 compression pickup truck 454s. The same deal as converting all the old small blocks to Vortec heads! These L-29 big block heads have the BIG oval ports, a modern heart-shaped 100 cc or so combustion chamber that would work great with flattops. Drawback is the special (but readily available) rocker studs to convert to adjustable rocker arms. Heads come with exhaust seat inserts, and the intake especially has nice-looking ports, that should provide swirl. The exhaust may need some clean-up around the valve guide, it's mighty blunt. There is no exhaust heat crossover passage.

I compared a core "049" casting head to a new L-29 head. Bought one of each gasket, the old Mk IV and a Gen 5/6. (Victor catalog lists same gasket for '91 through 2000.) I checked these with a core 454 block that I think is from '73.

What I can figure out is this:

MK IV block, no modifications
Gen 6 "vortec" head, no modifications
Use a standard, ordinary MK IV head gasket.
I can see NO problems with this installation. All the goofy-shaped coolant holes are covered where they need to be, open where they need to be, water should flow through the head in standard MK IV cooling pattern- It will be SERIES COOLED. That means the water enters the front of the block, goes to the rear of the block, transfers up to the rear of the head, and comes forward to transfer into the intake manifold and thermostat area. Millions of MK IV engines used this coolant flow, and they seem to get by just fine. Recognize that the coolest water comes in the front of the block, gets warmer all the way to the back of the block, transfers into the head, gets warmer still all the way to the front of the head. Coolest part of the block is right below the warmest part of the head. Even so, seems to work just fine.


MK IV block, minor modifications
Gen 6 head, no modifications
Gen 6 head gasket, no modifications
Drill four 3/8 holes in the block deck, using the Gen 6 gasket as a template. Elongate two existing holes, won't take much. (Three holes each side, between the cylinders at the lower part of the deck.)
Again, goofy shaped holes are covered where they need to be, and open where they need to be. This parts arrangement provides for PARALLEL COOLING. There are two large openings at the back of the block for coolant transfer into the head. The larger one is BLOCKED by the Gen 6 gasket. The smaller one is open. Coolant flows just as the example above, except in much smaller quantity. This smaller quantity is supplimented by the three additional holes on each side that you drill or elongate in the block. So coolant comes in the front of the block, some "geysers" up though the first hole, between the first two cylinders,some geysers up thru the second hole, between the second and third cylinders, some gyesers up through the third hole, and the last goes all the way to the back of the block and transfers up there. This is how the Gen 5/6 engines are cooled, again millions made and it seems to work. I consider this a "better" way, as it may "even out" the temperature extremes of a series cooled engine- from one end of the block to the other, and one end of the head to the other. This way, the back of the block should be a bit warmer, and the front of the head should be a bit cooler, I think Parallel cooling is the way to go!

What won't work, is:

Mk IV block, un modified, no extra holes drilled. (But see note 3)
Gen 5/6 gasket, Un modified
Gen 6 head, un modified
The cooling system will be series, with a touch of bleed though from one "geyser" hole on each side. Not enough coolant circulation, I think it's gonna run hot.

I'm gonna build a Mk IV block, Gen 6 head Frankenstein engine over the winter. I'll use a MK IV gasket, and NOT drill the extra holes. If it overheats, I'll rip off the heads, drill the holes, and slip Gen 6 gaskets in.

Note 1: This is going in a boat, and it uses (cold) lakewater for cooling. The existing Mk IV takes forever to warm up. It's not the best situation to test for overheating. If this was in a car with existing heating problems, I would drill the holes and be done with it.

Note 2: You could, if you cared, parallel cool a pure Mk IV engine. Just get a gasket that has the additional four holes, or use a Gen 6 gasket. The Mk IV heads already have the holes needed to line up with the extra holes you would drill into the block. No need to modify the heads at all.

Note 3: I only have one block to look at: I am suspicious that GM may have built MK IV engines that ALREADY HAVE THE EXTRA HOLES, and are Parallel cooled. I have seen a picture of a Mk IV head gasket that has the extra holes, makes sense that some blocks do, too. Unlike the Gen 6 gasket, both coolant passages at the back were still open, though. I'm thinking "who cares, the thermostat can regulate this".

Note 4: Swapping heads between Mk IV and Gen 5/6 got a bad reputation right away. It seems that it's only a problem when using older heads on a newer block. Using the Gen 6 heads on a Mk IV block is "almost" a direct swap.


Spec's on the L-29 Vortec BB head vs a peanut port BB head (PPH) per the article..

L-29 intake ports = 233.2(S) and 239.5cc(L).
PPH intake ports = 192.4(S) and 198.0cc(L).

L-29 exhaust port = 81.2cc.
PPH exhaust port = 101.3cc.

Chamber volumes. L-29 = 100 and PPH = 118.4cc.

Approx. CR's on a regular stock, small domed 502, PPH = 8.74CR. and L-29 = 9.74CR.

For a flat-top piston 502, the L-29 would make 9.3CR.

For a stock 454 flat-top P/U truck motor PPH = 7.9CR. and L-29 = 9.0CR!!

Valves = the same for both heads at 2.065"/1.72".

NOTE: Use Fel-Pro headgasket 1017-1 to use L-29 heads on the early IV BB blocks AND check coolant holes CAREFULLY!!!






P34097 Image Large
P34098 Image Large  
P34099 Image Large  
P34100 Image Large  
Mark IV head gaskets have two openings at the front; a GEN V-VI gasket has only one opening to force coolant to flow rearward through the block and cylinder heads.



frontpage hit counter every

hit counter dreamweaver unique