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Thread: big block conversion?

  1. #1
    Join Date
    Jul 2008

    Default big block conversion?

    Im just curious how many guys have considered upgrading to a BIG BLOCK ENGINE??

    how do you install a 454-502 in a C-4

    if you put a bbc with aluminum heads, intake and water pump in , in place of the standard iron small block you only gain about 50-70 lbs, not enough differance to cause any problems at all, , I have worked on several of these swaps now and Im in the process of getting ready to do another one,heres whats needed
    steering rack mounts cut and rewelded 3/4"-1" farther forward (that of course means the power steering pump lines/steering shaft, need to be extended 3/4" also)

    small notch (starting at rear and going 3" forward from rear edge X 3/4"deep X 5" wide works well in rear top surface of (K) frame cross member to clear damper and pulley)(if you use an internally ballanced big block with the 6.75" dia. damper you can most likely skip the notch but with the 8" dia damper its necessary, and some oil pans will also require the back 1 1/2 of the (K) frame to be notched at an angle slopeing to the rear to clear them so youll probablly need the notch of some kind anyway)(and yes before you ask you could shim/modify the motor mounts up to get the clearance, but that would slightly raise the weight center and slightly effect the handleing, and that also makes the windshield motor and distributor clearance a bigger problem)

    air conditioner shrouding fiber glass on pass side foot well around the air conditioning on the firewall needs to be modifyed for clearance, (the fiber glass cover from a LT5 makes this easy)(evaporator houseing cover)

    1971 bbc vette exhaust manifolds (or custom headers) and all brakets/pulleys (mods needed here)
    (see the post on building your own headers)
    oil pan needs to be only 7.5" deep max

    3" hood scoop unless you run a low rise intake and carb or a low height efi system

    for a step by step instructions with pictures get a copy of the august 1998 vette magizine article( starts on page 34)it helped quite a bit the first time

    otherwise its almost a drop in deal, but keep in mind that youll need a bigger radiator, the trans will not last to long with that amount of torque and it may not pass emission testing and a small size starter is needed, and your windshield wiper motor needs to be replaced with a much smaller one,(I don,t remember where we got them but alittle measureing and a trip to the salvage yard took care of that problem, and no tall valve covers don,t work well!

    btw install the short block then add the heads with it in the car its FAR EASIER THAT WAY than trying to install the long block

    BTW the earlier cars like the 1984-86 (Im not sure what years exactly)dont have the heavier forward frame braceing above the stearing rack that makes this swap more difficult to do! I have worked on this swap on the 84, 85, and 86 cars so I know they work fine, the later cars like the 1992 with the heivier forward frame braces above the stearing rack look like they will be more dificult but still do-able with some extra work, btw theres a guy at ARIZONA SPEED AND MARINE that has one you might want to talk to .just a few points
    an aluminum head, intake and water pump bring a bbc engines weight to within 70 lbs of the stock iron small block, so handling is almost unchanged

    any un-supercharged small block not useing nitrous or some other power adder that makes over 550 hp is highly likely to be at least somewhat unstreetable as a daily driver and your not likely to build a small block that makes "764 HP & 695 lb/ft at the flywheel" likely costs as much or more than a big block makeing similar power, look, good engine choice
    maybe I can help just a bit more

    if you can locate one thats been wrected or the components the firewall pieces for the LT5 give a great deal more room for headers, than the stock LT1 or L98 firewall parts. a large COMBO OIL /trans fluid cooler mounted where the spare tire normally is reduces the engines need for a huge radiator

    Perma-Cool 13318 $209 (summit)

    Hedman Hedders 68090 $181.95 fit on one side without mods and on the other one side need one tube re routed to get them to work
    if the header flange is strait and flat and your useing a decent gasket (personally I prefer the copper ones) and youve coated the bolt threads in ANTI-SEIZE like you should have almost any decent 6"-8" box end wrench can be used to snug the bolts up firmly

    and YEAH! the windshield wiper motor needs to be relocated swapped for a differant ,smaller one,or removed

    heres a few pictures

    Last edited by grumpyvette; 06-20-2010 at 08:31 AM.

  2. #2


    Looks good. Glad you painted it orange as well. BBC's just seem like they should be that color.....

    Lower pulley clearance looks to be very tight.

    As you stated, big cubes are hard to beat when you compare driveability vs. HP.... plus they just look cool.
    Lonnie Pavtis
    Lonnies Performance Automotive

    724-322-8505 9:00am-11:00pm eastern time - weekdays & weekends
    Celebrating our 10th year - 1999 to 2009
    Specializing in custom fuel systems, fuel injection components,
    suspension & all your supercharging needs.

  3. #3
    Join Date
    Jul 2008


    ITS not like IM the only guy to do this swap, BTW none of these pictures are MY car

  4. #4
    Join Date
    Jul 2008


    theres no way a c-4 will exactly match the weight distribution and handling of a C6 BUT the strait line accelleration CAN be equaled or exceeded with a decent well thought thru and executed BBC swap, and at about less than 1/2 the price of a new Zo6, and its no trick to easily exceed the hp of the stock Zo6, depending on the extent of the mods you want, and your fabricating and shopping skills somewhere between 15K and 35K should get you one very fast BBC C4 and that price COULD easily include the car itself, if youve already go the car you can knock a good chunk like 5K-15K of the cost off the total.
    PLUS if your like me, having built or modified most of the car yourself, and owning something rather unique, has a strong draw to my pride of ownership vs paying huge bucks for a Z06 that anyone with a fat wallet can own.
    plus theres nothing that sounds like the rumble and rolling lope of a high compression, BBC with over 500 cubic inch displacement.

    personally opening the hood to display a nice BBC in a c4 seems to me to be the better option and it shows more hot rodding skills than paying $70K plus for a Zo6

    Last edited by grumpyvette; 08-03-2008 at 03:13 PM.

  5. #5
    Join Date
    Jul 2008


    Quote Originally Posted by LD85 View Post
    Grumpy, lets say I pic up a 454, with iron heads etc. what kind of HP can I expect, if I port the stock heads, new cam and bore it out, no strokeing?

    this is well written info

    then look at (tech)....(Oval[/url] Port vs. Rect. Port - BBC cylinder head info. )

    now we didn,t always do things the best way in the old days , YET WE DID HAVE FAST BBC MUSCLE CARS , a decent machine shop can add longer valves,back cut the valves, add a 3 angle valve job, do a pocket port job , add beehive springs and clearance the heads for a .650-.700 lift, you then swap to pistons that give a decent cpr in the 10.5-12:1 RANGE ,(THE RADICAL CAMS REQUIRE MORE COMPRESSION) IF YOU NEED TOO, if the heads you have are open chamber designs ,TO GET THAT cpr, ADD A NITROUS KIT UNDER THE CARB,AND and add a good solid flat tappet cam, some 4.11-4.56 rear gears and a 3500 stall converter or a manual trans, A DECENT INTAKE LIKE THE rpm AIR GAP WITH A 780-850 CFM CARB, DECENT HEADERS, and you get an old school muscle car that kicks butt!and its fairly reasonable on the total cost per hp


    hot STREET
    Chevrolet Performance Camshaft; Part Number SS4242
    Chevrolet Performance Camshaft; Part Number SS4254
    Chevrolet Performance Camshaft; Part Number SS4265

    BUT WE EXCEEDED 500 HP VERY EASILY WITH A 427-468 bbc, and with the right parts 600hp plus is do-able


    Airflow Chart for PowerOval Street Cylinder Heads
    Lift Value Intake Flow CFM Exhaust Flow CFM
    0.100" 74 64
    0.200" 160 113
    0.300" 231 146
    0.400" 275 178
    0.500" 316 209
    0.600" 336 240
    0.700" 347 264
    Tests conducted at 28" of water (pressure). Intake with CNC-bowl blend and
    CNC-inlet with Fel-Pro 1212 gasket; exhaust with 2" pipe.

    BTW ,when I post answers its to a broad audiance, where I need to cover most applications, you can get that 500-600hp/tq from a 468 BBC but it will require some compromises in the driveability if your not useing a super charger,turbo or nitrous,and theres always guys that suggest that you can get 500hp from a SBC and thats true enought! but in any case the extra displacement and bigger valves and ports allow you to better any sbc results in almost any case where your not throwing huge buckets of cash at the project, and even then once you try to exceed about 500hp youll soon see the BBC has advantages and tends to be cheaper to build at some point

    550 Urban Assault Engine

    The goal was not top horsepower, although 600 is pretty good, but a broad torque curve. This engine had 625 ft. lb. of torque at 2800 RPM and still was above 625 at 4800. Based on the brand new Merlin III block and featuring Merlin iron heads and aluminum intake the new 550 has produced some phenomenal numbers on the dyno. The engine was designed for daily street use and starts great and idles at a smooth 700 RPM. On the dyno, 18 pulls were made to optimize timing, jetting, etc. Different rocker ratios and carb spacers were also tested.

    The engine features all premium components including 4340 steel crank, H-beam rods, forged SRP pistons, Sealed Power plasma moly rings, race bearings parts that will take a good shot of nitrous. A complete Comp Cams valve train is used including the latest technology hydraulic roller cam. Top line brands like MSD, Manley, Holley, and Moroso finish the package.

    for aluminum heads add $800
    many options available Complete engine carb to pan

    youll have a hard time building an HONEST 600hp/625 tq in a small block for $9K

    This is a special project for the Super class, and serious bracket racer, that needs power and torque, but also has to make rounds all day without motor maintenance. This engine now makes 900 HP at 6400 RPM with 830 lb. ft. of torque at 4800 running 33 degrees of timing. The cam lift is only .748 and the rockers are Jesel shaft mount. No need to check valve springs and lash between rounds. Engines are built with Merlin III blocks, Brodix BB3X, or Dart 345 heads, Merlin X intake, Ohio Crankshaft 4340 forged 4.75" stroke crank, H-beam rods with ARP 2000 bolts, Canton pan, Comp cam, Felpro gaskets, and Melling oil system.

    Every component is available off the shelf, the bore size will allow two rebores, and the compression is 14.3:1 which does not require the ultra expensive gas, or could be run on alcohol. The Best part is the price at $10995, less carb, ignition and valve covers, this is a really great deal.

    Holley 1250 Carb $975
    MSD Ignition $695
    Valve Covers $295
    Aluminum Block $2350
    E85 Carb $1300

    Complete Engine

    900hp/830tq from any sbc without a turbo is almost unheard of

    heres 675 HP for $9K

  6. #6
    Join Date
    May 2010


    grumpy what did you do for exhaust from the headers??
    did u tie it to the factory exhaust?
    i joind this form because i am kinda new to the vette scene, i say kinda cause this is my first vette but i grew up around them. my old man has a 61 its his first car he ever bought he bought it when he was 16 and still has it today. my friend has a few so i used to drive his all the time and now i finaly got my own and just love the idea of a BBC in a C4, cause i have never seen one in person out of all the car shows i been to so i HAVE to be different and drop in a big block!!!!
    this thread gave me quite a bit of info on doing it thanks!!!!

  7. #7
    Join Date
    Jul 2008


    I bought a set of these headers and cut and moved and re-welded the one tube on the drivers side that that was mandatory on,to get them to fit,on the pass side, they bolt on with only minor tweaking

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