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SBC to BBC conversion '68-'74

67K views 42 replies 18 participants last post by  escott0311 
#1 · (Edited)
Installing a BBC in place of a SBC in a 1968-'74 Nova consists of changing the following parts:


Frame Stands (unique to year and motor)
Radiator (copper-brass 19"x23" wide core by 4 rows thick, 1969 tank code IO) return hose connector bent 45° if equipped with A/C straight if equipped with solid tappets (no A/C was ever used in any high performance solid tappet motor)
Radiator Shroud ('67-'68 Short WP GM-PN 3916637 '69 Long WP GM-PN 3947619)
Radiator Support Bracket
7 blade fan 18 inches in diameter GM part number 3947772 (SBC used a 4 or 5 blade)
7 blade fan thermal control clutch
Heater Core
Heater Core Box
Bell Crank (Z-bar)
Clutch Linkage
Muncie Offset Shifter Bracket (1967-"68)
Muncie Hurst-supplied shifter (similar to the over-the-counter Hurst Competition-Plus model, but differed in the following ways: Slip-in "bayonet" style round handle. No adjustment bolts. 1969-'72 used a unique Hurst style aluminum shifter mounting plate.
TH400 Transmission Cross-member GM-PN 3912573
Muncie Transmission Cross-member
Alternator (14 AMP's bigger)
Battery (again higher AMP-Hour capacity)
Battery cables (heavier gauge wire)
Fuel Line tank to sub frame exit (3/8" instead of 5/16)
Return Fuel Line (only if equipped with the 325-350 horse 396)
Rochester QuadraJet stainless steel heat riser cross over block off plate
Intake Manifold (aluminum high rise #2161 4.85" max)
Valve covers, chrome plated or painted orange, with oil drippers (no dimple on drivers side that's for the Corvette)
Distributor
Fuel Pump 6415748 high capacity
Fuel filter (larger than SBC to act as a fuel reserve)
Fuel Line to Carb (Holley is different than Q-Jet)
High Torque Starter Motor 1108400
Starter Motor Brace 354353
396-427 Flywheel 361950 11" clutch 14" diameter 168 tooth
454 TH 400 Flexplate (externally balanced) 3992069 168 tooth
Power Steering Pump (return line pointing to drivers side)
Alternator Brackets (year and model specific)
Cast iron Harrison A6 air conditioning compressor brackets
Big block accelerator rod or cable (and mounting bracket)
Cast iron exhaust manifolds (are not reproduced)
Headers have to fit the application and most aftermarket heads have raised exhaust ports Caveat Emptor
Dual 2-1/2" diameter tail pipes (minimum)
Front coil springs 327 lbs per inch stock (or an Eaton #MC-126)
Sway Bar (lager diameter than the SBC)
Five leaf rear springs 150 lbs per inch
High Perf. deep groove set for short water pump 67-68:
3858533 crank - double deep groove, Z/28 and HP
3765947 crank - double deep groove, PS drive insert Z/28 and HP
3770245 water pump double deep groove, HP V8
3720616 water pump pulley spacer shim - reinforcement
481042 PS pump - single deep groove perf, HP V8
[High Perf. deep groove set for long water pump 69 (All 69 and later GM pulleys are of the deep groove type).
3941105 PS pump - this is stamped steel, not cast iron
3956668 crank- two groove
COLOR=blue]392456[/COLOR] water pump single groove
3829387 Fan Generator pulley-single deep groove 43/64" shaft

This is part one of many. Part numbers are for reference only as many of them are no longer valid; and parts are out of production. I will attemp to get a repop part number from several different sources and pictures of the parts to answer a lot of futer questions.

Finding parts is more challenging than I first estimated I have been searching for hours an no one site ahs all the parts but my list of reproduction parts is growing. When I find them all I will continue with my next post.

One of the things the factory did when you ordered the Heavy Duty Suspension (part of the SS package) was to add gusset plates and weld in reinforcing pads in the body were the frame mounts were and were the chassis bolted to the car in anticipation of heavy duty use that grandma's Nova never got because it had a six banger in it.

Big Dave
 
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#3 ·
Re: SBC to BBC conversion

Lots of great info. I made the swap last year on my 69 that originally came with a small block 350. Pulled the mouse out and dropped the rat in, a 454 big block. Everything went smooth as silk. I used the stock small block frame mounts, and also used moroso solid motor mounts for a small block. Didn't have to change out the heater box, car doesn't have ac as well. Bought cheap flowtech headers from summit racing. I'm running a turbo 350 tranny with a B&M holeshot 3000 converter. Ford 9" with 3.89 gears. Puts a grin on my face every time I drive it. This engine has a massive torque curve.
 
#39 ·
Re: SBC to BBC conversion

Lots of great info. I made the swap last year on my 69 that originally came with a small block 350. Pulled the mouse out and dropped the rat in, a 454 big block. Everything went smooth as silk. I used the stock small block frame mounts, and also used moroso solid motor mounts for a small block. Didn't have to change out the heater box, car doesn't have ac as well. Bought cheap flowtech headers from summit racing. I'm running a turbo 350 tranny with a B&M holeshot 3000 converter. Ford 9" with 3.89 gears. Puts a grin on my face every time I drive it. This engine has a massive torque curve.
were you able to use your power steering pump and alt from your small block with differant brackets
 
#7 ·
Re: SBC to BBC conversion

Hey Dave, I have owned bowties for a long time but this is the first nova...I have a 73 and I was putting in my bb today when I noticed 2 things....1- the mounts dont work, I have the moroso solids for bbc but they are not lining up with the frame mounts.........2- I need more height for factory crank pulley not to hit on frame...is this normal? I think the car had a sb in it before can you help me:(
 
#10 ·
Re: SBC to BBC conversion

Brian I am not 100% sure of who has the best mount (I am a 4th gen guy cause everything fits nicer:) ). A lot of the Camaro guys like dealing with Ricks Camaro. They sell 67-68 BB stands and the 69stands. Not sure what would be different except maybe the part number stamped into them.
 
#13 ·
Re: SBC to BBC conversion

Brian it is the rear steer issue that makes it tight. The steering box location is the biggest problem area. My buddy, whose name is Brian also :), used the shorty headers on his. The long tubes interfered with the manual clutch linkage. He also smoothed the fire wall and is installing a Vintage Air heat and AC unit to make for more room under the hood.
 
#20 ·
I didnt see anything about drive shafts? I just bought a 454 with a turbo 400 and plan on putting it in my 73 nova. I know i will need a different crossmember and i think a shorter drive shaft? I just got it so i not measured anything.
 
#21 ·
TH400 is a bigger version of the TH350 (which is a 4/5th scale model of the TH400). It is longer which requires a shorter drive shaft. You also have to change the output yoke because the out put shaft of a TH400 is bigger and stronger (higher spline count).

Big Dave
 
#23 ·
This is a common question and the answer lies in how correct you want your obvious up grade to be (the factory never put a BBC in a '73 Nova so your not going to be able to slide it by the white glove inspection judges at a car show as original).

In 1967 and '68 the factory was fat and happy and operated under the premise that what is good for GM was good for the country. Unfortunately we have lawyers like Ralph Nadir who was trying to get rich by suing the pants off GM for safety issues. (you know those guys on the evening TV who are always asking if you have ever taken or used this product to call us now because we want 2/3rds of the proceeds of a class action lawsuit so we can retire to a third world country). Anyway in 1968 GM was the first company in commercial history to loose a class action court case that resulted in a nation wide recall of a product (in this case it was every Chevrolet V-8 made from 1958 to 1968. The reason the motor mounts failed in service allowing the engine to roll over to the passenger side and jam the throttle open because they used to use a solid steel rod to open the throttle before 1969.

In 1969 GM issued a new design on all motor mounts that will not fit the earlier frame stands. This was to force you to buy new motor mounts of the recently designed interlocking style. (They were not a new design or even a new product. Prior to 1969 all engines over 300 horsepower used different frame stands and motor mounts to keep the vulcanized rubber biscuits used on six cylinders and small base engine V-8's from separating).

Because of this there are four different motor mounts for all Chevy V-8's. Two mounts that fit 1958-'68 cars divided into regular rubber biscuit and interlocking on the high horse engines; and another pair of motor mounts that fit 1969-'72 cars (in 1973 the factory introduced the final solution "clam Shell" motor mount that is still used today on all engines regardless of horse power.

These four motor mounts have different heights and widths and the bolt centerline hole for the grade eight engine mount bolt is different on all four. Because of this many people run into parts mismatch where the motor will not fit (B73nova Moroso: makes three different sized Chevy solid motor mounts (three different part numbers) to fit from 1958 to 1972 and each motor mount has different widths between the tangs, distance from the base to the bolt hole and the tang length is different on each one to match the frame stands the factory used over the years).

The factory is all about interchangeability but there are different parts for different applications (based upon GVW among others factors such as horsepower, even the speed rating of the original equipment tire affects the parts you have on the car: whether you are aware of it or not). Motor mounts are one of these black holes that information falls into and never gets out of (are you paying attention Dr Hawking?)

To answer your question (if I put this up front would you have read this monolog?) the 1969 kit is what you want. The 1967-'68 kit uses the very rare odd-ball size motor mount that is not sold at any corner auto parts store like the 1969 version is.

Big Dave
 
#25 ·
I look at it this way. I'm not getting any younger; and if I don't share what I know while I can still remember it, it will all be lost when I go. I didn't spend as much time in a dealership as you did, (only about two to three hours a day while waiting for my friend to get off work as he was the lead mechanic on the service line), but it was productive spent roaming the entire dealership from the parts stacks to the dumpster (a lot of old catalogs got tossed every year). My full time job was as an industrial engineer making the parts that went into if not Chevrolet parts bins some bodies as I was involved in heavy industry for 17 years before it all folded shop and was sent overseas. I designed and maintained dies and punches, castings (sand and investment) weldments(working with shears brakes and punch presses) and stampings (deep drawn to a depth of 14”), even making my own fasteners from bar stock with automated screw machines to make rockets, transformers, dishwashers, and electrical cabinets and enclosures for heavy power distribution. So I have played with every machine tool, and made every form of part imaginable over a career that spanned less than thirty years (I made a mistake and allowed myself to get promoted into management).

I want to share what I have learned over the decades; I learned a lot of it the hard way but I am a degreed mechanical engineer and I am willing to teach others what I can remember. By the way my misspent youth hanging around the dealership for my friend to get off was so we could go to the shop we shared and build race cars all night until we got up and started over again the next day. It wasn’t all textbook learn’en.

Big Dave
 
#26 ·
Thanks Big Dave for the info! Yes i would have read it if you put the answer up top! That info is helpful to know for future projects. I'm young so I pick at guys brains at work who restore cars! (I learn better by doing than that text book stuff)
 
#28 ·
Hello, Wow Dave, you really know you stuff!:thumbsup: My Nova is a 68 with a 454 from a 74? Motor mounts are in great shape with very low miles. However the factory rubber mounts still allow the engine to torque under heavy load. Last owner fixed this by using a cable bolted from the frame around the upper control arm shaft to a bolt on the head. Hard launch and the cable snapped the end off by the head, engine rocked and stuck at wide open like you said. Turned off with the key and nothing was damaged other than the end of the cable was snapped off. Have saw many big blocks with the engine chained or cabled and even the solid plate bolted across the front of the engine. Would solid motor mounts be better than the chain or cable or would it be better to have solid mounts and a cable? Would I need the Moroso solid mouns for the 68? Would it be smart to convert it to a cable throtle? If so is, What would need to be switched? Thanks, Dennis.
 

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