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Big Dave May 17th, 12 05:31 PM

Re: SBC to BBC conversion '68-'74
A BBC is 2 inches taller (with stock low rise manifolds), and wider and 2.3 inches longer than a SBC (this assumes it is the standard height block, a tall deck truck block makes it nearly 3.4 inches wider than a small block).

You could order A/C with a big block back in 1968-'70 (just not with the 375 horse solid lifter 396 version of it), so I know it can be done with factory parts that are no longer available from your Chevy parts counter. The BBC has different heater cores and heater core covers than a small block uses to move the hose outlets away from those big heads rammed up against the fire wall.

I suspect that the A/C air handler box is unique to the big block as well, and you know it won't be a high demand part for the reproduction companies to mold; but they are making parts for the first gen Camaro and most of the firewall is the same. So see if that part can be modified to fit.

Big Dave

jcirwin May 18th, 12 07:35 AM

Re: SBC to BBC conversion '68-'74
Thank you very much for your quick reply, Dave.

FYI, I had the block rebuilt by Lamar Walden of Atlanta (home of the world's fastest W-Block). I pick it up today.

The engine is (now) a 30 over 396 with rectangular port heads and 17 cc crowned pistons for a streetable 9 to 1 CR. On the surface, the part numbers look like it's a 375, but milder cam and CR will drop the peformance considerably. I have a totally outfitted '67 427 435HP Tri-power Corvette engine (actual 351 block casting) that I want to put in my living room under a glass table top (lol). On this engine, I installed aluminum open chambered heads, so I have the original cast iron closed chamber tri-power heads which I'm using on the 396. (These are the same heads as used on the 375-396 engines).

On the Nova, the A/C air box has a straight vertical side (against the engine) so that makes engine extraction less complicated. We'll probably pull off the front end so we have straight in access to the engine bay. We are going to have to do a "fitting" to see what the clearances are (or are not) to determine what surgery needs to be conducted.

As an aside, Lamar said that the new motor oils do not support flat tappet cams and suggests to all who have older flat tappet engines to use a zinc additive (available through Summit Racing). Lamar said he gets a large number of customers each month with wiped cams.

I really appreciate your valued input, Dave . . . Thanks! Jack

brngrhd Dec 23rd, 12 09:36 AM

Re: SBC to BBC conversion '68-'74
Great post but i have to ask.... Why? Why does the big block need to be moved to the right? I had a small block and am switching to a big block the trans cross member that i have is aftermarket and does not claim to be big block or small block so why can i have it centered?

Philip Dec 23rd, 12 11:34 AM

Re: SBC to BBC conversion '68-'74
If not moved to the right there are clearance issues with the steering gear.
Not sure on the AC box shape being different between BB and sb cars, but it may be possible.

Starting in 75 all the engines were moved to the right and the AC box had a recessed area in it. Not completely sure why the change was made but it may have been to clear the steering shaft with the front steer set up.

AC box change

Cross member change to an offset mounting position

Frame change, the yellow marks show the difference between the frame rail edge and the engine cross member position.

Big Dave Jan 9th, 15 10:06 AM

Re: SBC to BBC conversion '68-'74
There has been a question raise to the frame stand for a 1968-'70 Nova BBC frame stand so I wrote this reply:

If you need the dimensions of the big block engine stands there are two different sets because of the 1968 motor mount recall. The 1968 frame stand dimensions are :

Driver's side: 2- 9/16" tall; distance from engine mount hole to centerline of outer 2 mounting bolts- 2-3/16" (this is the same for both frame stands).
Pass side is 2- 3/4" tall.

Rick's EP-6 is concours correct and is dimensionally accurate copy of the OEM part. Rick's EP-199 is a cheaper knock off made off shore and they make no claims as to dimensions; only that it should allow a motor to bolt up.

In 1969 the frame stands changed to represent the tall and narrow interlocking motor mount then in use for the first time (NDP sells a rubber reproduction under part number TRU 31-2308HD that is made by Westar their part # is EM-2285). The dimensions are:

Driver's side: 2-1/2" tall; distance from engine mount hole to centerline of outer 2 mounting bolts- 1-3/4" (this is the same for both frame stands).
Pass side is 2" tall.

The shorter frame mount should be on the passenger side. The taller frame mount is on the driver's side. The original Chevy part numbers (discontinued part) where 3950113 (left), 3950114(right). You may be able to find a replacement in the reproduction houses such as Rick's Camaro that offers an installation kit that includes BBC frame stands, alternator brackets for BBC and a Long Water pump, and a BBC power steering pump mounting brackets:

If you want just the 1969-'70 motor mount frame stands then Rick's EP-7 is concours correct and is dimensionally accurate copy of the 1969 OEM part. Rick's EP-200 is the cheaper knock off made off shore and they make no claims as to dimensions; only that it should allow a motor to bolt up.

In 1973 the factory went to a clam shell motor mount which consists of a solid steel motor mount (similar to the Moroso solid steel mount) the difference being the factory solid steel motor mount bolted to a captured on the frame rubber mount. The captured rubber mount can be replaced with a polyurethane mount, but it requires that you remove the rubber mounts outer shell (you will need a spot weld cutter) and reuse it. Philip wrote a great post covering this issue. This is good info; but unfortunately it is irrelevant. If you are putting a BBC into a 1973-'74 rear steer Nova you will still need to use a 1968 or a 1969-'70 motor mount and matching frame stand to offset the motor away from the steering gear box.

The actual shift is a half inch, but because the motor is tilted up as well as shifted to one side the distance as measured from the centerline of the hood is an inch to the carburetor air cleaner bolt. The shift is obvious when you look at the transmission mount location on the BBC cross-member which is of course different from the SBC cross-member in your car now.
The BBC cross-member is on the bottom.

Big Dave

Big Dave Jan 24th, 15 09:44 PM

Re: SBC to BBC conversion '68-'74
The factory frame stands that are no longer sold by Chevrolet moved the motor a half inch to the passenger side and raised on the drivers side (so there is a left and right part that has to be installed correctly). To identify the two parts you need only place them side by side and you will see one of them is taller (the drivers side). If you compare the SBC stands to the BBC you will note that the motor mount holes do not line up with each other. Neither BBC stand has the hole in the same place though both SBC stands are duplicate of each other that have the holes at the same height.

Restoration parts are of questionable quality. They are not all bad but you have to examine the part closely to see that they match the factory dimensions. Most are formed out of a thinner gage metal as thicker steel is harder to bend into the correct shape and requires not only a very powerful punch press but a complex (expensive) progressive die that has to be well maintained by a tool and die maker. Chevrolet had thousands of highly skilled machinists and press operators in their foundry and more punch press machines than they could fit under the roof of the plant at any one time. The same can not be said for the country of origin.

Team Camaro has talked this question to death and they will refer you to David Pozzi's home page

to read all there is to know about your sub frame (the same sub-frame as was used under the first generation Camaro was also used beneath the Nova from 1968-'74). He talks about the steering geometry problems and lays out all of the fixes, the frame stands and everything else such as quick ratio steering boxes, brakes suspension parts and everything that bolts onto to the sub-frame.

Here is some information I have collected that is related to the frame stands.

The first thing is that the motor mounts are not all the same there are three different sizes that Chevy has used from 1958-'72. Here are the dimensions according to Moroso:

Energy Suspension sells the two different high performance interlocking variants that Chevy has used over this time frame:

Here is a set of BBC frame stands installed correctly and you can see the difference in the positioning of the motor mount bolt hole.

Big Dave

68SS427 Dec 30th, 15 07:56 PM

Re: SBC to BBC conversion '68-'74
1969 and 1970 cooling fan is a fixed blade steel 5 blade fan identified by a W stamping and there is no fan spacer, it bolts directly on to the pulley surface. They are very rare and go for around $750 on ebay or original. Repro sells for around $250 I think and they are a nice repro. There is a mistake in the assembly manual that shows a 1 inch spacer. It is wrong. As far as I know it is not the 7772 fan for 68 but it is a clutch fan. I will check my fan collection to see the number. Chevelle used the 7772 fan I believe. I could be mistaken but the 7772 part number does not ring a bell for Nova in 68.

smf396 May 20th, 19 09:48 PM

Re: SBC to BBC conversion '68-'74
thanks dave for the parts list greatly apre. so it looks like i can use the alt just change the brackets but not the power steering pump,again thanks everyone for all your info
now with the steering bar i gotta try and find headers

smf396 Jun 22nd, 19 09:55 AM

Re: SBC to BBC conversion

Originally Posted by jlowery78 (Post 64619)
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

Big Dave Jun 22nd, 19 11:52 AM

Re: SBC to BBC conversion '68-'74
Alternators interchange and will bolt up with the correct brackets (must fit the water pump). Power steering reservoir on the power steering pumps are different. If you used a SBC pump on a BBC the hoses discharges right into the head of the BBC. The BBC pump reservoir has hoses that enter lower on the pump and are bent at ninety degrees.

Big Dave

smf396 Nov 11th, 19 02:17 PM

Re: SBC to BBC conversion '68-'74
thanks for the parts info, its ben driving me crazy trying to put this 396 in .its just not sitting on the frame stands, now i will be changing them but i havnt had an ishue with my th350 transmission not being close enough i dont understand wht i would have to get another cross member?

Big Dave Nov 11th, 19 03:13 PM

Re: SBC to BBC conversion '68-'74

Originally Posted by smf396 (Post 318285)
thanks for the parts info, its ben driving me crazy trying to put this 396 in .its just not sitting on the frame stands, now i will be changing them but i havnt had an ishue with my th350 transmission not being close enough i dont understand wht i would have to get another cross member?

BBC frame stands move the motor. If you do not also move the mounting point of the transmission you put a strain on the transmission case and it will break. Additionally you change the pinion angle so the drive shaft will vibrate. If you use the SBC motor mounts you do not have to change the transmission cross-member, but you will not get off the shelf headers to fit because they are made for a stock installation that used BBC frame stands and matching motor mounts. Hooker used to make a set of headers for a BBC in a Camaro sitting on SBC frame stands but it didn't work with P/S or A/C. When Garry Hooker sold his business to Holley, Holley dropped that set of tubes from their catalog.

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