Nova Tech

Nova Tech (
-   1968-1974 (
-   -   SBC to BBC conversion '68-'74 (

B73nova Jun 21st, 09 02:59 PM

Re: SBC to BBC conversion
thanks , yea I put the shorty headers on as well for clearance reasons, I will order them and let you guys know asap

willie Sep 27th, 09 09:35 PM

Re: SBC to BBC conversion '68-'74
hey guys i put a 427 in friends 69 nova and had header (hookers) interference w/steering box we smoothed the fire wall and installed hot rod air unit, we ordered new stands ,any answers to this ?

newtonova Apr 6th, 10 10:49 PM

Re: SBC to BBC conversion '68-'74
dave i was just wondering if you had any ideas on how to fix the speedometer of a 74 nova all the lights work but the fuel level and speed dont....iv jus turned 16 and my mom said i could start drivin it after i got that fixed so any help would be appreciated

74bruiser May 12th, 10 04:16 AM

Re: SBC to BBC conversion '68-'74
B73 is it done yet? was wondering what u did for the motor mounts?

Spartan2222 May 16th, 10 10:43 PM

Re: SBC to BBC conversion '68-'74
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.

Big Dave May 17th, 10 05:43 PM

Re: SBC to BBC conversion '68-'74

Originally Posted by Spartan2222 (Post 102211)
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.

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

Spartan2222 Jul 5th, 10 02:23 PM

Re: SBC to BBC conversion '68-'74
Big Dave what engine mount kit should i go with for my 73 nova?

Big Dave Jul 5th, 10 03:33 PM

Re: SBC to BBC conversion '68-'74

Originally Posted by Spartan2222 (Post 105424)

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

Philip Jul 5th, 10 08:16 PM

Re: SBC to BBC conversion '68-'74
Dave I am glad you answered first, even though I knew it, I would not have typed all of that. I would have skipped to the last line and said the 69 and newer kit and not gave the reason why.:D

Big Dave Jul 5th, 10 10:37 PM

Re: SBC to BBC conversion '68-'74
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

Spartan2222 Jul 6th, 10 09:31 AM

Re: SBC to BBC conversion '68-'74
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)

7Nova4 Dec 27th, 10 02:44 AM

Re: SBC to BBC conversion '68-'74
:thumbsup:Excellent info. My Nova came with a BB 454 when I bought it and now I have the receipe to make sure its done right.

ducatidennis Feb 26th, 11 10:25 PM

Re: SBC to BBC conversion '68-'74
1 Attachment(s)
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.

Big Dave Feb 27th, 11 08:45 AM

Re: SBC to BBC conversion '68-'74
That cable was all that was left of the original GM recall kit.

What you are talking about is a torque limiter. I do not recommend solid motor mounts for the street not because of the engine vibrations they transfer into the car (on a poorly balanced motor it will rattle your teeth), but because of the stress it places upon your aluminum transmission case. A better solution is a plastic motor AND a plastic transmission mount.

Whatever style of mount system you use, you must use the same type mount at all attachment points. If you go with solid Moroso motor mounts then buy the solid steel tranny mount (Moroso part number 62600); and be sure to use a lot of red Loctite because of the vibration. If you use a plastic interlocking motor mount use the transmission mount made of plastic as well or you will crack the case of the tranny with time.

As to chains and cables. There are two issues. First it can not be mounted to an aluminum head. A single bolt will transmit enough force to pull the aluminum head apart. If you have aluminum heads you will need a steel plate to attach it to the head (such as the A/C front mounting plate on the big block that bolts to the front of the head and part of the block to distribute the load). Second is where you attach the other end. It will be under stress and by definition it will be bending (stress is synonymous with deflection in engineering). So if you are attaching it to your front suspension expect your steering to change when the cable/chain pulls on it.

Race cars all use a front and mid mounting plate to attach the motor solidly to the frame. Your car doesn't have a frame (a sub frame yeas but that gets bolted to sheet metal unless you have sub frame connectors and a roll cage to make a frame). As such I do not recommend a mid mount front mount system for the street.

Big Dave

jcirwin May 17th, 12 11:06 AM

Re: SBC to BBC conversion '68-'74
My son bought a '73 SS 350 Nova for his son (my grandson) and we are building a '69 BBC (long water pump) to put in it. Big Dave's list is lengthy (and discouraging). We will be using a built 700R4 tranny, stock BBC Nova exhaust manifolds, new Nova BBC frame mounts and oil pan.

The Nova has factory A/C and the evaporator box clears the SBC valve cover by about 2 inches. With the new frame mounts, will the BBC valve cover clear the A/C evaporator box??

All times are GMT -4. The time now is 05:09 PM.

Powered by vBulletin® Version 3.8.8
Copyright ©2000 - 2020, vBulletin Solutions, Inc.
vBulletin Security provided by vBSecurity v2.2.2 (Pro) - vBulletin Mods & Addons Copyright © 2020 DragonByte Technologies Ltd.