68 Impala Big Block swap update - Impala Tech
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post #1 of 3 (permalink) Old 12-31-2010, 11:53 AM Thread Starter
Join Date: Aug 2010
Location: Clarksville
Posts: 19
68 Impala Big Block swap update

Ok... if I ran into this problem someone else might. I figure I had to go through the pain, why should anyone else!

If you have a 68 Impala that you want to drop a Big Block into, there are several problem areas that I have found. First, the mounts. The mounts for those cars come in two styles, the "Short & Wide" and the "Tall and Narrow". To find out which ones you need, measure the tops of the towers. The widths are either 2 3/8" or 2 5/8". The heights are much different, either 1 3/4" or 2 3/16". If your car has the original engine in it, check out the width on the engine mounts before purchasing. I bought the interlocking style and they are too tall. Once the left side was in place, I had about an inch that the right side needed to sink to put the pin in. Way too much, they were the wrong height. Check out Energy Suspension for the right mounts:


Second, the position of the motor is tricky. Should you buy an after market oil pan, be careful. Yes, the manufacturer will tell you that it fits the car, but in reality it is extremely close to the steering arm. In my case the oil pan said it would fit, and it does... kind of. There is room, but not enough for me to feel comfortable with. I am going to move the engine and tranny 1/4" back. This will require either purchasing a new set of towers and drilling new holes 1/4" forward, or using the ones I have. Either way, in my situation I need another 1/4".

If any one has a set of towers for a 68, please let me know. I would like to purchase them and fabricate them for my needs. The same towers were used for small blocks and big blocks.

If you have any other questions about this swap, let me know. Thanks!

fathawk is offline  
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post #2 of 3 (permalink) Old 12-31-2010, 04:00 PM
Join Date: Jan 2006
Posts: 12,376
As I have mentioned numerous times GM made four sets of motor mounts between 1958 and 1972. Two were used from 1958 up until 1968.

Those two differed in that a factory installed motor with less than 300 horsepower got a rubber biscuit (two plates of steel glued together by vulcanized rubber; not physically constrained). Any motor rated above 300 horsepower (which includes all big block engines) were installed using a thicker interlocking style of motor mount. Because the motor mount was thicker (to accommodated two pieces of interlocking steel held apart by a block of rubber) it required a shorter frame stand. In 1968 in response to a law suit GM had to recall every V-8 powered car they had ever made going back to 1958 and install a five ton steel cable to prevent the motor from moving in the event that the rubber biscuit style motor mount failed.

In 1969 GM introduced two new motor mounts for their V-8 cars (once again a SBC mount used with cars that were rated at 275 horsepower or less and another motor mount for any engine small or big block that made more than 300 horsepower. Both designs of the 1969-'72 motor mounts are interlocking; with the above 300 horse being more robust (bigger) so it requires a shorter motor frame stand.

The difference is the 1969-'72 used a different mounting width than the 1958-68 motor mounts so they differed in thickness and in the width from earlier motor mounts (even though the under 300 horse version made for the 1969-'72 cars it is the only motor mount you can buy at the corner auto parts store). To obtain a correct rubber reproduction motor mount to fit your car you have to look to the aftermarket. (I prefer the polyurethane mounts sold by Energy Suspension myself).

Big Dave
Big Dave is offline  
post #3 of 3 (permalink) Old 04-06-2013, 10:55 PM
Join Date: Feb 2013
Location: Vegas
Posts: 22
The mounts I bought from Impala Bob's do not line up with any of the holes I have, I think I am going to send them back and get mounts from energy suspension. I will post pics later this week to see if you guys can help me out at all
1968fastback is offline  
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