Big Block in a '68 Impala - Advice Needed - Impala Tech
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post #1 of 8 (permalink) Old 06-05-2016, 09:07 PM Thread Starter
Join Date: Jun 2016
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Big Block in a '68 Impala - Advice Needed

I am putting a Big Block into a 68 Impala, and need some advice on engine mounts/frame brackets. It has Hooker headers, sized for a 502 which is the engine in the final plan. Right now it has a 454 from a truck with a 4L80E trans.

The issue is primarily that the headers don't clear the steering box. I believe there are two sets of frame brackets for the engine mounts, and two sets of engine mounts, one for SB and one for BB, but they end up the same overall height with the BB brackets being shorter and having more rubber in the mounts. Right now, it has the frame brackets that came with the car (SB) and SB engine mounts. I also fabricated 1/2" spacers that are installed, and give what I would call minimal clearance to the steering box. Only one pipe is bad, the rest are acceptable. But I don't really like the spacers.

The options I see are:
1) Remove the spacers, bend/dent the crap out of the headers to clear the steering box. The good point about this option is it keeps the factory alignment as much as possible.

2) Cut & weld the brackets to add the 1/2" of height, and modify the base to line up the mounting holes. This provides acceptable clearance, but I am concerned about maintaining alignment, especially driveline angles in the plan view, and engine level in the front view.

3) Any good ideas from someone who has done this before

Any thoughts appreciated.
reddogf5 is offline  
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post #2 of 8 (permalink) Old 06-05-2016, 10:14 PM
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Shorter frame stands is normal as the BBC and high horse small blocks used thicker interlocking motor mounts which when compared to the stock glued together motor mounts and taller frames stands had the crankshaft at the same height either way. I used to use the stock SBC stands and a torque limiter to keep the motor from going for a walk about. Without a torque limiter (such as a short length of 3/8th inch forged steel chain with a 3/8th inch bolt into the block and the other end bolted to the frame) it WILL break the stock vulcanized rubber motor mounts.

Another solution is polyurethane motor mounts. They interlock but are the same thickness as the old rubber ones that were only glued together. A wire cable with an eye at each end on the cable works also (what Chevy used on their 1968 safety recall for broken motor mounts), but getting one short enough and strong enough at the same time is more difficult to source than a piece of chain.

As to headers what model of car are those BBC headers supposed to fit? Reason I ask is the 502 is identical dimensionally to the earlier 396, 427 and 454 engines that preceded it. If those headers won't fit the 454 you have now they won't fit the 502 (which makes a good start on a rebuild towards a 540, or a 555).

Also are you using the stock cast iron heads? Many aluminum aftermarket heads raise the exhaust port a third of an inch to straighten it out to allow it to breath better (the BBC has a horrible exhaust port and is the bottle neck to a good breathing engine; which is why they respond well to a split duration cam with more duration on the exhaust side).

Because the steering gear box is practically next to the fire wall many headers will hit it. Two cars that offer headers that should clear are the Corvette (the Corvette uses a lot of Impala parts being designed as a full size car with the back seat cut out) and The Camaro (another car with rear steer when the rest of the GM fleet used front steer gear boxes).

If you have not purchased headers yet or know a friend with a BBC Camaro see if you can borrow a set of headers to try the fit in your Impala.

Big Dave
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post #3 of 8 (permalink) Old 06-06-2016, 06:36 AM Thread Starter
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Thanks. The headers are supposed to fit the car, a 68 Impala, and the engine is stock (iron heads). They *almost* fit, it looks pretty clear that they were designed to route around the steering box, but they don't quite make it. Can you suggest a source for big block or interlocking silicone mounts? That, combined with the frame brackets as-is would probably give me enough clearance.
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post #4 of 8 (permalink) Old 06-06-2016, 09:02 AM
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You are not going to find BBC frame stands except used off of another parts car.

Energy Suspension 3-114G | parts search

I looked and noticed that Global West (which makes a lot of HD suspension parts for your Chevy) is no longer selling interlocking Polyurethane motor mounts.

Big Dave

Last edited by Big Dave; 06-06-2016 at 09:18 AM.
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post #5 of 8 (permalink) Old 06-17-2016, 02:27 PM
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These headers worked great for me in my 1967 Caprice 454 peanut heads . I got mine at summit but you can get them other places if you choose.
3del is offline  
post #6 of 8 (permalink) Old 09-19-2016, 11:44 AM
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I swapped out a 350 for a 396 with 454 heads and headers cleared the steering box, my issue is the power steering hoses are to close to the headers. Anyone know if there is an aftermarket hose kit?
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post #7 of 8 (permalink) Old 09-19-2016, 02:48 PM
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Lee Manufacturing may have what you need - wouldn't hurt to call them and see what they have to offer.
They do a ton of power-steering stuff, mods, adapters, kits, etc.

11661 Pendleton St. Ca
Sun Valley, Nevada-91352, USA

BA. is offline  
post #8 of 8 (permalink) Old 09-19-2016, 03:12 PM
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Originally Posted by cpdimpala View Post
I swapped out a 350 for a 396 with 454 heads and headers cleared the steering box, my issue is the power steering hoses are to close to the headers. Anyone know if there is an aftermarket hose kit?
BBC uses a different power steering pump than the SBC. It is the same pump inside the reservoir; the difference is in where the hoses enter the reservoir housing. The SBC pump sends the hose directly out and back into the face of the BBC head. I might add that the power steering brackets are different as well but you know that as I doubt that the SBC would even bolt up.

Big Dave
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