66 impala convertible frame reinforcement - Impala Tech
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post #1 of 11 (permalink) Old 06-10-2013, 11:31 PM Thread Starter
 
 
Join Date: Jun 2013
Location: MN
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66 impala convertible frame reinforcement

I have a 1966 chevy impala convertible and a gen 7 bbc 8.1 engine that has dynoed at 581 hp and 630 torque. I would like the 2 to become good friends but I am and thinking the frame may not handle that much torque without some modifications. So I am wondering, what should to be done to the frame to keep everything straight with a high torque engines. The car originally came with the 396/325 so the suspension was already set up for a BB.
Also without tubing the car, what is the widest tires you can put in the rear without rubbing assuming 18 inch rims. I am trying to find a best offset and tire size because what good is that much power if you can't get it to the ground.

Any experience you have in this area would be appreciated.
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post #2 of 11 (permalink) Old 06-11-2013, 12:09 AM
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Welcome to the Team Bill!

Interesting horsepower number out of a Vortec 8.1L motor. Would be interested in hearing how you did that.

Big Dave
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post #3 of 11 (permalink) Old 06-11-2013, 04:02 PM Thread Starter
 
 
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A good deal of custom work.
Holley double pumper on a dart 8.1L carb intake
custom ground cam
custom pistons
stock heads with some port work.
about 10.5:1 compression premium pump gas.
Natrual, no super chargers, no turbos, no giggle gas.
link to a video of the dyno pull
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post #4 of 11 (permalink) Old 06-11-2013, 06:27 PM
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@Bill - You may not know this unless you have read some old threads but Big Dave there has (I believe) a 9 second BBC mid-80's Impala if I recall correctly. Not to mention a lifetime of owning some very bad-*** engines. (like the LS7 he put together)

I bet he'd love to hear more of the details on that cam.

Personally, I didn't know that even a ported stock head on these later Generation BBC's could support that much HP!

HOW A NOVICE REBUILDS A 66 IMPALA CONVERTIBLE:
http://www.impalas.net/forums/blog.php?u=1432
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post #5 of 11 (permalink) Old 06-11-2013, 09:05 PM Thread Starter
 
 
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The engine

The cam is a hydrolic roller that was custom ground for this build.
I can't go into the specifics because I don't know how much of Nicks secret recipes he wants given out.
But the engine was build by Nick Hienen from Nasty Engines and the dyno sheets from the last few runs had those numbers. I don't have reason to doubt the numbers because when we started I wanted a 550 to 600 hp engine (you heard the dyno run, its a stout engine) and nick's formulas said it was possible. I am not going to say the build was not without its hiccups, metric bolts and and one-offs etc because the gen7 is really meant to be a high torque truck engine and converting it back to a distributor/carb setup has only really been possible since the dart dual plane intake came out.

In any case, assuming I have a BBC engine that pushes 600+ foot pounds of torque, what should I be doing to keep the frame from turning into a pretzel the first time I stomp on the skinny pedal? I was wondering if I needed to put in frame reinforcing plates or a cross-member in. I know the frame comes from the factory boxed and its not as susceptible to twist as the 64 and earlier X frames but I don't know if there are any places the 65-66 frames are weak the forums I have lurched are unclear. What have people who have similar power level engines in had to do?
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post #6 of 11 (permalink) Old 06-11-2013, 09:43 PM
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You will discover that the tire is the weakest link.

I have over 780 ft/lbs of engine torque and I go through a set of tires a month. I have broken three 700R4 transmission in one month when I first started out, but switched over to a 4L80e and haven't had any problems since then. I broke a 12 bolt, but switched over to a Dana 60 and I haven't had any problems. I did rip the upper control arm off the car and bent the bottom one up like a pretzel (didn't do the drive shaft any good either, but I needed a bigger one anyway) just to test the drive shaft safety loop out (it held).

Aside from reinforcing where the control arms mount to the car welding in a 2x4 crossmember (and changing the entire suspension over to a four link with real frame rails in a S&W back half kit) I haven't had any other issues. Once again even with 29-12 x 15" tires I am spinning unless the track is properly preped with Rosen or VHT so the tire is the weakest link.

Big Dave
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post #7 of 11 (permalink) Old 06-12-2013, 12:08 AM
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Since my own 66 had a busted area at the (passenger-side) rear upper control-arm mount, I will 2nd the potential need for a reinforcing plate there!

HOW A NOVICE REBUILDS A 66 IMPALA CONVERTIBLE:
http://www.impalas.net/forums/blog.php?u=1432
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post #8 of 11 (permalink) Old 06-12-2013, 12:18 AM
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With the short, stiff sidewall of 18" tires, you will greatly reduce the shock loading on the drivetrain and suspension (they'll spin). If you go with sticky 15s, then you will have to get serious with beefing things up.

Two doors, four doors, wagons, and ragtops.
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post #9 of 11 (permalink) Old 06-12-2013, 04:53 PM Thread Starter
 
 
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I kind of guessed the 700r4 would not be up to the job. I am currently looking at beefing up a turbo 400 and when I get a few grand I don't know what to do with, I will put a gear vendors unit behind that.
I kind of like the idea of keeping computers out of my impala so I was avoiding the 4l80es but that may be a better choice long run.

You do have me wondering now, I figured a 12 bolt with a posi unit was going to be strong enough in the rear end. At what power level is a 12 bolt too weak and you need to go with a dana 60 or a ford 9?

Thanks for the information about reinforcing the control arms. I am definitely going to have to have to look into that. I am hoping that I don't have to completely replace the frame.

Re the tires: I have 15 inch keystones on it right now. I was thinking that 18s would stiffen the handling some (like Jason said stiffer side walls). I can live with spinning the tires at WOT, I was kind of thinking a good starting point of 10 inch wide in the rear. I just don't know the offset I need or if they will fit at in the rear. Has anyone manages to get 18 x10 in the rear if so what was the offset you used on the rims and what was the final tire size?
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post #10 of 11 (permalink) Old 06-12-2013, 05:35 PM
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It's later, but I use an 18x10 with a 295 35 18 on my 95 SS. Not sure if you could stuff that under the 66, but I suspect that with the correct offset, you could. I can't try them on my 65, they are the big 5x5 pattern.

Two doors, four doors, wagons, and ragtops.
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post #11 of 11 (permalink) Old 06-12-2013, 07:54 PM
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Again, not exactly up your alley, but, I have 17x9.5 in the back of my 66. it was an easy fit.
I don't have the offset at the moment, but, I believe I posted it in a thread here back when I first got them.

PM me if you need me to dig more.

HOW A NOVICE REBUILDS A 66 IMPALA CONVERTIBLE:
http://www.impalas.net/forums/blog.php?u=1432
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