Installing 455 into 1966 Tempest - Pontiac GTO Forum
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post #1 of 7 (permalink) Old 09-14-2019, 08:32 AM Thread Starter
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Installing 455 into 1966 Tempest

I have a 1966 Tempest that I am putting a 455 Pontiac engine into. The block may be marginally larger than the 326 but with exhaust manifolds and oil pan it's a really tight fit. I ended up putting spacers under the motor mount frame mounts to get some clearance for center link and exhaust. I've installed a T56 six-speed behind it. It sits higher on the rear cross member which also had to be moved rearward to compensate for extra length. The result is that the drive line angle had to be adjusted. So, I finally got the engine/trans sitting at an idle 2.5 degree angle downward toward the rear by putting a .4 inch spacer under the frame mounts. Now the problem is trying to set the pinion angle.

With coil springs and trailing arms I can see no possible adjustment for rear end. It currently sits at 1/2 degree angle but that's pointing downward at the front. The drive shaft is at about 3 degrees downward toward the rear. I never paid much attention to any of this with previous 5 speed I installed because it was only slightly longer than the original automatic. I only drove the car about 25 miles prior to this but I noticed no vibration from the drive train. The measurements were made with car sitting level front to back and side to side. So I have a few questions I hope someone can help with.

1. Is the current pinion angle of 1/2 degree downward toward front of car correct? It's the original rear end with no signs of alteration. The only thing I've done was remove it to change gears and replace all the bushings in suspension. The springs are good so ride height is normal. If the angle is not correct how do I adjust it?

2. If the pinion angle is raised then the driveshaft angle will lessen. In fact it looks as if it would be nearly straight. Perhaps that's why the pinion is nose down??

3. What is minimum clearance around engine to prevent it hitting something when it starts torquing up? I drive hard so that will happen often. Right now with new motor mounts there is about 1/4 inch clearance between oil pan and center link and one bolt in the frame mount is actually touching the oil pan on passenger side. I can fix that by using a bolt with a flat head but there will still be less than 1/4 inch clearance there too.

4. The engine does not want to naturally sit level (side to side). As you raise the engine the frame mounts move closer to each other. After slotting the bolt holes so they adjust for this the engine sits better but at the bottom of oil pan and at transmission mount it's still 1/4 inch higher on left than on passenger side. Interestingly, the frame mounts are different heights with the driver side about 1/2 inch higher than right. I was thinking of installing a taller, driver side mount on the passenger side to compensate. Pontiac made different height mounts for some reason (Anybody know why) so I hesitate to do that if there's another way. Am I worrying about something here that's not necessary?

5. Has anyone made this engine swap in an A-Body and did you have any issues or modifications.

The car is intended for daily use and lots of traveling so this set up is very important for comfort and reliability. Any comments or suggestions are certainly welcome.
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post #2 of 7 (permalink) Old 09-14-2019, 10:58 AM
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I've always read that all the Pontiac V8's, 326 & larger, are the same size on the outside, therefore able to use the same mounts, if there are motor mount holes are in the right place.

But, I've never swapped a 455 in where a 326 came out. So, maybe what I've read is not so. I assumed a '67 Bird 326 came with a Q-jet carb. Wrong ! So, there may be other stuff I don't know about the 326.

I have swapped 455's for 400's in '67 & '69 GTO's. Also swapped 455's for 350's & 400's, in 1st gen Birds. Same mounts worked for all. So, if the 326 requires different mounts than 350's 400's, & 455's, I'd like to know.

Most guys recommend some sort of hold-downs for the drivers side of the engine, in order to prevent that mount from coming apart & allowing the engine to come up on that side. I've used chains, turnbuckles, steel cable, & steel straps as hold-down materials, on my 455 bracket cars.

Some have used a solid mount on that side. But, some say that produces too much vibration, and/or puts too much strain on the side of the block.

Last edited by bigD; 09-14-2019 at 11:27 AM.
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post #3 of 7 (permalink) Old 09-14-2019, 12:56 PM
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In the upper right hand corner of the forum page is a box "Google Custom Search." Type in a specific word or phrase to pull up many of the past topics which you may find covers your questions. Here is a post on the 455 engine mount problem:

As you raise the engine higher, make sure you are not putting the fan blades into the fan shroud or binding your exhaust pipes up against the floor. It may also affect clutch linkages unless you have swapped for hydraulic.

I can't help on the pinion angle other than printed materials. But, if the trans angle is -3 (downward) degrees, the pinion angle should be in the range of +2.5 (upward) or so to match, but not be enough to create a "0" driveline angle. Here is a good explanation and simple diagram added:

"What is important are the front and rear operating angles. The operating angles are defined as:

Front operating angle: the angle between the output shaft of the transmission and the driveshaft.
Rear operating angle: the angle between the pinion gear and the driveshaft.
The front and rear operating angles must be equal and as small as possible without being zero. A little more angle in the rear may also be needed to compensate for axle wrap under acceleration. The amount will vary based on suspension components and the type of bushings. So some experimentation may be needed."

And from the internet is another explanation and How-To: Pinion Angle - Wolfe Race Craft

To adjust the pinion angle, you would need the adjustable upper control arms. However, you might just try the car as is and see if you get any vibrations out of the driveline and then go from there.

I suggest you invest in the upper/lower control arm braces. This will help stiffen the mounting points. If you still have the 10-bolt, it may not hold up if you drive the car hard as you say. But then again, beat on it until it pops, then worry about it.

Keep us posted.
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post #4 of 7 (permalink) Old 09-15-2019, 07:41 AM Thread Starter
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Thanks for the quick replies. bigD, the Pontiac blocks are the same size but I quickly found that exhaust manifolds, intake manifolds, and oil pans are not and that's where the problem comes in. The 455 in its native environment used different mounts than the 1966s, but it will accept the earlier mounts to allow it to bolt into the 1966 and I am using the 1966 mounts.

PontiacJim, thanks for the search link. I tried searching before posting this but came up with nothing. The link is really great but didn't provide anything I didn't already know. The 1966 Frame is slotted for the top two bolts of the mount stand on passenger side only. This will allow installation of the shorter, taller left frame stand to bolt onto right side without modification. I have an electric fan and hydraulic release bearing so those issues don't happen here.

I presented problem of driveline angles to American Power Train. Of course they state that angles must be equal and opposite but also said that their experience is that sometimes things that should work don't and things that should not work at all work perfectly in some situations. Since I experienced no vibrations before they suggested I simply leave it alone and test drive it to see what happens. If there are no vibrations then I should leave it as is. Since I posted this, I cut my driveshaft and shortened it by sliding one side into the other and stuck it in to measure angles again. The drive shaft is 3 1/2 downward. The resultant angles are within tolerable limits for general use, but the pinion-driveshaft angle could be better (i.e, reduced). Thanks too for suggesting the adjustable control arms. I searched for something like that but found nothing because I wasn't calling it the right thing. A repeat search on Summit Racing brought up many choices so I'll consider this. Readjusting the pinion angle causes the driveshaft angle to reduce at the transmission also and that angle now is just about 1. It may be that if pinion is brought up to 2.5 that the drive shaft will lift enough to bring the trans angle less than -1.

This driveline set up is a very important issue. It's also a simple concept too but the information given on the net is confusing and conflicting. Measuring from the passenger side is opposite to measuring on driver side and some examples (even those by well-respected vendors) tell you to subtract angles in one case, then to add them in another.

Once again I appreciate your input as it has helped me learn more and find some alternatives. Hopefully somebody else has made this swap and can tell me how they have their driveline set up.
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post #5 of 7 (permalink) Old 09-15-2019, 11:13 AM
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The 455 intake and exhaust and oil pans are all the same size as the 326 pieces, stock for stock. Ram air exhaust manifolds are bulkier. '66 A bodies don't have a lot of tunnel and floor room for the trans and driveshaft. Have installed a 455 into a '66 GTO and it fit just like the 389 that came out....same exact size. Agree with Jim that you may need adjustable upper control arms for the rear end to dial in your pinion angle. No, they don't point least not on my '65 and '67 GTO's.....
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post #6 of 7 (permalink) Old 09-26-2019, 08:24 AM Thread Starter
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It irks me when someone posts wrong information when the correct information is so easy to find. I always think they're too lazy to figure something out themselves or just stupid. So, here I go and do it myself! I checked the oil pan from my 326 and it is indeed exactly the same size. Thanks geeteeohguy for pointing that out. I just assumed it was bigger because there was an interference problem with 455 but not with 326. I have new motor mounts so why does the 455 touch the centerlink when the 326 did not? Is it because it's so much heavier it compresses the mounts more or perhaps I have cheap motor mounts?

Anyway, I purchased adjustable upper arms. Real easy to install. Now the transmission and rear end are real close to parallel at about 2.3 to 2.4 degree angles. I am using an app from Tremec that lets you use your cell phone to measure angles. The problem now is that the drive shaft is at within 0.1 degrees of the pinion and transmission giving a nearly 0 degree drive angle over all. I just did some calculations and it looks as if I drop the tail of the transmission about 1/2 to 3/4 inch it would bring the engine angle closer to 3 degrees (estimated 2.7 degrees). Then if I rotate pinion to be parallel the drive shaft will then have slightly more than a 1 degree angle at each u-joint which should be within desired specs.

There are other advantages too. It will increase the clearance between oil pan and center link and the clearance between the universal joint and floor pan. So, this is good news to me because it's an easy fix. I might just buy a new cross member rather than mess with cutting mine up and rewelding.

So the new question is: How much clearance should I allow between floor and drive shaft at the front u-joint? I would think 1/2 inch would be okay.
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post #7 of 7 (permalink) Old 09-26-2019, 07:39 PM
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I would install the yoke/driveshaft into the back of the tailshaft and put one of the ears (driveshaft or yoke) that holds the u-joint end caps facing up at the floor board. Then, with the back of the driveshaft hanging loose, work the driveshaft up and down at a few extreme angles just as the rear axle would move up and down. I am thinking this should give you a good idea if the 1/2" clearance between driveshaft/floor is enough.
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