Fixing Up 1976 Buick Junkyard Engine

If you block one wheel and turn the the drive shaft yoke, if it turns freely, it definitely isn't a positrac. It definitely sounds like a single trac since the the one wheel turns and the other wheel goes the other direction. A clutch type posi won't do that. I have a TrueTrac and it will because it is a worm gear type, not a clutch. I doubt yours is a TrueTrac.

You can redrill the axles to accept 5x4.75 bolt pattern and also the drums.

 

Thank you for the clarification. I had been googling a while already trying to figure it out. What would confuse me, was that when I spun the drive shaft yoke both axles turned the same direction. But really I am a noob, as far as buicks and differentials go, so I was not sure what to make of that. Thanks

 

Hello everyone. I have another question. Yesterday, the driveshaft was removed from my car. When I checked to see if the transmission yoke would fit on the th400, my oem yoke was too small. How do I go about purchasing a new one? Will any TH400 yoke fit? Or is there anything else I need to check?

 

Maybe this is a really dumb question, but with a set of older buick heads, would I be able to run a slightly bigger cam? If so, any ideas on approximately how much of an HP difference I would see between 1976 heads, TA112 cam, and dual exhaust vs older heads, maybe slightly bigger cam, and dual exhaust?

My goal is 300 hp instead of the stock low 200. Also, I doubt this makes much difference, but I am planning on running an open air cleaner, 1 inch 4 hole spacer and plugging the exhaust crossover passage. Is my goal attainable from either of the above combinations?

 

Well technically, you are correct about the intake lobe of the stock camshaft (which isn't much larger than the Buick 350's), but the exhaust lobe is way larger than the intake to compensate for the exhaust manifolds and stock exhaust system restrictions.

Federal Mogul OEM camshaft for BBB exhaust lobe is 225* duration @.050 and 328* @.006 with a .442 lift @1.55 rocker ratio.

This adds to the powerband on those engines as well, particularly when you open the exhaust up beyond the restrictive stock design. My 1970 455 "10:1" engine would pull all the way up to where it floated the valves, at around 5600-5800 RPM with the stock cam and stock valvetrain. It began to plane off after around 4800-5000 or so, but didn't nose-dive.

Opening up the exhaust will help the overlap pull through on the intake side, even with a smaller lobe lift/duration, adding to the powerband. At lower RPM's, the cam will act smaller, but when RPMs rise to where the overlap can start pulling through, the cam acts larger. It's all about airflow dynamics @varying RPMs.

People knock those stock cams, but only because they do not understand the engineering behind them. They won't outperform larger performance cams, obviously, but will outlast them by many times over for those of you who are interested in your camshaft lasting longer than 2-3 oil changes. :grin:


Gary

 

Right!? Realistically, it's about traction with those axles. If they ever hook up, it's bound to break something unless you spent money upgrading it to 28 spline axles and a steel carrier with a 3.23 gear 3 series and girdle to keep it from twisting, making the pinion gear walk up the ring gear and fubar'ing it...


Gary

 

A point of interest I'd like to add about those '75-'76 heads, and that is they are the 'open chamber' design, kinda like how the Buick 350's are. Open chamber helped with emissions with exhaust evacuation over the closed chamber heads, but pretty much eliminates any attempts at getting quench from the combustion chamber, which is needed with larger bores like the BBB. Smaller bores work well with open chambers, which is why the Buick 350 does so well with them.

For the BBB, the open chamber isn't as efficient because you can't run as high of compression without the quench platform, but they're still fine for street machines where one isn't as concerned about milking max power out of one. Compression will have to be lowered a bit, maybe .25 or .5 a point below typical 'ideal' dynamic compression ratio for intake valve closing points regarding the grade of fuel to be used.


Gary

 

With the full circle design of the piston dish of the earlier and later BBB 455 engines from the factory there isn't a quench pad in any of the years anyway, just basically a quench ring beyond where the chambers are for all years.

What I have read here about the later heads is that they can be made to flow as well as the earlier heads can with a difference that I can't recall at this time but can be made to work well(I'll try to find that thread and give it a bump). If the OP intends on changing out the pistons to a taller compression distance even a flat top at .005 in the hole with a .040" head gasket the quench ring would be optimized and should be as good as and older engine with closed chamber heads with full circle dish pistons with a similar compression ratio!

Only by changing to a piston with a quench pad can the closed chamber head's quench pad make a difference in how "detonation resistant" the engine would be. With the factory style full circle dished pistons with the closed chamber heads or with the open chamber heads there is basically just the same quench ring because of the pistons so as long as a full circle dish is being used the only difference in chamber design would be is chamber cc volume.


I recently did a bit of contemplating about the 2 different chamber designs and came to the above conclusion that using a full circle dish piston with either style head that the quench ring stays basically the same just with more or less cc volume to raise or lower the compression ratio just like the sbb version does with just a quench ring.

If a piston with a quench pad is used then the 2 different heads chamber styles will make a difference.



Derek

 

I should have clarified that, thanks Derek.

Factory stuff there isn't much difference in terms of quench between the two designs. Only way to get quench is aftermarket. Go Derek go!


Gary

 

I found what someone posted the difference as;

"The earlier Buick heads with the wider ports will flow more air put the short side radius is not as effeceint as the later model heads, so it is really six of one half a dozen of the other. The short side radius on the earlier heads is flat and makes a 90 degree dump into the valve were in the late model head the floor gradually climbs upward and has a his radius into the valve. I can make as much power with a later model head as I can with an earlier style head. The reason the deck height is great in the 75/76 engines is because Buick reduced the pin height in the pistons for emissions. put a 70 piston in a later model block and you have the same deck height. "


Posted form buickrat1 in the thread I bumped. Here is the link to the other thread;


http://www.v8buick.com/showthread.php?299425-cylinder-head-intake-port-comparison



Derek

 

Thanks for this great info. I had never considered swapping pistons to increase my compression ratio. I will probably save money compared to buying and reconditioning older heads.

 

Hey no problem, if you have a standard bore maybe you can find a nice set of the earlier higher compression pistons you can swap in? If you're really lucky maybe you'll find a set that are still on the rods? GL



Derek

 

A quick update on my build. I was going to keep my 76 heads, but found a killer deal on a pair of 73 heads and bought them. I already had them rebuilt, plugged up the heat crossovers, and used screws to plug up the air holes which the Edelbrock B4B intake will not cover.
After removing the OEM heads, and looking at the block and pistons, everything seems to be in excellent shape. I am thinking at one point, the previous owner had rebuilt it.
This week, my plan is to remove the timing cover, and install the TA-112 cam, and timing set. After finishing with everything, I will go with dual exhaust, and open filter air cleaner.
The following week, I will finally finish the swap (I hope) and take it to the track :grin: My goal is to hit 300 hp to end up in 14s. Hopefully my setup can take me there. Otherwise, anything is better than what my 307 would have done :laugh:

 

Today, I finally removed the timing cover, timing set, lifters, and cam. I was about to install the new cam, when my mechanic told me my cam bearings are messed up. He recommended I buy new ones. I have seen people in this forum highly recommend the TA Dual Groove cam bearings. My question is, are they that much better than oem replacement bearings? What advantages would I have using the dual groove, rather than the oem replacement? The reason I ask, is my budget is getting kind of low, and I was wondering if they are really worth it. I apologize If my question is kind of ignorant ou:

 

For sure the TA "Dual Groove" are worth it:TU:
Reason: The stock Buick cam bearings introduce the oil to the cam journal at the 9 o'clock position, as the cam rotates clockwise, the oil "leaks out" at the 12 o'clock position, leaving very little oil for the high load 4 to 7 o'clock position.
The TA "Dual Groove" bearings introduce the oil at the 3 o'clock position, right before the high load position.
Make sure your machine shop follows the install directions, the bearings have to be installed properly to work properly:grin:

 

Just ordered them :TU: Thanks for explaining this to me. I had always heard them get recommended here, but never knew why.

 

Your welcome!
We all try to help as best we can:TU:

 

Another couple of questions

Since I have 73 heads on a 76 block, which spark plugs should I use 73 or 76? Also, which spark plug gap should I run? Would .055 be okay?

 

Use the plugs for the 73 heads.
With the HEI on the 76 engine, gap was .060 But that was with a crappy 7.6 to 1 comp ratio.
I'd gap 'em at .045

 

Thanks! I had actually already bought and gapped the 76 plugs at .060 prior to my project. I am glad you clarified this before my engine got a bad start. :laugh:

Also, here is a quick pic of my, almost complete, engine. On Monday, I will paint the block red, and rebuild the carb. I am hoping my swap will be complete by next week.