Friday, April 14, 2017

The Story of an Old Firebird, Part 4.....


This section contains information about the cylinder heads, valvetrain, and intake/exhaust systems.


Heads and Valvetrain -

For the cylinder heads and camshaft, I planned on using the tried-and-true Ram Air IV combination. The parts were readily available, reasonably priced, and well understood by people I trusted.

I started with two brand-new 1970 Ram Air IV castings, casting number 614. I remember starting at the cast-in numbers “614” for HOURS as I ported the heads. I don’t think I’ll ever forget them. The valves, springs, retainers, locks, rocker arm studs, rocker arms, balls and nuts, push rod guide plates, push rods, lifters, and cam were all 100% stock Pontiac, purchased over the counter at Bert Adams Pontiac in Joliet, Illinois. The timing chain and gears were a Cloyes “True Roller”, and the cam was installed 4* advanced. When Jack installed the cam he also checked the cam timing from the published specs, and found out the cam was actually a few degrees retarded, as ground. Installing it 4* advanced made it basically “straight up” cam timing.

The first thing I did with the heads was to clean up any casting flash and “dingleberries” in the under-the-valve-cover and oil drainback areas. There was a TON on casting flash on the sides of the intake port runners, and some of it came off pretty easily. The rest took some grinding, and made me glad I’d purchased carbide cutters. High Speed Steel (“HSS”) cutters will remove cast iron easily, but they go dull quickly, after only a few hours use. Carbide cutters stay sharp, but they’re brittle compared to HSS, so be a bit careful using them. I didn’t polish any of the areas with sandpaper rolls as I couldn’t see the benefit vs the amount of time it would take. The nice, sharp carbide cutters did a “good enough” job, and after 10~12 hours, that part of both heads was cleaned up, and I started to work on the ports. I also opened up the machined passages in the heads for the pushrods. I’d read somewhere that it was pretty close with the larger diameter pushrods the Ram Air IV used, so I just “laid over” the upper end of the passage for a little more clearance.

The book I used to guide me in this engine rebuild was published by H-O Racing Specialties, and was called “Pontiac Heavy Duty Parts and Specs”, and had a wealth of information in it. I carefully studied the cross-sectional drawings of the ports in the Ram Air IV heads to see where material had to be removed, and just as importantly, where to leave material. You don’t just go wild and “Hog It All Out”, as the size and shape of the ports, particularly the intake ports, is critical to how well they function. There were a couple of places that needed careful work, like the port wall next to the passage the pushrod went through, and the area under the valve seats. You had to widen the intake port as much as possible in the pushrod area, but you had to be very careful not to break through the casting. The thickness of the casting in this area was about .125” thick (one-eight of an inch), and while H-O said you could thin it down to about .070”, I wasn’t comfortable enough with my head porting skills to go that far, so I opened it up to where the wall was about .080” thick. The book also pointed out areas that definitely needed rework, like the valve guide are of the intake ports, the “bump” in the exhaust port that was extra material for the air injection (“Thermactor”) system, and a few other spots.

The basic philosophy was again to “grind it out if it doesn’t look like it belongs there”, and to keep as close as possible to the OEM contours, opening them up where it would benefit airflow, and leaving material in other places. The valve bowls needed a LOT of work. There were huge “globs” of cast iron sticking out below where the cutters that made the valve seat and bowl bottomed out, and this area needed to be ground out to follow the “natural” contours in that area, and blend it into the rest of the port. The head/intake manifold and head/exhaust manifold flanges were matched to the gaskets I was going to be using, and then blended back into the ports as smoothly as possible, and as far as possible. Based on the 4 to 5 hours “per session” that I spent, times 16 ports, plus the ~10 hours doing the other parts of the head, I know that I had over 100 hours in the heads by the time I finished them, and Jack complimented me on the quality of the work I’d done. The final step was getting a proper “Three Angle” valve grind done, and Jack did that for me. It took some convincing to get him to grind the intake valve seats at the H-O Racing recommended 30* instead of the “standard” 45*, but when I showed him the published data in the H-O Racing book, he agreed, and ground the intake seats to 30*. It cost a bit extra because he had to buy a special cutter, but it paved the way for other Pontiac engines he built for other people.

The combustion chambers were almost “Good To Go” right out of the box, and all I did was break any sharp edges that could lead to hot spots, preignition, and detonation.

I didn’t weigh the heads before and after, but from the pile of cast iron I ground out of each port, I wouldn’t be surprised if I took almost a pound of cast iron out of each head.


Camshaft, lifters, and valve gear -

The rest of the valve train was 100% 1970 Ram Air IV. The camshaft (P/N 9794041) specs were: Advertised Duration 308* Intake / 320* Exhaust, Duration @.050 232/242, lift at valve using 1.65 rocker arms -.520”. Pontiac was at the forefront of “Computer Designed” cams way back then, and the 041 cam, along with the 9785744 (Ram Air III cam) were among the first computer designed cams released by GM. Prior to this, many cams just added duration using the “constant dwell” method, which resulted in what would be called “lazy ramps” today. I’m not a camshaft designer, and I don’t play one on TV, but from all I’ve read, you want the ramps to smoothly accelerate the valve open, and do the same as it comes down the ramp. One of the reasons racers went to roller cams was that the roller lifters allow much more aggressive ramps, to get the valves open, and then closed, right now. Roller cams and lifters were a little too exotic (read: Pricey) for me back then, so I stayed with a flat tappet cam, and what better cam to use than the one designed by the guys that knew the cylinder head flow characteristics? The Ram Air IV lifters were of a special reduced travel design, and after the engine was put together, I adjusted them ¼ turn of the rocker arm nut past zero lash. I had considered using a rocker arm nut with a separate locking screw, like a “Poly Lock”, but that would have required having the ends of the rocker arm studs ground flat to provide a proper place for the setscrew to tighten against, and I just never got one of those “round tuits”. I readjusted the rocker nuts one time after the engine had a few hundred miles on it, and they hadn’t really changed any from the initial setting, so I let it go at that.

It had a strong “rumpity-rump” idle at about 1100RPM, but I most likely had to run that idle speed due to the very light (12lb) aluminum flywheel.


Intake and Exhaust -

The induction system would be a QudraJet, something I understood very well, with a 1971/72 455 H.O. intake manifold. This manifold had “as cast” ports large enough to mate with the Ram Air IV heads, enough metal to safely allow port-matching, was a modern dual-plane high-rise design, and had a separate exhaust crossover which could be left off during warm weather, resulting in a cooler intake charge going into the engine. All I did to the intake manifold was to glue on a set of the intake gaskets I’d be using, and open the ports up to match the gasket. Then I blended that area back as far as I could reach with my die grinder. The only other thing I did was to use an aluminum “heat blocking” plate that had a fiber spacer about 1/4” thick on one side, and a gasket on the other, that went between the carb and manifold flange. I don’t know for sure if it helped any, but it looked pretty neat! This was recommended by the “Rochester Carburetors” book that I had. That book taught me more about carburation than any other book I read, including the “Holley Carburetors” book that I had by the same publisher.

The QuadraJet I used was purchased new-in-the-box through Bert Adams Pontiac, and was for a 1969/70 Ram Air IV with a manual transmission. It required one of the spring type choke coils and pull rod, which I also ordered new. Being a 1970 carb, it was calibrated a bit on the lean side for emissions reasons, and I wound up going 2 or 3 sizes larger on the main jest, along with a corresponding change in the primary and secondary metering rods. I wish I still had my notebooks, as I had extensive notes on how I figured out what a good jet and rod combination would be based on what was in a given car from GM, vs what it needed to be for better performance in various stages of tune. I re-jetted dozens of QuadraJets based on these calculations, and it was unusual that I didn’t get it “right” the first time.

Exhaust duties would be handled by a set of Hooker Headers, part number 4202, the only header available for the round port heads in a second generation Firebird. JR Headers also made a set that fit, and one of my friends had a pair on his 1973 Super Duty 455 Trans Am, but I thought the Hookers were made better, so I went with them. Mufflers were kind of an afterthought, and for years I was running Thrush “header mufflers”. They were cheap, lightweight, and worked “good enough”. Cheap was important, because the Hookers hung down fairly low, and with the lowered suspension I was always grounding them out, resulting in the muffler getting damaged enough to need replacement. I used to buy them two at a time at Sontag Speed Supplies. That way I always had one “in stock” for rapid replacement. I ran the exhaust in that configuration until I drove the car out to California, and which time I had a local muffler shop weld up some 2.5” pipes to the “Hemi” mufflers I’d bought years earlier. It made the car much quieter on the highway, an important consideration since it would be a 2,400 mile trip.


Fuel System -

The fuel system starts at the tank, and in order to provide an “unlimited” supply of fuel, I added a second 5/16” pick up and nylon “sock” filter to the existing stock pick up/sending unit. I just used a piece of 5/16” steel fuel line, bent to match how the stock pick up was made, drilled another hole into the top of the plate that mounted into the tank, and silver soldered the new line to the top plate. These two lines fed a pair of AC Delco electric pumps which were originally used on heavy-duty trucks that I bought from North Side Auto Parts on Ruby Street. If I had a part number, they could usually get what I wanted! The pumps had individual fuses, and were fed by a relay activated whenever the ignition was in the “Start” or “Run” position. The output of each pump went through an AC Delco filter, and then into a Moroso “Y Block” which was normally used to split a single fuel line to be used with a dual-inlet Holley carb. From there, a 1/2” diameter line was run to the engine compartment and connected to one of the blue Holley pressure regulators set at 6.5 PSI. One outlet from the regulator fed the QuadraJet, and the other was adapted down to 1/8” steel line which I ran to a fuel pressure gauge in the console. I know, having pressurized gasoline fed to the interior of a car is not a Real Good Idea, but I used steel line with compression fittings and checked it religiously for any signs of leakage. The fuel pressure NEVER budged from the 6.5 PSI I had it set to, indicating that the carb had an adequate supply.

5 comments:

  1. Enjoying the series even though most is over my head.

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  2. I kind of remember a discussion way back when about not making the intake ports too smooth because the argument was that some slight imperfections would cause the fuel and air to mix better. I wonder if there are dyno test results to prove who was right.

    Exhaust. I remember a GTO commercial from way back when that showed the driver switching between loud and normal exhaust.

    And you did all this with non electronic tools.

    Another very interesting post. Thank you.

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    Replies
    1. A little roughness on the intake tract is a good idea, especially with a carburated engine. It helps keep the fuel in suspension. The exhaust ports were usually polished, but my machinist said the flow improvement was minimal, and the carbon build up in the exhaust ports negated any improvement after just a few hundred street miles.

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  3. You went a LOT more indepth than I did on my Goat! :-)

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  4. I wanted to maximize the performance of what I had. The only parts I kept from the engine that came with the car were the block, valve covers, valley cover, oil pan, front cover and distributor. I replaced the cast aluminum bell housing (flywheel/clutch cover) with a hydro-formed steel Lakewood "scatter shield" and steel plate on the back of the block in case the clutch ever decided to come apart. I'd seen cars where the clutch blew, and it's NOT pretty! Don Garlits lost half of his left foot when his blew and cut the car in half.

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Keep it civil, please....