by IronDukeVega » Fri Dec 29, 2006 4:33 pm
Folks,
I was searching the web for info on the Edelbrock Pontiac HD 151 valvecover and found this thread - interesting. The valvecover, by the way, is no longer available.
I have a 1971 Vega with a 1978 Pontiac 151 non-crossflow that came out of a '78 Monza. I took the engine, Saginaw 4 sp (better ratios than the Vega version) and the front brake system (vented rotors, much bigger calipers and pads - and far better braking). This engine is probably the easiest engine sawp for the Vega (and the engine they should have used in the first place ...Chevy 153 derivitive). I thought I had the better engine than the stock Vega motor for modification but was wrong - there were far more aftermarker parts for the 2.3 Vega than the non-crossflow Pontiac. The pictures above brought back memories. I had the Offy dual port 4 bbl manifold with Holley 390 and later the dual Weber 45 DCOE9 side draft carbs at different times (this was back in the late 70s).
For the Vega motor, the 4 bbl dual port manifold was an interesting idea, but it did not work well. The primary side of the manifold was at the bottom which forced the majority of intake flow to move along the floor of the intake port - the worst part of the Vega intake port design (a sharp radius that angled back on itself. Later Vegas had a raised floor with longer radius). The manifold would probably have worked much better if the carb was rotated so that the primaries were on the secondary side of the manifold and the flow was on the top deck. This would in effect lead to a long, easy flow curve into the valve area. Never tried it though. The Webers looked awesome, but they never tuned right. Throttle response was unbelievable, but the intake suffered from low intake flow inertia at normal rpms and an inibility to sync the carbs effectively given the piss-poor IECO supplied linkage - turn your headlights on at idle and the rpms would drop from 1000 to 500. I still have the manifold but sold the carbs. This engine had a perf. cam and Hedman headers (great collector design). In the end, the stock Vega manifold with a Holley 350 cfm 2bbl worked the best. With impossibly odd engine problems (loooong story), I went with the 151 in 1984 when my wife's 1978 Monza got wrecked.
For the 151, I made the following modifications on a rebuilt motor (.030 over): decked head a total of .070 and the block .005 for a likely 9.75+:1 compression, perf. cam with .493 lift and 210 degrees at .050, HiPo valve springs, bronze valve guides, bigger intake valves (1.84 v. 1.74), ported head, Crane roller rockers, high volume oil pump, modified stock intake manifold with Holley 350 cfm 2bbl, custom 2.25 headpipe and 2.25 exhaust, HiPo cat, 2.5" Dynomax muffler and tailpipe in the stock path. I'm figuring close to 140+ hp at 5,200 rpm. My only issue with these modifications is that the engine has been very sensitive to lifter loads from increased lift and higher tension valve springs. My first cam was .554 lift and with valve geometry problems the lifters would suddenly bleed down at 4,000 rpm, making a sound like the engine was beeing hammered to death. Ultimately, I solved the problem by going to a different cam with less lift, using Wolverene lifters with a bigger oil feed hole, installing a high volume oil pump, and getting the valve train geometry set correctly. The geometry could only be checked once I installed the roller rockers since I now had an exact pivit point to check the rocker radius movement against. Still, the valve guides suffer from accelerated wear. The greater the valve-to-guide clearance the greater the engine vibration. Believe it or not, I now know that this type of vibration causes the Holley accelerator pump to pump fuel on its own starting at around 3,000 rpm.
What does it all mean in a 2,400 pound car with 3.36 gears? I'm guessing 0-60 in 8 and the 1/4 mile in 16. Problem is I need an overdrive trans since 3,500 rpm at 65 mph means only 20 mpg (my '06 V8 Tundra does better). The Tremec TKO 500 is my goal, but at $2,000 it's likely a ways off. The engine sounds great but is rough, causing the Hurst linkage to buzz badly at high rpm.
Back to the start of this all - the valve cover. In order to accomodate the roller rockers, I had to push out the front and back ends of the stock valve cover and weld in new metal - ugly!. The valve cover pictured above looks like it would actually fit on the non-crossflow but now looks to be an ebay item at best. One word of advice. If you modify your valve cover or have one that lets oil directly reach the PCV valve, when the car sits for about a day, an oil drop will form at the inlet of the PCV valve and hang there. When you start the car, that oil will be sucked into the manifold and cause a nice puff of blue smoke out the tailpipe. Drove me nuts thinking I had valve seal problems. Once I eliminated the space in the modified PCV baffle under the valve cover necessary to clear the rockers, oil no longer was slung against the PCV valve - and no more puff of blue smoke at start-up!
I'd like to post some pics of my car. Just about finished a restoration. It's now Cranberry red with silver fender stripes, 13" Cragar rims, fiberglass lift-off hood, custom rear spoiler, lowered suspension, 1975 Vega and Monza interior. Almost no other Vegas here on the roads around San Francisco.