Terry Hagen; Cornelius, OR: Longtime reader (as in “Honk” if you remember), first time writing in. First, I’d like to say project Sten is about as perfect and spot-on a project as you could have come up with. It really brings up memories of what the essence of what hot rodding really is. Stuff a V8 into something small, fun, and that we can get parts for. Make it street legal so we can actually drive it. Keep Sten rolling—I love it!
Here’s my question. I have a ’69 GMC pickup that is need of a new motor. It currently has a 0.040-over 350 that is equipped with cam, lifters, heads, intake, carb, headers, and exhaust. I liked the article you wrote up on the basic 290hp GM replacement long-block and its potential, while remaining very affordable. I’m wondering if the Vortec small-block would be a better choice at only $300 or $400 more? What problems would I encounter swapping in this motor, other than the intake manifold and fuel pump? What electric fuel pump would be a good choice?
Jeff Smith: Thanks for the comments on the Sten. It has been on the back burner longer than planned while we worked through a bunch of engine testing and Chevelle flogging, but now that I have some time, we can get back on the beast. Look for details soon.
To address your question, the engine we used was the GM Goodwrench replacement 350 from Scoggin-Dickey in Lubbock, Texas—not the 350 HO engine. The Goodwrench 350 (PN 10067353; $1,499.95, Scoggin Dickey) is a brand-new engine using the older, two-piece rear main seal block and crank along with a flat-tappet camshaft. The engine is rated at 245 hp and has a very mild hydraulic flat-tappet camshaft. It has generic 1.94/1.50-inch-valve small-block heads with 76cc chambers. The engine you referenced (PN 12499529) is a 290hp 350 engine long-block. It also uses the older-style, two-piece rear main seal, flat-tappet hydraulic camshaft, and 76cc combustion chamber heads. The increased horsepower is mainly due to the longer 222/222 degrees of duration camshaft that sports 0.450/0.460-inch lift, which is much more lift and duration than the Goodwrench engine. Scoggin-Dickey sells the 12499529 long-block for $1,999.95, which is $500 more for the addition of a longer-duration camshaft that you could do yourself (though that would affect the warranty). The long-block that has the best potential is the 290hp 350ci with the iron Vortec heads (PN 19210007, $2,899.95). But as you can see, this involves a significant price jump of roughly $900. If you’re willing to do a little parts-swapping, there is an alternative that involves using the best parts of these engines. First, we’d start with the basic Goodwrench engine and then add a pair of iron Vortec heads. The least expensive version is the stock Vortec heads (PN 12558060; $619.90, Scoggin-Dickey), but you do have to modify them to accept more than 0.450-inch valve lift—more on that in a minute.
As you know, these heads will require a specific Vortec intake manifold. We usually choose the Edelbrock Performer RPM Vortec (PN 7116; $189.95; Summit Racing). You could go with the stock 222/222-degree camshaft, but this is a single-pattern cam, and the Vortec exhaust ports are not quite as good as the intakes are, so a dual-pattern cam with more lift and duration on the exhaust lobe is a better choice to help make a little more power.
We used a very inexpensive cam from Summit Racing on our Goodwrench test, which worked very well. The cam is PN SUM-1105, and the specs are 224/234 degrees at 0.050 with 0.465/0.485 lift and a 114-degree lobe-separation angle. When we did our Slayer story in the May ’12 issue, the cam was $54.95, but when we re-checked the price, Summit has reduced it to $49.95. In addition, if you replace the cam before starting the engine, you can use the brand-new GM lifters and save even more money. This will require modifications to the Vortec heads, because the stock valvesprings cannot handle this additional lift, especially on the exhaust side. So if you decide to go with this bigger cam, we’d suggest ordering Scoggin-Dickey’s modified version of the Vortec heads. Scoggin-Dickey machines the valveguides to improve the retainer-to-seal clearance and adds a set of Z28 springs that allow the heads to accept valve lift up to 0.525 inch, which is more than enough for that Summit camshaft. These modified heads (PN SD8060A2; $779.90, Scoggin-Dickey) are a simple bolt-on and are certainly worth the $180 additional price over the stock Vortecs. Adding the bigger cam should put this package at roughly 350 to 360 hp, which is really good power considering the inexpensive components. The Vortec heads automatically improve the compression with their 64cc chambers instead of the 76cc heads that come stock with the Goodwrench engine. Another step you could take—as we did on our Slayer engine—is to switch to Fel-Pro 1094 head gaskets, which are thinner at 0.015 inch and will help pump the compression up to around 9.4:1. This would make a great package with excellent street manners and great torque, and it would deliver consistently good power for as long as you wanted to drive it. These changes to the basic Goodwrench engine will cost about $2,600, but they will help to make more power than the 290hp Vortec GM package and will save you about $300! Of course, you’ve also lost some of the warranty, and to some that might be worth $300. At least you have plenty of choices.
As for a fuel pump, there are probably dozens to choose from since 350 to 375 hp doesn’t require a tremendous amount of fuel volume. The classic Carter rotary vane (PN GP4070; $81.95, Summit Racing) or the Holley red pump (PN 12-801-1; $108.95; Summit Racing) are both capable of delivering sufficient fuel volume and neither requires a fuel-pressure regulator, keeping the price down.
Federal-Mogul (Carter); 810/354-7700; Federal-Mogul.com
Holley Performance Products; 270/781-9741; Holley.com
Scoggin-Dickey Parts Center; 800/456-0211; SDParts.com
Summit Racing; 800/230-3030; SummitRacing.com
Roger Miller; Farmingdale, NY: First of all, I have been a loyal subscriber for more than 20 years. I have cancelled other subscriptions but have always kept Car Craft.
I have a ’76 Trans Am with a Pontiac 400 motor. The motor is not original but is stock (year unknown), with stock intake and exhaust manifolds, Rochester Q-jet carb, and so on. It has 6H heads, which I believe came on 455s. It has a dual-exhaust setup without cats.
The problem is the engine will not rev past 3,200 rpm, even in Park, so it’s not related to the trans or rear end. When I floor the gas pedal, the motor revs to about 3,200 and then levels out. The motor seems to have decent power, and there are no other problems. I have checked the carb, and the throttle is opening all the way. I have been advised of a few possible causes: weak valvesprings, too low a compression ratio (400 motor with 455 heads = under 8.0:1), distributor timing/advance needs to be changed, carb secondaries not opening. What should I check first?
Jeff Smith: Over the years, Roger, I’ve found that it’s best to eliminate the easily fixable problems first when performing a diagnosis. There’s nothing more humbling than doing a major repair only to discover that the real reason was the throttle wasn’t opening all the way. Be sure that the choke lock on the passenger side of the carb has released the secondary linkage. The Q-jet uses a small lever on the secondary side that can be locked by the choke linkage to prevent the secondaries from opening when the choke is engaged. The linkage will make it feel as though the secondaries are opening, but you have to look inside the carburetor to make sure.
This would also be a great time to check initial and total mechanical advance. You can do this even if you don’t have a dial-back timing light. The easiest way is to buy an MSD timing tape (PN 8985; $4.95, Summit Racing) intended for the diameter of your balancer. If you don’t want to wait, you can make your own with a length of masking tape and a one-sixty-fourth graduated ruler. If your balancer is 8 inches in diameter, that makes the circumference 25.13 inches. Divide that by 90, and every 4 degrees will be 0.279 or nineteen-sixty-fourth of an inch. Mark off these graduations from zero to 40 degrees and lay the tape on the balancer with the zero mark in line with the zero mark on the balancer. Be sure to disconnect the vacuum-advance line from the carburetor, and with the transmission in Neutral or Park, rev the engine to 2,800 to 3,000 rpm. You should read around 36 degrees. If the number is much higher or lower, try adjusting the initial timing to compensate. If the engine runs worse after adjusting, then you need to check for the proper position of top-dead center (TDC).
The best way to check for TDC is to remove all the spark plugs and use a spark plug–style piston stop. Put the stop in the No. 1 cylinder, and then, by hand, very carefully rotate the engine clockwise until the piston hits the stop. Do not bump the engine with the starter, as that’s a good way to break a piston! Mark the balancer where the piston stopped, and then rotate the engine in the counterclockwise direction until you hit the stop. Mark that position and then measure to see if TDC on the balancer is exactly halfway between the marks. If not, the TDC mark on the balancer is incorrect. Often what happens is that the ring on the balancer has rotated on the hub, thereby creating the discrepancy. I suspect you’ll find the ignition timing is correct, or within range. This will likely lead us to what I think is the real cause of your problem: the valvesprings. But let’s try one more thing. With all the spark plugs removed, check the cranking compression. It should be between 160 and 180 psi. If the pressure is way down but consistent throughout all eight cylinders, it’s possible that the timing chain is very loose and has skipped a tooth. This would radically affect cam timing and perhaps cause your problem. Since you said the engine seems to run acceptably below 3,200, I think the valvesprings are the real culprit.
The best way to confirm this is the problem is to test one of the existing springs, before replacing all 16. You will need a source of compressed air, a spark-plug hose adapter to put the air in the cylinder (similar to what’s used on a compression tester), a valvespring compressor, and a checking spring. Once you have air in the cylinder, tap the valvespring retainer with a rubber hammer to help loosen the retainer locks. For your engine, a lever-type valvespring compressor tool will work, but we’ve also had good luck with the type that clamps on the outside of the spring and uses a knob that, when tightened, compresses the spring. Once you’ve removed the locks, retainer, and spring, place a lightweight checking spring in the spring pocket and reuse the locks and retainer. This way, you don’t have to rely on air to keep the valve in place. Next, take the old valvespring to your local machine shop and have them measure the spring pressure. Stock specs are generally around 100 pounds on the seat at the normal installed height of 1.60 inches. The installed height is the distance from the spring seat on the head to the underside of the retainer with the valve fully closed. A machinist’s rule will get you close enough on this measurement. Give that installed height to the machine shop, and they can measure the closed spring pressure. Valve-open pressure should be around 220 to 230 pounds at 0.500-inch valve lift. I think you will find the old spring pressure is down to maybe 60 or 70 pounds on the seat (and perhaps less) with roughly 140 pounds open. This poor spring pressure allows the valves to bounce off the seat when closing and won’t allow the engine to rev past 3,200. If you find the spring pressure is low, I’d suggest replacing all the springs. This will require measuring the installed height and possibly adding shims to ensure the height is the same for all 16 springs. This will certainly help engine performance. Stock replacement springs will suffice, as there’s no reason to install heavier springs since the cam is stock.
If the spring pressure is within acceptable range of at least 90 to 100 pounds on the seat, then I would check a second spring elsewhere in the engine. If that spring also checks good, then it’s possible the cam has gone flat. The best way to check is with a dial indicator on the valvespring retainer to measure lift. Even a stock cam should be able to generate 0.380 inch of valve lift. If the lift numbers are way down, you’ve found your problem! But my money is on the valvesprings.
Manley Performance; 732/905-3366; ManleyPerformance.com
Summit Racing; 800/230-3030; SummitRacing.com