D1SC ProCharger - Blower Rat
Jim Homick, via CarCraft.com: I am building a 454 Chevy with a D1SC ProCharger. It will be used primarily for the street, but I will be bringing it to the strip. Which style of cylinder head should I be using? I already have a set of oval-port heads upgraded to bigger valves that are otherwise stock. I'm thinking I should use a rectangular-port head to really move some air. This will be a budget-oriented project.
Jeff Smith: Generally, the words budget, big-block, and supercharger are most often mutually exclusive, but we're intrigued with the idea. A set of rectangle-port heads will certainly present less flow restriction on the inlet side. This will result in better cylinder filling, which is the whole idea behind adding a D1SC ProCharger. But as usual, there's more to the story. If you were to run a dyno comparison of the supercharged, rectangle-port heads against a set of oval ports, the first thing you might notice would be a significant reduction in manifold pressure -or boost. This might lead one to think that the change to the larger ports is a mistake, but the opposite is actually closer to the truth. Boost as shown on a pressure gauge is the indication of manifold pressure. It could also be used as a measure of flow restriction. As an example, the D1SC ProCharger is capable of moving 1,400 cfm of air, but this is with no restrictions to flow. Since the intake ports represent a restriction, the blower is capable of producing more airflow at a given rpm than the inlet side of the engine is capable of accepting, so the air (mixed with fuel, of course) begins to stack up in the inlet tract, creating pressure. This is what is indicated on the boost gauge. Because most (but not all!) rectangle-port heads can flow more air than oval-port heads, the boost will read lower, and in theory at least, the engine should make more power.
So now that we have the theory out of the way, let's get into the details. We'll assume your oval-port iron heads are the more attractive 119cc, open-chamber, oval-port heads with casting numbers ending in 049, 781, 241, or 359. These heads have small 2.06/1.72-inch valves but offer excellent flow potential with just a little bit of help. It sounds like your heads are already fitted with larger valves, but we have some additional ideas here. The hot ticket is to have a quality machine shop open up the seats to the larger rectangle-port valve sizes of 2.19/1.88 inches. If you are bold, you can even step up to a 2.250-inch intake size. Once the valve seats have been enlarged, there will be a sharp edge directly below the new seat that must be carefully blended into the throat to take full advantage of those larger valve sizes. One of the problems with production big-block heads is a sharp angle of approach on the short side radius of the intake valve seat. With the larger valve diameter, this radius increases. With careful blending, this really improves the low-lift flow potential of the heads. While some may think this extra work isn't necessary when using a supercharger, the truth is that anything that improves airflow through the engine will enhance the power that much more when adding a blower. This is especially important for the exhaust side of the cylinder head. Consider adding a 30-degree back cut on the exhaust valve to improve low-lift flow and help scavenge the exhaust gas after the combustion is even. This increases the amount of fresh air that will enter the cylinder on the following intake stroke. This means adding a good size primary tube set of headers. For a 454, the minimum primary pipe diameter is 1 3/4 inches, but 1 7/8 inches would be even better. Also consider adding 3-inch exhaust pipes to the mufflers and including a cross- or H-pipe to the system. Exhaust noise can be near offensive with a full 3-inch system, so consider adding 2 1/2-inch tailpipes that will tend to dampen the noise a bit.
Since this is Car Craft and our emphasis is on budget building, a well-prepared set of oval-port heads can offer almost as much power as a big set of rectangle-port heads, as long as you're not shooting for some outrageous horsepower number. A typical pump gas 454/468ci engine should be capable of around 500 hp normally aspirated using a single-plane intake and a decent cam with even mildly reworked stock heads. We tested a set of those tiny peanut-port iron heads on our 496 back in the Mar. '08 issue ("Big-Block Cylinder Head Test") and made an awesome 595 lb-ft and a respectable 521 hp at 5,400 rpm with tiny 2.06/1.72-inch valves. By recalculating the power based on 454 ci, it looks like your engine should be capable of at least 540 lb-ft and around 475 hp. Keep in mind that this was with those peanut-port heads, so our initial estimate of 500 hp is probably conservative.
The D-1SC supercharger from ProCharger is capable of a maximum flow of 1,400 cfm and a peak boost of 32 psi, which is impressive. But in reality, for a typical street engine, boost will be limited to roughly 10 to 12 psi max. At this point we think a 45 percent power increase is likely, which takes that normally aspirated 500 hp and ramps it up to a solid 725 and bumps the torque to something ridiculous like 740-plus lb-ft. If this isn't enough, adding the rectangle-port heads will likely improve the torque more than the horsepower numbers because the larger intake ports will represent less of a flow restriction to the supercharger. The limitation will then become the exhaust side of the heads. This is why working on making the exhaust ports flow as much as possible will add power. Then all you have to do is figure out how you're going to hook all that power to the pavement. Overall, it should be a killer package that shouldn't be prohibitively expensive. I think a good business to be in for the next decade will be performance rubber because it sounds like lots of tires will be going up in smoke.
Accessible Technologies Inc. (ProCharger); Lenexa, KS; 913/338-2886; procharger.com
Just thought you might like to see a really cool '70 'Cuda.
High Compression Experiment
Gerry Hill, Eastham, MA: About 10 to 15 years ago, one of your staff members commented on building a small-block Chevy with 17:1 compression using a special cam with delayed intake closing. The fuel mileage claimed was very good. Any info on this would be appreciated.
Jeff Smith: Great question. Gerry. The man behind that idea is Bruce Crower of Crower Cams fame. Bruce is one of the performance industry's great innovators. Bruce's idea was as simple as it was brilliant. He focused on the fact that higher static compression ratios create more power from the same amount of fuel, which is why diesel engines are generally more fuel efficient than gasoline engines. The problem with high compression ratios is they require expensive, high-octane fuel to avoid detonation. Crower's idea was to modify the cam timing to take advantage of the high compression while still allowing the engine to run on lower 87- or 89-octane fuel. Crower accomplished this with a very late-closing intake valve position. Let's first look at a mild Comp Cams flat-tappet intake lobe with 239 degrees of advertised duration. This lobe opens 9 degrees before top dead center (BTDC) and closes 50 degrees after bottom dead center (ABDC). These figures are at 0.006 inch tappet lift, or what Comp defines as advertised duration. Adding the opening plus closing figures plus 180 degrees equals duration (9 + 50 + 180 = 239 degrees).
A long-duration performance cam opens the intake sooner and closes it later. As an example, it might open the intake at 40 BTDC and close at 85 degrees (40 + 84 + 180 = 305 degrees). Note that this longer-duration cam closes the intake valve a whopping 35 de-grees later than the mild cam. This later-closing intake effectively moves the peak torque to a higher engine speed to make more horsepower. This later-closing intake also demands a higher compression ratio to make acceptable power below the peak horsepower point because the later-closing intake will bleed off cylinder pressure. The reason for the longer-duration and later-closing intake is to give the engine more time at higher engine speeds to fill the cylinder.
Crower's plan involved radically increasing the compression while closing the intake valve much later. The later-closing intake valve point bleeds off cylinder pressure at lower engine speeds so the capture ratio of air and fuel in the cylinder is lower. But because we're squeezing what remains much harder (with the higher static compression ratio), Crower's idea was that the high compression would improve fuel mileage. Crower actually designed a kit for the small-block Chevy that utilized this technique. It did work to some extent but didn't really deliver on the improved fuel mileage idea as much as planned, and the concept never caught on.
Now let's jump ahead to today when the L99 engine used in the '10 Camaro uses variable valve timing (VVT) to either retard or advance the camshaft as much as 52 degrees to enhance performance and mileage. In an ideal world, you would want to separately control the intake lobes from the exhaust lobes, which is what the '08 to '09 Viper V-10 does with a cam-within-a-cam design that allows the engineers to change the lobe-separation angle. This allows the computer to then vary the amount of overlap. The advantage is that widening the lobe-separation angle at idle and low speeds will improve fuel mileage and then narrowing the angle at higher engine speeds will improve power.
The aftermarket has always been more concerned about performance, but it appears that tuning these engines beyond the stock settings might enhance power and fuel mileage by altering the conservative OE parameters. For example, you could increase an engine's static compression ratio and then tune with overlap and intake valve closing to see if there are advantages to fuel mileage. It appears that EFILive addresses the VVT engines, but the tuning is, as you might guess, complicated. But hey, if it were easy, everybody would be doing it, right?
HP Tuners; Buffalo Grove, IL; hptuners.com
Jorts are huge in the Midwest!
Car Craft Summer Nats!
Summer is almost here. Join us for the CCSN at the Minnesota State Fairgrounds July 16-18, 2010, and have the time of your life!
A Serpentine Answer
Mickey Cummins, via CarCraft.com: I've been reading Car Craft since the '70s and got really excited about the budget serpentine beltdrive article (Nov. '09), as I would like to do this to the 350 in my '86 Silverado. However, the story brought up a few questions. You stated the beltdrive system for this story was from the late '80s/early '90s engines. Will this bolt right up to the '70s block I am using? Will the brackets bolt up to my stock heads? What heads were on the 383 you used in the story? What year was the block? I haven't had a need to learn anything about late-model blocks until this time, and I am woefully ignorant about them. I am guessing the late '80s to early '90s engines share the same block as mine? I thought the tip about changing fittings on the PS pump was trick. Can or does something similar need to be done to use the late-model A/C compressor?
Jeff Smith: The short answer is the system will bolt right up to any '70s or even '60s block. You will need '70-or-later heads that incorporate accessory boltholes in the ends of the heads since the drive mounts require these boltholes. If you have an '86 Silverado, then your heads will have the accessory boltholes already in place. This is one of the tremendous advantages of the small-block Chevy in that it will accept older and newer engine components with no problem, so your block will work just fine for this conversion. The brackets will bolt up to your heads, and one additional advantage is you can change the water pump without having to remove any brackets. That's a nice feature. The block on the 383 was a later model ('88-or-later Gen I) that uses a one-piece rear main seal, but the front of the block is the same as even earlier blocks back to the early '60s, which means you could use later-model heads on an early 327 or even a 283 and still use this serpentine system. The heads on that particular 383 are a set of Canfields, but they employ the same accessory boltholes as any later-model small-block head. The power steering conversion was something we learned the hard way, purchasing an expensive fitting to convert our older power steering system on my El Camino to a late-model serpentine belt system only to discover that changing the fitting will work just as well. As for the A/C system, I've looked into that and it appears that most of the later-model compressors are similar, and often all that is different is the manifold that is bolted to the rear of the compressor. My guess (and that's all this is) is that you could find the proper manifold that would adapt one of these newer compressors over to your older system. If you purchase a compressor, keep in mind that around 1994, GM converted the trucks from the old refrigerant R-12 to the newer R-134A gas. The best thing to do would be to consult a local A/C shop to get an opinion on the swap.
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Michael "Skinny Kid" Heath, Yadkinville, NC; I have a question I'm sure a lot of people could benefit from besides myself. What do correction factors on dynos have to do with horsepower readings? I know when you move this number up or down, it will change the horsepower readings. Are engine builders adjusting this figure to sell engines?
Jeff Smith: This is a great question, Michael, because there's far more to this than just the ultimate horsepower readings. Let's start with the basics. You're probably aware that atmospheric conditions like temperature, barometric pressure, and humidity all play a role in affecting engine power. A combination of cool air (60 degrees F), high pressure (29.92 inches of mercury), and no humidity (zero water in the air) offers the best opportunity to make the most power because this situation will cram in the most free oxygen into the cylinders. The opposite situation of 100-degree-F air temperature with pressure down around 29.15 inches and 90 percent humidity (perhaps a typical day in North Carolina) is guaranteed to drop horsepower. Since engine dynos use ambient air conditions and those conditions are constantly changing, it becomes difficult to establish a true horsepower number for an engine. A long time ago, the Society of Automotive Engineers (SAE) created a standard (called J607) that the hot rod industry still uses: standard temperature and pressure (STP), and the numbers are the same as our good air-60 degrees F, 29.92 inches of mercury pressure (or 14.7 psi, the air pressure at sea level), and zero humidity.
Keep in mind that when you run your car at the dragstrip, the engine is breathing ambient
So let's say we are testing our engine on the dyno and the actual conditions are 77 degrees of air with high humidity and the pressure is lower at 28.86. If we have a big-block Chevy on the dyno (because I have a dyno test with all these numbers) and at 6,000 rpm we measure 515 lb-ft at 6,000 rpm, this is what engineers call observed torque. Since our ambient air conditions are not as good as the SAE's STP values, there is a set of calculations we can apply to correct the observed numbers. The calculations create a correction factor of 1.057 percent, which we then multiply by the observed torque to come up with a corrected torque of 544 lb-ft. Then we can take that corrected torque number and plug in the standard equation: hp = torque x rpm/5252. Doing the math, we come up with a corrected horsepower number of 621.
We correct the numbers so we can compare this test with any previous or post test so we can evaluate the changes we did to the engine and not worry about the effect of atmospheric changes. This is important since it's possible that you could be testing an engine at sea level and then also test it at SuperFlow's facility in Colorado Springs, which is roughly at 6,000 feet of altitude. Since the air is much thinner (because the atospheric pressure is lower) at altitude, we need to have a correction factor that accurately accounts for this lack of oxygen in comparison with testing an engine right on the beach in Southern California.
SAE has changed its engine power correction factors a few times with the latest being the J1349 standard, which uses 29.23 inches of mercury, 77 degrees F temperature, and dry air (zero humidity). According to numbers I've seen, this represents a 2.6 percent difference in power compared with the older STP standard. This is the standard that all the new car companies apply to advertised horsepower ratings for cars and trucks. This leads us into a whole new area that a giant story could be written about concerning how we do dyno testing. Just to give you a taste, if you are a veteran CC reader, then you know we do much of our engine dyno testing at Westech. Like almost all engine facilities, Westech uses the older J607 standard because the corrected numbers are better. In addition, Westech knows that starting the testing with a hot oil temperature of at least 180 to 200 degrees F is worth some power as is water temperature readings of closer to 140 degrees rather than 180 degrees. The company will also test most often with open exhaust and an electric water pump rather than an accessory drive that runs off the crankshaft. These examples plus a few others are reasons Westech's numbers tend to be somewhat higher than numbers generated at other dyno facilities. These numbers aren't wrong, but they do look really good.
Can an unscrupulous engine builder/dyno operator cheat a dyno to make it read a higher horsepower number? The answer is an unqualified yes. That's why going to a qualified facility you can trust is important. It's actually very easy to cheat a dyno into reading higher. Sometimes this happens inadvertently because the dyno isn't calibrated as often as it should be. Other times, a less-than-reputable operator can easily cheat the inputs by jacking up the carburetor inlet air temperature or lowering the ambient air pressure number to inflate the correction factor and make the power readings appear higher. A favorite trick is to position the carburetor air inlet sensor right above the headers. This jacks up the inlet air temperature sensor reading and inflates the correction factor. As a way of monitoring dyno numbers, a typical correction factor should be between 3 and 8 percent. Sometimes these correction factors are displayed on the dyno sheet, but more often they are not only to allow room for other more important results. But if you ask to see the correction factor, that number is always available. The only time these corrections might be higher is at test facilities at higher elevations that are located in the mountains.
There's tons more information here than we can fit into this column. If you'd like to dive deeper into the effects of atmospheric conditions on internal combustion engines, we did a story in the June in '06 issue (page 50) on the effects of atmospheric conditions on engine performance and a reference tool called density altitude (DA). This actually comes from the aviation industry where the three main factors of temperature, pressure, and humidity are calculated into a single number represented as a relative altitude. For example, a DA of 1,000 feet is better than 5,000 feet since the amount of oxygen available at sea level is far greater than at a greater altitude. While useful, DA also has its drawbacks. There's also a great weather station software program sold by Patrick Hale at Racing Systems Analysis (RSA, the same guy who wrote the Quarter, and Quarter Jr. simulation programs) that can help when dialing in your drag race car. We clearly answered more than you originally asked, but that's the risk when you enter the What's Your Problem zone.
Racing Systems Analysis (Quarter); Oshtemo, MI; quarterjr.com
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