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Ford Mustang Valvetrain Secrets Revealed - Spin Control
Ever Wonder How Engines With Hydraulic Lifters Are Able To Rev To 8,000 Rpm? You Can See How It Works On The Spintron
Ever hear the saying "ignorance is bliss"? When it comes to the valvetrain on my Real Street pushrod engine, it might be true. For about a year, we've been looking for an opportunity to look at our valvetrain in a more technical manner. Over the course of several years, we've seen stock cam-and-lifter combinations being run well past 7,500 rpm. If you posted that on an Internet message board, you'd be laughed off. Still, I see posts where guys cannot believe how high we're able to rev our Real Street engines. I've read many stories about camshaft companies that use the SpinTron to develop valvetrain components. Of the companies we talked with, most were in constant use for NASCAR applications. Surely, a Real Street combo would benefit from SpinTron testing.
As fate would have it, I met Bob Fox at the PRI show in Orlando. While dining with friends from GM, I met Sue Christopherson and her husband, Steve, who-when the conversation turned to my Real Street combination-insisted I meet Bob Fox from Trend Performance. I had used Trend pushrods in my car with an improvement in stability. We eliminated some problems when I installed a set of Trend 31/48-inch, 0.135-wall pushrods. As it turns out, Bob invented and now owns the company that builds the SpinTron. He also owns Diamond Pistons-this guy obviously knows a thing or two about a thing or two.
When Bob offered the use of his in-house demonstration unit, we jumped. As many of you know, Don West prepares my Trick Flow heads for the Real Street class. He has extensive experience with the Trick Flow Twisted Wedge and GT-40 heads I used in Factory Stock. Don has spent countless hours on the flow bench working on improving flow below the 0.480 total lift we see in those classes. In addition, he has the Stuska Dyno we use to test our improvements. To say Don was excited about a little time on the SpinTron would be an understatement.
In the time I've been involved in the Real Street class, 98 percent of our increases in power were directly related to the valvetrain. With the Paxton supercharger, more rpm meant more horsepower. In our quest for more rpm, we learned a lot, but sometimes at great expense. In 2004, I broke valves at Bradenton and at Atco. In both cases the damage was extensive. The Bradenton engine needed an overbore with a new set of pistons. We had the head welded, but after about 10 passes it had to be freshened. The Atco engine also needed an overbore, pistons, one rod, and a new set of heads. I had been spinning that engine past 8,400 rpm routinely with the Novi 2000. With the large blower pulley, the engine peaked at about 8,100 rpm on the engine dyno. Looking back, it probably peaked there because the valvetrain was out of control.
After two engine failures, I chose to use the Paxton Novi 1200 for the '05 season. With that unit, our 307 had a horsepower peak at 7,400 rpm. Out came the 4.56 gears and in went the motive 4.29s. While experimenting on the dyno, we tested spring pressure as high as 500 pounds on the seat. Yes, you read that right: 500 pounds. When we lost control of the valves, several things happened. First, it beat the heck out of the seats, which I believe was due to the "bounce" of the valve as it was closing. And the keepers were difficult to remove, which was from the severe hammer effect that happens when you lose control of the valvetrain. For 2005, our effort was to stabilize the valvetrain. We found that anything over 380 pounds on the seat had no improvement. We did see considerable improvement with the new Trend 31/48-inch, 0.135-wall pushrods.
There are people out there who will tell you the lifters will break at a certain spring pressure. In all of our testing, we have failed only three lifters. We use the OEM Eaton lifters that are available from Ford Racing Performance Parts. We've looked at aftermarket replacements, but are staying with the FRPP pieces. The failures we've had were in instances where low spring pressure resulted in loss of valvetrain control. The hammer effect from the loss of control destroys lifters and valves. In all cases where we increased spring pressure, it reduced the loss of control.
Since we mentioned the lifter, we'll also tell you about how we adjust the preload. At high rpm and high spring pressure, the lifter tends to collapse and lose effective lift. The rules in R/S state that we cannot run the lifters "bottomed out," in effect running them solid. To determine if a lifter is bottomed out, spin the pushrod while the lifter is on the base circle of the cam. It should spin if it isn't bottomed out. Because of that, we run the lifter about 0.006 away from bottomed out. Once the engine warms and expands, we gain a little more. Setting the lifter this way ensures that you don't lose any effective lift and duration if the lifter starts to collapse.
If you don't run a stock cam, you might think this doesn't apply to you. Most aftermarket cams for our applications were designed years ago, and therefore have not had the benefit of testing on a SpinTron. Most lobe designs are based on old masters that are more than 25 years old. Remember, NASCAR and NHRA Pro Stock are the first priorities for cam companies. Managing your valvetrain is just as critical, especially if you're running something much larger than the stock cam.
We looked at several things in our SpinTron test, one being our '04 combination. We wanted to see the kinds of forces we subjected our engine to that broke two valves. Next, we wanted to examine our '05 combination to discover what was responsible for its huge improvement in wear and tear. Finally, we looked at the new '06 combination. For 2006, the NMRA mandated sweeping changes in the valvetrain rules in Real Street. Pushrod cars are now limited to 160-pound spring pressure on the seat, steel retainers, no shaft rockers, and no larger than 51/416-inch pushrods. Other changes to the class include smaller 151/48-inch headers, 50 extra pounds and no bigger than a 3.73 gear ratio. This is NMRA's intent to attract more street-oriented racers to the class.
Our first test was educational: We were losing control at about 7,800 rpm. While the bounce was there, I would learn later that it wasn't as bad as it could be. This combination used the Jesel Shaft Rocker, 320 pounds on the seat (down from where we had set them), Trend Products 31/48-inch, 0.135-wall pushrods, and Manley titanium retainers. I learned later this was a good point to reference all other tests. This test was at 8,000 rpm. While not optimum, it would live without beating up the valve seats (see '05 Setup Graph, p. 156).
Next we removed the Trend Pushrods and installed a set of 51/416-inch, 0.080-wall pushrods we had run in 2004. The valvetrain was out of control at 7,000 rpm. Look at the graph to see what we were doing at 8,000 rpm. This was concrete evidence as to why I broke those valves. The pitch the engine made when it lost control of the valve was scary. I can't believe the valves held up as long as they did (see '04 Setup Graph, p. 156).
That ended our first day, and I was depressed by what I learned. Knowing what the new rules in Real Street took away, I couldn't see how I was going to make any rpm and keep my parts from breaking.
The next day, we removed all of last year's components. Don worked on setting the valvesprings at their properly installed heights. He isn't used to working with these lame street-motor-type parts. We didn't have enough height on some valves and would have to run without seat cups. All the time, Don was grumbling about the new rules, and we had several items to test. First we had two sets of valvesprings. One was the single-conical style, or beehive spring. These springs seem to be the latest rage, and they've gotten a lot of ink because of their design. They are the same type of spring used on the Chevrolet LS engine series, and the advantages are myriad. They use an "ovate" string wound in a conical design. The small-diameter retainer is almost as light as titanium. The other set we tested were the Anderson Ford Motorsport Hi-Rev Series dual springs, which are more traditional springs.
The guys at Trend whipped up a set of 6.700-inch-long, 51/418-inch-diameter, 0.105-wall pushrods to comply with the new rules. Remember when someone would tell you they have "lightweight" pushrods? If they do, smile and be proud that you have the heaviest ones you can find in your engine. They fill up with oil, so whatever weight you save on wall thickness will be filled with oil. Oil isn't nearly as rigid as chrome-moly. The NASCAR guys use huge 11/42- to 91/416-inch pushrods. They may be heavy, but they don't flex.
During our tests, Bob Fox was hanging around answering all our questions. "Generally, you will lose power when you get control of the valvetrain," he said. At first I scratched my head but later understood what he meant.
We installed the guideplates and Trick Flow 1.7-ratio rocker arms. We used the 71/416-inch ARP rocker studs. Things weren't nearly as dire as I thought (just don't tell the NMRA's James Lawrence or those pesky nitrous racers). I had hoped to see a stable valvetrain at 6,500 rpm. Things started to get out of control at 7,000, but nowhere near where it had been in 2004 (see '06 Setup at 7,000 Graph, p. 156).
In addition to valvesprings, we tested some hollow-stem valves from Ferrea. We know other Real Street racers use them successfully, but we saw only minimal gains on the dyno. Because of issues with keepers, we could not test the hollow stems with the conical springs. Back-to-back tests on the standard-stem valves showed the Anderson springs to be as good or slightly better than the standard stems. The hollow stems with the AFM springs were only slightly lower on the rpm range before they lost control.
Jerry Pelkey of SpinTron told us we would leave with more questions than answers-and boy was he right. We did learn where we would lose control with various parts. We also could see the benefit of lightweight parts such as hollow-stem valves and titanium retainers. Most of all, we saw how different thicknesses of pushrods, coupled with spring pressure, changed the characteristics of the valvetrain.
We had heard about lofting a valve from the cam lobe. In essence this is free lift and duration. By utilizing certain components, it's possible to have controlled loft so it can land the valve gently as it closes. Most of the punishment of a valvetrain that has lost control is on the closing side of the camshaft. As you can see by the graphs, that's where the valve is literally bouncing off the seat (see Lofting the Valve Graph).
OK, you're asking, "What did you learn?" If the Novi 2000 were still legal and they hadn't changed the rules, I would rule the class. I saw where we went wrong, and I'm going to experiment with lofting the valve off the cam. It's like changing cams. The downside is, it can bite you in the butt. Missing a shift and over-revving the engine could result in the valve hitting the piston. Been there, done that-it isn't cheap.
These are my recommendations for a hydraulic-roller cam engine. Set spring pressure between 150 to 200 on the seat. Those springs from Anderson Ford work well. The conical springs are also good, but they will cost a bit more. Titanium retainers are not just for race cars. They are stronger and lighter than steel. They cost a lot more, but you'll appreciate it in the long run. Use only the lifters from Ford Racing Performance Parts, and check them regularly. Use the thickest-wall, largest-diameter pushrod you can. A 31/48-inch, 0.135-wall pushrod from Trend Performance works well. You may need to clearance the pushrod holes, but it will be worth it. Find a cam manufacturer that uses the newer cam-grinding machines. The technology has changed, but a lot of companies have not. The advancements in lobe design focus on controlling the valvetrain. Cams such as the Anderson Ford Motorsport Hi-Rev Series use this CNC technology. Upgrade to the 71/416-inch studs if you use a stud-style rocker arm. The Trick Flow rockers we used worked well.
If you plan to run the car on the street, adjust the preload as you would normally. When you go to the track, run the lifters as close as you can to bottomed-out. We use a dial indicator to find the optimum setting. Be careful not to run the valves so tight they are open, which can result in contact with the piston and a bent valve or two.
It's amazing we're able to see the numbers in these engines. Certainly no one except the NMRA will use stock cams. They aren't designed for high rpm and our testing showed that. But with some good parts and a little testing, you can make a hydraulic-roller cam run high rpm. Racers in the NMRA Pure Street class, such as Rich Groh (now in Renegade) and Ron Anderson, run in the 9,000-plus range.
Horse Sense: The SpinTron is a machine that's powered by a 50hp electric motor and is used for testing valvetrain components. Once an engine block has been mounted to a fixture on a SpinTron, a mandrel is installed in place of the crankshaft, and a hole is cut into the side of the block where a laser is used to measure valve movement. With the electric motor spinning the engine to 12,000 rpm, information from the laser tracking is sent to the SpinTron software where it plots valve movement. Different rpm points can be set up to capture data and review it with the software at a later time. Every NASCAR and NHRA Pro Stock engine builder uses a SpinTron. Most are in the hands of cam manufacturers. Initially, Bob Fox built three machines-one for his company, Trend Performance, and two others to help offset costs. Hendrick Motorsports and Comp Cams bought those two units. To date, about 100 machines have been built.
SpinTron has plugs for the lifter bores that aren't used. Several times, we blew out the plugs with the large volume of oil we had (I had sent Leif an old high-volume oil pump I had lying around). We had so much oil flow that we had to bypass some back to the pan. Next time I'll bring a used stock pump.
Don uses the most modern measuring equipment available. Here, he's using a combustion chamber burette to measure our installed heights. In the foreground you can see the beehive valvesprings along with the Anderson Ford Hi-Rev dual springs we tested. Don wants to keep me away from any measuring tools, as I've broken two of his burettes.
This cam is now dedicated to SpinTron use. While testing recently, I broke one of the stock Ford horseshoe retainers. It allowed the lifter to turn and cause the damage you see here. It isn't the same cylinder we use on the SpinTron, so we're good to go. An over-rev condition is usually what causes this to happen. Good valvetrain components should prevent this.
This little baby, a friction dyno, was sitting next to the SpinTron we used. It's number two of two built, and uses a 250hp electric motor to spin a complete engine to whatever rpm you're brave enough to run. With it, you can measure gains in reducing friction. Imagine testing different ring packages, skirt designs, or friction-reducing coatings. The first unit was sold to a NASCAR team. Don and I offered to bring a couple of Real Street engines to test, but Bob has his Salt Flats speed-record engine way ahead of us. Oh well.
This is our current '06 setup. We use the Trick Flow 7/16-inch studs and 1.7:1-ratio rocker arms. You can see the lightweight steel retainers and AFM springs on the exhaust valves. The intake springs in this photo were used on the dyno until our new keepers arrived.
'05 Setup Graph If you compare the baseline (blue line) to 8,000 rpm (red line) you can see several things. First, the spread from the opening is minimal. Toward the top of the lobe, you can see the valve is lofted slightly and follows the closing ramp. The line is away from the baseline so it has lost control, but, as you'll see later, it could be a lot worse. Notice the small blip at the bottom after the valve has closed. This indicates how much the valve is bouncing off the seat. In our car, this small amount won't tear things up. For 8,000 rpm, steel valves, and a stock cam, this isn't too bad.
'04 Setup Graph This graph shows several things. The opening line for 8,000 rpm is spread a lot farther than the previous graph. This is the pushrod flexing. As the pushrod releases its energy, it lofts the valve higher than the baseline. After that, it crashes back into the lifter and bounces back off the cam profile. When the valve closes, it does so with a lot more force and bounces the valve off the seat. This is out of control.
'06 Setup at 7,000 Graph For a stock cam profile, this looks decent. I'd guess the NMRA wanted to drop the rpm level between 1,500 and 2,000 rpm on the pushrod blower cars. This shows that we look fairly good at 7,000 rpm. Notice that there is little deflection as the cam opens the valve. Lower spring pressure helps this, as does a stiff pushrod. At full lift, the valve is close to the baseline trace. On the closing ramp, it follows the lobe well. After closing, the amount of bounce is minimal. Stock cam, stock lifters at 7,000 rpm.
Lofting The Valve Graph OK, here it is. We tried a couple of combinations and this was the result. We had heard about "engineered loft." It's possible to design in the ability to loft the cam, thus increasing effective lift. We're told the Cup guys run this type of setup. As you can see, the opening ramp is deflected so the pushrod has stored energy. Once it releases, the valve is tossed about 0.050 off the lobe. As it closes, it follows the closing ramp well. It does bounce the valve off the seat. I would bet a lot of racers are lofting their valves and don't know about it. Spring pressure must be maintained for all the conditions to be constant. If one cylinder has 20 more pounds of spring pressure, it won't have the same characteristics. Hmmm, I need to order a set of pistons with a lot of valve relief.
Out of Control Graph This graph is a lot like our setup from 2004. It's more dramatic in all areas. Notice the deflection at the opening followed by a rebound on the downside that actually is inverse of the baseline. The valve is slammed with such force that it bounces twice. After all the testing, we had to touch up the seats on our test heads. We could see the results of the pounding. Not everything we tried worked, and we even found a couple of things I had thought were good but weren't. This is what you get when you've lost control: broken valves, snapped rocker studs, keepers pulled through retainers, or broken lifters. All these failures can cost huge dollars. Spend a little time on your valvetrain. It's worth it.