Ford Mustang Valvetrain Secrets Revealed - Spin Control

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.