Small-Block Ford Follow-Up
Jeremy Wood; Tuscaloosa, AL:
I'm 30 and have owned my '68 Mustang notch for 15 years. I grew up wrenching on my own vehicles and find the blue-collar budget/DIY mantra of Car Craft refreshing. Last summer, the Mustang's original 289ci finally gave up the ghost (I punished her during high school and college). I picked up a 5.0L H.O. from a junked Mountaineer with only 96K, and I'm in the process of building it for the car. I was giddy like a little girl when I read your "$350 Junkyard 302" article (Aug. ‘14) and realized it follows my build pretty closely. I left the bottom end alone because the cylinders looked just like yours, but swapped in a Trick Flow Track Max camshaft (PN 51403001), Cloyes double roller set, and replaced the valvesprings with Crane PN 44308-1. I'm keeping the factory lifters, pushrods, and rockers for now. I believe all is well after scouring the Internet and finding this is a common setup for a GT40P engine, but your article has me sweating. I've never heard of exhaust valve rotators and have no experience with valvespring installed height. Will you help shed some light on the subject before I drop the engine back in the car? Is my combo going to work? I will also be running an Edelbrock Performer RPM intake, 600–650-cfm carb, and a Duraspark ignition. Thanks for your help!
Jeff Smith: It's great that our budget 302 article dovetailed so well with what you're building, Jeremy. We did a follow-up story on the cylinder head upgrades for the 302 in the Sept. '14 issue ("How to Upgrade Your GT40P Heads"). In case you missed it, the problem you mentioned is the exhaust valve rotators. Many factory engines use these retainers, most often on the exhaust side. Rotators are designed to rotate the valve to prevent hot spots from creating wear and minimize carbon buildup on the seat. In the case of the 5.0L Ford, the rotator is substantially thicker than a standard retainer. Because of the thicker retainer, there is less room available for the valvespring. So when you add a performance camshaft with more lift, there's not enough room for the spring to compress before it stacks solid, which is called coil bind. The thicker rotator reduces the available distance between the bottom of the rotator and the seat in the head, where the valvespring sits. This was necessary because both the intake and exhaust valves in the Ford head are the same overall length. To compensate for the thicker retainer, Ford lowered the groove for the retainer locks on the valve in order to have enough room between the top of the retainer and the end of the valve. This is critical because Ford also uses what is called a rail, or guided rocker arm. The rocker uses thin rails that straddle the valve tip to maintain rocker alignment over the valve. These rails require that the valve tip be substantially taller than the top of the valve locks. If not, the rails could hit the locks and unload them, causing the retainer to come loose, which is obviously very bad.
In order to have sufficient spring travel with a performance cam, the rotator and the valvesprings must be replaced with better springs and thinner retainers that can handle the additional lift and higher engine speeds. We chose to install a Manley exhaust valve that relocates the lock groove to allow the same valvesprings, retainers, and locks for both the intake and exhaust valves. There are a couple of other kits we mentioned in the story, such as those from TFS and the Crane kit you're using. These are designed to be used with the stock Ford valve. We decided to go with the new Manley valve because then the installed height is the same for both the intake and exhaust valves. In the other kits, there are different retainers and/or locks between the intake and exhaust and it might be easy for someone not familiar with the system to get them mixed up when reassembling the heads. We decided to avoid all that with the Manley valve.
Installed height is the distance from the spring seat in the head to the bottom of the valvespring retainer. This is the distance that the valvespring is compressed when the valve is closed, which also sets the closed spring load; this is important because the onset of valve float almost always occurs when there is insufficient spring pressure as the valve closes. At high rpm, the valve can actually bounce off the seat. This is not good. If you think about the induction process, once the intake valve closes, the rising piston can begin to compress the air and fuel mixture. But if the intake valve bounces off the seat, some amount of cylinder pressure is lost into the intake port. Less cylinder pressure means less torque and less horsepower. This means that valve control is critical, and it's why we need good valvesprings.
You mentioned you used the TFS hydraulic roller camshaft, which is similar in duration to the milder version of the Lunati cam we ran. The TFS cam specs are 221/225 degrees of duration at 0.050, with 0.499/0.510-inch valve lift with a 112-degree lobe-separation angle. This cam generates less lift than our Lunati, but because of the less aggressive lobe, this places less stress on the valvesprings. Over time, your engine will probably continue to deliver good power without abusing the valvesprings. Generally speaking, camshafts with more aggressive lobes (which we will define here as having more lift for the same amount of duration) tend to abuse the valvesprings to a greater extent and may create more stress in the valvetrain.
You also chose the Crane beehive valvesprings. By design, these springs tend to accommodate more valve lift for the same amount of installed height. This should work fine as long as the springs are set to the proper installed height. It's not uncommon for production heads to need additional shims underneath the springs to create the proper installed height to ensure that the spring has the proper seat load. Generally, if you're within 0.010 inch of the specified installed height, then all is well.
You mentioned that you're retaining the stock rocker arms and pushrods. The Ford GT40P head is designed around a net lash system, which means a 5⁄16-inch bolt is all that retains the rocker arm, and there's no adjustment. This makes it easier to assemble, but precludes adjusting the preload on the lifters. Essentially, the preload is set by the pushrod length. This isn't necessarily bad. Crane makes a conversion kit (PN 36655-16, $137.60, Summit Racing) that will convert the head to use adjustable rocker arms. This kit uses a 5⁄16-inch stud that screws into the cylinder head but uses a 3⁄8-inch stud to mount an adjustable rocker arm and also includes a slot to use as a pushrod guideplate. The kit requires adjustable rocker arms. The least expensive Crane cast steel rocker arm kit is roughly $190, so the whole conversion would easily run over $400 with pushrods. I understand why you might want to wait on this part. But also know that the load on that 5⁄16-inch bolt has now increased with the new valvesprings. This is why we decided on Tim Moore's engine to convert the head over to 3⁄8-inch stud rockers with 7⁄16-inch studs going into the head. That whole combination is much stronger and will not fail. Ultimately, I think that might be the best way for you to go, but you can certainly go with your existing combination and it should work.
; 386/258-6174; CraneCams.com
; 662/892-1500; LunatiPower.com
Trick Flow Specialties (TFS)
; 330/630-1555; TrickFlow.com
; 732/905-3366; ManleyPerformance.com