Our seven engine builders have used the ARP head bolts as well as the low cost ones that have flooded the market. The differences are dramatic.
Highest Quality, Proudly Made in the USA
ARP was the first company to design and engineer fasteners specifically for racing. We find the ARP head bolts to be superior in every way compared to the low cost head bolts on the market. Every engine we build uses them, including our base model 350 and 383 engines. There's not another company in the world that is as focused on building superior quality fasteners for all forms of racing and non-racing applications as ARP.
Our engine builders first noticed the general feel of the ARP head bolts to be much smoother than the low cost head bolts when torquing them down. This smooth feel is sure to give more accurate torque readings.
We recommend using high-quality, calibrated torque wrenches and proper method when tightening hardware, your engine depends on it.
Head Bolt Washers
The head bolt washers on the ARP set are another great feature. They have a well designed chamfering in the center. The chamfered center intersects perfectly with the radius in the head bolt. The thick radius in these head bolts is part of what makes them very strong. These specially designed extra thick washers are very important on aluminum heads. They allow the head bolts to have a glide surface to prevent gouging into the aluminum head. This is another reason these bolts will give more accurate torque readings, in our opinion.
There are a couple of bolt holes in the center on most aluminum heads that have an inherent weakness. Due to the location of these holes, the casting is usually much thinner to give way to the raised water jackets, which are usually raised to give way to larger than normal runners. Using head bolts without washers can crack the casting in this marginal area.
The thick, wide washers not only prevent the bolts from gouging into the head, they also distribute the pressure over a larger area as compared to the smaller bolt head. When the head bolt tightens down without a washer, the twisting force of the head will gouge into the surface of the aluminum, further weakening this area, and can cause it to crack.
Don't risk cracking your heads
We know first hand of this happening with a brand of cylinder heads we once carried about 10 years ago. We had many warranty claims on these heads over a year's time. These heads had multiple cracks around the center bolt holes. 100% of these heads had used head bolts without washers. At that point, we insisted on the use of ARP or an equivalent head bolt with the special washers.
Once we insisted on using head bolts with washers we have had zero center hole failures. As mentioned, this is an inherently weak area on most aluminum heads, some more than others.
Some of the low cost head bolt sets on the market do include washers, but they are not designed well, from what we have seen. The chamfering in the center of these washers did not mate up properly with the radius under the head of the bolt. This caused the washer to flare up slightly on the edges when torquing the bolt down, therefore defeating much of the washer's purpose. It's better than no washer at all, but it's poorly designed compared to the ARP sets.
When we torque plate hone our blocks, we use the ARP head bolts. We once tried the low cost head bolts, and noticed after just a few uses, they had stretched and deformed the threads so badly they couldn't be used again. We can use the ARP head bolts many times before replacing them.
We have sold the low cost head bolts for many years, and find them to be sufficient for those on a budget doing a mild engine build that will not encounter hard usage, but we do not advise using them on engines with over 10:1 compression ratio. We also do not recommend them on engines with aluminum heads due to the poor washer design.
Ultra-Torque Assembly Lubricant
There are a lot of opinions out there about which fastener assembly lube to use and what the torque value should be. ARP provides torque specs are based on using ARP Ultra-Torque.
If you're not using ARP specs and lube, you have no real idea what pre-load you're getting. ARP has done the testing where and can measure the torque applied and the resulting pre-loads.
Variety of ARP Fastener Applications
Consistent clamping force on each bolt is of paramount importance for proper performance and reliability of an engine. For many reasons, mostly the very well designed threads, the ARP head bolts will give you this consistency. Don't skip when it comes to hardware and be sure to follow the instructions when tightening. ARP hardware is available for valve-train, internal engine hardware, damper bolts, flex-plate bolts and many other applications.
Deep Dive - Fasteners are a spring
If you're still reading and want to learn more about hardware, threads, preload and proper torquing methods, please watch Chris Brown, Director of Specialty Products for ARP, as he presents a basic fastener knowledge seminar at the 2012 AETC Conference in Orlando:
If you have questions on which ARP hardware is right for your application, please call us at 423-722-5152.