In this episode of Project Underdog we are talking about torque plates. What they are, why you might want one and how to make the most of them. We also take a look at my DIY torque plate made from a junk cylinder head that I believe is not only more cost effective but also better than a traditional torque plate. Torque plates come into play when you need to bore and hone your cylinder block. When you want to rebuild your engine and install oversized pistons you need to overbore your block. In most cases a block is bored as a bare block, with nothing attached to it, and this leads to our issue. Ideally you would want to bore and hone the block with the cylinder head attached to it. Why? Because when you install and torque down a cylinder head your bores get distorted. They get distorted because they are hollow cylindrical shapes that get exposed to very significant clamping and other forces generated when you torque down the head. You want to bore the block in this distorted shape because this is the shape in which it will be running. This is why boring the block in the distorted shape results in better ring seal and thus better compression, more power and possibly even less oil consumption due to reduced blow-by. Of course boring and honing the block with the head attached is impossible because the boring and honing machine would no longer have access to the bore. This is where a torque plate comes in. A torque plate is essentially a thick piece of metal, usually aluminum, that mimics your cylinder head. It has large holes that match the size and spacing of your bores and it has holes that match your cylinder head bolt holes on your block. You bolt it down and torque it down just like you would an actual head and then you bore and hone your engine block. The result is that you’re boring and honing in the distorted shape as is optimal. But torque plates are expensive and if the machine shop that’s doing your build doesn’t have the right torque plate for your engine your options are to either buy one or have one custom made. Both options are usually very pricey, the custom route usually more so. When facing this same scenario in my engine build I asked myself: “why not mimic a cylinder head with an actual cylinder head?” And in the end that’s exactly what I ended up doing. I took my old junk 4AGE cylinder head which head irreparable damage (totally busted cam journals) and turned it into a torque plate. I took it to a machine shop and asked the shop to drill holes straight through the head. The center of the hole is the center of the spark plug hole, because that’s also the center of the combustion chamber and thus the bore. I asked them to drill holes with 83.5 mm of diameter. I went larger than my 81.5 mm of final bore diameter to leave some room for error in case the center of the spark plug hole isn’t the perfect center of the bore. The end result is what you can see in the video. It’s cheaper because old junk heads are usually 50-100$. Chances are you or a fellow enthusiast probably has some laying around that are just begging to be turned into torque plates so you might get one free too. The only other cost is the cost of machining which will of course vary depending on where you live and what kind of head you bore through. But it likely won’t be over 150$ for an inline four which means you’re getting a torque plate at a fraction of the price of a ready made one. The other benefit is that this torque plate is better because it not only uses the same alloy as the actual head it also better mimics the shape of a cylinder head because it used to be an actual cylinder head. This means that the distortion created should be even more accurate than that of a conventional torque plate. A few other important notes for using torque plates in general. Always use them together with head gaskets of the same brand and kind that you will be using in your final assembly and together with the head bolts or head studs you will actually be using. This is because the head gaskets and bolts are an important factor in the overall distortion generated. MLS head gaskets can be reused as long as you don’t heat cycle them. Also bore and hone with main caps or any main cap girdles installed as well.
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