So what can I do to improve the power of my 2.8???
This is one of the most common questions I receive. While the 3.1 motor sounds really cool on paper, it is downright expensive, and can be impractical for most people. So what head is the best for a higher performance 2.8? Ask 10 engine builders that same question, and you will get 10 different answers. As I have tried to stress, you need to look at the engine as a WHOLE. More often than not, we tend to buy parts for our motors, and indeed our car, in bits and pieces, rather than all at once. This presents several problems. First, it usually means we have failed to look at the motor as one unit, and are buying parts that are likely not compatible with the others we have. I am talking about performance parts, not things like water pumps, fan belts, etc.. I highly recommend that you sit down, and write out what you want as an overall goal with your car. Are you going to drag race it? Will it be a dedicated autocrosser? Will this be your daily driver? All these are important issues that must be addressed BEFORE you start. Let me give an example. I had someone write to me asking my thoughts on a buildup. Here is what he said:
"I want the engine to handle 9000 rpms....I want top end. I want to race autocross ....In other words. I don't care about street practicality or comfort. I want a race car. However comma, I would like to have good acceleration under 5k."
You see the dilemma? Those were his exact words. You can't have both. You need to determine what you want from your car first, then approach the motor as a WHOLE. Every part works with the others, Unfortunately, with many of the high rpm motors of today, when people sit down to buildup their ole' L6, they think they need that kind of revolutions to get great power. FALSE! First, let us look at an all out race L6. We are talking fully prepped, 50mm triple carbs, 600 lift, 330 duration race only cam, fully ported and polished, and a little magic added head. With this combo, you are looking at low 300 horsepower range. I am not kidding there. And these motors fly. Horsepower is a highly misunderstood and often bench raced issue. It is all relative. I could put a motor on a dyno, run it, show you that it made 400 hp at the flywheel, and in reality, it was half that. Engine dynos should only be used for tuning. If you want to know how much power your motor is putting out, go to a chasis dyno shop, where they will measure the power you are putting to the rear wheels. That is about the best you can do, and it doesn't lie. So how fast is the race motor turning? What RPM is this motor run? 9000, 10,000, 12,000rpm? Nope, less than 8000, with most of the power coming in the low to mid 7's, ie 7100-7600. The L6 just doesn't produce good power above that. It is a function of head design, and the long crankshaft. Harmonics start to play a bigger effect over 8000, and cancel the power you can produce up there. But if you are producing 320 hp from a carb'ed L6, belive me, you are doing really well. To get more than that, you need to look at turbo, supercharger, or Nitrous. The Turbo route is the easiest way to get lots of horsepower. There are L6 turbo motors putting upwards and over 400 hp to the wheels. But realize they have a lot of money in their motors, and lots of time spent tuning.
For all practical purposes, a streetable, NA,(Normal Aspirated), L6 motor won't see much over about 250 hp. And that is something like a 3.1, triple carbs, good size cam, well tuned motor. It will put near 200 hp to the wheels, over 200 foot pounds of torque and run the 1/4 mile in the mid to low 13's. About the best compromise you can get before it becomes like a race car. Why is that? It is largely a function of our outdated head design. When the 240 came out, the head design was a fairly good design for its time. However, take a look at a Honda/Acura head design of today. They are primarily 4 valves per cylinder, centrally located spark plug, and of a cross flow design. By cross flow, I mean the intake comes in one side, and the exhaust goes out the other side of the motor. The L6 motors intake and exhaust are on the same side and the spark plug is on the side, not the center of the combustion chamber. When you add something like a turbocharger, you can get around an inefficient head design. That is why you see some turbo'ed L6 motors putting out over 400 hp. Of course, for the power hungry, their is always a V8. It should also be noted that there are many V-8 Z-cars out there that can only run low 14's, mid 13's in the 1/4 mi,(but some are in the 10's or faster!).
The 99 Corvette runs it in 13.2 at 108, give or take a little. Add about a quarter to half a second for most well driven Camaros and Firebirds, another half for a Mustang. See what company you are in? This is assuming they are well driven, not your average joe. But not everyong is building your motors for drag racing, I am just using that for comparison. Sure, top speed is cool to talk about, but how often are you doing 150+, if your car is indeed capable of that? You will enjoy your motor most if you build it for driveablity and around town stuff. Lots of torque down low and a high numerical rear end for quick off the line acceleration. Check out the Datsun Garage for his 1/4 times with a fairly easy to build 2.8, he hit the high 13's! On SU's! That can outrun almost everything on the road.
With factory pistons, ie Cast, not forged, and other stock parts, your motor is good for the factory redline of 7000. You really want to keep it below about 6500, because above that speed, the ring lands start to pit and deteriorate from the pounding they are taking. Some have asked, what about using Forged pistons? Forged pistons are great for protection from detonation, and really high performance applications, but aren't really needed until you get up around 300 hp or more. They are a little harder to deal with in a daily driver because they expand more than a stock piston, requiring greater clearances when cold to account for that expansion. This wears the components faster, meaning your pocket is emptied again sometime in the near future. Not only that, you need extensive head and cam work to produce any significant power over 7000 rpm anyways. Bottom line, unless you are running a serious turbo motor, or an all out race motor, stick with the stock cast pistons.
I run mine up to 7000 a lot, and have yet to encounter problems in over 15,000 miles of driving, in everything from city driving, long distance, to all out racing.
I am not going to offer much over what Bryan Little has offered on his web page. He has clearly
laid out how to build cheap, reliable, powerful 2.8 motors. I can't add much to that, and certainly
can't say it as well. Here is his site again: The Datsun Garage
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