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Location:
The Central Coast
Registered:
October 2002
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Re: What to do with my head ......
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Thu, 19 June 2003 02:35
 
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This I got from either Phil Bradshaw's site or Bill Sherwood. Can't remember which one, I keep it in a word document for my reference.
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140hp - 150hp
Bolt-on external mods are all that is needed for this much extra power. Simple mods, such as a free flowing exhaust and cold air inlet pod will give you a few more HP. Synthetic engine oil will also give you a few more HP over conventional mineral oils.
By doing all of these things you'll gain a good 10hp or so over a standard engine, but anything more than that and you'll need to start digging around under the cam covers ...
Towards the 150hp mark, you'll need to go for cams of around the 256° duration. If timed properly, they'll idle and run just like a pair of standard cams.
Aftermarket 'chips' for the factory computer will also help the power output, but they vary greatly in quality and results - Do your homework before buying!
150hp - 160hp
The standard cam timing is 240° duration, from seat-to-seat, and this is typical for a modern road going twin cam engine. A pair of 256° cams and the mods mentioned in the 140hp - 150hp paragraph will get you around 150hp if everything else is right, but to get much more you'll certainly need bigger cams, around the 264° mark. This size cam is the upper limit of the cam duration that you can use with the factory computer, as they need a decent inlet manifold vacuum to sense to work properly. The AFM versions may be a little better off, but I've had no information on this.
You won't get 160hp with the factory computer, however, and so you'll need to spend a few dollars on an aftermarket system. I highly recommend getting a programmable system rather than a new 'chip' or a simple 'add-on' for the factory computer, as if you want more power later on then you won't be limited to whatever the chip/add-on has already programmed.
Once you have an aftermarket computer, you can run pretty much any size camshafts that you like, with little penalty, so to ensure that you end up with the power more like 160hp, you should run 272° cams.
Note that with cams larger than about the 260° mark you will actually benefit from removing the TVIS, if fitted. The TVIS, when used with cams smaller than about that duration, will give you more low end ( < 4,400rpm) power, but this effect disappears with the bigger cams.
150hp - 160hp is also the point at which you'll need to get some work on the head. Fortunately, there's not a lot to be done and if you've got the head off then it's worthwhile spending a little more time and effort to make the mods to allow the head to flow up to ~180hp - 190hp.
There are four areas that need attention on the 4AGE heads - The area just above the valve seats, the combustion chamber, and the ports themselves, and the valves & seats.
- The area above the valve seats are a little too parallel, and should be narrowed up a little to create a bit of a venturi effect.
- The combustion chamber has numerous sharp edges that need to be smoothed off, to eliminate pre-ignition, etc.
- The inlet and exhaust ports are quite good standard, but they are a little too big on the big port heads and a little too small on the small port heads. The small port head is easy to make a bit larger, but making the big port smaller is quite difficult, so don't try it - Just clean up all the nasty little bumps & casting marks in the head instead.
- The valves & seats benefit greatly from a good three or even five angle cutting job.
Please read my Engine pages for more information on porting, etc. Note that a lot of engine shops leave the ports with a near-mirror finish and the port dividers almost razor sharp - This is the wrong thing to do!
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There's more after that, but that should be enough to wet your appetite!
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