Ok, so i'll need to send the head out to you. Could you let me know what sort of over all costs are involved for this via PM.
Also, is there an option/plan to build a 'drop in' rockers for the AVL which can aid the lift. The AVL head seems similar to the big head as far as the rocker system design ( based on only visual similarities) It would be a great as it would certainly garner lots of interest from the AVL owners, especially where shipping is killer for large items i.e. the head assembly.
It is possible to make a drop-in rocker, but there are other issues involved.
The valve springs are not up to the job, and then we have to get into valve gear changes. The small valves which are standard really need some up-sizing to about 1.8" for the inlet, and and the port needs to be modified to flow better to feed the needs with the big valve. After that, we don't have piston clearance room for any more lift, unless we notch the piston. Also, the exhaust flow starts backing-up at over .400" lift, so the exhaust port needs porting when increasing lift much.
So, as you can see, things begin to cascade when you change something like this, if any real improvement is to be seen from it. Yes, just the added lift from the rocker will give something, but not anywhere near what it would be if the system was modified to work with it.
I just happen to have a flow chart here for the AVL, and the stock inlet port will flow about 155 cfm at the stock max lift. Let's say we make some modified rockers that can get that lift up to .400" max. The stock port will flow 170 cfm there. That's a decent bit more, and there will be some additional time open at all the lower lifts, so that helps too. But, if we do the big valve instead of the rockers, that will give us about 180 cfm at the stock lift, and also more at all the lower lifts too, because of more flow area. If we combine them both together, with lift and area, we can get about 206 cfm at that same .400" lift out of the AVL head. Use a TM34 carb on it, which can flow about 206 cfm, and it's a nicely matched package that should easily go 6500 rpm in top gear. And this will require either a new piston, or notching your existing piston for valve clearance, IF your piston can take being notched to the necessary depth.
If you want the maximum lift that our Ace valve spring and valve gear package can get, which is .500" max lift, you could reach 208 cfm flow, and get even more open valve time at all the lower lifts, which increases area under the flow curve that much more. If you want to open the ports up further to use a 36mm carb, then you can get it flowing up to about 227-230 cfm. and that's good for 7000 rpm. You'll need the .500" lift for that, along with the larger port. Even more piston notching depth needed for that.
Now comes the need for higher compression, because the high lift rockers add more time to the working cam duration, even if the seat timing is the same. So, this means that you have to increase the compression ratio, just to remain the same as it was. Or, if you want more compression, you will have to increase the compression ratio even more. So, then we have to start talking about the combustion chamber modification, to reduce the chamber volume for higher compression ratio, so it can use the flat top piston with valve relief notches in it, or a new piston. Obviously, we need more compression for an arrangement like this, and we would like to not make the piston any heavier, so we work the chamber in such a way as to improve the flow, increase the compression, and also improve the combustion efficiency, which can allow us to run an even higher compression ratio than previously possible on pump gas. We may need to adjust ignition timing, so the adjustable ignition box, and/or some off-set Woodruff keys for the timing adjustments would be good to have.
Now, coming back down to Earth, we can't make production rockers for the AVL like this. There is simply no demand for it. Making them one pair at a time is expensive. In fact, it is basically similar cost to make the .500" lift roller rockers at the specialist's facility, as it is to try to hand-make a pair of .400" lift modified AVL rockers. So, the cost effectiveness is definitely on the side of the custom made roller rockers, when it is all said and done. It's expensive, but at least you get the most you can get for your money.
Speaking of most for the money, the best bang for the buck is to use the standard lift rockers, and go with the custom big valves with the ACE valve springs and valve gear, and the chamber modification and porting, like Tooseevee did. Use your S Cams with it. That can be supported by the TM32 carb. It *might* not even need any piston notching, or very minimal. The maximum rpm will not be as high as with the 34mm carb, but the torque will be very good throughout the whole range, and it would still get over the Ton, and accelerate a whole lot faster because of much better horsepower over the entire range. Unless you plan to go over the Ton a lot, or be racing, the actual top speed is not a real critical factor in street riding. The midrange is much more important on the street. And if you already have the TM34, it will work just fine, and give a bit more rpm/mph on the top speed.
You should discuss/know all the options and benefits before deciding what to do, and what things cost.
Topic: Electra x rebuild (Read 7013 times)