I know this has been asked and answered before, but please bare with me. I am putting stage 2 1200 heads on my bike, I currently have SE bolt in cams, mikuni 42, SE selectable ignition, bassni Pro Streets, will my stock pistons be ok? What would I gain by going with another piston? And wich one should I go with, dished, dome,.....? And what will they do for me?
I emagine I have to rejet the carb, Could you give me a good place to start with the main and so on.
Also I seen that you have some paper work on motor work, can i get that from you? if so do I need to have it snail mailed or emailed?
And can you off the top of your head tell me with stock pistons around what kinda hp I am looking at and also with different pistons?
Thanks for your time.
Also if it means anything there is approx 7000 miles on my motor.

I know this has been asked and answered before, but please bare with me. I am putting stage 2 1200 heads on my bike, I currently have SE bolt in cams, mikuni 42, SE selectable ignition, bassni Pro Streets, will my stock pistons be ok?


They're going to limit your CR. We're talking about a 91-03 model, right? The stock hemi type head has about a 67cc volume and nets around 9:1 with a flat top. If you're doing that, I'd consider some combination of milling the head and using thinner gaskets to try to get closer to 10:1, especially with those cams. Dropping things too much can cause other issues, but .030 to .040 total of drop is pretty safe. Beyond that, think about shorter pushrods and start watching the piston to valve clearance more carefully.

What would I gain by going with another piston? And wich one should I go with, dished, dome,.....? And what will they do for me?


A forged piston is stronger and is more forgiving when it comes to detonation. We (and others) offer one with a dome that works in the 91-03 1200 chamber and gives 10.5:1 compression. Ours have large valve pockets as well as dual wrist pin oilers and expansion grooves.

I imagine I have to rejet the carb, Could you give me a good place to start with the main and so on.


185 main, 45 pilot, N65C needle (27094-88). But it's just a place to start. Every motor is different and to get it right, put it on a dyno with an a/f sniffer. Ditto the timing.


Also I seen that you have some paper work on motor work, can i get that from you? if so do I need to have it snail mailed or emailed?


http://www.nrhsperformance.com/NrhsInstructionSheet.pdf


And can you off the top of your head tell me with stock pistons around what kinda hp I am looking at and also with different pistons?


If you've only got 9:1 or so compression, I wouldn't look for more than about low 80's. with 10 or 10.5:1, it's capable of making around 90.

There's a fairly substantial amount of variability in people's numbers. I can send the same stuff to 10 people and they get 11 different results. Some of it is how carefully they put it together and optimized things, for example the squish. Much of it is the stuff around it, in particular the pipe. But one HUGE thing is the tune. A guy who spends an hour or two on the dyno, tweaking and dialing it in, knows what he's doing and how to zero-in on what the bike wants, does maybe 25 or 30 pulls getting everything just right, is gonna get a whole different answer than a guy who rolls it up and does 2 or 3 pulls.

There's a lot of skill involved in dyno tuning, too. You wouldn't believe how some people go about it and how they end up way out in left field. You have to follow a process, and you have to understand the instrument, and you especially have to understand how the motor behaves and what influences it's behavior.

All that aside, though, fundamentally a motor's power tends to not be defined by the sum total of it's parts, but rather be defined by the single part that's holding it back. To make more power, you have to identify what's constraining the motor and work on that item, working on anything else is a waste of time and money.

Case in point. I once had a bike in the shop that was underperforming terribly. I went over this thing with a fine tooth comb, trying to figure it out. Cam timing, ignition, ecm issues, I checked it all and then some. Even made a custom pipe of my own design, thinking his pipe was no good. Nothing I did mattered, I couldn't change it's power appreciably at all, or get it anywhere near the range it oughta be. I even pulled the heads, measured everything, flowed'em (they flowed excellent, it was a set our Stage 3's), and put together a set of stage 4's for it (welded up the ports and redid them, bigger valves, got 30cfm more out of them than the heads he had, basically made a set of race heads for him). Bike made the exact same power.

I was working on everything except what was holding it back and I wasted a huge amount of time and money. Eventually I did figure it out, and the guy left with 120 horsepower (he came in with 80). But damn if that wasn't a perfect illustration of the importance of working on the right thing.

Here's a setup similar to yours:

http://www.nrhsperformance.com/pictures/s287hp.gif

regular '96 XLH1200 hemi type heads with a Stage 1 porting job
stock flat top pistons
heads had been milled and CR was about 10:1
SE bolt-in cams
CV40/SE type air cleaner
this bike was properly dyno tuned

Thanks , it helped alot.

So what was holding his bike back that you overlooked?

To elaborate on the dyno tuning comments a bit ... this is a true story ...

Saturday a guy brought me a bike to tune. After 4 pulls it was at 87hp. Two and a half hours and 30 some pulls and numerous tweaks later it turned the drum at 102hp.

It was the cheapest horsepower the guy ever bought.

So what was holding his bike back that you overlooked?

Forgive me for keeping that to myself, I'd rather my competitors have to figure it out for themselves. I sure learned something though.

To elaborate on the dyno tuning comments a bit ... this is a true story ...

Saturday a guy brought me a bike to tune. After 4 pulls it was at 87hp. Two and a half hours and 30 some pulls and numerous tweaks later it turned the drum at 102hp.

It was the cheapest horsepower the guy ever bought.


WOW, I sure wish you were in WASH!! :cry1

Forgive me for keeping that to myself, I'd rather my competitors have to figure it out for themselves. I sure learned something though.


I totaly understand!

One more questio, or maybe two or three more.
Wich way do you prefer to do it, Mill and Thinner Head gasket or different pistons?
If I mill and tell you how much was taken off, you can tell me wich gasket to use?
If I mill can I still use the same Hardeware I took off the bike when removing the heads? I.E. Head bolts ect...
Also do you think I should or shouldnt install torque cones? Will they help at all?

One more questio, or maybe two or three more.
Wich way do you prefer to do it, Mill and Thinner Head gasket or different pistons?


Well, I much prefer a forged piston, and I really prefer a fitted forged piston. So if I'm going into a motor, yeah, I like to bore and hone and get the cylinder round and straight and the proper clearance. It helps ring seal, makes'em run quieter, and forged pistons are lighter and stronger at a given size.

But, I also understand that people have budget constraints. If your motor is reasonably well sealed up and in good shape and you want to save some money, you can certainly keep what you've got and mill the heads to get the compression up instead. People go that way all the time.

Another alternative is to get a head that's got a 62cc chamber, like a Lightning or '04 XL1200 head. That'll give you 10:1 with your stock flat tops as well. If you go with the '04 head, you'll also get a squish band, bigger valves, and the best ports HD has ever shipped on any of these heads. They *can* be fitted to 91-03 motors, we do it all the time. See here:

http://www.nrhsperformance.com/partsoemheads.shtml

When you really get down to it, though, the best piston & chamber combinations on these motors are (IMO) those with angled squish bands. Angled squish bands squeeze the fuel more directly toward the flame front, and give good compression without a fuel obstructing dome that taxes the octane of the fuel due to the separation that occurs when you ask it to turn a corner. They also unshroud the valves and reduce the shelf that the fuel must go around to enter or exit the chamber.

The only factory setup with a working angled squish band is the Thunderstorm, which is 15 degrees, a good place to be on a street motor. But it's a cast-in squish band, very rough and uneven and doesn't work that good. best bet is to machine in the squish band. We do that all the time. The '04 heads are particularly well suited for machining squish bands.

I would most definitely recommend using .030 head gaskets, and possibly even eliminate the base gasket (I use 3-bond 1104 instead) if the measurements indicate it gets you closer to zero deck height. It's hard to put the material back on the head, to the extent you can get there with gasket changes, that's a good thing. I like the Cometic EST gaskets, only gaskets I've found that'll hold the cylinder pressures of my nitrous bike:

http://www.nrhsperformance.com/partsgaskets.shtml


If I mill and tell you how much was taken off, you can tell me wich gasket to use?


Choose the gaskets to get you the proper head to piston clearance. For example, let's say at TDC your piston is down .010 in the bore, using a .020 base gasket. If you put it together with a .030 head gasket, you'll have .040 of clearance. Alternatively, you can remove the base gaskets and run a .040 head gasket, that'll give you .030 of clearance.

Most builders shoot for zero deck height, meaning the top of the piston is even with the top of the cylinder. They may shorten the cylinder to get there if they need to, for example. Then they set the clearance to the head with the head gasket thickness. But in reality, you can poke it out the top if you want and use a thicker head gasket, it'll work anyway. It does create a little more of a fuel trap at the o.d., though.

On the 1200 hemi head, the chamber is about the same diameter as the bore, but it's not unusual at all for the chamber to be poorly centered and part of it hanging over the bore, this is where you could have a clearance issue. Also, when you mill the head, you make the chamber diameter smaller, causing overhang. So even with the hemi head, pay attention to the piston to head clearance.


If I mill can I still use the same Hardeware I took off the bike when removing the heads? I.E. Head bolts ect...


Perceptive question! Yes, unless you get real crazy, the same hardware will work. I *have* seen head bolts bottom on the studs, but it was an extreme case. Ditto the intake manifold, at reasonable levels of drop, it'll still fit.


Also do you think I should or shouldnt install torque cones? Will they help at all?

Oh, I dunno, I've never found any benefit from them, but I'm not going to stand up and say they absolutely never help any pipe. Here are my thoughts on it:

http://www.nrhsperformance.com/tech_arcones.shtml