Rigid_EVO 10.5:1 compression

[johndw2015]

Morning gents,
asking around for help on my build, currently have a fresh 1200s bottom end with wiseco +.010 forged pistons and need some advice on cams and heads. Was really hoping to just slap my stock heads back on with maybe a set of N4s if needed but im hearing that it may be too much compression for stock internals? I only got this set of pistons since the price was right and my cylinders needed a fresh bore due to the bottom end bearing failure leaving some marks on the jug wall, so I assuming I could just bolt these in and go.

Having lots of guys tell me I need headwork and cams with crazy lift to get the power out of the pistons, but I'm honestly fine with the power it made before, just want maximum reliability out of it by the times its back together. Question is, will I be fine to bolt it back up with regular heads and cams? or is the compression ratio really need more parts along with it (in regards to reliability, I dont care about gaining power as long as i dont loose any.)
Thanks for any insight

[rejeanprimeau]

N4 and 1200 heads are a go. 883 heads need dished piston or material remove from the heads.

[aswracing]

Originally Posted by johndw2015

Morning gents,
asking around for help on my build, currently have a fresh 1200s bottom end with wiseco +.010 forged pistons and need some advice on cams and heads. Was really hoping to just slap my stock heads back on with maybe a set of N4s if needed but im hearing that it may be too much compression for stock internals? I only got this set of pistons since the price was right and my cylinders needed a fresh bore due to the bottom end bearing failure leaving some marks on the jug wall, so I assuming I could just bolt these in and go.

Having lots of guys tell me I need headwork and cams with crazy lift to get the power out of the pistons, but I'm honestly fine with the power it made before, just want maximum reliability out of it by the times its back together. Question is, will I be fine to bolt it back up with regular heads and cams? or is the compression ratio really need more parts along with it (in regards to reliability, I dont care about gaining power as long as i dont loose any.)
Thanks for any insight

What heads do you have? XL1200? Of what year?
What cams do you have?
Which Wiseco pistons specifically do you have?
This is a 1998?

[johndw2015]

1998, 1200s heads with the double plugs. Wiseco K1686, should be the +10.7 cc with the reverse dome, bored 10 over. I havent done any headwork or purchased a cam yet due to not really being sure what direction I should go in. A close friend is currently pointing me towards a Tman performance 625 cam with a valve job as a bare bones starter. I'm very hesitant to do work to these stock heads because not only is this rebuild bleeding my wallet dry, but I also would really prefer to hunt down some thunderstorm heads and build those up instead. (I also have a 98 S1W so I know that its a whole new level of power)

[aswracing]

Originally Posted by johndw2015

1998, 1200s heads with the double plugs. Wiseco K1686, should be the +10.7 cc with the reverse dome, bored 10 over. I havent done any headwork or purchased a cam yet due to not really being sure what direction I should go in. A close friend is currently pointing me towards a Tman performance 625 cam with a valve job as a bare bones starter. I'm very hesitant to do work to these stock heads because not only is this rebuild bleeding my wallet dry, but I also would really prefer to hunt down some thunderstorm heads and build those up instead. (I also have a 98 S1W so I know that its a whole new level of power)

OK well keep in mind that your 1200S heads have 62cc chambers, where standard XL1200 hemi heads of that generation have 67cc chambers. So you're going to get more compression out of those pistons than what they claim for them, since I'm sure their claim is based on hemi heads. But assuming their dome clears the 10 degree squish shelves in your chambers (check it carefully), they should work.

To manage the compression, though, you need to change the cams, because your stock "W" cams have a very early 25 degree intake close point. The resultant compression will be very high and it won't be a pump gas friendly combination. The N4's would be an excellent choice, their 46 degree IVC will bleed the compression down to a manageable level. If you're unfamiliar with how to run the numbers on all this, watch this video: http://www.hammerperf.com/ttvideos.s...mpressionratio

The T-man 625 grind is a long way from being a bolt-in. If you go that route, you'll need new springs, and probably lower profile guides as well. You'll also be doing a bunch of carving in the cam box to gain clearance, and really those should be run with roller rockers too, because of the side loading you get with that much lift. And honestly, with the stock 1.715/1.480 valve sizes, the heads are all done before they get to .500 lift anyway. In other words, opening them farther does not increase the flow. That set of cams is designed for well prepared, big valve heads.

[johndw2015]

I'm not afraid to lie I completely forgot about the chambers being 62 instead of 67 and am going to have to keep that in mind going forward. I was playing with the compression calculator tool but I'll have to go over it again, I think I was trying to get it around 9.5 corrected since I usually run 91 octane.
Regarding the Tmans, I was recommended them as I was hoping to swap to thunderstorm heads, but finding a set doesn't seem to be very easy.

I suppose the big question would be would it be easier to just go back to flat tops? I see that hammer offers services to get my current heads flowing a bit better but if they can't handle any lift of .500 its really just reaffirming my hesitation to not really do anything to them.

[Tomcatt]

Originally Posted by johndw2015

...I was hoping to swap to thunderstorm heads, but finding a set doesn't seem to be very easy...

I suppose the big question would be would it be easier to just go back to flat tops? I see that hammer offers services to get my current heads flowing a bit better but if they can't handle any lift of .500 its really just reaffirming my hesitation to not really do anything to them.

If you plan on keeping this bike and are considering a head change go with the later bath tub chamber heads. I believe the '04 - '06 heads are pretty much a bolt on. Getting away from the hemi chambers is a good thing as is getting away from your dual plug set-up that there are no new OE parts for...

Info about heads here: http://www.hammerperf.com/ttxlheads.shtml including what parts are needed to install '04 - '06 heads. You'll want flat top pistons to go with the bath tub heads.

[johndw2015]

Regardless a flat top piston is going to be the way to go no matter if I use stock heads of upgrade to XB heads from what im reading then

[aswracing]

Originally Posted by johndw2015

I'm not afraid to lie I completely forgot about the chambers being 62 instead of 67 and am going to have to keep that in mind going forward. I was playing with the compression calculator tool but I'll have to go over it again, I think I was trying to get it around 9.5 corrected since I usually run 91 octane.
Regarding the Tmans, I was recommended them as I was hoping to swap to thunderstorm heads, but finding a set doesn't seem to be very easy.

I suppose the big question would be would it be easier to just go back to flat tops? I see that hammer offers services to get my current heads flowing a bit better but if they can't handle any lift of .500 its really just reaffirming my hesitation to not really do anything to them.

You don't want Thunderstorms. They were a great head in their day, but their day passed a long time ago. Some people just haven't got the memo yet. The XB head, which came out in 2003, and the XL version of the XB head, which came out in 2004, are far superior.

Actual XB heads are discontinued and have gone unobtanium. But the XL version continues to be offered, and at an incredible bargain:



That price tag is actually less than a set of stock heads, by the time you buy the stock hardware to outfit them (the stock heads are only sold bare). You might even get the SE heads cheaper going through one of the online discount dealers. Go over to surdyke.com and do a search on 16500164.

You can put these heads over your stock 1200 flat tops and get a 10:1 compression ratio. Or you can put them over a flat top 1275 kit and you'll get 10.5:1. 1275 kits come in the matching big fin, black highlighted style, and the combination of big fin heads and big fin cylinders not only cools better, but it gives the motor a bigger, more filled-out look, that guys really like. And it maintains the factory black highlighted look, unlike Thunderstorms.

But it's not just the big fins that make these later heads better than Thunderstorms. Although valves sizes are the same as Thunderstorms, the valve stems are smaller and that makes the valves lighter, and the spring pack can handle more cam. The compact bath tub chambers have large squish bands on each side that make for a really turbulent chamber. Chamber turbulence reduces detonation, allowing you to run more compression. The ports are improved, too, with a lower roof and a higher floor, both of which make for a more laminar flow. Here, let me show one example:



This is an XL1200 hemi head, which all 1200's (except the S) came with from 1988-2003. Your heads have the same ports and valve sizes as the hemi heads, only your chambers are different.

Look down inside the ports, near the stamped numbers. See that sharp transition there? The air basically hits a wall and has to turn really sharp.

Now look at the Thunderstorm:



Much bigger valves obviously, but look again near the stamped numbers. It's not nearly as sharp of a transition. They added material there to smooth the transition.

Also note the squish area on each side of the chamber. All Thunderstorms that shipped from HD used a piston with a small dome that roughly matches that squish band. But the squish band is just cast-in, it's not machined, and it's all over the place in terms of the squish clearance. It really has to be machined to get a nice, even, tight squish clearance. In stock form it's pretty useless.

Your stock 1200S heads have a similar cast-in squish band. But since they were paired with flat tops from the factory, it's even more useless.

By the way, Thunderstorms all came with the same crappy stock springs and guides as your stock 1200S "Lightning" heads.

Now look at an XB head:



Same big valve diameters as the Thunderstorms, but note the smaller hole through the guide for the 7mm stems (TS and all stock heads of that generation used 5/16 stems). Also note the big flat squish bands on each side of the chamber. This gives great turbulence with flat tops. The chambers are 62cc, but that's where the similarity to your Lightning heads ends.

The main thing is that transition in the ports, down by the stamped numbers. Notice how it's basically completely gone. They added even more material, as compared to the Thunderstorms.

Not shown is that the Thunderstorm raised the floor of the port, what we call the "short side", and the XB raised it even more. Basically what they did at each generation was to make the long side (the roof) shorter and the short side (the floor) longer. That's a good thing, because it's the difference in length between the short side and the long side that makes the port turbulent (port turbulence is a bad thing that reduces flow, chamber turbulence is a good thing that reduces detonation).

These improvements actually added material to the ports in key places. It's not like you can just port a set of hemi heads or a set of Lightning heads and get these same improvements, because porting only removes material, it doesn't add it.

Sorry for the long winded explanation. My point is that later heads have better castings that give some real advantages over either your Lightning heads or the Thunderstorm heads. And with a set of late model heads out there at $909 with all the hardware, well, it's a bargain and a big improvement. Even with their crap porting job,those heads are a bargain.

What we advise to a lot of customers with your generation of 1200 is to get these heads as the first step of a hop-up process. That alone will make the biggest difference. Then down the line get a set of our 560 cams, which are basically a perfect match for these heads, although the 10:1 compression ratio is a bit soft. Then get a flat top big fin 1275 kit, which will bump the compression up to 10.5:1 which is perfect for the 560 cams.

You can, if you want, get the SE heads machined for the second plug. Or you can just go to single plugs. The dual plugs don't add any performance on a motor with good chamber turbulence and no obstructing dome (and I've tested it extensively). Hell, I have dual plug STD heads on my S1W, and I don't even have the second set of plugs hooked up. It makes 122hp regardless of whether those plugs are used or not.

You will need a new ignition, because these new heads with their turbulent chambers will have a much faster burn. You need a correspondingly softer curve to match.

[johndw2015]

I for sure appreciate the long winded explanation, its just more information to make my decisions on really. It might seem silly but would the late model SE heads be a good fit for my current pistons? I originally got them just since they where on sale and seemed to fit, but I honestly wouldve gotten flat tops at msrp if I knew that I was gonna get thrown down the head work rabbit hole. If I was chasing more power I feel like id be more inclined to drop the cash on the heads right away, but im more concerned about engine longetivity with the newer ones as opposed to continuing to run my current set.