I am not an engine builder so how do I check chamber volume ??

 

Removing the heads was not part of yoru original plan and while pulling them and sending them out for freshening up or a basic street port ala BigBoyz would be a good idea, you can achieve almost the same goal without pulling the heads; seat of the pants but better than just throwing cams at the engine.

If the 103" upgrade was done by a previous owner, there is a good chance cams were part of the upgrade; you need to know that.

You can pull a compression test on your engine and then use the BigBoyz compression calculator to back into a profile for you engine. You know the bore/stroke, you know the chamber volume should be 85c-86cc, if your engine is typical, deck height will be .003"-.007" so use .005", you know the cranking compression, you can assume OEM cans have been used, you can assume the piston dome volume is -1.5 and you can assume the OEM head gasket thickness of .045". Plug those numbers into the calculator and see how the calculated cranking compression compares with the actual that you measured. If they are way off, you know that cams were installed, head gasket thickness was changed, or both and the perhaps chamber are larger than 85cc-86cc. Like I said, seat of the pants but a place to start knowing more about the engine than you know now. Another benefit of the compression test is that it will give you a picture of the condition of your top end and you can retain the data for future reference.

The calculated values would look something like the attachment. The attachment is just an example, so don't anybody get their panties in a wad about the assumed data inputs.

 

Thanx I will do a compression ck and get back to you thank you Gary

 

I put SE255's in my stock 103. That and the TTS tuner really woke the bike up. Now it runs 2-up like it used to run with just me riding it...huge difference. And now riding by myself is that much better. Thanks for listening to likes of me.

 

Are there any items on a 2007 that need to be inspected when doing this cam job? Just a question to provoke thought, because some year models have problems inherent due to cutting production costs at the assemble line.

 

What are cams???? LOL!!!

 

+1 on fuelmoto. Check out the cams page for TW555 or TW777 and scroll down to see
the dyno sheets that they have posted.
Looks like each of those cams is still pretty good for torque on the left and there is a SE 255 cam comparison with a 96" and tw555 which can give you an idea of the difference there between those two cams.

Compression releases would be a good idea IMO.

Cheers,

Mark

 

Nothing stands out for that year. Just replace the inner cam bearings with the Timkin's and insert new cams. I do not believe this model year has any cam chain tensioner issues, but naturally they should be inspected.

 

I finally got around to checking the compression here are my # rear cylinder is @ 180 front is @ 160 20 lb diff ????

 

I want more torque where I ride 2400-3500 so I'm going with the Andrews 21H in my 96" and I think you'll have great results in your 103" and here's why:

WHAT MATTERS

The rpm at which your Big Twin starts to make useful power is determined by when the intake valves close. The later they close, the higher that rpm will be. I have said this many times and for a long time now.

I recommend cams that close the intake valves at or near 30 degrees after bottom dead center for any purpose short of racing. Useful responsive power will start at around 2,400 rpm with this timing. You can read more on this subject at Mikuni's website in an article I wrote 10 years ago (www.mikuni.com/fs-performance_guide.html).

How well the cylinders fill depends on the effective intake-valve opening time. Harley's lazy stock cams open the intake valve slowly and as C.R. Axtel put it, the air is left chasing the piston. They should open quickly. My rule of thumb is that Big Twin valves need to be open 0.400-inch by the time the piston is at its maximum speed, which occurs at 76 degrees after top-dead center. This sort of specification does not appear on any cam chart I know of.

What with all the other numbers on a cam specification chart, one of the most important is ignored. Take a look at the Andrews Twin Cam page. (http://www.andrewsproducts.com/PDF_f...ainCam0708.pdf). Most of the numbers are not very useful nor is the advice. There is hope, though.

BOTTOM LINE

All the TC96 cams you'll find on the Andrews website page come very close to my recommendations of .400-inch lift by 76 degrees. However, only the 21H also closes the intake valves at 30 degrees after bottom dead-center. This is the cam I would use for almost any purpose. It will begin to increase power over the stock cam by 2,200 rpm and make a much larger difference by 4,000.

In comparison, the 26H doesn't begin to work really well until 600 rpm later at 3,000. The 26H may do a little better at 5,500, but what do we care about that? Why give away 600 rpm at the bottom for nothing useful on top? You spend most of your riding time below 3,000, so buy the cam that gives the best performance where you ride.

You can find cams equivalent to the 21H for the other Big Twins on the Andrews website. The first of this type was the EV13 for the EVO. The picture featured in the article is of the EV13 prototype I keep on a shelf in my garage. The EV13 cam prototype was the first cam equivalent to Joe's current cam of choice, the 21H.



TECH TIP:
For any purpose short of racing, cams should close their intake valves at or near 30 degrees after bottom dead center. Useful, responsive power will start at around 2,400 rpm.

---Joe Minton