Good info, makes me almost ready to buy a PCV w/AT

 

Honestly, i wish the PCV was out when i got my PCiii, might not have got the AT at that time, but it would have been nice to be able to add it later on.

 

I've seen quite a few dyno charts here that reveal that TW26's in stock TC96's (with Stage 1 gear) lose a bit on the low-end. I'm referring to the low-end, like 2000-2500 RPM's. For some this is irrelevant since they rarely venture into those RPM's, but I do, and I want the pull in that range when I want it. If you look at the specs on the 204's and 26's you'll see that the intake close is much later, and that is probably the main ingredient in making 255's such torque monsters on the low-end and midrange.

I've always been careful not to suggest that the 255's are "better" than anything else, as the TQ curve of any cam may be good for one rider and bad for another. It's just that I don't think you can beat the 255's for low-end and midrange TQ with stock CR, but as I said you pay for it in the top-end. The 26's will undoubtedly produce more peak HP, and in a *****-to-the-wall drag race will likely pull a like-equipped bike with 255's. But for the ability to pass a truck with a fully loaded touring bike up a hill without downshifting, the 255's may be unbeatable.

I researched cams for about two years and talked to both Bob Wood and Andrews about their offerings. When I described what I was looking for, which was an increase in low-end and midrange TQ without moving the TQ curve to the right at the same time, Andrews said "We don't have a cam that will do what you want without a CR increase." He told me the 21's would make little difference over a stock TC96 and the 26's would definitely move the TQ curve to the right at the expense of the low-end. I thanked him and moved on. Bob Wood was high on the 6-6 with +4° gear, but despite the hype I never could find a TQ curve that produced what I was looking for except with bikes that had other mods.

After deciding on the 255's based on some dyno charts I had seen in stock TC96's, I did the job and the result was what I expected. That's all I asked for.

What takes the issue into another realm is CR, as when you start increasing CR the low-end weaknesses of most cams will start to disappear, how much depending on the grind. My statements were predicated on cams installed in a stock engine (9.2:1 CR and the usual Stage 1 components).

You're right that specs aren't the whole story, but I'm referring solely to bikes with stock CR. The 25° intake close and relatively mild duration result in a high CCP, and that is what makes torque. I could produce some dyno charts that show what I'm referring to, but I can't vouch for how good the tuner is with any of these builds, so I think charts may be irrelevant for comparing two different cams unless all other factors are equal, including an optimum tune for the setup.

 

Iclick, you are still missing my point. You keep saying the TW26's "lose" torque in the low-end. When you say "lose" do you mean they make less low-end torque than some other cams (e.g., your 255's) or are you saying they make less low-end torque than stock cams?From my real-world experience, they do NOT "lose" torque in the low-end!

What I am trying to point out is, when compared to a stock cam's torque curve the TW26's produce more low-end torque, not less. However I agree, some cams may produce more torque than the TW26's in the low-end on a given configuration (maybe the 255’s, maybe not). As I said in my previous post, you need to compare identical configurations to make that claim and to my knowledge, that hasn’t been done – not even by the cam manufacturers.

Now, if you have personally installed and tested both the 255’s and the TW26’s on the same bike, I apologize for being out of line.

 

Hmm. Talked to a buddy the other day and he had put TW 26's in stock 96 and had it dynoed with PC III. I need to run by and get a copy of the sheet. As for me the SE 204's are just right but i have more inches and higher compression.

 

If he had it tuned by the same guy in both configurations (before and after) that should be a good comparison, assuming no other changes were made.

 

I think a cam set like the 26's would cause a loss of TQ in the low-end compared to stock and 255's, in theory, not necessarily other cams. The 26's are fairly mild as cams go and are rightfully very popular in mild builds, so I think they would maintain the low-end power fairly well with stock CR. I think they would be a good choice for a bike with stock CR, but I think at the very low RPM's the power would not be as great as stock. I don't see how it could with a later intake close (35° for the 26's vs. 30° for stock) and a longer duration. However, if you increase CR all bets are off.

Like I mentioned before, I called Andrews and asked them about a cam recommendation to move my TQ curve up at least 5 ft./lbs. in the low-end and midrange but not shift it to the right, as well as no loss in the extreme low-end and no other engine mods, and was told "We don't have a cam that will do that." He said the 21's would make little difference over stock and the 26's would shift the curve to the right at the expense of some low-end TQ. The 54's might have been an option had I been willing to change springs, but I wanted a bolt-in for an otherwise stock engine (with Stage 1 additions).

That's what took me so long to make a decision, as few had meaningful charts to go by. Bob Wood has some, but most of those are by third-parties and often other mods are not listed, so you don't know what to compare to what.

I think you're right that the only way to find out is a direct comparison, a like-equipped bike that has been optimally tuned for each cam set. BTW, you're not out of line at all here, and truthfully all I can go by is Andrews' statements, theory, and a few questionable dyno charts. Charts will vary according to the tune, weather conditions, and other factors--so they are little more than fodder for discussion, IMO. I do like to look at them, though .

Correct me if I'm wrong, but compared to stock if a cam set has a later intake close and longer duration it will produce less TQ on the low-end. If you're not producing the CCP, which is reduced with a later intake close, I can't see how TQ can be equal or higher without increasing compression. There is no doubt that the midrange and high-end will be much improved, but I'm talking about the low-end, in this case 1800-2500. This is a very usable range for me, as I typically cruise there and want to be able to nail it and have the power available without downshifting.