So I decided to re-read Marcelino's camshaft mod. It had been a while...in fact I probably hadn't read it since I first found this site. I think I noticed a change to the thread, it seems updated to say that the mod won't do anything for the 351, and may even hurt it's performance. But was surprised at how easy it seems (except for the KACR removal) and was seriously impressed with the dyno numbers for the camshaft mod.
So...anyone still here that has done the camshaft mod? Did you go 351 later?
Which way to go?
My cheap side says do the mod, but I can't stop hearing the saying,"There's no replacement for displacement."
I'll be due for a valve check soon and it seems the perfect opportunity...to go with either. Although I'm leaning towards free, for now.
25 ponies would be nice.
TIA
And now I truly get the "he who shall not be named" reference.

 

Bore kit all the way, then a set of web cams afterwards. Cam mod seems kind of wonky and i would be afraid to mess something up and grenade the motor.

Just my .02 and its worth what you paid for it.

 

Uh, I can't remember the cam mod post fully but there is no way you get 7 hp from this mod.

25 total hp with a big bore = yes

25 total hp with a cam mod = not a chance in hell

Don't even waste your time, just do the big bore.

 

Having done both the cam mod and a 331 I would say the big bore is the way to go if funds allow. I did it as an interim mod and with full exhaust and intake mods it gave the bike a more "Dirt Bike" power band. It would surely smoke a modded bike that did not have the cam mod. I enjoyed the Cam Mod, it is proven that it does not work for bikes with the Big bore so I put the intake cam back to stock when doing the BB. I will get around to retiming the ACR next valve check and putting ex. cam to stock. The BB is great, I did it myself and if you cannot do the cam mod and are worrying about grenading your engine, do not even attempt to do the BB yourself. Do not fear the CAM MOD! It works.... edit - to be fully effective re jetting is required with the cam mod. i.e. bigger main.. Give it a try if you have it apart anyway. The ACR removal is easy, install not so bad with a large vise..KansasKLX method if I recall.

 

I guess i better go back in time and tell myself to not install the bore kit myself then. When should i expect my engine to blow ?

Sorry but swapping sprockets and messing with timing that has no baseline in any technical bulletin or service manual gives me bad vibes when the implications of not getting it just right are severe, not to mention the fact that i was already planning a big bore kit anyway why waste my time ?

 

Well the mod is free and simple, after taking it all apart, the mod itself (not including ACR) probably takes 15 minutes at most, when you do the big bore kit after you saved up the cash, just put the bolts back since you have the cams out anyway

 

how long does it take to do the ACR ? What if you don't have the tools sitting around to press the thing off ?

To each his own. I read through the threads and saw the reports on the results and decided to save myself the time and effort.

 

I don't know I haven't done it, but I've been in similar situations, I just used a brass dowel pin and a rubber mallet.

 

The cam mod has been an interesting issue since its inception. I feel it's much like the "adjustable" cam gear on the front of a small block Chevy engine that have advancing or retarding mounting holes to achieve a desired effect on performance...usually in concert with other mods. While there is the possibility of a small increase in power when paired with the appropriate mods to take advantage of the adjusted cam timing, it's usually just credited with moving the powerband within the existing range of power. When advancing cam timing on most engines, the power comes on at an earlier rpm point if the rest of the engine setup is capable of responding to that. Many engines will respond to advanced cam timing with quicker response. The downside can be that the powerband can also run out of steam quicker, and that is to say that the quicker performance response also signs off quicker as a result. This can be good or bad depending on the desired result. I think this may be the negative aspect of what David R. experienced in his results that caused him to go back to the stock setting. Performance cams are performance cams because they tend to provide the quicker response, but they can also maintain that response for a longer duration in the rpm range. Of course there is also the benefit of higher lift and such, all depending on what you want an engine to produce.

I've gotten into some spirited discussions with Marcelino and others about this, and I still admit to not being totally convinced that there is a true horsepower gain of any consequence, while there may indeed be a quicker response in the powerband. That can still be a good thing as long as the improved response doesn't bring an unpleasant signoff in power as you go higher in the rpm range. Obtaining an increase in quicker response and maintaining good or improved power through the range is usually what performance cams do. It's hard to receive a totally free lunch with just a cam timing tweak. Degreeing the stock cams in a performance effort can do this to a small degree, but you're really just "making perfect" the already designed and intended characteristics of the stock cams...at least in most cases.

I'm not saying that Marcelino's mod doesn't have a performance benefit. But until I see the same bike, equipped the same way, on the same dyno, in a true side-by-side, before-and-after comparsion, I'll continue to be su****ious of any noticeable horsepower gain. I'm also speculating that the kind of response you might feel with this cam mod can be achieved or exceeded with a pumper carb, and the larger pumper carb would provide continued and increased power as you go higher in the rpm band. The larger, flat-slide design of the pumper is superior in its airflow potential to the OEM CV carb. There would be less of a possible "signoff" in power.

 

I agree, however regarding horsepower increase. Perhaps he meant in the specific powerband. If you have cams timed to make max hp at 13000 rpm as has been discussed, and the engine never makes it there, you won't see the 25 horsepower, now if you move that powerband down to 8k rpm, you can take full benefit of the camshaft grind. So it IS possible to gain some horsepower in that range (obviously dropping off after 8k). But to what extent I guess we won't know without extensive testing could be 25hp could only be 21 (more likely). if I had the time and money I would love to experiment with this on multiple bikes