[Cliff R]

Good post Paul.

One item not mentions when it comes to LSA is CID and stroke. Piston speed and swept volume play a role here, and so does rod length to a lesser degree.

Most of my comments on cam choices are directed a the long stroke engines and pump gas street engine builds.

For race stuff we try to get all the compression in them we can and go to HUGE cams on tight LSA's. Race engines use high octane fuel and operate in a much narrower rpm range than a street engine, so most are fine with 265-285 @ .050" cams on tight 108-110LSA's.

For a street 455, you are trying to take a somewhat poorly designed engine and improve it's basic operating characteristics. The 455 engine has a long stroke, long rod, and relatively small runner cylinder heads. It's not going to be a strong running high rpm engine by design, and is going to try to throw all it's power at you right off idle, with power ending early in the rpm range.

What happens with small cams and tight LSA's, is that they further enhance the good qualities of the 455, and pull power down it the rpm range and make more of it. When peak VE happens early, you get a really high torque number early and high cylinder pressure to go with it.

This is why we have had quite a few troubled 455's in here to tune that had difficulties managing pump fuel, even though the SCR was at or even under 9.5 to 1. The very worst ones used cams with short seat timing events (Comp XE lobes), and the even better XR276HR cam, all of which produce peak power just past 3000rpm's and a LOT of it. Problem is, the engine mimics one with really high static compression, and they will NOT manage pump fuel with "normal" timing/fuel curves in them.

The XR276HR cam is the worst of the bunch, since it's roller lobes provide excellent cylinder filling without a lot of off seat timing or overlap. The last one I had in here to tune would ping at light, heavy and full throttle, and would take no amount of vacuum advance at all from the distributor. Anything beyond 26 degrees total timing and it POUNDED like sledgehammers in the mid-range. No amount of fuel dumped on it made any difference.

To prove the "too small of a cam" deal I installed HS 1.65 rockers on it, and was immediately rewarded with being about to put a few more degrees power in it without pinging, and I added 8 degrees from the vacuum unit as well. It helped some, but the engine was still octane sensitive and WAY down on power from what I thought it should have been.

The dyno charts put up earlier in this thread show why, the cam is simply too small, too good at cylinder filling, and LSA too tight for the 455 engine, at least one with a little compression in it.

Paul has pointed out that some folks don't care about big power from these engine builds, and will NEVER race them or rev past 5000rpms, so there is a customer base that would be fine with a small cam in a 455 build as long as it's user friendly. Most of the folks that come to me for engine work or tuning are wanting it ALL. Big power, decent idle, good street manners, no running hot/overheating/detonating on pump gas and run like a race car if/when they decide to go to the track. A good percentage of them also prefer or lean towards "stock appearing", so don't want or care to have a lot of aftermarket parts in plain view.

These facts have led us to test and use parts to extract optimum power from pump gas street engine builds, without a lot of bling, or crappy idle qualities and poor street manners. I've known for many years that 455 engines do NOT like small cams in them, especially when you start pumping up the compression in them and increasing head flow.

Anyone reading this should take a close look at the dyno charts, and read about how they came to be. NONE of that work was done here, it was done by a shop that does a lot of high performance engine builds and has their own dyno. They found out, that simply by choosing the wrong cam, they were leaving nearly 90hp on the table and built a relatively "low" compression engine that would NOT manage currently available pump fuel.

At least we have some direct testing to show why I've been dubbed the "Comp XE cam basher" for quite a few years now. My own testing and testimonials don't seem to have been sufficient, so I was glad to see a professional engine builder get some hard data on one of these engines to show what I've been talking about......Cliff