[Cliff R]

Practical application and experience trumps theory every single time.

What isn't taken into consideration is that we are discussing a Pontiac 455 engine. They are not very efficient engines by design, fed by cylinder heads with no more runner volume or cross section than the average small block Chevy head.

They are long stroke and under-square as well. What we have seen for many years now is how poorly they work with relatively small camshafts on tight LSA's. I've worked on and tuned more of these than most who will read this.

It is amazing the amount of power and efficiency that is left on the table putting the wrong cam in one of these engines.

Take a look at the dyno chart below, and you can clearly see what happens when one of the common camshaft choices from Comp cams is used in a 455 build with good flowing iron heads. This engine was also under 9.5 to 1 compression, but pinged so hard when placed in service that it had to be torn back down for rod bearings before it left the dyno.

The cam that we spec'd out for it was a clone of the Old Faithful cam from SD on a 114LSA. It was moved out on a 114LSA due to the low compression ratio, but chosen over the Stump Puller cam to meet the power goals of the owner. I felt the smaller 230/236 SP cam wouldn't have quite made the grade here.

The cam was swapped out with NO OTHER CHANGES, which seldom happens. So the test is valid. The new engine idles nicely making plenty of vacuum for power brakes and smooth off idle with good street manners.

The power increase speaks for itself.

I'd also note that the idle quality with the 224/230/110 HR cam with the much earlier closing intake was noted as "quirky" by the engine builder/dyno operator, and he also mentioned "chop" in the exhaust note at lower rpm's.

In contrast, the much larger cam idles relatively smooth, and very smooth off idle and low rpms. It also produced a LOT more upper mid-range and top end power, and a nice increase in average power, basically making more power at every rpm than the first cam.

It also easily managed pump fuel W/O detonation anyplace, and they were able to crank up the timing and throw fuel at it as well which is what got them into trouble with the first cam as it pinged HARD on they dyno when they tried to turn things up to make decent dyno numbers.......Cliff

[Formulajones]

While I don't disagree with your wide LSA success, and I do like the idea of a smoother idle "sneaky" running engine, there are many top notch builders around the country that also go the opposite direction with success. So I don't really think there is a right or wrong here.

A great example of an under square engine like your 455 examples but with everything exaggerated is the 571 that Tony Bischoff built for my father. A huge 4.750 crank with a relatively small 4.375" bore and smallish Edelbrock round port heads on top. With a 10.84:1 compression. Now with everything we all read here, these long stroke engines want the LSA spread out further. However, Tony custom spec'd a cam with a 110 LSA. I don't doubt Tony's knowledge and his success speaks for itself with several time winner of the EMC's under his belt. This engine made fantastic power given the cylinder head limitation. It never made less than 700 ft lbs. throughout the entire rpm range, and peaked at 726 HP at a low 5700 rpm, and 760 ft lbs at about 4,000 rpm. So we don't even have to spin this engine tight. And it did all that with a very small 950hp 4150 carb on top. You can shift this engine at 5,500 rpm or even 5,000 and it's still a handful. I don't believe he left power on the table with this one, it made exactly what he wanted within the rpm range specified.

I would tend to think if the LSA was spread out on this engine, the torque and HP peaks would move much further up the rpm scale, Up into a range where we really don't want to spin it. Even though Tony built this engine and said it would be good for 7,000 rpm my father said he didn't want to spin it passed 6,000 max. When it peaked at 5700 on the dyno I knew it was an excellent cam choice. This thing pulls like a locomotive with a table top flat torque curve, and simply makes me giggle when you stand on the throttle.
I really think the whole package has to be taken into consideration, intake manifold being used, max rpm restraints, the car and driveline it's going in etc..

Here is a clip of the dyno session, and a clip of the engine idling in the car. It sounds rambunctious for a street car, but that's what he wanted. Believe it or not it actually drives very docile on the street and idles down to 750-ish in gear without any problems, doesn't overheat, it's very quiet to drive and comfortable inside the car with a full exhaust system, and mileage really isn't horrible. He's barely touched 10mpg on a couple of trips already, 400 turbo, continental converter, and right now has 3.73 gears. Dropping that to a 3.50 gear 9" soon. Considering the size of the engine, no overdrive, it's doing pretty damn good. Pat on my back, I setup the carburetor, and Tony loved it on the dyno.

https://youtu.be/5WswK-m-zIA

https://youtu.be/DF1y0F-tJ3w

[tom s]

I used the same xr276 in a 9.5 455 but with completely stock 48 heads.Knowing about the 110 and detonation we set it in straight up instead of the factory instructions.Drove it on the street while I was building my 366 V engine.NO detonation on our CA 91 piss gas.In the process of doing a cam change to the OF on a 112 that I bought from a board member.The 276 made 432,will see how the OF does.Thinking im going to put it in straight up also to hopefully kill off some of the lowend.Tom

[Half-Inch Stud]

Cliff good ping-free info on the SP & OF Rollers. Have not taken my engine past 4500 RPM yet.

Restating:
469 with iron heads per 12.2 ET Sig, with 232/236/110LSA Flat HYD spec kinda like a Stump Puller HYD Roller, (12.2 ET sign spec kinda like an Old Faithful 236/245 112LSA but Flat HYD and poor cold idle and MPG manners).


Will likely NOT make a cam change until after Spring track time, where the Goal is to retain the ping-free performance at 89 Octane like i had. Have a bunch of intakes to T&T eval; eager to eval the stock 4234, an alum dual-plane, and the Dual Q-JETs vs 1050 or Q-JET on a hogged Torker I.

[Formulas]

Observations... Our heads are flow challenged scavaging is a tool to use to negate the lack of flow and tighter lobe centers are reported to increase the scavaging effect but lead to detonation and poor performance with some fast ramp lobe profiles... It's my hypothesis that the latest fast ramp lobe profiles have grown out of usefulness in our engines on tight lobe centers... Fast ramps do what ? They decrease seat to seat timing under and for a given .050 duration this is the area that is largely responsible for scavaging effect so I surmise the reason some profiles don't work when you tighten lobe centers is there is still not enough scavaging being provided due to less duration between seat and .050 and the intake valve gets closed to early overall resulting in poor power and detonation because you have a hot and polluted new charge being squeezed sooner creating a pressure spike for detonation and the lack of a fresh cool oxygen and gasoline charge kills power.... The phrase fast ramp is used alot perhaps more emphasis on lobe profiles instead of ICL and LC should or could be helpful in discussions, to me anything non stock is fast ramp but 1980 fast ramp is not 2017 fast ramp there has been what approx 4 to 5 generations of fast ramps... Hope I got what I was thinking across

[Cliff R]

"While I don't disagree with your wide LSA success, and I do like the idea of a smoother idle "sneaky" running engine, there are many top notch builders around the country that also go the opposite direction with success."

For sure there are folks out there building engines using cams with "tight" LSA's with success.

For sure they are NOT building 455 Pontiac engines with just a tad over 9 to 1 compression and putting Old Faithful size cams in them on tight LSA's and enjoying good idle quality and great street manners.

IF you were to put a 108LSA OF grind into a 9.3CR 455 engine you wouldn't like the idle quality. We woln't even use an OF cam in a 455 build with less than 10 to 1 compression W/O moving it out on a wider LSA, as the idle quality really starts to suffer, been there and done that.

Considering my 455 is 11 to 1 compression and only makes 13.5" vacuum at idle speed with the OF cam on a 112LSA, imagine taking nearly 2 full points of compression out of it. You'd be lucky to make 8" vacuum at 750rpm's, and idle quality would be considerably "rough" as well.......Cliff

[Skip Fix]

"What isn't taken into consideration is that we are discussing a Pontiac 455 engine. They are not very efficient engines by design, fed by cylinder heads with no more runner volume or cross section than the average small block Chevy head."

And why a single pattern or even reverse split-or at least more ratio on the intakes might make sense also as generally they are "Intake deficient" with decent exhaust flow.

[pastry_chef]

Originally Posted by Cliff R

The cam that we spec'd out for it was a clone of the Old Faithful cam from SD on a 114LSA. It was moved out on a 114LSA due to the low compression ratio, but chosen over the Stump Puller cam to meet the power goals of the owner. I felt the smaller 230/236 SP cam wouldn't have quite made the grade here.

The cam was swapped out with NO OTHER CHANGES, which seldom happens. So the test is valid. The new engine idles nicely making plenty of vacuum for power brakes and smooth off idle with good street manners.

The power increase speaks for itself.

I'd also note that the idle quality with the 224/230/110 HR cam with the much earlier closing intake was noted as "quirky" by the engine builder/dyno operator, and he also mentioned "chop" in the exhaust note at lower rpm's.

In contrast, the much larger cam idles relatively smooth, and very smooth off idle and low rpms. It also produced a LOT more upper mid-range and top end power, and a nice increase in average power, basically making more power at every rpm than the first cam.

On the power output.

The Comp 276 hyd roller has 145 duration @ .200.
The OF cam 160 at .200

How do you think this is an LSA test?

Comparing to Comp's dual energy hyd FLAT tappet-
Lobe 5002 , duration's are
283 adv
233 .050
146 .200

NOTE the flat tappet has MORE duration at .200 than the small roller in your chart! LMAO.

A 455 at that RPM needs more than even the OF is giving it BTW.
Especially when using a factory d-port head. At 5500 RPM piston demand exceeds 300 CFM.

---------------------

Interesting comment that closing an intake valve EARLIER will degrade idle??
Twilight zone stuff here.

Sorry something else was wrong.
At overlap TDC the OF had both valves open significantly longer than the 276HR.

[pastry_chef]

Originally Posted by slowbird

So what is considered low compression and what would be a cam too big for that compression?
I ran a cam that was 276-286 @ .050 in an engine that had a hair under 11:1 compression. It seemed to work pretty good.

Depends on the minimum RPM of the power-band.

SS racers will run huge cams on low compression (below 10) and make more power at the RPM they run (5500 plus).

[Cliff R]

Instead of your sarcastic and completely full of negative vibe/jerk-off answers how about:

Nice power improvement from a much better cam selection. For sure the big 455 with very well ported heads needed more cam than the XR276HR, even though it is quite popular and the Tech's at Comp will quickly steer anyone who calls there in that direction.

It could actually use even more cam looking at the dyno runs, but for making nearly 90 MORE peak HP and 45 MORE ft lbs peak torque combined with nearly 100ft lbs more torque at 5000rpms certainly shows that the relatively "low" compression 455 certainly responded very well to the larger cam on a 114LSA.

Your useless sarcastic and non-informative answers actually have me LMAF twice as hard as you are for sure. Talk about a guy who "can't see the forest for the trees", your first in line for that award for sure!......Cliff

[pastry_chef]

403 cubic inches. 4 inch stroke
10.3 compression.
98 LSA installed at 92 intake centerline. For real!!

TONS of TQ and HP, even down at 2500 RPM

[tom s]

Not a Pontiac

[pastry_chef]

Originally Posted by tom s

Not a Pontiac

Irrelevant
Which is why builders like BES and Kaase dominate!

[slowbird]

Originally Posted by tom s

Not a Pontiac

An engine is an engine, nothing special about a Pontiac

[tom s]

I call BS on the HP at 5200 and the 10.2 CR unless boosted or on the bottle and if so who gives a crap.Tom

[tom s]

Or a EMC dyno mule.Tom

[pastry_chef]

Originally Posted by tom s

I call BS on the HP at 5200 and the 10.2 CR unless boosted or on the bottle and if so who gives a crap.Tom

No, pure N/A engine. Legit numbers.
That is all I ever post about.

I never, ever BS.

The point is narrow LSA does necessarily kill low end, or efficiency in Cliff's words.
To really learn you should read from other forums, there is LOTS and lots to absorb.

We know you like smooth idle and 11s is fast enough for you.
That is disconnected from what LSA is best for maximum performance.

[STEELCITYFIREBIRD]

General Classic PONTIAC TECH > Pontiac - Street Forum?

[Will]

This thread certainly drifted off the track and into the weeds... LOL

[Formulajones]

I think we all knew it would go that direction, it's a camshaft thread after all, and people here can't get past their smooth idle and vacuum issues with an open mind and see a bigger picture. But that is to be expected here. Who said there was anything wrong with a choppy idle anyway? Just because we are talking about street engines doesn't mean we all have to act like they should idle like a Honda. Would be a pretty boring hobby that way.

I agree, Pontiacs aren't special in this respect so any example when it comes to LSA's are worth noting. The example I gave is a Pontiac engine that is on the extreme side of undersquare, and it doesn't have the peaky, early, short torque curve that is so often associated here with tight LSA's. It's table top flat. Another Pontiac example I gave was a 455 from Kauffman, and even he spec'd a tighter 110 LSA cam. Someone that I know Cliff and others are affiliated and very familiar with here. That engine made a nice flat 600 ft lbs. torque curve as well that didn't need to be spun tight, my father shifted that engine at 56-5700 and ran bottom 11's with it.

There is so much more to an engines characteristics and how a camshaft is going to work than just LSA. We have to remember that the OEM uses wider LSA for other more obvious reasons. Doesn't make it right or wrong.

What I took away from the main point is that the 2802 is on the small side for a 455 and only a handful are using it. The graphs that Dennis posted were interesting, I haven't seen them compared that way before.

For me personally, I rarely use an off the shelf cam in an engine build. I would rather have someone like Paul, or Tony, who have competed in the EMS who knows what it takes to make power custom spec a cam for me to squeak the most out of the combo. What ever LSA they come up with I trust it's in good hands, and I haven't been steered wrong yet. Those people are much smarter than me. If you give a great engine builder good information, you'll get good results.