[Gach]

Originally Posted by Jay S

The timing of the intake valve closing, and the exhaust valve opening are what determines the power band. The Wider LSA closes the intake later, increasing the time the engine has to pull air/fuel into the cylinder, providing more RPMs. The wider LSA usually opens the exhaust valve sooner also, keeping the air/fuel mix from getting diluted by the exhaust gases, and has more time to escape the cylinder for more power at higher RPMs.

Taking a cam and narrowing up the lobe separation narrows the powerband from the earlier intake closing , and later exhaust opening, but now has more overlap for cylinder scavenging. The increase scavenging causes reversion and dilution at the low rpms, moving the power band higher from low idle. But the intake closing and exhaust opening are doing the opposite, lowering the power band. In effect that is narrowing up the power band, and at the same time making more HP&TQ in a narrower power band because the increase in scavenging is making the engine more efficient in the now narrower power band.

perfect… could’ve have said it better

[Cliff R]

By "narrowing" up the power curve you will also see a higher peak torque number at peak VE, which occurring earlier in the RPM range (when the events are happening fewer times per second /more effective cylinder filling) RAISES cylinder pressure and INCREASES octane requirements.

This is where folks with these relatively "low:" compression engines get into issues with detonation on pump gas. Since I tune for a living and get hired to sort out these issues I get to see a LOT of engine combo's that were built at or under the proverbial "brick wall" of 9.5 to 1 compression ratio "for pump gas", but they are timing and octane sensitive and ping with "normal" timing/fuel curves, even higher octane 92-93 octane pump gas.

Almost every troubled V-8 engine I've had in here with such issues was using a relatively "small" camshaft on a "tight" LSA. I've tried to educate readers about this over the years to help them avoid these issues with their new engine builds. I'd also mention that since I get to work with these vehicles without exception using a "small:" cam on a "tight" LSA in a 455 build produces a "turd" right to start with, even though everyone involved was hoping to "increase low end torque" and didn't care much about how the engine did at higher RPM's.......FWIW........

[Cliff R]

"Cliff, please don't miss quote me, I didn't say........."

Your weren't "miss-quoted" so relax. IF and WHEN I decide to "quote" you it will by noted by ".........." on both ends of the comment....FWIW

My comments were general and directed at folks who think that tiny cams in big CID engines "build more low end torque". In actual use they don't effective fill the cylinders over a broad RPM right to start with, AND they leave a LOT of power on the table.

This LSA comment is one of the most miss-understood topics on the Forums, and not just this one.

Since I'm on the user end of this deal I'll tell everyone reading this that absolutely and for sure the BIGGEST complaints I get is from folks who have just put their new engine build in use and are having ALL sorts of issues with it at idle and low RPM's and every single time they have installed a cam with "tight" LSA. I guess they just don't get the fact that IF you reduce engine vacuum with all that overlap that you are going to have to INCREASE initial timing and ADD more fuel at idle to make it happy.

Not complaining at all as I've made a nice living and have never wanted for work because folks make poor decisions with these things..........

[ekancler]

Originally Posted by Cliff R

Almost every troubled V-8 engine I've had in here with such issues was using a relatively "small" camshaft on a "tight" LSA. I've tried to educate readers about this over the years to help them avoid these issues with their new engine builds. I'd also mention that since I get to work with these vehicles without exception using a "small:" cam on a "tight" LSA in a 455 build produces a "turd" right to start with, even though everyone involved was hoping to "increase low end torque" and didn't care much about how the engine did at higher RPM's.......FWIW........

Here's a question, and it's meant to be at least somewhat provocative: What if one man's turd is another man's gold nugget?

I'm not suggesting that running a small camshaft on a tight Lsa fits that bill. Just that if someone wants to make good power, yet focus *primarily* on a really smooth running, efficient build, that there must be ways to do that really well. Maybe it's a "turd" at the track relative to faster cars in the same class, but exactly what the owner wants.

For the most part, folks *seem* to be interested in making either all-out power or "streetable" power in the sense that power is always the primary goal. And they seek a level of efficiency, vacuum, idle, etc. that they can "live with." But what about building these engines to a reverse standard?

Yeah, I could go buy a Prius. That's not the point. To put specifics to this, I've got a 1977 W72 T/A that I'm building with my daughter. I want it to be drivable, fun, and - as far as these engines go - efficient. If it ran low 14s, felt responsive off the line, and pulled to 5000RPM, I'd be thrilled. I love the smell of gasoline and a lopey idle, but... I'm wiling to bet she and her friends won't.

This is the street section, not the race section, so it seems appropriate to put this out there. I know it's a bit unorthodox from a gear-head perspective. I'm not looking to do a lazy, cheap build either. "Just drop in an 066 cam and call it good" isn't what I'm after. I'm gonna guess many folks aren't interested in a build like this. But I bet at least a few of you are.

Maybe she takes it to the strip one day. And an old gear head says, "For as smooth and tame as that car sounds, it sure runs fast." That'd be about right.

[Ram Air IV Jack]

Originally Posted by Cliff R

"Cliff, please don't miss quote me, I didn't say........."

Your weren't "miss-quoted" so relax. IF and WHEN I decide to "quote" you it will by noted by ".........." on both ends of the comment....FWIW

My comments were general and directed at folks who think that tiny cams in big CID engines "build more low end torque". In actual use they don't effective fill the cylinders over a broad RPM right to start with, AND they leave a LOT of power on the table.

This LSA comment is one of the most miss-understood topics on the Forums, and not just this one.

Since I'm on the user end of this deal I'll tell everyone reading this that absolutely and for sure the BIGGEST complaints I get is from folks who have just put their new engine build in use and are having ALL sorts of issues with it at idle and low RPM's and every single time they have installed a cam with "tight" LSA. I guess they just don't get the fact that IF you reduce engine vacuum with all that overlap that you are going to have to INCREASE initial timing and ADD more fuel at idle to make it happy.

Not complaining at all as I've made a nice living and have never wanted for work because folks make poor decisions with these things..........

I get a great education from your posts Cliff. Since you have been working in this field for years and have seen so much, you are the person to listen too. My experiences with camshafts don't go much beyond the 3/4 and full race advertised flat tappet cams we use to install in engines in the 70's. Camshaft technology has really changed since those days. The stock RAIV cams as you know were quite radical for their day with 87 degree overlap. From your explanations, I now understand why the factory RAIV initial timing is set to 15 BTDC. The 273 Qjets I'm sure added more fuel at idle as well to keep the engine happy as you mentioned.

[Ram Air IV Jack]

Originally Posted by ekancler

Here's a question, and it's meant to be at least somewhat provocative: What if one man's turd is another man's gold nugget?

I'm not suggesting that running a small camshaft on a tight Lsa fits that bill. Just that if someone wants to make good power, yet focus *primarily* on a really smooth running, efficient build, that there must be ways to do that really well. Maybe it's a "turd" at the track relative to faster cars in the same class, but exactly what the owner wants..

Most of the people that run on a track are trying to win races. Why would an owner want a "turd" then?? That makes little sense!!

[Steve C.]

UltraDyne ground many of their Pontiac shelf grinds with a narrow lobe separation. Here their flat tappet Pontiac cams:

https://web.archive.org/web/20030325..._camshafts.htm

The hydraulic cams on 110 and 112

Working with Harold Brookshire at UltraDyne years ago and later with Chris Mays, Comps cam engineer at the time, both of them suggested a 108 lobe separations for my specific 4.210" stroke combos using solid roller cams. Depending on the intake used their peak power operation was at or over 6000 rpm.

And as a reminder Paul Carter has posted valuable information regarding a Voodoo cam with a 110 lobe separation with very specific information presented on that subject as to why they are much different than other cams, such as the Comp XE flat tappet lobes. And related comments originally Posted by Paul Carter:

"We all know that wider lobe seps make less peak power than narrower lobe seps, but in a broader RPM range. More average power. Certain lobe designs, by nature, benefit from wide lobe seps, while other lobes benefit from tighter lobe seps. If you have a lobe design that when ground on a 110° LSA, has a power band as broad as another lobe design ground on a 112° or 114° LSA, why not take advantage of the extra power if your not running the cam out of it's power band in the first place?"

"Let me make one thing perfectly clear. When I talk about narrower lobe sep cams in big engines, I am specifically talking about Harold cams. Not Comp XE or anyone else's tight LSA cams. Harold did many things differently to his lobes. Things NO ONE ELSE DID! These subtle little things created lobes that when ground on a 110 LSA, gave the power band performance of a cam ground on a 112-114 LSA. Just look at some of the Voodoo lobes."


.

[ekancler]

Originally Posted by Ram Air IV Jack

Most of the people that run on a track are trying to win races. Why would an owner want a "turd" then?? That makes little sense!!

Did you read the rest of my post? It answers your question.

[F ROCK]

I cannot explain lobe separation angle but I did build a turd.

I had the same attitude when i'd built my first 455. "I'm no racer, I just want a good running engine, w/ slightly over stock specs..." I'd thought.

I built a Turd.
Stock bore, reused pistons, performer manifold, 068 cam, Stock, 6X-8 heads.
The engine ran real reliable, fired right up and ran great; but it was never real responsive; or powerful. It didnt meet my expectations. I'd hoped for 350hp, I doubt I made 300.
My stock 1971 YS400 in my GTO, rated at 300hp seemed more powerful.

I took Cliff's advise on the next build: 455, 6X-4, stock intake; 041 cam with rhoads
lifters.
This engine runs great, responds quickly and makes GREAT power, but only when I want it; Otherwise, it's as tame as can be. Runs just like a stock engine around town. really.
Cost the same. Looks stock. sounds stock until you stomp it pretty hard. reliable, maybe more reliable.

[Stan Weiss]

Originally Posted by F ROCK

I cannot explain lobe separation angle but I did build a turd.

I had the same attitude when i'd built my first 455. "I'm no racer, I just want a good running engine, w/ slightly over stock specs..." I'd thought.

I built a Turd.
Stock bore, reused pistons, performer manifold, 068 cam, Stock, 6X-8 heads.
The engine ran real reliable, fired right up and ran great; but it was never real responsive; or powerful. It didnt meet my expectations. I'd hoped for 350hp, I doubt I made 300.
My stock 1971 YS400 in my GTO, rated at 300hp seemed more powerful.

I took Cliff's advise on the next build: 455, 6X-4, stock intake; 041 cam with rhoads
lifters.
This engine runs great, responds quickly and makes GREAT power, but only when I want it; Otherwise, it's as tame as can be. Runs just like a stock engine around town. really.
Cost the same. Looks stock. sounds stock until you stomp it pretty hard. reliable, maybe more reliable.

Would need to know more information about your "Turd" to know why it didn't perform. Pontiac built some good HP using the 068 cam.

If you used actual Pontiac cams. The 068 has a 116 LSA and the 041 has a 113.5 LSA.

Stan

[Half-Inch Stud]

" one man's ��turd is another man's �� gold nugget ". whaaaa?

Well for my point, and maybe to Cliff's point too: Consider the Cataloged "RV cams" such low duration lobes, and at pretty much any LSA is just gonna ping a 455 while towing.

[zippy]

Originally Posted by Ram Air IV Jack

Most of the people that run on a track are trying to win races. Why would an owner want a "turd" then?? That makes little sense!!

Seen lots of races won by old volkwagon beetles and 4cyl rangers. Sportsman class. Run your time. That's where the "turd" will shine because it'll be the same ET no matter track temp, air temp etc etc. all driver reaction time there. Put in D and hit the light.

[i82much]

Originally Posted by F ROCK

I cannot explain lobe separation angle but I did build a turd.

I had the same attitude when i'd built my first 455. "I'm no racer, I just want a good running engine, w/ slightly over stock specs..." I'd thought.

I built a Turd.
Stock bore, reused pistons, performer manifold, 068 cam, Stock, 6X-8 heads.
The engine ran real reliable, fired right up and ran great; but it was never real responsive; or powerful. It didnt meet my expectations. I'd hoped for 350hp, I doubt I made 300.
My stock 1971 YS400 in my GTO, rated at 300hp seemed more powerful.

I took Cliff's advise on the next build: 455, 6X-4, stock intake; 041 cam with rhoads
lifters.
This engine runs great, responds quickly and makes GREAT power, but only when I want it; Otherwise, it's as tame as can be. Runs just like a stock engine around town. really.
Cost the same. Looks stock. sounds stock until you stomp it pretty hard. reliable, maybe more reliable.

not busting your chops but a 455 with an 068 oughta run pretty good?

https://forums.maxperformanceinc.com...d.php?t=751422

[tom s]

I put a 2801 summit in a 455 at 9.5 CR and it pumped 200 plus and we had to run race gas.Not enough cam for a 455 IMO,Tom

[Stan Weiss]

Originally Posted by tom s

I put a 2801 summit in a 455 at 9.5 CR and it pumped 200 plus and we had to run race gas.Not enough cam for a 455 IMO,Tom

Tom,
Based on some numbers I have gotten from some different people. While the Pontiac 068 and the 2801 have almost the same 0.050" intake duration the Pontiac 068 has a good amount more 0.006" intake duration and would not have pumped near that high.

Stan

[77 TRASHCAN]

Originally Posted by i82much

not busting your chops but a 455 with an 068 oughta run pretty good?

https://forums.maxperformanceinc.com...d.php?t=751422

I just re- read that whole thread. It is a worthy read.

[ekancler]

I just read the thread below too. It included a link to this article by Jim Hand.

Building a Strong Street Machine – Part 5: Pontiac Camshafts
http://www.dapa.org/building-a-stron...afts/#more-144

This snippet is pertinent:

"Lobe separation angle (LSA) directly affects valve overlap. As the LSA is decreased (called a “tighter” LSA), the overlap increases. An LSA of 108° is considered tight; 115.5° is considered wide. Tighter LSAs may produce more peak torque, but will yield poorer idle characteristics. A tighter LSA will also move the power range down in rpm and peak the power in a narrower range. Wider LSAs allow the engine to idle better, produce more manifold vacuum at both idle and cruise, give better fuel economy, and produce a wider power band. However, a wider LSA also slightly reduces cylinder pressure, and consequently the engine may produce less peak torque. Since Pontiacs were fairly heavy cars and most were delivered with automatic transmissions, adequate lower-rpm response and a wider power band were considered more important than peak torque. Therefore Pontiac used wide LSAs on all factory cams. Also, remember that peak horsepower occurs for only a very short time in the upper rpm range, and it has very little effect on the overall performance of a vehicle that uses the total rpm range, from idle up. However, peak horsepower is important for a race engine that is operated in a narrow rpm range that’s close to the peak horsepower point."

[Cliff R]

"I put a 2801 summit in a 455 at 9.5 CR and it pumped 200 plus and we had to run race gas.Not enough cam for a 455 IMO"

I've had customers install larger cams than the 2801 in 455's around 9 to 9.5 to 1 and had them ping on pump gas, at least if you are measuring them @ .050". The Comp XE268 and it's HR cousin the XR276HR top the list of the WORST cams I've seen in 455's brought here that were pinging on pump gas.

I also had a 1970 LS5 Big Block Chevy brought here that pounded like SLEDGEHAMMERS on pump gas where the engine builder installed a Howards 221/221/110LSA cam. The owner wanted a stock 454 LS5 built, the engine builder substituted the Howards cam and told him that it was an "upgrade" over the factory cam and worked fantastic in a recent 396 engine he did for another customer........FWIW.....

[Stan Weiss]

This shows a 2802 (110 ICL), 2801 (110 ICL), and an OEM 068 (116 ICL) which has more seat duration than either of the other 2.

Stan

[zippy]

Originally Posted by Cliff R

I've had customers install larger cams than the 2801 in 455's around 9 to 9.5 to 1 and had them ping on pump gas, at least if you are measuring them @ .050". The Comp XE268 and it's HR cousin the XR276HR top the list of the WORST cams I've seen in 455's brought here that were pinging on pump gas.

That explains why my XE274 was so crappy in my 10.6-1 470 a few years back. LOL