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#41
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Last edited by Gach; 06-23-2022 at 11:31 PM. |
#42
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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........
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If you can read this, thank a teacher. If you can read this in English, thank a Veteran! https://cliffshighperformance.com/ 73 Ventura, SOLD 455, 3740lbs, 11.30's at 120mph, 1977 Pontiac Q-jet, HO intake, HEI, 10" converter, 3.42 gears, DOT's, 7.20's at 96mph and still WAY under the roll bar rule. Best ET to date 7.18 at 97MPH (1/8th mile), |
The Following 2 Users Say Thank You to Cliff R For This Useful Post: | ||
#43
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"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..........
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If you can read this, thank a teacher. If you can read this in English, thank a Veteran! https://cliffshighperformance.com/ 73 Ventura, SOLD 455, 3740lbs, 11.30's at 120mph, 1977 Pontiac Q-jet, HO intake, HEI, 10" converter, 3.42 gears, DOT's, 7.20's at 96mph and still WAY under the roll bar rule. Best ET to date 7.18 at 97MPH (1/8th mile), |
The Following 2 Users Say Thank You to Cliff R For This Useful Post: | ||
#44
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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. Last edited by ekancler; 06-24-2022 at 01:39 PM. |
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#46
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#47
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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." .
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'70 TA / 505 cid / same engine but revised ( previous best 10.63 at 127.05 ) Old information here: http://www.hotrod.com/articles/0712p...tiac-trans-am/ Sponsor of the world's fastest Pontiac powered Ford Fairmont (engine) 5.14 at 140 mph (1/8 mile) , true 10.5 tire, stock type suspension https://www.youtube.com/watch?v=qDoJnIP3HgE |
#48
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Did you read the rest of my post? It answers your question.
Last edited by ekancler; 06-24-2022 at 02:08 PM. |
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#49
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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. Last edited by F ROCK; 06-24-2022 at 04:49 PM. |
#50
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If you used actual Pontiac cams. The 068 has a 116 LSA and the 041 has a 113.5 LSA. Stan
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Stan Weiss/World Wide Enterprises Offering Performance Software Since 1987 http://www.magneticlynx.com/carfor/carfor.htm David Vizard & Stan Weiss' IOP / Flow / Induction Optimization - Cam Selection Software http://www.magneticlynx.com/DV Download FREE 14 Trial IOP / Flow Software http://www.magneticlynx.com/DV/Flow_..._Day_Trial.php Pontiac Pump Gas List http://www.magneticlynx.com/carfor/pont_gas.htm Using PMD Block and Heads List http://www.magneticlynx.com/carfor/pont_pmd.htm |
#51
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" 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. |
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#52
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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.
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#53
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https://forums.maxperformanceinc.com...d.php?t=751422 |
#54
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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
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#55
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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
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Stan Weiss/World Wide Enterprises Offering Performance Software Since 1987 http://www.magneticlynx.com/carfor/carfor.htm David Vizard & Stan Weiss' IOP / Flow / Induction Optimization - Cam Selection Software http://www.magneticlynx.com/DV Download FREE 14 Trial IOP / Flow Software http://www.magneticlynx.com/DV/Flow_..._Day_Trial.php Pontiac Pump Gas List http://www.magneticlynx.com/carfor/pont_gas.htm Using PMD Block and Heads List http://www.magneticlynx.com/carfor/pont_pmd.htm |
The Following User Says Thank You to Stan Weiss For This Useful Post: | ||
#56
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1977 Black Trans Am 180 HP Auto, essentially base model T/A. I'm the original owner, purchased May 7, 1977. Shut it off Shut it off Buddy, I just shut your Prius down... |
#57
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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." |
#58
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"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.....
__________________
If you can read this, thank a teacher. If you can read this in English, thank a Veteran! https://cliffshighperformance.com/ 73 Ventura, SOLD 455, 3740lbs, 11.30's at 120mph, 1977 Pontiac Q-jet, HO intake, HEI, 10" converter, 3.42 gears, DOT's, 7.20's at 96mph and still WAY under the roll bar rule. Best ET to date 7.18 at 97MPH (1/8th mile), |
#59
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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
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Stan Weiss/World Wide Enterprises Offering Performance Software Since 1987 http://www.magneticlynx.com/carfor/carfor.htm David Vizard & Stan Weiss' IOP / Flow / Induction Optimization - Cam Selection Software http://www.magneticlynx.com/DV Download FREE 14 Trial IOP / Flow Software http://www.magneticlynx.com/DV/Flow_..._Day_Trial.php Pontiac Pump Gas List http://www.magneticlynx.com/carfor/pont_gas.htm Using PMD Block and Heads List http://www.magneticlynx.com/carfor/pont_pmd.htm |
#60
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