[Steve C.]

"I have had better ET's with tighter LSA then wider LSA's at the track."
Pontiac Dude

And Nolan Jamora from Isky Cams....

"The prevailing trend today is to use a wide lobe separation on small-tire cars. It's not uncommon to go as wide as 118 to 120 degrees to make the low-end torque more manageable. These cams still make great peak power, but the differance is where in the rpm range the power starts coming in. On the other end of the spectrum, you don't want to run a wide lobe separation in a heavy car with 14-inch-wide tires. You need the torque down low to move the car out of the hole. Generally, a 108- to- 110-degree LSA works well in street cars since they offer a good mix of low-end torque, top end power, and idle quality."

The same cam tech article has input from Chris Mays, a head engineer at Comp Cams and like Nolan one of the sharpest minds in the industry. Years ago it was Chris Mays that recommended I use a 108 lobe separation in my 462cid combo with my 254 at .050 solid roller in conjunction with my 3700+ lb car with 10-inch tires. At the time I contacted John Partridge at Bullet Racing Cams, he also stated the 108 lobe separation would be fine.

[carbking]

Originally Posted by 70 Dream

We all know the stock 10.25 CR is too high for today's gas . . . .

We do????

I run one at 10.38:1 with a RA IV cam; runs fine on 93 octane. I run another (non-Pontiac) at 10.70:1 with a stock cam; runs fine on 91 octane, except when pulling the loaded 18 foot trailer. When pulling the trailer, I will get detonation if I don't use 93 octane, but no detonation on 93 octane.

Jon.

[bobzdar]

Originally Posted by 1967Tempest

I see. Cause my low SCR car pulls pretty hard for a heavy car with 200lbs of car stereo stuff and another 100-150 lbs of spare parts, tools, chairs etc for shows. Revs fast and never has an issue hitting the redline.

If I had a cam that was too big, would it take a really long time to rev and then take a long time to get going, similar to towing a car or very under powered?

I ask only because I want to make sure that when I tune and build I make the right choices. Kinda part of learning how to do things the right way.

Dave

Well, your car sounds different than the OP's car, so your choices will probably be different. If it were me, I would probably not be as agressive on cam with a station wagon vs. my trans am or the OP's GTO unless I were trying to race it. My main concern was generating horsepower with the goal of going fast on a road course. I did 1/8 and 1/4 runs to test the engine and get some baseline so I could see how modifications affected performance as it's cheaper and easier than going to a dyno. I also had a 4 speed so had no concerns with torque converter, shift point modification etc, which is why I asked the OP that as well since they play into what you pick for a camshaft. All out horsepower and/or performance is probably not your goal, so you have to look hard at what you want the car to do and what your limitations are (parts wise) before making a decision.

I would post a new thread if you're looking to modify your combination and get some opinions there. When putting a combination together, your limitations (parts wise, comfort wise etc) are as important as what your goals are.

[BruceWilkie]

Some might say "running the tight LSA cam caused pinging and switched to wide lsa similar cam and it didnt ping no more" .

This would lead some to belive it was the LSA that did this. Sort of. Actually it was most likely the intake closing point.
Intake closed point determines the number of degrees in compression.

Suppose you have a cam ground on 110 LSA installed at 106 ICL. Has a ping problem. Some would change to a different cam ground say on 112 LSA installed at 108 ICL. Both same/similar duration. Wider LSA and it doesnt ping anymore. Not pinging it runs better so they conclude that the 110 LSA was the culprit.

In all liklihood had they tried retarding their ICL to108 or maybe 110 icl with their 110 LSA cam they would have lost the ping problem and picked up power at a slightly higher rpm point.

The intake closing point being later lowers the dynamic compression because it decreases the amount of time/degrees that the piston is in actual compression.(True valve seat and seating time play an important roll here)
A big duration cam can get away with tight LSA like 106 and ICL at 102 because the added duration still creates a later intake closing point reducing degrees in compression.

Valve timing events are far more important factors than LSA or ICL. LSA ICL and duration at .050" cam lift are best used for checking/comparing purposes.

BTW dont let dynamic compression fool you.
For those that feel dynamic compression doesnt change....
At lower speed VE is usually not as great as at high speed. At low speed you will have a less dense intake charge less susceptible to pre-ignition and detonation than at higher speed where VE is greatest(usually at/near peak torque wot). At higher speed higher VE, the intake charge is much denser and being packed into the same volume. This increases the heat of the charge due to pressure difference of the charge density. (box of plastic balls vs same box filled with lead balls the volume is the same, the density different).

BTW Here is an excellent link on detonation vs preignition. http://contactmagazine.com/Issue54/EngineBasics.html

For the OP I suggest low enough compression you can "limp home" on cheapest gas available should you go somewhere need gas and they are out of premium.

[Ron H]

Shoot for 9.2 to 1 CR and a 067 stock blueprint cam.

[slowbird]

We ran fine at 10.25:1 compression and killed the engine at 10.75:1 compression with iron heads. We are now somewhere around 9.7:1 compression with a different cam and it is running as fast or faster than it did before and it is much more street friendly now than what it was also.

[grivera]

Originally Posted by BruceWilkie

BTW Here is an excellent link on detonation vs preignition. http://contactmagazine.com/Issue54/EngineBasics.html

Excellent article!

[1967Tempest]

Originally Posted by BruceWilkie

BTW Here is an excellent link on detonation vs preignition. http://contactmagazine.com/Issue54/EngineBasics.html.

X2!!

I liked this quote...from the article.. Probably the best thing to take from the read..

"For emphasis, the design compression ratio is adjusted to maximize efficiency/power on the available fuel. Many times in the aftermarket the opposite occurs. A compression ratio is "picked" and the end user tries to find good enough fuel and/or retards the spark to live with the situation...or suffers engine damage due to detonation."

[BruceWilkie]

I suggest printing the article and saving it as links sometimes no longer work.

Keep in mind diesels run in detonation, our gas engines arent built that strong but can withstand minor pinging for short periods without blowing up. (a tid rough on bearings though). Sustained heavy detonation(pinging) could lead to preignition but usually preignition isnt caused by just a little detonation. From personal experience pre ignition is ugly result and occurs fast and violent and gives little to no warning to react fast enough.

[mechanic17]

Don't forget the importance of the cooling system for SCR choice. Like Cliff said, there are a lot of "hands-dirty factors": if you know your car runs cool as a rule (your block/heads/radiator have no issues) then you you can bend the hypothetical limits a bit too. Anyone who has owned a LT1 '94 through '96 Firebird/Roadmaster/Caprice/Fleetwood ought to plain-amazed by the dead-reliable advantage of 10-1 SCR with a peanut cam on 87 octane (many with iron heads,) due to the reverse cooling. Those cars are proof-positive that, as many have stressed, COMBO overrides any hard/fast rule. As long as you don't cop out and say "Well, my combo has too many factors to figure out. . ." Any good scientist will RUN the experiment, be open minded about the results, and RUN it again and again until they've learned what's right. Then they don't have to take opinions from guys on forums.

[geeteeohguy]

70Dream, I have a '67 GTO convertible with TH400 and the original 400 engine that I've driven about 125,000 miles in the past 28 years. I've taken this car all over the US. I drive it a lot. Here's my take: in the early '80's, with the stock, never-been-touched 400, it would ping very slightly at WOT on 94 octane leaded gas. By the mid '80's, as octane dropped to 92 out here in CA, it ran worse. Pinged on light load, too. I rebuilt the engine at 173,000 miles because it had a burn exhaust valve. I bolted on a set of freshened up #12 '70 Ram Air heads. The car ran strong, but still pinged. I tried water injection, recurving the advance, fattening the carb, etc.etc. The problem? This car would not run without pinging with 92 octane and stock compression ratio. The car had a 3.36 gear, too. I ended up putting some huge chambered heads on the engine at about 190k miles, and it ran without pinging, but was sluggish. Compression factored out to 7.25 to 1. Stock grind, 067 cam this whole time. I ended up with an 068 cam and installed that. Ran a little better (turned out the 067 was keyed about 8 degrees retarded!). Finally, about 3 years ago, at 235,000 miles, I installed a set of 87cc #15 heads off of a '70 455. I reworked the heads (screw in studs, etc) and ended up with right on about 9 to 1 compression. I kept the 068 cam. Gas in CA is now 91 octane, and over $3.50 a gallon. The car ran like it dropped 1000 pounds of dead weight. It was fast, light on its feet, and a joy to drive. I next slipped in a 2.56 rear end (it was a posi and it was a freebee) and I lost a little accelleration off the line....but it was worth it. I've gotten over 20mpg with this set-up, and it will do it on 87-89 octane without pinging. It cruises like a dream, and the fact that it sips gas (for a GTO) allows me to drive it a lot without feeling depressed and broke. I applaud your choice of a 2.93 gear....It's a perfect ratio for a TH400 GTO. My long-winded point is, drop your compression to 9 to 1 or thereabouts, and enjoy the car. I have had a lot of stock Pontiacs over the years, and NONE of them ran without pinging on less than 94- plus octane fuel, which you can't get at the pump any more. My '65 GTO has stock HC heads that have been milled a little, and a huge cam....it needs race gas to run. I don't drive it very much at all for just that reason.

[screamingchief]

Originally Posted by mechanic17

Don't forget the importance of the cooling system for SCR choice. Like Cliff said, there are a lot of "hands-dirty factors": if you know your car runs cool as a rule (your block/heads/radiator have no issues) then you you can bend the hypothetical limits a bit too. Anyone who has owned a LT1 '94 through '96 Firebird/Roadmaster/Caprice/Fleetwood ought to plain-amazed by the dead-reliable advantage of 10-1 SCR with a peanut cam on 87 octane (many with iron heads,) due to the reverse cooling. Those cars are proof-positive that, as many have stressed, COMBO overrides any hard/fast rule. As long as you don't cop out and say "Well, my combo has too many factors to figure out. . ." Any good scientist will RUN the experiment, be open minded about the results, and RUN it again and again until they've learned what's right. Then they don't have to take opinions from guys on forums.

Closed loop EFI & computerized timing control with a knock sensor,something 99% of the guys on this forum dont have in their cars.

Yeah,not exactly an apples to apples comparison there.

And praising the cooling system of those LT1's is a twisted joke.

Have you ever actually worked on them?

One of the biggest clusterf*cks of a water pump design on a modern V-8 that I can think of.

And when the water pumps go bad on those,95% of the time they take out the optispark too.

Which just so happens to be the biggest clusterf*cks of a distributor design that I can think of.

Yep,you do any one of those,you better do ALL of those,and throw in replacing the thermostat and the plugs & wires too,as the passenger side of those engines is a major PITA if you have to take all that other stuff off just to replace some bad plug wires.

Then you gotta know precisely how to bleed the air from the LT1's cooling system,as it's not as simple as some might think it is.

I personally would'nt call these LT1's "dead reliable" myself,maybe I'd consider them somewhat reliable till something goes wrong,then you often got a real mess on your hands,and a he!! of an expensive repair bill for sure.

BTDT,have worked on plenty of 'em in my days.

My friend with the 9C1 caprice still comes over to beg me to work on his from time to time,I tell the cheap @$$ ba$tard to go pay a garage to do it,he can afford it,and I really dont need the headaches or bloody knuckles,and no way in he!! would he pay me what the work is worth,hell he does'nt even wanna pay for all the parts the whiny SOB.

He probably still has'nt replaced his leaking passenger side valve cover or fixed the arcing plug wire on that side.

He was too busy crying about the $600.00+ estimate from the garage to fix it.

It's like $100.00 in parts (vc gaskets/plugs/wires),& $500.00 in labor!!! LOL.

Yeah,ya' just gotta love modern engineering.

over...

Bret P.

[Don57]

geeteeohguy, I found your post interesting as I plan to run #64 heads on a 73' 400 with an 068 (as close as possible) cam in my 78 Grand Am with 3:08 gears, TH350 and 245/60-14 tires. Right now it has a stock 185 hp 400 from a 76 Trans Am. At 7.7 to 1 it runs fine at 87 octane. I just want more power. Anybody else ever feel that way?

[mechanic17]

So, Bret, the LT1 is NOT able to reliably run 10-1 SCR on 87 octane due to superior head cooling? Other than your first sentence, I have no idea what your remarks are doing in this thread. In fact, having a knock sensor isn't relevant either--it has nothing to do with the hard engine parameters.

Your "apples to apples" rhetoric is an obvious disguise for Chevy-bashing in a general engine theory discussion. I'm pointing out that heat reduction around the chambers will allow more CR. Am I somehow wrong because your buddy's valve cover leaks?

Yeah, I have dirt under my nails right now from changing a factory water pump that lasted only 181,000 miles. Real clusterf*ck design, sure. Did NOT take out the Opti.

Stick to cam theory, man, it's what you know.

[screamingchief]

Originally Posted by mechanic17

So, Bret, the LT1 is NOT able to reliably run 10-1 SCR on 87 octane due to superior head cooling? Other than your first sentence, I have no idea what your remarks are doing in this thread. In fact, having a knock sensor isn't relevant either--it has nothing to do with the hard engine parameters.

Your "apples to apples" rhetoric is an obvious disguise for Chevy-bashing in a general engine theory discussion. I'm pointing out that heat reduction around the chambers will allow more CR. Am I somehow wrong because your buddy's valve cover leaks?

Yeah, I have dirt under my nails right now from changing a factory water pump that lasted only 181,000 miles. Real clusterf*ck design, sure. Did NOT take out the Opti.

Stick to cam theory, man, it's what you know.

I have no problems with chevys,have owned plenty of them myself.

Worked on a ton more than those too.

I like them just fine myself,thank you,

I just dont think that the gen II LT1/LT4 is "all that",seems some chevy guys like to make them out to be the best thing since sliced bread,I'm just saying that were they half as good as those diehards suggest they are,then explain to us that after investing a staggering amount of time,effort,and money into that gen II small block engines redesign,why then did chevy dropped them w/o giving it a second thought after making them for only 5 years.

And if you dont think that closed loop EFI and full timing control with a knock sensor does'nt contribute to that engines ability to live @ 10:1 CR,then your kidding yourself.

The cooling system was not the only reason that worked.

Like combustion chamber design,the specific bore x stroke,and a host of other things did'nt contribute to that engines design & function.

The problem I have is that you were the one that was insisting it was a package deal that lets a combo do this,and in the same post you're suggesting that it was only the cooling system that was to credit with that engine living @ 10:1.

Sorry but you cant have it both ways.

Originally Posted by mechanic17

Those cars are proof-positive that, as many have stressed, COMBO overrides any hard/fast rule.

I've also worked on a few of the gen II LT1's that did'nt have the EFI and timing control,these were converted to carbs and HEI's with the LT1 carb intakes for use in classic cars and such,and guess what happens when you do that,they're not nearly as easy to "manage" like that.

If you got 180,000 miles on a water-pump,then good I'm happy for you.

Just remember that not everyone is that lucky.

If you optispark lived after having a water pump fail,then maybe go buy yourself a lotto ticket,seems your luck is strong.

But if your gonna put that all back together w/o replacing the optispark and the other stuff I mentioned,then apparently you also like playing the odds,and/or possibly like to make more work for yourself.

I'm not making up the problems those engine had,they're all very well known and well documented.

In closing...

All I was getting @ is this:
If all it takes to run a high static CR on pump gas is to run a reverse cooling system,then please do explain to us why everyone out there is'nt doing such?

It's not like reverse cooling is top secret info or anything like that...

Simple question right?

Let's see the simple answer???

Bret P.

[Cliff R]

"And if you dont think that closed loop EFI and full timing control with a knock sensor does'nt contribute to that engines ability to live @ 10:1 CR,then your kidding yourself."

No "kidding" here, I've never once had the first problem tuning or getting an SBC in any configuration (carbs and mechanical/vacuum advance distributors included) to effectively manage pump fuel at 10 to 1 compression with iron heads, some up near 11 to 1. Being a Chevy has little if anything to do with it, aside from the fact that they used some very good combustion chamber designs in later years to make it even easier for us.

"I've also worked on a few of the gen II LT1's that did'nt have the EFI and timing control,these were converted to carbs and HEI's with the LT1 carb intakes for use in classic cars and such,and guess what happens when you do that,they're not nearly as easy to "manage" like that."

I'm interested to hear some specifics about this, specific cam choices, dyno testing, track testing, etc. Once again, my experience with the little Chevy engines dates back to the 1970's. I probably know every decent SBC head casting number by heart, and have no problem whatsoever setting them up for pump gas at relatively high compression ratios.

To be perfectly honest SC, you are pegging my BS meter pretty hard ranting about them in the last couple of threads.

Those engines are actually easier to run at higher compression ratios on pump fuel than a long stroke Pontiac engine with less efficient cylinder head designs (chamber shapes) and with much greater mass to the total combination of parts. The SBC's have an excellent design (like it or not), nearly endless parts selection for them, and cylinder heads and camshafts in just about any variety the builder would want, at bargain basement pricing.

We just finished one up a few weeks ago powering my best friends 1 ton work van (1998 Vortec 350). We increased the compression ratio with flat top pistons, reduced quench distance to just over .030", and it laughs at low octane fuel pulling several tons of tools and equipment around all the time.

We used the stock 906 Vortec heads, cast pistons, stock replacment roller camshaft, and all of the factory emission control equipment. We upgraded the fuel injection system with the latest design/conversion, otherwise it is stone stock everyplace.

The only problem he's having with it is taking a LONG time to reach operating temperature, as it's a tad more efficient than it was before the rebuild/modifications.

FWIW, we've extended our tuning efforts and to Big Block Chevy engines as well. They respond as good as any Pontiac engine with careful parts selection. We worked with a customer last summer who refused to dump his Chevelle's "flat" 454 intake manifold and Q-jet. He's seen my car run, and wanted the type of power and vehicle performance we see from our 455 Pontiac engines using all of his factory equipment on his very expensive restoration.

We made some recomendations for him, quench distance, optimum compression ratio, longer connecting rods, cylinder head mods, camshaft (hydraulic roller on a wide LSA), etc, etc. He carried his 454 off to the dyno, where they just about laughed him out of the shop attempting to use the flat intake and factory Q-jet on his engine. The laughing all stopped when it cranked out over 590 ft lbs of torque and carried just under 500hp out the back door!!

Our current project is a 496cid BBC with 11 to 1 compression and solid roller camshaft. We're setting it up to run pump fuel only, and after reading some of the nonesense I've seen here, will certainly let everyone know the outcome here in a few weeks when we get it in service. The engine it is replacing is a 454 with a set of modified (by us) peanut port "Truck" heads, 234/244/112 Crower cam, RPM intake, Q-jet, HEI distributor. That engine has been in service since we built it in 2001, and has over 50,000 miles on it in a 69 Chevelle, and over 1000 drag strip runs in full street trim (low 12's at 112mph). It has 3.73 gears and one of our 4L60 transmissions. The CR is over 10 to 1 and it manages pump fuel without the first issue anyplace.

Funny how the N/A internal combustion V-8 engine shows so many similiarities following a few basic guidelines for setting them up, no matter what brand they are........Cliff

[Half-Inch Stud]

Ponder the finer things with ping-free & Compression CAM events & Ping;

On choosing to Widen LSA as a "forced compromise" on Intake Closing versus Exhaust Closing, I will always pick the Exhaust Closing LATER (unBOOSTED) and Leave the Intake Closing Point alone. The result should be improved MPG with reduced Ping from Idle to Peak TQ, and optimal Inhale at peak TQ & above.

[70 Dream]

Originally Posted by BruceWilkie

For the OP I suggest low enough compression you can "limp home" on cheapest gas available should you go somewhere need gas and they are out of premium.

Bruce, your comment above was not helpful in any way. The board can correct me if I'm wrong, but I thought the purpose of the PY Forums is all about knowledgeable members helping less knowledgeable members (like me) and sharing info, not looking down their noses at them. By the way, my name isn't "The OP," it's Harry.

[Cliff R]

HIS, Is that your version of describing scavenging events and improving cylinder filling above peak torque, while reducing the actual cylinder pressure the engine sees at peak torque, while flattening out the power curve a bit at the same time?......Which is a natural process we get from using cams on wider LSA's with greater seat to seat timing events, all else being equal.

One should also keep in mind that when we reduce the sharp rise in peak torque, we also reduce the sharp rise in cylinder pressure at the same point in the rpm range.

If the engine doesn't ping at peak torque at full load, it's unlikely that it will after peak torque as the events continue to occur many more times per second. In the N/A engine, the cylinder filling abilities are reduced accordingly. If you tune is on, the engine will not ping at higher rpm's.

We've observed on the dyno how this LSA deal plays out in actual use. Tight LSA camshafts, the XE274 in the 455 for example, make some very good peak torque numbers at a relatively "low" rpm. We've seen over 575ft lbs at 3400rpm's from some very mild builds with iron heads. At peak HP with the same engine (4900rpm's), torque was clear down to 414 ft lbs.

When one starts looking at average power, the high spike at 3400rpm's doesn't mean much, other than the engines tendency for detonation is high at that point.

I can build the same engine with a factory RAIV cam, Crower 60919, or Wolverine 5059, and make 30-40 ft lbs less torque at 3400rpm's, but still make OVER 500ft lbs clear out past 5000rpm's. The lower peak torque number will be more octane friendly, and the wider/broader power curve will make the vehicle faster on the street or at the track.

Peak HP will also occur later in the rpm range, so we have a broader, flatter power curve with more HP available in the upper mid-range and top end.

Folks quickly loose sight of these things as the focus is typically on the peak numbers from the dyno, not the average numbers, and, as it's been pointed out a few times, we DO NOT race dyno's, but the educated engine builder can certainly learn a LOT from them!.....FWIW....Cliff

[70 Dream]

Originally Posted by carbking

We do???? :


Jon.

Carb King, I apologize if you took offense at my comment.

Probably the one thing that I've heard the most since I've owned this car, and I keep hearing it and reading it over and over, is that you have to lower your compression to run on today's pump gas. That was all I was trying to say.

I do appreciate and respect your knowledge and experience.