[Cliff R]

Despite the on-going controversy we see on this Forum I'm going to post some DIRECT results as it relates to this topic.

It's not to argue with any of the Troll's that keep promoting this super "tight" LSA deal, just actual results that mimic what I keep seeing here with this sort of thing.

It's not a Pontiac engine built, wished it was but the information directly applies to all Detroit iron engines as they are nothing but round pistons moving up and down in round holes and pushing around relatively heavy vehicles and being asked to make good power on currently available piss-poor quality pump gas.

So here goes:

Local guy not too far from here (Oldsmobile fanatic) builds a 425 for his Olds 442.

It currently has a strong running 350 in it that I helped him with a few
years ago. Backed by a 200-4R I built/beefed up and a custom Continental
converter and 3.73 gears out back. The car runs so good I can't believe he even messed with it.

So he builds a 425 with around 10.5 to 10.6 to 1 compression, very tight quench, really good flowing heads (can't remember 5's or 6's maybe) with bigger valves, custom ground
Lunati cam specs at 287/293 @ .006", 230/236 @ .050, 110LSA.

Despite my warnings he wanted a "rough" idle with lots of "attitude" so had
them put the cam on a tight LSA and 4 degrees advance ground in, ICL at 106.. So he gets it running and it pings everyplace. Light throttle, heavy throttle, and full throttle. He has to
completely eliminate the VA and retard the timing back to 25 degrees total advance with strong distributor springs to get it to quit pinging. He tries everything but short of using Race Gas it just doesn't work.

Completely fed-up with the new build he ends up pulling the engine and puts the 350 back in it.

A year or so goes by and he asks me about what cam I would use in the 425 to get it to run on pump gas without any other changes. I tell him to basically have Lunati grind a Pontiac RAIV cam for him on a 113LSA. So he has them grind a 287/303 @ .006", 230/242 @ .050" on a 113LSA, I tell him to shoot for 109-110ICL, which he does.

He re-installs the engine. Calls me up yesterday and it flat ROCKS! No ping
anyplace, fine with 30 degrees total timing in it, fine with the VA hooked
up, and has a very slight bit of "attitude" at idle so he's OK with that
too.

Just goes to show how sensitive an engine can be to the intake closing point and LSA plus how tight LSA can do a good enough job of cylinder filling early in the RPM range to make an engine impossible to operate on currently available pump gas.

I have PLENTY of good examples with similar Pontiac engine builds but try to use examples not built here so it takes any bias OUT of the equation, just real results folks get when they don't end up with the ideal combination of parts in place when it comes to this sort of thing.......Cliff

[slowbird]

Fwiw i like tigher lsa on engines but you have to add duration when doing it in my opinion. We ran a 106 lsa for years on pump gas and 10.5:1. Car ran great

[ponyakr]

Originally Posted by slowbird

Fwiw i like tigher lsa on engines but you have to add duration when doing it in my opinion. We ran a 106 lsa for years on pump gas and 10.5:1. Car ran great

I don't have a clue. I

But, the back & forth is sometimes entertaining.

I've noticed that no matter how much 1st hand experience a guy has, on most all car forums, no matter what he says won't work, somebody else will ALWAYS post that they did that exact thing & it worked great for them, with no problems whatsoever, for many years. I suppose it's been that way since forums began, & will continue.

Every time the cam & LSA threads pop up, I always think of the forum I was encouraged to leave. Their engine guru & his loyal followers loved the XE cams & their 110° LSA, for most all Pontiac engines. I dared to mention how much I've always loved the 041/Rhoads combo. Those guys really badmouthed that old, outdated, 20th century technology. I'm sure Cliff remembers those discussions well. I recall some lively cam discussions he had on that forum, at the time. I haven't posted there in a long time, & very rarely ever even go to that forum. Don't know if their fallen guru still posts there, or not.

[J GLASGO]

I agree. We like wide lobe Sep with 4.21 and longer strokes. The 3.75 strokes deal much better with tight lsa, but I still like wider better on them too.

[PAUL K]

Originally Posted by Cliff R

Lunati cam specs at 287/293 @ .006", 230/236 @ .050, 110LSA. put the cam on a tight LSA and 4 degrees advance ground in, ICL at 106.



I tell him to basically have Lunati grind a Pontiac RAIV cam for him on a 113LSA. So he has them grind a 287/303 @ .006", 230/242 @ .050" on a 113LSA, I tell him to shoot for 109-110ICL, which he does.



Just goes to show how sensitive an engine can be to the intake closing point

Cliff

The first cam installed at 109 ICL would have the same intake closing point as the second cam installed at 109 ICL.....therefore the intake closing points would be identical....so in theory the "pinging problem" could've been easily solved without a cam change by degreeing in the cam three degrees later...and making sure it wasn't a starter shim hitting the flexplate sounding like detonation...just saying.

[pastry_chef]

Originally Posted by slowbird

add duration when doing it in my opinion. We ran a 106 lsa for years on pump gas and 10.5:1. Car ran great

Agree.
Combination!
The average Joe should not be stacking tolerances in the wrong direction.
When that line is crossed of course shifting centerlines can help, or adding duration or (more duration and different centerlines) or reducing CR.

We've had a "110 LSA" or tighter combo ping once at part throttle on a 100 F day, with vacuum adv timing was over 50 deg. Reduced the vacuum advance a bit, all good.

Originally Posted by PAUL K

The first cam installed at 109 ICL would have the same intake closing point as the second cam installed at 109 ICL.....therefore the intake closing points would be identical....so in theory the "pinging problem" could've been easily solved without a cam change by degreeing in the cam three degrees later...and making sure it wasn't a starter shim hitting the flexplate sounding like detonation...just saying.

^^^^^ what Paul said

[pastry_chef]

Originally Posted by J GLASGO

4.21 and longer strokes. The 3.75 strokes deal much better with tight lsa, but I still like wider better on them too.

Why stroke now? A to B dyno testing?

When it comes to valve timing I only listen to 3 or 4 people in the world.

[Jay S]

Did I follow that right Cliff? 5s or 6s for heads? He moved his 350 heads over to the 425? I have never flowed 5s or 6s. Are they anything like olds 455 heads? I had ours on our flow bench, seemed like that the E/I ratio was pretty bad. Just by my Olds experience and looking at those results if they flowed like my heads I do not think that retarding that particular cam would have done much good. That short exhaust event might cancel out the intake event?. Maybe someone that did the porting raised the floor on the exhuast when they ported the heads? If they did that, maybe they helped the big e/I flow split and retarding it would work, and would have been worth a try? I ported our Olds 455 and had them on our bench, the exh ports were hard to wake up, the intake with the big valve ran a little over 260 cfm irc. I don’t remember what the exh flowed just that they stunk. Second cam looks like a winner to me.

[Region Warrior]

Strange you brought this up Cliff...
Was planning to reuse my old sft 256/263-110 lsa that used in the 80's.
But been thinking have a new one ground on a 114-116 lsa hoping to improve power band, and not be so "peaky".

[Steve C.]

Stated- "I've noticed that no matter how much 1st hand experience a guy has, on most all car forums, no matter what he says won't work, somebody else will ALWAYS post that they did that exact thing & it worked great for them, with no problems whatsoever, for many years. I suppose it's been that way since forums began, & will continue."

Excellent point.

And as a example, Paul Carter. Here was one of his comments on that very subject of a 110 LSA.....

"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."
Paul Carter


.

[Region Warrior]

My 256/263-110 is one of Harolds early lobes. Still have note when from him to install 4* advanced in my 455 with 12.1cr way back then.
Ran great on 102-104 octane. Remember when every station had it...

[pastry_chef]

Originally Posted by Region Warrior

hoping to improve power band, and not be so "peaky".

Can you provide engine details?

To me "improve" means higher average power through the RPM range where the engine spends time. Will be achieved by using best I/E duration and centerline balances for the combination.
In the same manner more duration does not ALWAYS make more peak HP and certainly not more average HP.

[Cliff R]

"Did I follow that right Cliff? 5s or 6s for heads? He moved his 350 heads over to the 425? I have never flowed 5s or 6s."

No, he didn't move the heads over, and I'm not even sure they are 5's or 6's, might be something else but the guy is a heavy olds enthusiast so they are going to be among the better flowing castings.

The important point to make far as this thread goes is that there was only ONE change made, and the cams are very close in seat timing. He just pushed out to a much wider LSA, and later intake closing. When you are trying to manage pump gas at relatively high compression ratios the intake closing point and LSA can be a pretty big player, as seen from this particular example.

Even better here is that I really had nothing to do with the engine build until he ran into issues with the tight LSA cam. The owner was pretty devastated that it required race gas and/or butt tons of octane booster to even think about taming the detonation issues. He didn't run it all that long, and removed it once he exploited the tuning to a point where it just wasn't going to quit pinging.....Cliff

[Cliff R]

"The first cam installed at 109 ICL would have the same intake closing point as the second cam installed at 109 ICL.....therefore the intake closing points would be identical....so in theory the "pinging problem" could've been easily solved without a cam change by degreeing in the cam three degrees later"

Correct Paul, the intake closing point would be a much greater factor here than the LSA as nothing gets compressed above the piston until the intake valve closes. Since the cams are very close everywhere for sure it tells us that advancing a cam can be a big deal when it comes to octane requirements.......Cliff

[krisr]

Originally Posted by slowbird

Fwiw i like tigher lsa on engines but you have to add duration when doing it in my opinion. We ran a 106 lsa for years on pump gas and 10.5:1. Car ran great

Yeah my 3.75" 400 cube at 11.5:1 compression and e-heads runs great with 255/262@0.050 on 108LSA installed at 104, pump gas. Every combination is different, use whatever works.

[pastry_chef]

Some compression begins BEFORE the intake valve closes.

Originally Posted by krisr

Yeah my 3.75" 400 cube at 11.5:1 compression and e-heads runs great with 255/262@0.050 on 108LSA installed at 104, pump gas. Every combination is different, use whatever works.

Yes, runs better than most members 455's that are reading this.

[pastry_chef]

For a few years a local here ran a 10:1 compression Pontiac 455, ported iron 670 d-ports, shelf cam Comp 288 HR - 110 LSA hyd roller. Good quench. Ran fine on premium pump gas.
4.185 Ross pistons 20 cc dish, zero decked, head chambers were 74.5 cc.

[A.W.Dille]

The detonation issue is one of the reasons I don't drive my GTO right now. Lunati BMII cam in a stock bore stock stroke 400 with 670 heads. Too much dynamic compression to try to keep trying to run it on pump gas.
I have an old Ultradyne for my future build, hft 280-288. I was told to make sure my static compression was around 9.75 in order to keep the dynamic compression in the territory of being able to use pump gas.
I'm no expert by any means but part of this post is from experience and the other is on the advice of a former Pontiac engine builder. Just my .02.

[Jay S]

Originally Posted by A.W.Dille

The detonation issue is one of the reasons I don't drive my GTO right now. Lunati BMII cam in a stock bore stock stroke 400 with 670 heads. Too much dynamic compression to try to keep trying to run it on pump gas.
I have an old Ultradyne for my future build, hft 280-288. I was told to make sure my static compression was around 9.75 in order to keep the dynamic compression in the territory of being able to use pump gas.
I'm no expert by any means but part of this post is from experience and the other is on the advice of a former Pontiac engine builder. Just my .02.

Lunati bracket 2? Is that the 290/290, 230/230, 110lsa cam? I just went over and degreed a cam in that I had ground custom for a friend, might be like your ultra dyne, there were a couple different versions though. The one we did was an ultradyne 280/288, 232/240, .533, 550 (1.6/1.65 rockers) in a 70 gto 455 ho. I had it ground on 112LSA though.

Interesting thing was the SCR on that 70 455 ho, which was suppose to be 10:1, it came in at just under 9.3scr with speedpro forged pistons and the stock heads. It was a very early built 455, built early (maybe March?) in 69. Speedpro forged pistons which typically are few thou from zero on a 455, but these are .026 down in the deck, heads should have been 87 cc, they ran 92cc. You just never know until you get into an engine. Some people claim they are running 10:1, and they are not close to that. So you have an engine like that at one end of the scale, then some end up at the other end of the scale and the scr is underrated. Just seems like on these deals if you aren’t the type to check stuff, going conservative is a pretty good plan.

[A.W.Dille]

JayS it's the single pattern .490 lift 230@.050. It works fairly well but I haven't been overly impressed with it. The reason I got it when I did was cost. Should've went with something different but hindsight is 20/20 they say.