[scott70]

So they say you can have detonation without actually hearing it. .So if your car has good power,doesnt overheat,ping or anything else that would indicate having a detonation going on, how would you know your car may have damaging detonation happening if you don't have any signs of it going on? Look at your plugs? Beat up bearings which is too late by then?

[Jay S]

Originally Posted by scott70

So they say you can have detonation without actually hearing it. .So if your car has good power,doesnt overheat,ping or anything else that would indicate having a detonation going on, how would you know your car may have damaging detonation happening if you don't have any signs of it going on? Look at your plugs? Beat up bearings which is too late by then?

As you said-looking at your plugs is the only thing I know of. The strap is burnt back further than it is suppose to be is one sign. Which just means the engine needs a colder plug or some timing pulled out. Aluminum speckles on the porcelain around the electrode the other bad sign, but if it is silent it would probably show up on the strap first.

[Jay S]

Originally Posted by Jay S

As you said-looking at your plugs is the only thing I know of. The strap is burnt back further than it is suppose to be is one sign. Which just means the engine needs a colder plug or some timing pulled out. Aluminum speckles on the porcelain around the electrode the other bad sign, but if it is silent it would probably show up on the strap first.

Unless you have an engine burning oil, my opinion is it is better to stay on the cold side of what the engine is saying it wants when you read your plugs. More room for error if for some reason you get some bad gas or over heat your engine.

For laughs, here this last week I had a little 5 hp transfer pump that I left down at the river and it got some water up into it when we had all the flooding this spring. It had a NGK brk7 in it. I cleaned the engine up It fouled out a new plug in 10 minutes. Dropped to a brk6, made it maybe 15. So I got to looking and they made a brk2. Lol, so hot the strap is probably kissing the piston. It smokes blue, but it is still running...there is a time for a cold plug, and there is a time for a hot plug...

[70GS455]

Originally Posted by Jay S

I agree with Pastry here.



That cam that the first compression check was taken on was 296/304 and a 106 lsa, 104 Icl. The Intake closing would be 72* ABDC. It is an old ultra dyne profile, it is probably closer to 74* actual at .009 valve lift out at the valve.



The 2802 at .006 tappet lift or .009 out at the valve is is about 284-286 total duration at .006. It shuts the intake valve and 71*-72* ABDC.



If you plug those ICL numbers into this calculator:



http://www.wallaceracing.com/dynamic-cr.php



They have nearly the same pumping compression, AND the actual compression tests were nearly identical. 160 is about right on the lunati cam, it is to low on the summit, it should be closer to 180.



That is becuase that Lunati cam has 88* of overlap. The summit has 63*. Overlap pummels compression tests. They should NOT be the same on a CT test. The Wallace dynamic compression calculator always runs 30-40 lbs low on pumping pressure on most Pontiac engines that have around 60 degrees of overlap. Because it only looks at the intake closing event on cam specs. Chances are the cam is retarded to much and heating up the air charge. Far more likely this cam is currently retarded than it is advanced. Rarely have I seen a cam installed dot to dot need to be retarded, they almost always need some advance.



The 2802 cam should work in the combo. Good chance it is retarded to much and causing temp spikes on the intake charge.

I don't know where folks get this idea that overlap has any effect on cranking compression in a static test. Static CR, crank/rod geometry, and intake valve closing event ONLY (and cranking speed to a minor degree) will influence static compression pressure in a non-running engine. In a running engine, a dynamic situation, then yes overlap can have an influence on combustion cylinder pressures, mainly due to dilution of the intake charge from burnt combustion gases. In a non running engine, no way.

Overlap does affect idle quality, due to the aforementioned burnt gas dilution

Sent from my SM-T817V using Tapatalk

[Jay S]

[QUOTE=70GS455;6051118]I don't know where folks get this idea that overlap has any effect on cranking compression in a static test. Static CR, crank/rod geometry, and intake valve closing event ONLY (and cranking speed to a minor degree) will influence static compression pressure in a non-running engine. In a running engine, a dynamic situation, then yes overlap can have an influence on combustion cylinder pressures, mainly due to dilution of the intake charge from burnt combustion gases. In a non running engine, no way.

Overlap does affect idle quality, due to the aforementioned burnt gas dilution

Curious, did you every try a different cam with only a change in overlap to see if it changed the pumping pressure? Not trying to be hard on you, just asking.

I understand what you are saying. I did overstate the impact overlap has, I knew after a posted that I overstated it but I could not change it. The engine is just an air pump when cranking. I know overlap causes reversion but I don’t know how that translates to a non running engine. Not sure how much impact it has. We shall see when he takes it apart and checks it. Sorry for the rant, eureka moment not though through...

[pastry_chef]

Originally Posted by 70GS455

I don't know where folks get this idea that overlap has any effect on cranking compression in a static test. Static CR, crank/rod geometry, and intake valve closing event ONLY (and cranking speed to a minor degree) will influence static compression pressure in a non-running engine.

I've seen a test where increasing rocker ratio increased cranking PSI.
Overlap vs cranking PSI thoughts from Harold Brookshire below.

Originally Posted by UDHarold
The intake valve closing point mainly tells where the intake valve closes.
Get your favorite cam grinder to grind 2 cams with the identical profiles, but with TWO different LSAs, say 106 and 108, or 110 and 112.
Install one cam in the engine, then dyno it.
Install the other cam on the IDENTICAL intake centerline, so that opening and CLOSING points are the same for both cams.
The cams will have different cranking compressions, different power curves. This is not to say one is better than the other, only different.
What effects the REAL dynamic compression is HOW MUCH air and gas is in the cylinder when the intake valve closes, not at what degree ABDC the valve closes.
The different exhaust opening points affect the amount of back pressure, ie, reversion, that is present when the intake valve opens BTDC. The amount of reversion affects the rate of cylinder filling on the intake stroke, and the amount of air and gas in the cylinder when the intake valve closes. This is what gives you the actual Dynamic Compression. The operative word is DYNAMIC.

UDHarold

[Cliff R]

Cranking pressure is NOT an indicator of what the engines octane requirements will be. I see some folks are caught up on 160psi as safe. I've had engines in here to custom tune that made less than that and pinged pretty hard with "normal" timing/fuel curves in them, and I've had engine in here with quite a bit more that were fine.

Another thing that is seldom mentioned is RPM. A small cam will typically have excellent cylinder filling at lower RPM's when the events are happening much slower. Peak VE occurs early with a small cam, and combined with a high static compression ratio managing low octane fuel can quickly become difficult, if not near impossible.

Over the years I've ran into several engine combinations that were near impossible to run on pump gas, but they had relatively "low" static compression ratios. The worst of the bunch was a 460 Ford engine. I built it for a friend of mine, his 1987 heads were cracked so he found some 1973 heads. They had pretty big "open" chambers, compression was under 9 to 1 and that engine pinged everyplace but at idle! We had what I thought was a pretty well chosen cam for it, truck/towing application and the cam was (nearly as I can remember) 214/224 on a 112 LSA. An early adventure of mine using a small cam in a big engine with "crappy" combustion chambers.

The worst Pontiac engine I ever tried to tune for pump gas was a Super Duty 455. It had a slight dome on the pistons for just under 9.5 to 1, and used the Comp XR276HR cam. That engine would ping HARD with any heavy full throttle, and did NOT want any vacuum advance or it pinged at light throttle. I had to retard the total timing to 26 degrees and use super strong springs on the weights, but it wasn't happy with it. It would BARELY tolerate another 8 degrees from the VA. If I advanced the timing to 28 degrees it pinged everyplace. The "small" HR cam was so good at cylinder filling it acted like an 11 to 1 compression ratio engine, not md 9's.

Jump ahead to couple of years ago, one of our customers built a 455 at 9.3 to 1 and used 250cfm #96 heads on it and the XR276HR cam. It pinged so hard on the dyno they blew it up (spun all the rod bearings). Once again the cam was so good at cylinder filling that it made the "low" compression engine act like a high compression engine in actual use.

So when I see relatively "high" compression 455's teamed up with relatively small cams and excellent flowing heads I already know there are likely going to be issues with it as far as octane requirements are concerned. It's not a fixed-science for sure, some folks get away with it, others do not.

Decades ago I built a little 400 with 6X heads on it and it had all sorts of issues with running hot, overheating and detonation. It was right after HO Racing went out of business and I bought many of the parts and the cam (Ultradyne) thru one of the big Pontiac shops. It was right about the time Harold was trying to get Ultradyne up and running, so it's been quite while ago. Can't remember the cam specs at the moment but it wasn't a small cam, around 220/230 @ .050" on a 110LSA. After spending a ton of money on cooling system parts to get the engine under 200 degrees, just on a whim I went in and retarded the camshaft. I think I did that because it just acted so "aggressive" and heated up so quickly I wondered if retarding the cam might calm things down some.

Ready for this, we couldn't get the darned thing to warm up, it took seemingly FOREVER to reach operating temperature. No more running hot, overheating and it didn't even think about pinging anyplace! So when I read these threads, and think back to the troubled engines I've worked with, there is a LOT more going on here than just cranking pressure, ICL or intake closing point, and I know that you could just be off a few degrees with the cam and moving it the right direction could have a dramatic positive impact on the entire scenario......FWIW........Cliff

[pastry_chef]

Point of reference, very important to note Tom used cast iron heads. It made 435 HP. Tom drove this thousands of miles on California 91 octane. The OP here has aluminum heads!

The Summit 2802 is not "too small", valves do not close @ .050 tappet rise. IF the timing and fuel are correct and the Summit cam is installed correctly, then possibly a quench problem.

Originally Posted by tom s
FWIW,I built a 455 with bone stock 48 heads,not port matched heads or stock intake.9.5CR with custom dished pistons.I put it together with used parts I had in my garage.Used the 276 cam on a 110,

Originally Posted by tom s
I had a XE 276 hdr cam on a 110 in the engine,on the dyno with good headers and a dual plane intake it liked 36 degrees and pumped about 180-185.

Another reference:
455 - 9.1 CR with ported cast iron heads, XE276HR roller cam. 490 HP they ran 70 plus dyno pulls. They commented the engine was "insensitive to timing", ran 92 octane and used 36 for best power.
https://www.hotrod.com/articles/hppp...ne-stuska-dyno
This was running a Torker 2, this will help IMO.

[pastry_chef]

David Vizard.
https://www.hotrod.com/articles/0311em-power-squeeze/

Compression Pressure
Assuming your engine has good ring and valve seal, a simple way to determine if your engine has enough compression for the cam being used is to check cylinder compression pressures. For engines of my own utilizing a near-zero leakage ring package and intended for use with 93 octane fuel, I tend to set 190 psi as a lower limit with a preferable 200 – 210 psi target. For every octane number less than 93, the compression pressure needs to be about 5 psi less to avoid detonation under normal circumstances.

[TAQuest]

Instructions;
Start the engine.
Turn the distributor slowly in both directions and get an idea of where the timing likes to be. You can hear the engine idle start to drop.
Turn it to the retard side so it's just barely out of the range where it runs bad.
See if it still rattles.
Report findings.
If it still rattles then we will proceed with the same basic type of test with fuel.
Brutal honesty; If you don't do the 'basics' like this then you are just hiding from the truth and fiddly flocking around with it.

[Cliff R]

I'll add here that I've ran into three 455's now that pinged HARD on pump gas and under 9.5 to 1 compression.

Two used the XR276HR cam, the third the flat tappet version XE268.

I made significant improvements to one of them by adding HS 1.65 rockers to replace the 1.5'. This tells us the cam is too small, or in better terms too good at cylinder filling at lower RPM's pulling peak VE down in the RPM range, and increasing octane requirements at the same time.

My comments are not meant to "bash" these cams, some folks do OK with them. Just pointing out that you are going to have to look pretty hard to find someone with more experience tuning that I have, and I could NOT correct the detonation with any of them without retarding the timing pretty far to a point where it was hurting power production.

The one that I didn't build or tune was a simple fix. When it pounded the rod bearing out on the dyno and EVERYONE right down to the guy who took at the trash at the dyno facility was blaming the Q-jet, I got involved and told them to install a larger cam on a wider LSA and set the ICL at 110 degrees. The phone went silent for a moment when I told the shop owner/engine builder/dyno operator this. He went ahead and ordered and installed the 289/308, 236/245 @ .050" 114LSA cam and made NO OTHER CHANGES. They went back on the dyno, the engine behaved better everyplace, he even noted that the "quirk" in the idle was gone and it idled much smoother with a "deep/heavy" sound.

They were able to advance the timing considerably, and the power numbers came up dramatically, plus no ping whatsoever on the same fuel they blew it up with using the smaller cam on a tighter LSA with advanced intake closing.......Cliff

[Cliff R]

Another interesting and related point.

IF you think that a 230@.050" cam is a big cam in a 455 build, even one with relatively "low" static compression, take a look at the dyno chart below.

This is a "stock" 455 Super Duty engine. The only real changes were having it decked/squared for zero and adding "H" beam rods with Icon pistons hanging on them. It's well under 9 to 1 compression.

It idled DEAD SMOOTH clear down to 600rpms on the dyno and excellent throttle response. Even with the HR cam and high ratio HS rockers in it, it was done at 5200rpm's.......Cliff

[TAQuest]

Originally Posted by Cliff R

My comments are not meant to "bash" these cams, some folks do OK with them. .Cliff

I think you are a little ahead of the curve here Cliff.
What happens here is that folks chime in with 'the cam is too small' and that just confuses they heck out of the situation.
Some basic stuff needs to happen first for troubleshooting.

[TAQuest]

Originally Posted by Cliff R

I could NOT correct the detonation with any of them without retarding the timing pretty far to a point where it was hurting power production.

.Cliff

This part is useful. It shows you COULD stop the detonation retarding the timing.
That needs to be checked here early on in the troubleshooting.

[Cliff R]

Right to start with the 2802 is not a good choice for a 455 build with good flowing heads on it as you aren't going to take advantage of the much better ports and power potential. You might as well put stock 4X heads with 98 cc chambers in them with that cam, it will do better everyplace...IMHO.

Right on the dyno with a much larger cam and Edelbrock round port heads we made 505hp/551 tq, peak HP at 5100rp'ms. So how do you come in with a smaller cam and do any good with all that head flow.....you don't.

Plus the smaller cams, as we continue to see pull power down (torque), peak VE occurs earlier, cylinder pressure higher, and you can get yourself into a scenario where it may not be pump gas friendly.

I'll add here that I google up NOTHING, all of my responses are from actually doing this, and a LOT of it over many years.

What hurts the folks trying to figure out the problems is that some folks may get away with some of this, others don't. I'm just pointing out what I've seen and worked with that is related, nothing more, nothing less.

I'll close with stating this, no 455 in any configuration, even lower compression is leaving here with a cam less than 230 @ .050" and nothing tighter that 112 LSA. Matter of fact, the wider we go with LSA with the big long-stroke engines, the more power we see, more user friendly and the cars run quicker at the track without a butt-ton of gear or converter in them..........did I mention they do better with pump fuel as well?........FWIW.....Cliff

[TAQuest]

Originally Posted by Cliff R

Right to start with the 2802 is not a good choice for a 455 build

There you go again. Getting the cart before the horse.
Not a build thread. It's a broken engine troubleshoot thread until it isn't.
Is it just me or is everything you write a Cliff Ruggles advertisement?

[pastry_chef]

Originally Posted by pastry_chef

Yes, the cam is small and not ideal.

Yet, in the last year there have been two different members with this issue. Both swapped to a larger cam/112 LSA as the board prescribed and the issues persisted.

Back to the 041 / OF yet again.

So when the Crower 60919 does NOT fix the OPs issue who pays? I will tell you if it was me spouting go bigger I WOULD! Especially if I'd seen so so many people with too small cams pinging and I was just so sure.

TA I learned certain things here back in 2004. If what a person thinks badly contradicts a great like Vizard they need to sit back and learn some more.

[TAQuest]

Originally Posted by pastry_chef

Back to the 041 / OF yet again.

So when the Crower 60919 does NOT fix the OPs issue who pays? I will tell you if it was me spouting go bigger I WOULD! Especially if I'd seen so so many people with too small cams pinging and I was just so sure.

TA I learned certain things here back in 2004. If what a person thinks badly contradicts a great like Vizard they need to sit back and learn some more.

I could pay Vizard the $275 and sit through his seminar. Learn a lot.
It wouldn't change wanting to retard the timing and see if the engine still rattled.
Nothing is going to change a basic common sense move troubleshooting an old beat engine that has been sitting for 10 years.

[pastry_chef]

Originally Posted by TAQuest

I could pay Vizard the $275 and sit through his seminar. Learn a lot.
It wouldn't change wanting to retard the timing and see if the engine still rattled.
Nothing is going to change a basic common sense move troubleshooting an old beat engine that has been sitting for 10 years.

Agree.
I'd be checking the balancer for TDC accuracy first as a few have noted.

[77 TRASHCAN]

Originally Posted by TAQuest

There you go again. Getting the cart before the horse.
Not a build thread. It's a broken engine troubleshoot thread until it isn't.
Is it just me or is everything you write a Cliff Ruggles advertisement?

Your interpretation is different from mine...........

In the world of Hot Rodding, the olden days thinking was that, if a little more cam is good, a lot more should be excellent!!! Kinda like putting a 041 Pontiac cam in a 8.5:1 350 Chevy, I've seen that happen, a bunch!!!

Now folks know that too much cam is not good, and are CLUELESS about engine dynamics and put something like a 2802 or even a 2801 or worse some XE that is WAY short on duration. They read the info about the cam and make a decision NOT based on ANYONE'S real world experiences.

How many times has a member here posted a thread about their engine that is usually a 455 and is over 9:1 compression ratio, and has some cam the their "experienced" machine shop selected for them. THAT machine shop has a big reputation, and they only use THAT brand of cam, because they know their stuff.......LOL......AND we've seen the person posting their dilemma has quite a few posts.....You;d think that maybe they had read some threads about cams to use in 455's, not just Cliff's

I read stuff here, to learn. I work on all kinds of stuff. I am pulling togther parts for a 400 and a 455. My interest is for them to run reliably and powerfully as possible, with all the knowledge on hand, as possible...

I think there is an ignore feature, on this forum, some folks use it.....