Next step for my 350

It's entirely possible that one piston/cylinder had more compression in it than the others due to a fluke or something, and was never noticed.

As far as the 455 goes, if you have everything to make it happen, go for it. You'll get to compare your experience with the 350 with it. You may even go back to the 350, though some here will argue that once you feel the 455, there is no going back. I can respect this statement, as I know all too well the seductive nature of torque...but when is enough enough? Sometimes you have to be happy with a nice medium or compromise.

To each his/her own. I wish you well in all your endeavors Steve. Keep us posted on what you end up doing, and I'll follow your progress even if you 'jump ship'. Maybe you can do both a 350 and 455 and just play around with each.


Gary

 

Well I guess that answers my previous question. I guess I should have read through the other posts thoroughly first, eh?

Seems I'm on track though with my thinking, seeing as how it corresponds pretty close to what others have said.


Gary

 

Level 2 was never in this engine. Those SP hypers are as heavy or heavier than stock.

Not sure the knock detector would alert you fast enough to really save anything. Does it use an actual knock sensor or is it an O2 sensor? Anyone use it?

Also found at the .500" + lift the pushrods start rubbing the clearance holes in the head.

 

From Steve's post, the cars ET was dependent on the low end torque. Any change he made that affected the low end dramatically changed the ET.
IMO If the cam had been installed 4 degrees advanced instead of 2 retarded the ET would have been much better.
The cam didn't need to be retarded like the level 3 in order to help the upper end power, the longer duration takes care of that.

If the car could be run on a day when there was better air (And without a broken piston) the comparison would be even better.

Paul

 

Ah, ok. I remember you saying you used the level 2. I guess it was another engine. Just trying to toss out some ideas/possible causes.


Gary

 

Good points. Thanks Paul. (although the last point is kinda moot, if you consider the level 3 was also running on a broken piston (in all likelyhood)) Advancing the install point would have been a bit of a bandaid to make it act more like the level 3 that it was replacing. His gearing isn't terrible for the level 4 combo, and the statement of lower RPM pull loss is to be expected, but the higher RPM power didn't change much, which also shows that the engine needed to breathe better to take advantage of the extra cam, which was the main focus of my point.


Gary

 

A crack that's been there for a while will be a different color, as mentioned.
The rubbed bearing biased to one side indicates misalignment... such as bore tilt, untrue crank journal, (possible but unlikely) wrist pin bore tilted in piston, bent rod or either end of rod bore off axis with the other.
IF the piston failed from detonation then ALL of them will be suspect, being that all of the bearings have rubbing.
IF the damage is from a press mishap, they will all be suspect. (and of course, never have them "pressed" on again. Heat fit only)
I would throw them all away.

What was the actual bore clearance?
Any chance of just one piston being sized differently?
Did you measure the width of the ring lands?
Butting would widen them, and usually try to rip the top off.
Not suggesting that it was put together way too loose, it was just a reason for failure that I've seen before.
I took apart one that got noisy after a few months to find that the previous owner put new cast pistons in with .013" clearance at the tapered part of the bore!
IT NEVER MADE NOISE until the shirts completely collapsed and the vehicle lost some power (likely the offset pins kept them cocked one way).
A few had visible cracks, the others were difficult to see.
They DID NOT fail into the ring land area, that's fairly beefy there.
(I'm doubting this is the reason for failure, just adding for the sake of sharing info)

I've also driven one that had all of the rings, lands, and much of the skirt of one piston in the oil pan.
It would develop a slight miss as it kept oiling a plug, otherwise it drove just fine. Didn't wreck the bore either.
Showed signs of being driven a LONG TIME before my purchase.

Have a good close up pic of the spark plug, assuming it's dry?
Pre-ignition may not leave the telltale signs of detonation. It only takes one occurrence to destroy stuff. You would never hear that.
How much more evidence are you looking for?

Can't magnetically inspect aluminum parts. Dye penetrant is common after proper cleaning (but expensive). In a pinch you can use a highlighter and a black light, but...
Why even consider using pistons that have been subject to failure conditions?
Are you waiting for a person's opinion you trust better to tell you they might be OK?
Do you care if it comes flying apart next time?

Wish you the best on the next iteration of the car

 

To answer Steve's previous question, the valley side of the driver's side is the major thrust side of the piston.

If the cylinders are OK and only need to be honed, have Autotec make a set that puts the piston .025 in the hole.
That will give you the same compression ratio you have now.

Re-balance the crank, new bearings, degree the cam in at 4 degrees advanced and go again.

Paul

 

Pistons were installed with heat, not pressing. Bore clearance is/was .0035". Tough to measure that exact piston now.

I don't think that bearing wear is excessive or abnormal. What would you expect a bearing with 7000 miles to look like?

Rods were reconditioned and ARP bolts installed 7000 miles ago at the last build.

Will not be reusing these pistons. Also since this is a mostly street car it has full exhaust with real (Dynomax mufflers ) that are pretty quiet. Suggesting detonation might be heard although probably too late.

 

.0035 clearance seems too much. Minimum is .0012, believe D&S set clearance on my hypers at less than .002
They also mic'd each piston and had them labeled for each cylinder to be installed into.
Supposed to have size point checked at 2.020 from top of piston head. Seems they are real finicky pistons for sizing requirements.

I also would have liked to see that level 4 cam advanced like Paul mentioned.

 

That clearance is plenty safe.
Circle track sbc's last seasons @ .0035-.004" with Hyper's.
Ones like KB claimers for example, need to run loose or they will scuff/seize.
(they do transfer heat differently, also in the KB nomenclature)
That .013" clearance wonder machine I referred to had maybe 10,000 miles on it and didn't get noisy until full throttled and abused maybe 20-30 times.
Those were the fully machined heat treated KB's.
I just double checked, they are cracked on both sides of the pistons. Forgot they are still around!

I expect bearings at 7000 miles to look nearly perfect with only occasional drag use.
I see many that were subject to slow oil pressure starts with way more miles on them still have the flash coating.
Ones with lack of oil seem to wipe the bearing all the way around (except for the eccentric area) rather than just the top.
I will suggest that bearings might look much worse by the time a piston is shattered, that's why I thought of pre-ignition.
A nitrous mishap that destroys a piston might leave the bearing in good shape too.
Did the shop check the rods on an alignment fixture or just put some crosshatch in the big end? (Not related to piston failure, only alignment)
I suppose a slightly cocked rod might alter the oil wedge some, but I still don't believe the wipe is from lack of oil on startup.

 

Not sure what that gauge I posted the link for uses but the one I have has an actual knock sensor that is used to detect the "knock" with. That one I posted was the only one I could find for a quick reference.

I can't tell you how the one I have works because I installed the knock sensor and was going to hook it up but the engine had issues and had to be removed. I installed the sensor on the replacement engine and before I could wire it in the car had issues so I never got to try the thing ! I should probably install it on the 383 though seeing how it has Speed-Pro hypereutectic pistons in it with 9.8:1 compression with a dynamic on the higher side, I should probably do the math to see what the dynamic is on that engine too.

I'll go out to the garage later to see if I can find it and see if they sell those anymore to give you a choice if you're interested in getting one.

Do you think you might have a new set of pistons by this weekend? if so I think we can help you out and hang them for you, he has the rod end electric heater not with a torch. I'll be at Dave's shop this Saturday we can probably rebalance your crank to the new pistons while you're there maybe. We'll have to ask Dave if he can, if we set him up by weighing everything and gathering all the bob weights together so it won't take him that much time away from the building expansion project he's working on. But if we time it so that we have everything together by the time it starts getting dark he'll have plenty of time to balance the crank while you wait? Will still need to ask him if possible in case he has other things he needs to get out Saturday but it won't hurt to ask him? Unless you can and are planning on using the AutoTec pistons for the stock class, the AutoTecs are made to order as you know with a 4 week wait time or 2 weeks if you pay an extra $50. If so if you want when they come in I can drive out there again and we can help you get the rotating assembly ready?


Derek

 

Those Crower cams are built with 4* advance already built into them. Retarding it 2* put it at 2* advance already. Advancing it 4* would make it 8* advanced. He'd need to drop compression some from your suggestion to achieve his same compression he had before. It would be interesting to see the results of this much larger cam with such an advancement to see how it compared to a better suited cam (such as the level 3) for the rest of his combination. Careful attention would have to be paid to piston to valve clearance with this much advance.

I suspect it would help improve the lower end where it lost power (but I doubt it would be on par with the level 3), but at higher RPM I wouldn't expect much of an increase, for reasons I mentioned earlier...like I said...a bandaid. The level 3 was already ideally suited for his combination.


Gary

 

Crower's website says they are made with 4* advance built in. The LSA is 112*, and intake centerline @0* sits at 108*. Advancing install point to 4* would put intake centerline at 104*, causing the IVC point to happen sooner and increasing DCR.

The level nomenclature applies to all cams for all makes of engines. It's simply a way to describe their level of expected performance.


Gary

 

Gary

Crower Cam tries to set up the cam so if a person is using a timing gear set that doesn't have multiple keyways, the cam will come close to having the ICL sitting 4 degrees advanced or at 108 degrees ATDC in this case.
However they can not control the accuracy of the timing gear set but it is the best they can do.

When you have a multiple keyway timing set you put a degree wheel on it and set the cam where it needs to be whether there is an off set in the cam or not.
Whatever they built in as an offset no longer applies

That is why I asked Steve if he simply used the keyway positions marked with different timing settings or if he set the cam timing by way of the degree wheel which is absolute, not relative.

One of my best cam suppliers sent me a cam that had spot on lobe profiles but I had to skip a tooth on the timing chain to get it timed correctly. You just never know.

Now Steve had the level 3 cam set 6 degrees retarded and if he sets the level 4 cam advanced 4 degrees; you do the math and see which one will have an earlier intake closing ramp.

Paul

 

Hey Larry, what Gary is trying to say when he said that "4* is built in" means the cam will be 4* advanced with the timing gears set at the "straight up" setting "zero" dot to dot setting to get the cam to the suggested installed degree. Of coarse if the cam grinder is off then to correct that an adjustable timing set or one with a choose able advance or retard degree keyway are just a couple ways to correct that. The dots on the timing set can be off as well, I think some factory sets had the 4* "built in" to them.



Derek

 

I think Derek explained it best.

I had the level 3 cam set at 6 degrees retarded and the level 4 at 2 degrees retarded trying to see a more apples to apples comparison.

In the Crower cams I only use the Compu pro hydraulic cams with 112 lobe centers for good manners in a mild engine.

My past experiences with changing the cam by 2-4-6 degrees have very little effect. Shifting the RPM range maybe 100-200 RPM.

 

It rarely does show improvement in HP gains at the upper rpm range.
Retarded much beyond straight up shortens the blow down part of the exhaust cycle causing additional pumping losses at high rpm.
The piston as it move down from TDC during the beginning of the intake cycle is exposed to more exhaust from the later closing exhaust valve similar to increasing the valve overlap.
The time from when the intake valve opens to max piston velocity (75 degrees ATDC) is shortened decreasing the intake charge velocity.

If you set the level 4 cam to the intended 4 degrees advanced I think you will find it will give you better low end and better your ET with the present drive train setup and still make good upper rpm power.

Paul