[Va68goat]

MXTex,
Paul (the builder) recently had this motor broken down. I would hope he would have checked that. Here are the compression numbers that we took this week. I didn't want to post them until we verified with another gauge as well but this is what we got. Wide open throttle, plugs out and 5 cranks.

[tom s]

Now you need a leakdown test for sure.Tom

[krisr]

There is no way that engine made 500+HP with static compression that low.

[Va68goat]

JLMounce,
Read post #784 from Paul. He explains what occurred on the failed dyno.

krisr,
I did indicate that we wanted to verify with another gauge. Also want a fully charged battery. These numbers were posted to show the difference in the numbers from one another. That test will be done again soon.

[Pronto Poncho]

Originally Posted by MXTex

If I understand correctly; when the motor let go on the dyno, the crankshaft and two connecting rods were damaged. If/when this motor gets disassembled (which I think is inevitable), I'd recommend looking very closely at the pistons that were on the connecting rods that were damaged on motor #1. A failed connecting rod could apply some very strong and abnormal forces on a piston. Assuming that the piston locations from motor #1 were duplicated in motor #2, I'd look very closely at these two holes. Do we know which cylinder numbers received the replacement connecting rods? If so, what are the compression numbers for these holes? If one of the cylinders that received the replacement connecting rods has vastly differing compression than the other 7 holes, I think we're looking at piston damage from the original scatter as the root cause.

Thanks, Very insightful about the Pistons. We had the same discussion and wondered if there was piston and cylinder damage. A thorough compression check was made. All cylinders were within 5 lbs or less of each other.

As far as voltage is concerned. Two separate ignition systems were used with the same results. On one of the test a 12 V direct feed was run directly to the coil.

[krisr]

Originally Posted by Va68goat

krisr,
I did indicate that we wanted to verify with another gauge. Also want a fully charged battery. These numbers were posted to show the difference in the numbers from one another. That test will be done again soon.

Don't forget to get it up to operating temp so everything is warm/expanded/oil is circulated. Don't comp test it cold. The variation between cylinders looks fine, I think I have between 170-180psi in all 8 of my 400, but it has a 255/262 @ 0.050 solid roller on 108LSA. I would have expected yours to have around 190-200psi if it's on a wider lobe split plus your engine also sounds like it's running very well when it has some idle speed and sounds very raspy when the throttle is cracked.

[STEELCITYFIREBIRD]

I'd find the skip in the vacuum gauge firstly.If you locate and isolate or repair that issue it may or may not be related or causual to the "knock" sound.

Lots of good recommendations and observations I agree with, following my line of thought on diagnosing these issues.

-Agree Compression test should definitely be done on a hot engine.
-If a HOT cranking compression produces #'s that low, I can't imagine it running well or producing the #'s it did on the dyno. a cylinder leakdown test is indeed warranted.(also cam timing can't be off that far and make those dyno #'s), with that I think the compression test data is useless till verified and done under the correct conditions.(make sure the hose seals well if multi part and to s-plug hole..oil the o ring)


Which cylinders/crank pin/s had the problem?[
And full detail of damage. Damaged bearings or broken rods etc. Are the pistons floated or pressed pin pistons in this motor?

If I am following this correctly, the oil pump and shaft swap out was with the wiped dizzy bushing in place. So that testing is irrelevant.


IDK, the drip drip of facts, instead of full disclosure up front of what happened on the original dyno pulls has sent this diagnosis on many unnecessary tangents.
This doesn't make sense to me.. Oil pressure loss, dizzy bushing wiped, oil pump drive shaft contacted block passage unsymmetrical. IDK, seems there is more to the original failure... yet to be disclosed, just the status quo from the beginning

.

[STEELCITYFIREBIRD]

Originally Posted by Va68goat

I was told to let you guys know that the compression test read 150 when the car was cold and it was turned over 3 times on each test.

[Pronto Poncho]

Originally Posted by krisr

Don't forget to get it up to operating temp so everything is warm/expanded/oil is circulated. Don't comp test it cold. The variation between cylinders looks fine, I think I have between 170-180psi in all 8 of my 400, but it has a 255/262 @ 0.050 solid roller on 108LSA. I would have expected yours to have around 190-200psi if it's on a wider lobe split plus your engine also sounds like it's running very well when it has some idle speed and sounds very raspy when the throttle is cracked.

Some good perspectives. The engine was warmed up before testing. Throttle was open and a minimum of 5 cranks for each cylinder. One thing of interest is your correct observation that the motor runs well and is very responsive after it transitions out of the idle circuit. One variable not mentioned is that a new carburetor is being used. It is a custom build by Jeff Korner. (SP?). I am concerned about the lack of response to tuning while on the idle circuit. I am suggesting that temporarily the original carburetor be put back on until some of the basic idle issues are sorted out. It idled well with the original carburetor. We all have jobs but will do another compression test with another gauge to confirm correct total compression numbers ASAP.

[Formulas]

Skip in vacuum reading can also be the PCV valve plumbed into a single runner

7 cylinders will be slightly higher and smooth then the one cylinder will hit, it has to draw a vacuum in the PCV line then the PCV slams shut which you can also HEAR and also see on a vacuum gauge

Google how a PCV valve works to see internals

As RPM increases the frequency increases and your ability to detect it diminishes

.

[Va68goat]

Formulas,
Yeah..thats going to be addressed the next time we work on the motor. By then we'll have a new compression test gauge as well so we can take care of a few things that need to be addressed. Appreciate the info!

[Pronto Poncho]

Originally Posted by Formulas

Skip in vacuum reading can also be the PCV valve plumbed into a single runner

7 cylinders will be slightly higher and smooth then the one cylinder will hit, it has to draw a vacuum in the PCV line then the PCV slams shut which you can also HEAR and also see on a vacuum gauge

Google how a PCV valve works to see internals

As RPM increases the frequency increases and your ability to detect it diminishes

.

Very Good Stuff, Thanks

[dataway]

It would be weird if it ended up being something like the valley pan flexing under fluctuating vacuum signal ... like popping the bottom of a tin can back and forth.

[Va68goat]

STEELCITYFIREBIRD,

grivera just called me and told me to take a look at your last post and my quote. I forgot all about that post regarding the 150 reading on the compression test that we took last year. It took me a while to find it but it's post# 206 and dated 9/16/2018. That compression test was with the plugs out, engine warm, strong battery, 3 cranks and what was reported as a good gauge because it had been recently used and confirmed prior to being used for my test. That compression test read 150 across the board. I don't know if its where it needs to be or not but that is where it read on 9/16/2018. Is that anything to be concerned about or could cause a knock?

[Formulas]

Originally Posted by dataway

It would be weird if it ended up being something like the valley pan flexing under fluctuating vacuum signal ... like popping the bottom of a tin can back and forth.

The PCV valve by virtu of being in the pushrod cover helps to make the sound bigger like a drum skin

This isn't a theory or guess circa 1982 I put a p4b intake on my 1968 GTO removed the q'jet intake I totally forget what carb I used but i plumbed PCV through a front runner and thought i hurt my engine by foreign debris because it was making noise and idle was not as smooth

Since I am not in front of original poster's engine I won't go as far as to say this is his problem but its soooooo EASY and cost nothing to check to eliminate.

.

[STEELCITYFIREBIRD]

Originally Posted by dataway

It would be weird if it ended up being something like the valley pan flexing under fluctuating vacuum signal ... like popping the bottom of a tin can back and forth.

I could only see that happening if there is no or inadequate source of air in to motor.

Just pull PCV valve and cover with your thumb. No noise reduction or smoother running... move along.

Compression tester is nothing more than an air pressure gauge with a check valve inline. (motor is an air pump your testing). A quick check with your shop air from a rubber tip blow gun will verify your gauge and integrity of the hose and check valve against shop compressor line regulator gauge psi output . The only thing you can't check is how well it will seal to the spark plug hole.(without some fabrication).

Any info/pictures on which crank pin/s the problem occurred on or pics of crank and damaged/replaced rods/parts?

Take all the spark plugs out when doing compression test on an entire engine!

[STEELCITYFIREBIRD]

-Do you have idle speed, base timing / full advance specs from Paul /Jeff Korner?( carb builder) for this engine/dizzy/carb combo?

HWYSTAR mentioned he baselined the idle mixture screws @ 3/4T out.

-Where were they before adjustment?

Does the engine respond to adjustments, via the vacuum gauge reading?

We use Braswell custom carbs exclusively on all our race motors, the baseline on the gas motor is 1 1/4 to 1/1/2 turns out (4 corner idle). Purpose built, Custom carbs can vary greatly from an out of the box Holley.

A loss or drop in oil pressure is a big difference if it was at idle no load vs during a full pull at high RPM.

I'm disappointed and truly surprised Paul has drawn back from helping getting this figured out and remediated.

BTW:
I have no interest other than to help identify and repair this/these problems in a in a concise and logical way.

[Va68goat]

STEELCITYFIREBIRD,

Paul and Jeff did provide that information and it was done (Idle speed, timing etc). Next time we deal with the carb, we'll call Jeff though. Paul indicated that Jeff uses several different parts to build his custom carbs...I'm not sure what they are. I'm disappointed as well about Paul but for now...this part of the train is still moving. We are still driven to get it right. Jeff says he located a guy in my area that would be willing to take a look at the motor so I'm hoping that happens soon. The season will be over before you know it!

[HWYSTR455]

I was going to dial the idle mix screws out to 1 1/4 each, remove/move the PCV, make sure only the batt/12v is on the coil and nothing else, and verify initial timing. Maybe bring a new coil to try, and check the dizzy cap for carbon tracking.

And yes, was going to bring a tach and vacuum gauge, just so there's no question there.

Was hoping to go there tonight, but not up to par the last couple days, will have to see how I feel later.

The note Paul included on the engine was for total timing of 34 degrees, so with the 18 degree bushing, would call for roughly 14 initial. Since you can't determine the advance curve or vacuum advance needs of an engine in actual driving conditions on the dyno, those recommendation were obviously omitted.

So mentally reviewing theory, the firing order is #1, then #8, and if due to the PCV being on the #1 runner, potentially running lean, possibility of advanced timing, and the 'noise' coming from roughly the passenger rear of the engine, it's possible #8 is experiencing pre-ignition, which certainly can cause a knock type sound. Might be a stretch, but feel its worth eliminating that factor/question.

Dial-back timing lights can be tricky, have seen folks have erroneous readings, and not even realizing it.

.

[mgarblik]

Originally Posted by HWYSTR455

I was going to dial the idle mix screws out to 1 1/4 each, remove/move the PCV, make sure only the batt/12v is on the coil and nothing else, and verify initial timing. Maybe bring a new coil to try, and check the dizzy cap for carbon tracking.

And yes, was going to bring a tach and vacuum gauge, just so there's no question there.

Was hoping to go there tonight, but not up to par the last couple days, will have to see how I feel later.

The note Paul included on the engine was for total timing of 34 degrees, so with the 18 degree bushing, would call for roughly 14 initial. Since you can't determine the advance curve or vacuum advance needs of an engine in actual driving conditions on the dyno, those recommendation were obviously omitted.

So mentally reviewing theory, the firing order is #1, then #8, and if due to the PCV being on the #1 runner, potentially running lean, possibility of advanced timing, and the 'noise' coming from roughly the passenger rear of the engine, it's possible #8 is experiencing pre-ignition, which certainly can cause a knock type sound. Might be a stretch, but feel its worth eliminating that factor/question.

Dial-back timing lights can be tricky, have seen folks have erroneous readings, and not even realizing it.

.

It seems to me you will be dealing with two situations on this engine that may or may not be related. 1. very rough idling/running engine. 2. Engine noise.
Since the "engine noise" has been reported to have been there since day 1, it is probably safe to assume it isn't hurting anything immediately, given the many times it has been run in the car and on the dyno. So personally, I would concentrate on getting the engine to idle correctly and run right. Recently within the 1060 posts, it was mentioned that the engine now has a carburetor on it that is "new" to this engine and hasn't been run or tested on this engine? When you are dealing with problems, that's a bad thing to add to the mix. In our dyno cell, we have 1 carburetor we all refer to as the "go to" carb. It is a generic Holley 750 that was worked over by BLP in FL and donated to the school. Think of it as a "dyno carb". Whenever we have someone's engine on the dyno and it's doing weird things, just not putting up the numbers, whatever the reason, we take their carb off and just bolt this thing on. 9 out of 10 times, the "go to" carb fixes whatever the problem was and makes more power. It always "changes" the way the engine runs so it gets the thinking going the right direction no matter what.
I assume you guys have whatever carburetor was on this engine when it was idling smoothly and running correctly? I would strongly consider putting it back on to re-establish a base line for this engine. Once it's running and idling properly on 8 cylinders, you can turn your attention back to problem #2, engine noise, if it's still present. Good luck with the evaluation. This is the most bizarre sequence of events I have ever heard of on a Pontiac engine. Hope you can get it solved.