Any experience with camshaft dynamic compression induced ping?

[dfarr67]

I'll add info as requested, but working with a knowledgeable tuner for some time trying to beat a persistent ping in the high map 3200rpm or so. I have corrected a few problems along the way. Finally got around to do a compression test that shows some concern but apparently not enough to pull engine at this point. He is starting to suspect the cam which when I was dealing with Erson was the smaller of the two cams suggested- ecu is speed density and was worried about low vacuum. I know these TPI intakes may have some weird areas that need special tuning.

- engine SBC gen1 385
- Bore 4.040, stroke 3.75
- rods 5.7
- pistons unknown full dish, spec called for 9.5ish compression to run 87 octane, unable to run that to date (91 tune not completed).
- as I remember- running a tight quench of 0.035
- induction FIRST TPI
- heads alum AFR vortec, 1.6 rockers

Some of the comments from the tuner below.

Seems like the 1.60" rockers added 2* more overall to your cam specs, so by using an IVC of 41 instead of 39, your Dynamic Compression would come in at 9:19.1 instead of 9:3.1. Static compression would remain the same of course at 10:82.1 That's still kinda high for pump gas on the Dynamic Compression side with iron heads, as well as aluminum heads for that matter. We always try to shoot for an in between ratio of 8:1.1 and 8:5.1 for Dynamic Compression when running pump gas, it allows for the higher Static Compression to bleed off just before quench...
If it turns out the numbers above for your engine are close to accurate, and if you are hovering in between 10:5.1 and 11:05.1, then that is actually a good thing. That is the perfect static compression for a naturally aspirated engine. However the cam though, you would want a cam with an IVC at 0.50" of about 52 or a tad higher, as this will bring your Dynamic Compression with those aluminum heads down to about 8:52.1 and will allow for and tolerate pump gas a whole lot better. Your current IVC at 0.50" of 39 (41 with 1.6" rockers) causes your Dynamic Compression to be way too high at closer to 9:33.1 with your current cam...

[F-BIRD'88]

Where ever did you get the idea this engine would run on 87 octane? Change your theory. Its wrong.

[tjs44]

Looks like with the pumping compression it should run on 91?Tom

[dfarr67]

Where ever did you get the idea this engine would run on 87 octane? Change your theory. Its wrong.

All I was looking for was the stroked vortec. 9.5:1 with nice heads. Did Erson put me into a wrong cam?

[modok]

Long story,
I am not sure if I am getting it, tell me if this is right
You don't know what the compression ratio is.
And the tuner is trying to determine the compression ratio from the compression test results and cam specs.

[My427stang]

Really need real numbers to help. If you can share actual SCR, or components to compute it, and the specific cam, likely easy to determine what is happening.

However, lots of things can make it rattle

[Stan Weiss]

I'll add info as requested, but working with a knowledgeable tuner for some time trying to beat a persistent ping in the high map 3200rpm or so. I have corrected a few problems along the way. Finally got around to do a compression test that shows some concern but apparently not enough to pull engine at this point. He is starting to suspect the cam which when I was dealing with Erson was the smaller of the two cams suggested- ecu is speed density and was worried about low vacuum. I know these TPI intakes may have some weird areas that need special tuning.

- engine SBC gen1 385
- Bore 4.040, stroke 3.75
- rods 5.7
- pistons unknown full dish, spec called for 9.5ish compression to run 87 octane, unable to run that to date (91 tune not completed).
- as I remember- running a tight quench of 0.035
- induction FIRST TPI
- heads alum AFR vortec, 1.6 rockers

Some of the comments from the tuner below.

Seems like the 1.60" rockers added 2* more overall to your cam specs, so by using an IVC of 41 instead of 39, your Dynamic Compression would come in at 9:19.1 instead of 9:3.1. Static compression would remain the same of course at 10:82.1 That's still kinda high for pump gas on the Dynamic Compression side with iron heads, as well as aluminum heads for that matter. We always try to shoot for an in between ratio of 8:1.1 and 8:5.1 for Dynamic Compression when running pump gas, it allows for the higher Static Compression to bleed off just before quench...
If it turns out the numbers above for your engine are close to accurate, and if you are hovering in between 10:5.1 and 11:05.1, then that is actually a good thing. That is the perfect static compression for a naturally aspirated engine. However the cam though, you would want a cam with an IVC at 0.50" of about 52 or a tad higher, as this will bring your Dynamic Compression with those aluminum heads down to about 8:52.1 and will allow for and tolerate pump gas a whole lot better. Your current IVC at 0.50" of 39 (41 with 1.6" rockers) causes your Dynamic Compression to be way too high at closer to 9:33.1 with your current cam...

Since when is DCR calculated using 0.050 IVC?

What are your cam specs at the valve (seat-to seat) and where is the ICL?

What do you thing adding another 10 degrees to your IVC will do to your cranking compression? If you have the VTP clearance just retard the cam 10 degrees. I would guess cranking compression will drop over 20 psi.

Stan

[dfarr67]

Long story,
I am not sure if I am getting it, tell me if this is right
You don't know what the compression ratio is.
And the tuner is trying to determine the compression ratio from the compression test results and cam specs.

Morning, I wanted the compression to be around 9.5:1 static. Builder claims KB pistons went in, last time I had the head off the piston is a full dish type and I am only aware that KB makes a D-dish.
Was visiting a different machinist on another matter he took a look at this info and said it was around 10-10.5:1.
We worked through a couple issues- one being timing tab was incorrect, but when corrected was still pinging. Working through things- he figures the cam is the issue or a possible solution.
I'm also wondering.....the cam is ground +4deg, installing it -4 or straight up- is this worth the effort?

[dfarr67]

Really need real numbers to help. If you can share actual SCR, or components to compute it, and the specific cam, likely easy to determine what is happening.

However, lots of things can make it rattle

Supplied cam specs were attached in the original post.

[dfarr67]

I'll add info as requested, but working with a knowledgeable tuner for some time trying to beat a persistent ping in the high map 3200rpm or so. I have corrected a few problems along the way. Finally got around to do a compression test that shows some concern but apparently not enough to pull engine at this point. He is starting to suspect the cam which when I was dealing with Erson was the smaller of the two cams suggested- ecu is speed density and was worried about low vacuum. I know these TPI intakes may have some weird areas that need special tuning.

- engine SBC gen1 385
- Bore 4.040, stroke 3.75
- rods 5.7
- pistons unknown full dish, spec called for 9.5ish compression to run 87 octane, unable to run that to date (91 tune not completed).
- as I remember- running a tight quench of 0.035
- induction FIRST TPI
- heads alum AFR vortec, 1.6 rockers

Some of the comments from the tuner below.

Seems like the 1.60" rockers added 2* more overall to your cam specs, so by using an IVC of 41 instead of 39, your Dynamic Compression would come in at 9:19.1 instead of 9:3.1. Static compression would remain the same of course at 10:82.1 That's still kinda high for pump gas on the Dynamic Compression side with iron heads, as well as aluminum heads for that matter. We always try to shoot for an in between ratio of 8:1.1 and 8:5.1 for Dynamic Compression when running pump gas, it allows for the higher Static Compression to bleed off just before quench...
If it turns out the numbers above for your engine are close to accurate, and if you are hovering in between 10:5.1 and 11:05.1, then that is actually a good thing. That is the perfect static compression for a naturally aspirated engine. However the cam though, you would want a cam with an IVC at 0.50" of about 52 or a tad higher, as this will bring your Dynamic Compression with those aluminum heads down to about 8:52.1 and will allow for and tolerate pump gas a whole lot better. Your current IVC at 0.50" of 39 (41 with 1.6" rockers) causes your Dynamic Compression to be way too high at closer to 9:33.1 with your current cam...

Since when is DCR calculated using 0.050 IVC?

What are your cam specs at the valve (seat-to seat) and where is the ICL?

What do you think adding another 10 degrees to your IVC will do to your cranking compression? If you have the VTP clearance just retard the cam 10 degrees. I would guess cranking compression will drop over 20 psi.

Stan

This is all chinese to me- that's why I phoned Erson to get a recommended cam. Cam specs are attached to first post. I've seen the piston which are a full dish (cc unknown) and I don't understand how compression can get that high without at least a flat top. Maybe it's the 64cc chamber?

[rgalajda]

LOBE SEPARATION 112
ADV. OR RET. DEG. 4
INTAKE "LASH" DUR. 290
EXHAUST "LASH" DUR. 294
INTAKE DUR @ .050" 222
EXHAUST DUR @ .050" 226

Would think if those are dished pistons your static compression with those AFR 65cc ? chambers would be 9.5ish
You should be able to verify those pistons and Heads.
Is this a street vehicle? What distributor are you using?. What is your timing specs?

[Stan Weiss]

290 lash duration in @ 108 ICL / IVC 73 ABDC with the listed engine spec will crank about 160 psi with SCR around 9.05:1. 9.05:1 SCR will need a total volume of around 98 cc's. So with a 65 cc chamber heads the piston dish would need to be around 25 cc's.

Stan

[rgalajda]

290 lash duration in @ 108 ICL / IVC 73 ABDC with the listed engine spec will crank about 160 psi with SCR around 9.05:1. 9.05:1 SCR will need a total volume of around 98 cc's. So with a 65 cc chamber heads the piston dish would need to be around 25 cc's.

Stan

Stan his dry compression shows around 140 and wet around 160 so which one would you use?

[skinny z]

Has there been any mention of the compression test altitude?
If I'm not mistaken, this could be somewhere around 3000'.

[dfarr67]

These are the heads- untouched.
https://www.airflowresearch.com/190cc-s ... nder-head/

Elevation 980m/3200ft

At one time this was dyno tuned on 91 octane and worked well, changed from 34pph/gen3 to 36pph/gen4 bosch injectors due to a damaged plastic body and changed from 3/8 1.5 to 7/16 1.6 rockers. Probably need a good dyno tune again. But was hoping to step down in octane= not necessarily 87. But I have my own thoughts about freshness of premium in this area. Also was having oil sucked into the plenum- I figured it was burning and lowering the octane, fixed through adjustable PCV and catch can- no real difference, but engine was never smokey at any time and negligible oil usage.

I was running 10 deg advanced (overall) due to a timing pointer issue which was fixed, base timing is set at zero. ESC module and knock sensor are paired to a corvette roller cam application. Areas have cleaned up- but not enough. I am using a WB, but I am thinking it would be better to have a dyno WB backing that up.