Detonating 493 and what I did to stop it.

[2Luke2]

Awesome Red! Let us know how it turns out. It will be nice if you can get it all sorted out finally. Should definitely feel like a huge weight was removed from your shoulders after it's all said and done.

[505charger]

I built my 505 stroker for my Charger with Eddy heads, 240@ .050 cam, 10.7 compression. I live at 4000 feet. It pings like a pig on the 91 octane gas that is available. Checked timing, jetting, tdc Mark on the dampner. Still pinged on anything more than partial throttle.
        My cure was to mix 100LL avgas 50/50 with the 91 octane gas. I'm a pilot but it should not be a problem for most folks to find a small airport to buy the gas. $6/ gallon or less. A lot cheaper than race gas and cured my problem.
        I'm really upset at the bad advice I was given to push the compression so high. What would I have lost power wise with 10-1? 20 hp? It sure has been a pain to mix gas. I think conservative on compression would be the way to go. The engine is a beast! Everything I hoped for. Still working on a rear main seal leak. Seal number 4 this week. Having a pro put this one in.

[2Luke2]

I built my 505 stroker for my Charger with Eddy heads, 240@ .050 cam, 10.7 compression. I live at 4000 feet. It pings like a pig on the 91 octane gas that is available. Checked timing, jetting, tdc Mark on the dampner. Still pinged on anything more than partial throttle.
        My cure was to mix 100LL avgas 50/50 with the 91 octane gas. I'm a pilot but it should not be a problem for most folks to find a small airport to buy the gas. $6/ gallon or less. A lot cheaper than race gas and cured my problem.
        I'm really upset at the bad advice I was given to push the compression so high. What would I have lost power wise with 10-1? 20 hp? It sure has been a pain to mix gas. I think conservative on compression would be the way to go. The engine is a beast! Everything I hoped for. Still working on a rear main seal leak. Seal number 4 this week. Having a pro put this one in.

Where abouts are you located at 5,000 feet? We are at 6090 in Colorado Springs, we thought we had a pinging issue due to high compression. We tried to buy gas from a local airport and they said no can do. Is there a process to buying it?

[Kern Dog]

The practice of running race gas or mixing AVGAS with pump premium may have been okay if I only drove around here locally. I like driving the car and if the mood struck to take a road trip, I was SOL. The higher compression for me meant compromise. I had to limit my ignition timing to avoid knocking. If I ran the higher octane race fuel and advanced the timing, the car did run pretty strong without pinging.
Some feel that a point of compression could be worth 3-4% of the total HP. If I am making 400 HP to the tires, thats only 12-16 HP. Retarding the timing to avoid detonation has to cost more than that. This is why I decided to reduce the compression ratio and then advance the timing to a number that makes the most power without rattling.
My long work commute beats me down so I've had little time to get back to the car.
Maybe tomorrow?

[Kern Dog]

I decided to map the fuel curve in the car by taking the wife along to record the Air/Fuel readings while I drove.

Todays report:

* Idle in Neutral 1100-1200 rpms 13.1 to 13.5
* Idle in Gear 750-800 rpms 17.8 to 18.0 +

* Slow acceleration from 2000-3500 rpms 10,9 to 11.6
* Slow acceleration from 3000-5000 rpms 11.9 to 12.4

* Steady cruise @ 40 mph in OD 12.9 to 13.3
* Steady cruise @ 50 mph in OD 12.0 to 12.5
* Steady cruise @ 60 mph in OD 11.9 to 12.3

* Faster acceleration from 2000-3500 rpms 11.5 to 12.0
* Faster acceleration from 3000-5000 rpms 12.6 to 13.1

* WOT in 2nd gear, 2000-3500 rpms 12.9 to 13.1
* WOT in 2nd gear, 3500-6000 rpms 11.8 to 12.5
* Repeat run 11.6 to 12.1

*********************************************************************

With this info, I see that I need to richen it up a bunch at idle in gear. It stumbled and stalled twice while leaving 2 different stop signs. I suppose that since this occurs at idle and not on the primary circuit, this is a matter of tweaking the idle mixture screws?
I wouldn't think it would need more accelerator pump volume would it?

The "Slow acceleration" between 2000-3500 and 3000 to 5000 showed it to be really rich. This was done at light throttle , I assume entirely on the primary circuit? This makes me think I need to use smaller primary jets.

Steady cruise at 40, 50 and 60 were done in overdrive resulting in a final drive of 3.05 to one. The numbers there are more like what I'm supposed to have at WOT.

The faster acceleration testing showed leaner numbers than the slow acceleration. This was still done without hearing the secondaries open. I'm not sure what to make of that. Maybe I need a power valve that opens sooner there? I have a 3.5 in the carb now.

At WOT it shows that the higher RPMs it goes fatter. I guess that is safer than leaning out.

I welcome any suggestions or comments on my findings.
My gut tells me to adjust the idle mixture screws to obtain a richer in gear reading. It tells me to lean out the jetting front and rear. I'm not sure what to do regarding the Power valve. I'm not sure if I should use a lower rated one than the 3.5 I have.
Please tell me what you think!

[justcruisin]

Looking at your idle A/F ratio I would say you are dropping a lot of vacuum at 750 rpm and the idle circuit is not pulling the right amount of fuel. Not sure what the fix would be there but you need more fuel at those revs. I would try upping the revs to 850 in gear, why does it drag the revs down by 400 rpm, is the converter to tight? You may need to play with idle mix, IFR's and IAB's to get it right but 18:1 is no good. The right combo is going to be realized by experimenting. I would get your idle in gear around 13.5 - 14:1 with the idle screws and see what happens to the A/F at higher revs from there.

[oldschool]

I built my 505 stroker for my Charger with Eddy heads, 240@ .050 cam, 10.7 compression. I live at 4000 feet. It pings like a pig on the 91 octane gas that is available. Checked timing, jetting, tdc Mark on the dampner. Still pinged on anything more than partial throttle.
        My cure was to mix 100LL avgas 50/50 with the 91 octane gas. I'm a pilot but it should not be a problem for most folks to find a small airport to buy the gas. $6/ gallon or less. A lot cheaper than race gas and cured my problem.
        I'm really upset at the bad advice I was given to push the compression so high. What would I have lost power wise with 10-1? 20 hp? It sure has been a pain to mix gas. I think conservative on compression would be the way to go. The engine is a beast! Everything I hoped for. Still working on a rear main seal leak. Seal number 4 this week. Having a pro put this one in.

on a different note, what do you fly? I own and fly a Bonanza......

[Kern Dog]

I'm happy to report that the detonation seems to be behind me. Now its a matter of tuning the combination for a balance of power and efficiency.
Today I turned the idle mixture screws to 2 full turns out from bottom. The idle in gear A/F numbers went from high 17s to around 13.0. It responds much better with the fatter setting. The rpm drop going into gear is only 200-250 rpms. The idle vacuum isn't great but the engine feels better. I still need to lean out the carb for better cruise and WOT numbers.

[stuubi]

505Charger:Is your cam flat tappet,or roller?And i think that your and some other's problem with detonation in due to wrong cam.Intake side is closing too fast and causing cylinder pressures go to the roof.
Just change cam that has bigger value on intake closing and forget racegas-pump gas mixing.

Sound's to me that your pinging is caused by DCR(Dynamic Compression Ratio) being too high.
SCR(Static Compression Ratio) is what you are always talking about,DCR is what says how close to detonation with pumpgas you are.General rule of thumb is that DCR should float in 7.5-8.5 area,That's safe zone.

You can't mess whit SDR without machining,changing head's(always a big change),pistons.
DCR you can adjust by moving advance or retarding cam,or chancing different cam.

For examble,i helped a friend to build 383chevy that had AFR head's,Comp Cams X-Treme mech roller cam and true 10.5 comp.
When we tested it,with 32 degrees,it ran ok.So we gave little more to 36 asnd it detonaded so bad that even i heard it and i was standing outside of the car.
I created so much cylinder pressure that it forced head gascet ring to go around headstud!

We studied what caused it and find out about DCR.Calculated it and it was 8.9..
Changed to Comp's Magnum series,same degrees and lift,but mich more degrees on intake closing,and it survived 38degrees with no problems.Same piston's,head's etc.Only the cam was differen't.

[Kern Dog]

The issue of the Dynamic Compression Ratio is one that many are not aware of. I only read about it a few years ago and I have been a car guy since the 80s.
Take an 11.0 to 1 engine and run it with a HUGE cam and you might be able to get by on pump premium gasoline. That same engine with a milder cam would need MORE octane since a milder cam traps more cylinder pressure. The mechanical compression ratio is the same with both cams but the bigger cam results in less cylinder pressure.
Going the other way, Take an 8.0 to 1 engine and put in a small cam. That engine might make the exact same cranking compression as an 11.0 engine with a big cam since the smaller stick traps more pressure.

[stuubi]

Exat-ly-mundo.
I've talked with many,who had detonation,hard hot starting etc problem's and explained to them what is DCR.And when start to plan engine for myself or "customer",they allways think i'm weird because i spend so much time choosing cam,pistons and head's.

And this is why i dont understand why you have to start playing with mixing gas,retarding timing to a level you start to actually loose lot of power just because you builded engine that has wrong cam in it?
Get cam that work's and make more power on pump gas than previous combo with mix-up gas.

Even if you had roller cam,just take the 300-400 bucks and get another cam that suits your engine better.Buy race gas for 6 month's worth and most likely spended more than cost of new cam.

This is probably,most likely the reason people think that just strokin you engine makes it detonation sensitive.It's not the stroke or bore,it's too little cam.

[femtnmax]

Yes, dynamic compression ratio.   What was it before, and what is it now?   Was it ever calculated with measured data??   Sorry if I missed this info during reading your posts.

[Kern Dog]

Measured my compression ratio ?   
Uhhh, yes....many, many times. I've crunched the numbers using several online calculators and always arrived at the same numbers: 10.73 to 1.
THEN I pulled the heads and checked my numbers again.
Up until I had the heads off, I thought my pistons sat .017 in the hole. This time every hole was found to be .012 in the hole. Small discrepancy, but just wait...
I measured the old head gaskets. The are advertised to be .039 compressed but I measured .033 to .035. Again not a huge error but I was still not "Spot on" with the numbers. I had the heads ported and had the chambers open slightly. The man cc'd the chambers afterwards. They averaged at 82.5 ccs when they are listed to be 84ccs. I've had these heads on and off 2 engines a few times and have had them resurfaced slightly to get a good gasket seal.
My point is that the actual compression ratio I was running was closer to 11.22 to one when I thought I was at 10.73. One thing is certain, my cranking compression was 191 on average.
Regarding dynamic compression, I can now calculate 4 versions of what I came up with :
10.73 CR # & 509 cam : 7.98
11.22 CR # & 509 cam: 8.33
10.73 CR # & Lunati cam: 8.09
11.22 CR # & Lunati cam: 8.45


11.

[Kern Dog]

Now with 10.07 compression, my Dynamic CR with this Lunati is 7.61.

[femtnmax]

Measured my compression ratio ?   
Uhhh, yes....many, many times. I've crunched the numbers using several online calculators and always arrived at the same numbers: 10.73 to 1.

I don't know what your laughing at...your the one with the engine problem.
I asked what your dynamic ratio was.  It doesn't matter what the static ratio 10.73 is. 

[Kern Dog]

What, No sense of humor over there?
I was laughing because I have calculated the compression ratio many, many, many times. No need to retort with  "You're the one having engine problems".
I have tried many, many things to get this problem solved. I left no stone unturned. Part of the reason I write about it is to provide a record for others to see. I figured that it might be helpful to others.

[2Luke2]

Measured my compression ratio ?   
Uhhh, yes....many, many times. I've crunched the numbers using several online calculators and always arrived at the same numbers: 10.73 to 1.

I don't know what your laughing at...your the one with the engine problem.
I asked what your dynamic ratio was.  It doesn't matter what the static ratio 10.73 is. 

Femtnmax, I wouldn't get upset about it. Red had been dealing with this problem for awhile and while you may think he was laughing at you I believe he was more laughing at himself so he wouldn't cry when he actually thought about how many times he actually has measured.

[Kern Dog]

What guy hasn't measured?

Luke is right. I have done it so many times, often using different online calculators in an effort to find a different number. To me the question was the same as asking me if I like big chested women. No effort on my part to piss on anyones suggestions!

[stuubi]

Red 70 R/T 493:
I looked your story and read it again.I have to because i felt that i've missed something.
Pictures you put,shows glearly NO sign's of detonation.

I searched what i believe is your cam car for Lunati cam you are running.
30210912?Correct?Or 40312
It has same deg,but less lift?

http://static.summitracing.com/global/images/instructions/lun-40312.pdf

It says same 106 center you said you installed it.

If i found wrong cam,can you give me part nro?


Bore 4.35
Stroke 4.150
Below deck 0.012
and 6.750 con rod
Valve relief 6.6cc
Heads 82cc

Are these correct?

If they are,here's how i got your number's with Lunati Cam.


Static compression ratio of 10.98:1.
Effective stroke is 3.45 inches.
Your dynamic compression ratio is 9.30:1 .
Your dynamic cranking pressure is 192.98 PSI.

This calculation has almost identical Cranking pressure as you posted,but WAY higher DCR.
It is possible that detonation that you experienced,is minor,and is mainly caused by the fact that youre running really poor quench and too little timing to compensate that.And you builded heavily grud in your chambers.And that will start to burn on it's own if you have DCR thru the roof.

If you add quench,you'll "slow the head's",it slowes flame travel?This was open idea,not likely to be fact.
And you cant burn gas anymore effective way.

[Kern Dog]

Thanks for the suggestions. I think that your "effective stroke" is wrong though since mine is 4.15 inches.

[stuubi]

No it is not wrong.
Your stroke at crank is 4.15,but you have to think it this way:

When piston start's it's travel from bottom DC(BTDC),it start's 4.15" travel towards TDC,right?

As it start's to travel,there is intake valve still open,(check cam card,it says intake closes 56.5 ABDC(After bottom dead center).
When intake valve closes at 56.5 degrees,piston has traveled 0.7".
Do you follow?
4.15" minus 56.5deg=0.7" equals 3.45" of travel.

So when both valves are closed and ACTUAL compression starts,it has 3.45" of travel left to reach TDC.
You need less travel than that.So you do need a cam that has more degrees on intake closing side.

So this is your current Lunati with .039 gasket:
Static compression ratio of 10.98:1.
Effective stroke is 3.45 inches.
Your dynamic compression ratio is 9.30:1 .
Your dynamic cranking pressure is 192.98 PSI.

Change cam that has int closes at 70deg:
Static compression ratio of 10.98:1.
Effective stroke is 3.07 inches.
Your dynamic compression ratio is 8.38:1 .
Your dynamic cranking pressure is 168.81 PSI.

[XH29N0G]

Thank you both, and others for posting this problem solving process and the explanations.

[cdr]

No it is not wrong.
Your stroke at crank is 4.15,but you have to think it this way:

When piston start's it's travel from bottom DC(BTDC),it start's 4.15" travel towards TDC,right?

As it start's to travel,there is intake valve still open,(check cam card,it says intake closes 56.5 ABDC(After bottom dead center).
When intake valve closes at 56.5 degrees,piston has traveled 0.7".
Do you follow?
4.15" minus 56.5deg=0.7" equals 3.45" of travel.

So when both valves are closed and ACTUAL compression starts,it has 3.45" of travel left to reach TDC.
You need less travel than that.So you do need a cam that has more degrees on intake closing side.

So this is your current Lunati with .039 gasket:
Static compression ratio of 10.98:1.
Effective stroke is 3.45 inches.
Your dynamic compression ratio is 9.30:1 .
Your dynamic cranking pressure is 192.98 PSI.

Change cam that has int closes at 70deg:
Static compression ratio of 10.98:1.
Effective stroke is 3.07 inches.
Your dynamic compression ratio is 8.38:1 .
Your dynamic cranking pressure is 168.81 PSI.

you are correct stuubi

[2Luke2]

So that brings up the question... what was the DCR before?

[Kern Dog]

I have used online calculators that computed both the actual compression ratio and the dynamic ratio. I have never heard of the "effective stroke" term before. I see the point though. My cranking compression before switching to these .075 Cometic head gaskets was 191 on average.  The Lunati cam card shows an intake closing of 56.5 degrees @ .050. The dynamic calculators I've seen instruct to add 15 degrees to the .050 number.
The engine with the MP '509 cam had an average cranking compression # of 188. The entire point of installing that Lunati cam was to lower the dynamic & cranking numbers. I was given incorrect info on the intake closing of both the '509 and this Lunati. The 509 actually had a later intake closing so the Lunati cam was a step backward.

I have more carb and ignition tuning to do, but this weekend I'm adding an H pipe to the exhaust. I suppose that in some way this may skew the A/F numbers so I'll resume tuning after the exhaust work. Later down the road I might change to a 3 inch mandrel bent exhaust so I'll need to rejet the carb at that point too.