Detonation, 10.7 ratio and 91 octane isn't working. ****UPDATES ****

[Kern Dog]

Does anyone know how to make this work?
I have a 440/493 combo. 440 block with a 4.15 stroke crank. The pistons are .017 in the hole. .39 Fel Pro head gasket. This adds up to a 10.7 compression ratio. I was told when I bought the crank, rods and pistons that it would work on 91 octane pump gas. It does if I drive it in cool weather with a meager 30-31 degree limit on the mechanical advance. I have an 850 VS carb, 2" headers, An Edelbrock RPM intake.
This sucks. It is getting warmer and I hate dealing with the pinging and poor performance.
I am running the Mopar Performance 292/509 cam installed straight up. I used this cam in 2004 when I first built the engine. At that time I had it advanced 4 degrees. I had cranking compression over 225 and it rattled like crazy. I set it to straight up and it helped, but it still isnt right. I have read that cam timing can make it possible to live with high compression and pump gas. The idea is that the cam helps bleed off cylinder pressure.
I should probably state my goals of the engine and car. I want a great running, pump gasoline engine that never rattles. I don't mind a rough idle, since I am used to it with the '509 cam. I like to actually drive the car. I just returned from a 995 mile round trip for the Van Nuys Spring Fling. I don't need a peaky race engine and I'm not expecting to commute 40 miles to work in it. Something in the middle of those is what I am looking for.
Any suggestions?

[68CoronetRT]

First off, what heads are you running? Head Volume in CC's?(IE: 84/88cc Edelbrock, 80cc 440source etc..)

My first guess would be to stick a .051 compressed headgasket(staying with a standard gasket) in there and it should lower it to around 10.5:1(I think) which would be almost ideal IF your running aluminum heads. You could go ever thicker but then you would have to run a copper gasket(not sure about these??).

If they are iron heads then you are running waaaaay too much compression for pump gas.

[Kern Dog]

I'm sorry I forgot to mention. I have the 84 cc Edelbrock aluminum heads. They are basically out of the box.
I've seen the .51 gaskets listed. I've wondered if the thicker gasket and a different cam could be enough to get me a bit more detonation resistance.

[firefighter3931]

The 509 is building too much midrange cylinder pressure and that is why it is detonating under load. 

What you need is a cam with a wide 112*lsa to flatten out the torque curve and reduce cylinder pressure. The tight lobed cam profiles spike torque over a narrow powerband and when you hit that sweet spot it will detonate if things are not right. In your case it's a combination of too much static compression and not enough octane. 

If you're stuck on that particular brand....MP makes a wide lsa version of the 509 cam that i believe has a 114* lsa.


Ron

[Kern Dog]

If you're stuck on that particular brand....MP makes a wide lsa version of the 509 cam that i believe has a 114* lsa.


Ron

Stuck on that brand...

I may have forgot to mention. I started with this cam when I built the engine. I switched to a Comp cam stick that went flat within 100 miles. The replacement cam also went flat in short time. I went back with the MP cam to save cash. I am not married to any brand. I just want reliable performance.
The wider LSA theory makes sense. Maybe I'll call Comp or Hughes and see what they recommend.
Thanks everyone, Greg

[Challenger340]

Any chance the engine is running lean ?
Exremely lean mixtures burn fast & erratic exposing too much of the cylinder walls to peak combustion temps.

10.8:1 should not be a problem on 91 Octane with Aluminum Heads, with any Cam at, or approaching 70* ABDC IVC point seat to seat timing on the 6.76" Rods, even at sea level ?

Whats the cranking pressure now ?

[Kern Dog]

I had the engine apart in Feb 2011 to hone the cylinders and put in new rings. Before the teardown it was reading at a low of 178 and a high of 190. It was smoking under heavy acceleration and I suspected the rings were wasted. They were. Luckily I didn't have to go to .040. My machinist thought that the rings wore out from running too rich. I stepped down the power valve. It only smokes black when it detonates. 6 months ago I started installing a wideband air/fuel guage to get an accurate tune. Life got in the way and the furthest I've gone with it was to have bungs welded in the collectors.
I may go ahead and check compression PSI #s to have a baseline to work from.

[jlatessa]

I thought lean mixtures burn slower, hence the need for vacuum advance at
cruise??

An O2 sensor will point you in the right direction.

Joe

[Cooter]

I too am fighting this problem right now. Too much Static Compression with Iron heads.

[Kern Dog]

Today I spoke with Ken at Hensley Performance. I bought the rotating assembly from them in 2004 and they have been really helpful. Ken suggested using a .051 Fel Pro head gasket and a milder cam with a 110 LSA. I am confused though. Everything that I have read so far has told me that a MORE aggressive cam is what is needed to bleed off cylinder pressure. It seems that going smaller would increase cylinder pressure and ADD to the problem.
I wish that I had more experience with this stuff.

[mhinders]

As far as I understand both too lean and too rich mixtures burn slower than the optimum mixture, from memory I take 12.4:1 as the optimum performance mixture. Slow cruising can run leaner mixtures to save gas.

To lower the dynamic compression, and hopefully decrease the risk of detonation,  I believe you need a later closing intake valve, either by replacing the cam or retarding your current cam. 

[Kern Dog]

I have seen ads about the .020 steel shim head gasket. Any idea why they call it a shim? Is it because it can be used along with another gasket to achieve a greater thickness? I had an idea of seeing them on the deck, followed by a Fel Pro blue composition gasket above it. This would result in a .059 thickness for a fraction of the cost of a .060 Cometic. I have 2 pair of Fel Pro .039 gaskets already...

[Cooter]

I have seen ads about the .020 steel shim head gasket. Any idea why they call it a shim? Is it because it can be used along with another gasket to achieve a greater thickness? I had an idea of seeing them on the deck, followed by a Fel Pro blue composition gasket above it. This would result in a .059 thickness for a fraction of the cost of a .060 Cometic. I have 2 pair of Fel Pro .039 gaskets already...

In a word, No....The "Shim" gasket means just that, it is a Single 'Shim' style gasket instead of the Fel-Pro "blue" which is multi-layer, as is the Cometic gaskets.

Stacking up Head gaskets is NOT a good idea. I have done it on the race car AT THE TRACK to make the next round, but NEVER on something I want to last. EASY way to cause all kinds of problems like Leaking coolant into combustion chambers/Vice versa.
Bite the bullet and get the GOOD gaskets, do it one more time, and be done with it. Oh and BTW, I know it's harder to do than it sounds, but listening to too many folks who post Opinions, can cause you to do what I did. I was told my engine would "ok" with iron heads and now it runs on 100 Octane.
Shoulda listened to my instincts and just built a low comp Nitrous engine like I always did. Stick with what YOU KNOW is the real thing to do here. That is to lower the compression the tried and true way. You sound like you cannot afford to "Experiment" with fifty different options here, so Thicker head gaskets is the only TRUE way YOU KNOW to lower it.

[justcruisin]

I Have been following this thread with interest, I would have to question installing a thicker head gasket, my understanding is that a tight quench of around .040" is a good way of helping with detonation. You are at .057" now, is adding another .012" going to help or make it worse. You might find that more timing is needed to compensate for the slower burn. I would think that a cam swap would be the right way to go. Before you head in any direction I would be doing plenty of research, and making sure your fuel curve isn't to lean.

[Kern Dog]

Today I spoke with William at the Comp Cams tech line. He believes that the idea of using a milder cam is flawed like most everyone else thinks. He liked the idea of using the thicker head gasket, but to stay with the '509 cam. I was surprised that he didn't try to sell me a camshaft. He said that I should be able to make things work with a small drop in compression and some tuning.
I hear quite often that my current combination should work. The engine runs cool. The timing isn't cranked to 40 degrees. I run vacuum advance because Rick Ehrenberg from Mopar Action magazine feels that it promotes complete combustion. Maybe I could try plugging the cannister and see how it runs.

[cdr]

if you are running vacuum advance with almost 11 to 1 compression ,THAT is going to detonate,unplug it & set your total timing at 36 & go drive it,tune from there.

[firefighter3931]

if you are running vacuum advance with almost 11 to 1 compression ,THAT is going to detonate,unplug it & set your total timing at 36 & go drive it,tune from there.

Bingo ! Disconnect that stupic vacuum advance and re-tune the car. With the closed chamber E-Heads set the total at 35* because that's where it will make best power.  

I run vacuum advance because Rick Ehrenberg from Mopar Action magazine feels that it promotes complete combustion.

I get tired of hearing this complete combustion arguement   Vacuum advance is an emissions thing and designed to work with a stock engine that makes 18-20 inches of vacuum at idle. Throw a lumpy cam in the mix and it becomes a tuning headache !!!  

Every car i've tuned removing the vacuum advance has run a LOT better !!!!    

If you have 185 psi (or less) cranking pressure with a tight quench/closed chamber aluminum head the problem is tuning ; too lean or timing needs some tweaks.  



Ron

[HPP]

If you don't want to get into the engine, you could always try water/methanol injection. http://www.snowperformance.net/

[cdr]

if you are running vacuum advance with almost 11 to 1 compression ,THAT is going to detonate,unplug it & set your total timing at 36 & go drive it,tune from there.

Bingo ! Disconnect that stupic vacuum advance and re-tune the car. With the closed chamber E-Heads set the total at 35* because that's where it will make best power. 

I run vacuum advance because Rick Ehrenberg from Mopar Action magazine feels that it promotes complete combustion.

I get tired of hearing this complete combustion arguement  Vacuum advance is an emmissions thing and designed to work with a stock engine that makes 18-20 inches of vacuum at idle. Throw a lumpy cam in the mix and it becomes a tuning headache !!! 

Every car i've tuned removing the vacuum advance has run a LOT better !!!!   

If you have 185 psi (or less) cranking pressure with a tight quench/closed chamber aluminum head the problem is tuning ; too lean or timing needs some tweaks. 



Ron

i will repeat again,, disconnect the vac advance & retune!!!!!!!

[Kern Dog]

I still need to finish installing the air/fuel wideband guage. Is it fair to say that it would detect any difference in combustion when I disconnect the vac advance?
I know that with many things, it is the small details that can make the difference. I should have mentioned the vacuum advance in the first post. Thank you everyone.

[Musicman]

Vacuum advance is an emissions thing and designed to work with a stock engine that makes 18-20 inches of vacuum at idle.

I wouldn't call vacuum advance an emissions thing per say... the "Ported Vac" your plugging into is an emmisions thing yes, and it will interfere here, because as you said "Vacuum advance is designed to work with a stock engine that makes 18-20 inches of vacuum at idle."

[cdr]

yes the tune ,air fuel ratio on the wide ban will change with different timing.

[Budnicks]

if you are running vacuum advance with almost 11 to 1 compression ,THAT is going to detonate,unplug it & set your total timing at 36 & go drive it,tune from there.

I agree, could be too much mechanical advance too, added with what the vacuum advance adds, it could be tamed down also, there are adjustable vacuum pods on MP CEI distributors you can turn it down significantly &/or even try to change it mechanically with spring & weights... to have a total of 36* when the all the advance is in... Possibly if you have 36* in the distributor total, with the vacuum line unplugged & then have the vacuum advance added it's probably in the 50* range at part throttle... could be an issue, that's what I've done anyway, with an adjustable vacuum advance pod on a MP CEI Chrome Box/ECU & MP CEI Adj. vacuum pod on the MP CEI Distributor, from Mancini Racing... a different camshaft would make a world of a difference also, there's allot better cams than a MP 509 Purple Shaft for you combo out there, as some have mentioned here already... Good Luck

[69wannabe]

I agree with Ron completely about disconnecting the vacumm advance!!!! I have built a lot of engines for people in my area (mild 383's and 440's) and have never hooked up the vacumm advance. Tried adjusting the canister to where it doesn't advance too much and still plugging it off makes the engine's run better to me. Met a guy a couple years back with a 69 general lee charger and he asked my advise on a small issue he was having, went down the road and I told him to pull off for a sec so I could try something. Plugged the vacumm advance off and we drove down the road and it was smoother and ran more solid. He had read the same article about complete combustion and I just said well it runs great now so what do you want to do?? Hook it back up so that it runs like crap and his was pinging too or plug it off and it stopped pinging and ran much better?? He left it plugged off and has been happy with it every since!! If Ron says plug it off then that's what I would do!! He steered me in the right direction with some timing issues I was having with my 493. I haven't been on the forums long but this guy knows his stuff for sure!!!

[Kern Dog]

I pulled the vacuum line yesterday and took a 175 mile drive today. The part throttle ping is gone, but I still get some at around full throttle. Until I make some internal changes, I may need to run a few gallons of 110 Sunoco in a tank of 91. That ought to raise it to 95-96 octane.