Living with 10.8 compression on the street ??

[Kern Dog]

In 2004 I threw a rod in a 440 in the Charger. I had to build something to get the car mobile again. I went the route of adding a 4.15 crank to a .030 440 to end up with 493 cubes.
I bought my rotating assembly from Hensley Performance. Ross pistons, Manley rods, Eagle crank...All quality stuff. I already had Edelbrock aluminum heads.
I'm getting tired of being on the ragged edge of detonation with this engine. The 10.8 ratio means that I always have to run the highest pump octane available AND limit my total mechanical advance to 30 degrees or less. I am running a MP '509 flat tappet cam, so I also need about 17-19 degrees of initial advance to have some semblance of decent idle.
I just returned from a 900 mile round trip for a car show in Los Angeles. The car is fine when the engine or the weather is cold. Once the air gets over 70, the engine will ping at part throttle, full throttle... everything but idle. I have tried it with and without vacuum advance. It gets better highway mileage with it connected.
I once had a Comp Cams XE 285 HL cam in the car along with thicker Cometic head gaskets. The engine seemed less likely to detonate with this setup but that cam wiped a lobe before the hot weather hit. I swapped in another and it failed soon thereafter. I went back to my '509 with new lifters. It has held up since 2006. I have since learned about the need of oil supplements becaust of the reductions of ZINC in todays oils.
My question to you is....Can camshaft timing make the engine more resistant to detonation? If I need to pull the engine to install a dished piston, so be it. I just want the ability to drive in any weather without rettling apart. I want to maximize the potential of the build.

 

[6packMIKE]

Timing means a ton for performance. WOw that doesn't seem like you are advanced enough if you are at 30 degrees.....or less. Is your motor a turd when you jump on it? Normally if my ride was pinging under hard acceleration I would retard my timing a little. 30 seems like a lot to me. Is your carb set up properly?

I run 5 gallons of 110 with my 93 octane to get around 98 octane and have no issues in my 440. 11:1 comp. I was able to advance my timing more and get a lot more performance. 36-38 degrees. I had to get rid of the vacuum advance too.

 

[RustyRatRod]

You need a bigger cam.

 

[Kern Dog]

When I built the engine I was told that the compression ratio wouldn't bee too much for pump gas. I can't blame the guys at Hensley though. I should have done more research. I also should have considered the possibility that I may encounter situations when 91 wasn't available, like when on a road trip somewhere.
I have read that using a more aggressive cam can bleed off cylinder pressure.
The car scrams when it isn't pinging. I can run it hard when the weather is cold and it rarely pings. With 295 tires I have to walk it out of the hole. It will spin through 1st and halfway through 2nd if i want. I suppose that I can try running some race gas, but to me, that is only a crutch. I want the car to be able to run strong on pump gasoline. I can't run any water or methanol injection because the carb and air cleaner is right near the underside of the hood.
Most magazine dyno tests seem to show engines making the most power with 35-38 degrees of timing, so I know I am cheating myself out of power. I'm curious if a lower compression ratio with MORE timing would make more power. Some tests have shown a 4% increase of power for every point of compression though. If I drop mine by a point but then ADD 8 degrees of ignition timing advance, could this be a net gain?

 

[Hemirunner]

Tuning it would be a great start. If it's fine in cold weather but having issues in hot weather wouldn't the logical conclusion be that the carb is running rich leaving excess fuel available for detonation? 10.8 with aluminum heads will be more than fine on pump gas given the rest of the combination is right, although with your low octane west coast fuel, it will need to be very right. That camshaft isn't the best choice but should be fine in that combo. I'd start by looking at the carb, spark plug choice, and ignition timing curves to tune this thing.

 

[HorryMorry]

You need a bigger cam.

Can you explain why this would help with his detontion problem? I plan on running a similar comp ratio and am still learning the finer details.

 

[lewtot184]

there's too much cylinder pressure for the octane. closing the intake valve later will help but isn't an absolute cure. a camshaft with similar duration and 112-114lsa will help. a good quench will help. making sure there isn't any oil getting past the guides or sucking thru the intake gasket will help (oil in the combustion chamber will cause detonation).

 

[Cranky]

First off, what's your cranking PSI? As for a cam change, it can help a lot by bleeding off high PSI in the lower rpm range. What's your quench distance? Thicker head gaskets will lower compression but will also increase your quench distance which can actually increase problems with ping etc. Increasing quench distance is something I don't like doing....10.8 true compression is very workable so long as the rest of the combination is right but 10.8 isn't all that hard to work with on pump gas.

 

[6packMIKE]

Greg,

Sounds like you could have a couple things going on. Wait until your tank is almost empty and then put 5 gallons of race fuel in then try it again. And of course with the correct amount of timing. Not 30. If you mess with the timing you will also need to adjust the carb again too. You may also be able to gap your plugs more and run a little hotter plug. Both things I have had to do as well. What are you running now for gap and plugs? Keep messing with it.....you will get it. I don't think changing pistons and cams is the answer right now. I think it is more of a tuning thing.

 

[Garys1969RR]

Greg, can you tell us these specs on your motor? Head cc, distance below deck on your piston, piston dish or dome cc, head gasket thickness. Your stroke is 4.15 ", bore is 4.350? With this info, we can determine your exact C/R. It may be more than 10.8 to 1.

 

[Kern Dog]

The specs:
440 block, .030 over. Pistons are Ross with -6 cc valve reliefs. Pistons sit .17 below deck. Fel Pro head gasket, .039 compressed. Unless Hensley screwed up when I bought the stuff, this is the ratio that they calculated. I did the math as well and came up with the same number.
I'm running Champion RC9YC plugs gapped at .035. This is a change from the RC12YC plug I used to run. The 12s were recommended by Edelbrock. The engine had a severe case of dieseling/run-on until I switched to the RC9YCs. Mopar Performance chrome box ECU and a MP distributor.
The carburetor is a Barry Grant 850 with vacuum secondaries. 85 primary jets, 92 secondary. 3.5 Power Valve.
I am tempted to get a 5 gallon drum of race fuel just to see what changes I would see. I suspect that it would eliminate all detonation and allow even more advance. To me, this would suggest that the current combo would need to go one of two directions...1) Change some parts of the combination to run lower octane fuel or 2) Blend in race fuel to avoid detonation.

 

[Garys1969RR]

I would definitely try some high octane, such as Sunoco 100 octane race fuel. Thats what I run in my 451 with 13 to 1 C/R. Runs great with 38 deg total advance. At least that will let you know how the engine can run with the right fuel. I plan to go to E 85 this summer. Will need to change the metering blocks and jets in the Holley 780 to make it work. E 85 is around 105 octane, so should work well in a high compression motor.

- - - Updated - - -

And E 85 cost is 3.75 a gallon, compared to race fuel at 7.70 a gallon

 

[Kern Dog]

E-85 would be great if it were not for a few things:
Availability on road trips
Changes needed to run it
The fact that the engine needs MORE volume to make the same power. I'm averaging 12.5 mpg on trips now and getting about 200+ miles on a tankful. The stories I hear is that E-85 fuel gets 60% of the economy of gasoline, so I'd be down to 7 miles per gallon. I'd need to fill up at 125 miles or less.

 

[RustyRatRod]

10.8 with aluminum heads and spark knock doesn't sound like a quench motor at all.

 

[Kern Dog]

I thought that quench was effective at .040-.055.
With a .039 gasket and pistons .17 in the hole, I am just outside of the zone.

 

[Cranky]

.17 below deck or .017? Huge difference. I assume you mean .017.......and the tighter the quench, the better I like it short of the pistons hitting the head. Tightest one I've ever had a hand in was .019 and well, that was too tight lol but .040 is considered the norm but I shoot for no more than .030 on anything of mine.

 

[MikeStahl]

Like Cranky said tight is good!! here's a ? r they open chamber heads saw u had eddys but did not see which ones....being outside the zone harder to achieve (tight Quench)

 

[Meep-Meep]

The first thing you need to do is adjust the compression to the available fuel because anything else is a bandAid. 10.8:1 on the old engines is ridiculous for the crap we have in CA. Not only the static ratio, but the inlet charge temp, bore diameter, quench, swirl, mixture and cam timing all play a roll in the fuel octane requirement. I have a 10.1:1 440 and I can't hot rod it on 91 with the stock intake and 750 Eddy carb. But the 6 BBL seems to solve the pinging problems on the 91 gas but the power is down (based on 1/4 mile MPH).

Having a cam with a later intake closing point (like the .509") will bleed off some cylinder pressure. This might make a difference in the low RPM range but as your experience proves it's not good enough. Higher overlap has no effect on cranking compression. It also seems consistent with big cams that the initial timing needs to be advanced quite a bit.

If you want to play around with external components I suggest checking the A/F ratio and try a different intake and see if that helps the pinging.

 

[Garys1969RR]

With closed chamber heads, and a .020 steel shim gasket, .017 deck clearance you would probably be better off. The closer quench distance will help with the ping problem. My calculator says going from a .039" gasket to a .020" thick one will increase compression from 10.73 to 11.2 to 1 C/R. This is using a head with 84 cc volume. So I dont know for sure if the closer quench will off set the higher C/R

 

[Meep-Meep]

I'm running a 440 with -.015" in the hole with steel shim gaskets (~.020" thick) and my motor pings like an SOB when it's hot, under hard acceleration and with the stock intake and 750 Eddy. Carb may be a bit lean but it sure makes good power with a splash of 110 race gas. Just adding the 6 BBL makes the pinging go away but also killed some of my power, and according to an O2 sensor, the 6 BBL is lean! I say there is more going on with mixture delivery than an open vs. closed chamber head. I agree that a closed chamber may be a benefit, but the open chamber 906 type head is a quench head that will produce some swirl in the chamber. Just perhaps not as much as the 915 head.

One thing you can do to work on the pinging problem is to lower the thermostat temp. Put a 160 in it and see what that does. It's likely the engine will run closer to 180 anyway but not 200.