No more high compression street builds for me

Paul_G · Monday at 9:25 PM

My 505 is toast. 2 broke pistons and the rest scored. How did it happen? I dont know yet. It denotated horribly. so what can cause that? Too much timing? Running lean? Failing fuel pump, clogged carb? Bad gas?

This engine has a 440 Source 440-512-5060 kit in it. PP240 heads. That should put it around 10.6 compression. That should have been fine. It was a beast, got absolutey no traction. On borrowed slicks it spun through first gear with anything more than 1/2 peddle.

The plugs were changed every year. No signs of detonation. Timing was held around 28° for street driving. The AFR's at cruise were around 14, WOT in the low 12's. On the track with Race Gas additive and 91 octane, I would bump the timing to 32°. Even with my poor driving skills (4speed) it still ran in the 12's.

I am putting it back together with the 5074 pistons from 440Source. Compression should now be in the high 9's. Much better on the street in 110° heat with the AC blowing cold. That engine never ran hot. In the summer heat the temps stayed under 200°

threewood · Monday at 10:20 PM

You should go low 9's and supercharge it. :poke:

Paul_G · Monday at 11:49 PM

threewood said:
You should go low 9's and supercharge it.

I bought one like that two years ago. A 69 RR with a 528 Hemi and Procharger on it. Nice body and paint. It barely ran, blowing smoke out the breathers badly and noisy as hell. Just the car for me. I put an AFR gauge on it and it was hitting the 15's at WOT. Can we say detonation. The Hemi had 4 broke pistons. It now has a motor home low compression fresh 440 with the Procharger and nice big pully on the PC making just 8# of boost. I converted a Holley 650 to blow through. Hogged the thing out to get in the 11's at WOT, with a very conservative timing map. Drives like a dream.

That 528 is now a 540. It's at IMM in Indio, CA. Brian is working his magic on it. It will be going in my 72 SSP which should be back from paint any week, or month, now.

RJ Squirrel · Tuesday at 12:09 AM

Well that sucks, I am thinking it has something to do with all the heat, cooking off the high end volatiles in the fuel, the asphalt right under the fuel tank is about 150 degrees on triple digit days. Also the air density is very low.
That RR sounds pretty sweet

RemCharger · Tuesday at 12:33 AM

Play with fire you get fire. But good on ya with proceeding. Finding the edge

451Mopar · Tuesday at 3:13 AM

What octane fuel?
My 10.3:1 505" stroker pinged a bit on a hot day when I was still tuning it. I think getting the tune correct really helped, but still run 91 Octane pump fuel.
The new 512 build is getting the low compression -27cc pistons should be around 9.5:1 compression, and might have a cam smaller than the 505" engine.
Might need to start a thread for how to build a low performance stroker and get input on parts for a mild street build for junk pump gas and smooth idle with good vacuum for the car that don't get raced.

autoxcuda · Tuesday at 4:49 AM

9:5 to 9.7 to 1 compression on street engines with pump 91-92 octane. Aluminum heads or not.

Like you said, it had more motor than it's ability to hook up in the street anyways. A 505 has a tons of torque.

How much HP/TQ are you really going to loose reducing it from 10.6:1 to 9.6:1 ? And I bet it will still spin the tires at will on the street.

hunt2elk · Tuesday at 5:10 AM

The gospel has always seemed to be that 10.5:1 compression is no problem at all for a street car. I followed that advice for years and always struggled with detonation no matter what I tried. My motors have now been rebuilt to 9.5 and 9.6:1 CR and are happy on 91 100% octane gas. Maybe 40 years ago 10.5 was ok, but not anymore imo. I figure todays shitty gas is the biggest contributing factor.

icetech · Tuesday at 5:34 AM

Glad this was posted.. am in the planning stage of my 408 (block is still months out on machining) and was thinking 9.7ish instead of 10+ not sure what the loss is but for a street car.. meh. plus 91 is like $2 cheaper than 93 here

DanielSlocum · Tuesday at 6:10 AM

Perhaps ring gaps were too tight and/or you got some old pump gas that lost some octane or never had its advertised number in the first place?
My rule of thumb for pump premium is a max of 10:1 with iron heads and 11:1 with aluminum heads. That standard has worked well for me for years.
Another factor though is cam/valve overlap. More overlap will reduce cylinder pressure some which will reduce heat and octane requirement. Less overlap will do the opposite.
Perhaps a small cam in a big stroker is creating too much "dynamic" compression for you fuel to tolerate?

lewtot184 · Tuesday at 6:32 AM

I use an Icon 836 piston with edelbrock heads; 9.8:1 compression. I also use an old fashion solid lifter cam with a longer closing ramp. Never a hint of detonation. Very reliable and easy to maintain.

WileE · Tuesday at 8:57 AM

Could be something as simple as bad gasoline, water-contaminated fuel, etc. I'd think the heat in Arizona would not be a surprise, either.

Paul_G · Tuesday at 9:11 AM

WileE said:
Could be something as simple as bad gasoline, water-contaminated fuel, etc. I'd think the heat in Arizona would not be a surprise, either.

I think I am going to drain the tank of the fuel thats in it before the rebuilt 505 gets fired up. The hydraulic roller cam and lifters in the 505 is so loud, along with the exhaust I had on it, and the sound and heat insulation I put through the entire interior, I could not here detonation at all. It could have gotten a tank full of 87 at the 91 pump. Hot day, on the wrong day when I may have pushed it which I did often. That engine would rev quickly to 6000 in 3 gears, took a touch longer in 4th gear.

The newer cars that require 91 getting a tank of 87 by mistake would handle it without harm. The computerized nanny's would take over removing timing and limiting power with no harm to the engine. No one would be the wiser unless it threw a code. Our old cars dont have that ability. They go BOOM!

Paul_G · Tuesday at 9:14 AM

How about a sticking T stat? It didint over heat on me before it failed. Nothing I could see on my gauges. Can a T- stat stick closed one time and then be OK?

Doorkicker · Tuesday at 11:20 AM

@Paul_G Man I'm watching this thread closely... I'm super curious what happened.

Do you use mechanical timing? I know a situation where the spring came loose and it over advanced. Granted, he had the wrong limit bushing too...

I'm very curious about the gas and what octane was in the tank. Also, what additive did you use?

Just as a sidebar... I've stayed clear of octane booster/additive. A buddy of mine has an engine like yours & mine and he put in some octane additive, and it was super unhappy when it got hot out. Pinged like mad... we had to lower the timing to around 22 until we could get home to drain the tank.

Paul_G · Tuesday at 11:30 AM

I ran the engine with a stock distributor with an FBO plate for the first 4 years. Base timing at 18 degrees, all in at 28. Ignition modules were terrible. Performance was poor. Some just ran poorly, some would break up over 4 k rpm. Then I got a Progession Ignition distributor. Fully adjustable timing table using a tablet or phone. It is great.

Curiousyellow71 · Tuesday at 11:34 AM

Paul_G said:
I ran the engine with a stock distributor with an FBO plate for the first 4 years. Base timing at 18 degrees, all in at 28. Ignition modules were terrible. Performance was poor. Some just ran poorly, some would break up over 4 k rpm. Then I got a Progession Ignition distributor. Fully adjustable timing table using a tablet or phone. It is great.

Big bummer it melted on you. We are 11:1 running on 91 on several cars now. You are right margin of error is slim.
What camshaft did you have?

68 Sport Satellite · Tuesday at 1:00 PM

DanielSlocum said:
Perhaps ring gaps were too tight and/or you got some old pump gas that lost some octane or never had its advertised number in the first place?
My rule of thumb for pump premium is a max of 10:1 with iron heads and 11:1 with aluminum heads. That standard has worked well for me for years.
Another factor though is cam/valve overlap. More overlap will reduce cylinder pressure some which will reduce heat and octane requirement. Less overlap will do the opposite.
Perhaps a small cam in a big stroker is creating too much "dynamic" compression for you fuel to tolerate?

For cam/valve overlap - I'm not that knowledgeable, but I'm reading that a smaller LSA number means more cam/valve overlap and a larger LSA is less cam/valve overlap?

I'm watching this thread with interest. I run a mild cam (.475 lift, 220 int./226 exh. @ .050" lift) 112 LSA 451 motor with aluminum Eddy RPM heads and 10.2:1 compression on 91 octane. Total timing is 32 degrees or it pings. I chose the wrong pistons for this combo. So far the motor has 6500 miles on it. I've had it down the 1/4 mile track 20 times without issue, however, once it pinged like mad on a run with my foot in it for 5 seconds or so and when I pulled around the track and checked things out, the distributor clamp had somehow loosened and timing had advanced from 32 total to 38. Backed it back to 32, tightened it down and it's been ok.

@Paul_G - what kind of driving were you doing when this happened? I imagine with 2 broke pistons there was a sudden loss of power and a big boom?

threewood · Tuesday at 1:32 PM

My .040" over 440 has around a 10.2:1 CR with ported 440 Source aluminum heads and a solid lifter cam installed at 104° CL, 108°LSA, 246° / 250° duration at .050". 21 initial/36 all in timing and I run 88 clear gas without issue. I'm in NM and we get into the triple digits. My AFRs are great and controlled by a Holley Sniper EFI backed by a Walbro 525lph pump.

The only pinging I ever encountered was when I retarded to timing by accident down to 30° all in.

69conv · Tuesday at 1:35 PM

No more high compression street builds for me

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