No more high compression street builds for me

[Paul_G]

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?

Comp custom grind. Lift - 543 int 540 exh, Dur - @50 234 int 240 exh. 112 LSA on 108 ICL

@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?

It seemed to happen over a few days. Started to idle rough and smoking out the tail pipes and breathers. My driving style varies from old man to maniac. Depends on the day.

 

[Curiousyellow71]

Comp custom grind. Lift - 543 int 540 exh, Dur - @50 234 int 240 exh. 112 LSA on 108 ICL




It seemed to happen over a few days. Started to idle rough and smoking out the tail pipes and breathers. My driving style varies from old man to maniac. Depends on the day.

Is that a hydraulic roller?

 

[autoxcuda]

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

I have a 416 with edelbrock ported heads, M1 single plane, TTI's, 236/242 @0.50, 511", 110 centerline.

... It's 9.7:1 with California 91 octane. head cc's and piston to deck measured so pretty accurate compression calc.

No issues in 100 degree heat traveling over mountain to get out of valley I live in. mechanical fan and custom made shroud.
Spins the rear tires at will.

Have buddy with someone similar cam, intake, heads, in a 500" based on 440 block. He was planning on 9.5-9.7. But the deck needed more straightening that planned. So it ended up 10.3:1 or so. It had slight ping and dieseling. And was running slightly hot. Turned back timing and worked on carb tune. Then installed fan shroud and new re-cored brass radiator. All's good now.

 

[dvw]

Wife’s 360 Challenger. 224@.050, 9.0-1, iron head, 87 octane. 12.7@107 in street trim. Correct cam with low compression runs good.
Doug

 

[icetech]

Wife’s 360 Challenger. 224@.050, 9.0-1, iron head, 87 octane. 12.7@107 in street trim. Correct cam with low compression runs good.
Doug

I almost want low compression just to get away with 87 honestly Save $2.80 a gallon, it adds up...

 

[autoxcuda]

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

I have a 416 with edelbrock ported heads, M1 single plane, TTI's, 236/242 @0.50, 511", 110 centerline.

... It's 9.7:1 with California 91 octane.

No issues in 100 degree heat traveling over mountain to get out of valley I live in. mechanical fan and custom made shroud.
Spins the rear tires at will.

Have buddy with somewhat similar cam, intake, heads, in a 500" based on 440 block. He was planning on 9.5-9.7. But the deck needed more straightening that planned. So it ended up 10.3:1 or so. It had slight ping and run one dieseling. And was running slightly hot. Turned back timing and worked on carb tune. Then installed fan shroud and new re-cored brass radiator. All's good now.

 

[Cranky]

@Paul_G What was the cranking psi? Bought a 71 340 Cuda back in 86 that had a mild build. Was supposed to be 10.5 comp. The only visible high performance item were Hooker headers. Still ran the stock air cleaner even. The only time it would ping was when the water temp hit 185 but with just one gallon of avgas added to 91, no ping. Never did check cranking psi though.

 

[autoxcuda]

@Paul_G What was the cranking psi? Bought a 71 340 Cuda back in 86 that had a mild build. Was supposed to be 10.5 comp. The only visible high performance item were Hooker headers. Still ran the stock air cleaner even. The only time it would ping was when the water temp hit 185 but with just one gallon of avgas added to 91, no ping. Never did check cranking psi though.

The factory ones seemed to have less compression that advertised. Most measured cylinder head cc's were greater than advertised.

Also, once you put a good fel pro head gasket that thicker than OE on them they drop some compression.

I ran my 68 340 Barracuda with original std pistons and X-heads for years on 91 octane. It had the thicker fel pro gaskets. It had that tick above stock cam: MP 272/272? .455 lift

 

[Cranky]

The factory ones seemed to have less compression that advertised. Most measured cylinder head cc's were greater than advertised.

Also, once you put a good fel pro head gasket that thicker than OE on them they drop some compression.

This engine had been rebuilt....forged pistons, with a very mild cam. The TQ on the stock intake was tuned by someone that knew how.

 

[Doorkicker]

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.

Not to get off on a tangent, but you said it pinged at 30 but normal total timing is 36? Just curious.

 

[68 Sport Satellite]

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

too little timing can also cause pinging?