No more high compression street builds for me

[Paul_G]

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]

You should go low 9's and supercharge it.

 

[Paul_G]

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]

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]

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

 

[451Mopar]

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]

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 going to loose reducing it from 10.6:1 to 9.6:1 ? And I bet it will still spin the tires on the street.

 

[hunt2elk]

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.