Hi Eric. I ran a set of #12's for about 4 years after I took the #670's off of my stock '67 400. The 12's (RAIII) are excellent heads, make a lot of power, and flow very well. They also want about 100 octane fuel. On my engine, I had severe detonation at light load conditions. Nothing helped: (Timing retarded/water injection/104 octane boost, etc) I ended up putting lower compression heads on the engine. The hot ticket these days is to install Ross dished pistons. That way, yu can run the "good" Pontiac heads on 91 pump gas. Next time I overhaul one of mine, that's what I'm gonna do! Weird: the 670's seemed to do a little better on my stock 400 than the 12's, but detonated much worse under heavy load. The 12's only seemed to detonate at LIGHT load. These days, with 91-93 octane, yu need about 85-95 cc chambers if you are running iron heads. The rule of thumb is 150-175 psi cranking compression. Good luck!
hey Jeff, Thanks for the info....basically you feel that the # 12 heads will make more power,IF I use 100 octane fuel ? OR lower the compression with dished pistons. Correct? E
Hi Eric. If yu don't use 100 octane or thereabouts for fuel, it's not a power question but a detonation question. With the small chamber volume of the Ram Air lll heads, you will be close to 11:1 compression. Great stuff back in the day, but your engine will detonate itself to death (ping). The dished pistons will make your combustion chambers larger in effect, lowering your compression to the 9:1 range or so....maybe 9.5:1. You won't put out as much power as an 11:1 engine with all else being equal, but you will be able to drive the car on the street on pump gas. You could go with the Edelbrock or KRE aluminum heads....they will net you about 10.5-11.5 to 1 compression, and will work on the street without problems because they are aluminum and dissipate heat much better (no detonation). However, because the thermal efficiency of aluminum is inferior to iron, they need meore compression to make the same power as iron heads. If your car is mainly a street driven car, I'd recommend the dished pistons. If you want to save a lot of labor, you can do what I did and get a pair of later heads that still flow well, but have bigger chambers: 85--100cc. I put a set of 1970 455 #15's on my '67, and they have an 87cc chamber. Compression is about 9.2:1, it doesn't ping, and power is good. It did have more power with the 670 heads on it, but it was pinging ALL the time. Hope this helps.
Jeff
Jeff, Yes ! All great info,and much appriciated. I am THINKING of building an engine for "just in case" and I kinda like modified stuff. I would really like to build a nice street machine with alot of chrome and other cool stuff....Just gathering knowledge, and seeing what is out there right now.....Thanks, Eric
Rukee, That's the way I am leaning, the RAIII's were on e-bay. They sold for $510...If I am going to build a modified engine/car, I wouldn't want to use up a good pair of factory heads that someone could use to restore to OEM....GOTTA CONSERVE OUR DWINDLING RESOURSES Thanks, E
Hey guys, I'm with you. If I were building up a pontiac motor these days, I would run aluminum heads, better rods, etc. I would only go dished pistons if I were running original heads on a restoration. There is SO much good stuff available now for Pontiacs that wasn't around when I rebuilt my '67 (1988) and my '65 (1981)! I think I'll put the set of #12's I have in the garage on E Bay!!! Rukee: I priced the KRE and Edelbrock heads down here in CA, and they run around 2 grand ready to go. Where can I find a set for a grand?? Eric, for some pretty good info on engines, try the Jim Hand articles and also RRE (Rock N Roll Engineering). Good information.
Jeff
geeteeohguy, that was my bad. I was looking on Summit DOT com and mistakenly looked at the price per each thinking it was for the pair. They have them starting out at $899.00 each.
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Thanks, E
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