aTX427

I decided to change the heads on my 500efi's, but have a hang up on AFR, 305 w/ 114cc CNC domes, AFR 315 full CNC w/ 114cc domes or Canfield 310's with 113cc CNC domes. It is difficult to evaluate simply based on flow numbers due to the inconsistancies. I am expecting compression ratio 9.7:1 on the AFR and 9.8:1 on the Canfield's. Will that work with 87 octane and should I remap my ECU?

Thanks in advance, John

mikes280

9.7 with 87 no i dont think so

RLW

AFR 305 CNC'd Chamber will give you a 121cc chamber.
As cast is 119cc.
What is your current compression ratio and chamber volume?

cstraub69@comcast

I would get the smallest of the runners. The as cast version of either will CC around 300. This is more then enough for 502CID at 5500 rpm max.
Compression ratio. You can run a point higher with aluminum due to the thermal ineffeciency of the head. With all things equal and engine with iron heads and 9.5 compression is 8.5 with aluminum heads. So in your case, yes you can run 87 if you use aluminum heads.

Chris

aTX427

RLW,
The smaller domes in CNC version is from angle milling. I thought the compression ratio would be ~9.7:1, although after checking other posts it seems like 9.2:1. Can anyone verify the dome size on stock HP500EFI's?
Chris, I shared the same rationale, but wanted to ping the experts before learning the hard way. - getting tired of that.

RLW

Ahh yes, the "Hard Way". I know of it well.

aTX427

RLW, It Looks like the 114cc domes is 9.2:1. Do you think that will work with 87 octane?

RLW

John,
You are asking the wrong guy. What I can tell you is that my engine builder suggested that I use 93 octane despite my approximate 9.2:1 compression ratio. I would use 89 octane if that was the only thing available on the water. I am very conservative in the operation of my boat.
There are others on this board with far greater knowledge than myself as I am still serving my apprenticeship.
Russ

JimV

I think your asking for chamber volume, 119 on the GM heads. The way I would do it is to go with the smaller chambers that are not angle milled. You may have problems with pushrod clearance, intake alignment, bolt hole issues when angle milling although some of these issues are addressed from the factory. Then port the chambers to the desired compression ratio. That way you will improve airflow on both intake and exhaust ports. You will problably have to get your ecu reprogramed.

aTX427

Thanks for the input Jim. I believe the rev limiter is 5,250 so that will have to be increased for sure. How about max compression ratio on pump gas?