Reply With QuoteJust one ... Put that engine in a V-Drive...Just kidding...
Steve
What changes to set up should I make, if any, when replacing cast iron heads with aluminum. Specifically, I understand aluminum scavenges heat faster and allows the combustion chamber to run cooler. I was running 35 degree BTDC total advance in my last set up, maybe advance the timing a bit more? Compression ratio (9.6:1 in old setup), go higher? I usually run 93 octane or 100 if I can find it.
I have a Gen VI 502 block (casting 10237300) and I am replacing my Gen V cast iron (casting 14097088) heads with Dart Pro 1 aluminum heads with the 310cc intake runners (the mild version).
I have a roller cam with 580 lift, 240 duration, Vic Jr. air gap, Holley 850, EMI Thunder, MSD, Berk 12JG w/ plate, A/B mag/bronze, shoe, diverter spinning about 5,100 rpms in tight pump (old heads).
Any other setup changes to consider?
Just one ... Put that engine in a V-Drive...
Steve
Compression...due to heat absorbtion of aluminum you will want about 1 CR point higher than with iron heads. Compression builds heat and heat is power (in the combustion chamber) and alum will pull that heat away...
I think you could also get away with a higher lift cam if your valvetrain will handle it...
You might consider a step up on your exhaust, maybe a header or a dry set up if you go up in cam. Look at your exhaust duration @ .050 , if its higher than lets say 230 degrees (just to be safe) you are going to have reversion problems with that exhaust and many others.
Normally you can get away with a bit more timing, but 35 is plenty. You will most likely need to lean out the jetting some. A wise engine builder told me that "with iron heads you are always throwing fuel at it trying to cool things down and prevent detonation, but with aluminum you will have to take away fuel just to build enough heat for the thing to run right" I recently found his words to be correct with my Mom's boat. I pulled 4 jet sizes out of it and bumped the timing 2 deg. at the last race, just to get it back in the ballpark, and it still seems rich.
PS, with a motor under 10:1 compression, especially with aluminum heads, you are leaving power on the table by running 100+ octane fuel. Don't waste the money, especially if 93 is available in your area. Have fun!
A 502 with 9.6:1 compression can make a bunch of hp. If you want to squeeze a little more compression for a little more power and still run pump gas with the aluminum heads, you can. Most companies offer smaller combustion chambers.
The chamber and piston design have more to do with total timing than anything else.....unless you have way more compression than your fuel can take with normal timing. You'll have to find best total timing , however, I'd put it at 35 to begin with. More often than not, that seems to be within 1° or so of magic number with AFR, Canfield, Dart, etc aluminum heads with pump gas and marine.
I agree with the exhaust statement. Once a cam gets into positive overlap at .050" a tuned header can really start to make more power.
I also agree with getting more lift (with cam lobe) if possible. A swap of heads usually means a swap with cam.....big if here.....cam was optimized for previous heads.
I agree with the fuel. Premium pump fuel will be more than enough at 9.6:1 .
I would also try a 1" and then 2" carb spacer. Use what works best. A 502 with good aftermarket heads requires serious amt's of air !!! Very high air velocity coming thru carb coupled with rel short plenum of Vic JR (and most 4150 intakes) will like added area to make the respective turns.
BTW: The above is not 'must do's' but merely suggestions to try to optimize what you are doing. We all think about making more power ....right ? LOL.
Lastly, can we spin it a few more hundred rpms ? Getting a motor like this built for, and running at, 400-600 more rpm will make major amts more power.
There is a lot of good advice here. If however, you have trouble making 5100 rpm again, find a way to raise the temp to at lease 180. 200 is the best. Once the head are satutated with that kind of heat, they really start to make some power. Most boat engine builders will tell you that the biggest advantage of aluminum heads is that they weigh less and are easier to repair. My $.02
Thanks for the replies, all sounds reasonable (even the v-drive smart a$$ remark). For now I will just have the mechanic in Boulder City slap the heads on to set a baseline. I was intrigued by the comment on jetting, I had not thought about that one. May need to be prepared to lean it out some more, you think both primaries and secondaries?? Maybe pinch off the gate valve on the water intake line a bit to get some temp.
I will be crossing my fingers hoping I did no significant damage to the motor with the old cracked heads. I did run the boat for about 2 hours with a quart or more of oil in the pan, milkshake out of the breathers for sure. I did this once before in an old Chevy Blazer and the bearings were shot. However, my understanding is that it is the anti-freeze that is the death knell for bearings, hopefully not so bad with just Colorado river water.
Will probably take the motor to a pro engine builder over the winter just to make sure on the rotating assembly and to optimize the package. Thinking about a good shop with dyno, maybe DNE. Other suggestions welcome.
SOMEBODY MENTIONED A TUNED HEADER,AND SOMEONE ELSE A DRY SET UP.
WHAT WOULD BE THE BEST HEADER WITH ALUMINUM HEADS, WITH CARIB'S SET UP? I'M SIMULAR AND INTERESTED IN THIS WHOLE THREAD. YOU CAN'T DO DRY AND BE LEGAL RIGHT? (NOT RACING). I ASSUME A DRY HEADER WOULD MAKE MORE POWER THAN SAY AN INJECTED BASSETT OR A JACKED HEADER? I CAN SAY MY MOTOR IS MUCH HAPPIER HOTTER, IS 180-200 TEMP NORM BY OTHERS STANDARDS? WHAT IS IDEAL OIL TEMP? OK I'LL STOP NOW:idea:
One of the Dart heads showed up damaged by UPS (hey CPBrian, trust you are the Brian from CP Performance, those were my Dart heads, thanks for the follow up).
During the lull, mechanic tore into the short block and everything checked fine except scuff in #7 due to water in cylinder (nos. 6,5,7,2 all had cracks in the exhaust valve guides). Off to machine shop for honing and piston knurling, hopefully on the water next week.
Putting the mill back together as is and hope the reduced weight and more air (port matched the intake to the heads, about 1/8 inch cut) will add 1 or 2 mph. My expectations are rarely met with this barge, but you never know.
On the water reversion issue due to cam duration, we already addressed this with longer extensions on the exhaust water dump. Not an issue. Keeping my fingers crossed.
Posting Permissions