502 rebuild
11-02-2018 | 05:59 PM
#41
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Joined: Oct 2013
Posts: 2,888
Likes: 148
From: SF Bay Area
Thanks for catching my mistake on the intake and carb combo. For some reason I thought you stayed 4150. You did forget to mention your custom made hatch air ports. That boat starved for air after your engine swaps. Makes ya wonder if most consider after almost doubling NA power. When in doubt crack the hatch. lol 
11-02-2018 | 06:04 PM
#42
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Joined: Jul 2004
Posts: 11,332
Likes: 73
From: chicago
Lets look at the published flow data from both heads. Both with the cnc chamber option.
'
305/325
.200=168/170
.300=242/242
.400=303/304
.500=339/342
.600=360/372
at .600 lift or more, the 325 starts to outflow the 305 on the flow bench. But, its not that simple. The 305, has a smaller 2.25 valve, and a port thats 20cc less in volume. So, you have a head, thats flowing as much air, from the time the valve opens, till .600 lift, and its doing it thru a smaller hole, with a smaller valve. Which port you think is more efficient? Thats what we want, efficency. Anyone can make a big hole, with a big valve, and move tons of air on the flow bench. Its port efficiency that you want. The valve spends very little time at peak lift.
Personally, out of those two options you gave, Id go for the 305cc head. Unless, you are looking for a 7000rpm 502, I doubt youll gain a thing from the 325cc with larger valve, besides being more reversion prone, slight loss of low end torque, and slightly worse idle, thanks to the larger valve. Big valves work great when you need high rpm power, small valves work great when you want low speed torque.
'
305/325
.200=168/170
.300=242/242
.400=303/304
.500=339/342
.600=360/372
at .600 lift or more, the 325 starts to outflow the 305 on the flow bench. But, its not that simple. The 305, has a smaller 2.25 valve, and a port thats 20cc less in volume. So, you have a head, thats flowing as much air, from the time the valve opens, till .600 lift, and its doing it thru a smaller hole, with a smaller valve. Which port you think is more efficient? Thats what we want, efficency. Anyone can make a big hole, with a big valve, and move tons of air on the flow bench. Its port efficiency that you want. The valve spends very little time at peak lift.
Personally, out of those two options you gave, Id go for the 305cc head. Unless, you are looking for a 7000rpm 502, I doubt youll gain a thing from the 325cc with larger valve, besides being more reversion prone, slight loss of low end torque, and slightly worse idle, thanks to the larger valve. Big valves work great when you need high rpm power, small valves work great when you want low speed torque.
Last edited by MILD THUNDER; 11-02-2018 at 06:35 PM.
11-02-2018 | 08:48 PM
#43
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Posts: 14,097
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From: On A Dirt Floor
An AFR 305 on a performance marine 502 is a marriage made in heaven. An AFR 315cc will make it achieve a little more, like 15-20hp on top of a 625hp engine.....but only worth the extra $$$ to a few.
11-02-2018 | 11:08 PM
#44
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Joined: Oct 2013
Posts: 2,888
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From: SF Bay Area
The 325 is great if you have a blower or spend all of your time between 5k to 7k going down the 1/4 mile.
Motorcylce racers had had a period where technology let them leap up huge numbers in overall power. The dyno numbers where impressive but the lap times got worse until they realized it was acceleration that they needed. If you spend all of your time wfo then the 335 heads may be of help. I personally spend 95% of my time not at wfo so I’d opt for the smaller heads myself.
Motorcylce racers had had a period where technology let them leap up huge numbers in overall power. The dyno numbers where impressive but the lap times got worse until they realized it was acceleration that they needed. If you spend all of your time wfo then the 335 heads may be of help. I personally spend 95% of my time not at wfo so I’d opt for the smaller heads myself.
11-02-2018 | 11:19 PM
#45
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Joined: Jul 2004
Posts: 11,332
Likes: 73
From: chicago
While the 325 is a bit big, it still would outperform a GM rectangle iron head on a 502. The gm iron head was around 325ish cc if i recall give or take. It ran well on 5200rpm max 454s and 502s for what it was. Made a bunch of torque too for such a large head. They just dont flow well though, and imo, a 325 afr or dart would work totally fine on a 502. Its just i feel the 305 would be a little better fit.
I dont get too worked up over the CC part of the head, as long as its not way out in left field. Like some 360cc ports on a 396ci.
look at the torque at 4000rpm between a 308cc summit/dart and a 360cc trick flow. Within a foot lb of torque. Big-Block Heads Shootout - The Big O Vs. The Big R - Super Chevy Magazine
I dont get too worked up over the CC part of the head, as long as its not way out in left field. Like some 360cc ports on a 396ci.
look at the torque at 4000rpm between a 308cc summit/dart and a 360cc trick flow. Within a foot lb of torque. Big-Block Heads Shootout - The Big O Vs. The Big R - Super Chevy Magazine
11-03-2018 | 10:57 PM
#50
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Joined: Oct 2018
Posts: 36
Likes: 0
From: California
Here are the specs on my old engines.
509 CI
10:1 compression (I think)
Crane 741 cam
1.8/ 1.7 Crane Gold rockers
Brodix HPV 2001 intakes
Dart Pro 1 310 heads- ported by Jim Valako (320 cc after porting)
Dominator AED carbs 1050's
Daytona Sensor Ignition with stock thunder bolt distributor
Eickert Exhaust
This was a he!! of a combo- originally it came with Dart single plane intakes and Holley 950 hp carbs. Moving up to dominators really helped pick up some power. This combo pushed a Formula 292 to 88 mph. That is not a fast hull, and needs around 650 hp a side to hit those speeds.
If you are only building one engine, I have a new in the box Daytona ignition I'll make you a deal on.
509 CI
10:1 compression (I think)
Crane 741 cam
1.8/ 1.7 Crane Gold rockers
Brodix HPV 2001 intakes
Dart Pro 1 310 heads- ported by Jim Valako (320 cc after porting)
Dominator AED carbs 1050's
Daytona Sensor Ignition with stock thunder bolt distributor
Eickert Exhaust
This was a he!! of a combo- originally it came with Dart single plane intakes and Holley 950 hp carbs. Moving up to dominators really helped pick up some power. This combo pushed a Formula 292 to 88 mph. That is not a fast hull, and needs around 650 hp a side to hit those speeds.
If you are only building one engine, I have a new in the box Daytona ignition I'll make you a deal on.
