Looking for anyone that’s built a 489. Have a 454 that’s 0.030” over with 4.25” scat crank and rods. Need to figure out pistons/heads/cam. Looking for any help to point me in right direction.

I have:
Holley 850
rect port dart single plane intake

What are your HP amd RPM goals? Can't suggest a head without knowing how much air it needs to flow.

489/496 are better than a 502 large bore. Piston speed is higher and gives better signal to the carb/plenum. Better velocity in the intake ports.

Mike Jones or Bullet Cams, once you finalize everything else.

You need to start with heads first. Everyhting else is downstream.

461 builds will be very similar...just the HP curve will be a little to the left from the increased CID airflow lower in the RPM.

A 496...4.25 stroke and a 60 over 4.310 bore will have a larger change in head flows etc with less bore shrouding.

Care to elaborate on that? The bigger bore will allow better cylinder filling due to unshrouding of the intake valves. Even with optimized heads the bigger bore is going to come out on top.

Also, no replacement for displacement.

Piston velocity. Going oversquared is good..too much reduces piston velocity. Lower piston velocity reduces int port velocity.

Perf Marine rarely pushes past 6000rpm. Many not over 5400.

Nothing wrong with a 502, unshrouding is a factor. 2.300" valves also add shrouding issues. Bore notching helps all around.

If you visualise the air being drawn into the chamber...the faster piston speed will have a firmer spring, vs a slower piston shorter stroke, will have a weaker spring, where port velocity takes longer to achieve with the same displacement.

One of the factors why short rod ratios have an advantage. The Smokey Yunick days of long rod rsrio was based in the poor flowing heads of the time, where getting int/exb overlap interaction at TDC needed more dwell time. (Longer rod ratios have more dweel time at TDC and BDC)

Shorter rod rarios start drawing earlier...but don't achieve the same peak piston speed. Starting earlier is more important.

Obvioulsy this is all a factor of engine combo etc. Small port heads will have less need of piston velocity...as the prts will be far closer to their choke point. Large lazy int ports like what's on a 365Mag...need everything they can to help get the rec ports flowing air.

gm 088 heads

525 spec marine cam

-18cc dome SRP pistons

should be around 9.4 to 1 compression

One of the biggest issues with 088 heads is the exhaust port. It doesn't flow very well at all. The L29 1.720" exh port with a little porting help...puts the int/exh flow coeficient at close to 78%. Avg for BBC is 55-60%. 088 head...very low for a 1.880" exh valve. Chad Speier used to port these heads up for tractor pull BBCs. He cpuld get them better...but not really that great.

But they do make power. Thr 489 will help get your intake flowing. Not a good head for the single pattern cam that came in the FT 365Mag...with 088 heads. Needs lots of exh duration.

I've ported about 10 sets of 049 oval ports and the exhaust really responds with some mild porting, raise the roof about 100ths and clean up the short turn radius and they will gain 50 cfm, takes 15 minutes per port. I use oval ports on anything less than 500ci. Last 496 I did made 680 hp on pump gas with ported 049 781 heads. Hydro roller 256 267 at 50 630 lift. If budget allowed a set of afr 265 heads would be awesome.

I've used mike Jones cams for years, his stuff works. I will not use anyone else.

The 781 and 049 heads are grear performers for sure.

290 alum heads with 2.250" valves are way too big for most marine perf engines...but they flow well to male up for it. Some epoxy on the port floor would really wake them up. One ofntheblarger issues is that you can't really put a 2.19 valve in them.

The AFR 265s are an amazing option.

Great numbers on the 496 and iron ovals. What RPM did you turn?

Have you seen Vortec Pro's 781 and PP head results?

The 088 head exh port is worse than the oval heads.

Oddly...the L29 Vortec exh port may be the best factory BBC port ever cast. Small and fast..with a D port short side setup.