454 vs 502
 

Hi
Looking for some opinions. Reliability speaking, what do u think would last longer, a 454 cruising mostly at 4250-4750rpm or a 502 cruising mostly 3750-4250rpm. I'm less concerned with top speed (70 would be great), but would like a fast cruising speed.
Thnx

If you are talking merc motors or most others those are not cruising rpm's. Those would be starting on the upper part of rpm. 502 would be a better choice no matter what because of the extra trq and reliability is all about how the were built but def easier on the 502.
Also if you want to cruise fast just over prop the boat for it.

Gotta be a little more specific about the engines you are talking about. The parts in the Merc 454mag and 502mag are identical and there is only a 30hp difference because of the extra cubic inches.

502..

Like Griff said. Are we talking a 525hp 454 vs a 390hp 502 or what??

I have buddys that think automatically the bigger the cubic engine the more power it makes. Depends on the build.

It is no secret that the 454 MAG MPI more often than not made as much power as the 502 MAG MPI. They share the same camshaft, injectors, valve train.....

Not a stock engine, obviously a 502 built the same as a 454 will make more power. Let's say, motors making 500 horsepower. The 454 will need to twist higher to make the power but has less rotating mass. So back to original question, will the 454 revving slightly higher to go same speed as 502 last as long hour wise? ( less rotating mass)

RPMs wear motors out, period. If you're going to build the 502 to run lower R's at cruising speed, the 502 will last longer.

502, like said RPMs are your enemy.

The funny thing is people don't want used 454MPI's, they always ask for the 502MPI. :lolhit: Change the intake sticker and most would not know!

The 502 is not "stroked" It shares the same 4" stroke as the 454, the bore is bigger on each piston, almost a whopping 1/4 inch each :grinser010:

I would love to see them dyno'd side by side. Great marketing on Merc's part. What was the "upgrade" cost when they were offered at the same time?

502....

I'd actually like to see the hp500(502) vs the hp450(454) in a dyno comparison.

I myself, probably would not let this debate decide on which engine will last longer. If you are building from scratch, then yes, go for the 502.

Ive known marine 454's of all different hp variations, to last from 500 hours to 2000 hours. Its all in maintainance and conditions they were used. Like stated, they both use a 4" stroke and 6.135 Rod. They are very similar from a design standpoint.

48 more cubic inches means close to 48 more lb ft of torque. Since they both weigh the same it doesnt make sense to have less torque and 30 less horsepower in the same package now does it?

The bigger bore is the best benefit of the 502.

I agree. The bigger bore helps unshroud the valves, which means more airflow/hp.

I call B.S.

Given identical builds and compression ratios, the only way the 454 mag would ever make similar power than the 502 mag is if the intake being used was physically maxed out on flow with the 454, and even then the 502 would still have noticeably more torque and acceleration.

The cubic inch difference in the two motors is not the only reason the 502 makes more power, the other reason is that the bore is larger, thus unshrouding the flow from the valves where the 454's smaller bore requires bore notching to deliver equivalent results.

For the life of me, I can't think of a single situation where the stock block 454 would be the preferable choice over the stock block 502 unless you were running more than 20 lbs of boost and wanted the additional cylinder wall thickness to aid in stability of the block (but then we're still talking about if you were using a thickwall 454 block, not a thinwall passenger car block).

Rotating mass in the 502/454 comparison is a complete NON ISSUE in the sub-5,000 rpm world of 500 horsepower marine engines. The forged components used in the mags are plenty beefy that the only way you'll have excessive bottom end wear in either one is if you have a serious oiling malfunction.

MC