Rough HP / Torque Estimate?
 

Posted a while back about what I should do. I decided to put the extra 1200$ out and have a little "fun."

Im having my engine rebuilt at the current moment and my engine builder really doesn't want to give me a rough estimate because he has had people hold it against him. He rather provide me the specs after he dynos it.

PARTS
496 Stroker (Scat 4340)
Forged Dome SRP Pistons
COMP Cams Xtreme Marine (Full Hydraulic Roller)
Chevy Large Oval Heads (353049)
Edelbrock RPM Performer Air-Gap Intake
Holley Marine 750CFM
10.1 Compression

MACHINE WORK
Deck Height
Port Matching
Water Passage Increase
Block Honed
Tumble

A few notes:
- The cam shaft was provided by comp cam and was specifically tailored to my usage type, boat size, and load estimates. I do not know the exact specs off hand.

- This was originally a Merc 454 Mag, with an estimated 425 HP. It had square port heads and a standard dual plane intake. Unfortunately, both of these parts were unserviceable because of salt corrosion.

- The engine is being rebuilt after discovering a leaking riser. Further investigation lead to a rebuild because of severe internal corrosion. I rather rebuild then play the roulette game of replacing internals.

- Boat is a Liberator 241. Will most likely be adding a 23P prop.

- My goal with the rebuild was to put a little extra money out and get a small power gain. As noted in other posts, I got the Scat crank kit for pennies on the dollar as my engine builder had one that another customer defaulted on. Engine work would have been the same cost as I would have had to have the blocked machined regardless. Im looking for reliability over performance really but anything speed wise is good

So, this could make your engine from 400hp to 600 or so.

Find out the cam # and we can get a close power guess.

Ill call my engine builder this afternoon, but I think this is the one we were initially looking at. https://www.summitracing.com/parts/c...45-8/overview/. Not sure if thats the one in play or not.

I was way off. I misread the cam lift by .100!

duplicate

420hp at 4800rpm.

If that is the cam, I'd say its too small. Thats only slightly more cam than stock 454/502mag.

It should have good torque down low and midrange, but will fall off and max out hp around 5000rpms. I also think you should have used an 800cfm carb. I'd say 440hp

218* duration cam, in a 496ci , oval 049 heads, would work great in a dually truck! Should make peak torque right around 2800rpm. HP peak, I'd guess between 4500-5000.

502 415hp Mag cam was 224/224, 500EFI was 230/236, 525EFI 236/244, all were around 8.75 static and ran on 87 oct.

With that 218* cam, 10:1 static, I'd be running premium for sure, and be real careful on the timing advance curve. That thing is gonna be making some cylinder pressure getting the boat on plane.

Roller Cam specs for 502 MPI:
288*/288* seat
224*/224* @.050"
.483"/.483" valve
115.5* LSA
109* ICL
122* ECL

I just dyno'd a similar build. It was a 502 with 049 oval heads, same Comp cam, 8.9:1 compression, performer Qjet intake with Merc-Weber 750 carb, stock exhaust. Dyno'd in full marine trim and wet exhaust. 402.5 HP at 4800 RPM. It layed down hard at about 5100 rpm. It really needed a much bigger cam. It did make great low end torque, well over 500 ft. lbs. best I can remember and idled smooth at 650 rpm.

Bob Lloyd