Linster

You do not know what engine you really have. To call it a 500EFI would be a miss statement. Sounds like a engine that was assembled and used some EFI parts but started off something else. The stumbling to 2000 RPM sounds like it could have a cam with tight lobes or too large of a cam. The engine cant respond until enough vacuum is established. That also might be why it has a slow top speed. Either way, can you find out who built the engine & what is really in it?

I have had Velocity's in the past. They run very consistant from hull to hull with the same HP. If a 525 EFI runs 82MPH, you are under 500HP by a good amount.

Raylar

Remember that Merc HP525's produce about 540HP at the flywheel and have a much better set of headers. I don't think exhaust alone would give you much more that 25HP over the Eddie Marine manifolds and at about 1 mph per 15HP you are probably not going to see more than 1-2 mph max. If your cam specs are right you are a little short on what you need to make 525HP plus in that motor. I would look at lets say 230 to 236 intake and about 240 - 244 exhaust with about the same lift you are showing now. Use a 114 to 116 lsa for the efi. Make sure the cam is degreed in at straight up. The stumble problem sounds like a little fat in the fuel curve at that point and maybe not enough timing at that point. This issue will most likely disapear with more programming and Tyler is an expert in this area and I am sure he can correct that. Without a better cam , better exhaust and a 5400rpm rev limit I don't think you will see the eightys. Just takes a bunch of careful tweaking and the required horsepower and torque.

Good Luck,
Ray @ Raylar

Hy-Velocity

Thanks everyone for the replies, the engine is a true 2000 HP 500 EFI, it was a complete engine(take out) except for the heads. Everything for the engine and off the engine was there right down to the head bolts. I took the engine ID number and ran it by Mercruiser and they told me the history on the engine. The cam specs that I quoted came out of the 2000, 500hp service manual. The cam looks to be very mild for a 500 but maybe thats how Mercruiser detunes a 525 down to a 500. What do you think.

Pat McPherson

These are the spec for the HP500EFI.
Your manual is wrong.
The HP500EFI came before the HP525EFI...
The 525 has a bigger cam and aluminum heads.

If the stock 500EFI cam is in the engine, I would ask Tyler to remap back to the stock calibration. I bet the stumble would go away.
I believe that your engine will make peek power at about 5200rpm with a 500EFI cam, so 5400 rev limit is perfect.

If you have the time and $$, the HP525EFI cam and headers would really wake up your engine. The Eddie Marine manifolds are probably negating the extra flow of your nice aluminum heads.

Strip Poker 388

iTrader: (6)

Ray why would you want the 114-116 ls with a EFI. Would you mind explaining it to me please. Does it have to do with overlap?

Thanks
Rob

Pat McPherson

Good Question Rob, my guess is that the engine will make more vacuum at low rpm...

By the way, I just received some HP500 fuel injectors. The cam and other goodies I got from you may be going in my engine soon. I'm getting closer to having everything...

Raylar

EFI motors generally need a more stable vacuum signal at low rpms because they use a map sensor to run the fuel system program. If the cam has a lower LSA like a carbed cam lets say 106 to 112 and its in a EFI motor, the idle quality and control will be a problem.

Ray @ Raylar

Strip Poker 388

iTrader: (6)

Kinda of making it hunt around? making it rich?

I am running the 741 Crane with the 112LS . It actually idels pretty smooth. You can barley tell it from the stock cam but the Whipple could be covering it up. I am thinking the only reason I could run it up to 9.65lb boost on pump gas was because of the overlap. Had some blow thru


Rob