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Hey Guy's I Know That There Tons Of Info On These Motors,i Just Cant Seem To Find All The Awnsers To My Questions-the Motor Is Stock And Has About 300-350 Hrs On It-bravo Xr Drive -question Is Its Time To Tear The Heads Off(lots Of Leak Down)whats Best Bolt On Stuff To Increase Hp? From What I've Seen Dart/afr Heads,741 Cam,throttle Body,efi Remap-looking To Have About 600hp And Be Very Reliable -- Can You Guys Give Me Some Ideas On Whats The Best Reliable Set Up And To Reduce Future Reversion
Thanks In Advance Everbody!!!

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Wow Nobody's Got Any Good Info For Me?

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Wow Nobody's Got Any Good Info For Me?

Griff

Reversion should not be an issue with a 500efi. You need to find a reputable engine builder that has a proven dynoed package.

Young Performance

As an example, I just did 3 for a customer with a tripple engine Sonic. We did change the heads since the stockers were rusted away to nothing. They had spent 11 years in salt. I went with a set of Merlin cast iron heads since they were about the closest to stock. I didn't change the heads for performance but because I had to. That did allow me to bump the compression a little to 9:1. I also changed the cam to something a little larger, installed monoblade throttle body and milled the intake to match the monoblade. That's all we did and they made 600 hp at on the nose at 5400 and over 650 ft lbs of torque. We obviously reprogrammed the mefi 3 as well.
It was some very simple upgrades that really woke them up. They owner is on OSO so maybe he will chime in. Let me know if i can help.
Eddie

45SS

Eddie is right it woke the boat up BIG time. I will have to reprop, and will do so after Eddie does the retune in the water. It still idles and sounds like stock 500. Throttle response is great with the mono blade. The tune was also done on 91 octane fuel, and everything went great.

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I Pulled Off The Cmi Headers And Sent Them To Cmi For Repair- They Were Leaking Like Lawn Sprinklers Hopefully They Can Be Repaired

Thanks For The Info And Opions Please Keep Them Coming As This Is My Winter Project And Want To Get It Right! Thanks In Advace Everybody

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I Would Like To Have At Least 600 Solid Hp How Can I Acheive This With This Motor I Saw That Cp Performance Sells A Hp600 Kit -any Experiance With This?

MDGperformance

We did a set of500 efi that was upgraded to around 620hp ,afr cnc heads,cam upgrade ,mono throttle boddie,milled intake,55lb injectors,upgraded fuel system,i found on the dyno that the stock injectors and fuel system was having a hard time supporting the 600hp engine,can be done but the injectors were real close to going static(which can cause overheating and sticking)and the fuel pump was dropping the fuel pressure below the 38lb i had it set at,we also have a custom tune in the ecm engines run great and have been very reliable

bobl

I just refreshed 3 stock 500 EFIs. Dyno'd all 3 and they all made right at 510 HP at 5300 each. Not 5 hp variation. So, you picked up 90 HP basically with a cam change and monoblade throttle body with no rpm increase? I don't think the stock Merlin heads outflow the merc prepped 500 heads, unless you tweaked them. Do you have a base number for a stock 500 efi on your dyno? Do you run full wet exhaust on your dyno? If not that could account for some of it. Mine runs water all the way out the tips. A while back I prop shaft dyno'd a couple of AZM 500efi /540s with afr heads and monoblade TBs. Big cams, but I don't have the specs. They made 550 at the prop, which would be low 600's at the flwheel. What are your thoughts? Maybe the Merlin heads are better than I thought? Just trying to understand. I know your data is accurate.

Bob Lloyd
Full Throttle Marine