1999 5.7 mercruiser performance mods

[GA_Boater]

Im stumped , spent 800 on this thought i got a good deal already spent 700 in parts. Want advice before moving foward. Been watching videos for hours but at this point feel like i would have to replace everything

Any bets his next post will be "Problem solved"? :watermelon:

 

[xltier]

Ayuh,..... 'bout 20/ 25 hp, mostly at top end,.....

Small primaries helps with low end response,.......

speed shops claim 40hp increase. of course they r selling parts. the smaller primaries should be better on fuel at low speed and trolling I would think but more fuel on cruise.

 

[Leardriver]

I would question more than a 20 hp gain with the low RPM that these motors turn at. If they could turn 5500-6000, then a cam could earn its keep.
As we said in the Nascar engine shop, all of the power is in the heads. We could reach 935 hp on a 355 cubic inch normally aspirated engine.

 

[jimmbo]

I replaced the Holley 2bbl 500 cfm(flows about 370 cfm when flow rated like a 4bb) with a Holley 4 bbl 650 Spreadbore on my VP 5.7. It raised my rpms by about 500 - 600, requiring repropping and potential loss of Hole Shot. Very Small Primaries reduced the Loss considerably.
Intake didn't need changing as Volvo used a very good 4 bbl Intake with both 4 bbl carbs and 2 bbl carbs. I prefer the Holley over the Edelbrock/Weber/Carter carb, but others here may have different opinions. If you use the Edelbrock/Weber/Carter carb, make sure to get an Intake that is for a Squarebore Carb. Good Adapters are rare, and the more common ones are horrible.
The 650 is way more Carb than a 5.7 needs unless it turning around 7500 rpm, but the Vacuum Hollies, and the Edelbrock/Weber/Carter carb, will only open as much as needed. Stay away from the Double Pumper type carbs, unless it is a Drag Boat.

Boat engines operate under different Conditions and Parameters than Passenger Cars/Trucks/Race Cars, so what works in one application may very well not work in the other. You just can't drop in a Cam Grind that works well on the Street, or the track, and fool yourself into thinking you are going to turning the surface of the water to Steam. You might be lucky to even get on Plane...

 

[xltier]

I replaced the Holley 2bbl 500 cfm(flows about 370 cfm when flow rated like a 4bb) with a Holley 4 bbl 650 Spreadbore on my VP 5.7. It raised my rpms by about 500 - 600, requiring repropping and potential loss of Hole Shot. Very Small Primaries reduced the Loss considerably.
Intake didn't need changing as Volvo used a very good 4 bbl Intake with both 4 bbl carbs and 2 bbl carbs. I prefer the Holley over the Edelbrock/Weber/Carter carb, but others here may have different opinions. If you use the Edelbrock/Weber/Carter carb, make sure to get an Intake that is for a Squarebore Carb. Good Adapters are rare, and the more common ones are horrible.
The 650 is way more Carb than a 5.7 needs unless it turning around 7500 rpm, but the Vacuum Hollies, and the Edelbrock/Weber/Carter carb, will only open as much as needed. Stay away from the Double Pumper type carbs, unless it is a Drag Boat.

Boat engines operate under different Conditions and Parameters than Passenger Cars/Trucks/Race Cars, so what works in one application may very well not work in the other. You just can't drop in a Cam Grind that works well on the Street, or the track, and fool yourself into thinking you are going to turning the surface of the water to Steam. You might be lucky to even get on Plane...

so you are saying a edelbrock or holley with a good manifold,squarebore is the way to go.

 

[jimmbo]

Personally, I prefer Spreadbore carbs. I was saying if you want use a Squarebore Carb, get an Intake that it be installed on directly. Almost every Adapter that permits a Squarebore Carb on a Spreadbore Manifold are worse than useless, unless the Manifold is open between the Primaries and Secondaries.

 

[Bondo]

If you use the Edelbrock/Weber/Carter carb, make sure to get an Intake that is for a Squarebore Carb. Good Adapters are rare, and the more common ones are horrible.

Ayuh,....... This, ^^^, isn't quite true,......

The 1409 will bolt to either manifold,......
While I've never run 'em on a square bore manifold, I run 'em on spread bore manifolds,.....
The 1409 Is actually a spread bore carb, the primaries are noticeably smaller than the 2ndaries,......

 

[cptbill]

Change to fuel injected, efficiency, better performance yet still some ok fuel econ.