1999 5.7 mercruiser performance mods

[xltier]

does anyone have any good performance mods for a 5.7 mercruiser without pulling the motor.-cam -intake- carb etc.. it is a 2 barrel right now.. so many different intake and carb combinations I cant seem to decide whats best.

 

[Scott Danforth]

pull the motor is the only way to do a cam.

only thing you can do without pulling the motor is an intake and carb.

 

[Bondo]

so many different intake and carb combinations I cant seem to decide whats best.

Ayuh,...... A hi-rise cast iron intake, 'n a edlebrock 1409 AFB carb,.....

It's current issue from Mercruiser,.....

 

[Scott Danforth]

if you do a cam, you have to watch duration and lift

no more than 270 degrees duration in a boat with wet exhaust - period

no more than .420" lift with stock vortec heads - period

you can play around with 1.6:1 rockers (like the Merc 6.2's), however you still have to watch coil bind

i would also add a 2" carb spacer to help out with low and mid-range torque.

However if it was me

pull the motor
pull the heads
modify the heads for screw in rocker studs and valve lifts to .510"
clean the casting flash from the combustion chambers
port match the exhaust
mildly port the valve pockets
install a comp camp XM-264HR cam kit
install stamped roller tipped rockers (either 1.52:1 or 1.6:1)

install manifold and carb listed by Bondo

 

[xltier]

would that still have a smooth idle for trolling? thanks

 

[Silvertip]

So you want this thing to go like heck but you still want a passenger car idle quality. Engine mods are a compromise at best. You can build a high performance fuel sucking performer with rump-rump idle quality or you can have a nice smooth running reliable engine combination with good economy. Anything in between is a compromise.

 

[Scott Danforth]

would that still have a smooth idle for trolling? thanks

then you dont touch the motor, or you learn to troll at 7 knots

 

[QBhoy]

I think all advice worth taking has been said. Intake and 4 barrel are the best options.
Might you think about a cam...I can say a little. Mine has a cam, but on an MPI. Most of the time it’s not so efficient. At low rpm it overfuels. Only really comes alive at high rpm. Which is seldom the case. Even then it may even be under fuelling. As far as I know the fuelling has not been altered from the original setting.
Ups and downs I suppose.

 

[xltier]

So you want this thing to go like heck but you still want a passenger car idle quality. Engine mods are a compromise at best. You can build a high performance fuel sucking performer with rump-rump idle quality or you can have a nice smooth running reliable engine combination with good economy. Anything in between is a compromise.

that is not what I want. it was a simple question to learn all the ins and outs of whats possible and whats not practical which is what I thought this forumn was for.

 

[xltier]

Ayuh,...... A hi-rise cast iron intake, 'n a edlebrock 1409 AFB carb,.....

It's current issue from Mercruiser,.....

thank you sir.

 

[xltier]

if you do a cam, you have to watch duration and lift

no more than 270 degrees duration in a boat with wet exhaust - period

no more than .420" lift with stock vortec heads - period

you can play around with 1.6:1 rockers (like the Merc 6.2's), however you still have to watch coil bind

i would also add a 2" carb spacer to help out with low and mid-range torque.

However if it was me

pull the motor
pull the heads
modify the heads for screw in rocker studs and valve lifts to .510"
clean the casting flash from the combustion chambers
port match the exhaust
mildly port the valve pockets
install a comp camp XM-264HR cam kit
install stamped roller tipped rockers (either 1.52:1 or 1.6:1)

install manifold and carb listed by Bondo

thanks

 

[Scott Danforth]

if you need a good quality idle for fishing, skip the cam. what I listed will require you to raise the idle a bit (best with a Volvo drive or a Merc Bravo drive)

 

[xltier]

Ayuh,...... A hi-rise cast iron intake, 'n a edlebrock 1409 AFB carb,.....

It's current issue from Mercruiser,.....

the merc parts man is telling me only the 305 came with 4 barrel in my year (1999( motor.do you know of any aftermarket that would work. I am going to do just that for now. thanks

 

[Scott Danforth]

if you are looking for parts thru a mercruiser parts person, you are paying 4 times the cost of the parts.

long before that intake manifold had a mercruiser part number on it, it had a GM part number on it.

either go with a GM cast-iron intake, or an aluminum with bronze passages (marine) intake.

Edelbrock has marine aluminum intakes with bronze water castings (or get a Barr manifold - as Barr is the casting house for Edelbrock

 

[Bondo]

Ayuh,.... The 305, 'n the 350 use the same intakes,.....

 

[xltier]

got it,thank you

 

[josephkhan]

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

 

[Bondo]

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 everythingusd

Ayuh,..... Welcome Aboard,..... What thought have you spent $ 800.00 on,..??

Hmmmmmmm,....... Nevermind,..... A spammer that can't type,...... I'll edit it,....

 

[tacx]

So very interesting question. So if, he just replaces the intake manifold and a four barrel carb. What gain would be seen?

 

[Bondo]

So very interesting question. So if, he just replaces the intake manifold and a four barrel carb. What gain would be seen?

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

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