Mercruiser 5.7EFI Performance upgrades
05-14-2015 | 09:32 AM
#11
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From: Ft. Worth TX
I would balance your ride of the hull = S Rays are fairly light up front and stern heavy. I would make sure your Alpha is free of any nicks along with checking the bottom of the hull for any hooks and whatever else under there, strakes and chines straight and no hooks in them. I would play around with props. I would vent the engine compartment better boths sides - incoming air and venting. It seems the rec boats do not see as much air flow.. Test this by running and then open up the engine hatch about 8 inches - you would be surprise, these rec boats can pick up some rpms and tad bit of mph. Especially in the dead of summer.
I would put Aluminum exhaust manifolds and thru hull exhaust , take some weight out of the stern - and call it a day. Just my 2 C's
I would put Aluminum exhaust manifolds and thru hull exhaust , take some weight out of the stern - and call it a day. Just my 2 C's
05-14-2015 | 05:25 PM
#12
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From: Spicewood, Texas USA
Volvo Penta sold a 5.7 with TBI that was rated at 320 pshp. It was a Vortec 5.7 with an aluminum 4 bbl intake with the TBI adapted to it. So, the question would be, is your engine a Vortec (1998 or newer)? If not that's what you really need to reach your goal. You could upgrade intake and exhaust on a Pre-vortec, but you'd have to get someone to reprogram the ecu.
Bob
Bob
Don't Flame, I know its a SBC TBI motor..but I'm looking on some ideas to step it up.
As posted, I have a 5.7 EFI / Alpha set up on a Stingray 220SX. Reasonably light and efficient hull for its style.
What can I do to add some power to the motor?
Firstly, I'd like to keep the EFI - its TBI and I realize I may be limited to what can be done here. If there is gains in going with a better intake manifold and carb, I'm good with ditching the EFI and going that route.
Secondly,
I have thru hull exhaust now. They exit under the waterline with exhaust tips that have internal "crossbracing" in them that I assume is a muffler. I'd like to change these out to a more flow thru style.
Any reasonable investment builds will get me to the 300-320 pshp goal? Anything more I'm sure the Alpha will dislike.
As posted, I have a 5.7 EFI / Alpha set up on a Stingray 220SX. Reasonably light and efficient hull for its style.
What can I do to add some power to the motor?
Firstly, I'd like to keep the EFI - its TBI and I realize I may be limited to what can be done here. If there is gains in going with a better intake manifold and carb, I'm good with ditching the EFI and going that route.
Secondly,
I have thru hull exhaust now. They exit under the waterline with exhaust tips that have internal "crossbracing" in them that I assume is a muffler. I'd like to change these out to a more flow thru style.
Any reasonable investment builds will get me to the 300-320 pshp goal? Anything more I'm sure the Alpha will dislike.
05-14-2015 | 09:12 PM
#14
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Joined: Jul 2011
Posts: 9,594
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From: Ft. Worth TX
Yeah Volvo still offered a TBI in 2001 and 2002 that was rated at 315 hp. It was called the 5.7 GXI - the 5.7 Gi was 280 hp. Engine hop up & retuning these marine ECM's it is wise to have this done on the dyno & tested, then lake tested following the running parameters - it can get expensive over the long haul. And then the possibility of the retune needing to be retune to dial in it correctly. It really is not a simply plug and play in a matter of a day.. Depending on the app 50 hp gain can only be 3 to a MAX of 5 mph.
Last edited by BUP; 05-14-2015 at 09:16 PM.
05-14-2015 | 09:20 PM
#15
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From: Beaverton Or
Yeah Volvo still offered a TBI in 2001 and 2002 that was rated at 315 hp. It was called the 5.7 GXI - the 5.7 Gi was 280 hp. Engine hop up & retuning these marine ECM's it is wise to have this done on the dyno & tested, then lake tested following the running parameters - it can get expensive over the long haul. And then the possibility of the retune needing to be retune to dial in it correctly. It really is not a simply plug and play in a matter of a day.. Depending on the app 50 hp gain can only be 3 to a MAX of 5 mph.
05-14-2015 | 10:06 PM
#16
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Joined: Jul 2011
Posts: 9,594
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From: Ft. Worth TX
Well its the opposite I am not well written and far from being conservative. I just work on more stock apps than ever currently and really it is the catalyst engines. The OEM marine schools teach nothing but conservatism. Hell they are totally against messing with any of the OEM engineered design of all aspects especially with any of the CAT engines
I want to follow along so why is it interesting what I wrote. IMO a stock old school 350 TBI set up offered in a rec boat is not bad for the average family boater. Volvo wanted to fill the void of the 454 going away back at that timeframe in the 300 to 310 hp range hence the smallblock 350 with 315 hp and the GXI MPI 320 hp offered in 2003 and up. .Volvo got rid of all TBI in late 2002.
I want to follow along so why is it interesting what I wrote. IMO a stock old school 350 TBI set up offered in a rec boat is not bad for the average family boater. Volvo wanted to fill the void of the 454 going away back at that timeframe in the 300 to 310 hp range hence the smallblock 350 with 315 hp and the GXI MPI 320 hp offered in 2003 and up. .Volvo got rid of all TBI in late 2002.
Last edited by BUP; 05-14-2015 at 10:23 PM.
05-14-2015 | 10:08 PM
#17
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Joined: Feb 2011
Posts: 769
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From: Brookfield Wi
I put small cams and tuned using MEFI burn. Picked up a couple. Keeping in mind boats with crazy builds are usually harder to sell. If your planning on keeping it stroke the hell of it and put big heads on.
05-14-2015 | 10:16 PM
#18
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From: On A Dirt Floor
I can make a 350-375hp 350 idle like a stock 260hp 350...and with a carbureto even. If an unsuspecting new owne of the boat idled out of the cove, they'd have no idea.
When they put the go thottle arm down, they'd poop themselves.......in a boat this size of course.
Dead serious.
When they put the go thottle arm down, they'd poop themselves.......in a boat this size of course.
Dead serious.
05-28-2018 | 09:37 PM
#19
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From: Ohio
Sb. Lookin for some opinions on small block performance
Making that hp with a 350 is easy. Your boat will respond well.
However, only tough part maybe the EFI chosen - either you or a trusted tuner that will tune your boat 'live' is what is required.
Your Alfalfa drive will be fine.
This is a perfomance boat site, so:
3pointstar is just being a buzzkill. LOL.
Stock sucks unless Merc Racing engines.
However, only tough part maybe the EFI chosen - either you or a trusted tuner that will tune your boat 'live' is what is required.
Your Alfalfa drive will be fine.
This is a perfomance boat site, so:
3pointstar is just being a buzzkill. LOL.
Stock sucks unless Merc Racing engines.
