Mercruiser 5.7, how to up the HP?
10-14-2011, 10:14 AM
#1
Mercruiser 5.7, how to up the HP?
I just picked up a brand new 2009 Chaparral 236 SSX with the 300hp 5.7L Mercruiser w/BIII outdrive. Exact model pictured below.
I am (of course) looking for ways to increase the power. Whipple blower is the obvious option but, I want to let my 2 year warranty on the engine expire before I do something that big.
I was told that swapping to 1.6 roller rockers would really wake the engine up. Problem is I don’t know exactly what that will do. I don’t know what comes on the Mercruiser engine stock; it might not even be a roller rocker.
Let’s just say the swap is a legit possibility, what does that actually do? Change the cam profile? Are we talking more bottom end tq or top end hp?
Another option was aftermarket headers and the claim was 30-60hp just from this swap. They are not cheap at $1500-$2000. I already have the Corsa thru hull exhaust so maybe that’s not really something I need to be looking at.
Any Mercruiser experts out there got any ideas? I want to keep it pretty simple for the first 2 years. Then I’m all about a 383 stroked, Whipple blown engine.
I am (of course) looking for ways to increase the power. Whipple blower is the obvious option but, I want to let my 2 year warranty on the engine expire before I do something that big.
I was told that swapping to 1.6 roller rockers would really wake the engine up. Problem is I don’t know exactly what that will do. I don’t know what comes on the Mercruiser engine stock; it might not even be a roller rocker.
Let’s just say the swap is a legit possibility, what does that actually do? Change the cam profile? Are we talking more bottom end tq or top end hp?
Another option was aftermarket headers and the claim was 30-60hp just from this swap. They are not cheap at $1500-$2000. I already have the Corsa thru hull exhaust so maybe that’s not really something I need to be looking at.
Any Mercruiser experts out there got any ideas? I want to keep it pretty simple for the first 2 years. Then I’m all about a 383 stroked, Whipple blown engine.
10-19-2011, 01:53 AM
#2
I believe this is basically a L31 vortec engine like used in the 96-98 pickups.
A set of 1.6 ratio roller rockers would increase the amount of valve lift compared to your stock 1.5 ratio rockers. It is basically a poor mans cam only doing a rocker change. It would likely give you more power across the board, but more likely to provide the most gain up top.
If the Mercruiser engine is anything like the L31 vortec engine make sure you upgrade the valve springs when doing any kind of valvetrain modifications as the springs are maxxed out in stock form.
A set of 1.6 ratio roller rockers would increase the amount of valve lift compared to your stock 1.5 ratio rockers. It is basically a poor mans cam only doing a rocker change. It would likely give you more power across the board, but more likely to provide the most gain up top.
If the Mercruiser engine is anything like the L31 vortec engine make sure you upgrade the valve springs when doing any kind of valvetrain modifications as the springs are maxxed out in stock form.
10-19-2011, 02:51 AM
#6
The problem with any upgrade I've been looking at is, no one seems to be able to tune the 555 ECM in the Mercruiser powered boats. Only Whipple offers a tuned ECM with their blower pkg. I know somebody out there has to be doing this for guys wanting bigger cams, stoked engines, etc...
