Aluminum Manifold for more power?

[z1nonlyone]

I am in the process of rebuilding my 5.7 EFI mercruiser engine, 1997. I was wondering if any aftermarket intack manifold would compliment the performance of my engine?

 

[John_S]

Re: Aluminum Manifold for more power?

I am in the process of rebuilding my 5.7 EFI mercruiser engine, 1997. I was wondering if any aftermarket intack manifold would compliment the performance of my engine?

Probably not. Any manifold that could/would provide a noticable gain would require reprogramming, which I believe can not be done with the Merc modules.

 

[Howard Sterndrive]

Re: Aluminum Manifold for more power?

boat motors spin too slow to benefit much from aftermarket intake designs.
doubt you'd notice any difference.

 

[fossill]

Re: Aluminum Manifold for more power?

Since when are rpm's of 4600 to over 5000 too slow? Boat engines scream compared to automobile rpm's of 1800 to 2200 rpm in cruise in a comparable powerplant.

 

[rodbolt]

Re: Aluminum Manifold for more power?

5000 RPM is relativly slow, most any stock manifold can do it.
its all about airflow, like you were told,add more air and the ECU doesnt know.
now the engine is lean at 5000 RPM and your posting about tuliped intake valves.
EFI motors dont track airflow or fuel rail pressure on mercrusier market engines.
they use speed density so far not mass air flow.
if you alter rail pressure or airflow then you have to reprogram the ECU for fuel delivery or start playing with larger flowing injectors.
on the automotive side of the house you can monitor O2 sensor feedback and fine tune the ECU programming, the marine side,O2 sensor use was not mandatory for the 50 states until jan 01 2010 and jan 01 2009 for CA.
now we have O2 sensors and catalytic converters.
in the 1997 time frame it could be TBI or MPI but both work kinda similar and both were speed density not mass air flow.
save your money for filters.

 

[wca_tim]

Re: Aluminum Manifold for more power?

intake manifold can make a rather dramatic impact on a boat engine's performance. that being said, the factory ones usually aren't that bad and the fuel map has to be changed to benefit from the change in intake manifold. I know there are options around on reprogramming the merc set-ups, but they're relatively expensive.

 

[Bondo]

Re: Aluminum Manifold for more power?

5.7 EFI mercruiser engine

Ayuh,... Swapping Intake Manifolds is usually Not an option with EFIs...

 

[JustJason]

Re: Aluminum Manifold for more power?

Since when are rpm's of 4600 to over 5000 too slow?

My old Taurus SHO after valve springs, cams, ECU, fuel injectors, fuel pressure regulator, fuel pump would spin to 13,000

My last motorscooter hit factory redline at 16,500

So yeah... 5000 rpms is reasonably slow

 

[SeanMcl]

Re: Aluminum Manifold for more power?

My old Taurus SHO after valve springs, cams, ECU, fuel injectors, fuel pressure regulator, fuel pump spun to 13,000, once.

Fixed that for ya.

OK, now that the comedy routine is out of my system...

Z1N, if you look at the various dyno graphs comparing stock vs aftermarket intake manifolds, they usually show negligible gains until 4 - 5 thousand RPM, then they take off and give a 15 to 20 HP increase between 6 - 7 thousand RPM.

I also notice that most of these tests are done on engines that have some amount of modifications done, like better exhaust systems or ported heads or higher compression ratios.

So for me, I have come to the conclusion replacing the intake manifold isn't worth it. I can get some cheap performance by just washing and waxing the boat, though it never registers on the GPS for some reason.