Full Force

iTrader: (5)

Dyno... Marine trim VS Dyno trim..??

Who has dynoed both ways? Trying to see what changes happened going from a full race Dyno header and no accessories, then going to marine exhaust and alternator and sea pump....

Anyone done it both ways?

Looking for info and not guessing differences in output HP

turbom700

I'm wondering the same thing,

I was trying to find a place that I could run my marine manifolds on the dyno! (never found one), I have a relatively unique setup and I'm not sure how I would run it with out the manifolds. (twin turbos)

Full Force

iTrader: (5)

Precision is username here, he can...

Wildman_grafix

Don't know without but when we ran my stock HP500EFI motors we had everything on it including power steering.

I do know bad smashed air cleaner cost about 10-12 HP.

Knot 4 Me

Yes Ryan (Precision) dyno'd my engine with full accessories and wet exhaust. Bob Llyod from Full Throttle has probably done both ways on the same engine. He's since closed his shop and not sure how often he gets on the site anymore but you could PM him and see if he responds.

Gimme Fuel

I think there is something else that needs to be addressed here in these conversations. The following are good technical discussion points:

Performance MANIFOLDS whether Stainless Marine (not Gen III), EMI, Dana, Imco, Hardin will all flow nearly the same, all have similar construction and internal passage sizing. They are still a short runner manifold that dumps into a tubular riser with 3.5" ID and with long risers all generally dump just in front of the tip. I believe I remember reading on a Merc 525 that converts from the crappy CMI headers to Stainless Marine manifolds it lost over 20 horsepower. Mind you that this is on only a 525 hp engine, we are shooting for the 700's here. As with most horsepower related losses, it will not be a linear assumption or a standard "take 30 hp for wet exhaust" assumption, but more or less running into some kind of exponential curve of efficiency losses. So the harder you push, the even harder the restriction pushes back until you reach a point where you will go backwards.

Now, from what I have understood is that manifolds are a decent performance option but around that 650 hp mark will start to become a restriction again compared to a header or something with a TUNED primary length. Tim's engine, my engine and many others here that are at this 650-700 hp threshold yet are using manifolds. Going to a full dry tail will help because ultimately it reduces some back pressure and takes away some of the inherent design limitations. At what point do you need to stop chasing a lack of HP and upgrade to headers? At what point does the short runners, swirling of gasses in the collection chamber, lack of scavenging, and relatively sharp transition into that tubular riser begin to really rear its ugly head?

Now, we are all worried about exhaust flow bench numbers and port shapes. Has anyone ported their manifold openings to ensure a smooth exhaust transition? Made sure gaskets are trimmed? We all wouldn't mount an intake manifold without checking all that but how about exhaust? It is just as important. Has anyone ever flow benched a port on the manifold to see if it can even flow as much as your exhaust port?

Now, I've always taken Bob's speculated HP numbers to mean what I should see validated on a dyno. Now we all know there are skimpy, average, and happy dynos out there. None of us are dynoing motors like OEM vehicle manufacturers do to get a standardized "rating." I imagine this factor alone starts half of HP pissing matches.

bck

The variations in exhaust and accessories from one person to the next would make meaningful comparisons tough. Probably no one that replies to this thread will have the same combo of accessories and exhaust.

Full Force

iTrader: (5)

Not sure about that, there are TONS of guys with stainless marine systems, sea pumps and alternators, give or take a PS pump (that I don't have) I think comparing same with GIL and stainless marine are going to be pretty close over a header or such

Baja Rooster

iTrader: (1)

On my motorcycle engines the biggest gains were found in the exhaust ports. If you can't get the gassed out then the intake charge backs up like young girls in Uggs at Starbucks when the pumpkin lattes come out.

When Mercruiser rates their engines do they do it at the prop fully accessorized? So a Merc 385 would be closer to a 450hp crate motor?

bck

There might be lots of similar combos but I'll bet not so much when you narrow it down to people who've dyno'd and are posting