kdrolt

http://www.mercurymarine.com/8226hp575_sci_-_575_hp

and note that it uses Since we know the sbc TBI is good up to 300 fwhp (or shp in a boat!), then dual TBI would be good for 600 fwhp... or a similar power rating at a smaller rpm when using a small amount of boost.

The blower probably also benefits from fuel evaporative cooling so that may be one reason why they went with TBIs atop the blower instead of using MPI underneath the blower.
The TBI would be more fuel efficient than carbs, but just as easy to install and service.

Too bad no one here works for Mercury Marine....

TechSmurf

..... yanno... about a year ago I started quietly cooking up the plans for this never before seen dual-TBI setup slapped on top of a 6-71 blower slapped on top of a small block 427 in my head... I guess the only part of my never-before-seen I'll have a chance at now is the small block.. damn. They only got 575 horses out of it on a 502? *starts pondering a miniram again*

kdrolt

You're assuming that they wanted more than 575 hp. They didn't. Think about it -- they have a 502 engine WITH a blower and they're only making 575 hp. Why even bother with the blower if they have a 502?

The answers are, the blower gives them the low- middle- and upper-end power they want without resorting to a hotter cam, so it will run well at ALL engine speeds. 575 hp from a 502 means the cam is probably a stock GM cam, and the blower doesn't have to run a lot of boost because they aren't trying to make a lot of hp and torque. So the engine will last a very long time. And as I said before, providing the fuel before the blower gives them some vaporization cooling inside the blower, the TBI's are a cheap way to provide fuel injection and will be better than just using a carb, and each TBI only needs to provide 287 hp worth of air:fuel so they can use two stock GM 454 TBI. So don't make the mistake of thinking that the combo built/sold by Mercury Marine is a poor one because it's not. It's built for a purpose other than giant power numbers.

With that all said, the driver's and ECM MM is using to run the dual TBIs are what prompted my post. Here's another useful link to the MEFI:

http://www.gm.com/automotive/gmpower...marine/efi.pdf

HTH.

kevm14

That PDF is interesting. Looks like GM is still producing marine TBI solutions but they're using the modern equipment like coil-near-plug, drive-by-wire, the ability to use a WB02 and more. That's cool.

305RSlc

Gotta agree with kdrolt here. They apparently didn't want to make anymore power, simply look at the compression ratio of the engine...a staggering 7.5-1. I dunno if that is with or without the blower, but if you have that kind of intake, and threw on some better heads, I am sure it would make much much more power being a 502 with a blower. I wonder what kind of power a duel TBI setup on a nicely bored and stroked SBC would do?? TechSmurf, a 427 sounds like a good candidate, but like you pointed out, why "waste" money on old technology when you can make just as much if not more power with new FI? Too bad mini ram is freaken $1200, whereas the intire dual TBI, with blower, would run around that much too. Just my $.02
Lc

kevm14

I think the whole idea is that you don't want a high strung engine to power a boat. Think about it. When they cruise, they use WOT and the engine is sitting somewhere around the HP peak. Do you guys even trust your L03s enough to drive at 4500rpm all day long without really letting up or anything? Probably not. Marine setups need to be strong, and running a conservative setup is a good way to ensure the engine will last for a long time.