baronbob

I have a stock 7.4L MPI with a Bravo III on a 10,000# cruiser. I would like to hear from others who have applied a Whipple to this engine. My application ranges from occasional sea level operation, to more often hot California lake operation (1000msl), to most often Lake Tahoe (6000Msl). I would like to keep the stock MPI and I plan to prop such that I can keep the existing rev limiter set to 4600RPM. I would like to avoid changing anything during my yearly elevation changes except a set of props and perhaps a pulley. Has anyone Whippled a stock motor and been able to keep it alive? What should I look out for or potentially change out? I have been told to watch out for fuel pressure and to install a loud low pressure buzzer. Any other Ideas? Since I will be propping to keep my RPM's low and the Whipple making torque at lower RPM's should I be concerned about the drive? Would a shower help @ low RPM?

bobl

Dustin Whipple told me a few months ago that they didn't recommend putting their superchargers on the 7.4MPI(Vortec) engines. The Vortec heads are very prone to detonation and they had not had good luck with them. Maybe they've gotten it sorted out now. I would talk to Dustin personally about your setup to be sure.

baronbob

I talked to Dustin and he said If I had vortec heads that they currently did not recommend supercharging. He is checking my SR#. I have noticed that you do not think very highly of the 7.4L MPI. You have refereed to it as junk. Is the whole motor junk or Can it be brought alive to some degree?

bobl

baronbob...I do not mean to imply the 7.4 is junk. The MPI they use is designed for a truck. It makes great torque at low RPM but just doesn't work with modifications at higher RPM required for good HP. The Vortec heads are great when modified in a naturally aspirated application. It's pretty easy to get 425+ HP if you ditch the GM MPI and go with a carb or aftermarket EFI.

Ric232

Bobl, (or "Bobble" as I keep hearing in my head)

Why don't you just relocate to Central Florida so you can do a build-up on my motor.

bobl

Ric232, I was there for 2 days this week(St. Petersburg). Geeze, it rained like crazy. Didn't even get on the water. Think I'll stay here in Central Texas. But I'd still be glad to do your engine. Ship that puppy.

"Bobble" too funny. I guess that handle has stuck since the infancy of email when we had to use our first name and last initial.

Bob

baronbob

Thanks for the reply. Perhaps you can answer a question relative to high altitude operation. With a non EFI machine I have in the past advanced the timing (10-12 initial) to help compensate for the loss of power due to higher density altitude. Will the MPI perform in a similar manner (all advance relative to initial) or will the system automatically compensate and overcome the effects of higher initial. I have the Mercruiser service manual but can not find a good description of the MPI operation. I know you don't care for this system (especially @ higher RPM), but I plan to stay below 4700. Any reading you can suggest to better understand and possibly modify an MPI?

Offshore Addiction

have done several supercharged set ups on those motors,it can be done but your internal engine parts will need compinsated,basically set up for it,otherwise leave it alone,that weight to single engine set up is going to give you minamal gains anyway!

Smitty

iTrader: (1)

I would not supercharge this setup.

1. Your motor is far from ideal for supercharging.
2. Bravo 3 drive will not last. It will break under the load and torque from blower.

Sorry for the bad news

bobl

Baronbob, It would not hurt to advance the base timing a couple of degrees at altitude. The ECU has a built in timing map that provides a preset amount of advance at any load point. This is in addition to the initial advance. It's really not that much different than a standard advance curve, except rather than being just rpm driven, it is programmable at various vacuum and rpm points. I've done quite a bit of testing on 7.4MPI. They don't like much timing over stock or the knock sensor will start removing timing. The Vortec heads are a "fast burn" design head and do not require much advance. I've found most stock engines to be running around 24 degrees total at WOT. At about 28 degrees it will start to knock. This is at sea level. So, with that all said you may wake it up slightly with a couple of degrees more timing at high altitude. Truthfully, with your boat weight I doubt your going to notice any improvements no matter what you do, aside from supercharging.