DOCTOR DAVE

kaama, thanks for mentioning my name. i enjoy working on various projects when it comes to the marine hp world. i have only been self taught through my own experiences, and some knowledgeable people in the business.
kaamascarab30, my suggestion to you would be, at least a b&m 250 charger with 2 650 holleys, msd ignition, 4-5 lbs of boost and 28 to 30 degrees of total timing. camshaft change would be helpful, but not intirely nessary. this would add approx 125 hp and should see speed increases of 7-10 mph.
dave

X-Rated30

Doctor Dave - I was thinking of 420 Megablowers or 8-71 Weiands running that amount of boost. Would these make the engine live longer (keeping the forced air cooler) or just be overkill?

Also, what would changing the cam seek to achieve? (Cams are voodoo to me -- I don't understand how they affect hp and torque.) The specs on the ones I have are:
Valves (I/E): 2.190"/1.880"
Camshaft, Lift (I/E): Hydraulic Roller, 0.510"/0.540"
Dur. @ 0.050" (I/E): 211/230 degrees

Anyone else have any input?

Intolerant1

I spoke to Bruce Wolff at your suggestion awhile back and he helped me a great deal. I wish he was involved here. Spent half an hour on the phone with me even though I wasnt spending money with him. Plug guys like him all you want !

DOCTOR DAVE

kaaamascarab, any of those units would work fine. camshaft is a little small, but you can live with it. more cam would make more power. but if $ is issue, keep the one you have for now.
as far as heat, spinning a larger blower really doesnt make that much dif. it's compressed air that makes the heat under the blower.
dave

KAAMA

iTrader: (1)

Intolerant1,

I don't think Wolff is able to be on here much. Right now he's building a pair of super charged 650 cubic inch all aluminum engines for a 38 Cigarette with a staggard engine set-up and #5 drives with extension boxes---pretty wild.

Dave F

If it's a roots style blower you want, they do look cool, on a 454 you would be just fine with a 6-71. Especially with that cam.
The bigger the blower the more hp it takes just to turn it. The more hp it takes to turn it and not "getting it back" (so to speak) the less efficient it is.
A 6-71 will put approx 5# in at 15% underdrive without a cooler. I highly suggest an intercooler with a roots blower, such as the Whipple or PFM, just for examples. Now, I also suggest NO MORE than 7# on a roots blower WITH AN INTERCOOLER for reliability (and really, that's pushing it) For complete reliability without question 5-6#.
A 6-71 will get you approx 5-6# with a cooler at a 5% under drive.
So, as you can see even a 6-71 will be plenty for a 454. If I were going for a roots with a 454 on a boat and was worried about reliability thats what I would do.


Now, since cams are "vodoo" to you, lets talk about the plus and minus of a cam swap;
The bigger the cam:
The higher the RPM range for both torque and hp.
In a naturally asp motor you'll need more static compression to make it perform well in the low and mid range because there will be less cylinder pressure due to overlap. In your case however the blower will add something called "effective" compression ratio.
THE MOST IMPORTANT FOR A BOAT, is your exhaust system. Overlap, is when both intake and exhaust valves are open at the same time. The more overlap you have, the more prone you are to reversion.
The obvious plus to a bigger cam is the more potential for power.
However there is a point at which you can go too big. The amount of rpm your engine will run and your exhaust and cylinder heads can flow are the "choking" points.

As it's been said, you can live with that cam, but to make the most hp/torque possible I suggest the following patterns as a SUGGESTION. I'm not saying that "this is the cam" ya know?
I would need more details to offer that suggestion.

With stock exhaust:
In my opinion, possitively no more than 7* of overlap @.050. When measuring @.050 as a "rule of thumb" you can add approx 60* to the overlap figure for a seat to seat measurement. Meaning you actually have around 67* of real overlap.
Example: 226/236 .587/.610 112=7* of overlap
If that same pattern were on a 114 centerline then the overlap would get knocked down to 3*

With after an market exhaust that will guard against reversion the biggest cam I would suggest with 5-6# of boost and staying in the 5200 rpm range on a 454 would be something like a;
230/236 .598/.610 112. That equals 9* overlap.

Also, if you are gonna go this far, take you heads to a machine shop and get the necessary work done for better performace.

To answer your question of internal parts, No. You will not need to change any internals on a Gen 6 motor for these parameters. They already have the good stuff.

If you have any more questions feel free to email.
DAVE

Dave F

Dont forget, you'll need alot of hatch clearance or a scoop for a roots also.
DAVE

Cord

iTrader: (2)

Back when I was first getting into this sport, I too was looking at a blower. I spoke to BDS and their recommendation was for the 8:71. The reasoning was that it would still fit the block with the stock distributor and it could be turned slower for a cooler charge. I believe the recommended carbs were two marine 840's. They also recommended the serpentine belt so that the blower would slip during a backfire. The pop-off plates aren't coastie legal in a enclosed engine bay. They felt that the stock 454 mag cam, iron heads and compression ratio would be OK. One would think that with the intake being pressurized that the exhaust would need to be improved. But time and time again, I hear that the exhaust just isn't critical. A set of stock manifolds (ie gills) are more than adequate.

Dave F

Yea, I hear what you're saying Cord but I would simply look at what Merc's been doing for years. BDS is certainly a great company and they know their stuff for cars with out a doubt.

The "old" 525 SC's were 454's with 177 Weiands. They had around 5# and no cooler. The new 575 is a 502 with a 256 and no cooler.
A 6-71 is two steps above the 177 and according to Weiands own literature can support a 454 easily in the parameters we are speaking of and it's still underdriven. Therefore creating the cooler air charge.

Remember, a boat engine always has a load on it and boost doesn't start up till around 4,000 r's. So, the less hp you spend just cruising (around 3-3500) the more efficient the engine will be. A roots blower is a liability until it starts to create boost in the manifold.

Carbs are also a good point to discuss. I personally would go with a pair of 750's. Take them to Dean Nickerson and have him do his magic. And quite frankly they probably would flow around 840 by the time he was done.
Just a quick point a 454 with 6# of intercooled boost spinning around 5500 rpm will need approx 1120 cfm. So even a pair of 650's modified by Dean would most likely do the job.

Also, I agree with the exhaust statement, to a degree....as long as you stay with a cam with little to no overlap. In boats the real issue is reversion.
Exhaust won't give a measurable gain untill you start to modify the engine and spend alot of money on it. Good exhaust will scavange and increase performance, but, that goes back to the heads and cam. If neither can flow enough air for the exhaust to make a difference then there's your answer.
The more air you get in, it makes sense that you have to get out.

I know you were just relaying what BDS told you. I was just offering a slightly different point of discussion. A friendly debate if you will.

Keep this topic going. This could make a good debate.
C'mon I know some of you other guys want to jump in....

DAVE