you're better off to spin it higher with a little smaller (lower pitch) wheel than keep the rpms down and run a bigger wheel - the torque is what will kill it and having the drive turn a little faster (with fresh, high quality lube) is probably better. I routinely spin an alpha drive 5500-5700... I've scattered a couple of them, BUT each time I could trace it to my own mistake (primarily water in lube). 20 mph = gain of 200-250 horsepower, eh?
and the powerflows do make more horsepower than the emis according to the builder here. he also told me that for longevity, I would be better off with manifolds. he sees a lot of the cheaper headers crack... and there goes the engine when they do. I also had a clearance issue. I had to be really creative to get the engine and imcos in there - headers would have been a biotch. Also note that tall valve covers will fit under the imcos... not a minor issue if you're running aftermarket heads, rockers, etc...
btw. valve float with that mild cam at 5 krpms??? what spring pressures? surely not with new aftermarket springs? I can see that cam crapping out hard at 5k depending on the heads, but if the valves are floating at 5k there's something else running amok isn't there?
anyhow, enough rambling and living vicariously through the boating of others. in another couple weeks I'll be freed up enough to put things back together and go play. have fun!
Also, Tim what kind of gear lube to you run? I definitely want to run something synthetic. You seem to be the alpha drive expert from the threads I have read of yours. What do you think will be a good lube?
I've decided I'm probably going to get the IMCO thumper system. I can get them for $990 and they offer a 5-7% boost in power over my stock manifolds, which could equal 20-28 hp. The powerflows appear to be too tall to fit in my engine compartment, and after all the $ that has gone into this project I really can't put another 2k into the exhaust. Same with EMI - they are $1750. I still need to buy a flame arrestor and a few more things, and probably save up some $ for what will eventually turn into the new outdrive fund. Anyone have any experience with the thumper exhaust? There are some posts on other websites that seem to suggest it is a good system.
Just make sure the risers dump the water into the exhaust a bit further back then the factory exhaust. have you looked for a second set of stainless marine or imco manifolds? I see them for sale once in a while.
LOL expert? hardly. run merc synthetic lube to be safe. I've come full circle on this one. I don't know on te clearance. I do know that my flame arrestor with the airgap rpm and afr heads is the part that hit the hatch and required shimming it up... the risers are about to touch as well...
ps. check your pms, I'm sending you link to used set(s) for sale - not mine, just passing on info...
Im running Patroit Performance "Vortec" Style heads. I cant remember what the spring pressure is, but I remember the specs claimed to match up to the cam... Im not sure if there is something else up, or the springs werent up to the task as advertised.
I run a Gen 1 Alpha. IMO - better than Gen 2's because of their availability and price.
I also run a labbed 25" Mirage, which puts me at a decent crusing speed at friendly RPM's. I also have a stock 25" Mirage Plus with more cup, but I havent tested it much.
I think youll hit 65, but you'll have to work on boat set up for 70.
As luck would have it, I found a used set of Stainless Marine risers, and just bought the manifolds. $1400 total for a $2000 exhaust system - not a bad deal. The Thumper or EMI would have cost me $1250 so I am happy with what I got.
Copy of IMG_20110309_100754.jpg
Can you post a picture of what you bought? I lucked out on a set of "Stainless Marine" manifolds and risers when I was doing the engine build. If they are the same ones I bought - I wont tell you how much I paid... But I have $200 in the powder coat stripping and polishing.
The Stainless Marine manifolds and risers are nice. Youll save about 100lbs over cast iron. Dont bother getting the powder coat removed, they tarnish in a few months if polished.
Youll have to hook up your cooling system a little different than stock.
There are 3 openings (one Bottom, two top) on the manifolds and one on the risers.
Fresh water typically enters the bottom and exits one of the top ports. The problem is, if the fresh water hits the manifolds before the risers, they get real hot. So you could do 1 of 2 things. Open the back top manifold port and dump through a thru hull fitting or do like I did and use a Tee system, so the hot water from the manifolds and a fresh supply of cool water dumps into the risers.
(thise are just brass plumbing fittings used, you get them at a supply house - not a big box store) I will get anodized aluminum or stainless Hardin Marine ones if I feel like wasting money sometime later. Either way, you will have a plug in one of the 3 holes on the actual manifolds.
I have an engine Pic if you follow that link on my profile. Its not uploading right now for some reason?
Flysfloatsor, since you have the stainless marine manifolds, I assume you know how tall they are. Do you by any chance know what the difference in height is between this system and the stock mercruiser manifolds/risers? I know I am going to have to raise my engine hatch but I'm not quite sure how much, and I can't find it anywhere online. If you knew, that would be awesome.
I havent put a tapemeasure on the risers BUT I would say they are about the same as stock cast ones. Maybe only slightly taller, less than an inch. As you saw in the picture, I have an edelbrock intake manifold with a Holley Marine Carb and oversized 5" tall Holley flame arrester. The flame arrester is taller than the manifolds, and all fit under the sun hatch without modification.
Id bet You will not have to do any special modificatins for the risers, the Flame arrestor will be the tallest part on your motor.
The manifolds are nice, the manifold to riser clamping system is well engineered for easy installation. Which makes it really easy to install the manifolds with the engine IN the boat because they are light (without the riser attached). You would appreciate this even more if you've ever changed out a cast iron manifold with the engine in the boat...
Just out of curiosity, could you notice the weight difference when you switched from iron to aluminum? Some people say it is very noticeable, others say not so much. I've switched both the exhaust manifolds and intake manifold to aluminum from iron, so I should have somewhere around 100 lbs less weight in the back.
ditto on cooling system, have to swap outlets (assuming you're going regular freshwater cooling rather than closed...)
I personally like the black stainless marine finish, so I'll probably stick with that for now. Maybe at the end of the year polishing them could be a winter project. I don't have the $ to switch over to closed cooling right now so I'm going to go with raw water cooling. I'll post a picture of the cooling system setup once it's installed to make sure I've done it right.
Im not a good test case for the weight question. Because I went from a 200hp Mercuriser 305, to a 383 with the aluminum intake and exhaust. So, my power was way different. (I wanted Aluminum Heads, but didnt get them because Patriot Performance sold me cast ones for for a great deal because they had been ran on a Dyno test engine)
The above x rpms for the first y minutes is for a flat tappet cam... Otherwise, run it enough to be sure you're not leaking anything and nothing is rattling loose, check the oil and tune, then run it like you stole it - it's broken in...
Yea, like Tim is saying flat tappet are a big part of the "ole" break in rules. Which you dont have.
Also, inexpensive rings on rough finish cylinder walls.
With shops following piston and ring manufacturer's recommendations on cylinder specs, they break in really fast. Im guessing you have moly rings and they prob finished with 400 grit stones. Each piston was fit to each hole.
I would change your oil and filter if you haven't already.
Then run it like you stole it! Keep an eye on you're gauges! Oil and temp!
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