More horsepower
01-10-2003, 11:19 AM
#2
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nbvs629, nothing really comes cheap when it comes to HP. One thing you can probably do is:
1)Remove the heads and have them bowl/pocket ported ($250)
2)3-angle valve grind/job ($125)
3)You might be able to safely increase comp ratio by cutting the heads by about .020" or so ($100)
4)While the heads are off "Bore Notch" the cylinders ($100)
5)Add some roller rocker arms ($200)
6)Remove the stock air filter and add a K&N air filter ($50)
7)Add a computer chip ($ ?)
8)Add some Stainless Marine exhaust manifolds ($2500)
Plus any cost in takes in labor to remove the heads from the engine and reinstall unless you do it yourself and know what you're doing. Hope this has helped. Best wishes.
Mark/KAAMA
1)Remove the heads and have them bowl/pocket ported ($250)
2)3-angle valve grind/job ($125)
3)You might be able to safely increase comp ratio by cutting the heads by about .020" or so ($100)
4)While the heads are off "Bore Notch" the cylinders ($100)
5)Add some roller rocker arms ($200)
6)Remove the stock air filter and add a K&N air filter ($50)
7)Add a computer chip ($ ?)
8)Add some Stainless Marine exhaust manifolds ($2500)
Plus any cost in takes in labor to remove the heads from the engine and reinstall unless you do it yourself and know what you're doing. Hope this has helped. Best wishes.
Mark/KAAMA
01-10-2003, 02:53 PM
#3
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Increase HP of a 7.4 MPI, yes. Less expensive? No. 
Mine's being done right now. Looks like it'll end up in about 375-380HP range. Head work like KAAMA said, plus larger valves, new cam, also ported (best as he could) the TB jsut to get every little bit out of it, larger injectors (it's breathing real good now and couldn't get enough juice in ther higher RPM's) and the ECM is being reprogrammed again. The ECM is the last thing and hopefully it'll be right on this time, but it's pretty much starting from scratch since it ended up needing larger injectors. Of course labbed props which has already netted a solid 2 MPH.
It's going to end up a few thousand $$ though. Another option to get even more power would have been to scrap the really restrictive GM MPI it has and go carb or aftermarket EFI. Going carb should get you to about 425 HP. I decided to stick with the MPI. Hind sight---I may have done something different (carb maybe) but going into this I knew it was partially an unknown. Plus, I want to keep the stock look. I don't exactly have a boat that people expect to see HP gear on.
The sound alone now might freak some people out.
Yet another option is to go over to the "parts for sale" forum and pick up that 454 MAG for about $5k and do a swap then sell the 7.4 MPI (one just sold on eBay for $4300
that may be an all time record) The MAG is 385HP.
Mine's the lab rat and it's in Bob's laboratory right now at Full Throttle Marine!!
Mine's being done right now. Looks like it'll end up in about 375-380HP range. Head work like KAAMA said, plus larger valves, new cam, also ported (best as he could) the TB jsut to get every little bit out of it, larger injectors (it's breathing real good now
and couldn't get enough juice in ther higher RPM's) and the ECM is being reprogrammed again. The ECM is the last thing and hopefully it'll be right on this time, but it's pretty much starting from scratch since it ended up needing larger injectors. Of course labbed props which has already netted a solid 2 MPH.It's going to end up a few thousand $$ though. Another option to get even more power would have been to scrap the really restrictive GM MPI it has and go carb or aftermarket EFI. Going carb should get you to about 425 HP. I decided to stick with the MPI. Hind sight---I may have done something different (carb maybe) but going into this I knew it was partially an unknown. Plus, I want to keep the stock look. I don't exactly have a boat that people expect to see HP gear on.
The sound alone now might freak some people out.Yet another option is to go over to the "parts for sale" forum and pick up that 454 MAG for about $5k and do a swap then sell the 7.4 MPI (one just sold on eBay for $4300
that may be an all time record) The MAG is 385HP.Mine's the lab rat and it's in Bob's laboratory right now at Full Throttle Marine!!
Last edited by SeaRay Jim; 01-10-2003 at 03:02 PM.
01-11-2003, 09:37 PM
#4
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The intake system is your biggest restriction. A carb might be the best compromise for this as injection is expensive. Sea Ray Jim is on the right track. More compression would be high on my list, also. KAAMA's idea of cutting the heads is a good start, but I would cut them a lot more. This depends on how equiped and competent your machine shop is. An angle mill will really help, but you must also cut the intake side of the heads which many machine shops cannot do on a BBC. Also, check the deck height. If it is over .020", you might try different head gaskets. Mr. Gasket has some neat thinner ones. Be sure to keep about .040" deck clearance and be sure not to increase compression too far for the gas you intend to run.
01-11-2003, 09:53 PM
#5
You can't add much without changes in ECM and or injectors. This is hard or impossible to do yourself. You have to pay someone to reprogram ECM and then dyno time to make sure everything is correct. Unless you go with a proven package that someone else has done ($$$$). If you lik eto do this stuff yourself I would go with a carburator you are not as limited on cam selections and changes to heads as you can adjust easier. Just my opinion. Not to be to negative here I think it depends on how much of a gain you are looking for. I agree with searay jim it will not be cheap but HP never is!! Speed costs so how fast depends on how much you have to spend.
Oh yea welcome to the board!
Oh yea welcome to the board!
Last edited by paradigm shift; 01-11-2003 at 09:57 PM.
01-11-2003, 11:42 PM
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Ive heard a rumor about a after market ecm that is being tested that will let you set your pulse time on the injectors of merc fuel injection , if this is true you will be able to adjust the fuel mixture anytime you make a change and not have to do any reprograming
01-12-2003, 06:19 AM
#7
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If that adjustable e.c.u. comes out, it would solve many fuel injection issues. Has anyone else heard of this? Sounds to good to be true.
