More horsepower
 

What are some of the lesser expensive ways to increase HP of a 7.4 MPI

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

Increase HP of a 7.4 MPI, yes. Less expensive? No. :D

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 :D 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 :eek: 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!!

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.:D :D

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. :D

Oh yea welcome to the board!

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

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.

That would be awesome, until you run out of injector but, up until that point it would work good.

That would be slick. However, with mine it just flat ran out of injector.

.Thanks for the replies. This all good information, I am glad I found forum. I will continue utuilize it. Thanks Again
Baja 29'

One way to increase performance would be to change to a Pulsedrive. You get on plane quicker, and get 10-12% top speed increase over the standard merc outdrive. Five year warranty, and no maintenance. The down side to the pulsedrive is..... gee there isn't any! The last drive you will need to own because pulsedrive is a drive that lasts. 888-818-6039

Michigandle-are you a dealer for Pulse Drive? All 6 of your post so far have ben "rah rah pulse drive"
BVS is looking for an inexpensive way to increase power. I doubt that swapping over to an $8000. dollar drive, sealing the transome, moving the engine forward and adding extensions onto the exhaust is what this guy is looking for. Stop with the hidden agenda.
Bob

One down side is the cost of the drive system and the cost of fixing the holes in the boat and the cost of adding the trans and the extension for the trans.
If you had a carb you could intall the projection system from holley which could be dialed in. I remember a company that built a interceptor to change computer systems on the fly but, it was for autos. One in the marine industry would be sweet and a fix for several of the problems people have with there boats.

Hey Robert you beat me to it, damn dial up....lol

Hello, Guys,
ACCELL says they have something for the GM crate FI engines to allow programing on your own.. These engines use the same Delphi jJECU we are stuck with so it should work on the Mercruiser also-I hope!!!
If you will go to Mr.gasket.com, you can access Accell and ask for a catalogue. It has a LOT of good FI info-like how to make your injectors feed a few more horses and much more!!!

ROBERT (BLOWN 1500 )ARE YOU SURE YOUR NOT TALKING ABOUT THE 8HP BRIGGS & STRATTON I DROPPED OFF TO YOU THE OTHER DAY ??
ACCELL IS GREAT FOR THAT , SEE YA !!

Keep the 7.4 for a spare and buy a crate motor from Teague or I'm sure Blown1500 could set you right up!!!

Dyno!!!
He said "lesser expensive"!! Heads, intake and cam are very effective on this motor. How much did you say the crate motor costs??????????

I bought a 420 locally for 2K.....you play your cards right you can get by for less than shoving a ton of money in a 7.4. I did mine but thats becouse I had to it was shot. If you look you can find 502 take outs for not a whole lot more than if you sold the 7.4......my.02

Yeah Robert, what's the big idea with this 8hp Briggs & Straton bobby is talkin' about??? :p ;)

I have a fresh 7.4 in the garage now. I bent a rod and determined to step it up in the HP dept. when I rebuilt it. I have a buddy who runs a machine shop and had him do the machine work. I talked to him about some head work and cam change and he told me to scrap the heads. They have little potential even with a cam change. I decided to put her back to stock with the exception of a 3 angle valve job and plasma moly rings. Unless I buy a different boat I will build a big motor next year and I will keep the 7.4 for a reliable spare!

KAAMA AND BOBBY,
It is a 27 hp Briggs, thank you very much-it only used to be 5.