Adding a Prochager
 

Hi

I have a 1999 Mercruiser 7.4 MPI with 310hp. I have just fitted through the transom exhausts yesterday and are purchasing a Procharger kit next week. The boat is an 89 model 29foot Scarab and only has a top speed of 40mph, I am looking to acheive over 55mph or 60mph would be FANTASTIC.

What have other offshoreonly users purchased for their 7.4? What brand, what psi, what results and most importantly what problems?

I am looking at the 5psi kit to run on 91 octane unleaded and are hoping it to be very reliable. I am from Australia and would also like to know if Procharger is popular in the USA?

regards,

Richard

Re: Adding a Prochager
 

If your boat is running properly and is propped correctly and only runs 40 mph it will probably be hard to get 15-20 mph out of it with 5 psi of boost. There is a guy on here (baraon bob or something like that) that is running m-1s on 330 hp mercs,he definately got some gains out of it but motors ended up getting a ton of blowby,cast pistons don't really like blowers much. Your mpi can be made to run well though with a procharger but it might be difficult getting it tuned right being in Australia,prochargers tech support isn't the best,Smitty

Re: Adding a Prochager
 

There are a ton of hardcore hp places in Australia. Take a look around.

Since your engine is vulnerable to boost and other performance mods + the fact you are looking for a big % increase in speed, I strongly suggest adding better internals. The good news is that it costs no more $$$ to stroke to 496cid vs same 454cid when buying a new forged steel crank, good 4340 rods, and forged pistons.

To swap from fi to carb and turn your motor into a strong performance one will typically cost what Procharger w/ intercooler kit will cost for a fuel injection motor anyway. Here in the US, between 5500-6000 $$$ + $1000 or more in unknown miscallaneouses.

=========

Not telling you what to do, just putting another perspective on things.

Do your homework and talk to builders near you that you trust.

Re: Adding a Prochager
 

I ran a procharger for 3 years on a 7.4 with 9 pounds of boost. I did upgrade my fuel system to all 1/2 inch lines and ungraded fuel pump. I did end up blowing the motor after three hard years on it.

Re: Adding a Prochager
 

Hi

To: SB

How are you and thanks for your input/advice on alternatives for my 7.4mpi. Who in Australia does performance work on marine engines? I am in Melbourne, Victoria and are having problems finding anybody sutiable.

The complete Procharger kit is around $4400 USD, do you think I could have my bottom end rebuilt and put a carby on for that sort of money? If so what sort of hp what I be making?

regards,

Richard
Scarab29AUS

Re: Adding a Prochager
 

I believe we had emailed & talked a few times before about sc's for your Wellcraft.. To give you a basic answerto your current questions, there are naturally aspirated BB engines making big power some injected some carbed. Either way they are still more to do right then to add a low boost sc to your efi's.. Unless someone is cutting corners to save money & skimp on materials you wont get the same results as you will by adding an Procharger. Also carbs are not as efficent or as precise as fuel injection period. Stay low boost on a stock engine & for what you are looking to do it will cost you less. I have many clients running low boost units on stock engines with hundreds of hours on them. They do their normal regular maintainace and as a rule dont have any major problems. I would not tear off the efi system to go for a carb.. Its like trading modern laptop for a comodore 64 from the 80's. They both work & can compute but other than that there is no comparison in speed, performance, capability & reliability..... Just my 2 cents.. :) Jamie / Lakeside

Re: Adding a Prochager
 

Hi

Thanks DONZI33: your reply is exactly what I think. I beleive I can run a Procharger on low boose for at least a few seasons which would equate to around 200 hours for me and as long as I regularly service the motor I should stay away from major problems. Even though I will not have a 700hp or higher race style motor I will be able to take full advantage of my current engines configuration.....Bang for you Buck!

I am hoping that one day to purchase a Mercruiser 496HO and that Procharger can supply a kit to fit the Procharger and Intercooler I purchase for my 7.4MPI 310HP, basically the different hoses and clamps/pulleys etc.

regards,

Richard
Scarab29AUS

Re: Adding a Prochager
 

I may have communicated with you befor on this subject, but here goes with my latest. I had a stock single 7.4 mpi on a 31' heavy cruiser (9000#s). When I bought the boat it would do 39 MPH @ sea level (400hrs). I installed through the hull exhaust with out any improvement. I put a stern jack on and saw better hole power and less wetted area and maby a mile or two on the top end. I bought a m-1 with a supposed 5psi pulley. I changed two prop sizes up and got about 46 mph but the motor would not stay @ WOT and would fall off. I had oil pukeing out the dip stick and after completely going through the breather system I blocked off the dip stick and ran the season. The motor seemed to love 4200 RPM but would not stay @ 4600 rpm and would drop back to about 4400 RPM @ WOT. Most thought that I had blow-by and so I decided to freshen the engine over the winter. Here is what I did. Gill exhaust, Merlin heads (had to stay with oval ports so as to not to have to change out the injection) with 2.25 intakes and inkenel exhaust. Big springs and roller rockers. Mag cam, Mag pistons and bigger rods. Large volume oil pump. Same crank. With all the parts and machine work $4800 W/O the exhaust. No dought had I a line on a Mag or 502 that was either new or could be freshened I might be money ahead, however finding that engine is a whloe other issue. The problem I now have is programming my ECU. I have it re-programed it three times and I still have issues. I also have the smaller injectors and may have run out of flow. that means that if I change them out I will have to start all over again on the ECU. The other side of staying with the smaller injectors is running lean @ WOT. The rev limiter has been moved up to 5200 from 4700 and I now do 47MPH @ sea level 5100 RPM 7.5 #s of boost. Not a good place to be with this engine. I run 44.4 MPH @ home (Lake Tahoe 6200MSL), 5100 rpm, 5.5 PSI and the engine is happy. The expert procharger guy doing my programming says my current limitation is breathing through the oval ports. I really dont want more HP I just want to properly tune what I can make now, limitations and all. The best rout for me is to get it tuned in the boat by a professional ECU programmer. So what does this mean for you. If you might want to keep adding HP, ie going faster and faster then sell your motor and get a mag or a 502. If your going to tune yourself or rely on any body but a very good experienced re-programmer than go carb. They are easy and you may find an engine with a set-up. I go up and down in altitude and temperature and like the computer making decisions. It just needs to be properly programed. If you want a slight but completely reliable increase in speed say 5MPH go with a stock m-1 with a 5psi pulley but be prepaired to fall back to a lesser pulley if the motor does not like the higher pressure.

Re: Adding a Prochager
 

Hi

Thanks to all for your reply's. I am not happy with the results that Baronbob has acheived with the same motor and similar length boat to me. Is their any users at all on this forum that have had better success with a Procharger on a 7.4 mpi?

regards,

Richard
Scarab29AUS