[jimgoog]

Saw this post on TEAM.BAJAMARINE.com

Anyone have any input on this:


supercharging 7.4 mpi info I got from CP Marine
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Hi everyone , I called cp marine yesterday to talk to their techs about supercharging the 7.4 mp as i have read tons of diffrent opinions about doing this , and i wanted to know from a dealer that sells alot of these things , and diffrent brands what are the facts. from what they told me its not a bad thing to supercharge the 7.4 mpi, he told me the main thing that determins the life of the engine after the supercharger is all in the way you drive the boat , if your out to run the boat at W.O.T. all day then it will definatly shorten the life of the engine and it probably not a good idea. How ever if you guys are like most people that go boating an the weekends youll probaby cruise at around 45-50 mph and when another boat tries to go by you wack it down until you blow by him. (the super charger is your insurance to do that) but when cruising your not runnig the crap out of the engine (majorityof the time), with the supercharger you should be able to achive the same speed with less rpms so you will actually be putting less wear on the engine. Blake you said you were saving for the bigger motor But , why not do the supercharger, run it for a wile probably last quite a wile from what they were telling me and then after it does finaly go, rebuild the 7.4. with better internalcomponets and then you have supercharged power and reliability even for high speeds for long periods of time. the 496 is only 415 h.p. if im correct the 7.4 mpi with the charger is said to be worth 480 h.p. 5 lb. boost and 520, 7 lb. boost with fuel system mods. I think Im gonna start saving for the charger, the procharger runs $4,600 the whipple is like $5,200 and is more difficult to install so Im looking tword the procharger. If their speed increase calculatons are correct I should be right around the 80 mph mark wich is plenty fast for me. Oh 1 other thing he also told me it isnt nessary to change the exaust , you can , but you dont have to , you can basiclly jut bolt it on whith out major engine mods, you do have to change the prop.
let me know what you guys think.

 

[obnoxus]

DONT BELIEVE IT !!!!!!!!! Not only is the 310 hp intake not condusive to extra flow. and the lower end is not built for that kind of stress, nor is the valve train,,,,, you may get a couple seasons out of it if you take it easy,, but if you have to take it easy on it,,, whats the point ?????? I have 500 hours on my motor, and would expect to get anouther 1000 out of it,,,Also,,,, most people I have talked to said by the time you are done,,,its more like $8,000 an engine,,,,, you can buy alot of motor for $8,000 !!!!!!

 

[crmax]

you can rebuild your engine to make 480hp and be stronger for under that price, my problem is my boat needs to be 9' longer then I would go for more power, but at this point I can only go wot when the the lake lets me

 

[jimgoog]

My new thought proccess is that with my 22 footer if I get it going fast enough I can just skip across the waves instead of losing momentum and pounding into them. :gunner:

No for me in a year or two, I will probably rebuild the curent engine for more HP like you guys have said or go with a 496HO new. I am moving to east Central GA. and the lakes their do not have the large waves that KY lake sometimes gets. Not many folks have large cruisers down there and the barge traffic is little to none.

 

[crmax]

here an idea you can get a flat top piston stroker kit (crank, rods and pistons) for about $2500 and have a little work done to the heads and your right up there in hp

 

[obnoxus]

Wait till you find a good deal on a used 502 MPI like I did,,, drop it in and go with no problems

 

[OldMagicfloat]

I'm running a 502 mag with Stainless Marine exhaust and a stage 1 procharger. The boat runs great and there is not much that can touch it from 40 to 70mph. Top end is 78 with a full tank and 2 on board. The engine is very reliable and a real sleeper. Most people get gready and try to raise the boost to 7.5 and higher. Unless you build the engine you're asking for trouble above 5lbs. I run 40 to 50 mostly which has less than 1 lb at that rpm. It is also a little easier on the drive out of the hole since you are not packing that much boost our added torque.
I don't know how well the stock 7.4 would handle this though. The Mag is a stouter motor.

 

[obnoxus]

there is a HUGE difference between a 7.4L and a 502 MAG !!!! 502 has all forged rototing assy.....7.4L is cast.

 

[Candyman]

Listen to OB. If he thought it was reliable HP it would already be on his boat. You don't want to do that with cast parts.
Dan

 

[Speedwake]

jimgoog....

just buy my engine. It's built right, forged crank, forged rods, heads, valves, cam, etc all were done JUST for reliability and a blower. It's best to have the engine BUILT specifically for a blower not bolt a blower onto an engine that was never designed for a blower.

there's no messing around. You drop it in and GO!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

 

[OldMagicfloat]

Dan...how much you want to bet...if BN is faster than you know who...there will be a procharger installed over the winter...INCOGNITO if you know what I mean!!!!:laugher: :laugher: :laugher:

 

[obnoxus]

never happen !!!!!! to many problems... not worth it to me,,, I can get mid 500 HP out of mine with just head and cam work which is just fine with me .

 

[laster]

I don't know obnoxus. It is a very tempting package. I have a Whipple on my 502 MPI and I love it. Starts and idles just like stock and the power is phenomenal from right off idle. Transom sooting is comparable to stock if not less. Sounds the same too until I hit about 3700 RPM then you can hear it whistle a little. Only negative so far is being careful not to over stress the drive.

 

[Speedwake]

Laster you are Soooooooo right.

I have that whipple charged engine in my 222 Stinger and I have the 4-5lbs boost pulley installed. Man O Man does that accelerate. It is sooo much fun and yes the whine comes in about 3,700 when the boost reaches zero and starts climbing....

it's a wild ride!!!!!

- jeff

 

[Candyman]

Dan...how much you want to bet...if BN is faster than you know who...there will be a procharger installed over the winter...INCOGNITO if you know what I mean!!!!:laugher: :laugher: :laugher:

Skip.
I'd put my money on the Whipple charger. We better both be out when they run each other. I have never towed two boats at the same time before. :laugher:

If I had reliable injected 502's I would have already bolted the Whipple's on. They’re great as long as you don't run too much boost. I could never see supercharging a cast motor.
Dan