Small blocks and super chargers
 

I have a 2000 29 scarab with twin small blocks in it and I put new heads on with stainless intake valves and inconal exhaust valves same size heads as stock so Idid not change anything there and then I add 5 psi pro chargers the computers have been redone new fuel pumps checked timing and fuel pressure is all in the specs but @ 4000 to 4200 rpm the boat falls on its face if you push the throttles just a little pasted the 4200 mark you feel the boat fall forward everything checks out to be all in order fuel air boost spark but if you hold it it will slowly climb in rpms but only to about 4500 it runs its a$$ off up to that point of 4200 rpms O and its not the props because we even put smaller props on and it does the same thing runs out if you push the sticks all the way forward it all most seems like I need more fuel at WOT any help PLEASE

do you have a fuel psi gauge? it sounds like it is running out of fuel. pull a plug and see if is been running lean. i wouldnt keep trying to run it that way until i was sure what the problem was. what size injectors are you running?

No doubt, don't run a blower motor lean. They will gernade in no time at all. Like was said, check fuel press first, then go from there.



Darrell.

fuel pressure is not it we are running 57 psi at WOT the boat has about 10 hours on it since the pro chagers where put on there has been no sign of the motor running lean and the injectors are stock mer injectors these are the mer 350 mag mpi 300 H/P motors I'm trying to see if anyone else has had this problem and how they fixed it My only guest would be it needs bigger injectors because of volume of fuel the injectors wont produce enough fuel what do you guys think but if this is the case and they need to be bigger why wouldnt pro charger supply them in the kit if they are needed or say you need to up grade you injectors this has realy suck this year I have lost most of this season of boating

Who reprogrammed your ECU? They should know exactly what is happening. That is the person that wrote the cal. He should know how the boost tables (if you have a MEFI-3 and up. And are using a 2 Bar MAP sensor), pulse width, and timing will interact with your boost reference levels etc.

If it is boost referencing correctly, your plugs are right and you don't have any ignition problems, I doubt that there is much the rest of us can tell you. I do know that a stock kit does work. If you think that you are running out of injector, you can always try adding a few PSI of fuel pressure. That will tell you something. Don't jack it up to 75-80PSI or anything or the injectors will not open. Better do the trial and error on the rich side than the lean side.

I think those injectors are 50lbs ers. I ran that same combo in my Crownline. ASM did my recal for the 350 and then again when I upped it to 383. I didn't have any problems running those injectors even with the stock fuel pump. I monitored things with an air/fuel meter. I suspect your computer tune.

Mark at precision marine did the computers and has done several of them and know one else has had this problem so we are at a lost right now on what else to try its only when you push the throttles past 4100 to 4200 rpms that the boat falls forward and it acts like it is running out of fuel
B reak
O ut
A nother
T en thousand
in my case

Ouch. You do have a head scratcher then.

Hang in there. In the long run you will love the new hp

most of the bbc kits ive seen they said they were running around 70 at wfo,


does the fuel press change at 4200+?

In the pro charger kits it says the fuel pressure should be around 57 psi max

tsteph had that setup on his scarab , same config. Know his boat was a runner. Track him down and pick his brain.

Sense you have had your ecu reprogrammed Prochargers fuel press recommendation is no longer accurate. The tuner should have given you a the fuel press that he set up the tune for. If you are running 57 after the reflash I'm guessing you are way rich. After my reflash my fuel press was around 45.

ok I was tracked down.

Stock injectors are fine so don't spend more time wondering. Mark at percision did my computer as well. Do both motors have exactly the same issue? How did you set/check timing? What is it set at? How much boost are you running at WOT? Is the fuel pressure 57lbs WOT? I ran less with mine.

Also where are you checking fuel pressure at?

Both motots are doing the same thing at 4200 we are almost at 5 psi boost fuel pressure is at 57 psi at WOT and timing mark said to put it at 8 degrees get it at base timing and then go 8 degrees as far as set up pro charger says everything sounds right but the boat will not perform right

they have check the fuel pressure right at the motor

Did you set it into base timing mode before you adjusted it, using to special tool or paperclip?

There is a tool to put it in base timing, the same tool will tell you if there is any trouble codes with a diode light. The stock timing will work, the issue is if they were ever changed. You may need someone to use a normal scan tool on it to see what it is doing. It almost sounds like timing is being retarded real bad. I ran 45 lbs of fuel pressure wide open and 25 at idle if my memory is right. What is yours at idle?

At idle it is at 35 psi and wot is at 57 psi

any more ideas please

Have you considered going the route of installing O-2 bungs and hooking up an O2 sensor?

just putting this back to the top

Sorry I was at the lake :)

Have you tried a smaller set of props to see if this is rpm related? Do you know anyone with a scanner?

They have tried smaller props they put on a pair of 24 4 blade props and it still climbed slowly in rpms not sure what it got up to in rpms but they said there is a problem. You can feel the boat fall forward when you get it up to speed around 70 mph and when you push the throttles past that point that when you feel the boat fall forward it like it looses some power I think it must be in the computer program thats the only thing I can come up with

I would have to agree. Mark did mine also and I did not have a problem but who knows.

New heads you said ? What kind ?

Different valves you said ? What length ?

What springs ? What installed height ? (thus length question also)

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Are motors grounded properly to batteries ? Any grounds not reinstalled during engine builds ?

Voltage proper to ignition coil and ECU ? Does voltage drop at all on your gauge at this suspect rpm ?

Did you verify SC belt tension ?

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Bravo Drives I expect ? What mph are you at when tach is at this rpm fuss point ?

I took of the stock vortec heads and had the same size heads made they are vortec heads with stainlees steel intake valves and inconel exhaust valves as far as the size they are the same heads with upgraded valves as far as lenghts I do not know I didi not do the build my old shop did the build and also will never touch my boat again because of some thing they did Super charger belt is tight