Lester

Mike, were the ECUs reprogrammed by Vortech or did the SCs come with a different ECU? The reason I ask is I am using 2 remapped ECUs from vortech with my new rebuilt 502 MPIs this year and I am having a hell of a time getting them dialed in. The IACs just don't work well with their new program although they won't admit the speed of the IAC can not be controlled by a program so idling is always a challenge now. Also the pulse width at WOT does not seem suffiecent for the additional flow, plugs show this. They also fail to tell you that after installing the adjustable press reg you still need to cut off the vacuum to the press regulator or it will indeed pull down your new added fuel pressure, even during acceleration. Bottom line make sure you've got plenty of fuel at WOT by checking the plugs and install a fuel press gage.

ScarabMike

Lester,

The motors seem to be running OK. I just can't get the right setup.

I moved from Mercury Labbed Bravo I's to Standard 'Boxed' Bravo I's and got to about 79MPH. I have heard from several others that the added torque at high RPM's are causing the extra slip. Mercury removed most of the cupping in their labbing process.

I have ordered a pair of 30" Props from Darin at Houston Prop. He believes that adding some additional cup, slightly trimming the diameter and a satin finish will cut down on the slip ratio. According to my calculations, if I can cut down some slip and get my RPMs to about 5200, I should get to the low 80's.

Considering the fact that I am not dealing with a stepped hull and it's a production line boat, that seems about all I can do for it.

Pure Energy

Here is a long shot for you. Do you know what size your fuel pick up tubes are in your fuel tanks? I have procharged 502s on my 31 Sonic spinning 32 bravo 1s to 5300 rpm. I had to replace the fuel tanks and after that I could only spin to 4800 rpm. Motors sounded fine. I would hit 4800, push the sticks to WOT and no gain. After 3 trips back to the mechanic we switched fuel pick ups and it was back up to 5300 rpm. My point being you may not be getting enough fuel. You need a true 1/2" tube and fittings. Hope this helps.

What yr Scarab? I would think you should be mid 80s +

ScarabMike

Pure Energy,

I'll check that out. I seem to have that last bit of throttle left that doesn't seem to do anything. I've been going under the assumption that it is slip.

I should have my props soon. I'll see if there's any difference.

BTW, it's a 1997 31 Scarab. No Step. They went AVS Step with the 33 the following year.

tomcat

What was the RPM with the standard 30? If you were still at about 5000 RPM then you should still be going 84 mph, if the slip was the same as the 28. What happens when you try the original props? Do you still stop at 5000 RPM?

These props can absorb a lot more HP than you are giving them. I don't think the extra HP is making them slip. You never said whether you went to a shorter XR drive.

Pure Energy

I would check your tubes first!!! If your not getting enough fuel you may damage the motor. You should have an access panel right above the tanks and the pick ups are right there. Unscrew them and measure the tubes AND the fittings. You may have to drill the fittings larger or replace them.

Also that last little bit of throttle holds ALOT of power when you are supercharged!!!

ScarabMike

The stock 30's give me 4900 RPM. The setup is rated to run at 5200 with the rev limiters bumped to 5400.

I agree, mid 80's was my target number. I am running 5lb pullys but only making 4lbs of boost at 4900 RPMs. My first instinct is that I won't see the 5 lbs until I can get the RPMs up a bit.

Darrin at Houston Prop is going to cut down the diameter of a standard Bravo 30 just a bit in an effort to get the RPM's up by about 300.

I will pull the access panel off of the tank and check that size this weekend.

Thanks for the info.

Pure Energy

Good luck and post the results

tomcat

Can you spin the 28s against the rev limiter? If you could that would be 85 mph. At the higher RPM the blower is spinning faster too and would move more air. The 28 was really too much prop before. Good luck!

Treadwellmotorsports

first of all the prop is to big. second of all changing the drives automatically lost you 1.8 mph, and even more if you have low water pickup. but tomcat is right. sound like a 28 would do the job. if you wanted a bigger increase go with shorties and a pair of extender boxes. not having a stepped hull hurts so you need the props as far back as you can get them and a higher x dimension. that with the chargers would get you your 10 mph your looking for.
Treadwell