Late model downdraft 225 Efi 3 liter stage by stage build up

[RSWORDS]

This thread will be to document my build up of a 3 liter with the 555 Motorola ECM. Its going to eventually go on my hydrostream but until then I'm going to use it on my 25' C-Hawk to for testing. Right now the boat is running an old 225 carb powerhead converted to 250 4 butterfly intake with the twin computers, and a 300 on box. Its seen a best of 44mph.

I want to use this powerhead we are building up for a race this fall and to test it before it goes on the hydrostream. If I do something wrong and it eats itself on the chawk at WOT I get towed home.... on the stream I get wet.

The first stage is going to be Chris Carson reeds and stuffers. I've used his reeds in all my motors and countless customer motors with great success. This will be my first time with the stuffer though. I'm also considering stripping the cages and using his reeds for that. Thoughts from anyone?

Also in this first Stage Chaz will be cutting my heads to tighten the motor up some. Going to keep it 93 octane friendly for the moment.

Starting with a low hour motor I went ahead and pulled the heads to send to Chaz to cut. Need port height and style to do the math on compression. No compression relief notches and 45.5mm height.

[RSWORDS]

Chris Carson reeds and stuffers. I run these on all my motors, stick or not!

[RSWORDS]

Cutting the heads down. 64.5cc after the cut and cleaning the bowls up.

With these heads my warm cranking compression is right at 145psi.

The boat JUMPS on top and has matched its 44mph on the best with only the 225 ECM and less RPM (5800) first time out. It has more in the setup and props that I will iron out in the next week or so. The bottom end and mid range is just insane though

[Gamblinman]

Are you raising the ports ?

[RSWORDS]

Are you raising the ports ?

No. No need to as I wont be turning up the rev limiter.

It will be getting a side injected intake, a 250 ecm, and a notched CPS for a couple extra degrees of timing.

I do have another block that I'm planning on going full out on turning it into a 3.5L and that will get some good porr work.

[Gamblinman]

Interesting...why not have the ECM re-programmed for more timing at the proper RPM? The issue with modifying the position of the CPS is its always advanced across the board. What if you need to retard on top end to minimize detonation?

[RSWORDS]

Interesting...why not have the ECM re-programmed for more timing at the proper RPM? The issue with modifying the position of the CPS is its always advanced across the board. What if you need to retard on top end to minimize detonation?

Because with my porting there is no other benefit and not money well spent at this point. A flash to say a 300x would be useless because my motor will hit the wall somewhere around 6k.

Detonating is a big concern and something to being monitored. With a notched CPS I can adjust and tune. Same reason it's getting a adjustable fuel pressure regulator and engine mounted gauge. Basic tuning

As you can tell I'm sure this is a relatively "safe" setup but anytime you deviate from stock you're on your own.

Now... when I spray 200 more HP into it.... then I'll up the limiter lol

[Gamblinman]

Good luck to you. Keep us advised.

[RSWORDS]

Good luck to you. Keep us advised.

Will do.

Again with this build there is no point to bumping to the 250 tune for those couple xtra degrees. Besides, I may want more, or less later. As soon as I cut the heads, put on my side mount injection and deviated from what Merc sent out I tossed pre made tunes out the window. If I had the ability (or the money) to wrote my own tunes that would be different. But I don't. Maybe one day.

Until then I'll read plugs, run good gas, monitor for detonation, and tune away. :)

If it blows up it blows up. Shouldn't because this is pretty mild as far as mods go but you always run that risk playing with any motor




Intake is being started. That's a big expensive chunk of aluminum..... most will be on the floor.

[RSWORDS]

And just for poops and giggles....

[RSWORDS]

So, as we all know.... an internal combustion engine is simply a pretty complex air pump... so... better air 8n and out, more performance.... cleaning up the intake plenum by moving those pesky injectors and fuel rail outside sure will help.

[EuropeanAM]

Maybe... at least it may help clean up the airflow in that area.

The big "limit" is in the sleeve/intake ports.