OK let's talk about XB mods

[JOE54]

+1 really, might be drag boat runnin 140 octane

[WranglerSS]

Why are you cutting heads?

Those heads should bolt right on there. That should put you at 125-130 lbs cylinder pressure.

I guess I read it wrong. Looks like the 250 heads need to be cut and not the 300. I guess it would depend on how much is slightly less on a 225EFI.

#1 -You must do the heads. 300 heads(67 cc) work well and will bump compression to about 130 pounds on a 250XB(slightly less on a 225EFI), but getting the 250 heads cut to 61 cc will give you about 140 pounds of compression(MADEFI can cut your heads for about 170.00 a set). That's about the max you can do on pump gas(93 octane). FYI the 225 EFI heads cannot be cut enough to help much on compression. Simon does some nice heads with interchangable chambers but I haven't tried them.

[EuropeanAM]

Just be careful- I would recommend aiming for 130 psi (tops). It's been my experience that much higher than that and you have an engine that is VERY prone to detonation. And very unforgiving when it comes to fuel octane.

[WranglerSS]

Thanks Don, I'm expecting the 300 heads to get me around 125 as a bolt on. I did a compression check today in preparation and I had 110 on 4 cylinders, 109 on 1 and 112 on the other so I think my motor is a good candidate for the mods.

[PULSARE1974]

Can you add the higher compression heads with the stock 225 EFI ECU.

[jusmangrum]

Also can anyone let us know who does the reflashing of the ecm’s now. I’m not sure that Simmons does it anymore. Anywhere else you can find any of this stuff?

[EuropeanAM]

I don't believe you're going to find anyone that's modifying ECM's on these now.

[jusmangrum]

Thanks Don

[Passionre]

So what are the racers going to do for reflash now?

[Showard]

I’ve loved my 250 Xb on my champ- but now it bogs and won’t get on plain. Been slowly be coming an issue but has always got on plain after a brief lug. Now it’s a no go. At full down trim it sputters when hit the throttle- but if raise trim the rpms come
up- but not enough juice to lift it out of the hole. Any ideas before I take it to the mechanic?

[EuropeanAM]

I’ve loved my 250 Xb on my champ- but now it bogs and won’t get on plain. Been slowly be coming an issue but has always got on plain after a brief lug. Now it’s a no go. At full down trim it sputters when hit the throttle- but if raise trim the rpms come
up- but not enough juice to lift it out of the hole. Any ideas before I take it to the mechanic?

Please take a moment to review the Forum Announcements, and open a separate thread for your engine (with engine serial number). Thanks!

[Gamblinman]

Can you add the higher compression heads with the stock 225 EFI ECU.

Yes. I run 300PM heads, 225 EFI fuel, 300PM ignition ECMs on a fishing boat. Not going to see much difference on top end, but it adds quite a bit of punch to mid-range. Port work is necessary to really see any top end benefits.

[PULSARE1974]

Yes. I run 300PM heads, 225 EFI fuel, 300PM ignition ECMs on a fishing boat. Not going to see much difference on top end, but it adds quite a bit of punch to mid-range. Port work is necessary to really see any top end benefits.

Thanks.

[kllr bee]

Showard,you need to check your reeds. Sounds like you broke one or it is a bad sparkplug

[kllr bee]

I can't believe the stuff I did so long ago is still relevant. I am glad I helped so many fellow nutburgers
Richard

[Gamblinman]

I can't believe the stuff I did so long ago is still relevant. I am glad I helped so many fellow nutburgers
Richard

You gave us lots of good information. Only difficulty I ever had was finding a 250XB or 300PM fuel ECM that would work. Most would fall flat on their face at 5KRPM's, including modified Simon ECM's . They were all proven ECM's that I tried. I finally found one and the difference was night and day. That 2000 motor is still running with several thousand hours on it.