OMC braintrust, (racer) questions...

**TUFFboat** · 10-18-2002, 02:40 PM

I have recently aquired an 89 XP 200, the motor is stock and cranks 90psi one side and 95psi on the other. I like everyone want to squeeze a little more from it. The questions are...
-How much more compression can I increase and stay in 89 oct. fuel
-What was the factory purpose for the intake cover liner (noise, tunning) what is the effect of its removal
-What were the basic 'clean up' procedures for reliable increases.
-What does the power curve look like after 6000rpm, does it really fall off that fast.
What did the factory do to make 250 HP on pump gas with basically the block.
Thank for any enlightenment.

**Nosubforcid** · 10-18-2002, 04:09 PM

I have run 50cc chambers in RCHs on 89 but I wouldn't make it a regular procedure. Remove the baffle and replace it with the spacer off an stl or sle motor. Downsize the airbleeds about 12-14 sizes to start with, the high speeds will depend on what heads you run. The addition of fingerports is a good idea, you can use the factory cast piston if you keep the max rpm under 7200. That block will spin 7000-7200 readily with no increase in exhaust port time area. A modified exhaust adaptor also helps and isn't too costly to build. The old factory ModVP drawing for it was posted here some time back but searching is screwed up right now.

**TUFFboat** · 10-18-2002, 09:16 PM

Thanks nosub, Being a former Merc guy I'm not familiar with some of the terms you used, RCH, stl, sle? could you explain them.
How would you build rpm without raising the port timing. or is that the job of the new exhaust tuner.
Are the heads you mention the 86 225 heads? What if you add a gasket to slightly reduce the cc.s ?

just learn'in my omc's
thanks

**racer** · 10-19-2002, 12:14 AM

The spacers are from a 86/7 200xp, you will need to increase the main jets 11 to 12 numbers if you do no other mods, The head you mentioned is an excellent choice but on 92 octane. The exhaust mod nosub mentioned is in the adapter plate, not a tuner. A good clean up and finger ports will allow 7k revs without raising the exhaust. RCH stands for removable chamber head.

**Nosubforcid** · 10-21-2002, 08:02 AM

STL was part of the model number suffix on the XP/GT motors. It was used on the crossflows as well but in looper terms meant a 1986-1987 200XP/GT, however time has made the term insufficiently specific as the STL suffix was also used on the 3.0L XP/GT motors. SLE is a similar designation on the closed deck 200 Vindicator/Venom 1993 and later motors. Both suffixes indicated certain equipment: higher durometer engine mounts, louvered cowls(though they always came blocked off with removable plates), no intake baffle or spacers and larger diameter throttle venturis of at least the same model years 225 size.