"All HPT 850's received TD04HL-15G turbos, with stock boost for turbo and T5 models set at 9.6 psi, and T5-R and R models at 10.5 psi (stock hp are 222 and 240, respectively). (The European 850R received a 16T turbo)"

The plug gap can definitely be a culprit. OEM plugs have always come out the winner when it comes to performance and reliability. Copper is much less expensive and works well. Combating misfires with plugs is done by making the gap smaller. OEM setting is .028. Others have found that .026 works well, some lower and a small handful larger.

 

I've gapped mine to .028! I'm set at 14psi because the R ECU can compensate up to14.5psi with out having fuel issues. I also have it dialed in good where it does not boost spike. (go higher than the desired boost level then settle) waste gate setting and fuel delivery ability! (AKA better fuel pump) Let us know how it goes boost pressure and plugs!

 

Thanks, will do. If the R ECU can handle 14.5psi, then will the regular Turbo cars ECU only manage 9.6psi (stock setting), or can I manually up it a bit more once I get things running properly? Sorry for the redundancy here, I'm a newbie to Volvos (like 2 weeks in).

 

I would say maybe 3psi more would be safe. You would notice a big difference with 11psi and tighten up the waste gate about 1 turn. Or just adjust the waste gate and try it that way! Just don't go too much! I know alot of guys will buy R ECUs to up a little more boost, but the cars are different. HPT or LPT. I think alot of that is waste gate spring difference. Not 100% on that! I heard also that the R motors are a little stronger "built a little different?" once again not 100% on that just what I have read throughout the forums. Biggest things to keep up on these is PCV and timing belt stuff.. Welcome to Volvo! My 850R has 163000 miles on it. No leaks and no smoking!

 

The R engine is not any different than the standard Turbo engine. They are not built different.

Running a stock ECU and raising the boost is eventually going to hit a wall called 'Fuel Cut Off'...a built in safety mech that shuts your fuel off when boost gets to high. Any Performance ECU will have this disabled to achieve higher boost curves.

If you really want to know what you can do to your engine read this....

Modifying Fwd Turbo Volvos (Read, Don't Comment) - Volvospeed Forums

 

Two ways to go fast, more power or LESS WEIGHT !! You're just trying to get that edge !!