I have a 98 S70 T5 Turbo. I have some detonation using regular gas and need to run premium with octane booster to stop the detonation under acceleration. The last time I changed the plugs I went with whatever they gave me at the parts store and I believe they gave me a hotter plug because that is around the time this started. Does anyone know the type of plug to use that has a colder heat range?

 

Use the OEM heat range. If you have detonation using that, you could have carbon deposits on your pistons and in the combustion chambers, creating "false" compression... and if that's the case, you need to put seafoam the engine and see if that helps... if not, then you might need to pull the head for de- carbonizing.

 

Also are you modded at all? Meaning higher boost?

 

The vehicle is not modded...yet.

A while back I put Bosch Platinum plugs in and it was some time after that that I started having problems. I just switched to an OEM copper core plug last night and it has made a difference. However, the old plugs that I removed lookd pretty bad. Crispy and carbonized. I am thinking if they had that much carbon built up on them then I must have a significant amount of carbon in the combustion chamber from running the wrong plugs.

When you say put Seafoam in the engine do you mean running it through the tank or through a vaccum line?

 

You could do either one. They will both do the job.

When you up to boost drop the gap down to about .025 or even a little lower.
Stock boost works good with the .030 gap.

 

How difficult is it to install a manual boost conrtoll? I will probably need a boost guage if I do that right? I have read on another forum that it is not advisable to run more than 15-17 psi on a stock set up. Do you know what boost it is putting out stock?

 

I would only run about 12 or 13. Yes a boost gauge is a must.
It is not that hard to install it.

You should be between 5-7 PSI boost now.

 

I'm kinda experiencing the same thing with a 98 s70 t5 as well. It's fairly stock forge bv, k&n, about 14-15 lbs boost. I had my plugs at .30 regapped them to .25 and cleared up for about 2days and started again. My car is a 5spd car, it does it to me in 2nd and 3rd or in high gear at low rpm as I step on on it. I cruise 95% of the time, but I need it to respond when I want it to respond. Any HELP!!! Thanks