I am about to update my '98 GLT with ipd's ECU and exhaust. I am excited about the added power to the car, but was curious whether it is necessary to change the octane of the gas I am using. Currently, I put in 87 octane. Someone mentioned to me that it might be a better idea to put in the 89 octane, just because the compression is going to change in the engine. However, I was under the impression that the NOC sensors would take care of the situation. Is it truly important to change gas, or not really?

Also, can anyone offer some feedbck about the most effective way to get the stock exhaust off of the car. Is it best to use a saber saw, or will that cause some serious damage? Better to use some rust de-oxidizer?

Thanks so much,
David

On page 130 of this month's Road & Track the octane issue is discussed with regard to a 1995 Porsche 993.

It is worth reading

"Now, under favorable conditions - average temperatures and light duty driving - you can likely get away with 87 octane. But if the temperature rises or you put your foot down, 87 may not be enough to avoid pinging. this could lead to engine damage over the long haul."

The article also discusses the economics of lower octane. At 15 mpg and a 40 cent difference in price, you would save about $266.80 over 10,000 miles. I think that the figure will be much less than that as the cited milage is low and the difference in price is high IMHO. For me, I spend an extra buck a week.

The very next Technical Correspondance letter discusses injector cleaners and says

"Major oil companies say their regular gasolines have enough detergent added at the refinery to stop deposit formation. Premium gasolines have even MORE detergent, so they can cleanse away deposits that have already been formed" (emphasis added by me)

Make mine premium.
--
2 8s & 2 7s 600,000 miles total

Your engine has a 9.5 to 1 compression and technically it does not
change. But, with more air forced in by the turbo the compression "seen"
in the enigine is higher (turbo charged engines could be described
as a variable rate compression engine). So, I think you would have to
run as high an octane as possible since the chip is probably pushing
the design limits.

I have a 98 T5M and on mid-grade (89) I have heard it ping on a hot day.
This is a stock engine. It only pings once if this happens but it is
something you don't want to hear. I normally use 91 octane (highest
available in California) and sometimes wonder if I chipped my car
if 91 would even be high enough.

You definetly want to run premium fuel. I have had conversations with Scott @ IPD and he indicated that the lower octane will cause the engine to put out less HP, the knock sensors will detect and adjust. I have the IPD ECU & MBC and have set boost at 15 PSI. Scott actually reccomended 14 PSI (what the ECU runs), but I have not noticed any problems @ 15 PSI. Interestingly, there are guys running 17-18 PSI in UK, but they get 98 octane fuel, where we only get 91!
As far as the exhaust install, I am too lazy to climb under the car, my Mech installed the dual exhaust in 1 hour.

Wills
--
98 R Wagon IPD ECU, 2.5 Dual Exhaust, Dawes MBC, 94 854 turbo, IPD Goodies, 92 740 Rag Wag

You definetly want to run premium fuel. I have had converstaions with Scott @ IPD and he indicated that the lower octane will cuase the engine to put out less HP, the knock sensors will detect and adjust. I have the IPD ECU & MBC and have set boost at 15 PSI. Scott actually reccomended 14 PSI (what the ECU runs), but I have not noticed any problems @ 15 PSI. Interestingly, there are guys running 17-18 PSI in UK, but they get 98 octane fuel, where we only get 91!
As far as the exhaust install, I am too lazy to climb under the car, my Mech installed the dual exhaust in 1 hour.

Wills
--
98 R Wagon IPD ECU, 2.5 Dual Exhaust, Dawes MBC, 94 854 turbo, IPD Goodies, 92 740 Rag Wag

Correction: I believe the LPT is 9.0:1 compression. Sorry.

I wouldn't run anything but premium after the chip upgrade. Of course, that's all I run in my S70, so it's pretty much habit. I forget what Volvo asks for.

Re: Exhaust - Should come off without too much pain and suffering. Squirt the bolts down with WD40 and let them soak for a bit. Past that, it's really not that difficult. I did end up cutting one of the rear hangers off to get the old exhaust off in one piece.
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'99 S70 T5M, '83 245 DL

r u talking about the whole cat and exhaust, or r u just thinking cat back...cause if it's only cat back, u can easily remove that. only tricky part is to either cut the hooks or gently slide them past the shocks...

David - The compression ratio of your engine will not change, that is a function of the mechanical ratio of your engine's cylinder volume when it is at its maximum and its minimum, a chip will not change this. What will probably change is the timing of your ignition system, more spark advance could cause engine knock or corrections to be made by the engine's knock sensor.

It is quite possible that your engine management system can cope with a hotter chip vs. low octane fuel, but I doubt that you will get the maximum benefit of your new chip. Worst case could be engine damage.

What octane does IPD reccomend? I would never use 87 octane in one of my Volvos.
I think that it is cost effective to use high octane fuel in older vehicles, and my experiments with our 740s bear this out. Search this site and Volvospeed for fuel threads, I'm sure that you will find some interesting opinions ;)

If IPD does not give you guidance, I suggest that you try several tankfuls of each grade and compare performance. Comparing performance is not easy, but mileage figures may give you some evidence of performance. I'm sure that you will see a difference between the top and bottom grades of fuel available to you.

If you are going to cut the old system off, I suggest that you get an exhaust pipe cutter at Sears. It is a tubing cutter with 4 wheels, you only need to swing it a little over 90 degrees to cut a pipe. Be careful where you cut, don't cut up something you need.
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2 8s & 2 7s 600,000 miles total