I've bought from both companies. IPD's prices tend to be very high, often for the exact same product. I once ordered a timing belt and front seals from both companies because I was about to do two cars. The products were absolutely identical: same brand, same part numbers, etc. IPD's price was nearly twice as high as FCP's. If you ask for brand names, you'll find that FCP often has the same stuff for a lot less money. Both companies have told me they sell Scan Tech, but that doesn't necessarilly mean it's bad. Sometimes Scan Tech buys good stuff and wholesales it under the Scan Tech name. Another example: I got the same control arm bushings from FCP for a lot cheaper than IPD. Both companies have good service, in my opinion. I've had no trouble returning parts to FCP I didn't end up needing. On knowledge specific to Volvos, I'd have to say that IPD seems to know more. They seem to have a bunch of people who have spent time working on these cars. I don't have a lot of extra money, so I buy most of my parts from FCP, but I get the best quality option if they offer two different brands.

I've also had good dealings with Swedish Engineering.
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Thanks everyone for all the information and advice, Doug C. 81 242 Brick Off Blocks, stock, B21F (non-Turbo), M46; 86 244, B230, 140k , auto.