Remembering why I
dislike working on
AO Silver Member
Join Date: Sep 2001
FWIW...I'm still in the throws of supercharging a 12V 164 motor. First effort was to bolt an Eaton M90 on top of a mild aspirated motor. 10:1 CR, C&B mild road cams. Didn't work that well TBH. First attempt with a drive ratio that suggested about 8-10 psi made....almost 5psi. Engine was very prone to knock so had to run very retarded timing which kind of defeated the object of the exercise. I ran the blower quicker and it made 8psi. It felt a lot better but still pinked badly and then it popped a head gasket before I could get it re-mapped. This was most likely just due to me using a cheap nasty e-bay special gasket set, but in the end, I wimped out and restored that particular engine to aspirated. I decided to have another go but doing it a bit better. 8.8:1 forged pistons (so they will take some abuse unlike the cast ones), some custom ground cams which should give decent off-boost performance as well, and a rebuilt/ported blower. I also did some valve work.
Sadly, I can't report any results yet as I've got a minor problem with the clutch at the moment so the car isn't driveable until I can replace the relase bearing (again...long story...).
In more general terms....personally I wouldn't use a Vortech style device - they seem to have the worst of both worlds as far as I can see but YMMV. Use as modern a positive displacement blower as you can, don't make it too big. For a 3.8l and 10psi you are looking at an M90 (or equivalent) I should think. High CR is bad for a load of reasons. Too low is bad too, so take care. Using a decompression plate sometimes works, sometimes doesn't - only one way to find out on a given engine. I briefly considered trying some but decided it was too risky. Doing all that work and spending all that cash to find it pinks even worse due to losing the squish wasn't a risk I wanted to take. Cool charge is very important. Water/air coolers are often better for a road car I reckon but there are so many variables it comes down to each case probably. I went for water/air.
If you are serious, go buy a copy of Greg Gordons book on Supercharging the Alfa V6. Money well spent. I started with a copy of AG Bells book - that's interesting as well. Both based on sound theory and lots of practical experience - not opinions.