Join Date: Jan 2003
Location: Boolarra, doh! :-/
Re: what do ppl think of the ef xr6?
I just recall reading from an old Jim Mock article that non-XR heads are better for porting & shaving, due to the XR heads already having some work done to them. Think of the non-XR heads as being a "blank slate" on which better working can be achieved.
Having said that, XR heads tend to respond better to your basic N/A mods I am lead to believe, such as exhaust, extractors, XH snorkel, etc. (if I'm wrong, someone please correct me!)
As for turboing a car, you don't want a high(er) compression head! Boost from a turbo will "give" your car extra compression, and more compression = you need a higher octane-rated fuel to avoid detonation. Since a non-XR head has a lower compression rating than its XR counterpart, it will perform better if that particular motor has a turbo hanging off the side. I think every 2PSI that a turbo pumps into the motor = 1 point of compression. And once you go above (I think) 10:1 compression ratio, I think you need 95RON (premium) fuel for your motor.
So, if your car normally runs on 9:1 compression, having an 8PSI turbo will bump up the compression to 13:1 (8PSI = 4 points --> 9 + 4 = 13). So you'll probably need 98RON fuel for this compression ratio. This is why higher-boosting turbos need intercoolers, water injection, timing retardation, etc, to control/minimise detonation.
Your XR head might have a 10:1 compression ratio, so slapping that same 8PSI turbo on will give you 14:1. You might need 100RON fuel for this, being either 98RON + octane booster, or some form of avgas, etc etc. (or better intercooling)
Makes the car a bit more of a bitch to run.
Oh, and then there's toughening up the bottom end, such as the pistons, so that they're happy with that compression that they're dealing with. Holed piston = ouch!
'91 EB Fairmont Ghia V8.
Pacemaker PH4000 extractors
Meaty semi-twin system
AUII XR8 t/b & maf, ELGT snorkel
BA semi-manual shifter conversion
Electronic shift kit
4.11 Hydratrak LSD
Explorer intake manifold
Contra 16x9 rims, rubber: 225(f)/245(r)
Chiptorque HP2 chip
ET: 14.78 @ 91.48mph, 137rwkw!