<VV> Aftermarket Camshafts in Turbo Engines

[Tony Underwood]

At 02:44 hours 08/26/2006, Jim Bannister wrote:
>Hi all,
>How much tweaked and what does it do for\to you?



The tweaking can be simple or radical, although a simple tweak is 
swapping the stock turbo heads (junk, imho) for 95hp heads, which 
have a much better combustion chamber.    They also allow you to have 
a less radical ignition advance, no more of this 24 degrees initial 
advance stuff...  less likely to have to put up with pinging, which 
in a turbo engine under boost can be critically damaging in a very 
short time, just a few seconds.

Exhaust improvements are also a "tweak" for a turbo engine.   A free 
flowing muffler ('Vair turbo mufflers are *not* as free flowing as 
many people think) can allow more boost on top end.

The Isky cam (or other manufacturers' equivalent) adds a bit of 
breathing ability which can really wake up a turbo engine if you have 
better heads and exhaust on it.   It depends on what you expect from 
the engine.     Some people have condemned the Isky 280 for being an 
older grind and somewhat obsolete, mentioning that a dual pattern 
grind can help a Vair engine run better...  IF the engine is 
naturally aspirated.   Forced induction such as turbocharging brings 
in other factors and, as far as those modern cam grinds are 
concerned, all bets are off.    This is where that old obsolete Isky 
280 wakes up and struts.   Not too bold, not too mild, pretty much 
right where it needs to be in a turbo engine intended for "spirited" 
street driving, IMHO.   But that's just me...

I'd look into swapping those stock turbo heads out for 95 heads in 
*any* event.   They aren't very friendly.   The 95 heads work much 
better on a turbo engine, to the point where I wonder why GM didn't 
use that chamber design in the first place.



The mild tweaks mentioned here are simple bolt-ons, requiring no 
machine work or expensive aftermarket hardware installations outside 
of installing a drain in the right side head for the turbo oil return 
line, not hard if you just copy what you see on the factory head; a 
pipe thread tap, and a brass nipple to fit, works out well.

You WILL need to run the best gas you can get if you put your foot in 
it often, since the engine is gonna make more boost and more power 
and basically run hotter in the process, so *Don't* forget GOOD oil 
as well.


You *will* have to play around with the distributor a bit... maybe 
experiment with advance weight springs if you get really seriously 
nitpicking... although for the most part, using a 95hp distributor 
(with the pressure retard installed) gets you in the ball park, and 
you will NOT have to run 24 degrees advance... more like 10 or 
thereabouts for starters, give or take.    Since you're changing the 
basic engine parameters by doing this, your engine will need to be 
"walked in" via experimenting with the timing to see what it 
likes.   Do NOT add too much advance or allow it to ping, especially 
under boost, ever.


When you get it right, you may well be surprised at how well it will 
run.    Others in here have also done this same general tweak to 
turbo engines.   Bend their ear, and learn from their experience as 
well.    Again, it all depends on what you expect out of the engine 
as to what sort of level you wanna tweak it.



tony..