EGT and backpressure...

[Charles]

=46rank wrote:
> saw similar 1600 deg temps in a custom turbo Honda vtec I did BUT
>I found the cause was high back pressure from restrictive exhaust and
>cat. At only 5 psi of boost, I had 9 1/2 # of back pressure. When I went
>to bigger dia exhaust and bigger cat, the back pressure went down to 2
>1/2 psi and boost rose to 9 psi at same wastegate setting. Temps dropped
>150 deg.=20

	I have a cat that shows 5 psi backpressure at 16 psi boost. I
noticed that boost was about 1 psi lower at the same wastegate setting
than with the cat off...

>. If you are rich and have high back pressure, you will have
>essentially a afterburner and the high emps you see.

	This may be part of the problem. I'm running 8:1 compression
(forged pistons), and to get 15 psi boost on 93 octane takes a very
rich mixture to suppress detonation. Plus the ignition timing needs to
be retarded at full boost. I have 35 degrees total timing above 2200
rpm (stock), then use an MSD boost retard box set to about 0.75
degree/psi, so this should be about 23 degrees BTDC at 15 psi.
	I may try water injection next...
-Charles
'81 745i
p.s. would the person who listed the "good" stainless i.e. 310 please
e-mail me directly? Sounds like what I need to order.