Partial success
Walter Sherwin
wsherwin at home.com
Tue Aug 22 21:52:28 GMT 2000
This message did not seem to go through yesterday, so I'll try again.......
If really bent on keeping the blow-thru config, then what about a couple (or
more) BOV's between the S/C and the TB in order to gain adequate flow and
response? Pilot them all via manifold vac from beneath the TB. Smallish
Turbo BOV's may have a short life span because they just weren't designed to
be open/stressed all the time in that manner. Vortech make a Mondo Race BOV
that may prove successful, as do Cartech/BEGI. Magnuson/Eaton have a
universal flapper style BOV/bypass that may offer even better life.
Locating the TB downstream of a S/C does have it's merits if worried about
things like 1) the TB area unduly restricting the inlet flow capacity of
the S/C, or 2) exposing the S/C end lube seals to substantial vacuum and in
turn causing lube entrainment, or 3) you wish to retain a wet engine inlet
manifold setup, but wish to keep the S/C and intercooler dry.
Most any S/C type can be made to work in this config, but some will impose
considerable heat and parasitic power loss issues no matter how much BOV
flow you have (ie: S/C's with internal compression). The BO discharge will
be noisy but a length of tubing, with a filter on the end, directed to a
remote spot, can help. Excess air can be dumped from pretty much any point,
but closer to the S/C is better. Be careful about your dump point if
running MAF as opposed to MAP fuel.
In all other cases, the best bet is most likely to locate the TB upstream of
the S/C, and install a vac operated bypass loop around the S/C that would
connect the underside of the TB to the S/C outlet under high engine vac
conditions. Magnuson/Eaton have a number of different styles and sizes for
this purpose. Response and control are almost instant from a driver's
perspective, and the resultant cruise input shaft parasitic losses are
miniscule (eliminating the need for an expensive clutch with controls).
Walt.
-----Original Message-----
From: dzorde at erggroup.com <dzorde at erggroup.com>
To: diy_efi at diy-efi.org <diy_efi at diy-efi.org>
Date: Monday, August 21, 2000 5:35 PM
Subject: Partial success
>Hooray, I've finally got my Fiat 850 sport running on fuel injection,
>however I'm now in need of some suggestions for the next part. I have a
>Toyota MR2 s/c connected in a blow through configuration with the throttle
>body (it should be geared for 120kPa full boost, 17psi), my problem as it
>stands:
>
>At idle the ecu reads a vacuum (-21kPa to be exact) while the s/c side is
>seeing 90kPa (throttle blade shut). At higher revs (no load) the boost
>will build up even more (over 250kPa) as the throttle is only just opening.
>Obviously if I keep going like this the s/c is likely to blow a seal
>somewhere.
>Now here's my question, do I just fit a blow off valve and let it bleed of
>any excess boost above say 140kPa ?
>And what sort of blow off valve would I use, the ones I have seen on turbo
>cars are very small and the s/c has like a 62mm outlet, so that is a lot of
>air to remove ?
>I have looked at a few available blow off valves (greddy, hks, etc), but
>they are all specced as turbo applications, isn't there anything for s/c
>applications ?
>
>I'd appreciate any light people can shed on this unknown area I've ventured
>into.
>
>Dan dzorde at erggroup.com
>
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