[Supras] losing performance

Sun Nov 18 21:56:52 CST 2007

I've had more of what I believe to be fuel cut incidents on long straightaway WOT pass runs at 40 to 50 degrees F ambient at 10psi with the stock AFM. Isn't the air denser at lower ambient temps that cause fuel cut sooner than at higher ambient temps? When it does the fuel cut I get a nice large black puff of cloud out of the exhaust....

Rockey 91T

----- Original Message ----
From: "berniek at technicaldevelop.com" <berniek at technicaldevelop.com>
To: csmyczek at molbiores.com; "Supras at supras.com" <Supras at supras.com>
Sent: Sunday, November 18, 2007 8:31:43 PM
Subject: Re: [Supras] losing performance

Nick:

    I get the feeling you are correct.  I've got the top end apart now,

and found that one intake valve is at .011", a little above limit, but 
I'm going to leave it considering the effort involved to get it down by

.002" or a little more.  Both cam covers are back on, but I do intend
 to 
pull a plug or two to see if any signs of detonation exist.  Back in
 the 
'60's a friend used to run a DeSoto (Chrysler Hemi, but smaller at 
something under 300 CID) with lots of spark advance.  There was no 
detonation sound, but upon pulling out the spark plugs, in some cases 
half of the insulator was gone longitudinally up the plug!.  There were

no other symptoms and the car ran great.  Today we have knock sensors 
and ECUs, much better than the old days. 

    One of the main reason for getting the cam covers off was to remove

the fuel pressure gauge I installed in rail at about #5 cylinder, by 
tapping it leaning back almost against the intake cover with 1/8" pipe 
thread.  There was a posting (forget by whom) referring to use of a 
Schrader valve for checking pressure, as opposed to wearing out a gage 
from constant use.  Back in '67 when my dad died (scary, I'm almost 65 
but he died at 60), I kept a lot of his stuff from his plumbing 
business, and guess what was among the goodies:  an 1/8" male threaded 
Schrader valve connection.  I replaced the core with new, installed it 
(a "fitting eater"), and checked the fuel pressure using a read and
 hold 
tire gauge.  Pressure was just as I thought, 50 PSI with Fp jumpered, a

little too high for 550 cc injectors.  Lowered it to 45 PSI, and we
 will 
see how it does (after the salt is gone if the road department puts it 
down due to the little bit of snow we are supposed to get).

    Installed a 1-1/2 inch copper coupling in the accordion hose to 
route the Turbonetics BOV to, but temporarily blocked it up with tape.

The valve will go in a copper tee in the hose from the pipe coming out 
from the right fender to the plastic piece connecting to the 3000 pipe.

Im a bit concerned that the spring may be too stiff, however.  There
 was 
supposed to be a lighter spring shipped with it, but it was not.  
Pulling full vacuum on the top of the diaphragm with a vacuum pump just

about  cracks the valve open. 

    Pulled one spark plug before getting the engine together tonight, 
and found the shell rich with carbon, but the insulator was perfect,
 but 
with only a few hundered miles it it too early to tell for sure. 

    Bernie

Chris Smyczek wrote:
> Running continuous boost past 8 psi and other upgrades will warrant
 colder
> plugs. I would recommend one range colder for your setup if you want
 to run
> around on the throttle. Fouling plugs is the only risk you take. I
 use ngk
> iridium 2 ranges colder road racing, no fouling, but in this case the
 engine
> is started, idles for 10 min, runs from 4k to redline in third
 through fifth
> gear abuse for 30 min practice, qualifying, and race sessions, cooled
 down
> at idle w/ electric fans and then shutdown. Heat soak is prevented by
 big
> radiator on r.o. water, oil cooler on silkolene, intercooler, and
 most
> importantly shrouding and ductwork for less overall drag without
 eddies and
> high velocity air past the exchangers being drawn out by a low
 pressure
> region aft. Monitoring your knock will tell you when the ecu retards.
 Chris
>
> -----Original Message-----
> From: supras-bounces at supras.com [mailto:supras-bounces at supras.com]On
> Behalf Of berniek at technicaldevelop.com
> Sent: Wednesday, November 14, 2007 11:19 PM
> To: Supras at supras.com
> Subject: [Supras] losing performance
>
>
> Tonight I thought I would have some fun with the rejuvenated toy
 (550cc,
> Lex, Walbro, 57 trim, 3" turbo back exhaust, etc.).  Rt 80 was almost
> empty and relatively free of cops.  So I did a couple of runs through
> second third and fourth gears (first run:  5900 RPM in fourth, 120
 MPH,
> beautiful before shifting to fifth and coasting down).    Each time,
 the
> performance got worse, with some light bucking in high gear.  I know
> that fuel starvation is not the cause for several reasons, including
> fast responding A/F ratio between 9.5:1 and 11:1.  It seems as if the
> performance is best when just warmed up, and then decreases as full
> boost runs are made.  And then again, at 15 PSI boost, I'm starting
 to
> consider if spark plug heat range it too hot.
>
>
> Right now I still have the stock platinum spark plugs, abrasive
 cleaned
> and gapped a little tighter due to 15 PSI boost.  I'm beginning to
> wonder if the heat range is too hot, leading to detonation and
 retarding
> of the spark by the knock sensors.  No ECU codes have ever been set
> since first startup after the engine swap.  There has been quite a
 bit
> written about use of copper core plugs due to heat dissipation
> considerations, but a plug made of any metal can be configured to be
> cold or hot.  So why should copper or other metal of construction be
> different from a standpoint of heat range, assuming the heat range is
> correct to begin with?
>
>
> Suggestions would be appreciated.  Thanks.
>
>
>     Bernie
>
>
>
>
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>
>
>
>   

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