[Supras] 57 trim driveability

[berniek at technicaldevelop.com]

Dear VAn:

Thanks for the response.  I, too have thought about taking a driving
course, but the onset of boost is so sudden with virtually nothing at
about 2800 RPM, and full boost accompanied by probable opening of the
wastegate at an estimated 3300-3400 RPM.  One of the reasons might be that
I did not get the turbine wheel clipped, a subject which some controversy
exists about.  Rather, I had the wastegate passage bored out to accomodate
additional exhaust gas flow, with the result that the boost does not rise
with RPM.  That would appear to be a reasonable indicator that wastegate
flow is adequate, although volumetric efficiency is falling at the same
time as RPM increases.

Bernie

> Bernie,
> As much as I hate to admit, it has taken me over two years to learn how to
> adjust to the power and control the car. My synapses just aren't what they
> used to be...
> I too was thinking of different elegant "fixes" to that veritable
> quandary,
> but I chose to do this my self with training. Last year, I spent the money
> and went for two days of training on a local track to get to know the new
> "beast". The course work included time on a skid pad, obstacle cone
> course,
> as well as track time for a day with a professional driver, giving me
> valuable understanding into vehicle dynamics/car control skills. Just
> about
> the best money I've spent on myself!
> Van
> ----- Original Message -----
> From: <berniek at technicaldevelop.com>
> To: <Supras at supras.com>
> Sent: Monday, January 28, 2008 10:25 PM
> Subject: [Supras] 57 trim driveability
>
>
>>
>> For the last two days, I've taken the '91 out on the road again after
>> most of the salt has washed off the roads.  Mods are based upon a 57
>> trim CT26, 550cc injectors, Lex, Walbro, 3" exhaust, Treadwell Spearco
>> knockoff and the usual supporting changes.  Raising the boost to 16-18
>> PSI, the car feels absolutely great, sometimes breaking loose in second
>> gear on a dry road (need to fill the gas tank).  For straight line
>> acceleration, I could not ask for more, once into second gear, since
>> first is unusable at WOT as stated before.  I may add a microswitch and
>> solenoid valve in addition to a second boost controller to reduce first
>> gear boost, but that is only a partial fix for the real consideration
>> which follows.
>>
>>
>> Most of the controllability regarding power occurs in perhaps the first
>> 20-30 degrees of throttle opening, notwithstanding the "digital" way the
>> boost comes on at 3000 RPM.  Although I'm well satisfied with the power,
>> the car is hard to drive from a power modulation standpoint in the real
>> world as compared with a normally aspirated engine of the same power.
>> I'm curious if anyone has come up with a more linear way of controlling
>> boost as a function of throttle position to make the car more drivable
>> when getting into corners at high speed.  Ideas that come to mind (some
>> are hairbrained) are as follows:
>>
>>
>> 1.  Modification of manual spring type boost controller, where spring
>> preload is a function of throttle position through a lever link to match
>> spring compression to throttle position.
>>
>>
>> 2.  If elecronically inclined, develop a pulse width modulation circuit
>> to drive a high speed solenoid valve to modulate boost bleed as a
>> function of TPS potentiometer position.
>>
>>
>> 3.  Revise throttle linkage to provide most of the opening within the
>> last 10% of accelerator pedal travel.  That could be done with a
>> progressive radius cable saddle on the throttle shaft.  Ford
>> accomplished the same thing with linkage angles and a bellcrank in the
>> '50s and early '60s when they had the Paxton blown 312 CID engine.
>>
>>
>>    Looking forward to ideas.
>>
>>
>>       BernieK
>>
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>
>