DG wrote:
< Here's my proposed wording:
< Turbocharger units may not ported, clipped, or otherwise modified from
stock.
< Turbochargers may be updated/backdated, provided that:
< the donator and target car were both turbocharged
< the displacement of the engine in both donor and target are exactly the
< same the configuration and number of cylinders of the engine in both donor
< and target are exactly the same that oil and coolant lines use the stock
source < and/or return points
< Twin turbocharger units and their associated control hardware must be
< updated/backdated as a complete unit; Individual turbochargers may not be
< separated out, nor may single turbochargers be combined to provide a twin
< turbocharger configuration.
< GH, how does this look to you?
I have also read the follow up letters and a few points never came up.
I am a serious turbo head. I have autocrossed only turbo cars except for one
year out of 12. My current car is a custom turbo system that I designed
myself and have run 3 different turbos in an effort to make the most power
with the best response and widest power band. I had been running the car in
EMod so there were no rule concerns. I learned alot about boost that is not
being adressed here.
As far as I can see, under the current rules most turbo cars are a bit
overclassed, but that is not the issue here. Anyone who knows how an engine
works can see a 2.0L turbo motor will not make as huch power as a 5.7L
engine. But the SPAG seems to think other factors equalize this. Hopefully
the adding of another SP class will move cars to where they can be more equal.
Now back to the turbo rule proposal. The stock turbo is a major limit and
requiring the stock boost control is also. Put together they greatly limit
how much power can be made. Many factory turbo cars don't have good boost
control, and changing exhaust and intake parts can alter the boost a bit, as
the rule is based on stock boost control which is fine for what they are
trying to do. And this is where the DSM turbo update/backdate has a problem.
If you backdate to the old turbo which has better flow, do you then also have
to run the older cars LOWER boost pressure?
I started with a smallish T-3 60 trim turbo and ran as much as 15 psi of
boost. I then changed to a better flowing TO4E and at the same 15 psi of
boost, I ran severely lean and had to drop the boost at least 3 psi (only 12
psi) to have the injectors keep up and flow enough fuel. This means I then
made the same or more power at less boost, and the exhaust pressure was half,
freeing up even more power. I think I had a bigger change then the T-25 vs
TD05-14B change, but it still makes the point. The small newer turbo makes
more power in stock trim because they run it at more boost, the bigger old
turbo runs a lower boost level and has a flatter power curve but more lag.
The porting in the engines have also been tailored to the rpm range intended.
If they are allowed to do this swap, then the Porches should be able to put
the new twin turbo setup on the older cars, right?
Now to say why this is a problem, the whole motor and boost control system
works together. The boost on these cars is controlled by an ECU controlled
valve. When I ran my 87 GrandAm Turbo a few years back, I could not use any
chips or aftermarket EFI because the WHOLE ECU was controlling the boost.
Almost evry new newer tuebo car does this also. Unless boost control is
opened up and policed another way, the engine and turbo have to be treated as
unit.
This is a problem. I don't see an easy answer, but allowing the turbo to not
follow the control system and engine is going to open a can of worms. I can
envision many other cars where turbo up/back dates can influence the power
curve and/or max power.
I feel a better solution is going to be some form of flow restrictor or pop
off valve. In the prepared rules they alow any turbo with an inlet
restrictor. This is easy to police. A range of sizes would be needed, but
inspection only requires a dial caliper. Pop off valves can be tested with a
simple air compressor and regulator. Just come up with a max boost or flow
for each class or by weight or something. Then turbo size and boost control
is no longer as gig of an issue.
Gary M.
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