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Khaled Mounir

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Hello Mike. I understand that you have a lot of experience with LH, T5 and T7. I drove my Viggen (T7) and my 1988 C900 ( LH) back to back on a hot day at elevation of approximate 1500 feet. I noticed that both cars suffered in performance. The Viggen is stock and only was hitting half the stock boost and the c900 was hitting an average of 14-15 psi.  Both cars had 91 octane. Once I was back at sea level and with the temps noticeably cooler, the viggen was boosting again to full boost and the 900 was hitting 18-20 psi. I have for a long time been debating the need to convert to T5 on my c900 due the damage it can do to a stock gearbox. Now after that I have seen both the Viggen and the 900 suffering with heat and maybe elevation, I am wondering if a T5 conversion on the 900 would have an advantage in that kind of condition, while still keeping all safety parameters. The C900 has water/ alcohol injection which is set to spray ( boost juice) into the intake at 10psi. For testing purpose I turned off the sprayer and I was only hitting 12-13 Psi. So the spray did allow for an extra 2 lbs of boost. 
I always liked the power curve on the c900 as it climbs gradually in a progressive curve and keeps pulling at high rpm. I think that is a good thing as it helps control the heat generated form the engine as the air flow increases with speed.  It is also more friendly to the gear box. I say that even though the last 3 gear boxes blew in 4th gear at hight rpm. 

So what are your thoughts on this matter. 

Thank you in advance.
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Mike D

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Holy long winded question batman!! lets try to reproach this in a logical order

To start, lets go over altitude concerns, T7 has a barometric sensor, LH does not, T7 also detect knock, LH/apc doe a really bad job of this, especially if the APC has been modified 

in both situations it sounds like your cars were responding to knock situations, T7 is simply more sensitive to this, especially if parts are getting old, 

T7 can adjust for this more accurately after a tune.  

T5 does not have any atmospheric adjustment, it simply trys to make the intake manifold a certain pressure, despite the atmospheric condition. If and engine leans out, or gets too warm in a condition of high atmosphere, (and the knock maps have been properly calibrated) it will not turn the pressure down until it recognizes the right level of knock, in T5 this is a map, that can vary knock sensitivity based on load, and RPM. in LH/apc this is a static note it picks up, that can also be set off by high energy ignition systems. (hence why DI/APC was a combined unit in the first few years) 

T5 does not kill gearboxes, Drivers do.  when used properly t5 can save a trans by lowering engine bay temperatures, and delivering smoother power. 

as a final word, water meth doesnt do a whole lot, yes it can help prevent knock, and it can cool the intake charge, but this is a band aid for lacking proper hardware. in your case this band aid allowed for an extra 2psi Backing the timing down 1-2 degrees would have done the same thing, so would have fattening up the mixture.

unless you are making more than 250hp per liter of displacement, time should be focused on other modifications
 




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Mike D Tuning

Specializing in Trionic 5,7 & 8 tuning, as well Megasquirt conversions.   Creator of the first well documented Trionic 5 conversion on a c900
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Khaled Mounir

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Thanks Mike. I understood everything except for " unless you are making more than 250hp per liter of displacement, time should be focused on other modifications "

I am obviously not making 250hp per liter,  so what is it you are recommending that I should focus on? 

I know this is going to sound so old school to you but you should also know that my modified ABC box is supposed to have the OEM safety knock parameters untouched. It's a swedish dynamics stage 4 which is known for allowing maximum boost pressure ( 22- 24 psi on cold days within safety parameters). 

When you call water meth a bandaid. what is the real cure then ? 

Also, how does T5 lowers engine bay temps ?

I really appreciate your advice.
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Mike D

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250 hp per liter, on a 2 liter motor is 500hp,, you are making 500hp??

T5 lowers engine bay temperatures because it it can make the same power, with less boost, less boost= lower temps

If you compare heat levels of the two system, at the same power mark, with the otherwise same hardware. T5 cars run colder

the cure for water meth? simple, a good intercooler, efficient exhaust, heat wrapped everything, and a properly set up timing, and fuel system. 





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Mike D Tuning

Specializing in Trionic 5,7 & 8 tuning, as well Megasquirt conversions.   Creator of the first well documented Trionic 5 conversion on a c900
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