[Land-speed] Sorta off-sorta on-topic..turbocharging theory

[Jon Bishop]

On Nov 14, 2007, at 11:28 AM, Ray Buck wrote:

> At 01:37 AM 11/14/2007, Jon Bishop wrote:
>> On Nov 13, 2007, at 5:32 AM, MEIERLE Mike wrote:
>>
>> > Isn't some of this happening during valve overlap? It's not really
>> > sucking the exhaust out but actually pushing it out during this  
>> event.
>>
>> Turbochargers don't like overlap. The less overlap in a turbo car the
>> better.
>>
>> Beyond that, I'm not sure I quite understand the original question.
>> Could you reword it so that I might understand what it is you're
>> trying to accomplish?
>
> Hmmm...let's see.  The original question was about using a  
> turbocharger to improve the performance of a motor that had a  
> limitation of valve size because of a relatively small bore.  A  
> Chevy 305 in particular.  A friend is considering dropping one into  
> his son's 76 Nova to replace the tired original motor that's in  
> there now.
> <snip>
>
> As I considered further, I wondered if a second driven impeller on  
> a turbo might be used to suck the exhaust out of the cylinder and  
> force it into the turbine side of the turbocharger.  I know it  
> sounds like a Rube Goldberg type of perpetual motion thing...but  
> who knows?  David Adin reminded me that "nothing is free" and I'm  
> aware of that, but still, I wonder if there was a way to help  
> extract the exhaust through the exhaust valve by assisting it in  
> the same way that the mixture is forced through the intake.
>
> I hope that's a little clearer.  If not, maybe we can just chalk it  
> up to the pain meds as the result of some oral surgery. :)
>
> RtR
>

Alright, now I understand. But yea, it sounds like you're trying to  
develop something to compensate for small valves.

There's been a lot of good info posted, so I'm just going to  
summarize my suggestion.

Twin Turbos sound really cool when you're describing your engine to  
someone, but a single larger turbo will be easier to tune.

Get a cam with minimal overlap, and then decide how many RPMs that  
motor's going to generally run at, figure out the approximate airflow  
at that RPM, and get the turbo that will flow that much efficiently...

Don't undersize your turbo, it will overheat the air and that causes  
you to lose air density. It's almost better to go too big (you will  
experience a slight delay from the pedal hitting the floor and the  
power coming on, as the turbo spins up, but it will more efficiently  
compress the air, and it won't heat as much) than too small (instant  
throttle response which is then negated by overheating issues, and  
flow problems)


Otherwise, get a nice set of heads and a roots blower.

~Jon