think of it like a drag strip. You have two cars, and both go down the strip and both trap out at 110mph but one of those cars ran a 10.0 and the other ran an 11.5
This is my concern as well. But my understanding is changing, 5one9 might run 14-21 lbs boost and be safe, due to his build, I might be safe in the same or slightly lesser 4800 rpm shift point with 8-10 lbs of boost.PJ, my engine spins 6000rpm balanced, H-beam rods, forged pistons, studs, etc. When I boost it this winter it will get shifted at 5000rpm for this very reason, combination of boost and rpm together equals mucho stress in every direction.
Oh boy!!! Lol these are the issues I need to be thinking about.If this isn't enough to worry about: There is also thermal stress- excessive heating or cooling in a short period. The rapid expansion or contraction can put a lot of stress on parts like exhaust manifolds, turbos, and pistons. Cast components don't like these extremes in cooling or heating. Add this stress on top of the other stresses discussed above.
Alrighty Folks, if I understand the links that Darius has supplied along with the information everyone else supplied. It "Might" go like this??
The time it takes to get to a fixed rpm (5000)can change but the distance the piston travels doesnt. The piston travel is fixed because the stroke doesn't change.
The added power applied (turbo) doesn't effect piston speed either. The extra power from a turbo is applied to the crank but the piston speed is the same. So the added power is what gets you down the track.
So, I see how a turbo can help the pistons because compressed air can act like a spring and "cushion" the piston @TDC.
Does the extra volume of air also help on the exhaust stroke too?
In my mind, I think it could, expanded exhaust gas filling up and pressurizing the exhaust side of the stroke. Helping to equalize the load on top of the piston.
Am I on the right track here?? If not what am I missing? This is fun stuff.
Doesn't their have to be a trade off? If more power then more wear due to bigger loads on bearings etc???
Which really brings me back to the first point I was trying to make. I used piston speed but still, How much applied power before stock parts start to fail??
I guess that's the magic question for everyone.
LOL, I need to learn a lot more before I do any boosting.
This is my concern as well. But my understanding is changing, 5one9 might run 14-21 lbs boost and be safe, due to his build, I might be safe in the same or slightly lesser 4800 rpm shift point with 8-10 lbs of boost.
I gotta get my mind around the loads and stress the turbo puts on the different components of the engine. Then I can make an educated decision on boost numbers.
I guess that's enough questions for now. Please help in every area my thinking. I really enjoy this topic.
FYI, I've been reading about 2hrs a day on this topic. Well, reading a little and thinking a lot.
Thanks Red, I have studied back pressure and boost also done the math for my stock flowing heads. Ive "mapped" what turbo would be efficient from my math numbers with an efficiency rating above 64%. The turbo I mapped out using the chart with a bunch of island rings gave an efficiency of 76%. I have been studying turbos from Garrette's online learning program. This States for my son, who is a 4banger, and is also studying to become a mechanical engineer. So I had to "up my game" as his mind is fas and his vocabulary can be confusing. In this process I found myself enjoying the learning curve and excelling in the FREE ON LINE PROGRAM. I highly recommend it. So my sons math for his car/ my math for the Trans Am, My son will have around 800hp for that little scion to coupe. But he has to get a trans and fuel system tires etc ect . so anyway hopefully we will have a father son shoot out. Sometime in the future. But thats how my journey started.First off I would like to say, well damn look at that screen shot. Couldn’t have timed it better myself .
a lot of what you are talking about is in the realm of “advanced understanding” and nothing wrong at all with those questions!
boost should by all means be taken seriously, however if you aren’t pushing the envelope to the bleeding edge you can take the worry down a notch.
as I understand it the boost does “cushion” to a small extent but what is worrisome is that it is also attempting to compress a greater amount of volume in the same speed, which can be stressful to the bearings as the see a greater load/time.
now for the super tricky stuff, boost actually will work better with less exhaust overlap (gotta keep cylinder fill) so there are cams specifically made for boost by turbo vs boost by supercharger. I wish I could be more detailed than that but I am still learning myself.
something I believe gets overlooked and or misunderstood is judging boost based on PSI. What we should really be talking about if CFM.
I get that the industry standard is psi, it’s just bothered me as depending on the housings you could be running the same psi but two totally different flow numbers and backpressure.
also @PJ McCoy and @5one9. You should both begin studying back pressure and it effects. Also a lesson in turbo sizing would be a great help as well. The math can be difficult, but it’s worth it to know so you can plot your own numbers without relying on a computer app.