So, I continue to toy with upgrade planning, but it occurs to me as I read the threads on here, they all talk about what breaks at different horsepower levels. However, everything that should cause something to break is based on torque. Force on transmission parts is based on torque. Pressure inside the cylinder is based on torque. Detonation limits are based on torque. Break mean effective pressure is roughly proportional to torque.

Then I did some basic math. Many tuners put over 600 ft-lb through the long block, but claim that over 600 hp the rods become questionable. However, when I do the math at 550 ft-lb * 7200 RPM / 5252, I get about 750 hp. Then I look at the dyno curves of these tuner kits and the power curves are flat like torque curves and the torque curves peak at crazy levels, then fall with RPM.

Two observations:

1) If I can run 600 ft lb at 4000 rpm, why can't I run the same level at 7200 rpm without breaking rods, but limit it to 600 ft lbs across the entire range. This relates to boost mapping.

2) Why not decide a torque limit that is pretty safe, like 550 ft lbs, and try to get a turbo sized to produce that torque at 7200, then limit it to 550 across the entire RPM range. Yes, you'll give up a little performance but you'll max performance at a given level of mechanical reliability. Yes, you might lag a couple hundred RPM because of the bigger turbo, but it will feel much better with a constant pull to redline instead of a falling torque output.

What am I missing?

 

thats why i have no headers,plenum,ypipe anything that help spooling to fast my alpha28s!...
my boost controller is set at 1.4bar from 3500-4500 then high boost 100%duty with meth 1.8-1.9 bar in upper rpm 7100 max

 

Nothing. You are missing nothing. Most guys like the low end hit and all kits are tailored to it. A engine that you wish to build will be faster then one that hits hard in the bottom then drops off.

 

Thanks, mtlsp. Do you happen to have a dyno run you could share with us? I'd love to see what your torque curve looks like.

Tim, do you happen to know someone who makes a kit with a rising boost at high RPM to produce a flat torque curve?

 

For the purpose of rods, I'd agree that you can simplify the discussion down to torque. But hp is important to consider especially at high rpm and extended operation as that more directly suggests the amount of heat that's produced and therefore timing.

 

first of all , you need some turbos that will provide that kind of TQ down low... and that starts with A28s... k16 billets on pump will not give you issues...not even k24 billets...
I would choose a gt30R turbo over a gt28 anytime just for that reason... it hits later and you get more power... Ive gone thru alot pf turbos over the years, but as someone said, most guys want the kick down low not thru out the rpm range like I do... thus I would sacrifice a few hundred rpms anytime for a more powerful car all around,and your nor wheel spinning in 2nd gear as well, and be kinder on the rods too... to each his own I guess...
markski

 

Torque is just force over a distance..... our engines pull like freight trains 3400-4800 rpm, no need for more torque at higher revs as the "momentum" of the car is already such that speed and acceleration is achieved, especially in 3rd-6th gears.

Just look at those high revving lower torque engines in cars like the old M3 and the ferraris that rev really high.. they sco along just fine