Tweet
I was sitting around looking to see if the RSM throttle body looked like it was worth the money. I decided to do some basic math.
As we all know:
Airflow rate = cid x rpm x 0.5 x Ev /1728
where Ev is volumetric efficiency.
I'll be working with the 3400 LA1, which is rated 204 CID according to this site.
I'll work 6000 rpm for startes, since most of you redline about there stock.
Math is based on stock TB
354 = 204 x 6000 x .5 x Ev /1728
You get an Ev of ~100% needed to max out the TB.
Take a 20% to account for the throttle body being less than perfect, and you still need ~80%.
Now correct me if I'm wrong, but I highly doubt our engines are pumping through a volumetric efficiency of near 80-100% at 6000 rpm.
Let's hit the stock TB with 7000rpm now.
You'd need ~86% VE if the TB is 100% effiecient, and ~69% if it is only 80 % efficient at letting air through.
Let's look at the most common upgrade it seems, the 62 mm TB.
Wow...just wow.
At 6000 rpm you'd have to hit a VE of 123% to max it out, ~98% if the TB maintains 80% efficiency
7000 rpm you'd have to his 105% VE, or 84% if the TB is 80%.
I calculate stock our VE at HP peak is about 76%.
6000 rpm stock motor I calculate about 62%
Spun up to 7000 rpm stock and it drops below 50%
Now let's pretend someone has modded a motor to hit 220 crank hp at 6000 rpm. That's about 175 at the wheels with 20% drivetrain loss, which is doable with a decently modded LA1, still NA. I know my motor won't beat that while it's NA
About 81% VE is what I calculate at 6000 rpm.
This is within 1% of the 20% safety margin I threw into the stock TB.
At 7000 rpm I estimate VE drops to about 63%, which is once again below the safety margin of 20% I imposed, by about 6% this time.
Now I know this is a lot of math and somewhat hard to follow, but I find it hard to justify going to a larger throttle body when my stock one seems to meet my goals just fine. Feel free to add your input to this and correct my math as I do make mistakes from time to time.
As we all know:
Airflow rate = cid x rpm x 0.5 x Ev /1728
where Ev is volumetric efficiency.
I'll be working with the 3400 LA1, which is rated 204 CID according to this site.
I'll work 6000 rpm for startes, since most of you redline about there stock.
Math is based on stock TB
354 = 204 x 6000 x .5 x Ev /1728
You get an Ev of ~100% needed to max out the TB.
Take a 20% to account for the throttle body being less than perfect, and you still need ~80%.
Now correct me if I'm wrong, but I highly doubt our engines are pumping through a volumetric efficiency of near 80-100% at 6000 rpm.
Let's hit the stock TB with 7000rpm now.
You'd need ~86% VE if the TB is 100% effiecient, and ~69% if it is only 80 % efficient at letting air through.
Let's look at the most common upgrade it seems, the 62 mm TB.
Wow...just wow.
At 6000 rpm you'd have to hit a VE of 123% to max it out, ~98% if the TB maintains 80% efficiency
7000 rpm you'd have to his 105% VE, or 84% if the TB is 80%.
I calculate stock our VE at HP peak is about 76%.
6000 rpm stock motor I calculate about 62%
Spun up to 7000 rpm stock and it drops below 50%
Now let's pretend someone has modded a motor to hit 220 crank hp at 6000 rpm. That's about 175 at the wheels with 20% drivetrain loss, which is doable with a decently modded LA1, still NA. I know my motor won't beat that while it's NA
About 81% VE is what I calculate at 6000 rpm.
This is within 1% of the 20% safety margin I threw into the stock TB.
At 7000 rpm I estimate VE drops to about 63%, which is once again below the safety margin of 20% I imposed, by about 6% this time.
Now I know this is a lot of math and somewhat hard to follow, but I find it hard to justify going to a larger throttle body when my stock one seems to meet my goals just fine. Feel free to add your input to this and correct my math as I do make mistakes from time to time.
Comment