F/I Blowing motors facts

[CSG Mike]

Originally Posted by Cal3000

I've been daily driving e85 at this power level for 4 years and over 100k miles now. Vortech 3.48 pulley at like 8.5 psi max. High hp low torque. The blower doesn't come alive until 4k rpm, but if i'm banging through gears, I don't see below 4k. The stress on the motor down low is not that big of a difference than stock. Everyone scoffs at the vortech's torque when in reality it's the SC kit that makes the highest hp with the lowest boost pressure.

Actually, the Rotrex kits make more than that pound for pound, on E85, as does the Edelbrock/Harrop.

Here's an edelbrock kit on the standard (CARB) pulley which makes a *maximum* of 9 psi, with a Delicious flex fuel kit. Stock header, stock front pipe.



The Vortech was better than the Innovate kit (which was first to market), but has been surpassed by the kits released afterwards.

To put it in perspective, I make more power at 5.5 psi boost at peak power, on ethanol (300whp), with my GReddy turbo kit.


That all being said, lower torque, and lower power, means less stress, and a high probability of more reliability.

[Cal3000]

Originally Posted by CSG Mike

Actually, the Rotrex kits make more than that pound for pound, on E85, as does the Edelbrock/Harrop.

Here's an edelbrock kit on the standard (CARB) pulley which makes a *maximum* of 9 psi, with a Delicious flex fuel kit. Stock header, stock front pipe.



The Vortech was better than the Innovate kit (which was first to market), but has been surpassed by the kits released afterwards.

To put it in perspective, I make more power at 5.5 psi boost at peak power, on ethanol (300whp), with my GReddy turbo kit.


That all being said, lower torque, and lower power, means less stress, and a high probability of more reliability.

Oh wow nice. That's pretty high for a dyno dynamics. How is calibrated? Baseline? I have a FBO (minus intercooler) Evo that made 281whp on a Dyno Dynamics. 350whp on that dyno is like 420whp on a dynojet.

[CSG Mike]

Originally Posted by Cal3000

Oh wow nice. That's pretty high for a dyno dynamics. How is calibrated? Baseline? I have a FBO (minus intercooler) Evo that made 281whp on a Dyno Dynamics. 350whp on that dyno is like 420whp on a dynojet.

Here's how my personal car dynos. Bottom line is stock 2017.

[toast]

I constantly hear this convention batted around that low end torque is what breaks/bends rods or that the 'hit' of a turbo down low does it.

That makes zero sense from a physics standpoint. Every two engine revolutions any given rod will go from almost no load to full load on the power stroke. No matter how fast your turbo hits it can't cause a delta faster than that. I also don't see how having higher torque down low could be worse than having it up high.

Someone explain why I'm wrong.

[Brayden_23]

Originally Posted by toast

I constantly hear this convention batted around that low end torque is what breaks/bends rods or that the 'hit' of a turbo down low does it.

That makes zero sense from a physics standpoint. Every two engine revolutions any given rod will go from almost no load to full load on the power stroke. No matter how fast your turbo hits it can't cause a delta faster than that. I also don't see how having higher torque down low could be worse than having it up high.

Someone explain why I'm wrong.

My understanding is it isn't necessarily where the torque comes in that is the issue. It has to do with engine load.

The theory *from my understanding* is that high torque combined with high load at low RPM is going to have a higher chance of breaking/bending a rod than if you are at a higher RPM since engine load is typically lower at higher RPM

[ajc209]

Originally Posted by toast

I constantly hear this convention batted around that low end torque is what breaks/bends rods or that the 'hit' of a turbo down low does it.

That makes zero sense from a physics standpoint. Every two engine revolutions any given rod will go from almost no load to full load on the power stroke. No matter how fast your turbo hits it can't cause a delta faster than that. I also don't see how having higher torque down low could be worse than having it up high.

Someone explain why I'm wrong.

Its the inertia on the rotating parts. If you cut fuel the engine keeps spinning due to inertia right? so when you are WOT the intertia pulling the piston down, helps relieve some of the stress put through the rods. The effect is stronger as you go up in revs due to more inertia in the rotation parts.

Think of a merry go round at a play park. When its spinning slowly you can push really hard, but as it builds speed the inertia makes it harder for you to push it as its already moving.

The effect is nothing like as strong as people like to make out though, and we still see plenty of cars with centrifugal supercharges blowing rods once they go much past 280whp.

[why?]

This is a great way of saying it. Low rpm's and high load are an awful combination for boosted vehicles. If you go over to nasioc you'll see tons of people say number one about an STI is to never floor it at low rpms in 5th or 6th because that is where most issues occur.

Originally Posted by ajc209

Its the inertia on the rotating parts. If you cut fuel the engine keeps spinning due to inertia right? so when you are WOT the intertia pulling the piston down, helps relieve some of the stress put through the rods. The effect is stronger as you go up in revs due to more inertia in the rotation parts.

Think of a merry go round at a play park. When its spinning slowly you can push really hard, but as it builds speed the inertia makes it harder for you to push it as its already moving.

The effect is nothing like as strong as people like to make out though, and we still see plenty of cars with centrifugal supercharges blowing rods once they go much past 280whp.

[toast]

Originally Posted by why?

This is a great way of saying it. Low rpm's and high load are an awful combination for boosted vehicles. If you go over to nasioc you'll see tons of people say number one about an STI is to never floor it at low rpms in 5th or 6th because that is where most issues occur.

You have issues on turbo charged cars because you get boost spiking when the load is very high.

Its the inertia on the rotating parts. If you cut fuel the engine keeps spinning due to inertia right? so when you are WOT the intertia pulling the piston down, helps relieve some of the stress put through the rods. The effect is stronger as you go up in revs due to more inertia in the rotation parts.

Think of a merry go round at a play park. When its spinning slowly you can push really hard, but as it builds speed the inertia makes it harder for you to push it as its already moving.

The effect is nothing like as strong as people like to make out though, and we still see plenty of cars with centrifugal supercharges blowing rods once they go much past 280whp.

If the inertia of the crankshaft pulling the piston down relieves some of the compression force in the rod you are effectively saying that the net force on the rod is lower. If the net force on the rod is lower the net force on the crankshaft is lower. If the net force on the crankshaft is lower you would measure less torque on a dyno. This does happen and it is why most NA motors do not generate max torque near redline. When you stuff more and more air in as rpms rise you can create this (ie centrifugal supercharger).

Second paragraph, no. If a machine can generate 100 lbs of force it does so regardless of how fast it is applied. You have a tougher time pushing a faster moving wheel because of timing issues and the fact that your are not a machine; if you were mechanically constrained to the rotating system and your 100 pounds of force did not require a ramp-up time like muscles do your force would always be applied at the correct time and you would generate the same amount of rotational acceleration.

If the above argument is correct it really comes down to how long the maximum compression force is applied to the rod. If that is the case and someone can point me to a reference I would be happy. I would think from a materials standpoint it would be the opposite; if maximum torque occurs at higher rpm the transition from compression to tension would lead to work fatigue faster.

[NoHaveMSG]

Originally Posted by toast

I constantly hear this convention batted around that low end torque is what breaks/bends rods or that the 'hit' of a turbo down low does it.

That makes zero sense from a physics standpoint. Every two engine revolutions any given rod will go from almost no load to full load on the power stroke. No matter how fast your turbo hits it can't cause a delta faster than that. I also don't see how having higher torque down low could be worse than having it up high.

Someone explain why I'm wrong.

Are you talking about in general or just with the FA motor? I think there are a lot of misconceptions about mode of failure. But most of the threads I have seen about blown FI motors, SC or turbo, are from setups that were running in the upper threshold of what the stock internals could take.

[gtengr]

Originally Posted by toast

...

The inertia effect is real. Also check out my post on oil pressure about halfway up the previous page

[toast]

Originally Posted by NoHaveMSG

Are you talking about in general or just with the FA motor? I think there are a lot of misconceptions about mode of failure. But most of the threads I have seen about blown FI motors, SC or turbo, are from setups that were running in the upper threshold of what the stock internals could take.

Yes. My point is that if your stock motor is generating 250 ftlbs of torque is is no less likely to snap a rod if you make that torque at 3500 rpm or if you make that torque at 6500 rpm. There is some form of conventional wisdom on this site that seems to point to the opposite and I would think that is false from a purely physics-based approach.

[toast]

Originally Posted by gtengr

check my post on oil pressure about halfway up the previous page

I missed that. Thank you, that is the first post I've seen on this topic that actually makes a valid point.

Is oil pressure really a full function of rpm? There is no relief valve at some point? What is the maximum oil pressure in this motor and at what rpm do we reach that

[NoHaveMSG]

Originally Posted by toast

I missed that. Thank you, that is the first post I've seen on this topic that actually makes a valid point.

Is oil pressure really a full function of rpm? There is no relief valve at some point? What is the maximum oil pressure in this motor and at what rpm do we reach that

Yes, oil pump is a driven part. Don't know the answer to the rest, except that it is on the low side.

This is one of the reasons I am leaning toward SC over turbo, that and engine bay heat.

[gtengr]

Originally Posted by toast

Is oil pressure really a full function of rpm? There is no relief valve at some point? What is the maximum oil pressure in this motor and at what rpm do we reach that

I don't have gauges yet, but here is some data (http://www.ft86club.com/forums/showthread.php?t=76760). Pressure is still building towards the max between 2000-4000 rpms.