LS3 E85 & Boost advance

[SiriusC1024]

Could be a dumb idea, but just out of curiosity. Would it be sensible to rig up one of the old style smog pumps to draw vacuum on the crankcase? I know low ring tension alcohol cars run a pump, for the ring control kingtal0n is describing, but it's application-specific.

[Alvin]

People used to do that a lot in the early LS days. They would repurpose a AIR pump to do it. The problem is the volume of air even on healthy engine is way beyond what any electic pump could do. It's almost a "why aren't there electric superchargers" question.

I worked with a couple other guys and shops to do like cam only records and crap like that... We really picked at fly shit looking for power on these cars. On a few we did some belt driven vacuum pumps. You would see like 4-7 rwhp from an otherwise maxed out setup with them.

.... From that time doing that.. What would you think performs better? Open headers, 18 inch collector extensions, magnaflow bullet mufflers (basically glasspack), or single chamber flowmasters?

[SiriusC1024]

Oh I didn't even know they made electric ones. Reason I was wondering is because I saw a weird belt-driven thing on my friend's 87 Dakota. Had heard about them but never seen one in person.

Rhetorical question? I really don't know. Sprint cars are open headers. Nascars used to have boom tubes. Myself I think Aeroturbine 3030 if the stock exhaust routing is intact. What do you think?

[Alvin]

Oh. I know.. we tried each while the car was straped to dyno.. It was Flow single chamber by like + 8rhwp over open headers being the worst. Next best was collector extenions.

[SiriusC1024]

Are you talking something like a Flowmaster 10? 8hp is a pretty decent spread.

[kingtal0n]

If you get the right crankcase pressure monitoring and vacuum pump electric it can work well, here is an example

While I was doing this I decided the short the Hobbs switch to check out the vacuum with the air pump turned on. To my surprise it wasn't turning on. Upon inspecting the 15amp fuse it had blown so it was not working when under boost. This might explain why I had oil pushing past the rear main seal. I swapped in a 20amp fuse and it works like it should and pulls ~5" at idle. Because I monitor the pressure with my AeroForce Gauge it allows me to set a warning light. I now have the warning light come on anytime the PCV presssure exceeds 0psi

https://www.evolutionm.net/forums/ev...l#post11930508


Monitoring is the key no matter whether you used a vacuum pump or OEM PCV (which uses the engine intake stroke as the vacuum pumping for PCV) you should know the crankcase pressure as it will be the crankcase pressure which will show the first signs of any weakness in the ring sealing or bottom end components. Crankcase pressure is like the life line of the engine.

[NotSure]

That boost activated air pump sounds like a good idea, since they are not designed for 100% duty cycle and would tax your charging system anyways. The air pumps I have found are rated around 5-10 scfm of flow with no restriction. Need to watch how you pull it from on an LS. The orifice in the left bank PCV connection at the valve cover is about 0.10" diameter on my engine. Some old saying about a golf ball through a garden hose comes to mind.

[kingtal0n]

Flow through the orifice is easily calculable and negligible at wide open throttle making it a poor choice for evacuation

the flow of the restrictor
https://www.corvetteforum.com/forums...post1605229916

Lets calculate the flow rate of a .100" diameter circular orifice with a pressure differential of 0psi crankcase to 18" Hg intake manifold pressure.
18" Hg is approx -8.8psi
If we assume a crankcase pressure near 0psi, 100*F air temp, .100" diameter orifice, -8.8psi intake pressure
Using this equation

and an online calculator, I get 1.65CFM @ .1" Diameter
At WOT when intake pressure is near -0.5PSI , I get .65CFM @ .1" Diameter

You can input the pressure difference and size of orifice to find flow

[ns158sl]

Boost is not a major determining factor. For example 9:1 compression and 32psi of boost with zero degrees of timing is fine on 93 octane fuel at 112*F in an 86x86 engine like a 4g63, 2jz or sr20. 500-600rwhp that dynojet.
14psi of boost in the same engine at 150*F IAT is a disaster in progress, total destruction on 93 octane even with zero degrees of timing.

While boost can give us some idea of cylinder fill that has some influence on rate, IAT is far more influential as the fuel quality goes down.

And then as fuel quality goes up, e.g. alcohol we can get away with roughly similar timing at 15 as 30psi on some engines. Again showing that boost is not a limiting.
For example a RB25 could be fine 16* at 20psi on E80, hundreds of those out there running air to air intercoolers and 108-112*F IAT
Say we install air/water and get down to 65-77*F IAT, boost drops but the wastegate detects it and the turbine demand increased wheel speed to maintain the same boost pressure.
Now massflow has increased at the same boost pressure, wheel speed is higher, power increases at the new lower IAT, and we are removing couple degrees of timing instead of adding it despite same boost and reduced IAT.

Thus, boost can go down and we remove timing. Boost can go up and we remove timing. Boost isn't the deciding factor and cylinder VE only plays part of the role in timing decision.

No where was IAT's, ECT's, PCV were introduced in question. Totally another thread which has beaten to death probably since the ICE was invented lol. All vital points you had. But lets not railroad the thread.