MSP volumetric efficiency

OK, this thread got better responses than I expected! I'd like to redirect it slightly to get where I want to go with this now: cams.

Let's start talking about what needs to be done to the stock MSP cams to compliment the stock T25R (stock regrind, weld, or entirely new cut). What's the stock lift & duration? Anyone have an actual cam lift@degree graph for the intake and exhaust? How about a compressor map for the T25R (I can't find it anywhere)? Try to avoid cam phasing for now. That will come later.
 
<table style="text-align: left; width: 800px;" border="1" cellpadding="2" cellspacing="2"> <tbody><tr><td colspan="2" style="vertical-align: top;">Valve Timing
</td> </tr> <tr> <td style="vertical-align: top;">Intake cam duration
</td> <td style="vertical-align: top;">230 @ 0.003"
</td> </tr> <tr> <td style="vertical-align: top;">Intake cam opening
</td> <td style="vertical-align: top;">2 BTDC
</td> </tr> <tr> <td style="vertical-align: top;">Intake cam closing
</td> <td style="vertical-align: top;">48 ABDC
</td> </tr> <tr> <td style="vertical-align: top;">Intake cam lobe height
</td> <td style="vertical-align: top;">43.700mm (1.7205")
</td> </tr> <tr> <td style="vertical-align: top;">Intake cam base circle
</td> <td style="vertical-align: top;">35.052mm (1.380")
</td> </tr> <tr> <td style="vertical-align: top;">Intake valve lift
</td> <td style="vertical-align: top;">8.6487mm (0.3405")
</td> </tr> <tr> <td style="vertical-align: top;">Exhaust cam duration
</td> <td style="vertical-align: top;">230 @ 0.003"
</td> </tr> <tr> <td style="vertical-align: top;">Exhaust cam opening
</td> <td style="vertical-align: top;">48 BBDC
</td> </tr> <tr> <td style="vertical-align: top;">Exhaust cam close
</td> <td style="vertical-align: top;">2 ATDC
</td> </tr> <tr> <td style="vertical-align: top;">Exhaust cam lobe height
</td> <td style="vertical-align: top;">43.225mm (1.7018")
</td> </tr> <tr> <td style="vertical-align: top;">Exhaust cam base circle
</td> <td style="vertical-align: top;">35.052mm (1.380")
</td> </tr> <tr> <td style="vertical-align: top;">Exhaust valve lift
</td> <td style="vertical-align: top;">8.1737mm (0.3218")
</td> </tr> <tr> <td style="vertical-align: top;">Valve overlap
</td> <td style="vertical-align: top;">4</td></tr></tbody> </table>
 
TurfBurn said:
One of the best books out there that I highly recommend is by A. Graham Bell and it is called Performance Four Stroke Tuning. Fantastic book.
Click to expand...
I ordered this book last night. Gotta love drunken shopping. I feel special.
 
This is why I love this forum!



TurfBurn said:
<TABLE style="WIDTH: 800px; TEXT-ALIGN: left" cellSpacing=2 cellPadding=2 border=1><TBODY><TR><TD style="VERTICAL-ALIGN: top" colSpan=2>Valve Timing


</TD></TR><TR><TD style="VERTICAL-ALIGN: top">Intake cam duration


</TD><TD style="VERTICAL-ALIGN: top">230 @ 0.003"


</TD></TR><TR><TD style="VERTICAL-ALIGN: top">Intake cam opening


</TD><TD style="VERTICAL-ALIGN: top">2 BTDC


</TD></TR><TR><TD style="VERTICAL-ALIGN: top">Intake cam closing


</TD><TD style="VERTICAL-ALIGN: top">48 ABDC


</TD></TR><TR><TD style="VERTICAL-ALIGN: top">Intake cam lobe height


</TD><TD style="VERTICAL-ALIGN: top">43.700mm (1.7205")


</TD></TR><TR><TD style="VERTICAL-ALIGN: top">Intake cam base circle


</TD><TD style="VERTICAL-ALIGN: top">35.052mm (1.380")


</TD></TR><TR><TD style="VERTICAL-ALIGN: top">Intake valve lift


</TD><TD style="VERTICAL-ALIGN: top">8.6487mm (0.3405")


</TD></TR><TR><TD style="VERTICAL-ALIGN: top">Exhaust cam duration


</TD><TD style="VERTICAL-ALIGN: top">230 @ 0.003"


</TD></TR><TR><TD style="VERTICAL-ALIGN: top">Exhaust cam opening


</TD><TD style="VERTICAL-ALIGN: top">48 BBDC


</TD></TR><TR><TD style="VERTICAL-ALIGN: top">Exhaust cam close


</TD><TD style="VERTICAL-ALIGN: top">2 ATDC


</TD></TR><TR><TD style="VERTICAL-ALIGN: top">Exhaust cam lobe height


</TD><TD style="VERTICAL-ALIGN: top">43.225mm (1.7018")


</TD></TR><TR><TD style="VERTICAL-ALIGN: top">Exhaust cam base circle


</TD><TD style="VERTICAL-ALIGN: top">35.052mm (1.380")


</TD></TR><TR><TD style="VERTICAL-ALIGN: top">Exhaust valve lift


</TD><TD style="VERTICAL-ALIGN: top">8.1737mm (0.3218")


</TD></TR><TR><TD style="VERTICAL-ALIGN: top">Valve overlap


</TD><TD style="VERTICAL-ALIGN: top">4</TD></TR></TBODY></TABLE>
Click to expand...
 
TurfBurn said:
Shawn, I was pointing out that typically any given vehicle will vary in VE over different RPM's. Typically more efficient toward lower RPM's. So in other words, our cars may run around 95% efficient at 3,000 rpm's... but drop off to only around 75% at 6,00 rpm's. Also, modern vehicles, especially imports, tend to run more in the 80%+ range for efficiency, often well over 90%. Add PandP and the like to it and it is possible through inertia charging and the like to actually get over 100% efficiency.

EDIT: So if anything, your graph is probably conservative for the actual throughput of the motor. AND I see you did state right in your last post that you realized VE varied... my bad!
Click to expand...

The only reason for that is because VE is inversely proportional and directly dependant on RPM. It is a informational tool and if you want to create another tool that isn't RPM dependant it will still give you invaluable information about flow characteristics. The RPM side of things will help you in determining what cams you should use, but has nothing to do with the helping you see how much restriction in flow your ports are giving.
 
VE, while characterized as proportional and dependet on RPM is not entirely so. When I was in college we did studies on piston based compressors and others. VE is directly affected by the amount of restriction on both the intake and exhaust side ports. To think about it simply just picture starting a piston at TDC and rotating it very slowly by hand with the intake valve open all the way... by doing it slowly and from the moment it starts the downward travel to the moment it hits BDC the valve is open and air flows in... Now at BDC you have all the valves closed and you have exactly one full stroke of volume of air at atmospheric pressure. You compress it, ignite it and then exhaust it... well you have hot air you are exhausting and the piston doesn't go all the way to the top.. so you have some left over. Now you repeat the process and you've only refilled about 98% of the volume with fresh air for combustion. Now that's fine and dandy. Now this is where ports and so forth come in and why VE is NOT just based on an equation other than "ideal" if you have X port and Y port... and you are at a certain number of rpm's, each port will have a pressure drop across it due to the resistance of the walls and so forth (I can go more technical if you want after this) which means that while you have atmospheric pressure at the port opening (assuming no intake manifold) you will have a different value at the port exit into the combustion chamber. Just assume that port X results in a pressure of -5"Hg and port Y has a pressure of -10" Hg. Now if you look at the cylinder contents at BDC with the valves all closed you have one cylinder with a -5"hg charge and one with a -10"hg charge... Now compared to atmospheric the -10"HG charge is less efficient.. you have less air than a full atmospheric draw of air for that cylinder. So the ports will matter for this type of VE considerably!! Now if you start getting to a point where more air than the "choke" levels of the head are required, you will see a dropoff in VE. Air has inertia and resistance to motion, so the faster the motor spins, typically the lower your VE as the air can't keep up and the cylinder face experiences even more vaccum as it pulls down due to the "mass void" it creates because the air can't keep up... So the equations you guys listed aren't completely correct... they are the idealistic versions.. and the above is why PandP matters because it allows for less pressure drop and greater charging of the cylinder... Also, the reverse happens on the exhaust side.. the more resistance there, the more positive pressure that is left in the cylinder, and thus the more leftover mass of gas before the next cycle... so the more restriction on either side of the flow, the less mass exchange occurs, the less you have for burning fuel, and the less power and efficiency you can create/have.

Here is more info:
http://www.tpub.com/engine1/en1-105.htm


And spooled.. thank TheMan and the Protege FAQ for that info that i posted before.
 
Spooled said:
OK, this thread got better responses than I expected! I'd like to redirect it slightly to get where I want to go with this now: cams.

Let's start talking about what needs to be done to the stock MSP cams to compliment the stock T25R (stock regrind, weld, or entirely new cut). What's the stock lift & duration? Anyone have an actual cam lift@degree graph for the intake and exhaust? How about a compressor map for the T25R (I can't find it anywhere)? Try to avoid cam phasing for now. That will come later.
Click to expand...

As far as the T25... none exists from my understanding... if you can find a T28 map you can "scale" it and get an approximate idea...

As far as the cams... very little to nothing can/should be changed... we don't need greater overlap with turbo because of the FI... you don't rely on or really gain much from scavenge affect. Greater lift could yield some gains, but we already have pretty reasonable lift and you'd run into other issues doing that, same thing with duration at max lift... there are reasons they run the lifts/durations the way they do for valve wear, rpm etc.

You can however get some reasonable gains by altering lobe seperation angle with cam gears.
 
Ok, that makes sense. I didn't really think of it to the point where the piston is going through more strokes when the engine is at a higher RPM and thus the efficiency could be reduced the faster it goes. Good info.
 
O.K. -

This might be getting a little off topic, but I'd like to bring it up anyway.

Here is a GT28RS Compressor Map with the airflow requirements for an FS motor operating to 7000 rpm using an 80 % VE, shown at various Pressure Ratios:

DiscoPotato3.JPG


Here's the calculation I use for Pressure Ratio:

PR = [(Intake Manifold Pressure)+(Intercooler Pressure Drop)+(Atmospheric Pressure)] / [(Atmospheric Pressure)-(Air Filter Pressure Drop)]

Intake Manifold Pressure = Boost in psi
Intercooler Pressure Drop = 1.5 psi (avg.) - some have more, some have less
Atmospheric Pressure = 14.7 psi at sea level
Air Filter Pressure Drop = 0.5 psi (avg.) - some have more, some have less

So, a PR of:
1.6 = 6.52 psi
1.8 = 9.36 psi
2.0 = 12.20 psi
2.2 = 15.04 psi
2.4 = 17.88 psi

At every PR, the majority of the operating rpms stay in the 70 % and higher efficiency islands. This turbo is a perfect match for the FS motor.

-Shawn
 
Last edited:
TurfBurn said:
As far as the T25... none exists from my understanding... if you can find a T28 map you can "scale" it and get an approximate idea...

As far as the cams... very little to nothing can/should be changed... we don't need greater overlap with turbo because of the FI... you don't rely on or really gain much from scavenge affect. Greater lift could yield some gains, but we already have pretty reasonable lift and you'd run into other issues doing that, same thing with duration at max lift... there are reasons they run the lifts/durations the way they do for valve wear, rpm etc.

You can however get some reasonable gains by altering lobe seperation angle with cam gears.
Click to expand...

Wouldn't the lobe seperation be the same thing as altering the overlap? I wouldn't think that we would benfit from much less overlap, and I understand that too much overlap would just blow fuel out the exhaust ports, but I haven't really seen anyone play with the phasing on an MSP yet. I've heard rumors, but no actual reports on successful gains. Also, I think the people that were playing with that had a different turbo. Any thoughts on this?
 
I like where you're going with this, although I imagine that the T25R is very different fro the GT28RS. That has the T25 turbine and the T3 compressor if I remember correctly, along with a (higher?) A/R.

Edit: took out image for less scrolling

Chojin said:
O.K. -

This might be getting a little off topic, but I'd like to bring it up anyway.

Here is a GT28RS Compressor Map with the airflow requirements for an FS motor operating to 7000 rpm using an 80 % VE, shown at various Pressure Ratios:

(edited out image)

Here's the calculation I use for Pressure Ratio:

PR = [(Intake Manifold Pressure)+(Intercooler Pressure Drop)+(Atmospheric Pressure)] / [(Atmospheric Pressure)-(Air Filter Pressure Drop)]

Intake Manifold Pressure = Boost in psi
Intercooler Pressure Drop = 1.5 psi (avg.) - some have more, some have less
Atmospheric Pressure = 14.7 psi at sea level
Air Filter Pressure Drop = 0.5 psi (avg.) - some have more, some have less

So, a PR of:
1.6 = 6.52 psi
1.8 = 9.36 psi
2.0 = 12.20 psi
2.2 = 15.04 psi

At every PR, the majority of the operating rpms stay in the 70 % and higher efficiency islands. This turbo is a perfect match for the FS motor.

-Shawn
Click to expand...
 
Last edited:
peepsalot said:
Page 23
http://www.limitengineering.com/catalog.pdf
I know, it is for the GT25R which is different than ours, but I can't imagine they are vastly different
Click to expand...

I've been wondering how different the GT25R is fro mthe T25R, too. I can find maps all over for that one. I think that the GT25R is dual ball bearing, while the T25R is single. That would give a quicker spool and a slightly lower output temp, so the islands would probably be the same, only rotated clockwise slighty, pivoting at 0,0. That's just a guess though.
 
"Garrett Ball Bearing Turbochargers always end with an "R" as in GT28R. The R denotes the "rolling" element found in thesingle cartridge, dual ball bearing design Garrett uses on all GT Ball Bearing Turbochargers contained in the PerformanceProducts Catalog."


That's out of the Garrett catalog. Nothing about the "s"
 
So looking at that GT25R compressor map, it looks like 11-12psi is ideal as long as you have the flow capabilities through the engine. I can see what Calloway originally wanted 9psi on the stock MSP.
 
Spooled said:
I've been wondering how different the GT25R is fro mthe T25R, too. I can find maps all over for that one. I think that the GT25R is dual ball bearing, while the T25R is single. That would give a quicker spool and a slightly lower output temp, so the islands would probably be the same, only rotated clockwise slighty, pivoting at 0,0. That's just a guess though.
Click to expand...
I just emailed a contact at garrett asking for them to provide the T25R compressor map. We'll see how that turns out...
 
peepsalot said:
I just emailed a contact at garrett asking for them to provide the T25R compressor map. We'll see how that turns out...
Click to expand...

Ha, I was just going to see if anyone had tried that. I noticed that they don't post an email address in the contact section.
 
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