Manifold pressures

[UUJ_Racing]

Hi,

For part of a Formula student project, I am currently trying to design a carbon fibre plenum for an N/A R6 Yamaha engine. To size the thickness of material to be used, I need to find the maximum vacuum that will be present within the plenum and hence work out the forces involved.

Max Vacuum will obviously occur when the throttle is closed at high revs (max 15,000 RPM I believe). Is there anyway of working this value out - or would the best thing be to stick a MAP sensor on the existing manifold and datalog it. I presume the answer depends on the idle flow on the throttle body (The plenum is running a single 50mm TB).

I know from the boost gauge on my turbo'ed car that the vacuum levels out at a certain value when on the over-run and doesn't vary with engine speed.

Anyone point me in the right direction/any ideas

Kev

[UUJ_Racing]

Hi,

For part of a Formula student project, I am currently trying to design a carbon fibre plenum for an N/A R6 Yamaha engine. To size the thickness of material to be used, I need to find the maximum vacuum that will be present within the plenum and hence work out the forces involved.

Max Vacuum will obviously occur when the throttle is closed at high revs (max 15,000 RPM I believe). Is there anyway of working this value out - or would the best thing be to stick a MAP sensor on the existing manifold and datalog it. I presume the answer depends on the idle flow on the throttle body (The plenum is running a single 50mm TB).

I know from the boost gauge on my turbo'ed car that the vacuum levels out at a certain value when on the over-run and doesn't vary with engine speed.

Anyone point me in the right direction/any ideas

Kev

[MikeDutsa]

It seems like the most you would have to design around would be a complete vacuum, so the walls would have to sustain the atmospheric pressure, roughly 14psi. Correct me if I'm wrong.

[Roger]

In my turbo car, I see up to 28 inches of vacuum. If you are worried about strength, I'd make sure you can handle a backfire that might occur during tuning of the engine/ECU.

[exFSAE]

20-30 kPa is pretty nominal pressure top in plenum on these cars. But hey, I'd design for full vacuum. Why not.

Actually. What I'd really do, in the interest of gettin-r-dun, is just lay one up with a bunch of carbon, and test it.

[murpia]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Roger:
In my turbo car, I see up to 28 inches of vacuum. </div></BLOCKQUOTE>
Surely you mean MAP = 28" ... (http://en.wikipedia.org/wiki/Negative_pressure)

Regards, Ian

[UUJ_Racing]

Yeah - will just spec it for absolute vacuum - ie -1 Bar (or equivalent)

Cheers

[civicsit]

Might want to think about those backfires. If you spec it for absolute vacuum only, a backfire may crack or explode your plenum.

[UUJ_Racing]

Well what pressure am I going to assume the backfires are going to inflict on the plenum?

[A Richards]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by UUJ_Racing:
Well what pressure am I going to assume the backfires are going to inflict on the plenum? </div></BLOCKQUOTE>

Quite large. i would suggest making your plenum have a weakest link. In the case of ours the restrictor blows off first. When designing a CF plenum its quite important to make it ridged, or the sides will suck in and if you use a core it can delaminate over time.

[kuck]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by murpia:
<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Roger:
In my turbo car, I see up to 28 inches of vacuum. </div></BLOCKQUOTE>
Surely you mean MAP = 28" ... (http://en.wikipedia.org/wiki/Negative_pressure)

Regards, Ian </div></BLOCKQUOTE>

On most boost gauges, vacuum is in inches of Mercury so I'm guessing that's what he meant.

[murpia]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by kuck:
<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by murpia:
<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Roger:
In my turbo car, I see up to 28 inches of vacuum. </div></BLOCKQUOTE>
Surely you mean MAP = 28" ... (http://en.wikipedia.org/wiki/Negative_pressure)

Regards, Ian </div></BLOCKQUOTE>

On most boost gauges, vacuum is in inches of Mercury so I'm guessing that's what he meant. </div></BLOCKQUOTE>
Maybe the joke was too subtle? I dislike it when people mix up units and make up assumptions.

28" of mercury is almost exactly 1Bar. Therefore 28" of vacuum could be interpreted as a negative pressure - a physical impossibility!

I think he means 28" of boost pressure... If he meant a manifold abolute pressure (MAP) that's not much of a turbo either... Although I expect you could make some money selling MAP gauges as 'boost' gauges for these... (http://www.essexracing.com/product_info.php?products_id=1120)

Regards, Ian

[VFR750R]

What's impossible about 28"Hg vacuum?? That's probably exactly how much you have with closed throttle from high rpm. The gauge probably has at least an inch of error however.

[Marshall.Hagen]

Here is an approximate scale for inches of vacuum to KPa.

27" ~~ 10 KPa
20" ~~ 30 KPa
18" ~~ 40 KPa
15" ~~ 50 KPa
10" ~~ 65 KPa
8" ~~ 75 KPa
4" ~~ 85 KPa
3" ~~ 90 KPa
1" ~~ 97 KPa

To answer the original question - we are seeing about 10-12 KPa spikes when we let off the throttle at high load, high RPM.

[UUJ_Racing]

Thank you Marshall.
Just out of interest.. How did you quantify your vacuum?

[Marshall.Hagen]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by UUJ_Racing:
Thank you Marshall.
Just out of interest.. How did you quantify your vacuum? </div></BLOCKQUOTE>

The scale I pulled off of a tuning software that lists both on the load vs rpm table.

Our manifold pressure was measured via datalogs off our DTA ECU. I'll be back on the engine dyno today, I'll try and remember to take a screen shot of the data chart.