volumetric efficiency

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Big words, I know..I'm still trying to understand what they mean..

Anyway, has anyone actually done a volumetric efficiency test on a b3 b6 or bp? I've searched google, and here, and the only thing I can really find is a post/thread over on a miata forum that says one of they're bp motors came out at 88%. Just wondering if there's any evidence to support that, it was word of mouth, someone said that someone said their engine came out 88%... Also, when I'm nerding out with a pen, what % should I use for volumetric efficiency for a b3/b6/bp?

[NovaSS]

80 cubic inches making 63 HP

I would guess VE around low to mid 80s (SWAG )

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Yea the general consensus for Ev of all engines I've seen so far is 75-90%, I was just wondering if anyone had a actual number I could use for a stock motor. I figure if I use a close to accurate number, after a port job it would be better than expected.

[NovaSS]

Yea the general consensus for Ev of all engines I've seen so far is 75-90%, I was just wondering if anyone had a actual number I could use for a stock motor. I figure if I use a close to accurate number, after a port job it would be better than expected.

Have you ever looked at an exhaust port in a b3? anything would help.

[Christ]

Volumetric efficiency literally means the amount of available cylinder volume being drawn per intake stroke.

If your engine is 1ml, and it is capable of filling completely on it's intake stroke, it would have 100% VE.

Engines with boost, and many N/A engine designs have VE in excess of 100% in parts of the RPM range. Things like Helmholtz tuning (frequency charging) will effect VE.

VE also has a direct affect on "dynamic compression ratio", or the ratio of the actual volume being compressed versus the volume of the chamber at TDC.

Larry Widmer has a few nice articles on this at www.theoldone.com in the archives.

[blkfordsedan]

Volumetric efficiency literally means the amount of available cylinder volume being drawn per intake stroke.

If your engine is 1ml, and it is capable of filling completely on it's intake stroke, it would have 100% VE.

Engines with boost, and many N/A engine designs have VE in excess of 100% in parts of the RPM range. Things like Helmholtz tuning (frequency charging) will effect VE.

VE also has a direct affect on "dynamic compression ratio", or the ratio of the actual volume being compressed versus the volume of the chamber at TDC.

Larry Widmer has a few nice articles on this at www.theoldone.com in the archives.

Good explanation. :p

Yea the general consensus for Ev of all engines I've seen so far is 75-90%, I was just wondering if anyone had a actual number I could use for a stock motor. I figure if I use a close to accurate number, after a port job it would be better than expected.

For perspective, a really well designed and built N/A performance street motor (pretty radical) will have a VE in the low 90% range. I just ran the Dyno2000 program on my B6 SOHC last night. With ported head (estimated the flow), FMS cam, 9.4:1 CR and small tube open header, it calculated a peak VE of about 88% at 5500 rpm. Max hp was 113 @ 6000. Changing to a high performance exhaust manifold with muffler lowers the VE to around 86% and 105hp. Keep in mind that I don't know the actual head flow or FMS cam specs, however, I have done a lot of research, comparisons and playing around with the program. the output numbers seem to all fall in line as expected and I would bet a chicken nugget happy meal that I'm pretty darn close.

A lot of the older muscle cars had a VE in the low 80% to 83% range. Keep in mind that modern engine design is much improved and the old muscle cars were rated at GROSS hp and not NET. The NET HP/CID of the B3 is right up there with many of the '60s muscle cars. That said, I agree with NovaSS and would estimate a completely stock B3 somewhere in the same low 80% range- maybe 80% to 82%. If I get a chance tonight, I'll run a few simulations on a stock B3 and see what it says.

[91mcnasty]

I wish I was half as smart as a couple of you guys.

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@blkfordsedan, that's some hardcore tuning :p what size is the exhaust ports on your "performance header"? The diameter of the pipes may be too big to keep the velocity exiting the chamber up? Is it port matched? What's it shaped like?

I don't know how that program got the Ev number it gave you, but to calculate airflow, multiply cidxrpmx0.5xEv and divide by 1728

B6=1597cc=97.454(97)cid
97x5500x.5x.88/1728=135cfm @5500rpm

I was actually after some bp numbers, but these will work as something for me to play with. Are you planning on turbo'ing your b6 or you keeping it NA?

Arty was supposed to get an fms cam card I believe, it would be nice to see what kind of difference it made in the valve timing.

[blkfordsedan]

Desktop Dyno is a dyno "simulation" program. IIRC, it's based on actual dyno pulls and trending the results as opposed to actually calculating the physics.....or something like that. I don't understand how it actually works, but from what several noted performance gurus and publications have said, it's supposed to be very accurate to real world results. I believe Hot Rod Magazine or someone similar actually did a motor build based on the program and then did the actual dyno test. The results were within like 5% or something crazy like that.
It does not specify the header tube size, it just gives you simple options like stock manifolds w/mufflers, high performance manifolds w/mufflers, small long tube or large long tube headers with or without mufflers or stepped race headers. You can add your own airflow files for heads or use some default values. You can also use your own cam specifications or import a specific cam from a huge file on a seperate disc. In other words, you can down load the cam specs from a Crane cam available for a 460 Ford and use them in a dyno pull of a 348 International Harvester V8.
Needless to say, it's hours of fun!

I doubt I'll ever turbo my B6, but who knows. I'm going to use the stock B6 long runner exhaust manifold. The stock manifold runner size is actually plenty large for a B6 and slightly larger than the port size in the head. The big choke point is the collector area and the tiny down pipe. The manifold outlet is 1.75"ID and stock down pipe is only 1.5"ID. I have a custom down pipe built out of 2.125"ID mandrel bent pipe and will be doing some serious porting on the manifold outlet.
I will also be using a degree wheel to map the valve timing events of the FMS cam. I'll post all the info in my build thread when I do, so others will no longer have to wonder what the specs are. I've also considered having a local place put my ported head on a flow bench to get a good idea of what these SOHC heads actually flow. It just depends on what they will charge me. Sometime in the next couple weeks I'll be posting some pics and updates in my build thread.

[91mcnasty]

looking forward to it!!

[FestYboy]

Arty was supposed to get an fms cam card I believe, it would be nice to see what kind of difference it made in the valve timing.

yeah, the card never showed up.... kinda ticked about that

[blkfordsedan]

Ran a quick pull on a stock B3 using estimated head flow and stock default for stock camshaft. Came up with 63hp at 5000 and a VE of 82 pct.

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Haha love the 2000 rpm hp numbers! I almost always kept my b3 under 3500 rpm. I may have revved it to 6k twice. Kinda suprising the hp doesn't peak till 4500 with the torque peaking @ 35, where's the most pulling power at?

That is a pretty neat program you have, what do you mean your using an estimated head flow? How are you getting that number? J/w..

[blkfordsedan]

You have to kinda take it with a grain of salt...the results are only as accurate as the input (crap in - crap out). However, the 63hp would indicate the VE is probably pretty close.
The power/tq curves are most likely off, since the head flow and cam specs are guestimated.
I have a fairly extensive list of head flow values for a wide variety of heads. I've messed around with it a lot an came up with an estimated flow based on similar head designs. Once you find a flow value that produces results that coincide with known values,you know your in the ballpark. You begin to notice trends in factory head flow based on displacement and power output. Increasing head flow outside of the optimum window results in a decrease in power. You also notice a trend in the increase of flow for ported heads over factoy stock, in terms of percentage. Basically, I'm just guessing, but based on somewhat reasonable examples.