Is there any FLAPs tool that will determine displacement?

a set of calipers and a handheld calculator?

I love digital calipers, they are so handy and don't require the skill that the mechanical ones need to get a reading...

Harbor Freight has a cheap digital caliper.

Measure cylinder bore and piston stroke in the bore. Multiply together to get volume.

Multiply by 4 if it's a 4 banger.

Find the area of the circle of the bore, multiply it by the stroke. The Cap'n

Displacement would be figured as follows: volume of the cylinder times number of cylinders.

3.14 x bore/2 x bore/2 x stroke x #cylinders

3.14 is pi

bore/2 x bore/2 is the same as r squared or radius squared

My interpretation of his question is that he was asking if there's something he can use to determine this in an existing engine, not "what is the formula for volume of a cylinder?"

OK. The direct answer is: Yes, if your FLAPS sells handheld calculators and you paid attention to your 8th grade math teacher. Oh, and don't forget to add in the volume of your combustion chamber in the head. The Cap'n

I was aware of that, but since the answer is NO, I had a little fun instead.

At last, an opportunity to shoot the Cap'n down.
Combustion chamber volume has absolutely nothing, thats NOTHING, to do with displacement.
Engine displacement = swept volume period
Stick with mechanics bro.

We need a smiley for being shot down in flames ...............

OK, I paid attention to my math teacher, but it didn't take all that well. Thank heavens for geometry! I added that little qualifier as an edit. Guess I shoulda stuck with my original post. I forgot, it's SWEPT volume.

The Cap'n

pies are square. Oh, wait, that's Pi R Squared. Pi times the radius squared determines the area of a circle, any circle, even a tetherball court. Multiply the tetherball court by the stroke and that's your displacement.

Silly people. This isn't a geometry problem, it's a calculus problem. You see, you take 2pi*r*dr and integrate from 0 to R, where R is half your bore. Then you integrate that result (pi*r^2)dL from 0 to your stroke!

Pfft, geometry.

What The Cap'n meant was, without geometry, he'd still be in high school. What he didn't mean was that this is a geometry problem.

The Cap'n

in the isle next to the can of compression, muffler bearings and majic smoke.

check out, isle 5



mike

Thanks for dredging up those long repressed memories of High School

But since we are back there maybe Archemedes can help. This is just theory - there may be lots of reasons why it would not work so reload and open fire.

IF it is permissible to fill a cylinder with oil then:

1. Remove the plugs and park one cylinder at precisely BDC with the valves closed (ready for compression stroke).

2. Fill the cylinder with engine oil to the bottom of the sparkplug hole. You could rock the engine back and forth a bit to confirm you are at BDC.

3. Fit a collection tube into the sparkplug hole. It would want to fit snugly so that oil won't leak out. fill the collection tube with oil and maybe put an elbow on the top to make collecting easier.

4. Get a graduated beaker ready.

5. Sweep the engine up to and past TDC collecting the oil that spills out into the beaker.

6. Volume of oil in the beaker equals the displacement of the cylinder.

7. Figure out how you are going to get all that oil out of the cylinder.

Steve,
It's your engine. You decide what is permissable. Lots of effort though when all you need are the values of the two variables, bore and stroke. Do you have some reason to think your crank is not one of the stock throws?

There are setups that will do that, but I believe the accuracy is best summed up in two words: "Not very". Still, it could give you some idea. The margin of error may very well be larger than the difference between the popular displacements, though.

Do you know if you have 2.0 heads? Do you have 2.0 heat exchangers? Was the engine built on a 2.0 crankcase? Those won't tell you what displacement you actually have, either, but if they all agree that's a pretty decent indicator.

Or you can just pop the heads off to measure the bore and stroke. Then do the math as mentioned above. (If you really wanna do the calculus instead of the geometry, you're welcome to. But the geometry works just fine.)

--DD

Purely a thinking exercise Rob. Not sure what dflesburg's situation is but using a volume measurement might be useful if you don't want to pull the heads off to try to identify what sized jugs are on your engine. My original engine has oversized P&C's on a 1.7 block. That rebuild was done back in the 70's and any record of the work is long gone. I was pretty naive back then and all I can remember is that the engine was just below a 2l.

Dave has identified the problem though. Accuracy and repeatability. The difference between a 1.7 and 2l is only 30/4=7.5cc A little bit of dripping could skew the results pretty significantly. If I really want to know what jugs are on the car I'd have to remove the heads and measure it. Maybe though, since the engine is out and just sitting there, I'll try the volume measurement and see how close I can come.

Is it really that easy to just 'pop off' the heads?

Sure is! Only 8 nuts hold each one on!

...Of course, you have to drop the engine, pull off the engine tin (and all of the induction), yank the pushrods and pushrod tubes, yadda yadda yadda. But it's easy once you get in there!

--DD

2000-1700+300. 4/300+75cc, not 7.5cc. Pretty substantial difference/cylinder, last I checked.

The Cap'n

Thanks everyone. Interesting thread.

Hey - I said high school memories were repressed!

of course I was talking about centilitres and not cubic centimeters. that's my story and I'm sticking to it!

so each 0.1 liter is about 3 oz - 3 shots - I can visualize that! That should be measurable.

Yeah sure - and then you have to put it all back together again!

So you're suggesting that he use Vodka, rather than oil when he fills his cylinder to test?

Naw, too thin - would run past the rings. Pusser Rum would work much better.

Hmmm. We got a special tech one day. The marshalls plugged something in our spark plug hole. I was told it checked displacement, some sort of whistler. So they were f'n with me?

It does sort of. It's something like filling the cylinder with oil, but they measure the air. Still subject to a decent error margin, I would think. Air is much more compressible than oil.

--DD

Yeah, decent barely sums it up.... My thought is that it's like quantum physics, by measuring it you're compressing the air, and thus adding error. I don't think I'd trust any displacement method based on air to 30%, much less 3-5%. Now , this is just me thinking about the issue, but air is hugely compressible, non of my fluids homework even remotely applies to it....

PCA uses a whistler to check displacement on stock cars occasionally.... I've seen it used 2x in the past... both time the accuracy of the whitsler was enough to see one dq, and the other was ok.

I believe other organization use the whistler as well... Its the first check of an engine that is though to be out of spec inre displacement....rather than a full teardown..

Though really in PCA is someone going to insist on a full teardown of a suspect engine?

Someone else drinks that? The Cap'n

This was ALMS a couple of years ago. Apparantly we passed.

Do you think the tech officials found the whistler at their FLAPS?

So by the rolleyes are you suggesting I shouldn't have tried to provide input that something may be available to check displacement without tearing down the engine? Maybe not at the flaps, but probably online somewhere.