CC ing chambers

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Truckedup
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CC ing chambers

Post by Truckedup »

How close to you match the chamber volume? Does it make for a smoother running engine. A builder who seems to know something claims he gets 70 cc chambers with .2 cc's of each other....Is this close practical or possible?
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hoodeng
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Re: CC ing chambers

Post by hoodeng »

This depends on the cylinders capacity. With a 845cc cylinder i would be ok with within .2cc on the money is much preferred.
If you are dealing with a 325cc cylinder 1cc variance is equal to .2 of a point of comp.
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Re: CC ing chambers

Post by rustbucket79 »

Any head center can get valve heights the same, leaving the chamber themselves the controlling factor in the head for chamber volume. A little tidy up as required will finish the job.

That being said, you still are relying on mixture quality and airflow to be identical in all 8 cylinders which they aren’t, never mind tolerance stack up with stroke, rod length, piston compression height, etc.

It’s great to shoot for perfection, but you’d never know the difference in a running engine.

Edit: I was referring to balancing chamber volumes on an 8 cylinder engine. Swept volume as mentioned plays a significant role, what engine are we talking about OP?
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Re: CC ing chambers

Post by ProPower engines »

Truckedup wrote: Sun May 02, 2021 8:09 pm How close to you match the chamber volume? Does it make for a smoother running engine. A builder who seems to know something claims he gets 70 cc chambers with .2 cc's of each other....Is this close practical or possible?
Absolutely
I have seen some shops that have done work on heads that just think the valves play no part in the running performance.
You must have the valves parallel to the deck face as well as the same depth in the chambers/ While most shops have no idea how to check this or for that matter do it that way.

Just sinking the valve in the seat to get a decent looking seat not only interrupts the short side flow but also enlarges that chamber significantly.
Its for this reason new castings are always better to start with then old used 50 year old Junk but guys only see the cost of the head castings as too much because they have OE castings they read and believe are just as good.
It takes a lot of work and effort to make good power producing heads and if every thing is the same hole to hole you have a chance to get even power balance all things considered it just costs more and most guys never see the extra time till they get the bill.............................. :lol:
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Truckedup
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Re: CC ing chambers

Post by Truckedup »

hoodeng wrote: Sun May 02, 2021 9:38 pm This depends on the cylinders capacity. With a 845cc cylinder i would be ok with within .2cc on the money is much preferred.
If you are dealing with a 325cc cylinder 1cc variance is equal to .2 of a point of comp.
Twin cylinder bike , 375 cc cylinders. So a .2 difference chamber cc would be .04 compression difference?
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hoodeng
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Re: CC ing chambers

Post by hoodeng »

Yes. Negligible as it is, for me it's more about keeping all my numbers as close as in a build. Bit like the .0005" range given as a piston/bore clearance, i would be well under half of that as a finished sizing. Consistency in our work.

This might be of interest to you Truck, this years results at Gairdner.
http://www.dlra.org.au/2021.htm

Cheers.
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Re: CC ing chambers

Post by Truckedup »

hoodeng wrote: Mon May 03, 2021 7:52 pm Yes. Negligible as it is, for me it's more about keeping all my numbers as close as in a build. Bit like the .0005" range given as a piston/bore clearance, i would be well under half of that as a finished sizing. Consistency in our work.

This might be of interest to you Truck, this years results at Gairdner.
http://www.dlra.org.au/2021.htm

Cheers.
Is any piston dome or dish volume figured in , or just chamber volume.?
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hoodeng
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Re: CC ing chambers

Post by hoodeng »

Being lucky [if that is the correct word] enough to be only doing one brand of product, there is a wealth of data and tested outcomes on hand to be quite confident in what we can expect on the dyno for a given combo.

A number of things are given to us, we can easily calculate volumes, cylinders, gaskets, chamber wet outs. Piston crown volumes positive and negative are accurately given by the pistons manufacturers, [these have been wet out in the past to confirm their accuracy.]
If Wiseco or CP tell me a crown has a negative value on chamber volume of say -6cc to give me a calculated comp of say 11:1 in a 872cc cyl with a 85cc head and a 8cc gasket, from this i can adjust my final comp to suit the cam that will be used. The cam in this case has a in 55°@.053" close so we want around 10.75-10.8:1 comp for good street manners, after we sink the valves for seat shape we have a 87.5-88cc chamber, this will give us our target comp with no further machining, if we want more we can deck the head, decking -.12mm on this head will gain a .1 of comp, this repeated cut remains pretty constant as the chamber is stadium shaped and has pretty straight sides for around 2.5mm up.

Conversely if we have a chamber that we don't want to deck [possibly because of valve to piston, cam timing etc] and the comp is higher than our target we can deck the piston providing there is enough under-crown thickness, i use a minimum of .200" for crown thickness, a good set of scales helps here as 1cc of forged crown material weighs 2.7g. This is only one method for example.

The biggest mistake i see made when guys calculate comp, is when they presume something is a given volume without measuring, how many times have we heard " Just deck the head ... you will have that much comp" or, the last one was 85cc the one before was 85cc, so, they all must be 85cc... wet it out, there is nothing like finding something is not what is claimed. We know what standard head thicknesses/heights are so we know if it has been decked in the past, but i have found with some NC chambers claimed and actual are not the same, as is with valve depths, a 2" valve dropped [from std protrusion] .040" is 2cc . This brings another variable, valve manufacturers provide shorter o/s valves that when installed at -.040" have the same stem protrusion as stock, so you need to check lengths against each other to see where the bench mark is. This can also apply to seats that have been replaced and blended into the chamber,,,looks stock? it ain't, get the burette out.

One caveat on this is that all calculations are true only if squish clearance is .040" [in this case] this needs to be checked on disassembly. in this engine compression height is 1.085" this is used for performance forged pistons and standard cast pistons fairly consistently, i get customers to check the squish on disassembly with two pieces of solder .080"ø 10mm long placed over the pin bores at 90°and get them to send me the pistons and gaskets used for the test, from there squish is easy to calculate and adjust if reqd.

Cheers.
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Re: CC ing chambers

Post by Truckedup »

This stuff is above my pay grade....The shop I use has a Newen valve machine so the stem protrusions are all exactly the same and on spec.....
I did do CC and compression ratio calculations based on .032 squish with domed pistons on one of my street bikes. It did come out as planned but the math and measuring was exhausting for me... #-o
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Re: CC ing chambers

Post by ProPower engines »

When cc'ing things that are for class racing rules the most common thing guys forget is the volume from the top of the piston to the top of the top ring in their final measurements and loose a bit.
Not alot but its still there. I think that NHRA allows 1cc variance for that where others do not allow past what the real world amount is when measuring compression. Nascar comes to mind there :roll:
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Re: CC ing chambers

Post by dannobee »

nascar officials commonly use that Katech Whistler thing for checking compression, which brings up another point (pardon the pun). Be cognizant of how the officials will check the compression ratio. Carefully observe their method for checking and compare their results with your own measurements.
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Re: CC ing chambers

Post by hoodeng »

You are right PPE crevice volume is a given factor in comp, but as we are pretty much only dealing with the active area of the chamber and use the same calculations every time this becomes a constant.

I know the crevice/volume area is in the active zone but it does not contribute greatly to the combustion process in regards to HP, although this area in emission compliance is of concern as far as un-burnt fuel contamination in exhaust.

And as pointed out, the fine dust particle rules of Nascar would have a clause about this. As far as i can see, every rule in Nascar was bought about by a guy stretching a previous rule.

Cheers.
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Re: CC ing chambers

Post by ProPower engines »

dannobee wrote: Thu May 06, 2021 10:18 am nascar officials commonly use that Katech Whistler thing for checking compression, which brings up another point (pardon the pun). Be cognizant of how the officials will check the compression ratio. Carefully observe their method for checking and compare their results with your own measurements.
Unless you are given the option to disagree with it which in my case happened it was wrong and we had to tear down at the track to measure things. We were considered over and DQ'd till I brought up the small yet still measurable volume between the top ring and top of piston. They conceded after that and we got the win money =D>
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Re: CC ing chambers

Post by Truckedup »

I land speed race bikes at tracks other than Bonneville. Same rules but no tear downs or protesting because it's not an International record event like Speed Week and no prize money or trophy, just a fancy time slip.



Race what you bring that passes the safety, and take the man's work for what's inside.
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Re: CC ing chambers

Post by dannobee »

ProPower engines wrote: Sat May 08, 2021 2:03 am Unless you are given the option to disagree with it which in my case happened it was wrong and we had to tear down at the track to measure things. We were considered over and DQ'd till I brought up the small yet still measurable volume between the top ring and top of piston. They conceded after that and we got the win money =D>
There are a few ways to...how should I say this...influence the reading of the Katech Whistler. The easiest is the temperature. If you don't get the reading you like, retest at a different temperature. Usually you can stall, obfuscate, question the equipment's calibration, conditions, etc., long enough that the engine cools down and the Whistler gives a different, more favorable reading when retested. And the cylinder/piston will cool down quite a bit faster with the spark plug out. And since people are inherently lazy, use your people skills to get the official to use the car's water temp gauge instead of a thermometer inside of the cylinder. Since Whistling is usually used in conjunction with"the bubble tool" to check displacement, the two rockers are removed. Use this to your advantage. A crafty racer can tap on the valves with a hammer (in full view of the official, "to seat the valves"), allowing a bit of fuel in the cylinder that will skew the reading of the Whistler.
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