UCCR

[THE358BANSH]

Question for the original poster, how do you like that BiMotion software? I have and use TSR and like it. I never found the computer calculations of cc volume to ever be what the actual cc volume is that i measure with my burette filled with kerosene. I just do it the trusty burette way and know the actual. Some the calculations on paper or in theory, don't quite seem to equal what the real world measurements are.

 

I have never used the BiMotion software. The TSR software is the universally accepted standard, but sucks now because Tom is no longer handling everything. I would like to get my hands on a copy at some point in time to do some comparing. If I remember correctly the TSR software also has a recommended octane starting point based off inputted figures and dome profile, right? The burette has its issues also with fluid sometimes not getting into every crack and crevice, along with people getting carried away when applying the grease seal. I think the best way to figure all of this would be FPV the dome with a spark plug, then account for other volumes by software/calculation to arrive at a compression value. Then use software of choice to determine the MSV of the entire package... Evan

[locogato11283]

Kick ass thread!

 

Maybe some of the other builders will share some input.

[trickedcarbine]

This thread can get really good. I hope people with higher knowledge of this subject can do a little more sharing here. These motors still have more room to grow and it is exciting to see what people are uncovering with experience and R&D. I wonder if we will touch on squish band width and clearance in relation to performance.

[sheerider11]

This thread can get really good. I hope people with higher knowledge of this subject can do a little more sharing here. These motors still have more room to grow and it is exciting to see what people are uncovering with experience and R&D. I wonder if we will touch on squish band width and clearance in relation to performance.

Yeah squish will be good to touch on. I would also like to know more about dome design. Like why builders cut at certain angles and how that directly relates to pipe choice.

[mopar1rules]

I have never used the BiMotion software. The TSR software is the universally accepted standard, but sucks now because Tom is no longer handling everything. I would like to get my hands on a copy at some point in time to do some comparing. If I remember correctly the TSR software also has a recommended octane starting point based off inputted figures and dome profile, right? The burette has its issues also with fluid sometimes not getting into every crack and crevice, along with people getting carried away when applying the grease seal. I think the best way to figure all of this would be FPV the dome with a spark plug, then account for other volumes by software/calculation to arrive at a compression value. Then use software of choice to determine the MSV of the entire package... Evan

I hear ya about Tom retired and not supporting his software any longer. Yes TSR gives octane estimates, but I'm 100% sure its based off of the UCCR and not dome shape. I don't recall the octane requirement change when I played with the head design package. I only notice the octane requirement change when I play wih the compress program. You don't have Bi-Motion? Your picture looks just like Bi-Motion. What program do you have then? Yeah I hear ya about people possibly getting carried away with the sealing grease. I give only enough for the head and gasket to seal and no oozing goes on. IMO I do it very accurately. Everyone has there own way I guess. I just never had the cc volume program answer equal what my actual measured amount. I don't know if the creator of the software has his formulas round to high up or whatever and that's where my differences come from, but I just continue to measure with the burette and SOMETIMES use the software to get me in the ballpark.

[Wildcardracing]

I have found that software, while it may get you close is limited to the experience and theories of the software designer. There is no replacement for trial and error R&D. Area, volume and MSV calculators are the only software I use. I come up with my dome designs and port layouts based on real world trial and error. Just as the theories discussed in Jennings and Bells books are a good starting point, but not going give you the "beat all/end all" build if strictly adhered to.

As for piston dome volume, I haven't found an efficient method of cc'ing one without using a dome volume calculator. I use a berret to cc head domes and cylinders though. But, as mentioned the results are only good if done with precision and repeatability.

 

-Brandon

[THE358BANSH]

To add some more to this thread about piston dome volume I played around for a bit today while parts were washing. I weighed a 65.5mm 795 series Wiseco with no rings, no wrist pin, and no wrist pin bearing. Total weight of the box stock piston was 207 grams. I chucked in in the lathe and turned .160" off the dome to make it a flat top. Total weight of the flat top piston was 188 grams.

 

Original piston weight 207 grams - Flat top piston weight 188 grams = 19 grams of material removed

 

19 grams removed x .0022 lbs/gram = .0418 lbs of material removed

 

.0418 lb of removed material / .0980 lb/in³ weight per in³ of aluminum = .42653 in³ of material removed

 

.42653 in³ x 16.387 cm³/in³ = 6.989 cm³ of piston dome volume

 

Obviously that number will change with piston series, bore size, and if the dome angle as been modified.

[mopar1rules]

Someone likes math and making sure their Texas Instruments scientific calculator still works. Lol.

[Makr]

I hate to see some good thinking slide into oblivion, so I will throw in.

 

THE358BANSH, your numbers look good to me on your cut dome. I drew it as a solid model in solidworks and came up with pretty close numbers.

 

120mm radius with .160 from the peak. 18.399 grams and a volume of .413 ci. .413 x 16.387 = 6.767 cc

 

I am sure there is a variance in dome profile from your piston to my drawing that would explain the minor differing in values.

 

 

 

I don't remember exactly where it came from. I want to say either the old MacDizzy site or a RZ350 forum, one of those two almost positive.

 

As for the dome profile, I just went next door and looked at a 795 series for a 65mm bore because it's all I have around now. I measured it up and I am coming up with 10.32cc? Seems a bit far out and in the wrong direction to me...

 

As best I can measure here is the cross section of the piston dome profile...

 

 

This dome has a weird radius but I drew it to compare numbers. I plugged in the exact dimensions from your drawing.

 

.495 ci = 8.11 cc

 

 

 

So my question is: what values are you guys shooting for in compression and squish velocity? Are you setting a standard at static? Do you do a comparison to what you think is happening at different RPM ranges?

 

Seems to me there would be drastic changes in both compression and squish velocity as the rod/crank/piston stretch at different RPMs. The pistons just start to leave marks on the combustion chamber on my RD400 at 10,000 RPM with squish at .02.

[Wildcardracing]

So my question is: what values are you guys shooting for in compression and squish velocity? Are you setting a standard at static? Do you do a comparison to what you think is happening at different RPM ranges?

 

Seems to me there would be drastic changes in both compression and squish velocity as the rod/crank/piston stretch at different RPMs. The pistons just start to leave marks on the combustion chamber on my RD400 at 10,000 RPM with squish at .02.

 

This by chance Mark? Tried calling you the other day.

 

As for your question, there are some things I won't share. However I establish sqiush velocities based on fuel and application then use a standard rpm to calculate them even if the engine may not achieve that rpm. This give's me a constant to work with. In my opinion, if you're getting piston to head contact within your motors operating range your squish clearance is too tight. You can achieve the same MSV numbers by changing the band design and loosening the squish clearance some.

 

-Brandon

[Wildcardracing]

To add some more to this thread about piston dome volume I played around for a bit today while parts were washing. I weighed a 65.5mm 795 series Wiseco with no rings, no wrist pin, and no wrist pin bearing. Total weight of the box stock piston was 207 grams. I chucked in in the lathe and turned .160" off the dome to make it a flat top. Total weight of the flat top piston was 188 grams.

 

Original piston weight 207 grams - Flat top piston weight 188 grams = 19 grams of material removed

 

19 grams removed x .0022 lbs/gram = .0418 lbs of material removed

 

.0418 lb of removed material / .0980 lb/in³ weight per in³ of aluminum = .42653 in³ of material removed

 

.42653 in³ x 16.387 cm³/in³ = 6.989 cm³ of piston dome volume

 

Obviously that number will change with piston series, bore size, and if the dome angle as been modified.

I come up with 6.785cc dome on a 65.5 piston. One thing not taken into account in your calculation is alloy. That Wiseco is not pure aluminum, it is a high silica alloy and will have a slightly different weight per volume. Interesting how you figured that, and gave you much closer figures. Would become quite expensive to cut a piston everytime you built a motor just to establish dome volume.

[Makr]

 

This by chance Mark? Tried calling you the other day.

 

As for your question, there are some things I won't share. However I establish sqiush velocities based on fuel and application then use a standard rpm to calculate them even if the engine may not achieve that rpm. This give's me a constant to work with. In my opinion, if you're getting piston to head contact within your motors operating range your squish clearance is too tight. You can achieve the same MSV numbers by changing the band design and loosening the squish clearance some.

 

-Brandon

 

Hey Brandon, I suck at the phone. Text me and I will call you back.

 

I dont run at .02 squish, but I have no idea how else to check dynamic stretch other than seeing a witness from a running engine.

[trickedcarbine]

Another question I am pondering. I have heard a little info on this but can no longer find it.

What exactly happens to the motor with say a wider squish band that is on the tight .045 side and a dome that has a wide squish with a looser clearance, say .060? Then also a dome that is to be considered a narrow squish band on both the tighter and looser side?

[Wildcardracing]

Hey Brandon, I suck at the phone. Text me and I will call you back.

 

I dont run at .02 squish, but I have no idea how else to check dynamic stretch other than seeing a witness from a running engine.

Guess you found the limit lol. I have seen a couple of engines do this as well. It's not good to see piston numbers stamped into the squish band.

 

Another question I am pondering. I have heard a little info on this but can no longer find it.

What exactly happens to the motor with say a wider squish band that is on the tight .045 side and a dome that has a wide squish with a looser clearance, say .060? Then also a dome that is to be considered a narrow squish band on both the tighter and looser side?

 

Wider squish bands (within useable limits) usually improve burn efficiency at lower rpms, divergency angle and combustion chamber shape also play a part here. Too tight of squish clearance can lead to piston-head contact and/or detonation. Squish band width and clearance are directly related to MSV. Ideal MSV numbers are dictated by several factors and influenced by several parameters. Loosened squish clearance can shift the heat range in the pipe/s making them act longer at some rpm's, effectively smoothing the curve on some engines. There are many factors at work here, very briefly touched on.

-Brandon

[trickedcarbine]

Thanks Brandon. Now you got my gerbal wheel spinnin' and I'm trying to come up with other valuable questions.