[LotusElise]

Connecting rod measurement calcualtion for an inquire - please help!

Hi folks,

I just have a few question to you, as it will get my first K-series engine build . I listed below my calculation table and with my question to it (unit is zoll and mm in brackets).

• Compr. Height 1.181 (30.00)
• Big End width 0.935 (23.75) according to http://www.k20a.org/forum/showthread.php?t=70447
• Big End bore 2.008 (51.011) to 2.0088 (51.024) according to ACL bearings
• Pin End bore 0.8664 (22.01) according to http://www.k20a.org/forum/showthread.php?t=70447
• Pin End width 0.780 (19.81) according to http://www.k20a.org/forum/showthread.php?t=70447
• Rod C-t-C 6.098 (154.88)
• Piston-t-Deck -0.045 (-1.14) according to Nyborg post #6, there are also recommendations of -0.030 to -0.060 in other engine forums
• Decking -0.005 (-0.13)
• Gudgeon pin offset 0.034 (0.87) - took this value from a stock K24A3 piston. Are there any different recommendation on that?
• Deck height 9.114 (231.50)
• Stroke 3.571 (90.70)

This is for a destroked K24 with a new F22C1 crankshaft (part # 13310-PZX-A01) and stock K20A2 head. The the piston will be new and customized, so I have to fix values for the block for now and adapte evtl. negative claying results via head gasket thickness or machining of the piston later on.

Thanks in advance for your help.

 

[LotusElise]

Luag holt ning do ...not to say anyone with advice?

 

[LotusElise]

Anyone, who can help?

Get already quotations from Cunningham, Arrows and ZRP...260-600 $/rod. Having the validated correct measurement of the piston rod would be anyhow of importance when drawing has to be signed for the final production order.

Thanks in advance.

 

[LotusElise]

Where are all that engine builders gone? Is there something wrong with my question :what:? Not understandable?

I would like to measure it by myself, but I still have no K24 block, so no chance for disassembling and measuring by my self.

Would appreciate your help.

 

[LotusElise]

Did another two inquiries at Hoeckle.com piston (result = no offers for K24 block) and Pankl.com piston. Next will be at Krause-Mauser.com.

Still would appreciate your help.

 

[Nyborg Garage]

Re: Connecting rod measurement calcualtion for an inquire - please help!

Depending on how far you want to push the piston speeds, but you need about 0.045in piston to head clearance. I have experienced that the hard way.

Sent fra min D5503 via Tapatalk

 

[Nyborg Garage]

Re: Connecting rod measurement calcualtion for an inquire - please help!

And remember if you overbore the cylinder, the piston will first hit the edge on the outside of the combustion chamber, unless you machine the head to match the bore.
You can also have zero piston to deck, mill the head til the squish area is even with the deck, and use a 0.045" cometic gasket.

Sent fra min D5503 via Tapatalk

 

[LotusElise]

Re: Connecting rod measurement calcualtion for an inquire - please help!

Depending on how far you want to push the piston speeds, but you need about 0.045in piston to head clearance...

Thanks Nyborg, very valuable experience :up:...I will limit it to 27.5 m/s (mean) for oil distribution reasons. Does that change your deck clearance advice?

 

[LotusElise]

Re: Connecting rod measurement calcualtion for an inquire - please help!

And remember if you overbore the cylinder, the piston will first hit the edge on the outside of the combustion chamber, unless you machine the head to match the bore.
You can also have zero piston to deck, mill the head til the squish area is even with the deck, and use a 0.045" cometic...

Yes, it will be +0.5 mm overbored :up:...to set for a squish height of about 1.6-1.8 mm (not sure about the ideal one, quenching vs. accelerating) without P-t-V or P-t-H contact even @11 krpm (= safety limit, [email protected] krpm) will be the challenge. Once the rods are ordered, solutions for that issue will compromise other things like possivle VTC range, which is for that hill climb racer very important.

So, many thanks for your advice !

 

[Nyborg Garage]

1.6mm clearance (squish) will be more than enough.

If you know what cams to use, you can design your pistons for the perfect valve to piston clearance. In theory.

In reallity, I think there will always be a piston to valve contact problem on the k-series (with big cams), if you want to run as much VTC as possible. So in reality you just want as deep valve pockets as possible, and then limit vtc to what ever clearance you want.

 

[LotusElise]

1.6mm clearance (squish) will be more than enough.

Ok, thanks...motivated me to do some research . According to e.g. Harold Bettes there is a thumb rule for squish heigth calculation (steel rods): 0.005 * bore [in] = squish height [in]. For high engine speed concepts there should be 0.005" to 0.010" added. So for the case of a 89 mm bore, steel rod and high rev engine it would be 0.64 mm. This is a great challenge to reach as it is so tiny and the tolerances in that game are about 20 % of it. Is that something you would say aim for that?

...So in reality you just want as deep valve pockets as possible, and then limit vtc to what ever clearance you want.

I plan with stage 2 cams and Wiseco pistons K650M89AP...VTC of 40-45° should be possible.

 

[Nyborg Garage]

Re: Connecting rod measurement calcualtion for an inquire - please help!

Custom rods are usually very expensive, custom pistons not so much. So I would go custom with both. (have them design a perfect piston for your app, then design the custom rods to fit). Narrow rings, maybe smaller (tool steel) bolt, shorter piston height (longer rod), lighter piston, and so on.

4piston have done a few custom rod/piston combos for road race apps.

That is roughly the same ideal squish as I have read other places (books), but this is for perfect burn/power, not for safe clearance . That is why your formula does not account for rod length and stroke. If you run 0.64mm your pistons will hit your head. (btw, I have run much less squish than that on other smaller engines).

I would look in to the new ultra 1 or 2 cams. Much better primary lobes from all graphs I have seen, and better vtec also.

Sent fra min D5503 via Tapatalk

 

[LotusElise]

Re: Connecting rod measurement calcualtion for an inquire - please help!

Thanks Nyborg, very valuable information!

Custom rods are usually very expensive, custom pistons not so much. So I would go custom with both. (have them design a perfect piston for your app, then design the custom rods to fit).

After getting three quotations for connecting rods fitting in a 87x90.7 K24-block I calculated some alternatives, not for cheaper build but for a less risky one concerning the squish clearance result: 89x86 (2144 ccm, K20 block). As you said, custom pistons are more cheap and for reference I can easy measure my own engine :up:. The risk no is more shifted to get the block sealed perfectly and inline with the ideal vertical axis of the piston movement. Just for having an alternative...but it has also an great charme to me...bad ass rev engine with an even better VE production as the K24 short stroker...a further tiny step to the IMEP 19 [email protected][4.5;8.5] krpm goal.

Narrow rings, maybe smaller (tool steel) bolt, shorter piston height (longer rod), lighter piston, and so on.

Like a wish list for Christmas ...I still think of an compensation technique, beside the right squish, for the bigger bore. A faster combustion, also the possibilty to shape the heat release curve for lower knock propensity and shorten the ignition delay time would be a nice project goal.

4piston have done a few custom rod/piston combos for road race apps.

Do you have experience with compression height's of 28.5 mm and lower? The 3rd ring land will get cut by the bore for the piston bolt...doesn't have it an maybe negative influence on the tribology? Anyway, the effect of an R/S of 1.63 instead of 1.62 don't touch the piston movement in the combustion relevant zone, the rod bolt forces are reduced due to the marginal lower piston acceleration just by about 100 N, the side load reduction...did I overseen something of value? Please open my eyes, my knowledge in the high revving sector is very low, I would appreciate your experience and knowledge on that.

That is roughly the same ideal squish as I have read other places (books), but this is for perfect burn/power, not for safe clearance . That is why your formula does not account for rod length and stroke. If you run 0.64mm your pistons will hit your head. (btw, I have run much less squish than that on other smaller engines).

Ok, we get nearer to the best compromise ...((1.64+0.64) / 2) mm = 1.14 mm (= squish velocity of about 54 m/[email protected]° BTDC!). What do you think about that?

I would look in to the new ultra 1 or 2 cams. Much better primary lobes from all graphs I have seen, and better vtec also

Mmmhhh...have no profile data of them. Skunk2 has some nice valuable parts like their nice designed ProSeries-TB, but also some other parts of lower quality and design...beside the valve motion effect on the engine behaviour, are there any endurance experiences already available?

 

[LotusElise]

Re: Connecting rod measurement calcualtion for an inquire - please help!

Ok, we get nearer to the best compromise ...((1.64+0.64) / 2) mm = 1.14 mm (= squish velocity of about 54 m/[email protected]° BTDC!). What do you think about that?

Estimated thermal and mechanical lenghtening and got with the above mentioned ideal squish clearance a minimum height of 0.91 mm without concerning of measurement tolerances of block height, rod and crankshaft lenght, compression height, gasket thickness and casting tolerances of the cylinder head.

Any ideas for that?

 

[Nyborg Garage]

Re: Connecting rod measurement calcualtion for an inquire - please help!

I have experience using extremely short piston on the B-series. 11mm shorter than stock. Arias two ring piston with buttons (oil rings keep the button and bolt in place). The main reason is not R/S but weight and most of all friction.

I have pictures if you would like to see. It me up on FB, Karl-Kristian Moeng at Nyborg Garage email [email protected]

Sent fra min D5503 via Tapatalk

 

[LotusElise]

Re: Connecting rod measurement calcualtion for an inquire - please help!

...The main reason is not R/S but weight and most of all friction...I have pictures if you would like to see...

Thank you Nyborg,
very kind of you, I appreciate that much...email is on the way to Norway .

Markus