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Help in Selecting Correct length for a Connecting Rod
http://prodracing.com/viewtopic.php?f=7&t=18947
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Author:  March 79B [ Mon Feb 04, 2019 2:23 pm ]
Post subject:  Help in Selecting Correct length for a Connecting Rod

Could any one on the forum provide information on the correct length of a connecting rod for the following engine? Here are the Specs: Cylinder Block deck height: 9.29" or 236MM, Stroke: 3.40" or 86.4MM Gasket thickness, Variable, but using 0.065" or 1.65MM. Pistons specs are as follows: Piston "A" has a compression height of 1.32" or 33.5MM, Piston "B" has a compression height of 1.20" or 30.6MM. The Pin diameter is variable at .787" or 20MM with an alternate pin at .827" or 21MM. Piston "A" has a deck clearance of 0.027+ (POSTIVE) or.069MM and Piston "B" will have a Deck clearance of "0" with a 15CC dish. Am working for a "ZERO DECK". Thanks for any information and insight!! Jerry

Author:  Protech Racing [ Mon Feb 04, 2019 5:37 pm ]
Post subject:  Re: Help in Selecting Correct length for a Connecting Rod

If you draw it on white paper , you should be able to get the rod sizes. Use metric for simpler math IMHO.

I always engineer around common parts. In my case I use the VW rods @ 144mm and set the deck height around stock bits and simply make stuff smaller. Deck the block a ton and top the pistons to my deck size of minus 026.

Author:  FP Racer [ Mon Feb 04, 2019 8:38 pm ]
Post subject:  Re: Help in Selecting Correct length for a Connecting Rod

We all know rod length is not free, right?

Bought a pro built motor from someone who had bought it from someone who bought it from someone, etc. I knew who built it from serial number. It had the wrong length rods. Wow and was I shocked.

Author:  March 79B [ Tue Feb 05, 2019 3:12 am ]
Post subject:  Re: Help in Selecting Correct length for a Connecting Rod

The engine I am building is not going to be checked for any legal/non legal items, I am just asking a basic question for an engine build. Thanks, Jerry

Author:  FP Racer [ Tue Feb 05, 2019 6:51 am ]
Post subject:  Re: Help in Selecting Correct length for a Connecting Rod

Figured that but it was a great opportunity for a reminder. With the free rods, it might tempt someone to make the change. And we do check them at the Runoffs. Be a shame to lose because of that oversight.

This is a great place to ask questions like that because of the wealth of knowledge. Glad you got a quick and to the point answer. Years ago, you would have never gotten an answer. Great time to be a newbie. Wish I were just starting and had all the chances to ask. I would save a fortune in destroyed parts!

Author:  engineerted [ Tue Feb 05, 2019 9:01 am ]
Post subject:  Re: Help in Selecting Correct length for a Connecting Rod

ok, someone can check the math. i just used the cal for this site: http://www.wallaceracing.com/rod-length-calc.php

33.5mm CH pistons assuming zero deck= 159.3mm rod length
30.6mm CH pistons assuming zero deck= 162.2mm rod length

Just plug the numbers in and go!

Author:  March 79B [ Tue Feb 05, 2019 11:51 am ]
Post subject:  Re: Help in Selecting Correct length for a Connecting Rod

Thanks for the information. I had used the "Wallace Rod Length Rod Calculator" but just wanted to be sure before going forward. THANKS!!!!!! Jerry

Author:  Protech Racing [ Wed Feb 06, 2019 6:55 am ]
Post subject:  Re: Help in Selecting Correct length for a Connecting Rod

Like I stated in my email to you, use the stock rod and Skim the piston tops to set deck clearance . Out the hole 10-20 works great with the common gaskets or 065 or 57 .

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