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Topic: Compression Email this topic to a friend | Subscribe to this TopicReport this Topic to Moderator
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Murphy
February 06, 2019 at 07:39:26 PM
Joined: 05/26/2005
Posts: 1212
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     What effect does compession have on the cost and longevity of a sprint car engine?




BaylandsRP
February 06, 2019 at 10:09:06 PM
Joined: 01/09/2013
Posts: 183
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Posted By: Murphy on February 06 2019 at 07:39:26 PM

     What effect does compession have on the cost and longevity of a sprint car engine?



$4,245 higher cost and 4.75 less races between overhauls per each compression point increase.   



Murphy
February 07, 2019 at 06:46:16 AM
Joined: 05/26/2005
Posts: 1212
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Posted By: BaylandsRP on February 06 2019 at 10:09:06 PM

$4,245 higher cost and 4.75 less races between overhauls per each compression point increase.   



     You're pulling my leg-right?



EasyE
February 07, 2019 at 07:05:04 AM
Joined: 10/29/2017
Posts: 158
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Less races between freshening for sure



BaylandsRP
February 07, 2019 at 10:14:42 AM
Joined: 01/09/2013
Posts: 183
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Posted By: Murphy on February 07 2019 at 06:46:16 AM

     You're pulling my leg-right?



A little bit- but the idea of the cost increase and fewer races between rebuilds is sincere.  We ran 12.5-13.5 compression in the 80’s. Typically 25 + races between major rebuilds.  Now, 15.0 + compression with lighter parts, and 12-15 races between rebuilds on our regional, but still quality 410s.  In reality, if we had a compression rule today, our engines would cost the same because we would still use the same quality parts and manufacturers, only lighter.    A Bryant crank would still be roughly $4,000 either way, etc.  Always too many variables for a real answer. 



revjimk
February 07, 2019 at 11:10:30 AM
Joined: 09/14/2010
Posts: 4425
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Posted By: BaylandsRP on February 07 2019 at 10:14:42 AM

A little bit- but the idea of the cost increase and fewer races between rebuilds is sincere.  We ran 12.5-13.5 compression in the 80’s. Typically 25 + races between major rebuilds.  Now, 15.0 + compression with lighter parts, and 12-15 races between rebuilds on our regional, but still quality 410s.  In reality, if we had a compression rule today, our engines would cost the same because we would still use the same quality parts and manufacturers, only lighter.    A Bryant crank would still be roughly $4,000 either way, etc.  Always too many variables for a real answer. 



Thanks for the knowledgable reply

So is compression the main reason for 200+ HP increase over the years? or what else?



BigDog
MyWebsite MyResults MyPressRelease MyPhotos MyBlogs
February 07, 2019 at 11:35:00 AM
Joined: 07/01/2006
Posts: 566
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Here is a article from hot rod that explains it pretty well 
The Power Squeeze Written by David Vizard on October 10, 2003


My Signature

Murphy
February 07, 2019 at 12:57:33 PM
Joined: 05/26/2005
Posts: 1212
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Posted By: BaylandsRP on February 07 2019 at 10:14:42 AM

A little bit- but the idea of the cost increase and fewer races between rebuilds is sincere.  We ran 12.5-13.5 compression in the 80’s. Typically 25 + races between major rebuilds.  Now, 15.0 + compression with lighter parts, and 12-15 races between rebuilds on our regional, but still quality 410s.  In reality, if we had a compression rule today, our engines would cost the same because we would still use the same quality parts and manufacturers, only lighter.    A Bryant crank would still be roughly $4,000 either way, etc.  Always too many variables for a real answer. 



     Thanks for the reply. I'm not mecanically inclined but I do have a good head for math and logic. Your post made sense at first but then the little man in my head said "Hey! wait a minute....".

     If I'm understanding this right, a 12.5 compression engine would cost about the same as a 15.0+ engine because they are basically made out of the same parts? But the number of races between rebuilds might be longer with the 12.5? Would the cost of rebuilds be the same on a 12.5 verses a 15.0+



racefanigan
February 07, 2019 at 01:06:53 PM
Joined: 07/31/2007
Posts: 191
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In my head, though I am not 100% sure as I have never really had engines of a far different Compression Ratio, but your rebuild costs should in theroy go up with higher compression, just for the simple fact that higher compression puts more stress on the internals. Though, the same could be argued that you are replacing the same parts at the rame rebuild interval, they are just closer together if that makes sense. Example, on a 12.5 CR engine, say you can go 25 shows between rebuilds and 12 shows between rebuilds on a 15.5 CR engine. You may replace your rods every 2 rebuilds, or your pistons every 2 rebuilds, etc, but rather than those replacements being after 50 shows on a 12.5 CR engine, they are every 24 shows on a 15.5 CR engine, even though that is still "2 rebuilds". Even though the rebuilds may cost around the same in general, they are more frequent in relation to each other. Again, I could be wrong, and the rebuilds themselves cost more, I have been out of the loop on that stuff for some time now. Bottom line, it ends up costing you more money no matter how you look at it lol.



Nickules
February 07, 2019 at 02:46:17 PM
Joined: 08/05/2015
Posts: 1132
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Posted By: Murphy on February 07 2019 at 12:57:33 PM

     Thanks for the reply. I'm not mecanically inclined but I do have a good head for math and logic. Your post made sense at first but then the little man in my head said "Hey! wait a minute....".

     If I'm understanding this right, a 12.5 compression engine would cost about the same as a 15.0+ engine because they are basically made out of the same parts? But the number of races between rebuilds might be longer with the 12.5? Would the cost of rebuilds be the same on a 12.5 verses a 15.0+



Not Baylands and he could probs answer better than me, but thought I'd chime in with essentially you are correct. # of races between rebuilds would be longer with a 12.5 compression vs 16 -16.5 which most 410s are nowadays. Higher compression = much more stress on internal engine components. Depending on track, conditions, etc. some outlaw teams "big track" engine gets rebuilt after 8 or so races (I've heard of one or two teams who rebuild their big track engine after 6 races). 12 - 15 races in a vacuum is pretty standard for most engines with Outlaw teams. But again sooooo many factors. 



Wesmar
February 09, 2019 at 09:32:58 AM
Joined: 09/29/2005
Posts: 602
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Posted By: BaylandsRP on February 07 2019 at 10:14:42 AM

A little bit- but the idea of the cost increase and fewer races between rebuilds is sincere.  We ran 12.5-13.5 compression in the 80’s. Typically 25 + races between major rebuilds.  Now, 15.0 + compression with lighter parts, and 12-15 races between rebuilds on our regional, but still quality 410s.  In reality, if we had a compression rule today, our engines would cost the same because we would still use the same quality parts and manufacturers, only lighter.    A Bryant crank would still be roughly $4,000 either way, etc.  Always too many variables for a real answer. 



  Baylands is pretty spot on.

  Compression = horsepower.  Most 410's are around 15:5 to 16:0, much more than that they get into detonation. 

  Like Baylands said, everything is exactly the same and yes to an extent you could go a little longer in between rebuilds.

  BUT no matter what these guys will still zing these engines to 9,200-9,500 (and sometimes more) RPM's.  In my opinion a compression and RPM rule would be a step in the right direction.



Wesmar
February 09, 2019 at 09:35:47 AM
Joined: 09/29/2005
Posts: 602
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Posted By: revjimk on February 07 2019 at 11:10:30 AM

Thanks for the knowledgable reply

So is compression the main reason for 200+ HP increase over the years? or what else?



Compression, cylinder head technology, injectors, and cam profiles are the main contributors.



Murphy
February 09, 2019 at 10:10:25 AM
Joined: 05/26/2005
Posts: 1212
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Posted By: Wesmar on February 09 2019 at 09:32:58 AM

  Baylands is pretty spot on.

  Compression = horsepower.  Most 410's are around 15:5 to 16:0, much more than that they get into detonation. 

  Like Baylands said, everything is exactly the same and yes to an extent you could go a little longer in between rebuilds.

  BUT no matter what these guys will still zing these engines to 9,200-9,500 (and sometimes more) RPM's.  In my opinion a compression and RPM rule would be a step in the right direction.



    A hundred years ago or so, I remember reading about a track in Rockford Illinois(?) that was touting a way to make racing at their track more affordable and increasing car counts. Among the "Rockford rules" was a compression rate of something like 11.5:1 and a tire rule. Of course, like everything else in racing those rules eventually got tossed out so guys with more money could buy faster cars. 

     I can visualize how you could have a compression rule. How could you have an engine RPM rule that would not in essense be like putting a governor on the cars? Would having a maximum(?) gear ratio rule prevent the advantage of running super high RPM's?



revjimk
February 09, 2019 at 12:48:39 PM
Joined: 09/14/2010
Posts: 4425
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Posted By: Wesmar on February 09 2019 at 09:35:47 AM

Compression, cylinder head technology, injectors, and cam profiles are the main contributors.



Thanks!



linbob
February 09, 2019 at 07:29:42 PM
Joined: 03/12/2011
Posts: 1212
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Posted By: revjimk on February 09 2019 at 12:48:39 PM

Thanks!



16 comp or more is common in 410 engines.  You do not need as high strength parts in a 12.5 .  In 12.5 engine $700 rods and crank would work.  In 410 16 ratio you would need $2000 rods and $3000 crank.  The 12.5 engine could run 30 races with out rebuilds.  The 410 ab0ut 8-10 races.



Murphy
February 11, 2019 at 07:38:24 AM
Joined: 05/26/2005
Posts: 1212
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Posted By: linbob on February 09 2019 at 07:29:42 PM

16 comp or more is common in 410 engines.  You do not need as high strength parts in a 12.5 .  In 12.5 engine $700 rods and crank would work.  In 410 16 ratio you would need $2000 rods and $3000 crank.  The 12.5 engine could run 30 races with out rebuilds.  The 410 ab0ut 8-10 races.



    Would a 12.5 engine with $700 rods be just as powerful as a 12.5 engine with $2000 rods, or is it a situation where puring money in makes a big difference?

(Note: I'm not a gearhead so some of my questions just sound dumb.)





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