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Forum: HoseHeads Sprint Car General Forum (go)
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Topic: Under pressure Email this topic to a friend | Subscribe to this TopicReport this Topic to Moderator
Page 4 of 4   of  70 replies
Eric Smith
December 11, 2017 at 09:25:02 AM
Joined: 11/29/2011
Posts: 128
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Posted By: Murphy on December 10 2017 at 11:03:17 AM

That's what I gathered, but it seemed a little odd. So, further back in this thread it was said that a 360 runs about a 14 to 1 compression ratio and a 410 somewhat higher. Yet there are some groups or tracks running engines limited to 10.75 to 1 ratio? Am I following that correctly?



Yes.  Theoretically, i think that's a great idea.  But for every rule written, people will buy their way around it.  I'm not smart enough to know what it is, but I'm sure there's an expensive way to get around compression limits.


Pennsylvania.  Where the 1% of the vocal Posse fans 
make the other 99% look bad and make the entire racing 
world hate all Posse fans.  

zeakemedia
MyWebsite
December 11, 2017 at 10:25:07 AM
Joined: 01/27/2006
Posts: 86
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Posted By: Eric Smith on December 11 2017 at 09:25:02 AM

Yes.  Theoretically, i think that's a great idea.  But for every rule written, people will buy their way around it.  I'm not smart enough to know what it is, but I'm sure there's an expensive way to get around compression limits.



If you know what cylinder they check putting a cigarette butt in there "lowers" the compression ratio. When you fire the car it gets burned up. 

Blake



Murphy
December 11, 2017 at 01:16:02 PM
Joined: 05/26/2005
Posts: 720
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Reply to:
Posted By: zeakemedia on December 11 2017 at 10:25:07 AM

If you know what cylinder they check putting a cigarette butt in there "lowers" the compression ratio. When you fire the car it gets burned up. 

Blake



     I'm not sure how that would be. The math doesn't seem to work. The volume of a cigarette butt in comparion the air volume of an engine cylinder wouldn't amount to enough to change the compression ratio more than perhaps a couple percent.



champphotos
MyWebsite
December 11, 2017 at 01:29:44 PM
Joined: 05/21/2011
Posts: 158
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So... I will tell you a trick that was used long ago and it worked to perfection. It was noticed by someone that the hose that was threaded into the spark plug hole to check compression, was shorter than the plug itself. A crafty person with a mill, put a set of heads on the mill and proceeded to drill a small hole in the threads of the plug, every plug. The hole was covered by the plug but left open by the hose. When the cylinder was checked the small hole provided more cubic area and lowered the compression. We... I mean someone always put never-seize on the plugs so they were sealed. wink

Not sure how a cigarette butt would lower compression, seems it would take up space and add compression. I would guess this would help beat the cubic inch test...

DA



zeakemedia
MyWebsite
December 12, 2017 at 03:45:45 PM
Joined: 01/27/2006
Posts: 86
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Posted By: champphotos on December 11 2017 at 01:29:44 PM

So... I will tell you a trick that was used long ago and it worked to perfection. It was noticed by someone that the hose that was threaded into the spark plug hole to check compression, was shorter than the plug itself. A crafty person with a mill, put a set of heads on the mill and proceeded to drill a small hole in the threads of the plug, every plug. The hole was covered by the plug but left open by the hose. When the cylinder was checked the small hole provided more cubic area and lowered the compression. We... I mean someone always put never-seize on the plugs so they were sealed. wink

Not sure how a cigarette butt would lower compression, seems it would take up space and add compression. I would guess this would help beat the cubic inch test...

DA



You are correct. I screwed that explanation up. I knew cigarettes were good for something though. 

Blake



Salina Engine
MyWebsite
December 14, 2017 at 06:54:58 AM
Joined: 11/22/2017
Posts: 2
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Posted By: Murphy on December 11 2017 at 01:16:02 PM

     I'm not sure how that would be. The math doesn't seem to work. The volume of a cigarette butt in comparion the air volume of an engine cylinder wouldn't amount to enough to change the compression ratio more than perhaps a couple percent.



I've never seen a cigarette used, but I have seen a cotton ball used. The whistler (device used for testing compression built

by Katech) measures the resonance in the cylinder. If any of you have ever been around one they hum as the measurement

is being taken and it calculates the compression off of the frequency or resonance of the vibrations. A cotton ball/cigarette

will dampen these pulses and will change the reading. The other issue with a whistler is dome pistons will effect them as 

well. As the air enters the cylinder it hits the dome and throws the number off. On an ASCS 360 a 14:1 engine might read

12.5:1 depending on the dome design.


Salina Engine 
Salina Ks
(785)823-2273

MoOpenwheel
December 14, 2017 at 09:07:31 AM
Joined: 07/27/2005
Posts: 465
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What affect does leakdown have on the cubic inch pump test?  And why does temperature affect it and how you need to measure temp and adjust to get an accurate reading?   Thanks. 



champphotos
MyWebsite
December 14, 2017 at 12:18:46 PM
Joined: 05/21/2011
Posts: 158
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Air and metal change size base on temperature, it is called thermal expansion. My math could be off a little but 12” of aluminum can change 0.010” on a 50 degree temp change. This is one reason for water heaters on the engines today. They try to keep them around 180 all night.

1 cubic foot of air at 90 degrees does not contain the same volume of air as 1 cubic foot at 40 degrees. The air density will also change based on humidity. So if you are using air as a gauge for volumes on a cylinder made of metal, you must have all the temperatures and air density correct. If not, someone with a 409 cubic inch engine could have a 411 and be illegal fairly quick. The opposite could also be true.

I have equipment to measure down to micron’s, 30 micron’s equal 0.0012”. The equipment has sensors for temp, pressure and humidity. I entire the material of the piece I am working with and the software makes the changes for thermal expansion based on what I give it.

DA



JeremyAnderson
December 16, 2017 at 09:45:39 AM
Joined: 01/31/2009
Posts: 87
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Its been a long time since I've logged on here Smile, but I was researching a RCD crank trigger (for a home project) and I stumbled on to this thread.

My observation on high compression has always been this: High compression is only hard on ring gears and starter drives......since sprints have neither, its not a concern. Compression does not fail head gaskets, it does not fail connecting rods or break cranks. Compression does make tune-up ultra critical. Compression can cause detonation on a poorly tuned engine. Just a few pill sizes of a few PSI on a high speed bypass can be disaterous. A tune up that is off just a little bit on a 16:1 engine will have negative consequences, while a missed tune-up on a 13.5:1 is a good bit more forgiving.

People often mistakenly blame compression for failures that are related to cylinder pressure. Cylinder pressure is the force created by ignition of the fuel and air mixture. Generally, cylinder pressure is highest around peak torque. This is what pushes head gasket out, lifts heads and hammers out rod bearings. More cylinder pressure=more power. More fuel and air=more power. Better heads=more power. More compession=more power. Its simply not fair to blame compression, there are too many factor. Lowering compression will only help those that miss their tune up.

I big problem that I see in the cost to build and in higher failure rates is weight. Light weight component simply don't last as long as their higher weight counterparts. I've seen 35lbs cranks that scare the hell out of me. Racers are always concerned about weight. Engine builders need customers to stay in business. Customers (the racer) drive the industy. If engine builder Y has an engine 10lbs lighter then engine builder X , the lighter version will be more appealing to the racer. Now, engine builder X must use the lighter parts to be competitive. Unfortunately, cost and rebuild intervals have now increased. Who pays for this? The racers pays for it. The same racer that is stuggling with escalating cost. It is a spiral that is driven by competition.

 

 



Murphy
December 17, 2017 at 08:00:45 PM
Joined: 05/26/2005
Posts: 720
Reply
Reply to:
Posted By: JeremyAnderson on December 16 2017 at 09:45:39 AM

Its been a long time since I've logged on here Smile, but I was researching a RCD crank trigger (for a home project) and I stumbled on to this thread.

My observation on high compression has always been this: High compression is only hard on ring gears and starter drives......since sprints have neither, its not a concern. Compression does not fail head gaskets, it does not fail connecting rods or break cranks. Compression does make tune-up ultra critical. Compression can cause detonation on a poorly tuned engine. Just a few pill sizes of a few PSI on a high speed bypass can be disaterous. A tune up that is off just a little bit on a 16:1 engine will have negative consequences, while a missed tune-up on a 13.5:1 is a good bit more forgiving.

People often mistakenly blame compression for failures that are related to cylinder pressure. Cylinder pressure is the force created by ignition of the fuel and air mixture. Generally, cylinder pressure is highest around peak torque. This is what pushes head gasket out, lifts heads and hammers out rod bearings. More cylinder pressure=more power. More fuel and air=more power. Better heads=more power. More compession=more power. Its simply not fair to blame compression, there are too many factor. Lowering compression will only help those that miss their tune up.

I big problem that I see in the cost to build and in higher failure rates is weight. Light weight component simply don't last as long as their higher weight counterparts. I've seen 35lbs cranks that scare the hell out of me. Racers are always concerned about weight. Engine builders need customers to stay in business. Customers (the racer) drive the industy. If engine builder Y has an engine 10lbs lighter then engine builder X , the lighter version will be more appealing to the racer. Now, engine builder X must use the lighter parts to be competitive. Unfortunately, cost and rebuild intervals have now increased. Who pays for this? The racers pays for it. The same racer that is stuggling with escalating cost. It is a spiral that is driven by competition.

 

 



     Thanks for chiming in on this. What you said makes sense and I actually understood it. It sounds like you have some experience with racing engines. It appears you don't think setting a lower compression would help much in costs, other than the little guys would get themselves in less trouble with tuning and perhaps killing some engines.

     From your perspective, what should the sprint car racing world be looking at as far as containing costs?




Keyboard Jockey
December 18, 2017 at 09:17:16 AM
Joined: 04/16/2014
Posts: 222
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Reply to:
Posted By: Murphy on December 17 2017 at 08:00:45 PM

     Thanks for chiming in on this. What you said makes sense and I actually understood it. It sounds like you have some experience with racing engines. It appears you don't think setting a lower compression would help much in costs, other than the little guys would get themselves in less trouble with tuning and perhaps killing some engines.

     From your perspective, what should the sprint car racing world be looking at as far as containing costs?




Jeremy has a wealth of knowledge when it comes to race car engines. If you are interested you can google his name and add race engines to the back of it and you will probably find out more.





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