Static Compression VS Dynamic compression

[swampbuggy]

It all runs hand and hand or together to create the needed fuel requirement. IE-----anything that effects the where the cylinder pressure level is at when the spark plug fires is relevant to his original question-------no ??? Mark H.

[ClassAct]

So this is like the 128 thing

Not really. The 128 thing is a rough rule of thumb.

Cranking compression is essentially useless. I've had engines with 140 cranking that were a nightmare to tune and were so detonation prone it was impossible to get happy.

I've also had as high as 220 cranking, and it was beautiful. Tune up window a mile wide and you had to miss pretty big to get it to rattle.

Cranking compression means very little, except maybe on the same engine, with the same battery, starter etc.

[Orr89rocz]

So this is like the 128 thing

Not really. The 128 thing is a rough rule of thumb.

Cranking compression is essentially useless. I've had engines with 140 cranking that were a nightmare to tune and were so detonation prone it was impossible to get happy.

I've also had as high as 220 cranking, and it was beautiful. Tune up window a mile wide and you had to miss pretty big to get it to rattle.

Cranking compression means very little, except maybe on the same engine, with the same battery, starter etc.

Fromthe 8 pages in this thread do you not draw the same conclusions that its (SCR and DCR) also a rough rule of thumb

[Stan Weiss]

So this is like the 128 thing

Since you wanted to bring 128 in to this. The enhanced version does do DCR and Cranking Compression and also based on usage does display a message about DCR being to high for that usage.

Stan

TMC_DCR_ERR.gif

TMC_DCR.jpg

[ClassAct]

So this is like the 128 thing

Not really. The 128 thing is a rough rule of thumb.

Cranking compression is essentially useless. I've had engines with 140 cranking that were a nightmare to tune and were so detonation prone it was impossible to get happy.

I've also had as high as 220 cranking, and it was beautiful. Tune up window a mile wide and you had to miss pretty big to get it to rattle.

Cranking compression means very little, except maybe on the same engine, with the same battery, starter etc.

Fromthe 8 pages in this thread do you not draw the same conclusions that its (SCR and DCR) also a rough rule of thumb

Nope. Not even close. The 128 can actually be very close. The cranking compression isn't. Unless you are comparing the same engine with all the same parts.

[ClassAct]

So this is like the 128 thing

Since you wanted to bring 128 in to this. The enhanced version does do DCR and Cranking Compression and also based on usage does display a message about DCR being to high for that usage.

Stan


TMC_DCR_ERR.gif


TMC_DCR.jpg

WTF??? Other than DV, who sits down to build something and then cripples the build with 87 octane fuel? That's ridiculous.

If you can afford 20 cents more a gallon for 93 octane pump junk go get a moped. Unreal.

[Orr89rocz]

So this is like the 128 thing

Since you wanted to bring 128 in to this. The enhanced version does do DCR and Cranking Compression and also based on usage does display a message about DCR being to high for that usage.

Stan


TMC_DCR_ERR.gif


TMC_DCR.jpg

I have used pipemax in the past for cranking comp calcs. It does seem accurate on the few engines i tried it on. I wondered about the fuel recommendation tho. How is that determined. From what it sounds like in this thread so far that DCR and cranking comp is only a guideline within a known sample set (like say same engine family like sbc with conventional 23 deg heads) and even then its not a necessary end all be all term. Hence a reference to 128. A simple guide line rule of thumb that may not be applicable to all engines combos within the family.

It seems like any guy who goes out to build an engine, can only rely on other similar combos others have done to know what compression, static and dynamic, and what cranking comp to shoot for on a set fuel.

[Orr89rocz]

Not really. The 128 thing is a rough rule of thumb.

Cranking compression is essentially useless. I've had engines with 140 cranking that were a nightmare to tune and were so detonation prone it was impossible to get happy.

I've also had as high as 220 cranking, and it was beautiful. Tune up window a mile wide and you had to miss pretty big to get it to rattle.

Cranking compression means very little, except maybe on the same engine, with the same battery, starter etc.

Fromthe 8 pages in this thread do you not draw the same conclusions that its (SCR and DCR) also a rough rule of thumb

Nope. Not even close. The 128 can actually be very close. The cranking compression isn't. Unless you are comparing the same engine with all the same parts.

128 was for typical small block chevys. Is there any relative DCR or cranking comp rule of thumb for that particular family of engines that could apply to guide someone for what fuel is needed?

[Stan Weiss]

So this is like the 128 thing

Since you wanted to bring 128 in to this. The enhanced version does do DCR and Cranking Compression and also based on usage does display a message about DCR being to high for that usage.

Stan


TMC_DCR_ERR.gif


TMC_DCR.jpg

WTF??? Other than DV, who sits down to build something and then cripples the build with 87 octane fuel? That's ridiculous.

If you can afford 20 cents more a gallon for 93 octane pump junk go get a moped. Unreal.

WTF??? You just like to Botch????

The user selects what they want as far as Application.

Stan

TMC_DCR_ERR2.gif

[GARY C]

Because I prefer a smooth idle street engine that responds right off of idel and will run a tight converter with a 2.73 to 3.08 gear but I also want good performance, I find DCR combined with SC in conjunction with proper head size helps to get the most cam I can for my preference.

If I was looking for max performance with gear and converter then DCR would be less of a concern but then again so would the fuel needed to power it.

[ClassAct]

Since you wanted to bring 128 in to this. The enhanced version does do DCR and Cranking Compression and also based on usage does display a message about DCR being to high for that usage.

Stan


TMC_DCR_ERR.gif


TMC_DCR.jpg

WTF??? Other than DV, who sits down to build something and then cripples the build with 87 octane fuel? That's ridiculous.

If you can afford 20 cents more a gallon for 93 octane pump junk go get a moped. Unreal.

WTF??? You just like to Botch????

The user selects what they want as far as Application.

Stan


TMC_DCR_ERR2.gif

LOL. I wasn't botching at all. Pointing out the fallacy of trying to run the cheapest fuel you can find. People read this crap and then come in and want me to do it. I show them the door.

[GARY C]

Since you wanted to bring 128 in to this. The enhanced version does do DCR and Cranking Compression and also based on usage does display a message about DCR being to high for that usage.

Stan


TMC_DCR_ERR.gif


TMC_DCR.jpg

WTF??? Other than DV, who sits down to build something and then cripples the build with 87 octane fuel? That's ridiculous.

If you can afford 20 cents more a gallon for 93 octane pump junk go get a moped. Unreal.

WTF??? You just like to Botch????

The user selects what they want as far as Application.

Stan


TMC_DCR_ERR2.gif

Stan, you should know by now that someone is going to B about anything DV does, he got the same Sh when he did his VP MS109 vs 92 octane 496 test... Then it was, Oh Yeah but how would it run on 87??? Thats part of why he dynos most of his builds now on 87 just to show the potential at it's least tuned point.

It's no different then a street turbo guy having 2 tunes, one for pump gas and one for race.

[digger]

Not really. The 128 thing is a rough rule of thumb.

Cranking compression is essentially useless. I've had engines with 140 cranking that were a nightmare to tune and were so detonation prone it was impossible to get happy.

I've also had as high as 220 cranking, and it was beautiful. Tune up window a mile wide and you had to miss pretty big to get it to rattle.

Cranking compression means very little, except maybe on the same engine, with the same battery, starter etc.

Fromthe 8 pages in this thread do you not draw the same conclusions that its (SCR and DCR) also a rough rule of thumb

Nope. Not even close. The 128 can actually be very close. The cranking compression isn't. Unless you are comparing the same engine with all the same parts.

That's the thing it's just a relative number. It's silly to think that somehow there is a simple way to include the influence of combustion chamber dynamics. That's the problem with using any pressure or temp data even measured.

[hoffman900]

Sportbike engines run very high compression ratios, with relatively low overlap, on pump gas. I’m talking like 12.1:1 with bore sizes pushing 4.4” (Ducati twins). Lot more to it than “DCR”.

[GARY C]

I would think that the only way one could develop a DCR usage for a race engine would be to spin it at 2000+ RPM... Not sure that there would be anything worth while to learn that would make it worth developing a system like that.