compression question???

[7.3 man]

Heard on powerstroke nation that you could lower the compression in the 7.3 engine and it would make it a better daily driver?? Me I think the high compression is better more torque, and steady RPM, but why are some people saying lower compression is better? To me if you lower the compression it wont start right or run right.

 

[FordGuy100]

I dont think it will effect driveability to a certain extent. I mean if you were to drop compression down to like 15:1 you would probably have problems, but for the most part as long as everything is working properly, it should start fine.

Think of all the worn out IDI's with low compression that start up fine, cant be any worse than those.

 

[icanfixall]

Making a blanket statement like lowering the cr makes for a better daily driver is really broad.... Kinda like the wifeys a$$... I know I'm going to hel for that but at least I know... anyway, lowering the cr from 21 1/2 to 1 down to say 19 will not change much if any. It will allow you to run more boost if you have a turbo. Going to 17 to 1 will make it a really difficult starter and bang fluid is a must that low. A psd is something like 17 to 1 cr but they have at least 20,000 lns of fuel being squirted into the cylinders and they are direct injection into a piston cup... Nothing like our precups either. Just go to ebay looking at psd pistons or cummins pistons to see the dome appearance. How much was the poster thinking about dropping the cr???.

 

[Black dawg]

I wonder what these lowered compression ratio motors blow for compression psi?

 

[FordGuy100]

I think other factors are involved. The Justin's are running lower compression, NMB2 said his is slightly below 17:1

I remember listening to the audio from Ken's low compression IDI, that thing cranked like crap. Does anyone know if he was running glow plugs? Sure doesnt sound like it.....

 

[riotwarrior]

NMB2 Justin has lower comp....

Racinndrummin Justin has stock setup....

IMHO which is worth about two wooden nickels and a 5ver from Monopoly....I'ld drop safely to 18.5 no less and boost more! that's just me and my HO

 

[PwrSmoke]

DI engines do better on lower compression ratios than IDI engines do generally. No firsthand experience with the Fords but I know the GM 6.2s (which have the same type Ricardo V combustion chamber) start like crap at 19:1 or lower in cold weather. I have a tractor with a DI diesel that is at 15:1 (or what's left of that after 8300 hours) and it simply doesn't start below 40F unless I plug it in or use ether. Why do you think Ford/IH upped the CR twice from the original engine... cold starting. It's just a trade. If you need or want the extra performance and mods, you can sacrifice a little in another area. Or, if you live in a warm climate or your truck isn't a daily driver, it may not be an issue. Me, I just love the way my 6.9L starts on the first quarter revolution and will start without using the block heater at -15F. Day to day, that's worth a few HP. 'Course I finally saw the effect high compression and boost had on my heads and head gaskets but that's largely fixed now.

 

[Hardass559]

more fuel lower egts and more boost makes room for more horsepower and a torque you sacrifice cold starts... enlees you find a way to make boost with out the truck running like a leaf blower you can just hook to the intake shuld solve cold start ishues

 

[FordGuy100]

The problem isnt the amount of forced induction when starting cold, its the fact that the compression itself is what creates heat (besides glowplugs). The lower the compression, the lower the cylinder temperature when the piston is at TDC. You could probably try to cram 30psi into it and start it and it would probably do nothing.

 

[7.3 man]

Thank ya for all the help guys, I was just wondering I had two shop classes and couldnt figure it out

 

['94IDITurbo7.3]

who told you this on PSN? For the most part you have to take anything you hear on PSN with a grain of salt.

 

[7.3 man]

reply to post

who told you this on PSN? For the most part you have to take anything you hear on PSN with a grain of salt.

I'm not sure i cant rightly remember sir, but what did you mean by take it with a grain of salt, did ya mean it is sometimes a good thing?

 

[icanfixall]

I don't think so... This fourm wil guide you in most anything that comes up. Normally this forum is cutting edge. If I see a post slipping away from whats been found to be true I draw it back to reality. I'm not attempting to "show up" a poster. Just bring the truth back to the front of the line. Probably every question and problem has been talked about here many times. Lots of effort and money has already been spent to find what really works. Thats where this forum is above the reat. We don't have any experts here.. Just amatures... Remember this. The Tiatanic was built by experts and the ARK was built by am amature.... I'll be an amature all my life please.... I may know something most don't but... I continue to learn something here all the time and I enjoy doing that...

 

['94IDITurbo7.3]

but what did you mean by take it with a grain of salt, did ya mean it is sometimes a good thing?

No, i just meant that you need to be careful about executing some of the things that are said over there. there are some real a-holes over there. So just use your common sense.