Cylinder Pressure?

[Proaction14]

Just curious what cylinder pressure you guys have that are running 20+ lbs of boost, AWIC, with c16, etc are starting at? Of course it can and will vary depending on LOTS of stuff, but I was just curious if there is an optimum cylinder pressure you tried to obtain when you build your motors?  Im right at 120, after running high comp nitrous motors for years, 120 CP just seems so dang low. Guess a little boost can change that quickly 

[hotrodder_101]

It's not cylinder pressure that everyone talks about. It is compression ratio. 120 psi would be used for a compression test. Compression ratio determines how much or how little boost you can run as well as other factors. Such as Meth injection, intercooler, etc.
Luke

[Proaction14]

Yeah, I know low CR for blower or turbo motors, I was wondering if any engine builders or anyone for that matter tries to achieve a certain cylinder pressure when they build motors based on cam design and where its installed/degreed, amount of boost they plan on running, type of intercooler, fuel they use, etc??

[hotrodder_101]

Ohh never heard of that. You might want to try the engine specific section.
Luke

[nosnova]

i'l be interested in this subject. i always had 225 plus cranking comp on a sbc with  15.1 comp nos motor
i think the cranking comp. on a turbo motor will have something to do with turbo spool up

[hotrodder_101]

The higher the compression the quicker it will spool up.
Luke

[nosnova]

The higher the compression the quicker it will spool up.
Luke

so the higher the cranking compression the faster it will spool
or the higher the static comp the faster it will spool

[g80malibu]

Ive read somewhere you want to keep cranking pressures between 150 to 185 or so for turbos, to run on high test pump gas without detentation,there is alot of varibles to this, though this is what iam going through too ,I do know mine is insant boost up against the converter makes for a fun ride, but you have to watch your tune closely..

[hotrodder_101]

Yes static compression. If you are running pump gas the tune has to be almost spot on. If you get too high of a compression you can add a methanol injection kit to help fight detonation.
Luke

[vern]

I feel to many people talk about mythical compression ratios and not enough about cylinder pressure on pump gas n/a street cars I shoot for 180 but the last 5.0 I built shocked me with 240 psi and it ran real strong on premium. I guess i will keep experimenting and looking for chat like this thread

[slowboat]

To the O.P. You should get this thread moved to the advanced tech section. You will probably get more feedback/info on your question about cranking compression.

[Proaction14]

To the O.P. You should get this thread moved to the advanced tech section. You will probably get more feedback/info on your question about cranking compression.

Thanks bud. I actually was reading a similar post on another site that answered my question.

[slowboat]

Your welcome. What was the answer for your question out of curiosity ? I'd think you can run more.

[littlebluefoxbody]

cranking pressure is not directly related to performance.  i know a a couple of car with low cranking pressure and very lower ets.  total combo will give you performance

[Proaction14]

cranking pressure is not directly related to performance.  i know a a couple of car with low cranking pressure and very lower ets.  total combo will give you performance

Basically what I gathered was exactly what littleblue said. It all depends on the overall combo, too many variables come into play. GUys were running anywhere from 90 to 150, but most were in the 110 to 130 range on gas. Some guys that run alcohol said they went higher with cranking pressure just because alchy is more forgiving with boost and compression. I was suprised to see some as low as 90 but some of those guys were running real fast cars so I guess they have their combos figured out.

[ash]

so the higher the cranking compression the faster it will spool
or the higher the static comp the faster it will spool

yes..
helps engine 'climb' onto the converter...

[ash]

Basically what I gathered was exactly what littleblue said. It all depends on the overall combo, too many variables come into play. GUys were running anywhere from 90 to 150, but most were in the 110 to 130 range on gas. Some guys that run alcohol said they went higher with cranking pressure just because alchy is more forgiving with boost and compression. I was suprised to see some as low as 90 but some of those guys were running real fast cars so I guess they have their combos figured out.

yeeh, basicly...
really when you think about it cylinder pressure is the result of combustion..
how you arrive at the "control able" figure it up to the indiviual..

low static compression engine " tend" to take more timing , and boost to reach the cylinder pressure figure...
high static compression  engines,  " tend" to require  LESS timing to reach that same level....
you can also have a mild compression engine, and have HEAPS of timing ( nearly as much as a N/A engine ), but you require a high bsfc to cool the cylinder TEMP , to stop detination....

many, many ways to skin a cat....

cylinder pressure is the result of combustion,
the beast way to see what that is, for your combo.... is to read the spark plugs...
to much of the "monkey see , monkey do"  goes on, and bad advice..
let the engine talk to you, and the engine parts will tell a story...
freating main caps, big end caps,  smeared bearings, blow head gaskets, just don't happen for no reason...
lean condition is TOOOO  MUCH  cylinder pressure....and uncontrolled...

ive had a 7.2: 1 compression engine , methanol fuel , with 40 + psi boost , and 36 degress timing, with oem heads/ head gaskets..... and it lives.

best advice, let the parts tell you what they like..


ash

[PrecisionTurboMustang]

My na/nitrous 4 banger is over 300 cranking compression. I street drive it on e85

It could probably use more cam, lol.