Taetsch Z-24 wrote:stock motor,
overdrive crank, under drive charger pulleys. upwards of 10 psi. ( i think the belt is slipping bad)

93 octain, and i am running a little tomuch timing, i rich'nd it up to help, did'nt have any KR, but i wan to pull timing to let it runn leaner, in hopes to net more HP.

i have toyed with running higher comp. BUT i will not run a pop up piston, i feel a flat top piston to yield a more efficient burn.


Chris

Awesome, that is great news for me....

I know that the MP45 charger that we all use is limited.... so i am trying to build my engine to best compliment the SC's range. I figured on between 5-11psi....

I know my engine runs like a top at 9.7:1 compression and 5psi stock. and this is with the factory tune and nothing tweaked at all. I was thinking about going with a 10:1 for a little more power across the board, and should make little difference on boosting considering my pre-existing limitations.

Well i found a killer deal on some 10.5:1 weisco forged pistons. I thought that would be nice... but didnt know if that would knock me out of pump range at 5psi of boost. so started doing some calculations... i figure if some of you guys can run 20+ psi of boost on pump gas.... that i should be able to manage 5psi. the only hard figures i could use for my comparison was effective compression.

It is just a base-line... and i know there is ALOT more that goes into it that just this.... but this is not a comeptition racer, this is my daily driver. I was about to buy myself a used vette as my fun car... but then developed some engine issues on my cavy... so instead decided to use my vette money to fix my cavy and make her into my "fun car" at the same time. this way anywhere i go, i am in my "fun car"

i can add, adjust, tune, tweak, change... just about anything later on... but dont want to have to tear my engine back out and change my pistons again. So just making sure 10.5:1 wont be something i regret.

I know you guys with big turbos lower your CR to give the turbo more room to do its thing.... well i dont have that luxury. so instead i am trying to max out my engine so as to rely less on my psi, and let the supercharger stay more comfortable. build the engine to match the boost... you guys lower to allow 30psi.... i want to increase to get the most out of my 5-11psi.


my poor baby is sick... someone help me...
(2.4L engine in my cavy is ticking bad... need to make it stop)

SweetnessGT wrote:You can run 30 psi on 94 octane if you want at 9.5:1... so long as you rape the ignition advance to something paltry.
I'm not trying to be rude... more forward than anything. It's good to see you're calculating dynamic compression, that's a good start. What makes you think 15:1 dynamic is a limit of sorts?
Also, nowhere in there are you mentioning intake air temperatures and cylinder temperatures. Yes cylinder pressure plays a huge role but 5 psi through a M45 GM Supercharger/Hairdryer is nothing like an intercooled Turbo or even the aide of meth injection.
My plan from day 1 has always been to be able to run up to 30 psi on street gas, and I built my motor around that concept. So far I have taken it up to 22 psi on pump gas (94 Octane). I am yet to put race gas through it... I'm saving that for a surprise dyno for the .org.... my initial goal has always to be the first to 500 on pump gas - and then put in race gas to see what it can really do.
Ignition timing as well as charged air cooling plays a huge role in your decisions.
Just to note - the reason you were able to run 87 and "hardly noticed" was because GM provided that in their tune. Ignition timing is very very tame. You'd be surprised what you can get BACK by re-tuning with HPTUNERS and putting in the proper higher octane gas. You'd be even more surprised to see what Alcohol injection + High octane gas + a few more degrees of ignition advance can yield.
If you are stuck with a GMSC M45 unit.... run it at 10:1, premium octane gas, alcohol injection, HPTUNERS to fine tune it and do everything you can do to get the engine to flow better. You'd be surprised, with a fully flowing setup the boost doesn't even get that high anyway.
It took a lot of research for me to figure out what wasn't in the range of pump gas in terms of dynamic compression. I've watched a few members build motors without keeping this concept in mind and have seen them limited to race gas at even medium boost levels because of it. 15:1 dynamic compression very much within the safe range.... just keep the cylinder temps down. Remember, you could knock/detonate at 9:1 dynamic compression if you let the cylinder temps get high enough.
Good luck!
-Chris-

15:1 is not a "dynaminc limit" but 15:1 would be a comfortable daily driving compression for my car.... 10.5:1 static and 6.5 psi of boost.... if i could run that on pump gas i would be a very happy camper.

then if i could get away with 11psi boost on race fuel (18.36:1 effective), i would be equally as thrilled.

as i mentioed above... most anything else i could change and tweak after the fact...i can tune, and add ach injection, and do all the other stuff down the road a bit... but right now i just want to make sure i am not being un-reasonable with my expectations based upon my limitations. I know all i can hope for out of my MP45 "hairdryer" is 11psi, and so i figured 10.5:1 compression would take the focus off the psi, and take better advantage of what i do have... 10.5:1 at 11psi is about the same as an 8:1 at 19psi. (effective compression wise at least)

my car spends 99% of its life at 70-80mph at around 2-3k rpm.... so at this point there isnt much help from the SC anyway... so higher static will give me added power here.

my car sees the track maybe a few runs a year... and that is just so i know what i can run... so when people ask me i can tell them.


so big question here is "can i run 15:1 easily and safely on pump gas... and Can i run 18.3:1 safely and easily on race fuel"





my poor baby is sick... someone help me...
(2.4L engine in my cavy is ticking bad... need to make it stop)