pistons for forced induction

[RicE-ter]

http://www.superchargersonline.com/content.asp?id=104

found this, they dont have any references but the stuff they say makes sense

it seems that with compression u are trying to find the most u can run without detonation- within the power threshold of the engine it is a balancing act between all the factors mentioned: octane, tuning, etc

so i guess the idea of running a super high compression if the ideal octane, pressure and heat thresholds of the pistons and engine, and so on are attrained it is possible...its just not very likely anywhere but in prodrag racing. so some of us, like me with only 91 as the highest, will have to settle with a lower compression

[Teufel Hunden]

Originally posted by phoenix64:
Its great to talk about smaller tuning windows and such, but as far as I know I'm the only person who has done any extensive tuning with a wideband.

So you tuned 1 car and now you're the expert on everything? There are more tuners around here than you might realize... just because they don't give out free advice online doesn't mean they aren't here.


In a real world car, you wouldn't want to throw much boost at a high C/R motor. Even a half point can make a pretty good difference in my experiences. Unless you figure out a way to build your motor as stout as a Diesel engine, there's no amount of fuel or methanol to comp for the increasing cylinder pressures with every added point of compression, as the components themselves can't handle the stress.

A good example of how much even half a point can make would be on the 2000 to 2001 Mustangs. I forget exactly what year it was, but they received an extra half point of compression for whatever reason. It wasn't really put in the specs, and all the engine components were of the same material. But, starting after that certain model year, the same S/C kits that we put on every Mustang on years prior were breaking the ring lands on the pistons. It limited the motors to 7psi, and any more than that, you were risking some serious potential damage. No one really understood it, as the spec sheets were unchanged, but once you started tuning the cars, it was very obvious there was more compression in the new motors. For a while, it added a certain "unreliable" aspect to putting an S/C kit on a stock block Mustang. Once everyone figured it out, it was an easy fix to just run less boost.

I've built more than a few race application GN motors (none ran slower than 10.1s in the 1/4), and none of them had more than a 9.5:1 c/r. The motor i'm building for my car is 9.0:1. A good friend of mine has 9.4:1 in his low 9 second Eclipse (30psi on a GT42 turbo). I could never realistically see going much higher than 9.5:1 on a high boost car, where the owner can't afford to throw a new motor in after every pass. Sure, on paper, high c/r, high boost wins every time.. but on paper and on the track are two different things.

Having said all that, I don't necessarily think an incredibly low C/R motor is a good thing either. On the other side of going no higher than 9.5:1, I would go no lower than 8.5:1, unless i just wanted to build a car specifically to boast extremely high boost pressures. I agree with Nocutt on the point he made that the answer is to find a happy medium.

[ June 17, 2005, 10:20 AM: Message edited by: Teufel Hunden ]

[nocutt]

...Its great to talk about smaller tuning windows and such, but as far as I know I'm the only person who has done any extensive tuning with a wideband...

ROFLOL...you aren't serious are you?
T-H finished it...it is unfortunate GM builds crappy internals for this cars...because in the import world you will be surprised what ppl are getting away with...that is why I NEVER narrow my horizon with this engines/car...anywayz compromise is ultimately the key...

[phoenix64]

Originally posted by Teufel Hunden:

So you tuned 1 car and now you're the expert on everything? There are more tuners around here than you might realize... just because they don't give out free advice online doesn't mean they aren't here.

[/QB][/QUOTE]

Why would you lurk around a message board watching people struggle, when you could be helping them? Whats the point?

Who says these motors are weak?
Aparently I'm not up to date with who's doing what, but seems like the vast majority of broken motors around here are due to running lean and/or detonating.

[Teufel Hunden]

Originally posted by nocutt:
it is unfortunate GM builds crappy internals for this cars...

I think the internals on the series II motors are pretty stong, all things considered. When i first wanted to do the turbo on my car, everyone kept telling me that the motor would blow up in a matter of weeks. Now it's been a year, 22,000 miles (on a motor that had 90k on it when the turbo system was completed) I ran 15psi for several months, now down at near sea level, i run 10-12psi every day. Before i start running the built motor, i'm going to test the extreme limits of the stock short block just to see what i can throw at it.

[nocutt]

No matter how you slice it...the internals are crappy for performance...we only make 'lemonade from lemons'...seriously if not for the rugged bottom end...and the fact that the L67 even exist...no one will mess with it...I have worked with this motors and helped charged a dozen over the past 8yrs...yes crappy...yes stout...but it could be 101% better...wouldn't you agree?

phoenix64
trust me you only see a small window in your world...that is the problem with the internet... www.westcoastfiero.com has been working on this motors since '94 literally...adn have been using aftermarket PCM/ECM haltech to be exact...and use WB to tune...if not for the advent of HPT/DHP...most of you will still be in teh dark ages...and that been honest...as soon as the PCM code or part of it got cracked it opened a new trend...the messiahs...anyhowz...it was a nice string!

[phoenix64]

I'm well aware, guy localy has a tube frame 98+ body N/A 3.8 that would own the records on the timeslip page. He's never even heard of this board. I was talking about people here.

As for our motors, mine ate 14psi non-intercooled and untuned(other than timing retard) on pump gas. Maybe crappy, but I'll take it.