C/R for forced induction
Thread Starter
Racer
Joined: Jun 2000
Posts: 469
Likes: 0
From: Norfolk VA
C/R for forced induction
Please help me understand the theory......
Take a 9.9 to 1 C/R forged piston setup like mine. When going forced induction the first concern is the C/R. The target for any kind of real PSI is between 8.5 to 9.5 to 1. I understand how detonation kills and why you get it. The question is on a 9.9 motor do people lower the compression because they do not have access to their timing maps to lower them during boost? Or Is there something I am missing.
The way I figure it as long as you can retard the timing back under boost, assuming you have enough advance to start with, where you are getting no knock and plenty of fuel wouldn’t you benefit from maintaining the quench area in tact and be able to run a few PSI of boost?
Take a 9.9 to 1 C/R forged piston setup like mine. When going forced induction the first concern is the C/R. The target for any kind of real PSI is between 8.5 to 9.5 to 1. I understand how detonation kills and why you get it. The question is on a 9.9 motor do people lower the compression because they do not have access to their timing maps to lower them during boost? Or Is there something I am missing.
The way I figure it as long as you can retard the timing back under boost, assuming you have enough advance to start with, where you are getting no knock and plenty of fuel wouldn’t you benefit from maintaining the quench area in tact and be able to run a few PSI of boost?
Le Mans Master
Joined: Feb 1999
Posts: 5,877
Likes: 1
From: Park Ridge IL
Re: C/R for forced induction (HJV11)
In order to run any meaningful amount of boost with a 9.9 CR on pump gas, you'd have to retard timing so much you give up alot of power.
On a forced induction application one degree of timing can be worth as much as 50 hp. You want to run as much timing as you can, minus a safety margin against detonation.
Quench is still important but doesn't seem to be as critical as it is on a naturally aspirated engine. Alot of forced induction engines use a fully dished piston, with nothing more than a 1/4" wide raised crown around the circumference.
On a forced induction application one degree of timing can be worth as much as 50 hp. You want to run as much timing as you can, minus a safety margin against detonation.
Quench is still important but doesn't seem to be as critical as it is on a naturally aspirated engine. Alot of forced induction engines use a fully dished piston, with nothing more than a 1/4" wide raised crown around the circumference.
