Posted by Xiled1 (firstname.lastname@example.org) on September 10, 1998 at 13:36:16:
Before I ask my question I would like to set up a scenario. Lets take
a completely stock B18c, GSR motor. Then add the ENDYN s/c kit to it. You
had stated previously that, on a stock bottom end, the boost should be
limitted to 17 psi, peaks. This set up creates a certain amount of HP to
the wheels. Now lets say more HP is desired from the motor. The option
of turning up the boost is out, without rebuilding the bottom end. Now
lets say we sent the head out for some port and polishing, valves, and
valve job. Lets assume this head work was of good quality, increased volumetric
effiency, better air fuel mixture. This translates into more power to the
wheels. Now assuming the engine was at its limits, with the 17 psi of boost.
Wouldn't this extra HP push the engine over the edge. We are not running
any more boost, but we are producing more HP. This HP is coming from increased
energy from the combustion of the air/fuel in the combustion chamber. This
in turn puts more force on the piston, and the rod. Which then is translated
to the wheels. Therefore your motor is under more stress.
My conclusion is that you would blow your motor, if you were already at its limits. Tell me if this is a correct assumption and if not, why. This question spawned from all the people out there running Turbos. They have solved the fuel/detonation problems and have reached the limits of the stock bottom end. It seems that many of them are going for other HP increases, other than more boost. They seem to believe that as long as the HP comes from somewhere else, it won't increase the load on the motor. It just doesn't make sense to me. Thanks for any help you can provide.
Posted by T.O.O. on September 10, 1998 at 19:32:03:
You're correct in your assumption that HP causes engine failure, and
anything you do to make more is enviting trouble.
Boost can also cause damage, as it provides tremendous cylinder pressures at crank angles that a normally aspirated engine wouldn't see. The trick is moving the cylinder pressure curve well past TDC. Endyn proved these notions back in '85 only to be blasted for the idea.
A boosted engine is going to be working very hard to compress the mixture, and it's also going to be under considerable pressure during the burn and the power stroke. You are most likely to experience failure during those two strokes, where with a N/A engine will almost always fail on the end of the exhaust stroke (overlap), so you get the added benefit of having both valves off their seats when the rod fails and the piston slams the head. It can reconfigure combustion chambers and valves quickly.
I'd be tempted to say that if you were to increase Hp by porting, less friction, etc. the engine might not experience the stresses that a boost only gain would cause. You must keep in mind that most import heads are so good stock that the numbers that someone may gain by porting, etc. would be minimal, and those "free HP" are the most costly mods. I suspect that even with reworked heads, etc., people will still be turning up the boost and the result will be the same, except the parts you break this time cost a lot more.