If this is not the appropriate forum for this topic I will gladly repost it in LT1 Tech or whereever is appropriate.

I was thinking about adding boost to an LT1, generally the consensus has been that a stock LT1 won't hold up too long, even running low boost ~6 lbs. because the pistons are too fragile and the compression is too high. I can remember discussions in here about static compression vs. dynamic, and how dynamic CR is the important one. Well, that begs the question, can you lower the dynamic CR significantly enough with a custom grind cam that it would make a boosted LT1 more than a ticking time bomb? Of course I know that even with a lower CR you can still have detonation and that will quickly crack the stock hypereutetic pistons, but I'm hoping with a custom cam you could drastically increase the life of a boosted LT1 on the street. Has this been done, or considered and shot down for other reasons? Maybe a cam that would lower DCR by a meaningful amount also has so much overlap it isn't suitable for a boosted application? Educate me please.

 

As long as it’s tuned properly you shouldn't have a terrible issue with life at 6psi.

I wouldn't do anything to try to make the conditions better with a different cam or anything like that. Just bite the bullet and lower the compression (a touch!) and use a good piston with ring lands made for a blower application.

The point where you make more power with less compression is the point where your intake pressure sits at a higher pressure than your instantaneous exhaust pressure at/near TDC exhaust. So keep the compression up for power, and a touch down for knock resistance.

 

I'm not sure I get the part about the lower compression engine having a larger volume? The engine is a positive displacement pump and the swept volume of the cylinders, aka displacement, is a measure of how much air it is able to pump at 100% volumetric efficiency.

I'm running 16cc dish tops on my 385 but only to bring compression down where the pistons will live on 92 octane fuel, if running them on a stock 350 the engine would be a total dog. Running dish top pistons does increase the total cylinder volume (but doesn't change the swept volume or displacement) but decreases the compression ratio, robbing power if not needed. Using the most compression you can run is what makes the best power. You run as much compression as you can without getting detonation and preignition because more energy is released. Never heard of dropping compression from max the fuel will tolerate to increase cylinder volume and increase power. Or maybe I misunderstood you?

About the 6 psi of boost on stock pistons, as long as you have adequate fuel delivery ( don't lean it out) a healthy engine will tolerate it well. There is very little margin for error, rattle it just a little and chunks of the piston will be flying down the exhaust

Michael

 

Unless you have a magical exhaust sytem that evacuates all the exhaust gas from the cylinder then the dish is filled with leftover exhaust gasses when the intake valve opens. This isn't some empty space, it's occupied by leftovers from the previous cycle. The space available for fresh air/fuel is that which is vacated as the piston moves downward. VE and likewise displacement are measurements using the swept volume of the engine, not the total cylinder volume at BDC.

Everyone uses pistons with the proper dome/dish volume to optimize the compression. There's a good reason you don't see formulas for optimizing dome volume in a tradeoff of compression vs. cylinder volume at BDC, there is nothing to be gained. Dropping compression below the most you can get away with running to increase the total volume at BDC is bassackwards and is pretty much always going to decrease power.

 

Citing material for your theory would be more direct: increasing power by decreasing compression ratio while increasing cylinder volume at BDC through the use of dishtops or larger combustion chambers on NA engines. Unless I misunderstand you that's what you're claiming. Fire away