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Rocker ratio - which to use?

SnowDrift

SnowDrift

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I have this Optimizer block, not a P400, so I'm not going for crazy numbers. If I was going to swing for the +$1700 forged crank, then I might want to push my luck. I guess 1.5 ratio is the stock configuration. TSP is using a mixed ratio on his P400. Others have used 1.6. How should I determine what ratio I'm going to want to use?
 
1.5 stock, 1.6 or 1.7 roller options.
Higher ratio is opening the valve more and risking piston/ valve hitting slightly more.
Timing gears rather than chain eases the fear because of eliminates chain stretching allowing this.

Crude way of thinking is
The more ratio means the more air that comes in each time. This means the more fuel that NEEDS TO/ GETS TO come in each time as well. This bad if you want mpg, good if you want power.
But really this engine was designed so skimpy cam and as a NON TURBO. So the amount of boost or air volume shoved in by the turbo has far more impact.

Think 10 lbs of boost times
1.5= 15
1.6=16
1.7=17
But to get to 17 on 1.5 ratio is just 11.333 psi boost if everything else is exactly the same.

It is like having a bigger turbo, but no added losses for the heat, and you dont have the loss at bottom of rpm for the higher rpm gains. The gain is from idle to redline.
Or if you are familiar with putting larger diameter valves in a head- same thing, kinda.
Or if you could buy a cam with higher lift but same duration.

There is my stab at explaining- hopefully someone else does better...
 
@Will L. what aftermarket cam options are out there aside from the Heath one?

From what I've read the Heath cam is specifically designed to compensate for the imbalance in the exhaust in the side mount turbo design and whatnot. For those who want to get away from/ upgrade the stock setup, I'd be curious to know what else, if anything is available/ possible

@SnowDrift I'm not sure if valve reliefs would be needed to be machined into the pistons if going to a higher rocker ratio than stock, Chris would be the man to answer that question. I went with 1.6 more or less because it seemed like the middle ground, slight step up from stock but not full limit of the engine. I also had the compression ratio lowered, so keeping in step with adding more air seemed logical to me
 
sound like from what @Will L. is saying, "it's all about the Turbo" !!

this thread and Will's explanation sparked a curiosity for a future build for my rig (that is if I ever get around to it)

this 6.2 block I have that basically fell into my lap, I am assuming that it has the factory 6.2 heads still on it but has been turboed with a GM-3. I have heard talk about some folks running a 6.2 block with 6.5 heads due to the valve and chamber sizes. I can't remember if the 6.2 head has larger valves or it's the 6.5 heads that are larger. But which is the better way to go for decent every day driver power and best mpg's?

My plan is to (some day) get this engine up and running along with investing into a better turbo like a HX35 just to get less pressure on the exhaust side of the engine hoping the combination will result is a long lasting every day driver with an over-achievement on fuel mileage all the while still having some power when it's needed.

in the end, it will have a DB2 and trans controller, but that's gonna be a while at least until my money tree I planted starts producing a crop.
 
@SnowDrift as was mentioned timing gears would probably help with reducing the risk of pistons hitting valves

I think a slightly thicker head gasket could help as well?

Any reason for not having the pistons machined outside of cost? AFAIK lowering compression will reduce mpg but make for lower cylinder temps and prolong engine life as long as you play nice with the go pedal :)
 
Yes, cost is the only reason.

I'm trying to make a reasonable engine out of this that I can use for a good long time and for lots of miles, but realistically can't be breaking the bank in doing so. I have to keep it within my means. While I'm not rushed, I also don't want it sitting around for years while I piece things together a little bit at a time. I've decided to spring for some things, such as having it balanced, TSP recommended valve springs and some other items, but have to draw the line somewhere.

It sounds as though the only mechanical reason the valve would have touched the piston is due to the timing chain being stretched - is that correct? That is keeping in mind that I don't have a reason to believe this engine was ever taken apart after it left the factory.
 
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