I've got a few questions about our engines. I'm wondering what our compression ratio is, 'cause I've been thinking about planing the head a little. Has anyone tried this? No one seems to talk about it but it seems like some untapped power to me. Have to stud the head of course, but no big deal.
Which leads me to my next question. What sort of pistons are we running? If they're aluminum, planing the head won't be an option 'cause they'll cook. And if the crowns have recesses for the valves it'll make it all a bit more involved. Unless aftermarket pistons are available. Ideas on this?
Darn, I have another one but can't remember !! Well, that'll do for starters.

Keran

 

17.5:1.

More compression is not a good thing on a turbodiesel. You want less compression when you are making more power.

 

I was just reading today on Diesel Power Mag's website about that. They were saying that drag and sled-pulling trucks were lessening their ratios because they wanted a longer burn and to keep the crowns cooler. But those guys are over fuelling in a huge way and have much more fuel to burn than I ever will. I'm just looking for a little more power, not another 300HP.
Agreed, too much pressure is a bad thing, but how much is too much? If we're running 17.5:1, what would 17.75:1 do? Surely that isn't going to throw conn rods out the block. Or is it??? Hard to say if the power gain would be worth the trouble. Mmm...
Is this a case of ??

 

Yep.

 

The other problem is your head is flat. You can plane down to nothing and it won't increase your compression ratio. lol You can purchase pistons that will run less compression, but I don't think they are very streetable. According to your sig there's a lot of other stuff you should do to your truck before you get to that point.

 

Not quite true. The valves are recessed in the head, so planing it down to nothing would increase the compression ratio slightly, however you also run the likely hood of touching valves and pistons together doing silly stuff like that.


You're not going to gain any power thats worth having going from 17.5 to 17.75.

Speaking from experience, I know that running a +.010 or +.020 head gasket on a block that hasn't been cut will lower the compression ratio enough to effect the cold starting enough to notice and be a pain at times.

 

According to your sig there's a lot of other stuff you should do to your truck before you get to that point.[/QUOTE]

There is, but I tend to take a LLLOOOOONNNGGGG time to do things. This question of mine is more theoretical, although if it was going to work then yeah, I would do it. Think of it as a 'what if...?' From what you guys are telling me, it's a waste of time, so on to easier and safer upgrades!

Thanks for the input, I appreciate it!

 

Cummins makes a B series that runs 18:1, but it's non automotive. I don't know what it's in or how it's built, but seriously doubt it's feasible to put in a pickup.

 

Yes, but they are naturally aspirated. They have a square top ring thats machined in aluminum vs. the keystone ring that sits in steel on a turbo piston.

 

Just run more boost. It's sort of a modifier to your compression ratio mathmatically. That 18:1 compression ratio cummins is N/A lke JD730 said.

Large compression ratios mostly belong to IDI N/A and low boost engines.

Most big power diesels DECREASE compression ratio to accomidate higher boost (which is more efficient with the same MEP's of a higher compression engine, but less efficient in low boost conditions obviously).

 

Aha! There's the missing link. I've been thinking and thinking on this, and it seemed to me there was something missing in the equation. That's what I've been over looking, the boost. It seems completely obvious really, but you know when you're in the middle of something, it's hard to see things that're right there in front of you. You need to get some distance from it to get a better perspective. Thanks Dzl Damon!


Keran

 

We have a non-turboed Cummins in a 5130 Case IH it is a totel dog compaired to the trucks , if you'er looking for internel mods I have heard about stroke and bore kits but I don't know anything about them you'ed have to pick some other brains on them....Don't have too much fun with your truck it's addicting

 

Mine dropped about a 1/2 a point with the .020 over head gasket and o-rings, and now it hazes at idle. Not worth it in my opinion. Sled Pullers run 11:1 because they have 150psi of boost and are trying to inject 1,100cc of fuel in a short amount of time

 

Not to mention the fact that at 17:1 and 35+psi of boost you're looking at really interesting cylinder pressures. Assuming you get studs and rings and twins or whatever the very last thing you'd want to do is increase your comp ratio.

 

Plus 40° of timing, in order to burn most of that fuel, with the remainder being used to cool the crown due to ridiculous cylinder temps. That's what I recall anyway, from your fine publication's article I read last week. Thanks for your $0.02 Jason.