10:1 compression gen 2

[Wheysted]

Got 10:1 compression pistons cause I was told it'd be safer and from what I read that seems to be true

Buuuuuuuuut

Now I'm hearing that it will be sluggish:/

I'm aiming for a safe 700hp on pump and 850 on e85
Is 10:1 a mistake? Anyone have the same compression?
Is this still obtainable? I'll be adding more boost
I'm also on a vortech

Cheers !

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[Cory S]

I would run your 10:1’s. It’s not like it’s going to be 9:1. A mere 1-1.5psi of extra manifold pressure will make up for it. Feed it fuel, feed it boost. You can also use a slightly thinner head gasket and mill the heads .004-.005”, which could put it closer to 10.5:1 as well. There’s options here while still utilizing your pistons for the build.

 

[ice445]

You'll be just fine. 10:1 is a nice compromise between the factory setup for good NA power, and what an OEM would use in a boosted application for ultimate safety (they have to assume people are dumb and will use crappy gas).

 

[engineermike]

Dropping from 11 to 10/1 will lose 3-4% torque at the same boost level, probably closer to 3 based on published curves. At 400 ftlb, that’s a loss of 12-15 ftlb.

If your tuner is worth his salt, he would know that the torque-to-load tables need to be scaled by about the same 3% when the CR is lowered. An accurate torque-to-load table will automatically offset any loss in part-throttle torque with an increase in throttle angle at the same pedal position. In other words, the part-throttle torque would be unchanged for any given pedal position.

 

[Avispa]

Just for a data point....the '03/'04 Terminator 4.6 motors were 8.8 compression. Put a Whipple 2.3 on em and "sluggish" is not a word that comes to mind.

 

[Plimmer]

I’m 10:1 compression with gen 2 heads. At 10psi to 11psi I’m getting 800whp.

 

[Wheysted]

I’m 10:1 compression with gen 2 heads. At 10psi to 11psi I’m getting 800whp.

Oh ok amazing! I'm not worried then

 

[WildHorse]

I'd go 13:1. That means less boost, which means less intake charge heat for the same power levels. Just my idiotic opinion.

 

[Wheysted]

I'd go 13:1. That means less boost, which means less intake charge heat for the same power levels. Just my idiotic opinion.

But that's higher cylinder pressure ?

 

[engineermike]

I'd go 13:1. That means less boost, which means less intake charge heat for the same power levels. Just my idiotic opinion.

Can’t....tell....if...joking.

 

[Wheysted]

Can’t....tell....if...joking.

Haha ikr. I'm gonna say not serious

 

[K4fxd]

The other school of thought is to go low compression and more boost. This gets more fuel into the cylinder. Fuel is what makes power.

On a PD blower this works, on a centrifugal not so much, unless dedicated drag car.

 

[TexasMetallic5.0]

Go 12:1 especially since you’re going to run e85. Don’t lower the compression like in the old days.

 

[K4fxd]

I'd like to see 2 all out builds. One at 12 to 1 and one at 9 to 1. If the 12 to 1 engine could support the same amount of boost and being able to use MBT the 12 would win. But can you use MBT even with E85 and 30 Lbs of boost?

 

[silverbullet85]

I wouldn't go lower then what the car comes with factory especially since you plan to get some good numbers. Go with what you want but I know I wouldn't go 10 to 1 if I was building a motor. I would just run 12 to 1 if the plan is e85. Kind of pointless to lower compression just to raise boost to make up for it, when the car is off boost it will feel weaker. Is it that big of a deal? No, but it's an easy choice to fix now before it's built.

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