2v 5.4 Build Safe Compression Ratio

[Michael Gibson]

Okay, so I'm building a 2v 5.4 and I cannot decide if I want to run factory pistons or run these 3cc pistons I have from a teksid block 4.6, I like the idea of having high compression but I'm concerned the 4.6 piston I have, will put it too high for a blower if I decide to install one down the road, any advice or opinions?

 

[Deleted member 38176]

What kind of fuel is available to you? Are you open to the idea of converting to E85?

 

[Michael Gibson]

Looking to run 93 since there is only one gas station in town with e85 but 110 is available locally too but that would be out of the question for me to drive daily

 

[Deleted member 38176]

Ouch. If going FI in the future is a sure thing, I'd say anywhere from 9.5-10 would be the limit.

 

[Three50won]

Your best bet is to get some forged pistons. If you're planning on forced induction then I would stick with 9.0:1 - 10.0:1. That way you'll be safe up to around 15 pounds with a good tune..even more with meth. 3cc pistons if I remember correctly will give you a compression that I would not recommend boost. Check with DSS...those guys will get you pointed in the right direction.

 

[Mr. Rustypwnz]

You will only be around 10.8-1 with those pistons, which is nothing to worry about N/A. Throwing boost on a stock 5.4 is not going to last very long. If you want a good cheap shortblock, source some takeout 2007-2012 pistons and rods from a gt500. It will only be at around 8.0-1 comp but will have the ability to hold much more HP.

 

[Deleted member 38176]

You will only be around 10.8-1 with those pistons, which is nothing to worry about N/A. Throwing boost on a stock 5.4 is not going to last very long. If you want a good cheap shortblock, source some takeout 2007-2012 pistons and rods from a gt500. It will only be at around 8.0-1 comp but will have the ability to hold much more HP.

That compression N/A is going to SUCK!

 

[Michael Gibson]

My thought process was that I would use factory ford pistons, forged rods, and factory forged crankshaft, my biggest concern was the limitations of the pistons at a high compression level with boost, if my math is right I should be around a 10.32:1 but I may be wrong

 

[Three50won]

Run 03-04 Cobra pistons and hit it with meth. Keep a decent tune along with a good intercooler for the blower. And go a few heat ranges colder on the spark plugs. You might be able to get away with it.

 

[Deleted member 38176]

My thought process was that I would use factory ford pistons, forged rods, and factory forged crankshaft, my biggest concern was the limitations of the pistons at a high compression level with boost, if my math is right I should be around a 10.32:1 but I may be wrong

Too high for 93. You'll detonate like Hiroshima and fry those pistons. Three50 makes a good point, meth may be the answer to your problems.

 

[Michael Gibson]

Thanks for the help guys, I think I'll just stay n/a for now if I do eventually go FI I'll prolly go e85 might be more available in a couple years.

 

[sneaky98gt]

Don't forget that just because you can't run as much boost with higher compression doesn't mean you can't make the same power. Power is all about cylinder pressure. It doesn't matter if that cylinder pressure comes from compression ratio or boost. So, yes, it's true that you can't run as much boost with a 10.5:1 compression ratio as a 8.0, but at the same time, you don't have to run as much boost to make the same power.

For reference, new Coyote 5.0s are 11.0:1. And there's more than a plenty of them running around making 600+ rwhp on boost. But notice that it's only at 5-7 psi. That extra compression is a lot of the reason why it doesn't take a ton of boost to make big power. The problem with high compression is that it's a lot more sensitive to things like intake air temps, fuel octane (bad gas), a poor tune, etc. as well as being more finicky at lower loads (i.e. part throttle and idle), whereas lower compression and higher boost are a little easier to deal with. Done right, high compression and boost are just fine together.

 

[Deleted member 38176]

Don't forget that just because you can't run as much boost with higher compression doesn't mean you can't make the same power. Power is all about cylinder pressure. It doesn't matter if that cylinder pressure comes from compression ratio or boost. So, yes, it's true that you can't run as much boost with a 10.5:1 compression ratio as a 8.0, but at the same time, you don't have to run as much boost to make the same power.

For reference, new Coyote 5.0s are 11.0:1. And there's more than a plenty of them running around making 600+ rwhp on boost. But notice that it's only at 5-7 psi. That extra compression is a lot of the reason why it doesn't take a ton of boost to make big power. The problem with high compression is that it's a lot more sensitive to things like intake air temps, fuel octane (bad gas), a poor tune, etc. as well as being more finicky at lower loads (i.e. part throttle and idle), whereas lower compression and higher boost are a little easier to deal with. Done right, high compression and boost are just fine together.

I haven't seen a boosted 5.0 that WASN'T on E85

 

[sneaky98gt]

I haven't seen a boosted 5.0 that WASN'T on E85

I've seen quite a few, and they make very good power on relatively low boost. Unless I'm mistaken, Ford even offers a blower for them that makes over 500 on the tires, under warranty.

 

[Deleted member 38176]

I've seen quite a few, and they make very good power on relatively low boost. Unless I'm mistaken, Ford even offers a blower for them that makes over 500 on the tires, under warranty.

Wow. Never heard of this.

 

[sneaky98gt]

Wow. Never heard of this.

Yea, they do. There's a warrantied 550 hp version (around 475-500 on the tires), and an unwarrantied 625 hp version (about 550 on the tires). Both come with Ford tuning that'll even run on 87 octane.

Search around Youtube. There's a TON of guys making 500-600 horsepower on pretty much stock 5.0s with 6-8 psi on 93 octane. Granted, the ECU control systems on these newer cars are much more sophisticated, but it's not exactly fair to just issue a blanket statement saying "boost and high compression don't work together" when they actually work fairly well together with a good tune. A higher compression motor will also make a lot more low-rpm torque and get better fuel economy.