Figuring compression ratio for 347

[Broncojohnny]

get an LA3 computer set up for 35's

All it needs to do is run good at WOT and all options are open. I need to run a 12.5 or so. That is a tall order to fill in a supercoupe. This one will get a thousand pound diet though.

[akfodysvn]

sure, but the " turbo motors need low compression" is a myth. The guys making big power with SBF's arent running low compression. Brooks and the like have higher than factoy compression with lots of boost.

OP, what block is in the car? All of this may be a very moot point if it's not aftermarket.

Stock block... Not looking for block splitting power. 450ish with a good tune... I realize some people say thats enough to do it in, but thats the risk im willing to take while only spinning to 6000.

Here's a calc with some assumptions for you:

Cylinder Bore Size: 4.030"
Stroke Length: 3.4"
Head Gasket Bore Diameter: 4.1" (FelPro 1011-1)
Compressed Head Gasket Thickness: 0.41"
Combustion Chamber Volume: 61cc
Piston Dish Volume: 11cc
Piston Deck Clearance: 0.010" (a lot of people will zero deck when doing new builds... I assumed yours is not and used something probably close)

That comes out to a static compression ratio of 9.567:1

The deck height won't do much for your static compression, but it affects your quench volume, and optimizing (lowering) quench volume can allow you to run higher compression with fewer detonation concerns.

If you're really concerned about it you could dig into dynamic compression ratios, but with an assembled shortblock and a cam already installed you can only do so much.

Thanks. Ive been trying to understand quench better today but ive been busy on the ambulance. This was the original block from the car that was taken to a 347.

[DON SVO]

get an LA3 computer set up for 35's

Supercoupe, not Turbocoupe.

[Broncojohnny]

Supercoupe, not Turbocoupe.

Official car name is Thunderturd Superpoop. I'll be selling scratch and sniff T-shirts in my merchandising efforts. When the car explodes I am going to drop it off in Naynus' front yard.

[svauto-erotic855]

sure, but the " turbo motors need low compression" is a myth. The guys making big power with SBF's arent running low compression. Brooks and the like have higher than factoy compression with lots of boost.

I like relatively high C/Rs for a boosted engine but I am a good tuner. Lower C/Rs are an effective EGR that adds a larger margin of error for tuning.

How much boost you can run with a given CR depends greatly on the cam specs.

You would be shocked at how many people have no idea what you are talking about.

Official car name is Thunderturd Superpoop. I'll be selling scratch and sniff T-shirts in my merchandising efforts. When the car explodes I am going to drop it off in Naynus' front yard.

Since he dropped off the site I have been considering parking the white XR that he kept nagging me about in front of his house with a license plate on it that says "SVO". I have also considered filling one of his cars with feral cats one night just to be able to film the ensuing hilarity when he finds them in the morning.

[DON SVO]

Official car name is Thunderturd Superpoop. I'll be selling scratch and sniff T-shirts in my merchandising efforts. When the car explodes I am going to drop it off in Naynus' front yard.

I was replying to Forrest because LA3 processors are used in the 4-banger Turbocoupe, not the 6 cylinder supercoupe.

[akfodysvn]

What do you guys think about fox fuel lines and rails for e85. I know I'll need more pump and injectors but reading about the raw fuel smells has me second guessing that idea. Ive got a lot of research to do before making any decisions.

[Cooter]

I was replying to Forrest because LA3 processors are used in the 4-banger Turbocoupe, not the 6 cylinder supercoupe.

yep, I should have caught on with the mention of 30's and 42's also... high impedance and all that

[Broncojohnny]

What do you guys think about fox fuel lines and rails for e85. I know I'll need more pump and injectors but reading about the raw fuel smells has me second guessing that idea. Ive got a lot of research to do before making any decisions.

Smells come from using rubber lines, it lets the vapor out. You'll be fine with stock lines because the rubber portions are lined with Teflon. People worry about E85 because of corrosion but it is not corrosive in and of itself. It attracts water though and that is the problem. If you store it for long periods the container it is in should be airtight and as full as possible, if it isn't the ambient air will bring water vapor with it when the temperature changes. Your tank and lines obviously aren't going to be air tight.

[Broncojohnny]

I was replying to Forrest because LA3 processors are used in the 4-banger Turbocoupe, not the 6 cylinder supercoupe.

Yea I know. I wish I could find a junker turbo coupe, it would be a much better car for this. I am still on the hunt for one.