Compression vs mpg ??
 

So my Tahoe gets shit mileage. It has from day one bone stock. It's a little better now than stock. However, it is sporting ls6 heads and about 8.8:1 compression. I'm wanting to improve the put of boost mileage on this thing and I think going to 4.8 flat top pistons will do it. It should get me to about 10:1 like the new 5.3's. so what I'm wondering here is what you guys think of how compression can effect mileage.

It seems to me if the compression goes up the lower end torque should go up and should help move the heavy bastard around while out of boost. My throttle response off the line is like grandma getting out of bed. Let me here your ideas. I'm use to tuning stock silvy's to get about 20-21. This thing is about 13.

I think youre on the right path, low end tq equates to better mpg. Less total power but better out of boost in your case mpg aka power.

Make that sucker more efficient!

On my 04 (weighed 6500ish), I got better milage with a 11:1 408 with a tvs1900 than my stock 5.3

This is my thinking as well. Between the cam and the heads it feels the same as it did stock out of boost. It never was real punchy. But I did a heads cam header install on a Tahoe with nnbs intake and a edelbrock 90tb and it was snappy as hell. But the heads were shaved.

My hope here is with enough meth I can still run the same boost and timming. Actually a tad more with a new turbo set up. I want to do a compound setup but I'm now wondering if I should twins. With the compounds or just a single I can't run my o2's. the right bank sees both banks and when logging you can see them start to battle because correction "look funny" to the computer. Then everything goes wonky and trims get all skewed.

If I run twins each bank will have its own o2 and turbo and I should be able to use the o2's better for small corrections and lean cruise should work a little better. Of course this is just theory that I hope works in real time. :)

Oh much better was better, More than 13? I have seen as much as 16 with the A/C off all highway. With it on it robs like 2-3mpg, It's insane. You would think it would be easy for a big v8 to turn a little ole compressor. Lmao

I think it was 10-15percent better. Not much but it surely didnt loose anything with twice the power.

I bet a 11:1 408 with a tvs had an ass load of torque.

Haha yea, off-idle tire shreading 35s for days.

The higher compression ratio will most definitely help with more MPG. The higher your compression ratio is the more theoretically efficient the engine can be, and what I mean is you are getting more out of the fuel for ever gallon burned.

Your average normal gas engine sits in the mid 20% efficiency. That is to say the other 70/75% is wasted on heat..moving stuff and all the other crazy inefficient nonsense that is the ICE.

The only way to get more out of it is to compress the air more and more and it will get you some ways. I thought I remember reading we are into the lower 30s with direct injection.

Diesel gets much better MPG because they are in the 40% efficiency range compared to their gas brothers. Diesel is able to run at much higher compression ratios because of the gas..it can be compressed more and more without self detonation thus allowing for the high C/R ratios. This is the limiting factors in the normal LS engines like ours. Ours are just a bad design unfortunately.

However if you have looked at the new engines most of them are all direct injection..cough 2014 Silverado. What that allows is to take in the charge of air...squirt in the gas later and it will cool the air allowing us to have higher C/R ratios. I have seen some things that are taking it even further by squirting the gas in and letting it explode by itself much the same as diesel engines do.

Personally I would take it up as high as you can go with premium or even e85 if its in your area. If you could harness the real power of e85 unlike we do now I think you could see some big gains in not only low end power and power in general but MPG.

I wonder if anyone will actually read all this nonsense haha.