The Amazing 5.3 L83 V8

[4x4LJB]

I was reading up on our L83 engine on GM's website, because I wanted to know more about it.

 

I'm fascinated by the fact that with 11.0 to 1 compression, it runs on 87 octane unleaded.

 

I know it has engine management and direct fuel injection and variable valve timing and all that. But what I want to know is what are the specs for the Camshaft?

 

I figure it has to be a high lift, and especially a high overlap cam. High overlap cams produce power at higher rpms but "kill" compression by their nature. That's probably why it needs 11.0 to 1 pistons. But I figure variable valve timing shifts it to produce better torque at lower speeds, higher HP at mid range to higher speeds, etc.

 

Anybody have the specs on the cam?

[bdbake01]

I bet you'll be surprised at how mild the cam is. Direct injection is magical.

[UplandPa]

Yes Sir, the 5.3 is a great little motor!

[SILVER SLED]

Oh no. Here we go again.

[CH15GMC]

I had to bump up to 89 octane to get my truck to run well and how I think it should run. Now that I've done that I enjoy my truck. Until I jumped up to 89 I wasn't pleased about my performance and wished I had gotten the 6.2...I'm satisfied now but there are times I wish I had the 6.2!

[4x4LJB]

I had to bump up to 89 octane to get my truck to run well and how I think it should run. Now that I've done that I enjoy my truck. Until I jumped up to 89 I wasn't pleased about my performance and wished I had gotten the 6.2...I'm satisfied now but there are times I wish I had the 6.2!

 

Why would it make more HP and torque on 89 octane? Does the engine management allow more spark advance with higher octane?

[fondupot]

Yes its a good engine, and it runs 10x better on 89 octane.

[Willshire]

 

Why would it make more HP and torque on 89 octane? Does the engine management allow more spark advance with higher octane?

Less spark retard due to knock. That said, i recorded no KR on my 5.3 with 87 in it WOT pull from 10mph to 90mph

[CH15GMC]

I never had any knocking on 87 but at ideal it would run really low RPM's and just didn't run great. I tried some 89 because I read it runs better on it (high compression). I thought it ran awesome. Just to see if it was mind games I filled up with 87 and it didn't have the get up and go as it did with 89. I'll never do that again!

[HondaHawkGT]

87 vs 89 vs 91+ has been discussed in the engine tuning thread. Here's what Jennabear/Justin have brought up in the discussion:

 

At 11:1 compression ratio (DI or otherwise) the engine *cannot* efficiently run 87 octane under any circumstances. As a result, knock occurs (heard or unheard) and the ECM retards ignition timing both immediately and long term. The result is reduced fuel efficiency (sometimes as high as 3-4mpg) and considerably less power output than would be seen on 89 octane. You won't notice this power loss under light throttle though due to the ECM's method of controlling throttle angle... essentially, the throttle will be opened more for the same power output target on 87 as 89 so that it feels exactly the same to the driver.

 

In terms of ignition timing, where 18-19 degrees of advance might be the target by GM under the factory tuning, on 87 octane, that timing drops to under 10 degrees of advance to prevent knock from occurring (in response to knock that has already occurred). Anybody that has dealt with ignition timing should see this as a very poor situation. The knock retard occurs early and quickly and then the lasting effects (octane scaler blending the high and low octane tables) will stay in effect for dozens of miles before decaying out.

 

GM doesn't recommend any higher than 87 because they know that a) they will be vilified for doing so by consumer reports, motor trend, car and driver, etc and b) they know that people won't listen.

 

http://www.gm-trucks.com/forums/topic/158551-2014-engine-transmission-tuning/page-53?do=findComment&comment=1762274

 

My truck runs like shit on 87.

[Daryl Z71]

Hell GM says I can run 87 in my turbo charged Cruze. I don't ever remember hearing 87 being just fine to run with a forced induction engine. I run 93 in it, and it runs noticeably better, especially in the summer when it's hot, humid, and I'm running the A/C.

[tnchevy]

I do not believe that there is a 3-4 mpg loss between 87 and 89 octane. I have ran back to back tanks of both as well as a couple of 93 octane tanks and my mpg's are always in the same place.

[Rkaroll953]

anyone notice say sitting in a parking lot with 87 in the tank at idol, the truck will vibrate weird? like it vibrates like my old 6.0 2500. thats why i went to 89 for good, noticeably smoother. didn't notice the mpg difference but i dont keep track that well.

[HondaHawkGT]

Hell GM says I can run 87 in my turbo charged Cruze. I don't ever remember hearing 87 being just fine to run with a forced induction engine.

Same thing with the EB. Ford recommends 87 for their EcoBoosts but if you read the owners manual they strongly recommend 91 when putting a load on the engine like towing or aggressive driving. Same with the mew EB Mustang, it doesn't make its advertised power numbers unless it's running premium, but 87 is recommended if you look at the Ford spec sheet.

 

Sorry to get off topic. I think the L83 is a great engine. The high-compression, DI system is a great platform for mods and tuning. Even stock, this thing is pretty mean with E85.

[glcbn]

I do not believe that there is a 3-4 mpg loss between 87 and 89 octane. I have ran back to back tanks of both as well as a couple of 93 octane tanks and my mpg's are always in the same place.

 

Never ran 87 so I wouldn't know the mpg gain/loss. I have ran 91 from day one. I tried 93 a few times and found no mpg difference between that and 91.