High compression small cam combo in ecotec bad combo??

[DanBt1]

Just wondering ive got about 10:1, 10.5:1 compression in my ecotec but its got a small crow cam and 1.8 roller rockers in it. Only reason for not changing the cam when the engine was rebuilt was for the fact that i had it and was happy with the performance.
The car is really bad on fuel and i have gone through everything from vacuum leaks to o2 sensors putting a standard thermostat back in to injector and ignition u name it. Question i have is would having a small cam in a higher comp engine have any major effects on performance ie huge fuel consumption?? Would it be beneficial to install a larger duration cam?? Any help would be appreciated cheers.

 

[badnerve]

I have the wade 992a cam in mine with the same rockers, drinks petrol too. I get maybe 350 out of a tank babying it...

 

[DanBt1]

Ah right, max i got was 283kms from the tank, fill up every 4-5 days. Just doesnt drive right either unfortunately.

 

[acarmody]

I I have the MACE Stage 1 COMP Cam in my VX Ecotec and compression around the 10.5:1, and was getting about 11.5L/100Km.

Cam Specs,
210°/210° at .050"
• Intake Lift .317" (.507" lift at 1.6:1 rocker ratio)
• Exhaust Lift .317" (.507" lift at 1.6:1 rocker ratio)
•113 LSA

You did get the car tuned when you installed the cam right? I would say there is a problem with the tune.

 

[Cava454]

You have rebuilt a motor, increased compression and installed a bigger camshaft. Assuming the tune is correct why are complaining about fuel economy? It takes fuel to make more power and this is what's happening.

 

[Immortality]

It depends on the cam specs, to much dynamic compression is going to mean that you will have to pull out a lot of timing which will cost you torque and use a good quality fuel to prevent pinging.

Without the actual cam specs it's a really hard question to answer.

 

[DanBt1]

Put it this way I know sticking a cam in a 6 and boring it out will increase fuel usage, im not on here to complain about it but 18.5 litres per 100 km isnt normal!! Im just trying to make it use less, it has a crow stage 2 @ 50 thou its 201/206 lobe Sep 113 with 1.8 yt roller rockers. Ran much better before engine rebuild, only reason it was done was because it chipped a piston with the turbo kit I put together for it. If anyone has suggestions for the massive fuel usage would be much appreciated, cams not that much bigger than standard so unsure what to look at next??

 

[Immortality]

Ok, that's not normal. it's not a huge cam and not a huge amount of lift either. What was the CR before the engine rebuild? IF the CR has increased since the rebuild, has it been retuned since the CR increase?

I'm thinking that IF you have greatly increased the CR but you are still using the old tune that it will have to much timing and the ecu is pulling out a lot of timing because it's pinging (because of the raised CR) which will be costing you torque which will effect your fuel economy.

Other then that, i'd be looking at maybe a vac leak or something like that. What are the O2 sensors like?

 

[DanBt1]

Cheers immortality for the input, the cr was standard before with the same cam which I guess as 9.4:1. Its got the same cam and yt 1.8s from the previous setup, except now it has about 10:1, balanced, little bit of match porting, new o2's maybe 2 weeks old, all vac lines checked for crack and or leaks, iac and tb cleaned, plenum cleaned and new pcv, o2's earthing checked, tune has been changed for this setup not running same tune as before. Only difference now is a 2400 stall from the standard 1800 but it shouldnt affect the fuel this much!!!!

 

[Immortality]

I'd be putting my money on the tune. Best bet would be to hook up a laptop and data log it so you can see what is happening. Stall shouldn't effect fuel economy, especially if it has retained the factory lock up function.