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Hi all, I'm new here and after a lil help.
So I have just finished installing a 350 in my car and got it running and it's a fuel guzzling turd . I built the bottom to 9.0 to 1 comp for future turbo fittment but just running na atm.
Engine is a 350 with afr 195's, rpm air gap and a Holley 650 ultra xp dp. Bout 3000 stall power glide with a 3.25 rear. I know it's a bit of a miss matched combo atm but still thought it would be better than it is, only does about 9mpg and struggling to be 300hp flywheel I'd say. Cam is as above with 1.6 rockers, any advice appreciated. I'm unsure what's the issue unless it's just a bad parts combo. I didn't expect it to be a power house but it's using enough fuel that it should be better I think?

 

What is your air fuel ratio at? What do the plugs look like? Degree your cam? Idk if a 3000 stall converter will be the best for mileage but it's good for turbo though. 109 lobe sep is a little on the narrow side for turbo something in the 112 neighborhood would be better . I'm not saying your cam won't work though.

 

Hi mate, I'm running about 14-14.5 at cruise which leans off and surges a little with light acceleration (needs to go up
One more jet size I think) drops to 12 when I tread on it. Plugs look like new, suggests it's a little lean? I did degree the cam and it should be right, I purchased the cam to suit the current combo and I'll change it when I get the turbo on. Since I leaned it out I'm now getting about 11mpg (au gallon 4.54 litres) but that's all. Must be loosing a fair bit though converter slip perhaps, do you think that maybe it's just the way it is?

 

ps what effect do you think a turbo friendly camshaft would have on mileage at say a constant 50-60 mph? Aiming for about 600hp at the flywheel, my build was basically to have about 600hp with some resemblance to fuel economy vs high comp and a fairly wild cam and less power.

 

why 9:1 compression, why such a large cam for a very tame goal? you wanna know why the mileage sucks.... thats why

I would've kept the cam in the 218-220 duration @ .050 with compression and a goal like that.

mileage = engine combination, rear end gear, converter/rpm crusing. tuning is a big part but its a fairly simple aspect to dial in.

 

Is it a locking converter?

 

Hi mate, compression numbers are just where the package ended up. I thought 9:1 was a pretty good number for a turbo pump fuel engine?

Camshaft is what was recommended to me for the current combo so I just put it in. I'm intending to go single turbo it was just a cam to get it running, I didn't really realise it was that "big" of a cam. My understanding was that it was basically the next step up from std, which is why i thought the mpg would have been a little better. So basically the cam is to big and the converter is to loose?
I'm all ears, what comp and cam would you recommend to get 6-650 crank hp?
Thanks

 

Nah mate

 

Are you seeking to have a 650hp daily driver? They don't really go hand in hand. In the interest of fuel economy, try this
https://www.summitracing.com/parts/hup-pg20/overview/
https://www.summitracing.com/parts/sum-1104/overview/make/chevrolet

 

Sounds like you need a power valve that opens at a lower vacuum.
If you happen to have a motortrendondemand account, look at episode 29 of roadkill garage. He goes bit by bit for tuning a carb in the real world.

 

This is probably not a bad idea. Open the valve earlier then reduce the main jets down in size.

Do you know what your converter's doing? Calculate out the RPMs you're slipping at cruise.

What are you doing for vacuum advance? If you're not running a can chances are you're cheating yourself. The LSA is pretty tight for mpg, there may be a bit to gain there.

I'd be most inclined to focus on powertrain though.

 

Timing? I find cruise timing has more of an effect on economy then cruise afr within reason. I would probably look for 42 ish degrees at cruise on that thing to start. If your running just locked out or have no load based advance you are going to have less then great economy. Especially considering your cruise afr seems reasonable. The old rule of thumb of 10* vac advance at 10 inches.

With that cam you are going to have a fair amount of EGR at cruise. EGR requires more timing to light the fire earlier.

Good luck