04SilveradoMykk

Hey Guys,

As inspired by a recent road trip to L.A. and back, as gas prices were increasing. It's time to see what I can do to help the amount of fuel consumption by the 357ci SBC in my Silverado.

The engine is:
86-95 roller 350 block, bored .040" over
ZZ4 rotating assembly, H345NCP flat top pistons
Comp XR276HR10 cam, 1.52 rockers
Patriot 'Vortec' heads, 185cc int runners, 64cc chambers, 2.02"/1.6" valves
10.7:1 static compression, 8.5:1 dynamic compression
Super Victor copy single plane, Mighty Demon 750cfm annular boosters



First thing, I went through the carb. installed one size smaller jets all the way around. installed a 4.5 power valve to delay power enrichment. made a primary to secondary link out of coat hanger to delay the opening of the secondaries.







I installed my swirly 4 hole spacer under the carb to see if it would help, and it did minimally.



I've plugged and deleted the PCV to see if that could help any, the carb and engine ran better without that vacuum leak. But the engine oil is suffering because of it and I will ultimately reinstall the PCV, probably with a limiter in the vacuum hose.

I bumped up ignition timing a couple degrees, and so far with these subtle changes I've managed to go from 8-10mpg to 14mpg.

I dusted off the RPM air-gap copy intake I've had on the shelf, I smoothed the throat of the manifold to flow with a 1" four hole tapered carb spacer.













While the distributor was removed during the intake swap, I went through it. Cleaned and lubed it up. Installed a 21 degree bushing, and an accel adjustable vacuum advance set to begin to pull at 5" vacuum and max out by 8-9" vacuum, roughly 2" less than manifold vacuum at idle, adding 11 degrees of timing. I'll use manifold vacuum for the advance to take advance of the high initial timing and this lower idle fuel settings in the carb.



This should give me 36 degrees max mechanical advance at 3200rpm, 15 degrees while cranking. 26 degrees idle and will give 34-47 degrees of timing at highway, low load, cruising speeds. (2000-3000rpm)

I sold my 22"s and will be running these 08 GMC 17" wheels with 265/70-17 (32") rears and 245/60-17 (29") fronts



I will also play around with different tailgate and custom rear roll pan designs in an online wind tunnel simulator to see if I can't help out aerodynamics any. I've also considered making belly pans to aid in airflow under the truck too.

However, I am trying to utilize materials & parts already in my possession as to not spend so much money it will never be recovered at the pump.
Once I get back to Los Angeles where I will be living for a little while, I'll get a wideband O2 guage in the truck and will really dial in the carb for a 14:1 idle, 15:1 cruising and 12.3-12.8 WOT

I'm using a 180 thermostat, delayed the electric fans until 185-190. And I'm using NGK TR6 plugs gapped @ .055"

Any other thoughts, ideas, or something worth trying? Please post them up! Cheers ~Mykk

04SilveradoMykk

Finished installing the dual plane intake and recurved distributor. The engine has never fired up, idled and reved so well in it's entire life.

http://www.youtube.com/watch?v=HHO1dZRMwwo

Gadgetized

iTrader: (9)

Very nice. I would like to see a fuel injected engine be that throttle responsive. Or even idle like that for that matter.

04SilveradoMykk

Thank you, I sacrificed a bit of the 'Choppy idle' from the 276/282-110 roller cam by using so much initial timing. But It's worth it for the increase in driveability.

There are a few fuel injected SBC's that have a similar throttle response, one that comes to mind is a fully built/full race LT1 vette that was in my shop not to long ago.

(Check out the coil packs)

http://www.youtube.com/watch?v=0Lsf-icCSPQ

Beatdown Z

iTrader: (18)

Damn, your truck sounds and runs good. I need you to come play with the Demon on my 377, lol.

viciousknid

iTrader: (8)

Not trying to dog your setup by any means cuz you got a great thing going there but why did you decide to move Backwards in technology and efficiency in a newer model truck? If you would have done the same mods to a GenIII you'd be making more power and you could have even used carb if you don't like to mess with fuel injection.
LS based engines have proven themselves over the older designs time and time again.

Again. By no means am I ******* the great setup you have. I was just curious. Engine sounds great and I'm sure it runs like a beast.

Gadgetized

iTrader: (9)

Man, that Vette sounded good too. I have never heard a fuel injected engine so responsive. Who tuned it?

04SilveradoMykk

I understand, after all we're on LS1Tech. I didn't have a GenIII v8 block to start with. The SBC was sitting in my machine shop awaiting a rebuild kit.

I wanted to do something different. Since this engine swap over two years ago I've got a few copy cats too. BTW, the mexican 2000+ 400SS chevy trucks are a NBS with a L31 vortec 350.

04SilveradoMykk

What's it doing, or not doing? I bet 90% of the problems can be fixed in the ignition timing and the other 10% would need a wideband to dial in the A/F's

Beatdown Z

iTrader: (18)

When I roll into it in second gear (powerglide so it's 1:1) around 50-60 mph, the motor revs up to 5,000 like it's pulling strong, but then drops to about 4,500 and sort of flat-lines.

In first gear, it pulls pretty normal but starts dying off quick around 6000. Believe that's partly due to the mild cam. I'm going to be stepping up the cam in the near future and will probably rebuild and put my old Holley 850 back on. Current carb is a 750 Annular Mighty Demon.

I think the timing is set at 18* initial with 18* advance, and a vacuum advance canister hooked up to manifold vacuum.