Irockthedrag

I currently have a chevy 350 sbc stroked to a 383 and I'm looking to add a 142 or 144 blower and need to lower my compression ratio. I beleive currently I'm at a 13:1 which is much to high for forced induction. Does anyone here have any suggestions on what they consider is the best way to lower compression without compromising too many power adding modifications on my car? Also, what do you consider as the best compression ratio for this style sc. Being entry level I assumed a 10:1 or 9:1 would be sufficient. If possible if like to retain my heads but if it goes that way I guess I'll have to swap them. May have to swap my intake as I'm running an air gap and with the height of the sc I may have change it or my hood. Thanks in advance.

Orr89RocZ

iTrader: (20)

Swap pistons. Get down into the 9's : 1 ratio

anesthes

iTrader: (12)

Might be slower with the blower. Those little blowers make a bone stock 350 hopped up, but I don't think you'll see much on a 383.

-- Joe

Street Lethal

iTrader: (16)

I absolutely agree with Joe. When it comes to an engine that is already making decent power from the getgo, meaning a better flowing engine to start with, a supercharger won't benefit you as much as it would an engine that is already down on power, especially with the pulleys that come with the kit. Whenever your down on boost with a supercharger you need to consider how much power your making naturally aspirated, and then you'd select the proper supercharger pulley (smaller), and/or crank pulley (larger), to force the supercharger to spin faster and create more pressure (boost). Here is exactly what your looking for, click the link. In this article you will see that they could only muster 3.5 pounds of boost with the 144 on a 383 using the supplied pulleys, and this is because the engine is already flowing the air that it needs at that RPM, so they up the crank pulley and get 9.5 psi of boost pressure...

Happy reading...

http://www.superchevy.com/how-to/eng...3-small-block/

As for compression, consider E85 and stick with 11.0 compression, that's its' sweet spot.

Night rider327

iTrader: (13)

The blower comes with it's own intake, you can not re use your carb intake you have now.

I would not run more than 9.5:1 compression, In fact I feel even that is still too high.

To drop compression you only have 2 options.. Larger CC chamber heads, or dish pistons.

What heads do you have now?

DIGGLER

iTrader: (1)

what heads are on it?

Kingtal0n

Weiand makes a 177 roots-style blower (or they did) that would mate nicely to a 383 with a stock-ish camshaft. You know, idle->5500rpm stuff.

A fun car yes, but a fuel drinker if carb'd. That was the one issue I always had with the roots-style blowers, you had to throw a carb on top. And TBI doesn't cut it.

Better off going turbo and some real nice modern OEM style injectors, an efficient aluminum head with a smallish chamber, a clean dish, 9:1 is fine, good stuff. I always shoot for 30~ mpg if I can get vehicle weight below 3000lbs it is always possible if you watch the combination, whether your engine makes 400 or 700rwhp.

redneckjoe

what was the decision? what route did you go?

heres some tech info;
http://documents.holley.com/techlibr..._tech_info.pdf

run race gas if not a daily driver.
meth injection could help alot too.
colder plugs?
fly cut the pistons if possible.

anesthes

iTrader: (12)

Hah. I don't even think my bike gets 30mpg.

-- Joe

redneckjoe

i got the opinion he was talking about a ***** Joe ?

sreZ28

I'm new to the sbc, so there are probably more qualified people here that can better answer your question. But from my research it seems like there are a variety of things you could try.
1) You could go for some deep dishes. This is kind of the quick and dirty way to do it, and may mess with your quench. It is by far the cheapest route.
2) You could swap your heads for ones with larger combustion chambers. AFR makes a nice set of 80cc's that would drop static CR dramatically, but they're expensive.
3) If you are dead set on keeping those heads you could drop down to a 3.48" stroke, but you'd lose significant torque and maybe some street cred.
If you are looking for moderate boost (7-10psi) you generally want to shoot for 9.0 to 9.5 as a static CR. You can probably give yourself some wiggle room with a variety of changes that would help you stave off detonation (cold air intake, hopped up ignition, cold plugs, a really nice quench, aluminum heads, a water to air aftercooler, EFI, piston and valve coatings, electric radiator fans, octane booster, any weight reduction mods, a good cam selection, etc etc). With all of these things and a really nice tune you could pull off 10:1, dynamic compression is more important (~8.5), but it would be one hell of a tune. If you're determined, I would start with as many little things as you can, as many of them will add to your build anyways, after that drop on the AFR heads and do a compression test. If cranking pressure is over 220 you should look for some light dishes. Then again, race gas may be your best bet here.
I hope that helps.

anesthes

iTrader: (12)

Which has it's place. The wifes 2014 Rav4 is great.

Every few years I go to the Toyota and Nissan dealer's and ask them if they have a truck that will actually tow my horse and heavy equipment trailer. Maybe one day.

As far as lowing compression, we need to know what you are running for piston and heads. Complete specs.

Since this thread is a month old, and the OP is awol I guess he figured out his answer.

-- Joe

Orr89RocZ

iTrader: (20)

My 1000 hp car gets 7.6 mpg mixed driving, mostly city stop and go type cruising lol

anesthes

iTrader: (12)

Funny, so does 6.0 truck

-- Joe

Orr89RocZ

iTrader: (20)

Lol my 6.2 vvt truck does 12-13 average daily commuting, 17-19 highway

My car is still open loop and hasnt really been tuned for part throttle efficiency lol i expected more to be honest, i wanna see 12

Kingtal0n

ok so, this is one of my specialties. Because I am so poor, I have to find ways to improve my fuel economy, otherwise the car is not practical. I cannot drive anything that averages below 25~ mpg that is for SURE.

First clarification about the word average, When I say average I mean when driving the car like a normal daily driver out of boost, with 50% highway commutes. The word average is useless because traffic conditions change how the engine is run, affecting mileages. Still, it is useful to use miles per gallon as a measuring stick, my example is highway cruise situation since this is the ideal situation for driving any car, driving at a steady speed without stopping or turning or doing anything else will achieve maximum fuel economy at some speed.

Now, on to the gory details,
To achieve this kind of economy requires patience to say the least. There are several factors affecting fuel economy on all cars;
First let us tackle the tuning. My average air fuel ratio while cruising is 15.4:1, and I have developed a sort of "checker board hypothesis" whereby the fuel map gradually dips from high 14's (14.9:1) to mid 15's(15.7:1 max) in cruise situations, and to ensure engine longevity the fuel map resolution in those areas has been enhanced (a typical feature of many stand-alone ecu is you can decide what sort of resolution you would like by changing pressure/mass breakpoints) such that a slight movement outside of the cruise range (even just a steep hill while cruise control is set) will drop the air fuels quickly to about 14.5:1 which is much closer to the average closed-loop air fuel ratio you would see when using a narrowband sensor (they tend to flip from 14.3 -> 14.9 quickly). In the past I have used a simulated wideband analog output to keep my ECU in closed loop at these air fuel ratios ( 15.5:1 @ .002volts, 14.9:1 @ 1.002 volts) but I have found open loop to be just as effective when the engine is mostly stock (mainly because of the great vacuum a stock engine will produce, makes each load point more well defined)

Now, all of that is fine and dandy, but it does not have that great of an effect on fuel economy as you might expect. And I have discovered this because I data-log everything for hours of driving for years and years on different cars. The best way I have found to measure fuel economy is by comparing injectors duty cycle, engine vacuum, and road speed all at once. If you also include the injector flow-rate, you can write an algorithm to generate a real-time fuel economy display from this data, but it is un-necessary to simply find out if your changes are saving you gas. The more important tuning aspect of fuel economy is ignition timing. Finding the best timing for your highway cruise at different load points. And here is my method.
Load your car with luggage, full tank of gas, passengers, Turn on A/C and headlights, weight it down as heavy as it will ever be. This will ensure your load cell is just about as low-vacuum as possible for a highway cruise, this will ensure that if you tune your timing then later on decide to add all of this weight, you do not run outside of your intended cruise load cell and into the part throttle acceleration zone.
Now, set your cruise control to eliminate the movement of the tps to keep the acceleration enrichment out of the picture as much as possible. In my case, I simply disabled my TPS enrichment feature for this tuning session. Cruise along at a speed low enough that wind resistance will not factor in (yet). I usually start at 65MPH. Find your load cell, remember the vehicle is heavy, on my car this cell is right about 10" of vacuum at 65 MPH. Set your timing to a low number, something like 30* that is much too low to be the final result, and drive for 20~ minutes while logging your fuel injector duty cycle and engine vacuum. In my case, injector duty was about 8%. Now, advance your timing. I used 35* next. And repeat the above procedure. My injector duty cycle dropped from 8% to 7.6% average, and my air fuels became slightly richer in fact, allowing me to remove even more fuel. If I had an EGT gauge I would have also noticed the temperature drop at the exhaust manifold around 50*F~. This is all a very good sign that the additional timing was a welcome change. You can now see where this is going; repeat the procedure, adding timing and logging fuel injector duty cycle, and look for the signs of a welcome change, that is, reduced injector duty cycle, lower EGT, increased engine vacuum. At some point you will encounter diminishing returns, and then the application of the vehicle will tell you what to do next. For me, safety is number one, so I never run off into the deep end for that extra .2% (it took another 12* BTDC of timing to drop the injector duty only .2% so clearly the additional timing was unwelcome). My final timing is right at 37* btdc for this engine, some have appreciated as much as 45* btdc (big cam(s), big manifolds, large displacement engine)

Now, it is important to realize that before you start playing with the engine's tune, there are several other factors to consider when trying to get the best fuel economy, they should be taken care of first.
1. Rolling resistance. Do your brakes drag? grease the backs of your pads. Grease your wheel bearings. Spin your driveshaft by hand and feel it, does it feel rough or notchy? Push your vehicle by hand, often, get a feel for how easily it rolls. Update and maintain all of the aspects of driving straight, such as the alignment, toe and caster. Consider the tire compound.
2. rotating weight. Use the lightest wheels you can find. I also have a light weight flywheel (but not too light!). Anything in your drivetrain you can afford to have lighter is a fuel saving benefit. You do not want the rotating assembly too light on a street car (no knife edged crankshafts), if it is a full street car with A/C and it has an aggressive clutch. A very light rotating assembly behind an automatic would work great, if the stand-alone is capable of handling idle and transitions, and the torque converter is configured for the lighter parts.
3. ride height / wind resistance. Speaks for itself, is your car suitable for high speeds? Get it lower to the ground if possible.

and finally, the way you drive is very important. use your brakes as little as possible. Every time you brake, you waste the energy that was extracted from the fuel you burnt and send money out the window. Engine braking for long distances pissing everybody off behind you that wants to speed up to the stop light is essential. My car will engine brake with zero fuel input from 60mph roll for about 1/2 mile.

anesthes

iTrader: (12)

Fuel economy has never really been something I've been concerned with.

-- Joe

Kingtal0n

There are benefits to precisely metering fuel. The object is to burn it, to use it, not to coat parts with it or have leftover partially oxidized fragments of carbon chains hanging around. Carbon deposits are left-behind remnants of combustion, unburnt, or partially burnt, that coat parts, isn't it? An engine runs richer, and everything gets black soot on it, the coating speeds up the richer you go, you can even see and smell at some point.

You can go too far. Running an engine severely lean will increase temperature dramatically and has consequences of it's own. Your engine's will run at 15:1 and 16:1 and even 17:1, under most conditions, and should run quite normal in fact, except you may notice things are getting hot. Perhaps hot enough to warp or melt. For us tuners, we really need to watch EGT for this situation, if a fuel pump is having trouble keeping up at 8,400rpm and the engine is making 747rwhp thanks to a large turbocharger, a sudden spike in EGT might mean the fuel is gone, or there is was an ignition retard. The IDEAL situation would be to keep all of the hot air inside the exhaust system, and none would leak out into the engine bay or anywhere else. To this end, I suggest you wrap and coat every part you can afford to. In addition, sometimes the overlap situation of valves opening and closing simultaneously can be used by the hot, fast moving exhaust to create a scavenging effect on the cylinder. Hotter exhaust also takes up more space and will spool a turbo quicker.

Back to cruising, the reason I do not hold the engine at 16:1 while cruising is, and this is something we already covered,
1. I do not go into the deep end for insignificant gains
2. The lean condition heats the engine up UN-necessarily, the EGT goes up and cannot be controlled with advanced timing. While it may be fine to hold it here, just cruising, imagine I suddenly want to put the pedal down and make some REAL heat. I made the personal decision that I would NOT tip-in throttle into a hot, lean engine for a WOT pass, after driving 150miles at 16:1 as an additional risk I was unwilling to take. That is why I checkerboard the fuel map from 14.9 -> 15.7, with 15.7's being almost rare and difficult to achieve. Also take note, I keep a little extra fuel at the ultra-high vacuum situations. Think of holding an engine at part throttle boost, imagine 4psi (and your wastegate is set to 10) part throttle acceleration. You lift, but not completely, and the engine shoots to 18" of vacuum, for only an instant though because you get right back into the gas. If that area if the fuel map is set to "lean cruise" air fuel ratios, you just took an engine from a demanding power producing situation, and "dipped" it into a super lean, hot situation for a moment. And so, this is what I have come to call, my "dip" spot. I have decided to "dip" my engine into 14.5:1 air fuel ratios instead of anything lean. Remember the engine sits here for an instant, and then you either lift completely (fuel cut) or get back into it and vacuum drops.

anesthes

iTrader: (12)

I understand that, I'm an engineer. However I:

1) Don't care about fuel economy on my toys

2) Don't tinker with my daily drivers, and I replace them with new models every 2 years. On my trucks I'm more concerned about towing and hauling capacity than fuel economy, and on everything else I just want it to be reliable, low miles, and have a warranty with roadside assistance.

3) On my toys I run a hair rich because I used to blow motors up back when I tried to achieve efficient combustion.

I understand and appreciate everything you're explaining, and if you look at some of my posts from back about 10 years ago I used to spend a lot of time chasing tunes and trying to get clean burns and all that. Then one day I just lost interest. Now I tune until it stops going faster, then I add a little more fuel for safety and call it a day. I don't worry about little random pops or ticks throughout cruising or decel. Besides, if I put 5 miles on the car a year that's a lot.

I bought another new bike this year and only had time to ride it 3 times...


-- Joe

Kingtal0n

My target audience is daily drivers, street cars that go 15,000 miles / year.

My post(s) was/is/are never directed at anybody posting, but rather, those browsing that wish to pick up the information they see fit.

anesthes

iTrader: (12)

Just buy a new car every 2-3 years and let the manufacturer worry about the tuning

-- Joe

Orr89RocZ

iTrader: (20)

Thanks for the tips. This year while the car is together and running i will spend time doin drive tuning to see how it goes. Hopefully gas stays 3$ a gal or cheaper

DIGGLER

iTrader: (1)

Why worry about gas mileage when you are maintaining maximum depreciation on your autos? Lol

redneckjoe

if i put a supercharger on my car, the last thing i'd be worried about is gas mileage.

i dont even know or care what mileage my car gets, lol. i can tell you its pretty good around town driving easy. down the highway or beating on it, she drinks dino fuel.

its just a toy to me. i certainly wouldnt care about gas on a dirtbike or mud truck.

and no, i'm not rich. i expect to pay, to play.

anesthes

iTrader: (12)

Yeah well. Tis life. That's kinda why we switched to leasing for the wife because she just turns it in every 3 years and picks out a new one.

I'll be coming up on the 3 year mark next August so I gotta figure out what I'm gonna do. I almost traded in for a new 2015 this fall.

-- Joe

Irockthedrag

This thread took a serious turn... Sorry for the late response guys, I have a lot going on. Also I decided to go a different route. Rather then pull my already running built engine and build it to handle boost, I picked up a chevy 350 sbc block bored .040 over. I couldn't bring myself to tear my toy apart again now that it's nearly done, I just put the finishing touches in my roll cage, welded in new pans, built my new rear end, and I'm starting to prep for paint.

I'm going to finish painting it then enjoy it while I build my new engine and find a t56, get the new combo ready and then drop er in.

Now that I decided what I'm actually doing, does anyone have any good suggestions for my build? I've never ran boost before but I'm quite excited. I helped a freind a little on his turbo build and I caught the boost bug.

The only thing I have right now is a bare 350 block .040 over, starting almost completely from scratch and I'd like to keep it carburated. It's a pre 86 block aswell. I'd like to get as much tq and hp as possible without breaking the bank, and would like to maintain a low profile blower so I don't need to get a taller cowl, (currently 3-4 inches)?

Any info or suggestions are welcome!

DIGGLER

iTrader: (1)

how much are you looking to spend on a t56 setup? er, how much is a swap going for nowadays? i have a '94 Z28 i've considered selling the t56 and stuff out of.

Irockthedrag

There's a local guy up here with a wrecked firebird with a good 6 speed and sbc in it and he only wants 800 for the whole car since he totaled it. I'm not looking to buy it all at once as it will just dig a hole in my pocket before I can even put it in the car.