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 General Questions about tuning and engine setup. 
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Joined: Tue Aug 23, 2016 10:38 am
Posts: 84
So I have a little experience with somewhat powerful cars so most of my tuning is typically only worried about bigger better faster. You know we need to get the most hp we possibly can. This typically leads to a car that gets to rarely see any thing but the track because it is obnoxious to drive.

So I am now working on specifically a 74 Malibu I drive to work but also a 84 k10 with a dirt track refuge 383 that doesn't works so great on the street. The thing is I want to have my cake and eat it too. I want plenty (more than plenty) of hp and to attempt to get more mpg out of them.

So here are the things I assumed I knew and after reading here and there I wonder.

How do you set your idle a/f? I always used to set it too the highest vac reading. A few times I have tried using "lean drop". I noticed with highest vac reading the mixture is 12.5-13.5 most of the time. If I have my wide band on the vehicle I sometimes will lean it out to 14.5-15. it is always very unhappy (compared to best vac) but I was under the impression it would help mpg and maybe lower the amount of costing richness I see when the engine back drives going down a hill or coasting to a stop. Visard recommends this in his holley book but though I really like most of his stuff I tend to question everything. Maybe that is just with Holleys and rochesters and carters are different?

Intake heat, As a drag racer and circle track racer cross overs are plugged right away. Of course you want the densest air getting into the port possible. Of course those are WOT engines were the runner velocity is high and fuel drop out should be lessened. On street engine running mostly at part throttle this intake heat can help driveabilty. Where is the point that it is too hot? How do you control it? Is it needed with an aluminum intake that will heat up much quicker than cast iron?

Thermostat temperature
I tend to like my temp gauge pointing at the C and my oil pressure gauge pointing at the high. I was a huge fan of 160 degree stats forever. Now I am more inclined to do 180s. I realize that there are many things that may our may not be changing with coolant temp. My line of thinking always was that 10 degs equals 1% of hp but I have never seen proof of that a thermostat plays any part in this. I do tend to think a cooler thermostats will allow a bit cooler intake charge and help to keep detonation away a bit easier than a hotter one but this is merely speculation. I have seen the losses a turbo car will make with no intercooling but this isn't exactly what we are talking about.

Inlet air My car has a thermac and my truck a open element air cleaner. Both pull in whatever air that is in the engine compartment. Would ducting them to the grill make a significant difference?

Dist type So my car is the last year of points dist from gm. I am planning on a q-jet, cam, headers so the dist will be out. I have a bucket of HEI dist will changing the dist make any real difference in power or the ability to run a leaner mixture or make my children smarter or will it just make it so I don't have to worry about adjusting dwell once a year.

Gearing I know how to gear for performance but how do you gear a street car? How do you decide the rpm your engine is happy at? Does low numerical final drive guarantee better mpg? What about the inverse, does low gears guarantee a loose? if I move from 2.73 to 3.23 or 3.42 or 3.73 will the mpg get substantially worse? I ask because my Camaro on drag week got between 9-12 mpg with a 30" tire a loose converter and 4.10s turning between 3800-4200 for hours at a time. Though that is pretty bad for a solid roller bbc it doesn't seem so horrible. I plan on changing my Malibu to 3.23s from 2.73s, will it drop from 16 to 14 mpg?

If this gets any attention I may add to list later. These are just things I think about.

Thu Oct 13, 2016 2:28 pm
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Joined: Fri Feb 08, 2013 5:50 pm
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Idle A/F.
Every engine is different, but most should be able to idle at or near 1 Lambda or 14.7 to 1. I have a test car with full exhaust, 427 SBC with a 285/295 @ .050 roller cam at 108 LSA, it idle fine right at 1 Lambda. Tight converters add load in gear depending on the cam, and may need a little more fuel. My suggestion is to get the engine to normal operating temp, adjust for the least amount of turns out that doesn't lose RPM. Check it in and out of gear, make sure it doesn't drop too much in gear. Once you figure what yours likes you can use the O2's to monitor if you make changes to different carbs.

I'll group intake and engine temp together along with inlet air temp. Your combination will decide for you how much or little heat is required. The better the carb is at atomizing the fuel the lower the heat needed to vaporize the fuel. The higher the inlet temps are the less engine heat you will want. Fuels that have a lower vaporization curve will need less engine/induction heat. Engines with a higher overall velocity induction will keep the fuel atomized/vaporized better, and will need less heat. So what does this say? We know that the colder engines will make the most power if you can properly atomize, vaporize, and equally distribute the fuel, those things result in quality combustion. If distribution and/or poorly homogenized air/fuel mix results in poor or inconsistent combustion power suffers, and heat from any source can usually help. Fuels with poor vaporization properties also fall here,pump fuels are notorious for needing heat, carbs that are too large as well. A carb that's too large has lower vacuum/pressure difference at WOT, higher pressure difference aids vaporization but adds to pumping losses to do it. There is a balance to every combination...

If you get the advance curve right the HEI is a fine choice. A GOOD HEI, there is a lot of aftermarket junk out there.

You run the engine RPM where YOUR engine is most efficient at burning the fuel at the speed it will see the most. Overdrive transmissions seem to be the best solution, allow for a lower numerical gear and still have good stop and go manners.

Fri Oct 14, 2016 10:52 am

Joined: Tue Aug 23, 2016 10:38 am
Posts: 84
I guess what I am asking about gearing is without cut and try how do I collect the information to accurately decided a gear or compromise gear for my particular engine? I have access to a chassis dyno and I can attempt to get a fuel flow meter in an attempt to find the place that in creates the most hp with least fuel input. Is this the proper way? My internal combustion fundamentals book by John Heywood suggests that the curve for BSFC is inverse of torque but I still have trouble finding how torque and hp change at part throttle. WOT numbers are mostly useless for this.

obiously I can stick 2.73 and a .70 overdrive in an automobile with 28 tires so it will turn approx. 1400 to go 65 mph. This kind of reduction works with a T56 but it also employees 2 overdrives in the event you need more multiplication.

So for this car I plan on building a 505 with a small 265 afr head, mild hydr roller and other components to support a 5500-6000 rpm max and then plan on under gearing it and allowing it to use the tq it makes in an attempt to get some kind of mpg.

I am not trying to be a pain I just want to do a better job selecting parts.

We could talk about regearing my nitroused bbc for the track but that is a pretty bag can of worms.

Fri Oct 14, 2016 11:28 am
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When you find where peak torque is I would thing around there would be the best RPM for your average cruise speed. Dropping your RPM to cruise at 1400 probably isn't going to work either without a very small cam, Chassis dyno should help figure it out. As far as BSFC it is lowest at peak torque with everything tuned well, cures upward on either side.

Fri Oct 14, 2016 10:32 pm

Joined: Sun Jun 23, 2013 1:41 pm
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Location: Phila. Penn.
Idle A/F.
Every engine is different, but most should be able to idle at or near 1 Lambda or 14.7 to 1.

Can you elaborate? This appears to be a different point of view than Tuner and Shrinker; tune idle for best power efficiency for closed throttle and that will tend be somewhat less than stoich especially with a non-stock cam.
For example "0% load, idle, rich as necessary (13/1?) for whatever valve timing."

" Engine's idle the fastest when the mixture is correct for the engine design. As you screw the mixture screw in and out you find the point of correct mixture.
So how you set idle is to set the mixture screw to where the engine runs the fastest then set the idle speed with the throttle stop screw then reset the mixtures until the engine runs the fastest and keep doing that process back and forth until you have the engine running the fastest with the least amount of throttle opening. That is the basic rules of idling."shrinker 06-06-2011, 06:40 PM demon metering blocks post #6

"Your claiming a discrepancy from maximum vacuum and engine idling speed with the tune settings so its likely that the timing is too advanced at idle. If the timing is too advanced the mixture to get maximum idle speed needs to be too lean, the side effect from that is that the engine wont respond especially when talking about performance cams. The idle mixture settings and the vacuum dont correlate in your case, so its likely you have not got idle timing optimized."shrinker 06-07-2011, 03:28 AM demon metering blocks post #12

Sun Oct 16, 2016 1:03 pm
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Yes, you do want to tune for best idle RPM, but since load is usually low at idle you should not need much fuel. Now this can vary, incorrect ignition timing, bad cam design or improper cam timing, insufficient stall for the cam, very poor distribution in the induction can all play into the picture. Again we are talking idle, and most should idle with a reasonable tune in the 14 to 1 range. And remember that some engines can be run at light loads above stoich, so that puts your curve in the correct perspective. Again, my test engine with a large cam (full exhaust) will idle best around 1 Lambda. Different fuels will tweak it a little one way or the other, fuels with lower vaporization temps burn leaner and it depends on engine as well.Cold engines need more, warmer less.

Mon Oct 17, 2016 11:05 am
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