jason's education thread

[Scoobum]

Jason...with the heads you have I'd opt for the 340 LPH pump. That pump has ben hit or miss with needing a larger return line. Some have drilled out the Saginaw fittings...or gone with a larger return line...and some have been fine as is. My car is a duplicate of Grumpys. I think he used a 255 LPH pump to hit the 9's with alky...but don't quote me on that.

[good2win22]

I should be ok with what I have. Installed the DW 300 with -8 feed and a -6 return. We'll see what happens when the boost gets turned up. Just wanted to calculate the fuel needs of 80's vs the 60's that I am currently running. Trying to dot the i's and cross the t's

[Steve Wood]

Got a given hp, the 80's require the same amount of fuel as the 60's.  It's only when the 60's cannot supply enough fuel to feed the hp that the engine is capable of, that 80's may be of benefit.  That's why bsfc is used to size injectors.

60's plus dual spray alky have edged into the nines on a 255 lph pump.

On race gas, I would start thinking of larger than 60's around 125 mph in the quarter mile although I have seen faster.

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[Scoobum]

Eric had/has it on his site that 60's are good for 10.5 on race gas. PL data tells me he's right.

[Steve Wood]

agree completely!

[good2win22]

My plan is to have a chip for race gas and one for alky.  Eric also has on his site that the 80's require a dual pump or external pump.  That's what got me interested in learning the fuel pressure/pump volume stuff.  Like we talked brad, I'm going to see where and when these 60's peak and go from there.

[Scoobum]

I'm betting those heads you have will suck the 60's dry earlier than mine. Start watching your IDC at 7 flat. I run my fuel pressure a tad higher than Erics recommendation .

Steve, I got PL data from Dan Kellers car from Napierville. Comparing 02's with AF. 10.8 and 750's for 02's. I start seeing KR in the low 750's with my own engine...surpr ise surprise. From what I see with Dan Kellers data, I don't think my NB tuning is that far off.

My thot is this. If I keep pulling fuel till I see a hint of KR...then I've pushed it as far as I can. I know what the NB reading is...does it really matter what the WB says.

[Steve Wood]

People are hung up on the wide band because they want a magic number. Joe Blow went 9.3 using an AF of 10.4 so that is  what I set mine to. 

As I said, it takes X amount of fuel to support Y amount of HP.  That does not change very much.  How you got that hp is another matter. 

Aluminum heads tend to make less hp than iron because of poorer thermal efficiency but they may provide more air flow while allowing more boost, compression, and timing-again due to the lower thermal efficiency. 

In the end, its about combination, ambient conditions, and tuning ability.

How often do we see 12 sec cars with 10 sec parts?.  People tend to call vendors and ask what to buy without understanding how the system works.

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[good2win22]

I've been trying, without success, to find some info/specs on what is generally determined to be acceptable rotating assembly balance numbers.  I have the balance sheet from my barn motor build, which was balanced at 36% but the other numbers at specific rpm's baffle me.  Any help and links is appreciated!

[Steve Wood]

From http://www.nmradigital.com/2014/02/26/how-to-balance-a-rotating-assembly/

A rotating assembly can be balanced to varying degrees of precision, and a moderate-rpm street motor can get away with far more imbalance than a high-rpm race motor. So how close is close enough? Since Americans don’t subscribe to the metric system, the standard unit of measurement for crankshaft balancing is an ounce-inch. There are 28.34 grams in one ounce, so balancing to ½ ounce-inch means that a crank has roughly 14 grams of imbalance one inch from its centerline. “Many production domestic V-8s are balanced to around two ounce-inches while a 7,000-rpm street/strip performance engine is usually balanced to ¾ ounce-inch,” Judson explains. “A very high-end race motor will get balanced to ¼ ounce-inch, which is seen as the holy grail of balancing by engine builders. Even at ¼ ounce inch, the rotating assembly is still 7 grams out of balance an inch from the crankshaft centerline. That might seem like a lot, but a 10,000 rpm NHRA Comp Eliminator motor will run all season long when balanced to ¼ ounce-inch.”
According to Judson, the distance from the crankshaft centerline to the edge of the counterweights is roughly three inches on most domestic V-8s. In the realm of balancing, this distance is called the correction radius. The problem is that not everyone factors in the dynamic effects of the correction radius when balancing a crank. “Many shops will balance a crank until the balancer reads ¼ ounce-inch,” Judson explains. “However, once you factor in a three-inch correction radius, the crank is actually ¾ ounce-inch out of balance. So even though they think they balanced a crank to ¼ ounce-inch, it’s actually ¾ ounce-inch out of balance. The reason you can get away with it is because a crank balanced to ¾ ounce inch will run just fine in a typical street/strip motor, and it’s still far better balanced than a production engine.”


Don't think this answers your question precisely, but it's an interesting article.    Most of the sheets that I have seen don't specify the particulars when they state 1 oz balance, or such.

Our Buicks were balanced at 36.6% from the factory which moves the vibration into the horizontal plane. High rpm engines over 6000-7000 rpm generally move the vibrations into the vertical plane by going to 50% and I think some circle track and other consistently high rpm engines over balance to 52% or so.  Thus we correct for a specific rpm range to keep the bearings from being pounded and to extend engine life.

Charlie is pretty well informed on this subject...at least compared to me and perhaps he will show up and give some better info more to the point.
 

[good2win22]

Thanks Steve. You are correct in thinking that I was looking for something else.  Going to attach the balance sheet for the barn motor.  My question or rather the lack of understanding remains, what are acceptable numbers?  I understand the hammer analogy and the overbalance and under balance and can assume the lower the number the better.  Thoughts?


Edit:  thinking I can do some interpolating with the numbers.  If the 1/4 oz is the preferred race balance the just need to convert that into a decimal. 1/4 ounce equals 0.015625 of one pound.  That would mean that this assembly is above that "limit" at 1000 rpm. Even at 1/2 ounce = 0.03125 and would mean it's above that "limit" at 1000 rpm.  So I guess the question is at what rpm does the 1/4 ounce race balance apply?


.04 pound = .64 ounce
.06 pound = .96 ounce


Should I be happy with us balance?

[Steve Wood]

I think this is balanced quite well.  I believe it is better than 1/4 oz which used to be the old standard....lo oks like it is less that .2 oz and both sides are pretty close to being even.

As you know, the imbalance quadruples as rpm is doubled which is what the numbers show.

Given the rpm that this engine will run, there is very little load on the bearings.  I think you should be very happy.

hmmm...calcula ted it another way and got 1/4 oz...anyway for the rpm being turned...it's a good job


I swear, the more I read, the more confused I get...still the numbers at 6000 and 8000 rpm are low so its a good job from what I can see

[good2win22]

Does a chart exist that compares wideband verses narrow band numbers to see the correlation?

[Steve Wood]

there is no real correlation.  The narrow band is only meaningful at stoch and the A/F's for wide open throttle are way outside the pass band on the narrow-band.   We just give nb numbers that seem to be typical for what it takes to run safely....

If we forget so called numbers that seem to be common for max performance, then the wb seems to fall somewhere between 10.8 and 11.2 depending upon turbo size and boost.  Larger turbos pushed toward the upper boost limits seem to be around 10.8 and smaller turbos at their upper limits seem to be 11.0-11.2

On the other hand, NB numbers seem to be be around 740-760 consistently in spite of turbo size from what I have seen.  Also, nb numbers at light pedal for a given a/f are much different than those given for the same a/f under boost as the narrow band is very sensitive to temperature and pressure.

In the end, no matter what you are using for guidance, the best performance seems to come with being as lean as is possible without incurring detonation/timing retard which is what aggravates me when some one posts, quite knowingly, you should be running at 10.8 without any data to substantiate it other than they read Joe Blow was running it when he turned a 9.30 at an altitude density 23 feet below sea level. 

And, while I am on my usual rant, third gear timing is not as beneficial as boost when running pump/alky.  Note, I said third gear timing.  In fact, i have seen a few that ran faster with 18 degs of timing than they did with 21 degs of timing when they were running mid tens.

Typically, the bigger the turbo, the less timing will be and also the less performance will be affected by changes in the timing...again third gear.

First gear is different because additional timing heats up the chamber and gets the turbo spooled quicker and is most effective when alky is being sprayed.  Some tend to forget that it takes heat to spool the turbo and simply have high velocity due to a loose converter is not the main factor.

In the end, we use the term "tuning" because it is an iterative process to find out what a given combo on a given day, in a given location needs to perform the best...and not because there are certain god-given numbers that everyone needs to know to go fast. 

[motorhead]

Not going to argue with Steve on any of that. 

I would add that you can log both your WB02 and NB02 and overlay the data; what that will do is show how/if the data is correlated (assuming it is repeatable and consistent).  Truthfully we would all be better served if we moved away from gasoline scale AFRs and just started using standard air–fuel equivalence ratio (aka Lambda).  Reason being so many of us run strange brews of fuel (gas, gas + alky, gas + alky + propane, racing gas + unicorn piss) that the 14.7:1 scale is flat-out incorrect for the fuel concoction being delivered.

http://www.enginebasics.com/EFI%20Tuning/AF%20Ratio%20Basics.html