carb size recommendations for dual quad 363 stroker

[PRH]

The way I read it, the frictional losses are taken out, then correction applied, then the friction losses are added back in.

99.9% of my dyno experience since 1989 has been on SF-901 dynos.
When I have the uncorrected hp, and compare it to the calculated uncorrected hp based on the fuel flow and bsfc, the numbers usually come within a couple of hp...... which can usually be closed up even more if you took the fuel flow and bsfc numbers out another decimal point or two.

As an example, just grabbing a sheet on hand here.......
The displayed numbers are: 252.5 lbs/hr, .47 bsfc, which calculates to 537.2 uncorrected hp.
The measured/displayed uncorrected hp was actually 539.0.

539.0 hp from 252.5 lbs/hr is a bsfc of .4684...... which is rounded to .47 if you’re only displaying 2 decimal places.

The sae correction for the weather is pretty simple if you have the barometric pressure, air temp, and vapor pressure for the location of the dyno when the motor was tested.

As long as the fuel flow numbers are accurate, you can use the results from the flow and bsfc as the uncorrected power, plug the weather numbers into the formula, it will give you a correction factor....... and in theory, the results should agree with the dyno sheet....... at least within a couple hp.

This one uses humidity instead of vapor pressure:
http://www.wallaceracing.com/dyno-cor-calc.php

Of course, if the fuel flow numbers are off, then the bsfc numbers are off, meaning you can’t base the uncorrected power off them....... in which case all you have is the number on the dyno sheet to be taken at face value.

[PRH]

Looking at some sheets I have here where the J607 c/f is being displayed, it looks like the frictional loss changes that SF uses in their formula, changes the actual applied c/f by less than 1%.

[F-BIRD'88]

What is the total effective combined true frictional hp loss of say a 350 sbc with a 6-71 blower 650 stp hp @6700 rpm?
How does a SF dyno deal with that? Does it?

The uncorrected fuel flow and bsfc should show the difference. The blower consumes a lot of power. And the engine needs more fuel to cool combustion to avoid detonation. (Non intercooled)
How do you calc and correct for this.
I belive that the SF software does not ...

[MadBill]

One error that creeps in as the CF rises much above 6-8% (especially for high RPM engines) is that the friction power values in most dyno's programs are very rough approximations, often based only on the engine's stroke or perhaps also the bore and rod ratio. Circa 1994 I compared the Superflow numbers for a 350 SBC to the GM measured friction on an LT1 small block and found errors as large as 25%. Modern ultra-low tension rings, windage control, crankcase vacuum, etc. can further skew the numbers.

Blowers/turbos are another can of worms, especially if the latter are controlling to absolute pressure...

[Flatheadpopup]

Looking at some sheets I have here where the J607 c/f is being displayed, it looks like the frictional loss changes that SF uses in their formula, changes the actual applied c/f by less than 1%.

Interesting, well that shoots my idea about where the extra hp came from out of the water. I think my best bet at this time would be to try and optimize the tune/efficiency on what I have and be happy to finally have it running.

Any ideas on why the bsfc is so high? Thanks all,

Tony

[PRH]

With nothing to really go by other than the dyno data that’s been presented....... if I had to guess(which is exactly what I’m doing)...... I’d say it’s from an erroneous fuel flow reading.

I’m basing my guess on the big disparity between the two flow readings....... and I’m “assuming” each fuel line was hooked to one carb, so the readings are carb A and carb B.

The other possibility is the flow readings are correct, and one carb has a big problem...... which is hurting the power....... which results in poor bsfc numbers.

Had I been running it, and saw that......... I would have swapped the lines from carb to carb to figure out if it was an erroneous reading, or a malfunctioning carb.

[Flatheadpopup]

As far as the carb A vs carb B fuel flows--I asked the shop that dyno'd the engine and they said "All the meters show is total fuel flow, not necessarily per carb. They will never read exactly the same due to carb placement on the engine and various other factors" so I guess they weren't concerned with the disparate numbers. They did tell me that there was an issue with getting it to idle down below 1200 rpm or so but I figured that I could get that figured out at home. Now I wonder if one of the carbs has an issue (they sat for quite some time between purchase and actually running on engine).

[MadBill]

That's a total crock! Sure, carb-to-carb flow can vary for those reasons, but by maybe 5-8%, not 75% like yours. If you're ever in that situation again, demand that they switch meters or otherwise identify the problem.

[F-BIRD'88]

I'm not even sure the dyno air bells will measure cfm accoratly at that high a elevation. As the density thus mass of the air acting on the air vane is much lighter weight at high altitude. The mass weight of the air vanes would need to be re-calibrated to match the reduced weight of the reduced air density that weights less.
O2 sensors in the exhaust would help a lot.
At high elevation the carbs are going to need to be leaned down some.

[F-BIRD'88]

If you do lean jet it for 7000 ft, then if you ever bring the car down , out of the clouds, to sea level. Stay Off the Throttle until you can rejet the carbs for dense sea level air. Or you may burn it up @wot.

[Olds455]

Heres what we will do put a annular booster in the primary to keep patching this shit up will call it avs 2 sell a few more carbs. Then when sales die down on it again will add annular boosters in the secondary side and call it the avs 3. Lol. You see me with an edlebrock/ afb on my car then you will know, i went senile.

I think you got there already.

Don't be like that. You post just as much as he does, and sometimes the rambling is just as bad. Especially when you post 3, 4, & 5 posts in a row, all jumping around to different subjects in each one. Come on. Don't be a hater. You see yourself in him, don't you?

[F-BIRD'88]

I said it in a friendly jab way.. I don't I was real harsh on him. Ya his line goes all over the map. He's just having fun there. I put up with a lot more harsher. Mean spirited comments around here from the peanut gallery. Used to it.

[F-BIRD'88]

I'd like to ask the OP if he had noticed a "curtain" in the plenum between the 2 carbs that partially blocks the passage as NormS has shown us ,on the SBC 2x4 eddy manifold. See anything like that in the upper or lower plenum between the carbs?

[Flatheadpopup]

I'd like to ask the OP if he had noticed a "curtain" in the plenum between the 2 carbs that partially blocks the passage as NormS has shown us ,on the SBC 2x4 eddy manifold. See anything like that in the upper or lower plenum between the carbs?

Do you have a picture of the "curtain" you are talking about that you can post? I can pull a carb and take a look if you let me know what I'm looking for. Thanks

[PRH]

That's a total crock! Sure, carb-to-carb flow can vary for those reasons, but by maybe 5-8%, not 75% like yours. If you're ever in that situation again, demand that they switch meters or otherwise identify the problem.

I agree...... IF........ the fuel lines were hooked up so one fuel channel was feeding one carb.

If the two lines were connected together, with the combined flow then hooked to a common line that was feeding both carbs...... then we wouldnt know what each carb was doing.
Not that I have any idea why you’d want to do that if you have two fuel channels and two carbs.