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carb size recommendations for dual quad 363 stroker

General engine tech -- Drag Racing to Circle Track

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Re: carb size recommendations for dual quad 363 stroker

Post by Little Mouse » Mon Apr 15, 2019 5:15 pm

German van buran built us a saturn 5 rocket so we could put a man on the moon 1969 fifty years ago so for fun wed did it again 1974. Other day our VP Pence said we will go back 2024, thought done that twice nothing to prove waste of money and complained to one of my government loving friends, well he explained to me the reason. It seems its a known fact that the moon is hollow and alians have bases there, they only come out when moon on our dark side, and they have afb/ edelbrock carbs powering there stuff, with alain f- bird88 as there leader. So we have to go back to moon put a stop to this nonsense. This is known fact because late night TV show hosts say it is so.

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Re: carb size recommendations for dual quad 363 stroker

Post by PRH » Wed Apr 17, 2019 4:28 pm

I’m just asking...... not hatin’.......
What’s with the fuel flow variance between A and B....... along with the rather poor BSFC numbers?

I don’t know where the motor was tested at, or what the atmospheric conditions were....... but there’s some serious correction factor going on there.

Just looking at one line for example(6400rpm), 204.2lbs/hr fuel flow and a bsfc number of .579 shows 352.6 uncorrected hp.
That’s a 39% correction factor.


Even if the fuel flow numbers are way off, the bsfc numbers are derived from the uncorrected power........ so even if the bsfc numbers were better, it wouldn’t change the 39% correction to get from 352hp to 490hp.

The 5100rpm line....... 164.7lbs/hr, bsfc of .501 = 328.7hp. 328.7hp@5100 = 338.5tq.
36% correction.

Or..... someone can tell me what I’m missing here.
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Re: carb size recommendations for dual quad 363 stroker

Post by Flatheadpopup » Wed Apr 17, 2019 10:44 pm

Ah, I do live at 6300 ft in Colorado Springs so there is a correction going on. The shop told me that it was running rich (AFR in the 12's dipping to 11's at one point) and needs dialed in more. I'm not sure how most of the dyno stuff works but the correction factor that day was supposed to be 24-25%. These guys build some killer race stuff so I figure their numbers are legit. I have been trying to figure out the differing fuel numbers between A and B--could it be because it is set up as a progressive linkage (serious question)? I wish I had more info but all I've got are phone pics from the dyno screen.
Guess I'll find out when I get it into the car and final tuned.

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Re: carb size recommendations for dual quad 363 stroker

Post by MadBill » Wed Apr 17, 2019 11:15 pm

Re A-B fuel numbers, with carburetted engines whenever possible I disconnect the secondaries, dial in the mixture on the primaries alone then hook up the secondaries and re-optimize via the rear jets only. Especially with a Holley of unknown origin, mismatched jetting is common (Holleys are factory fitted with anywhere from 4 to 10 or more sizes larger secondary jets to compensate for a primary P.V.)

For example, this drill on a Quadra-jetted ~400HP circle track engine gained 13 HP with virtually the same overall AFR as before.

Also, you can always switch meters F to R to verify it's not a meter problem.
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Re: carb size recommendations for dual quad 363 stroker

Post by PRH » Thu Apr 18, 2019 10:11 am

My “assumption” in this case is that since the motor was run with dual carbs, that A and B were each hooked up to one carb.

If the progressive linkage was operating correctly, it shouldn’t have any bearing on the A/B fuel flow difference....... since both carbs “should” be at WOT for the pulls.

If I would have seen that kind of difference in fuel flow, I definitely would have tried reversing the lines to see if it was a flow meter problem, or a carb problem.
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Re: carb size recommendations for dual quad 363 stroker

Post by Flatheadpopup » Thu Apr 18, 2019 11:10 am

Good info...thanks guys. I appreciate it. I am definitely here to learn.

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Re: carb size recommendations for dual quad 363 stroker

Post by PRH » Thu Apr 18, 2019 12:39 pm

I have zero experience dyno testing at high elevations, so I have no data to look at to see how the theoretical losses compare to the real world losses.

However, it seems that the accepted loss for elevation is 3-4% per 1000ft.
If we take the avg of that(3.5%), and figure the motor was tested at 6,300ft, it works out that the motor would lose 22% of its power from sea level.......in this case around 452hp uncorrected.......based on the bsfc and fuel flow from the screen shot(which works out to 352hp. 452 x .78 = 352.5).

That means in order to get to 490hp....... there would still need to be another 8.5% of correction......... that isn’t related to the elevation.


Did you happen to get a screen shot or dyno sheet with the uncorrected numbers on it?

Where I’m at, the correction rarely even gets to 10%.
Had one on the dyno last week...... 3.8%.
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Re: carb size recommendations for dual quad 363 stroker

Post by Flatheadpopup » Thu Apr 18, 2019 1:21 pm

No, dyno was older and didn't have print capability. I wish I had more data to share. It was ran in and tuned on before I got there...they just gave it a quick pull after I arrived. I will see if I have any video footage that is useful but I doubt it.

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Re: carb size recommendations for dual quad 363 stroker

Post by MadBill » Thu Apr 18, 2019 1:33 pm

Perhaps you could ask the dyno shop to verify their flow meters by doing the suggested switch on any engine with two or more fuel lines.

However, per PHR: 'since both carbs “should” be at WOT for the pulls...', a linkage misadjustment is the most likely cause of such disparate flow numbers. If the system has not since been disturbed, you can still check it.
Last edited by MadBill on Thu Apr 18, 2019 1:55 pm, edited 1 time in total.
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Re: carb size recommendations for dual quad 363 stroker

Post by PRH » Thu Apr 18, 2019 1:46 pm

We use an orifice in one of the fuel lines to check/verify the flow meters are reading close to each other, and to adjust the fuel pressure regulators with fuel flowing.
We use the same line/orifice on each outlet(A & B) to eliminate that variable.

The fuel flow difference in the posted screen shot is pretty extreme imo, if in fact it’s one line going to each carb.

In doing a little reading, it appears the STP correction is only supposed to be accurate for corrections in the +/- 7% range.
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Re: carb size recommendations for dual quad 363 stroker

Post by F-BIRD'88 » Thu Apr 18, 2019 1:48 pm

Look the race track that is listed on this site that is close to you and similar elevation too.
Look up the historical weather data for the date and time of the dyno test. Now you can calc the correction factor and corrected vs raw power that day.
https://airdensityonline.com

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Re: carb size recommendations for dual quad 363 stroker

Post by Flatheadpopup » Thu Apr 18, 2019 2:58 pm

I'm at work but I believe it was April 4th that the dyno run occured.

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Re: carb size recommendations for dual quad 363 stroker

Post by F-BIRD'88 » Thu Apr 18, 2019 3:11 pm

Well on April 4 at Bandimere Speedway at 5:00 pm the
Density altitude was 7813 ft. ,, percentage air density was 79%. (The worst air of that day ) The Density altitude was at or above 7000 ft all of the most likely time of day that day. 10 am to 9 pm.

You can also find the historical data for your exact location day and time . I believe the data is on the Weather Underground web site.

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Re: carb size recommendations for dual quad 363 stroker

Post by Flatheadpopup » Thu Apr 18, 2019 8:58 pm

I messed around on the Weather Underground site and a density calculator. The best guess I have is that my density altitude was 7306 ft at the time of the dyno session.

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Re: carb size recommendations for dual quad 363 stroker

Post by Flatheadpopup » Mon Apr 29, 2019 2:05 pm

PRH wrote:
Thu Apr 18, 2019 12:39 pm
I have zero experience dyno testing at high elevations, so I have no data to look at to see how the theoretical losses compare to the real world losses.

However, it seems that the accepted loss for elevation is 3-4% per 1000ft.
If we take the avg of that(3.5%), and figure the motor was tested at 6,300ft, it works out that the motor would lose 22% of its power from sea level.......in this case around 452hp uncorrected.......based on the bsfc and fuel flow from the screen shot(which works out to 352hp. 452 x .78 = 352.5).

That means in order to get to 490hp....... there would still need to be another 8.5% of correction......... that isn’t related to the elevation.


Did you happen to get a screen shot or dyno sheet with the uncorrected numbers on it?

Where I’m at, the correction rarely even gets to 10%.
Had one on the dyno last week...... 3.8%.
My engine was tested on a Superflow dyno. From my reading it looks like Superflow includes frictional losses in the correction factor. I wonder if this is where the extra 8.5% is coming from?

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